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GoldcountryJim
02-19-2018, 09:02 PM
I've been all over the forum looking for information on what to do with 2470 drivers without diaphragms. The general answer seems to be the original phenolic ones are discontinued, install 2425h diaphragms. This has me wondering:

1) How will the different BL affect the sound? The 2470 motor is 19,000 Gauss and the 2425 is around 17,000.

2) What are phase plug differences and how might that affect the frequency response? 2425 is 800 hz to 20,000.

I understand there are limited options with drivers like these. The drivers were free and in pretty bad shape when I got them, dirty, missing screws and terminals. I cleaned them up and put them aside for years. They've been handy at filling empty shelf space. Its time to do something with them, but it just raises a lot of questions about what the result will be. :confused:

Any input would be helpful. Maybe someone who has installed the 2425 diaphragms could chime in.

grumpy
02-20-2018, 03:11 PM
For $80/ea, a pair of radian dias will make those cores usable again. A bit more for titanium from JBL.
Regardless, the phenolic drivers didn't warrant a impedance control ring on the pole piece to extend the
frequency response, so I wouldn't expect them to turn into 2420 or 2425 equivalent drivers, but maybe
close enough, depending on your application (i.e., might need a tweeter).

GoldcountryJim
02-20-2018, 07:40 PM
Thanks for the reply grumpy.

This helps with my expectations. It'll be short on the high end.

I'm planning to use these, for a while, in a man cave setup. I scored some 2226's in very good condition for mid-bass, am hunting for 2241's or something for subs, mids and possibly a tweeter. I've got a driverack px, but will upgrade to the driverack PA and run 3 way from crown x1000/xls 1002's. Something that could cover mids and highs would be good.

So, I was looking at the 2470's and thinking mids and highs. I know I will want to upgrade at a later date. I would have to push the xover to 800 or above, which doesn't fit perfectly with the 2226's. It would be an ongoing project. I'm still relatively young! LOL

I actually have some Radians in my 2410's and could upgrade those to free up the Radians. I had been thinking of that anyway.

Thanks again. This should get me going.

Jim

speakerdave
02-20-2018, 11:28 PM
According to the data sheets the 2420 and the 2470 both have the silver ring.

GoldcountryJim
02-21-2018, 12:45 AM
SpeakerDave,

You're right! Its right there on page one of the literature, just waiting for me to read it. Actually, I did read the sheet, but the part about the silver ring didn't really register. :blink: I'll be doing some more reading.

I'll probably have to run a sine wave sweep and see what it can actually produce in the higher range. I'm curious to see how the stronger motor will affect the lower range as well. Its about 4000 Gauss bigger than my 2410's and it will be interesting to see how the Radian diaphragms behave. Testing will be a bit crude. I'm planning to run pink noise and record with RTA into Pro Tools 12, then run frequency/spectrum analyzer. The preamps tend to color the signal, but it should be good "ballpark" data. If I get anything useful, I will post it. I'll have to get new diaphragms for the 2410's first. I can try both diaphragms, just to get a reference.

Now I'm excited to see what I get! It will take a few weeks for the new diaphragms.

Thanks,

Jim

grumpy
02-21-2018, 11:25 AM
Always happy to be corrected :)
May have had 2460 on the brain (shrug). Seems odd they’d bother trying to extend response with a phenolic diaphragm, but looking forward to your result.
Maybe someone can confirm or debunk same motor/plug was in common to both 2420 and 2470? both being 19000 Gauss.

Ian Mackenzie
02-21-2018, 12:32 PM
I've been all over the forum looking for information on what to do with 2470 drivers without diaphragms. The general answer seems to be the original phenolic ones are discontinued, install 2425h diaphragms. This has me wondering:

1) How will the different BL affect the sound? The 2470 motor is 19,000 Gauss and the 2425 is around 17,000.

2) What are phase plug differences and how might that affect the frequency response? 2425 is 800 hz to 20,000.

I understand there are limited options with drivers like these. The drivers were free and in pretty bad shape when I got them, dirty, missing screws and terminals. I cleaned them up and put them aside for years. They've been handy at filling empty shelf space. Its time to do something with them, but it just raises a lot of questions about what the result will be. :confused:

Any input would be helpful. Maybe someone who has installed the 2425 diaphragms could chime in.

I am using 2470 cores with 2425 diaphragm

They are fine.

