Adding 2405H to my custom JBL system

[Beowulf57]

I'm in the process of adding 2405Hs to my system (pic below) and would appreciate comments on the decisions to be made.

I have Brociner-modified back-loaded folded corner horns (not identical: left has a D131 and right has a D130), LE85 compression drivers with HL91 horns and lenses; crossover is the LX5. Given the slightly lower sensitivity of the D131, the LX5 HF crossover level is set Low for the left channel and Mid for the right. This gives a fairly well matched balance between the two channels and the separate tube-regulated monoblock tube amps are adjusted to match channel levels.

I'll be using 3106 crossovers for the 2405s and plan to cascade the LX5 and the 3106.

At this point, my thought is to mount the 2405s in Minimus 7W (walnut) cases and locate the box horizontally on top of the LE85/HL91 enclosures which will provide a nice finished look and allow a bit of positional tweaking with respect to time delay between the LE85s and the 2405s.

Thoughts, suggestions?

Thanks,

Beowulf57

[Beowulf57]

Well, lots of views but no comments. I guess I should just assume that silence means consent...though there certainly won't be silence once I fire those 2405Hs up!

[Zilch]

Same suggestion I just made in another thread:

http://audioheritage.org/vbulletin/showthread.php?p=209677#post209677

3106 alternative is shown, and the links indicate how to do 10 kHz, a better option, even, for 2405.

Biamp.

Behringer CX3400 or equivalent as the main crossver, $99 at Guitar Center or similar.

HL-91 is not a 500 Hz horn. You'll be able to find the optimum crossover frequency for your system by dialing a knob on the active.

Sonic Impact T-Amp II to run the mids and highs, if you don't have something already. $70 at Parts Express.

Tubes might be nice up top, too.... :yes:

[Beowulf57]

Same suggestion I just made in another thread:

http://audioheritage.org/vbulletin/showthread.php?p=209677#post209677

3106 alternative is shown, and the links indicate how to do 10 kHz, a better option, even, for 2405.

Biamp.

Behringer CX3400 or equivalent as the main crossver, $99 at Guitar Center or similar.

HL-91 is not a 500 Hz horn. You'll be able to find the optimum crossover frequency for your system by dialing a knob on the active.

Sonic Impact T-Amp II to run the mids and highs, if you don't have something already. $70 at Parts Express.

Tubes might be nice up top, too.... :yes:

Thanks for the suggestions! I'll look into those crossovers.

Actually, the HL91 was used down to 500Hz with the LX5 crossover. This spec and configuration was provided in JBL's 1976 catalogue and was used in the S7 system.

[Zilch]

Actually, the HL91 was used down to 500Hz with the LX5 crossover. This spec and configuration was provided in JBL's 1976 catalogue and was used in the S7 system.Yes, and it suc..., uhmm, did not do it well.

JBL subsequently used HL91 at 800 Hz in several products, but ultimately dubbed it a "1200 Hz" horn. Check later literature, and you'll see it was progressively derated.

At 800 Hz, even, the longer HL92 is preferred, as used in L300 and monitor products.

In 1976, JBL was still calling HL91 "500 Hz," but HL92, introduced around that time, "800 Hz."

http://www.lansingheritage.org/images/jbl/catalogs/1976-comp/page9.jpg

By 1979, HL91 was a "1200 Hz" horn:

http://www.lansingheritage.org/images/jbl/catalogs/1979-comp/page10.jpg

Horns generally have a reputation for sounding, well, "horny," and JBL's early [mis]application of HL91 played a role in that.

I'm saying using an active crossover will allow you to make an empirical determination of the optimum crossover frequency for your particular combination of components.... :yes:

[Robh3606]

Here's what a 2307/H91 looks like on a baffle. It's with in a 5db window from 500hz till 10k. 500hz looks like the cutoff for the horn. You should never use a horn down to the cut-off point. Should try to use it an octave above so say aprox. 1K

Rob:)

[Beowulf57]

Thanks muchly for the advice...so how about I spring for a pair of N1200S to handle the LF to MF and raise the crossover point to 1200Hz and use them with my recently acquired 2405hs and 3106s? My system has sounded pretty good even using the 500Hz LX5 crossover, though I know it was never designed to be used with the D130.

P.S. Which horn is the 2307? I thought the HL91 was the consumer model of the 2391?

[Beowulf57]

Yes, and it suc..., uhmm, did not do it well.

JBL subsequently used HL91 at 800 Hz in several products, but ultimately dubbed it a "1200 Hz" horn. Check later literature, and you'll see it was progressively derated.

At 800 Hz, even, the longer HL92 is preferred, as used in L300 and monitor products.

In 1976, JBL was still calling HL91 "500 Hz," but HL92, introduced around that time, "800 Hz."

http://www.lansingheritage.org/images/jbl/catalogs/1976-comp/page9.jpg

By 1979, HL91 was a "1200 Hz" horn:

http://www.lansingheritage.org/images/jbl/catalogs/1979-comp/page10.jpg

Horns generally have a reputation for sounding, well, "horny," and JBL's early [mis]application of HL91 played a role in that.

I'm saying using an active crossover will allow you to make an empirical determination of the optimum crossover frequency for your particular combination of components.... :yes:

Thanks Zilch! Very helpful. I'm afraid that biamping is a little out of reach in my present setup with two very large tube-regulated monoblock tube amps driving my corner horn systems from the room below my listening room. I don't have room to bring in more amps and I have worked on carefully voicing my present setup over the past 20 years. I agree with you that the "horny" sound can be an issue, though I have been able to tame it at least to a listenable point, running Class A push-pull directly heated triodes (6B4Gs).

What I'm thinking of now after considering your and others' advice is to add N1200 crossovers to raise the crossover point to 1200Hz and then use the 3106s to handle the existing LE85s and the 2405Hs that I'm adding to the system.

Sound okay?

I have two other concerns:

1. I could pick up a pair of N1200S crossovers, but don't know if these are modified from the N1200 model in some way I would need to consider.

2. My bass drivers are 16 ohm models and I believe the N1200/N1200S was designed for an 8 ohm load? Would this create a peak in the crossover region that I would have to compensate for, or will the 3-position level adjustment on the crossover allow me to compensate for this? I would note that I get very good bass response with the folded corner horns and have to shelve the LE85's level down at present.

Thanks for your help!:bouncy:

[4313B]

1. I could pick up a pair of N1200S crossovers, but don't know if these are modified from the N1200 model in some way I would need to consider.
Here is what Pro has. I'll try to scan my version and post it later today.

http://www.jblproservice.com/pdf/Network%20Schematics/N1200.pdf

[Beowulf57]

Here is what Pro has. I'll try to scan my version and post it later today.

http://www.jblproservice.com/pdf/Network%20Schematics/N1200.pdf

Thanks...and do you know if there are any differences with the N1200S? I'll be interested to se your scan.

[4313B]

Thanks...and do you know if there are any differences with the N1200S? I'll be interested to se your scan.The N1200 and N1200S share the same schematic diagram. I'll try to remember to post it after I scan it later.

***

[Beowulf57]

Great! Thank you 4313B.

[Mr. Widget]

I have worked on carefully voicing my present setup over the past 20 years.Then don't change the LX5s and go back to your initial idea of simply adding on the N8000s or 3106s and the 2405s and be done with it. If you pull the LX5s and start messing around it'll be another 20 years before you get it right again...

30 years ago I had a system that was nearly identical to yours and I improved it and improved it until there was no part of it still in my listening room. Pop in the tweeters and enjoy it. It has worked for you this long.


Widget

[Robh3606]

If you pull the LX5s and start messing around it'll be another 20 years before you get it right again...

Yes good point especially if you are happy with it.

Rob:)

[Chas]

30 years ago I had a system that was nearly identical to yours and I improved it and improved it until there was no part of it still in my listening room. Pop in the tweeters and enjoy it. It has worked for you this long.


Widget

Funny how that works, isn't it?:yes::yes:

[Beowulf57]

Then don't change the LX5s and go back to your initial idea of simply adding on the N8000s or 3106s and the 2405s and be done with it. If you pull the LX5s and start messing around it'll be another 20 years before you get it right again...

30 years ago I had a system that was nearly identical to yours and I improved it and improved it until there was no part of it still in my listening room. Pop in the tweeters and enjoy it. It has worked for you this long.


Widget

Yes...good point, though I am still young enough to experiment. As well, to return to the LX5s if I do try the N1200s would be as simple as disconnecting and reconnecting a few wires, since everything is easily accessible at the back of the top cabinet housing the LE85s. Nothing to open up or unscrew. Maybe, I'll just try it for fun and report back with my results.