If you look closely the difference in spec is 117 dB versus 118 dB plane wave tube

Depending on prior use the age of the driver being alnico is possibly going to impact on the bl

Clean them up that’s s what l did and see how you go

Get all the dust and dirt out of the gaps.

For religious reasons l prefer alnico over ferrite compression drivers

I can post a FR response if you want on a 2307/2308

grumpy
02-21-2018, 01:26 PM
Thanks Ian. I’d be interested in your 2307/8 plots when you have time.

Ian Mackenzie
02-21-2018, 01:43 PM
On the weekend.


Of course a new diaphragm always sounds better than an old fatigued diaphragm...Lol.

I had to really clean them out to get them working but they are good now.

Maybe we should find Ken’s cleaning post?

I think it was double sided tap, a solvent clean and compressed air?

Then the diaphragm alignment. That’s the tricky bit as sometimes the holes needs a slight ream out to centre in the gap.

Then check the pad on the back plate.

That stuff matters

GoldcountryJim
02-21-2018, 07:26 PM
Ian,

Plots would be great!

Cleaning was a big chore on the motors and I'll probably go over them one more time just for good measure. Ken's cleaning post? Maybe I should look for this before starting.

Foam is gone from the back caps, turned to crumbly mush when I last cleaned them, so replacement is needed before using them. Not entirely sure what the best replacement is.

I was looking at the motors last night and saw screws taped on the inside of one of the caps, probably what I found with them. These were probably what was holding the fried diaphragms in. There are black oxide type and what looks like aluminum screws. What type of screws did you have holding your diaphragms? I'm also missing the screws for the back caps. Still a little work to be done here.

You really do have to love this stuff and my wife jokes I love my speakers more than her! :D

GoldcountryJim
02-21-2018, 11:37 PM
Looks like the screws may be #6-32 by 3/4" for the diaphragm (non-magnetic) and #8-32, unknown length for the back cap. I found this elsewhere in the forum:


For a 2410;

The 3 screws ( machine bolts ) for the diaphragm are #6-32 by 3/4" long ( or @ 19 mm long )

The 2 screws ( machine bolts ) for the back-cap are #8-32 by 1.5" long ( or @38 mm long )

For a 2420/1; Don't have one to measure

For a 2426;

The 3 screws ( machine bolts ) for the diaphragm are #6-32 by 3/4" long ( or @ 19 mm long )

The 3 screws ( machine bolts ) for the back-cap are #8-32 by .5" long ( or @ 13 mm long )

The bolts that hold in the diaphragm should be nonmagnetic ( brass ) - if you can find them .

regards <> Earl K:)

Pretty cheap at Home Depot or Lowes'.

Ian Mackenzie
02-22-2018, 12:46 AM
Ditto on the wife.

No worries

They all corrode

I have seen this a lot. I think it’s moisture inside and non compatible metals.

In the back cap foam or Felt

What horn are you using?

This is a ground plane measurement 10 dB per division @ 2 m using LinearX LMS
2425 dusted diaphragm on 2307/2308 lens assembly
Copyright Ian Mackenzie 2018

GoldcountryJim
02-22-2018, 04:08 AM
Up late and saw the measurements. Awesome to see this. I'm surprised at the levels down to 500 hz, as I expected it to roll off at 700. Definitely not making it to 20K.

I haven't decided on the horn. I've been using some 2410's with Smith horns I built for my main system, with O76/2403 above. Crossovers are 3110 and 3105's. I believe the xover is around 5k to the 076. I like the combination. I'm thinking an active xover and time delay might improve it a bit.

I suppose, if I can't get above 16k with the 2470's, I may have add an ultra high driver. That would probably affect my choice of horn.

On a fun note, I saw these mini Smith horns that use a 2404, on the forum and almost wanted to build a couple! LOL They are not as efficient as a stock 2404.

http://www.audioheritage.org/vbulletin/showthread.php?12697-Walnut-Smith-Selsted

Maybe a 2344 would work. The 2307/8's look smooth between 500 and 10k. I've heard 2370's can be harsh. On the other hand I've wanted to play with some modifications to the Smith horns and they would be less expensive, at least to get things going.

If you have suggestions, I'm pretty open to looking at options.

Ian Mackenzie
02-22-2018, 04:40 AM
Cool mate.

Spin the wheel it’s up to you!

The 2470 is not ideal on the 2 inch Smith horn. A 4 inch driver is better.
A mini Smith horn might be better on the 2470 plus a uhf device.

The 2 inch smith horn cuts off above 10000 and you will need a uhf device so it’s expensive.

The 2344 bi radial horn based on personal experience is an excellent stand alone bi radial horn.horn for the 2470
Designed to across over atv1000 it will mate well with a 10 -15 inch driver.
It’s good up to 16 k hertz on the 2344 due to the narrow diffraction throat.

The 2307/08 is imho a very accurate combination with the 2405 with the right crossover network using the 2123
It’s strength precision but it’s not a CD horn.

At the moment the 2344 is Big Bang for buck in your space.

Look at Jamin Jersey for the 2344

Have fun

ivica
02-22-2018, 10:12 AM
Cool mate.

Spin the wheel it’s up to you!

The 2470 is not ideal on the 2 inch Smith horn. A 4 inch driver is better.
A mini Smith horn might be better on the 2470 plus a uhf device.

The 2 inch smith horn cuts off above 10000 and you will need a uhf device so it’s expensive.
.........
The 2307/08 is imho a very accurate combination with the 2405 with the right crossover network using the 2123
It’s strength precision but it’s not a CD horn.
......
Have fun

Hi Ian,
But 2307 WITH 2308 has very wide horizontal dispersion, and if listening in home room, it would be very useful, not to mention that
it would produce almost flat response (due to its narrow vertical response on high frequency).

regards
ivica

Ian Mackenzie
02-22-2018, 11:16 AM
http://www.jblpro.com/pub/obsolete/Acoustic_Lens_Family1.pdf

The above link to Jbl data sheet

The curve above is on axis

In use the compromises are listener position in the vertical plane is critical hence my comment it’s not CD.

The curves don’t tell you everything. See comments below.

The 2405 is required with the 2307/2308 in practice.

In terms of a single driver application the 2344 bi radial horn wins

It does a lot of things well and it’s diy friendly.
But mass break of the diaphragm is the limiting factor ultimately.
(THD rises quickly above the mass break up frequency due to the boost of the CD EQ for the 2344)

But it works in spite of the facts.

In comparison setting up the passive voltage drive and adjustment of the Lpads for the 2307/2308 is critical for optimum performance. But done precisely the addition of the 2405 has the alluring subjective piston range quality.

Ian Mackenzie
02-22-2018, 12:16 PM
Up late and saw the measurements. Awesome to see this. I'm surprised at the levels down to 500 hz, as I expected it to roll off at 700. Definitely not making it to 20K.

I haven't decided on the horn. I've been using some 2410's with Smith horns I built for my main system, with O76/2403 above. Crossovers are 3110 and 3105's. I believe the xover is around 5k to the 076. I like the combination. I'm thinking an active xover and time delay might improve it a bit.

I suppose, if I can't get above 16k with the 2470's, I may have add an ultra high driver. That would probably affect my choice of horn.

On a fun note, I saw these mini Smith horns that use a 2404, on the forum and almost wanted to build a couple! LOL They are not as efficient as a stock 2404.

http://www.audioheritage.org/vbulletin/showthread.php?12697-Walnut-Smith-Selsted

Maybe a 2344 would work. The 2307/8's look smooth between 500 and 10k. I've heard 2370's can be harsh. On the other hand I've wanted to play with some modifications to the Smith horns and they would be less expensive, at least to get things going.

If you have suggestions, I'm pretty open to looking at options.

On your post above l have not personally used the 2307 on anything other than a 4343-4344-4345 system so crossover lower is something you would need to access. You can passively EQ the 2307 for more HF extension like the Jbl 4320 monitor
http://www.jblpro.com/pub/obsolete/4320.pdf
http://www.audioheritage.org/vbulletin/showthread.php?34534-jbl-4320-with-3110-or-3110a-network

The mini smith horn combination sounds like fun.

“I've heard 2370's can be harsh.” If you meant the 2370 that is more a pro pa horn.
The 2307 it needs to be integrated carefully and the newer Jbl networks used in the 4344-4344mk11 do that.
Also the older 2420 aluminium diaphragm was not ideal and it got a reputation of being live sounding in the 4343.

Adding a uhf driver is the next step.

I would play around with a few options and see what works for you.

ivica
02-22-2018, 01:34 PM
http://www.jblpro.com/pub/obsolete/Acoustic_Lens_Family1.pdf

The above link to Jbl data sheet

The curve above is on axis

In use the compromises are listener position in the vertical plane is critical hence my comment it’s not CD.