First step, I agree is to add the 3106s and 2405Hs to my existing setup and listen and tweak.

4313B: thank you very much for the schematic; no change as you said, but nice to have the documentation.

[Beowulf57]

Well...i have the 3106s and the 2405Hs in place!:applaud: Preliminary listening: an upper midrange hardness/glare seems to have disappeared and the subjective effect is increased presence and level in the bass region. On the top end: clearly more extension, air and detail revealed, e.g., the shimmer and decay of cymbals which was mostly absent before is now clearly present.

I still have to set the levels of the various drivers to taste, but this is a very good beginning. I may try .01 uF bypass caps (relcaps that I have lying around) across the 1.5uF HF cap in the 3106 and see if that will smooth out the sound.

I'm curious if anyone has knowledge concerning the development of the LE85/2420 midrange compression driver: a JBL spec sheet from 1970 shows a response peak of around 4dB centred between 5KHz-15KHz (the 2440 shows roughly a 3dB hump between 5KHz-9KHz). However, on a 1977 2420 spec sheet, this hump is gone, and although the response rolls off sooner, it is more gradual. I wonder if JBL was using a resonance to extend the response on earlier models and later modifications to the design removed this and extended the response in another manner?

This might account for my impression of a distinct upper midrange hardness/glare which the addition of the 2405Hs has removed, since the response of the LE85s has been reduced substantially in the region surrounding the 8KHz crossover point.

[Zilch]

Yes, it's there on the 2307 horn, less so on the longer 2312....

[JBL 4645]

Beowulf57

Heat rises and I would ether reposition the plasma or LCD what ever, and place it a safe place away from the fireplace otherwise the rising heat will sooner or later add additional heat and it will more like shut down as I have read on the AVS boards with one poor sausage who started noticing it with his flat screen.

Or shut the fireplace down and use radiator to heat the room up during the wintertime period.

Other than that make it loud and make it shake the house.:D


http://audioheritage.csdco.com/vbulletin/attachment.php?attachmentid=32439&stc=1&d=1210176670

[Beowulf57]

Yes, it's there on the 2307 horn, less so on the longer 2312....

Ah soo...I've picked up a pair of N1200S networks (good price, $80 ea.) as my cabinets wouldn't adapt easily to the longer horn. I'll give them a test run when I get them and post results.

[Beowulf57]

Beowulf57

Heat rises and I would ether reposition the plasma or LCD what ever, and place it a safe place away from the fireplace otherwise the rising heat will sooner or later add additional heat and it will more like shut down as I have read on the AVS boards with one poor sausage who started noticing it with his flat screen.

Or shut the fireplace down and use radiator to heat the room up during the wintertime period.

Other than that make it loud and make it shake the house.:D


http://audioheritage.csdco.com/vbulletin/attachment.php?attachmentid=32439&stc=1&d=1210176670

Thanks for the thoughts...however, I checked out this potential problem and there was no significant temperature increase around the Pioneer Elite Pro-110FD when a fire was running. The fireplace is very deep and when fires are kept to the back, the flu is kept open and the chimney is kept clean I have no problem. The cooling fans in the plasma display have never come on, even with a fire going and I get no soot deposit on the screen.

[Beowulf57]

Well, after some preliminary listening I think the LX5 crossovers may win out over the N1200Ss. :( I'll do more auditioning with high quality LPs and SACDs, however, the midrange is over-emphasized with the N1200S to the detriment of warmth and the bass region. The deepest bass is fine, but the mid/upper bass balance is not as good as with the LX5.

After studying the response curves of the D130/131 and the LE85 (2420), I think this may be due to the rising response of the D130/131 which shows a peak between 1KHz and 3-4KHz. The 1200Hz crossover point brings this peak into play as the response is down 4dB at 1KHz and 13.5dB at 2KHz for the LF section; with the LX5, it is down 20 dB at 900Hz. Further down at 500Hz, the N1200 is 0dB, whereas the LX5 is -9dB. Good clarity with the N1200 (and good for dialogue on films), but not as well balanced for music, which is after all is said and done my primary concern.

The LX5 seems to have been designed to compensate for the drop off in response and power handling of the LE85 with the HL91 horn below 500Hz. So far, to my ears this is a better combination than using the 1200Hz crossover with the D130/131.

[Beowulf57]

Okay, a little more help would be appreciated. I'm considering the suggestion to try an L-pad in the low frequency section of the 3106 (N8000) that feeds the LE85 to see if that will ameliorate the mid-range peak problem introduced by the use of the N1200S (rather than the LX5). Would this be the L-pad of choice:http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=260-252? Or, should I use a higher quality unit? Suggestions?

This is a bit of a gamble, as I rather thought the problem was the higher crossover point of the N1200S bringing in a peak from the D130/131 as mentioned below.

Second issue: the LX5 I have been using is rated for a 16 ohm load (matching the impedance of the D130/131), however the LE85 is an 8 ohm model. On the other hand, the N1200S is rated for an 8 ohm load, matching the LE85, but not the D130/131. How do these mismatches alter the crossover points/response curves?

Third issue: I had previously replaced the switches in the LX5s with sealed Grayhill units and bypassed the HF caps with 0.1uF MIT multicaps...would this be a good idea with the N1200S if I can get the midrange problem sorted out?

[Mr. Widget]

Re-read post# 13.

That said, these crossover networks are not designed for generic use. Each network was designed for a specific set of drivers. If you read the crossover chart here: http://www.lansingheritage.org/images/jbl/catalogs/1976-comp/page7.jpg

You will see you were already going about it all wrong, but with years of messing around you came up with something you liked.

Anyway, all of that aside, there are no 8 ohm LE85s. Some are printed with 8 ohms and some with 16 ohms. Typically they are ALL more like 10-12 ohms. If you were designing a network, it would make a real difference, but going this route, I wouldn't sweat it. Keep screwing around until you find something you like or you blow something up. With care the risk of driver failure is low... you might create an impedance that your amp isn't thrilled with though.


Widget

[Beowulf57]

Re-read post# 13.

That said, these crossover networks are not designed for generic use. Each network was designed for a specific set of drivers. If you read the crossover chart here: http://www.lansingheritage.org/images/jbl/catalogs/1976-comp/page7.jpg

You will see you were already going about it all wrong, but with years of messing around you came up with something you liked.

Anyway, all of that aside, there are no 8 ohm LE85s. Some are printed with 8 ohms and some with 16 ohms. Typically they are ALL more like 10-12 ohms. If you were designing a network, it would make a real difference, but going this route, I wouldn't sweat it. Keep screwing around until you find something you like or you blow something up. With care the risk of driver failure is low... you might create an impedance that your amp isn't thrilled with though.


Widget

Thanks Widget! The info on the LE85 impedance is useful. It is an interesting experiment...and to find out that so far using the recommended N1200S + 3106 for the D130/131/LE85/2405H does not yet sound as good as the use of the LX5 which was designed for the LE15A/H is intriguing. I'm going back to that combination for awhile to see if i notice anything the "properly matched" arrangement is doing better.

I won't have problems with my tube amps as they are built like the proverbial brick ****house, with industrial grade components. They put out around 30 watts, but I rarely listen to more than 1 watt output...10 watts drives everyone out of the house and it ain't distortion. I've had real fun with the corner loaded horns by cracking the windows of the listening room open about three inches and listening to pipe organ music from outside...the whole neighbourhood has fun with this "horn-loaded resonant chamber" effect..

[speakerdave]

Can you point me to a place where there are details about those horns?

Thanks,

David

[Beowulf57]

Can you point me to a place where there are details about those horns?

Thanks,

David

David,

I've never found specific detailed plans of the design. My father, John Ross Cann (president of Raytheon Canada) and a friend (Henry Northcote, who was the head of the machine shop at Raytheon Canada) built these cabinets back in the late 50's, early 60's.

I may have a rough plan of the cabinet configuration somewhere and if I can locate it, I'll post it.

The horn is exponential. Behind the front firing bass driver is a ^ chamber (looking from above) and the throat of the horn feeds from the front edge of the chamber on both sides (roughly a 1.5" gap). Then the exponential flair passes to the rear, turns at the back of the cabinet (which has a wide "^" shape) and returns to the front flair which is a 90 degree angle to fit into the corner of the room. From the throat of the horn backloading chamber to the mouth, the cabinet has two braces continuously on the horizontal plane, so you have three exponential horn chambers on each side as you look at the cabinet from the front. The wood is 3/4" plywood with mahoghany veneer for the finish surface.

I know this is difficult to describe using words alone, so, I'll try to provide a pictorial view of the design.

It loads the bass driver to 40 Hz and drops off at a rate of 12dB per octave after that point. i have usable response down to 28Hz.