The curves don’t tell you everything. See comments below.

The 2405 is required with the 2307/2308 in practice.

In terms of a single driver application the 2344 bi radial horn wins

It does a lot of things well and it’s diy friendly.
But mass break of the diaphragm is the limiting factor ultimately.
(THD rises quickly above the mass break up frequency due to the boost of the CD EQ for the 2344)

But it works in spite of the facts.

In comparison setting up the passive voltage drive and adjustment of the Lpads for the 2307/2308 is critical for optimum performance. But done precisely the addition of the 2405 has the alluring subjective piston range quality.


Hi,
I have 2420 with Ti diaphragm with 2312 and 2308. Its HF response is quite usable, and dispersion in the room (7x4m) is OK, I have to say without any beaming at HF, but its LF response is not something that I have to say 'enjoyable', so I have exchange such combo with 2441 (Radian) with 2311 and 2308 (usable up to 10kHz), but I have to put 2405 as UHF driver. I have to say that 2405 is very nice driver, especially A-version with JBL 'blue' diaphragms.
I can imagine that with 2441 using JBL Be (476 diaphragm, or JBL AL-2441 diaphragm) can be properly EQ up to 15kHz.
2441&2311&2308 is much better , especially in lower frequency range then 2420 & 2312 &2308. I can imagine that 2420 (2470 motor) &2307&2308 is very much the same
I have no experience with 2344/A horn

regards
ivica

Ian Mackenzie
02-22-2018, 02:59 PM
Hi Invica,

Can you post some measurements?

Below is a link to some solid Jbl data on directivity of the Jbl 4331 system and the 2307.

See a fig 4 , figure 12.

As you can see the vertical polar reduces to 45 degrees above 5000 hz then falls away.

The impact of this is the height of the horn/lens assembly must be exactly at ear height much like your head in a vice situation. Just something to be aware of.

I don’t mind sitting still in my favourite chair listening to an album with a glass of Knobs Creek Bourbon if it sounds good....Lol (the good stuff)

The whole EQ of a room and power response thing was the intent of the bi radial approach in studio situation with the document below.

I won’t elaborate on that because it’s a big topic. But it can invite challenges in the diy space like CD equalisation and room curves and it goes on and on.

Depending on your own preferences and scenario this may be relevant.

http://www.cieri.net/Documenti/JBL/Documenti%20tecnici/JBL%20-%20Improvements%20in%20Monitor%20Loudspeaker%20Sys tems%20(Smith,%20Keele,%20Eargle)%20(1983).pdf

Below is the raw driver response (top) and the EQ with the schematic posted in the link previously.

The raw driver is 110 dB at 1 khertz and 105dB at 10 khertz.

The equalisation gives 100 dB at 1 khertz and 10 khertz.

The lower curve is flattened and extended a bit and the crossover slope.

That’s the difference between just trying it casually and setting up the driver to perform its best. You of course need something to do reliable measurement with.

Again my acquplas dusted diaphragm being a tad more mass may not extend as much as the factory 2425 Ti diaphragm.

You may be able to do this with your drive rack

GoldcountryJim
02-22-2018, 11:02 PM
Ian,

What you are pointing out makes sense. With the correct EQ, the hi frequency range may be extended out, possibly and hopefully, to the frequency range I'm aiming for. This is for the driver output. The horn selection is the second part that determines what I'm actually going to hear and the sound field. In reading the articles, the 2344 may provide a single compression driver solution, as it was designed as a two-way component. The 2307/2308 has a higher directivity and will roll off so that I need a UHF driver. I also noticed that the vertical alignment of the woofer and 2344 driver are closer, which may help with phase alignment. The 2344 was designed as a studio monitor, if I'm reading this right, and that means near field. This is not good or bad for me, just part of the trade offs. Much to think about.

I also read JBL Technical Notes Vol.1, No.8 focusing in on the differences of the 2" diaphragms vs 4" diaphragms (2445/2446's). This was pretty enlightening on the second and third harmonic distortion differences between the two sizes. I've worked with the 2445's on 2380 horns and compared them, subjectively to my 2" diaphragm drivers. The 2445's do have a "clarity", but I always attributed it, incorrectly, to the 2380's rapid expansion/lower distortion. I'm left wondering if it will be inevitable that I upgrade to 2445/2446's on this project in the future.

I have to assume the rapid roll off on the plots is the mass break-point frequency and -6 db/octave drop above that point. This is really interesting to me, as I am targeting a flat response. What constitutes a "studio" monitor "flat" versus listening "flat" may be subjectively different. The Driverack could store both as presets, which would be pretty cool. I'm going to have to look at what the cut/boost limits are in the Driverack. I do a little home recording with Pro Tools and I could see a use for this.

The Driverack PX has one crossover built in, though its really supposed to be used for the sub/main feed. I could use this if I go with the 2344's and have something (two way) that I can implemented quickly and then build on later. Its actually a pretty robust xover, but I don't think it has the ability to set a delay/phase correction. I'll have to explore it.

I'm also still reading up on why 1" throat drivers are not as good on Smith horns. Enquiring minds want to know.

I've got to thank everyone for the input. My brain is full and I'm going to bed!

Ian Mackenzie
02-23-2018, 01:07 AM
One question

What are you planning on using your system for?

Home theatre?

If you plan to start off and use the 2470 cores then 2344 is a good entry point and can operate down to 800 hz.

What you learn from that can be applied to something more ambitious

Another option is this horn for a 1 inch driver

Elsewhere on the forums this thr as investigates some horn
Horns including a 1 inch horn here

http://www.audioheritage.org/vbulletin/showthread.php?36686-New-JBL-waveguides-5006812-90x50-vs-PT-F95HF

GoldcountryJim
02-23-2018, 08:51 AM
Music listening and home theater will be the primary use. Mixing and reviewing recording tracks would be a pretty small part of it. My experience has been that studio monitors reveal more about the recording process and content, while listening systems tend to be more "musical". I suppose its about psycho acoustics and whether you perceive a true flat response as "natural".

With regard to the difference I'm hearing between 2" and 4" drivers, I should be cautious of ascribing sound differences to particular causes. There's a lot of factors that could be involved. I do hear a difference, but it could even be the different rooms that I'm hearing. I am trying to be more methodical in analyzing these things.

I'll read the linked material tonight. I remember seeing something about those horns in my readings.

Thanks!

ivica
02-23-2018, 10:08 AM
Hi Ivica,
Can you post some measurements?
Below is a link to some solid Jbl data on directivity of the Jbl 4331 system and the 2307.
See a fig 4 , figure 12.
As you can see the vertical polar reduces to 45 degrees above 5000 hz then falls away.
The impact of this is the height of the horn/lens assembly must be exactly at ear height much like your head in a vice situation. Just something to be aware of.
I don’t mind sitting still in my favorite chair listening to an album with a glass of Knobs Creek Bourbon if it sounds good....Lol (the good stuff)
The whole EQ of a room and power response thing was the intent of the bi radial approach in studio situation with the document below.
I won’t elaborate on that because it’s a big topic. But it can invite challenges in the diy space like CD equalisation and room curves and it goes on and on.
Depending on your own preferences and scenario this may be relevant.

http://www.cieri.net/Documenti/JBL/Documenti%20tecnici/JBL%20-%20Improvements%20in%20Monitor%20Loudspeaker%20Sys tems%20(Smith,%20Keele,%20Eargle)%20(1983).pdf

Below is the raw driver response (top) and the EQ with the schematic posted in the link previously.
The raw driver is 110 dB at 1 kH and 105dB at 10 kH.
The equalization gives 100 dB at 1 kH and 10 kH.
The lower curve is flattened and extended a bit and the crossover slope.

That’s the difference between just trying it casually and setting up the driver to perform its best. You of course need something to do reliable measurement with.
Again my acquplas dusted diaphragm being a tad more mass may not extend as much as the factory 2425 Ti diaphragm.
You may be able to do this with your drive rack

Hi Ian,

You can see some of my measurements in the:
http://www.audioheritage.org/vbulletin/showthread.php?34180-2445J-with-2311-Horn

And if we are talking about the 2308 dispersion ( with 2307, 2311, 2312 ) JBL horns it is evident that its horizontal dispersion is respectable, reaching +/-45 deg ( I think just a few of known horns have such good results), but its vertical dispersion over 10kHz is almost less then +/-10deg (that is not so huge results,and is much LESS the 2405/2), but it has to be emphasized that from the seated position to standing position with the distance of about 3m from the speaker totally changed angle in the vertical plane would be about 15deg (that would correspond to +/-7.5deg), so even i such situation (without 2405) 2308 combo can be acceptable solution ( such as 4331 )

GoldcountryJim
02-23-2018, 11:06 PM
Ian,

The PT's are an option. They certainly are easy on the pocketbook! I think the stx825 horn (JBL part #5006815) at Reconing Speakers is the 1" horn.