[Beowulf57]

Here are a few more pics of the Brociner modified folded corner horn. The cabinet is about 29.5" high, with a 24" front section across (the baffle is 18" wide by 27" high); the ports are roughly 9.5" across and the side sections are 19.5", with a 9.5" section at the rear. These are exterior dimensions. The cabinet is 20.25" deep. Internally, the ports are 7.875" wide by 27.125" high at the mouth of the horn and the horizontal braces are 8.25" from the top and bottom and 9.25" apart in the centre. These dimensions are for the D130 15" bass driver; the dimensions for the D131 12" bass driver are similar, but the height of the cabinet is a few inches less.

I prefer the 15" cabinet designed by my father as the baffle is fixed by 4 large bolts to an internal steel framework; the 12" cabinet (built by Henry Northcote) uses a large brass mounting plate which is bolted to the front face of the cabinet (the D131 is bolted to this plate).

The diagram give s a rough layout of the interior from the top. This design requires considerable woodworking skill (my father was a skilled craftsman in the use of wood, metal, etc., and was a fine furniture maker as well).

[johnaec]

My biggest concern is what looks to be about a 4 foot delay of the sound coming out the horn sections vs. the direct radiator. It seems like certain frequencies would really be additive while others would cancel.

John

[Beowulf57]

My biggest concern is what looks to be about a 4 foot delay of the sound coming out the horn sections vs. the direct radiator. It seems like certain frequencies would really be additive while others would cancel.

John

Yah sure...about 3.25' path difference (you can calculate the effect at various bass frequencies). There is very little horn output above 150-180Hz. To my ears the effect is not that noticeable (yes a few spots with emphasis that can be heard with cello for example), and less of an impact than the room resonant nodes which result from corner loading in the bass region. I could live with the path difference between the D130/131 and the LE85 (in fact the LX5 crossover has the polarity reversed between the LF and HF sections in an attempt to compensate for the path difference, as per JBL's instructions), so this is not a big issue.

Nice bass transient performance with very little overhang...in the end it works quite nicely.

[Beowulf57]

Okay...back to LX5 and first impression is that the midrange balance is better and the lower bass has better presence, but there may be a slight upper mid-bass emphasis. I will report more on the tweaking. I await the L-pads to adjust the LE85 level more precisely and will compare the N1200S and the LX5 once that is in place.

[Beowulf57]

Question for the crossover experts: Will the use of a Zobel (conjugate RC) designed for a particular bass driver with another bass driver change the frequency response curve of the crossover/driver combination? The Zobel in the LX5 (500Hz, designed for use with the LE15A) is a 13.5uF cap + 10 ohm resistor across the LF driver. The Zobel in the N1200S (1200Hz, designed for use with the D130) is a 12uF cap + 15 ohm resistor. What I notice is increased bass level using the LX5 with the D130, compared to the N1200S. Actually sounds better balanced and more extended with the LX5, despite the fact that it is the incorrect crossover.

[grumpy]

I didn't try to simulate it, but I would expect the answer to be something like
"certainly, but not significantly."

...but the crossover change 500->1200, the spectral balance of just the 15"
driver will change... which could lead one to "hear" a change in bass
emphasis. If listening to the entire system (as opposed to just the bass
driver), the change in characteristics of a 15" driver vs. compression
driver/horn in the 500-1200Hz range could also change the perceived system
balance (e.g., more or less pronounced midrange emphasis).

Seems like you have a strong preference for the LX5 in this system. Unless
you have an interest in crossover design, I'd sell the 1200S and buy some
nice source material (CD/vinyl/whatever) to enjoy the speakers with. :)

ah... and I make no claim to being a "crossover expert"... there are folks
that have direct experience (some decades) and earn a living in that capacity.

[robertbartsch]

...Over the years I have listened to two bass horn systems on many occassions and each produces great sound. These include:

1. Altec VOTT in bass horn trim with the cast HF horns mounted "nudie style" on top
2. Klipsch in the corner horn cabinet, which is similar to the one below except in a taller CAB, I believe

Obviously, the Klipsch style cabinet is more pleasing to the eye, so that might be one consideration if you are married to a person who HATES big speaker boxes in her (??? Huuu) home, for example.

Personnally, I think both designs are very distintive and provide an interesting showcase for discussion by visitors who might come to your home for a visit.

[Beowulf57]

I didn't try to simulate it, but I would expect the answer to be something like
"certainly, but not significantly."

...but the crossover change 500->1200, the spectral balance of just the 15"
driver will change... which could lead one to "hear" a change in bass
emphasis. If listening to the entire system (as opposed to just the bass
driver), the change in characteristics of a 15" driver vs. compression
driver/horn in the 500-1200Hz range could also change the perceived system
balance (e.g., more or less pronounced midrange emphasis).

Seems like you have a strong preference for the LX5 in this system. Unless
you have an interest in crossover design, I'd sell the 1200S and buy some
nice source material (CD/vinyl/whatever) to enjoy the speakers with. :)

ah... and I make no claim to being a "crossover expert"... there are folks
that have direct experience (some decades) and earn a living in that capacity.

Thanks grumpy. I have lots of music to enjoy...was mostly interested in learning a bit more about the possible effects of the Zobel network. Yes, the perceived balance is affected by the characteristic of the D130 around the region of the higher crossover point. I seem to recall the D130 was originally designed for musical instrument reproduction (e.g. guitar) and perhaps the rising characteristic with a peak in the 1-3KHz region was to bring out the midrange presence in live performance. This is not quite what I want in a home system, so the LX5 may work better.

[Beowulf57]

...Over the years I have listened to two bass horn systems on many occassions and each produces great sound. These include:

1. Altec VOTT in bass horn trim with the cast HF horns mounted "nudie style" on top
2. Klipsch in the corner horn cabinet, which is similar to the one below except in a taller CAB, I believe

Obviously, the Klipsch style cabinet is more pleasing to the eye, so that might be one consideration if you are married to a person who HATES big speaker boxes in her (??? Huuu) home, for example.

Personnally, I think both designs are very distintive and provide an interesting showcase for discussion by visitors who might come to your home for a visit.

Here's a pic of the system with the 2405H added. I like the look with the HF driver in the open, as does my wife. My wife was much more concerned (she is a musician) that I might prefer the higher crossover point as she did not like the imbalance resulting from greater midrange presence and lesser bass (perceived or actual not yet fully determined).

[Beowulf57]

Well...I've done lots of reading through the forums, checking of specification sheets and calculations and have some questions before I lose my mind!

1. Is the LE85/2420 a negative polarity transducer (as in the diaphragm moves inwards in response to a positive going signal)? Both the D130 and the 2405H appear to be negative.

2. The LX5 and 3115 appear to be identical networks, however, the LX5 network service bulletin for the LX5 calls for a reversal of the leads to the HF driver, the bulletin for the 3115 does not? Which is correct? I've been using the HF reversed connection to the 3106 network and left the UHF 2405H connected in sync with the LE85. When I used the N1200S network, I did not reverse the HF connections and thus the 2405H was in a different phase relation to the D130 using the two networks (in phase with the N1200 and out of phase with the LX5) Also with the addition of the 3106, the phase of the LE85 gets a 2nd 180 degree filter...yes? no?! Don't worry about it? :banghead: Help!

3. If a 2nd order crossover results in a 180 degree phase shift, why is it claimed that the HF driver should be connected in reverse to the LF driver to compensate specifically for this phase shift? Both drivers are fed by a 2nd order filter...would they not be therefore be in phase? Or is this due to different phase characteristics in the stopband of the LF and HF sections of the crossover?

4. Using the D130 and the LE85, the driver offset due to the HL91 horn is approximately 8". This would lead to a 180 degree phase difference a little above 800Hz, but does the horn length also affect the phase shift in addition to the driver offset?

5. The LX5/3115 crossover is spec'd at 500Hz, however the network service bulletin shows the response to be down 9dB (LX5) and 7.5dB (3115) at the crossover point and 18dB down at 300Hz, so it's clearly not a simple 12dB/octave rolloff from 500Hz and perhaps was adjusted to compensate for the use of the LE85/2420 down to the 500Hz crossover point with the HL91 horn. The 3dB point looks to be around 1000Hz as the network measures 5dB down at 900Hz for the HF section.

I know this is a lot of questions...but help on any would be appreciated...I'm even wondering if I should try the N1200S with the connections to the 3106 reversed as that midrange emphasis relative to the LX5 could have been a crossover point hump. I'm not just looking to optimize my driver interactions, I love to understand what's going on...so any education will be gratefully received.

Beowulf57

[toddalin]

Well...I've done lots of reading through the forums, checking of specification sheets and calculations and have some questions before I lose my mind!

1. Is the LE85/2420 a negative polarity transducer (as in the diaphragm moves inwards in response to a positive going signal)? Both the D130 and the 2405H appear to be negative.

2. The LX5 and 3115 appear to be identical networks, however, the LX5 network service bulletin for the LX5 calls for a reversal of the leads to the HF driver, the bulletin for the 3115 does not? Which is correct? I've been using the HF reversed connection to the 3106 network and left the UHF 2405H connected in sync with the LE85. When I used the N1200S network, I did not reverse the HF connections and thus the 2405H was in a different phase relation to the D130 using the two networks (in phase with the N1200 and out of phase with the LX5) Also with the addition of the 3106, the phase of the LE85 gets a 2nd 180 degree filter...yes? no?! Don't worry about it? :banghead: Help!

3. If a 2nd order crossover results in a 180 degree phase shift, why is it claimed that the HF driver should be connected in reverse to the LF driver to compensate specifically for this phase shift? Both drivers are fed by a 2nd order filter...would they not be therefore be in phase? Or is this due to different phase characteristics in the stopband of the LF and HF sections of the crossover?

4. Using the D130 and the LE85, the driver offset due to the HL91 horn is approximately 8". This would lead to a 180 degree phase difference a little above 800Hz, but does the horn length also affect the phase shift in addition to the driver offset?

5. The LX5/3115 crossover is spec'd at 500Hz, however the network service bulletin shows the response to be down 9dB (LX5) and 7.5dB (3115) at the crossover point and 18dB down at 300Hz, so it's clearly not a simple 12dB/octave rolloff from 500Hz and perhaps was adjusted to compensate for the use of the LE85/2420 down to the 500Hz crossover point with the HL91 horn. The 3dB point looks to be around 1000Hz as the network measures 5dB down at 900Hz for the HF section.

I know this is a lot of questions...but help on any would be appreciated...I'm even wondering if I should try the N1200S with the connections to the 3106 reversed as that midrange emphasis relative to the LX5 could have been a crossover point hump. I'm not just looking to optimize my driver interactions, I love to understand what's going on...so any education will be gratefully received.

Beowulf57

This stuff can drive you crazy.

I used to select a tone on an oscillator at the crossover frequency and using a sound level meter, determine which way was louder. This is usually the correct orientation. I'd do it for the mid relative to the woofer, then the tweeter relative to the mid. ;)

After I got the Behringer, with 61 bands of real-time analysis, I determined that the above method may not be the best. Other portions of the band are also affected and other frequencies may be louder with the other orientation.

Ultimately, I just use the Behringer and determine which orientation gives the overall smoothest response in the room, which is also part of the equation that is typically not considered.

The Behringer cost ~$125 with the mic on the 'Bay and is definately a worthwile investment in sound.

And before I get flamed here, I only use it for measurement and the rest of the time it sits in the closet. It is nowhere to be found in the audio chain. :p

[Doc Mark]

Hey, Todd,

What model of Behringer did you get? Thanks, and God Bless!

Every Good Wish,
Doc

[toddalin]

Hey, Todd,

What model of Behringer did you get? Thanks, and God Bless!

Every Good Wish,
Doc


I use an Ultracurve DEQ 2496. Many of us use it on this forum..., probably lots people more than will admit to it. ;)

For my ~$125 'Bay purchase, I also got the ECM8000 microphone.

http://www.enjoythemusic.com/magazine/equipment/0705/behringerultracurve2496.htm

[Beowulf57]

This stuff can drive you crazy.

I used to select a tone on an oscillator at the crossover frequency and using a sound level meter, determine which way was louder. This is usually the correct orientation. I'd do it for the mid relative to the woofer, then the tweeter relative to the mid. ;)

After I got the Behringer, with 61 bands of real-time analysis, I determined that the above method may not be the best. Other portions of the band are also affected and other frequencies may be louder with the other orientation.

Ultimately, I just use the Behringer and determine which orientation gives the overall smoothest response in the room, which is also part of the equation that is typically not considered.

The Behringer cost ~$125 with the mic on the 'Bay and is definately a worthwile investment in sound.

And before I get flamed here, I only use it for measurement and the rest of the time it sits in the closet. It is nowhere to be found in the audio chain. :p

Thanks for the suggestion Toddalin. :) Before I start spending more...any other responses to my queries :bouncy:?

[1audiohack]

I've read this and your new thread with complete empathy.

Like Todd said, this stuff can drive a guy mad.

The last thing anyone wants is to have some little acoustic god come and clap your room and tell you everything thats wrong with everything you own!

That said, do you think there may be someone in your area with some measurement equipment?

I'm not sure about anything I don't own, CLIO or the like, I have TEF and a TEF unit, or something similar capable of TDS measurements in the hands of someone experienced with it could answer most all of your questions about the absolute polarity of your playback system from the preamp to the speaker components and leave you with graphed measurements of frequency response, magnitude, and phase.

If you set up in advance to be able to swap things around, like having the crossovers out of the cabinets, you could probably get it done in two or three hours, and at least know what you have to work with.

One of the first tools I bought was a Cricket. I was happy with it until I dicsovered that it really struggled with polarity with horns, many measurment systems do I believe due to the changing apparent apacey with changes in frequency. spelling? I have RTA as well, a good tool with limitations.

The TEF opened up a whole new world for me, I can make big system changes and get it close in very short order, electronic crossovers make it easy though.

Best of luck, it isn't easy unless your deaf.

[Beowulf57]

I've read this and your new thread with complete empathy.

Like Todd said, this stuff can drive a guy mad.

The last thing anyone wants is to have some little acoustic god come and clap your room and tell you everything thats wrong with everything you own!

That said, do you think there may be someone in your area with some measurement equipment?

I'm not sure about anything I don't own, CLIO or the like, I have TEF and a TEF unit, or something similar capable of TDS measurements in the hands of someone experienced with it could answer most all of your questions about the absolute polarity of your playback system from the preamp to the speaker components and leave you with graphed measurements of frequency response, magnitude, and phase.

If you set up in advance to be able to swap things around, like having the crossovers out of the cabinets, you could probably get it done in two or three hours, and at least know what you have to work with.

One of the first tools I bought was a Cricket. I was happy with it until I dicsovered that it really struggled with polarity with horns, many measurment systems do I believe due to the changing apparent apacey with changes in frequency. spelling? I have RTA as well, a good tool with limitations.

The TEF opened up a whole new world for me, I can make big system changes and get it close in very short order, electronic crossovers make it easy though.

Best of luck, it isn't easy unless your deaf.

Many thanks 1audiohack...I'll check out the possibilities in my area. With your help and that of the other great folks here, I'm beginning to get my head around the important parameters and how to approach the voicing/phasing issues for my system. Thus, :banghead: has with the help of others :applaud: led me closer to :D!

[Mr. Widget]

Best of luck, it isn't easy unless your deaf.:applaud: :rotfl: :applaud:

If I used a signature, I'd change it to, "It ain't easy unless you're deaf."

I love that line... it is soooo true!


Widget

[Beowulf57]

If a pair of 2312's were available ...does anyone know from experience if this would make an improvement over my HL91's when crossed over at 500Hz?

[Mr. Widget]

If a pair of 2312's were available ...does anyone know from experience if this would make an improvement over my HL91's when crossed over at 500Hz?An improvement?

It would seem that we are too far down the subjective path here to make that kind of recommendation. It is quite possible you would like them better, but it is also quite possible that you would find the difference modest or even unacceptable.

Your system as you have described it seems to be one that has been dialed in by the owner for his own pleasure. I wouldn't feel confident about making any recommendations.


Widget

[Beowulf57]

An improvement?

It would seem that we are too far down the subjective path here to make that kind of recommendation. It is quite possible you would like them better, but it is also quite possible that you would find the difference modest or even unacceptable.

Your system as you have described it seems to be one that has been dialed in by the owner for his own pleasure. I wouldn't feel confident about making any recommendations.


Widget

Fair enough, though having received and read a number of posts concerning the "problems" of using the LE85/HL91 combo with a 500Hz crossover, I'd like to hear any comments (to be more specific;)) on the changes in the sonic signature which others have encountered using the longer HL92/2312.

Yes, it is subjective and yes, I have listened to the existing combo for many years with no driver damage (not sure I can say the same for my ears:D) and enjoyable sound, however we do tend to report on the subjective effects of changes to our systems and seek improvements over time.