I checked out Jammin Jersey and he has some 2344's. It was difficult to know the condition.

Its a little harder to find 2307's.

I came across JBL/Selenium, which has some horns. Some are plastic, some aluminum. There's some discussion on the forum of the HL 14-50 as being similar to the 2311. The JBL/Selenium HL 14-25 is a 1" conical horn that may be based on the 2307. However, its ABS plastic or similar material. I didn't find much information on them other than you can get them for about $6. LOL

ivica
02-23-2018, 11:38 PM
Ian,

The PT's are an option. They certainly are easy on the pocketbook! I think the stx825 horn (JBL part #5006815) at Reconing Speakers is the 1" horn.

I checked out Jammin Jersey and he has some 2344's. It was difficult to know the condition.

Its a little harder to find 2307's.

I came across JBL/Selenium, which has some horns. Some are plastic, some aluminum. There's some discussion on the forum of the HL 14-50 as being similar to the 2311. The JBL/Selenium HL 14-25 is a 1" conical horn that may be based on the 2307. However, its ABS plastic or similar material. I didn't find much information on them other than you can get them for about $6. LOL


HI JIm,

I think that for 1" driver you have to use
http://reconingspeakers.com/product/jbl-jrx-prx600-sf-replacement-horn-lens-338800-001/

horn, as STX825 / 815 horns are 1.5" horn throat.

Mentioned HL-14-50 is 2" throat horn, but a kind of 2308 like lenses have to be applied to prevent beaming. The same would be for HL 14-25 as i it is 1" throat horn.....

regards
ivica

Ian Mackenzie
02-24-2018, 01:03 PM
In terms the practical application of these various horns my recommendation is look at a Jbl design and see how Jbl used these horn component. For example have a look at the two way systems such as the 4320/4325 and the 4331 and the 4430. In particular the crossover schematics and the design specifications.

You can use the Drive rack to Biamp the crossover function and the passive EQ with the crossover to shape the horn response. This way you have the flexibility of Biamping and be close to on target with the EQ based on jbls measurement and engineering. Bi amping will allow matching the sensitivity of the 2226 woofer to the horn. I would not worry about the appropriateness of the 2226 with a particular horn at this early stage as your focus is on the horn.

That way you can audition the options and make a judgment call with the assurance you set up the horns close to optimum. Attempting to finalise a design on paper without auditioning some options first removes your auditorypreferences from the process. You also will miss out on some of the diy fun. Trust your own ears and take it step by step from there in terms of your final horn selection. It’s okay to get some opinions here on the forums but let your own ears do the listening. This isn’t about telling you how to suck eggs just stuff to be aware of in working out your project as you progress.

A short story:
For example way back l compared the 2397 horn, the 2344 and the 2307+2405 using Jbl crossover schematics and some measurements. I then narrowed it down to the 2344 and the 2307+2405. This took twelve months or more of listening.

Earlier on l used the 2397 (1 inch driver crossed over at 800 hertz on its own with an Altec woofer. I then added the 2405 and optimised the crossover with IMP measurements. That validated my design. I eventually sold the Altec woofers and used those proceeds to buy two Jbl 2245 and two Audax eight inch paper mid cones. I also used an online measurement software called Airr.

Using Audax crossover recommendations and measurements l had a response +-5 dB and it sounded smooth
I Biamp the woofers with a Crown two way active crossover with a Clair Bros Phase Linear 700B and a diy Pass Labs Aleph 5.

I then bought two Jbl 2122 10 inch mid cones at a tent sale and swapped out the Audax drivers.

At that point l started comparing the 2344 using the Jbl 3134 crossover with the 2397+2405.

I then acquired the 2307/2308. At that point l did not have a schematic for the 2122 transition to the 2307 so l email Jbl and to my surprise l got an email from Greg Timbers with the engineering notes for the Jbl 4345 design. With some collaboration an equivalent network was devised as the split core inductors used in the Jbl network were nla. That was back in 1998 -2003 when the internet was really primitive. Sometimes it pays to ask and l got lucky.