A different bass driver may provide more extended bass, leaner upper midbass, a warmer sound, etc.; a midrange driver may sound clean and detailed, rich, hard, bright or have excessive glare, etc.; a tweeter may roll off too soon and lack air, or it may have a sibilant spit, or as in the case of adding the 2405H to my system the high frequencies became more noticeable and there was a distinct improvement in the sense of "air" of the acoustic recording space and in the delicate shimmer and decay of cymbals. As well, a slight hardness/glare diminished.

So, if anyone can comment on the subjective changes in the sound of music noted when switching to the longer horn, I'm all ears:bouncy:.

[Beowulf57]

For want of a detail, polarity was lost.
For want of polarity coherence was lost.
For want of coherence, 25 years of enjoyment was lost.
And all for want of a detail!

Just kidding, I have enjoyed the sound for 25 years, however:

I have been using an LX5 for 20+ years with an LE85/HL91 with the polarity to the HF section reversed. This was based upon a JBL Network Service Bulletin (6-74) I was given when I acquired the LE85/HL91s from a local audio emporium. The components had come from an S7 system. I recently changed the connection so both the LF and HF connections were the same polarity and the sound improved markedly: a lower midrange "suckout" disappeared and the presentation was richer, more coherent and more delineated. Also, less in your face midrange and much better balanced sound. As it seems now, that bulletin referred to the use of the LX5 in the S8R with the 375 and the shorter HL93 horn and not to the use of the LX5 with the LE85/HL91!

So, onwards and upwards I go: thanks to this forum for returning the Kingdom of Wonderful Sound to me through all the excellent advice!

Now, I acquired a pair of 2312 horns and will try them after revisiting the N1200 crossovers...hmm, perhaps I'll reverse the phase and see if that ameliorates the hot midrange.

[Beowulf57]

Replaced my H91/2307 horns with the H92/2312 horns. I had forgotten that years ago I had surrounded the horns with grey, sticky crack insulation putty to dampen the metallic resonance of the cast aluminum horns (flick the inside of the horn with your fingernail and you can hear the ringing. So, off to the hardware store for more putty (11.5" of horn to cover, rather than 8.5").

It took about three hours to remove the cabinets, replace the horns and reconnect. Once everything was in place I settled down for some listening with LPs and SACDs. First impressions: smoother sound, less strident (e.g., massed strings) and less aggressive on vocals. A good start. However, when listening to satellite programming and DVD films, voices sounded muted and a bit muffled. I played with the level control on the LX5 crossovers, and went back and forth between too much midrange and too little. What next?

Hmm...the three drivers are all hooked up in phase which sounded best with the shorter horns, but the new horns are 3" longer which affects the phase response lobes around the crossover (500Hz). I reversed the phase of the connection to the 3106 network: Eh Voila! Much better: the sound was better integrated and richer and I could listen to satellite/DVDs without needing to add sound from the TV speakers to hear dialogue clearly.

Another tweak: I reversed the connections to the 2405H tweeters and the top end was more lively and better balanced with the rest of the audio spectrum. At the moment, I am running the LX5 crossovers at minimum and so far I'm not sure I'll need to add L-pads to the LE85s in order to get more level form the 2405Hs...sounds hot enough on top at the moment.:applaud:

[Beowulf57]

From the following thread on JBL POLARITY CONVENTION: http://audioheritage.org/vbulletin/showthread.php?t=9&page=3

"A comment on "correcting" JBL polarity
If you are going to reverse the polarity of a JBL cabinet, it must be done AT EACH COMPONENT in the cabinet. You should not simply hook-up the cabinet red-to-black. That will not have the proper effect, because that will result in the signal being pathed through the transducer before the capacitor(s) - this is a DC circuit, and that is backwards. For the crossover network to work properly, the capacitor(s) must see the signal BEFORE the transducer, regardless of cabinet (and transducer) polarity.

To "correct" or re-phase a vintage JBL cabinet, you need to reverse-wire at each component. Simply alter the signal path AFTER the crossover and before the transducer, at each component binding posts. "

My question: is there really any difference (other than when testing for polarity using a 9V DC battery) between reversing the leads from my LX5 to the 3106 and then reversing the HF so it is in phase with the LF, and leaving the 3106 in phase with the LX5 and reversing the MF alone? The goal is to put the MF 180 degrees out of phase with the LF and HF. Audio is AC and the capacitors are non-polarized, so my common sense tells me the result is the same in both cases. However, perhaps my brain is fogged and missing a crucial point.:confused:

[Zilch]

No.

Audio is AC.

[Beowulf57]

No.

Audio is AC.

:yes::cheers:

[Beowulf57]

Information please: what is the effect of adding an 8 ohm l-pad to the LF section of the 3106 network, after the 20 ohm resistor rather than before?

[Beowulf57]

Functionally, I'd expect you'd want to keep the L-pad (whose job it is to
present the preceding circuit with a nominal resistance, e.g. 8 ohms) right
after the LC network, such that the crossover frequency and response shape
remain fairly constant.

Also, having the 20 ohm "dampening" resistor nearest the compression
driver has it's intended function there as well.

Would you hear a difference if you swapped where the L-pad was
relative to the driver? Maybe. I'd -think- unsoldering one leg of the 20
ohm resistor to find out for yourself might be worthwhile.

Thanks Grumpy. Perhaps I'll try both then. By the way, what does the "dampening" resistor dampen? The resonant impedance peak?

[grumpy]

That's what I'd expect... that and cut down the level a smidge, since the source
impedance feeding the resistor and driver in parallel is non-zero. Other effects
such as giving a low-ish DC path for driver EMF have been posited, but this is
more than I know.

More simply, that it sounds better with the resistor in place seems
to be the repeatedly conveyed experience here. I can't honestly say
I've bothered testing audibility of this, but have no reason to doubt
the folks here with direct/years of hands-on experience.

[Beowulf57]

That's what I'd expect... that and cut down the level a smidge, since the source
impedance feeding the resistor and driver in parallel is non-zero. Other effects
such as giving a low-ish DC path for driver EMF have been posited, but this is
more than I know.

More simply, that it sounds better with the resistor in place seems
to be the repeatedly conveyed experience here. I can't honestly say
I've bothered testing audibility of this, but have no reason to doubt
the folks here with direct/years of hands-on experience.

Well, to start I simply hung the 8 ohm L-pad across the network output terminals to the LE85s. So far I like the LX5 set to the "mid" attenuation which gives a nice degree of HF output from the 2405Hs (max is too hot and with the mid setting, I can set the HF (3106) L-pad to max and it is effectively out of the circuit). The MF needs a little attenuation and I dialed in approximately -2dB with the external L-pad. Sounds nicely balanced...but I have more listening to do to check this out.

What is interesting is that at the -2dB setting, the L-pad measures approximately 4.5 ohms in series and 17.5 ohms in parallel with the LE85 driver (impedance~12 ohms). The impedance flattening resistor is 20 ohms. So by my calculations, I get ~7.4 ohm load on the network. Without the L-pad it is ~7.5 ohms. Pretty close and the LE85 still has 17.5 ohms across it to flatten that impedance peak. On the other hand, if I try the L-pad before the 20 ohm resistor (and assuming that I finally settle upon the -2dB setting) the load seen by the network would rise to 9.8 ohms, 30% higher than the original nominal load.

Now...I don't know all the implications of this? Perhaps with the higher load, the network response would rise and show less attenuation (I recall a JBL network instruction manual which showed that placing a lower than nominal load on a network resulted in a response dip in the crossover region, so possibly a higher load would raise it), thus requiring a higher degree of attenuation to reach the desired MF level. A higher L-pad setting (when placed before the 20 ohm resistor) would actually increase the overall load slightly.

All this leads me to wonder if (in my case) placing the L-pad right across the driver is optimum from the point of view of the network configuration?

[grumpy]

All this leads me to wonder if (in my case) placing the L-pad right across the driver is optimum from the point of view of the network configuration?I'm not sure what you're measuring... or what your -2dB is indicated on, so it
might be worth confirming a few things:

http://www.apicsllc.com/apics/Misc/filter2.html ... go to the bottom and plug in
driver impedance (in this case, use "8", as that's the L-pad you're using) and
"2" as the attenuation; with the l-pad knob set to "-2" you should be able to
measure R1 between the Lpad input and speaker output, and R2 between the
speaker output and ground/common, with nothing else attached.

...but the point of an L-pad is to approximate a consistent load as viewed by
the circuit upstream, while being able to vary the attenuation as seen at the output.

If you use an L-pad that isn't roughly close to the speaker load (or speaker plus
resistor load), the impedance seen by the upstream circuit (L-pad plus speaker)
will change with attenuation, and in a passive crossover, also affect the frequency
response. Dropping the 20 ohm resistor and finding a single optimized setting
for the 8ohm L-pad (attenuation - and parallel resistance) was just lucky.

If the upstream circuit is expecting the parallel load of 20ohms plus driver
(or a nominal 7.5 ohms if you make the -assumption- of a 12ohm driver), then
inserting an 8ohm L-pad seems appropriate. In setting up the 3133A network
though, JBL decided to use a 16ohm L-pad, so perhaps the 12ohm assumption
isn't the best. Do you have an impedance plot of an LE85/2420 on the horn
you're using? If not, I think I can set one up at home this weekend (no lens though).

[Beowulf57]

I'm not sure what you're measuring... or what your -2dB is indicated on, so it
might be worth confirming a few things:

http://www.apicsllc.com/apics/Misc/filter2.html ... go to the bottom and plug in
driver impedance (in this case, use "8", as that's the L-pad you're using) and
"2" as the attenuation; with the l-pad knob set to "-2" you should be able to
measure R1 between the Lpad input and speaker output, and R2 between the
speaker output and ground/common, with nothing else attached.

...but the point of an L-pad is to approximate a consistent load as viewed by
the circuit upstream, while being able to vary the attenuation as seen at the output.

If you use an L-pad that isn't roughly close to the speaker load (or speaker plus
resistor load), the impedance seen by the upstream circuit (L-pad plus speaker)
will change with attenuation, and in a passive crossover, also affect the frequency
response. Dropping the 20 ohm resistor and finding a single optimized setting
for the 8ohm L-pad (attenuation - and parallel resistance) was just lucky.

If the upstream circuit is expecting the parallel load of 20ohms plus driver
(or a nominal 7.5 ohms if you make the -assumption- of a 12ohm driver), then
inserting an 8ohm L-pad seems appropriate. In setting up the 3133A network
though, JBL decided to use a 16ohm L-pad, so perhaps the 12ohm assumption
isn't the best. Do you have an impedance plot of an LE85/2420 on the horn
you're using? If not, I think I can set one up at home this weekend (no lens though).

Thanks Grumpy...I don't have an impedance curve on the LE85/2312 combination. Curves I've seen seem to suggest around a 12 ohm AC impedance...so, I used that as a guesstimate. If you can do a curve with the 2312 horn, that would be great.

I didn't remove the 20 ohm resistor, and my L-pad values were drawn simply from the resistance measurements I made once I found a setting I liked (with the L-pad out of circuit of course). My "dB" calculations were wrong if I go by the examples from http://www.apicsllc.com/apics/Misc/filter2.html. Extrapolating from the values possible using the calculator (in this case with a load of 12 ohms since the L-pad is right on the LE85 input), I think my attenuation with the two L-pad legs measured (4.5 & 17.5 ohms) comes out more like ~-4.0-4.5 dB. I tried to use 10*log [(R2/R1+R2)^2], which comes out to -1.98dB...got it wrong I guess.

In any case, I calculated the load on the network simply using the series and parallel resistance values in the circuit. Gosh, I hope I got that right at least!:blink:

[grumpy]

Equation is OK, if you first combine Rload in parallel with "R2" -as- R2 in
the equation. (not simply the L-pad R1, R2 voltage divider).
(then, realize that this isn't exact either as the source impedance feeding
this from a passive network isn't zero, but ignore that for now).

Personally, I'd show the equation as 20log... for voltage ratios and drop the ^2,
(just so it's more obvious to those still sorting this stuff out) but it's the same result.

Weird L-pad reading combination though...

I'll try to do a sweep. It'll give me motivation to try out the new (as of September)
S&LA WooferTester2 v4.0.

If someone has a plot handy and can post before I get to it... great.
Meanwhile, here's one on a 2370A:

http://www.audioheritage.org/vbulletin/showpost.php?p=135084&postcount=9

Looks like in the target crossover range, the driver impedance is a bit higher than 12 ohms
(on that horn, probably not on a baffle).

[Beowulf57]

Right...:o:. I forgot to include Rload in the calculation of the attenuation. Now I get -4.25dB which makes much more sense. The load impedances seen by the network still work out pretty much as per my first calculations. My horn has the lens and sits on a baffle.

[grumpy]

Purpose? 1) Illustrate magnitude of impedance at/around proposed
crossover frequencies... affecting frequency determining component
values. 2) Install/use S&L's new WT2 software update :)

Didn't have time to dig out box w/ 2420 and disassemble...
I also have no 2308-type lenses, so these plots are all without.

Note that adding a (flat) baffle did not significantly change resonant
frequencies, but lowered the amplitude (Q) at the 600Hz peak.

Also note that changing drivers did not appreciably change the
impedance peak frequencies until well below 1KHz (presumably
predictable horn effects). Could the low freq peak shift be partially
due to the difference in in-driver throat length (deeper in alnico
driver) or ??

(no time for ringing tests this weekend... maybe in 2 weeks)

[Beowulf57]

Wow..nice software! Thanks for the impedance sweeps. Which I wonder would be closest to the 2420/LE85?

Taking a cue from the Network Service Bulletin on the LX5 which quotes attenuation at 900Hz (-5 -7 -10 for the max, mid and min settings), I note that the 2425J has an impedance around 50 ohms and the 2421A around 17 ohms. Using my L-pad values, this gives -2.6dB and -3.6dB attenuation at 900Hz respectively. Given that my LX5 is set to the mid position (to allow sufficient level to the 2405H) this suggests that I'm pretty close to the "Min" position level on my LE85 (-9.6 to -10.6)...at 900Hz. If I use the value from Zilch's curves, ~24 ohms, this gives -3.2dB, so all three are in the same ballpark.

The curves posted by Zilch on the LE85/2370A horn are similar to your 2425J curves (though the impedance peaks are shifted) and both seem to agree with Widget's comment that these drivers (whether marked 8 or 16 ohms) are all around 10-12 ohms. Though I'm not sure on the method for determining the nominal impedance from the curves? Your curve for the 2421A however looks like a "true" 8 ohm driver...I've noticed that aftermarket diaphragms spec a DC resistance of 3.2 ohms for the 8 ohm models and roughly twice that for the 16 ohm models. Did JBL change the impedance of the 2421A from their old convention, or perhaps it has an aftermarket diaphragm?

[4313B]

Once again... the 2421A is "8 ohms" (D8R2421) and the 2421B is "16 ohms" (D16R2421)

An LE85 was equivalent to a 2420 and both used the D16R2420 diaphragm.

The LE85/2420 diaphragm (D16R2420) no longer exists so either core can use the D8R2421 or D16R2421 (official replacement) depending on the end user's wishes.

The D8R2425 (2425H) or D16R2425 (2425J) titanium diaphragms can also be used.

[Beowulf57]

Once again... the 2421A is "8 ohms" (D8R2421) and the 2421B is "16 ohms" (D16R2421)

An LE85 was equivalent to a 2420 and both used the D16R2420 diaphragm.

The LE85/2420 diaphragm (D16R2420) no longer exists so either core can use the D8R2421 or D16R2421 (official replacement) depending on the end user's wishes.
The D8R2425 (2425H) or D16R2425 (2425J) titanium diaphragms can also be used.

Thanks 4313B, knowing that the 2421A actually had a lower impedance diaphragm confirms what I suspected from the curves. I hope you didn't feel exasperated with my ignorance.;)

[Zilch]

Well, the plot thickens then, doesn't it, impedance-wise?

I didn't know that, actually, other than to observe that DxR2421 (don't know which I have, actually,) measured differently from the stock LE85 diaphragms when I sprung the big bucks for a pair.

Why'd I do that? Because the aluminum ones are inherently more damped than the titaniums, and even with the diamond surround, sound smoother to me.

So, I guess there IS value inherent in wax-sealed LE85/2420s (assuming 2420s were sealed,) in terms of having the original D16R2420 diaphragms, though they should probably be opened, cleaned, reconditioned, realigned and tested in any case, there being other elements subject to aging, such as the rear damping pad. It's not as if the front is sealed from environmental exposure, either.

The overall condition of the diaphragms also being a function of how they were used in their former life (or lives,) it's a wonder these old horses can still run well at all, but when they do, they're mighty sweet.... :thmbsup:

[4313B]

I hope you didn't feel exasperated with my ignorance.;)I try not to answer posts while feeling exasperated anymore. :D
So, I guess there IS value inherent in wax-sealed LE85/2420s (assuming 2420s were sealed,) in terms of having the original D16R2420 diaphragms, though they should probably be opened, cleaned, reconditioned, realigned and tested in any case, there being other elements subject to aging, such as the rear damping pad.I would imagine the red wax seals appeal to collectors.

[Beowulf57]

Well, the plot thickens then, doesn't it, impedance-wise?

I didn't know that, actually, other than to observe that DxR2421 (don't know which I have, actually,) measured differently from the stock LE85 diaphragms when I sprung the big bucks for a pair.