Adjustment of the Lpads for the 2307/2308 and the 2405 is tricky and l came up with an approach using an analogue Tandy spl meter and test tones by simply adjusting the Lpad to full then turning back the Lpad -3 db on the Meter on the Mid and -4 dB on the horn and 2405 to get the levels right.

So with further listening l started to hone in on my preferences. The Lpad adjustments on the Jbl 3134 are really cool btw. I also messed with class A amplifiers and crossover parts and found (then)class A amplifiers and Hovland capacitors had a significant influence on my impressions of the 2344 and 2307/2408+2308 compared to class ab amplifiers and Mylar capacitors. I still hold those views and today you can read about charge coupled crossover networks which is a really clever way of improving the performance of capacitors in these networks.

Comparing the 2344 and the 2307/2308 set up optimally it wasn’t chalk and cheese and it came down to what l thought was more accurate, my music preferences and that way my room acoustics interacted. I also weighed up the visual aspects of the system.

Back to the advice part in the diy loudspeaker space sometimes the horns are not setup correctly and the judgement call falls back on sub optimal application of the horn rather than the characteristics of the horns. In the absence of a measurement tool and Jbl crossover recommendations to validate the design any opinions are only opinions.

GoldcountryJim
02-24-2018, 04:58 PM
Ian,

Appreciate you sharing your experiences. Validates that this is a journey not just a destination.

Today, I really have been thinking how the purpose of the system should dictate more of the design than I'm admitting. Do I need near field or long throw? And, will it always be in the same room? My living room is 22' by 32' with wood floors, but the man-cave is smaller. Plenty of time to refine this.

Totally agree that in the end, its about what sounds good to the listener. But, it should be guided by the hardware specs and design principles. And a bit of truth should be applied: never spend money on equipment that doesn't give you an audible difference that you can appreciate. I am at a point where I can hear deficiencies in my main system and this project is my effort to improve on that. I like the smith horns because they don't have the beaming or ringing that pro sound reinforcement can have or metal ring like Altec 811's. I can hear that! I'm now seeing the trade off in it.

I think my original question has been well answered: the 2470 will be usable and could have the characteristics that I'm looking for, depending on the purpose, horn, and a few other components that will impact what I hear. This is good. The discussion is rewarding and pushes my knowledge of why the systems behave as they do.

Somewhere on the forum there's pictures of wood 2308 lens. Appearance wise, they're pretty cool. Perhaps. . .

Off topic, I had need to contact a JBL authorized recone service and found out Orange County Speaker is closed, as is one in the bay area. Seems like there are fewer of them these days. Fortunately, I did not need a recone.

Ian Mackenzie
02-24-2018, 07:23 PM
Near field is at the end of a mixing desk. It’s not that.

Long field is like pa to reach the back of a hall. It’s not that either

It must be “medium” throw.

If you imagine an equilateral triangle and ideally your speakers are say 3 or 4 feet from the side walls so they will be 14 feet apart. So you will be around 14 or so feet from each loudspeaker (ideally subject to waf)

Maybe put your 2226 in project boxes and sit your horns on top while your trying out ideas.

Btw l have a similar scenario in terms of room size. What to do? The big room sounds awesome!
The jury is still out in the big room....Lol. The pool’s done so l am told l can do anything as long as it looks good.

GoldcountryJim
02-25-2018, 09:19 AM
"Short throw." I've seen that in some JBL literature.

2307's are difficult to find, but I'm more curious about them than a week ago. Experiencing this type of horn before spending $$$ seems like a good idea. I've decided to order a couple Selenium HL 14-25's (its $5.99 at Parts Express) and experiment. There's a bolt on adapter for $3. The HL14-25 more closely matches the 2312 and I wouldn't expect it to be identical to the JBL in performance. The Selenium does appear different at the mouth. Depending on the results, more $$$ could be spent for the real deal.

https://www.parts-express.com/pedocs/specs/264-315--hl14-25-spec-sheet.pdf

Not sure what I'll do to model the lens.

Haven't seen a Phase Linear 700 in some time! Nice amp.

Ian and Ivica, I appreciate your time and knowledge.

ivica
02-25-2018, 09:53 AM
"Short throw." I've seen that in some JBL literature.

2307's are difficult to find, but I'm more curious about them than a week ago. Experiencing this type of horn before spending $$$ seems like a good idea. I've decided to order a couple Selenium HL 14-25's (its $5.99 at Parts Express) and experiment. There's a bolt on adapter for $3. The HL14-25 more closely matches the 2312 and I wouldn't expect it to be identical to the JBL in performance. The Selenium does appear different at the mouth. Depending on the results, more $$$ could be spent for the real deal.

https://www.parts-express.com/pedocs/specs/264-315--hl14-25-spec-sheet.pdf

Not sure what I'll do to model the lens.

Haven't seen a Phase Linear 700 in some time! Nice amp.

Ian and Ivica, I appreciate your time and knowledge.


Hi Jim,

But using HL-14-25 WITHOUT 2308 like lenses, would be a great mistake, either in the on axis response or off-axis response.
You can make yourself lenses like 2308 from cardboard keeping 'inter-plates' distance round 1/4", angled round 40degs, and the shape of the "V" curve can be found here on the forum, searching "2308 lenses".


http://www.audioheritage.org/vbulletin/showthread.php?8635-2308-Lens&p=296009&viewfull=1#post296009

regards
ivica

Ian Mackenzie
02-25-2018, 02:29 PM
http://www.lansingheritage.org/images/jbl/catalogs/1979-comp/page10.jpg

The Selenium look more like the consumer HL92

That longer than the HL91/2307

We look forward to your progress on horn evaluations

I will post the voltage driver of the EQ network discussed previously later in
The week

GoldcountryJim
02-25-2018, 08:20 PM
Cutting the plates for a 2308 on my CNC laser would be pretty easy. I just have to find a .bmp file or drawing of one plate and correctly size it. Its basically a rectangle, but the V notch specs are the unknown. Tap Plastics can provide the ABS sheet material. Or I can use a cheap 1/8" plywood for experimenting.

It will take a few days to get this all together.

Will post more when I make some progress.

HL92 is close, but not exact. 2312 maybe?

Ian Mackenzie
02-25-2018, 09:03 PM
http://www.audioheritage.org/vbulletin/showthread.php?8635-2308-Lens/page4

ivica
02-25-2018, 11:06 PM
Cutting the plates for a 2308 on my CNC laser would be pretty easy. I just have to find a .bmp file or drawing of one plate and correctly size it. Its basically a rectangle, but the V notch specs are the unknown. Tap Plastics can provide the ABS sheet material. Or I can use a cheap 1/8" plywood for experimenting.

It will take a few days to get this all together.

Will post more when I make some progress.

HL92 is close, but not exact. 2312 maybe?

Hi Jim,

If you do like formulas, as I have sent you a link, you can redraw from the
http://www.audioheritage.org/vbulletin/showthread.php?8635-2308-Lens&p=186755&viewfull=1#post186755

regards
ivica

GoldcountryJim
03-02-2018, 02:20 PM
The patterns for the plates are really helpful. The plan is to cut prototypes this weekend.

I read somewhere on the forum that the plates have to be spaced less than 1/2 the wavelength (of the highest frequency?) apart to work properly. It seems the actual number of plates is less important and just needs to cover the horn opening.

Does anyone have information on this?

Have a bunch of parts ordered (horns, adapters, diaphragms) and just waiting for them.

Earl K
03-02-2018, 02:34 PM
http://www.lansingheritage.org/images/jbl/reference/technical/lens/page01.jpg (http://www.lansingheritage.org/html/jbl/reference/technical/lens.htm)


http://www.lansingheritage.org/_derived/index.htm_cmp_lansing-heritage010_bnr.gif (http://www.lansingheritage.org/)

:)

GoldcountryJim
03-02-2018, 06:18 PM
Earl,

That's really good information! I had a moment of enlightenment about the "potato masher" horns in there. It starts to make sense, but also spawns so many questions like: Can you shape the waves differently to improve the stereo image? Why did JBL choose a V notch rather than a curve on the 2308? Could I filter particular frequencies by changing the lense plate (2308 style) density?

This is going to be more interesting than I expected. I was thinking of the 2308 as more of a directional device.

I think my question of plate spacing remains. I'll keep digging.

GoldcountryJim
03-02-2018, 08:19 PM
Found the information! It was page 3 of the same paper. Should be a fun weekend! :bouncy:

http://www.lansingheritage.org/images/jbl/reference/technical/lens/page03.jpg