Why'd I do that? Because the aluminum ones are inherently more damped than the titaniums, and even with the diamond surround, sound smoother to me.

So, I guess there IS value inherent in wax-sealed LE85/2420s (assuming 2420s were sealed,) in terms of having the original D16R2420 diaphragms, though they should probably be opened, cleaned, reconditioned, realigned and tested in any case, there being other elements subject to aging, such as the rear damping pad. It's not as if the front is sealed from environmental exposure, either.

The overall condition of the diaphragms also being a function of how they were used in their former life (or lives,) it's a wonder these old horses can still run well at all, but when they do, they're mighty sweet.... :thmbsup:

Yes, yes, yes...I love the sound of the LE85s and even better now with the longer 2312 horns.

My LE85s are 30+ years old (the bass drivers are more like 45 years) and still sealed. I recently picked up a pair of 2420s (still sealed and with 2307 horns attached) in case I ever destroy (:bs:) my LE85s and to test them out, wired them in parallel with the LE85s. Sounded fine, though they seemed and bit brighter and louder than the LE85s. Your notes about aging had me concerned at first :( but then I remembered to think through the details of the test situation carefully.

Ahh so...the 2420s were attached to the shorter (and brighter, more aggressive sounding) 2307 horns, the horns were undamped and not attached to a baffle (For whom the Bell Tolls) and they were wired out of phase to the LF (given the driver offsets, I had determined that this was good for the longer horns and not so good...as in harder and brighter...for the shorter horns). Whew...I guess my LE85s are not on their last legs.:bouncy:

I am getting quite fascinated with this impedance question and still wonder if there is any reason to place the L-pad before the 20 ohm damping resistor, given that the parallel leg of the L-pad provides a 17-18 ohm resistance across the driver?:confused:

[Zilch]

I am getting quite fascinated with this impedance question and still wonder if there is any reason to place the L-pad before the 20 ohm damping resistor, given that the parallel leg of the L-pad provides a 17-18 ohm resistance across the driver?:confused:It varies with the setting, of course, and the damping resistor is no longer 20 Ohms, in any case.

What is optimum? Measurements of the actual performance might hold a clue, but I doubt it matters significantly.

Did some of that, actually. Stuff behaves in a more predictable fashion when the damping is there.... :dont-know

[Beowulf57]

It varies with the setting, of course, and the damping resistor is no longer 20 Ohms, in any case.

What is optimum? Measurements of the actual performance might hold a clue, but I doubt it matters significantly.

Did some of that, actually. Stuff behaves in a more predictable fashion when the damping is there.... :dont-know

Right, if I set the L-pad to give me very close to 20 ohms in the parallel leg, I have an attenuation of ~-3.7dB and the load on the network is 7.3 ohms.

So, I would guess it's a trade off between slightly changed damping effect with a lower value damping resistance across the driver (though if that 20 ohm resistor is +/- 10%, it could be as low as 18 ohms in any case) and the change in the load seen by the network.

If I assume a 12 ohm nominal value for the LE85, the original load for the 3106 low pass section with the 20 ohm damping resistor is 7.5 ohms. Place the L-Pad directly across the driver and the load is 7.4 ohms (at my desired attenuation); place it before the 20 ohm resistor and it likely rises to 9.8 ohms.

Now, I haven't actually measured the L-pad values with it before the 20 ohm resistor, but even if less L-pad attenuation were required, the load on the network would still be roughly 20% higher than the original 3106 setup.

Without further performance measurements, I'm inclined to favour placing the L-pad after the 20 ohm resistor...at least with the attenuation settings I'm using at present. This would I assume keep the load on the network closer to the original design value. In the end as you say, it probably doesn't matter to a significant degree, but I'm having a great deal of fun experimenting:applaud:. Thanks, and any other thoughts?

[grumpy]

Sorry for mixing in 2425J's and 2421A's when the question was about LE85's...
I'm now thinking that even my 2420's (not measured) probably
have titanium diaphragms, so that still wouldn't have been spot on... it's
what I had.

So... I would draw from this that it's OK to use the "nominal" impedance for
attenuation calculations for most of the driver's bandwidth, but if one wants
an accurate crossover frequency calculation, then some knowledge of the
impedance at and around the crossover frequency can improve the calculated
estimate (since even the "8-ohm" driver had substantial impedance peaks in that range).

[Beowulf57]

Sorry for mixing in 2425J's and 2421A's when the question was about LE85's...
I'm now thinking that even my 2420's (not measured) probably
have titanium diaphragms, so that still wouldn't have been spot on... it's
what I had.

So... I would draw from this that it's OK to use the "nominal" impedance for
attenuation calculations for most of the driver's bandwidth, but if one wants
an accurate crossover frequency calculation, then some knowledge of the
impedance at and around the crossover frequency can improve the calculated
estimate (since even the "8-ohm" driver had substantial impedance peaks in that range).

Your curves were nevertheless very helpful as they provided me with some ranges of values to work from.:D Working with the impedance peak (around 900 Hz) of 17-50 ohms (drawn from your curves and Zilch's) I get between -0.6 and -1.6 dB less attenuation than over the rest of the MF assuming a nominal value of 12 ohms. At the crossover of 500Hz (20-30 ohms), there is -0.8 and -1.2 dB less than over the rest of the range. These differences don't seem to be any significant problem and I doubt they are that much different than the differences which would show up if I measured the effects of the tapped inductor/resistive network in the LX5.

Unless further issues come to light, I think I'm good to go using the L-pad right across the driver at least in the attenuation range I'm using at present.:cheers:

P.S. I could run the LX5 wide open rather than at the "Mid" setting, however then I would have to bring the HF L-pad of the 3106 into action to knock the 2405Hs down; at the mid setting, I think I'll be able to keep HF L-pad out of the circuit completely.

[4313B]

I'm inclined to favour placing the L-pad after the 20 ohm resistor...at least with the attenuation settings I'm using at present.JBL put the 20 ohm resistors across the "16 ohm" drivers to present a better load for the "8 ohm" L-Pads to function somewhat correctly. They helped to flatten out the impedance curves somewhat. The exponential horns presented a real impedance mess in the high pass crossover region. You can flatten them out but it takes a ton of parts.

[Beowulf57]

JBL put the 20 ohm resistors across the "16 ohm" drivers to present a better load for the "8 ohm" L-Pads to function somewhat correctly. They helped to flatten out the impedance curves somewhat. The exponential horns presented a real impedance mess in the high pass crossover region. You can flatten them out but it takes a ton of parts.

"Round and round the mulberry bush...":dont-know

The 3106 crossover has the 20 ohm resistor across the LE85/2420 to flatten the impedance load for the network itself as there is no L-pad in the MF section. If my L-pad has 17-18 ohms (the +/-10% 20 ohm resistor could easily be 18 ohms) in the parallel leg across the driver, does this not also help to flatten the impedance curve?

Also, as I noted below: "If I assume a 12 ohm nominal value for the LE85, the original load for the 3106 low pass section with the 20 ohm damping resistor is 7.5 ohms. Place the L-Pad directly across the driver and the load is 7.4 ohms (at my desired attenuation); place it before the 20 ohm resistor and it likely rises to 9.8 ohms." From what I have read, JBL indicates that using a load higher or lower than the design value will change the network response?

Which is more important and why? Keeping the L-pad before the 20 ohm resistor or keeping the load close to the original design value?

[4313B]

Oops, my fault. I didn't read through the whole thread.

[toddalin]

"Round and round the mulberry bush...":dont-know

The 3106 crossover has the 20 ohm resistor across the LE85/2420 to flatten the impedance load for the network itself as there is no L-pad in the MF section. If my L-pad has 17-18 ohms (the +/-10% 20 ohm resistor could easily be 18 ohms) in the parallel leg across the driver, does this not also help to flatten the impedance curve?

Also, as I noted below: "If I assume a 12 ohm nominal value for the LE85, the original load for the 3106 low pass section with the 20 ohm damping resistor is 7.5 ohms. Place the L-Pad directly across the driver and the load is 7.4 ohms (at my desired attenuation); place it before the 20 ohm resistor and it likely rises to 9.8 ohms." From what I have read, JBL indicates that using a load higher or lower than the design value will change the network response?

Which is more important and why? Keeping the L-pad before the 20 ohm resistor or keeping the load close to the original design value?

Try it in the various configurations and monitor the output on a spectum analyzer. (That's what I use my Behringer for and can spend hours assessing small differences.) Look for the smoothest response using your components in your setting.

[Beowulf57]

Oops, my fault. I didn't read through the whole thread.

Ahh, dats OK ;) This monkey forgot to include the driver impedance in his first attempts at calculating the L-pad attenuation.

[Beowulf57]

Try it in the various configurations and monitor the output on a spectum analyzer. (That's what I use my Behringer for and can spend hours assessing small differences.) Look for the smoothest response using your components in your setting.

Thanks Toddalin...but I haven't got one of those wonderful toys. I used to work with a $25,000 spectrum analyzer decades ago when I was with Raytheon Canada. Now I haven't even got a speculum analyzer...though I know they don't cost that much for audio frequencies.

I'm just trying to iron out any potential problems working from the advice of those more experienced. I want to see how far I can get with the very simple measurements I've used so far and calculations based upon the behaviour of network filters, L-pads and drivers. Hmm...perhaps I could work out a test setup using my high quality HP handheld scope and my audio signal generator.:D

BY the way...how have your 2312 horns worked out?

[toddalin]

BY the way...how have your 2312 horns worked out?

Each horn is receiving 11 oz of a spray-on rubber coating. On the first horn I did, it changed the "ting" to more of a "tingk" so I figured I would do the other two also. They've now each received 3 coats and will get their final two coats tomorrow.

As my old moil friend used to say "Couldn't hoit."

It is actually pretty cool stuff and leaves a really nice, hard-squishy type feel and looks like they've been powder-coated. No problem sticking to the raw aluminim on the one that had been stripped of finish after wiping them down with alcohol either. (It seems to stick better than paint.)

The rear warts have been complete for some time and today I bought the hardware to mount them.

Now it's just a matter of cutting up (oops, out) the cabinets, mounting the horns, and of course removing and revising the crossovers as best possible using what is available in the parts bin.

[Beowulf57]

Each horn is receiving 11 oz of a spray-on rubber coating. On the first horn I did, it changed the "ting" to more of a "tingk" so I figured I would do the other two also. They've now each received 3 coats and will get their final two coats tomorrow.

As my old moil friend used to say "Couldn't hoit."

It is actually pretty cool stuff and leaves a really nice, hard-squishy type feel and looks like they've been powder-coated. No problem sticking to the raw aluminim on the one that had been stripped of finish after wiping them down with alcohol either. (It seems to stick better than paint.)

The rear warts have been complete for some time and today I bought the hardware to mount them.

Now it's just a matter of cutting up (oops, out) the cabinets, mounting the horns, and of course removing and revising the crossovers as best possible using what is available in the parts bin.

"Looking good Billy Rae...feeling good Louis!" :bouncy:

[Beowulf57]

I finally decided upon my optimal L-pad setting and got rid of those alligator clip leads. Soldered wires to the L-pads and hooked them up to the LE85 driver terminals. Rather than solder pin 2 to the LE85 + wire...I used good old electrical brass insert marrette connectors. Good connection and easy to change later if I wish. Pin 1 to the 3106 ground and pin 3 to the low pass + connectors and all's well.

Final L-pad values: 4.3 ohms series leg and 19.0 ohms parallel leg. This provides roughly -4dB assuming a nominal driver impedance of 12 ohms. If I use a 20 ohm value at 900Hz, it's ~ -3.2dB, almost identical to the difference between the Mid and Min settings on the LX5. So, I've ended up with the LE85 at the effective Min setting and the 2405H at the Mid setting. THis sounds good, though I may lower the HF level very slightly after more listening.

The results to my ears are excellent: gone is any hint of "horniness" :D (not in me though ;)), no more glare or excessive brightness and the top end is extended, detailed and refined. Now I have a wonderful bottom to top balance: powerful, deep and controlled low end...rich, clear, detailed midrange...and a far. far better upper octaves than I have ever known before (with apologies to Dickens).

All genres of music sound great:classical, jazz, rock, folk, blues...! I can move through Steve Winwood (Back in the High Life), Celtic harp, Pink Floyd, Oscar Peterson, Bach (Glenn Gould), Vivaldi (viola d'amore), Baroque, Brahms, Beethoven, Jennifer Warnes (Famous Blue Raincoat), B.B. King...well you get the idea. Never once moving from SACD to LP to CD to DVD Audio did I ever feel there was too much of this, or not enough of that. :applaud: I'll keep everyone updated of any further adjuastments/tweaks and for now would like to send my heartfelt thanks to all of you who have helped me and this forum! I couldn't have done it without you. :thmbsup::dancin:

[toddalin]

I finally decided upon my optimal L-pad setting and got rid of those alligator clip leads. Soldered wires to the L-pads and hooked them up to the LE85 driver terminals. Rather than solder pin 2 to the LE85 + wire...I used good old electrical brass insert marrette connectors. Good connection and easy to change later if I wish. Pin 1 to the 3106 ground and pin 3 to the low pass + connectors and all's well.

Final L-pad values: 4.3 ohms series leg and 19.0 ohms parallel leg. This provides roughly -4dB assuming a nominal driver impedance of 12 ohms. If I use a 20 ohm value at 900Hz, it's ~ -3.2dB, almost identical to the difference between the Mid and Min settings on the LX5. So, I've ended up with the LE85 at the effective Min setting and the 2405H at the Mid setting. THis sounds good, though I may lower the HF level very slightly after more listening.

The results to my ears are excellent: gone is any hint of "horniness" :D (not in me though ;)), no more glare or excessive brightness and the top end is extended, detailed and refined. Now I have a wonderful bottom to top balance: powerful, deep and controlled low end...rich, clear, detailed midrange...and a far. far better upper octaves than I have ever known before (with apologies to Dickens).

All genres of music sound great:classical, jazz, rock, folk, blues...! I can move through Steve Winwood (Back in the High Life), Celtic harp, Pink Floyd, Oscar Peterson, Bach (Glenn Gould), Vivaldi (viola d'amore), Baroque, Brahms, Beethoven, Jennifer Warnes (Famous Blue Raincoat), B.B. King...well you get the idea. Never once moving from SACD to LP to CD to DVD Audio did I ever feel there was too much of this, or not enough of that. :applaud: I'll keep everyone updated of any further adjuastments/tweaks and for now would like to send my heartfelt thanks to all of you who have helped me and this forum! I couldn't have done it without you. :thmbsup::dancin:

You're gettin' me jazzed to get mine done. Unforetunately, a few other thing have gotten in the way lately (like redoing our mother-in-laws house who just passed away..., as well as making a living).

Anyway, work progresses slowly.

I've decided to replace the upper center port of my center channel with the H92 and block off the hole where the "potato masher" currently is. This way my L,C,R woofers and horns will all be identical and will all be at ~ the same height.

As it is now, I reach in through this center port to adjust the mid and high levels, so these pads will be moved onto the new block-off plate.

Because the port has a 4" ID and ~4-1/4" OD, if I simply knocked out the port tube, the horn would have a gap around its perimeter. So, I cut a piece of the port material to 5/8" long and using a flapper wheel, milled out the inside diameter to fit around the horn and center it in the hole. When I finally open the cabinets, I like everything ready to go to minimize down time as this is our everyday sound system for our TV viewing

http://www.largescaleonline.com/eimages/lsolpics/Team_Member_Pics/toddalin/center-2235-w15gti.jpg

[Beowulf57]

You're gettin' me jazzed to get mine done. Unforetunately, a few other thing have gotten in the way lately (like redoing our mother-in-laws house who just passed away..., as well as making a living).

Anyway, work progresses slowly.

I've decided to replace the upper center port of my center channel with the H92 and block off the hole where the "potato masher" currently is. This way my L,C,R woofers and horns will all be identical and will all be at ~ the same height.

As it is now, I reach in through this center port to adjust the mid and high levels, so these pads will be moved onto the new block-off plate.

Because the port has a 4" ID and ~4-1/4" OD, if I simply knocked out the port tube, the horn would have a gap around its perimeter. So, I cut a piece of the port material to 5/8" long and using a flapper wheel, milled out the inside diameter to fit around the horn and center it in the hole. When I finally open the cabinets, I like everything ready to go to minimize down time as this is our everyday sound system for our TV viewing



Wow...now that is going to be some fun system to audition! I like drivers at the same heights...actually sawed the feet down on my larger cabinet so the horizontal CL of the drivers lined up from left and right.

A bit more tweaking happened today...massed forte strings sounded fine on SACD and CD, but somewhat hot and edgy on LP. Why? Then I recalled that 25 years ago I raised the VTA on my Linn Ittok LVIII tonearm on the LP12 Sondek turntable to compensate for the rolled off top end with the LE85 drivers. Now with the 2405Hs added it was unnecessary and sounded too hard. Down with the tonearm and VTA and after the adjustment: much better! Will the tweaking never end? I hope not! :bouncy: