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toddalin
09-29-2007, 03:06 PM
On Friday, 9/28, Grumpy (Dave) came by loaded with an arsenal of testing equipment to get to the bottom of the "hole" issue of the depressed midrange of the 2235 and more specifically, 2205J recently recharged and reconed as a 2235 by Orange County Speaker (OCS).

Sitting drinking my morning coffee, I looked out the windows at about 9:00 a.m. and Dave is walking up the walk. We had talked about the date and time, and not hearing anything (Dave was out of town), I wasn't sure this was going to happen. But Dave was right on time and it did.

First order of business was load software onto my laptop for the test. Dave brought the Parts Express Woofer Tester 2 along with his Mac laptop with the necessary software to determine the differences and possible reason that I was getting a "suck-out" in the 600-900 Hz range. I'm sure that Dave will chime in and tell us exactly what was done, but I know that I needed a bunch of nickels to perform some of the testing. ;)

What we found that was OCS used a legitmate JBL 2235 cone and all parameters supported the JBL tag that was still on it. But the BL, reportedly a measure of the magnetic strength in the gap, was down around 17-18 whereas the 2235 specs call for 20. Dave brought two real 2235s along and the measured BLs were 22-24.

This difference (~15% off spec) could account for some roll off, perhaps, and anyone is welcome to chime in here for an educated opinion. Has anyone had a 2205 recharged and measured the BL and if so, what were your results?

While woofer testing was typically performed in Dave's calibrated lap, all in cabinet testing was done with an L200 cabinet. Most tests were performed with one port blocked. Dave's graphics clearly showed the benefits of blocking one port, although at those frequencies the result is less audible than visual in the plots.

Replacing the Alnico-framed 2205/2235 with a new 2235 in the L200 cabinet did alter the response somewhat, but after many measurements and mic placement changes, we decided to move the speakers relative to the walls. Dave feels that sidewall reflections appear to be the main suckout culprit in the 500-900Hz octave. The real 2235 did exhibit a response similar, though not identical to the 2205/2235 and in these cabinets, in this environment, and using these crossovers did have the dreaded dip in response (that most people don't seem want to acknowledge :blink:).

Scooting the systems closer (inches) to the rear wall helped smooth the response a bit elsewhere.

The day quickly passed and we headed off to Ruby's for lunch. We got back to the house and continued the tests going through various combinations of crossover settings, and slight movements of the speaker and mic placement, and after reinstalling the 2205/2235, testing the right and left speaker for similarity.

BTW, Dave's tests did prove what I asserted all along that a 16 ohm resistor in series with the woofer did smooth out the troublesome 600-900 area to a large extent! (Actually we used a 20 ohm in this case.) I know that many here said that this is strickly taboo (putting a resistor in series with the woofer), but there it is! :blink: The really weird thing is, it hardly had any effect on the woofer's volume! Dave has the plots. :p

When I reconnected the speaker to the amp, because the speaker had now been moved back to the wall (was pulled out) I couldn't see the wires and inadvertantly put the + on the red and - on the black (wrong for my system). I fired up "You're So Far Away" (on Brothers in Arms) and Dave instantly said "something's wrong". He instantly knew the polarity was wrong and the Yamaha's self test agreed.

Later when testing the speakers for similarity, we found differences in the plots because the right tweeter was out of phase. I phased them using a sound level meter looking for the louder volume for a tone near the crossover point. But that portion of the spectrum is suseptible to combing, so that small differences in frequency have large differences in volume. Anyway, Dave's plots clearly showed the difference and both speakers track extremely well together now both in volume and frequency.

According to Dave, the speakers are +/- 3dB from ~40-14KHz (albeit 1/3 octave) and that's still nothing to sneeze at. Some by-ear tweaking of levels for the listening position made the system pretty smooth to listen to (the point, after all). L-R matching for frequency response tracking is within 1/2dB almost throughout the useful bandwidth, according to Dave, in no small part due to my carefully measured speaker placement and fairly symmetrical room.

I looked at the watch and it was now 4:00 p.m. Time for Dave to head back to the family. A lot of data was obtained and there may be some suggestions out of this to make the "keeper" crossovers work even better to fill the hole.

What a great day! Thanks for stopping by Dave! :bouncy:

boputnam
09-29-2007, 04:04 PM
Interesing afternoon...

But, I'm confused:


...to determine the ... reason that I was getting a "suck-out" in the 600-900 Hz range.

and


...a 16 ohm resistor in series with the woofer did smooth out the troublesome 600-900 area to a large extent!

You had both a "suck-out" (I guess that means acoustic cancellation...?) and a "troublesome" character to the frequency response from 600-900Hz...? Maybe I'm lost - I don't understand the resistor remedy. Did it smooth the measurement or the sound or what?

wrt the latter, how did the "troublesome" character to the frequency response from 600-900Hz manifest before the remedy? Was it audible and/or merely in Dave's measurements?

Thanks.

Steve Schell
09-29-2007, 04:49 PM
Hi Toddalin,

By putting the 20 ohm resistor in series with the woofer you have effectively lowered the amplifier damping. There will be an efficiency loss from the power dissipated in the resistance, but the lower bass will increase relative to the midband due to the loosening of the amp's grip on the woofer.

Since the advent of solid state amps we have been sold on the supposed virtues of high damping factors. I regard this as another case of "If you can't fix it, feature it." A high damping factor works okay with low efficiency floppy cone drivers, but can be detrimental with high efficiency speakers; the amp grips the speaker so tightly that the low end response is rolled off. We have all gotten used to that super tight, heavily damped sound, but there are other ways of looking at the amp/speaker relationship.

The best article I have seen on this subject was written in the mid 1950s by D.J. Tomcik, chief electronics engineer at Electo-Voice. Here is a link:

http://www.paulspeltz.com/tomcik/index.html

I have often used resistors in the speaker line to try to come closer to what Mr. Tomcik refers to as "critical damping." I also use fine gauge magnet wire for speaker cables, which helps in this regard. I have heard through a first hand account that Jim Lansing used to advocate placing resistors in the speaker line until the bass sounded best.

It does make sense that a driver with lower BL will be missing some of its top end. Lowering BL has the effect of moving the mass break point, above which the reponse rolls off at 6dB per octave, lower in frequency. Response below the break point is pretty much unaffected, or at least it appears so in simulations.

toddalin
09-29-2007, 05:49 PM
Interesing afternoon...

But, I'm confused:



and



You had both a "suck-out" (I guess that means acoustic cancellation...?) and a "troublesome" character to the frequency response from 600-900Hz...? Maybe I'm lost - I don't understand the resistor remedy. Did it smooth the measurement or the sound or what?

wrt the latter, how did the "troublesome" character to the frequency response from 600-900Hz manifest before the remedy? Was it audible and/or merely in Dave's measurements?

Thanks.

A "suck-out" meaning a big, fairly broad dip in frequency response. "Troublesome" also referring to the dip area and its irregularities. Perhaps Dave will post some of the curves and you'll be able to see what I mean.

Yes it manifests itself audibly, to my ear as a muffling or reduction in intelligibility of the male voice. Putting the resistor inline brightens the voice up and increases intelligibility.

Steve, another possible effect of the resistor in series with the woofer is in raising the crossover frequency that is obviously dependant on the woofer impedience. This may be why these crossovers work so well with the 12 ohm load of the W##GTI series too.

4313B
09-29-2007, 06:31 PM
The real 2235 did exhibit a response similar, though not identical to the 2205/2235 and in these cabinets, in this environment, and using these crossovers did have the dreaded dip in response (that most people don't seem want to acknowledge :blink:).The lack of acknowledgement is probably based on most people's experiences. Your experience might be unique. Some people have trouble getting 2235H's to do what they want them to do, most people do not.
BTW, Dave's tests did prove what I asserted all along that a 16 ohm resistor in series with the woofer did smooth out the troublesome 600-900 area to a large extent! (Actually we used a 20 ohm in this case.) I know that many here said that this is strickly taboo (putting a resistor in series with the woofer), but there it is! :blink: The really weird thing is, it hardly had any effect on the woofer's volume! Dave has the plots. :pOnce again, your experience sounds unique. Most people don't go around sticking 16 to 20 ohm resistors in series with their 2235H's. If that's what you have to do to get your stuff to work then who are we to argue. Do what you have to do.
This may be why these crossovers work so well with the 12 ohm load of the W##GTI series too.It sounds to me like you need to dump the 2235H's and go with the W##GTI series. You need to run an impedance curve of the 2235 with that conjugate you are using and compare it to an impedance run of a W##GTI with that same conjugate. Looking back in other threads I think that conjugate is a 33 uF capacitor and 7 ohm resistor.

boputnam
09-29-2007, 07:22 PM
...but the lower bass will increase relative to the midband due to the loosening of the amp's grip on the woofer. This change should be readily measurable in Dave's work - i.e., pre and post.


The real 2235 did exhibit a response similar, though not identical to the 2205/2235 and in these cabinets, in this environment, and using these crossovers did have the dreaded dip in response (that most people don't seem want to acknowledge :blink:). What you are describing would seem to be EQ'able.

Two questions?

1. What EQ / room measurements had you done beforehand, to optimize/minimize the room's influence on the output? If none, then Dave's work would be truly a step forward.

2. What "necessary software" was Dave using other than Woofer Tester?

toddalin
09-29-2007, 07:30 PM
This change should be readily measurable in Dave's work - i.e., pre and post.

What you are describing would seem to be EQ'able.

Two questions?

1. What EQ / room measurements had you done beforehand, to optimize/minimize the room's influence on the output? If none, then Dave's work would be truly a step forward.

2. What "necessary software" was Dave using other than Woofer Tester?

The Yamaha RX-Z9 ($4,500) has it's own self eq that is not user adjustable once set (though you have some control over what band range you consider most critical). You can defeat it and use the graphic eq, but not both. Even so, I still hear the dropout effect.

Dave will have to describe the software.

boputnam
09-29-2007, 07:42 PM
The Yamaha RX-Z9 ($4,500) has it's own self eq that is not user adjustable once set (though you have some control over what band range you consider most critical). You can defeat it and use the graphic eq, but not both. Even so, I still hear the dropout effect. Holy-moly, that is some pricy unit. Surprised I don't know it... :o:

So, help me out - it does some sort of room response measurement and auto-EQ's to that reading? The "YPAO" (Yamaha Parametric Room Acoustic Optimizer)? How do it know? :p

The noise on the website sez the YPAO "..checks the speaker connections and phase of each speaker." But, you said one of your cabinets was still out of phase? :blink: So...?

And, then: "...it sends out tones which are captured by the microphone to analyze the room acoustics and sets a variety of parameters, such as the speaker size, the distance of the speakers and even the sound pressure level, etc. Until it achieves the best sound conditions for your room and you don't have to do anything!"

Just curious - where is this little mic? Imbedded in the unit, or movable into the listening area?

Yammie makes some powerful pro gear, for damned sure, but I am (personally) not a fan of their consumer stuff.

speakerdave
09-29-2007, 09:39 PM
. . . . the depressed midrange of the 2235 and more specifically, 2205J recently recharged and reconed as a 2235 by Orange County Speaker . . . .

I'm confused by the terminology. The 2235H is a 2nd generation ferrite motor. A 2205J would also be a ferrite motor, so it would not need recharging. Do you really mean a 2205B which would be Alnico?

You may have a room problem with reflection, etc, causing a null in that frequency range, though I would think it would not be huge.

I do not believe the ferrite 2235H has a depressed midrange, although I have not listened to it extensively. I have had a remagged Alnico core (2135) reconed with the 2235 kit and do not believe it can be expected to perform exactly the same as the ferrite 2235, although I have not been able to measure either.

David

toddalin
09-29-2007, 11:15 PM
Holy-moly, that is some pricy unit. Surprised I don't know it... :o:

So, help me out - it does some sort of room response measurement and auto-EQ's to that reading? The "YPAO" (Yamaha Parametric Room Acoustic Optimizer)? How do it know? :p

The noise on the website sez the YPAO "..checks the speaker connections and phase of each speaker." But, you said one of your cabinets was still out of phase? :blink: So...?

And, then: "...it sends out tones which are captured by the microphone to analyze the room acoustics and sets a variety of parameters, such as the speaker size, the distance of the speakers and even the sound pressure level, etc. Until it achieves the best sound conditions for your room and you don't have to do anything!"

Just curious - where is this little mic? Imbedded in the unit, or movable into the listening area?

Yammie makes some powerful pro gear, for damned sure, but I am (personally) not a fan of their consumer stuff.

Yes, its the YPAO system and autoeqs the room based on pulses and tones.

After we replaced the woofer in the box, and I reconnected it to the stereo system, it was moved back to the wall so this was done largely by feel (50% chance). It was connected correctly previous to the tests.

The Yamaha wouldn't be expected to give an out of phase report for an out of phase tweeter so long and the woofer and mid were correct.

Mic is on a long cord and I put it at the center of the listening location (couch) on a tripod. (One leg extended over floor and two legs on the couch with mic over exact center of couch cushion.

But the tests performed by Dave were at ~1 and 2 meters at the tweeter level with no eq at all. The speaker was totally disconnected from the Yamaha and Dave brought over a dedicated JBL amp and interface for his Mac computer. That guy was prepared!

This is Yamaha's top home unit and carries a 5 year (rather than the usual 2-3 year) warrantee. It's been in for warrentee work a few times and I expect to send it in again before the warrantee expires next Feb for the rotary volume knob.

toddalin
09-29-2007, 11:21 PM
I'm confused by the terminology. The 2235H is a 2nd generation ferrite motor. A 2205J would also be a ferrite motor, so it would not need recharging. Do you really mean a 2205B which would be Alnico?

You may have a room problem with reflection, etc, causing a null in that frequency range, though I would think it would not be huge.

I do not believe the ferrite 2235H has a depressed midrange, although I have not listened to it extensively. I have had a remagged Alnico core (2135) reconed with the 2235 kit and do not believe it can be expected to perform exactly the same as the ferrite 2235, although I have not been able to measure either.

David

Was the 16 ohm version of an Alnico 2205.

http://www.largescaleonline.com/eimages/lsolpics/Team_Member_Pics/toddalin/Woofers.jpg

4313B
09-30-2007, 07:00 AM
I took a little time to review other posts about your woes with these 2235H's and it seems this has been going on for quite awhile. You've posted your dissatisfaction with them several times. Rather than beat a dead horse you should probably just go with better stuff from the get-go and that means no 2370's or 2425's either. Perhaps some 800 Arrays or 1000 Arrays would balance with your $5,000 Yamaha. To be blunt, I think you are throwing good money after bad.

boputnam
09-30-2007, 08:51 AM
The Yamaha wouldn't be expected to give an out of phase report for an out of phase tweeter so long and the woofer and mid were correct. Yea, I wondered about that, too. I suppose it was intended for detecting basic cross-wiring to the cabinet.

Still interested in some before/after plots, if you've got 'em. :)

toddalin
09-30-2007, 10:26 AM
Yea, I wondered about that, too. I suppose it was intended for detecting basic cross-wiring to the cabinet.

Still interested in some before/after plots, if you've got 'em. :)

There was a lot of data and Dave said it would take a few days to crunch the numbers.

subwoof
09-30-2007, 03:04 PM
I was buying a LOT of JBL frames during the intial ferrite crossover and the first gen 2205"H" frames used a gray magnet that was bolted thru the frame to the magnet assembly's back plate and *that* one had a different design than the later black magnet 2225H ( which also had a longer voice coil ).

I wonder if the BI loss you had / have ( even with recharging ) is because they used the *current* ferrite recharge procedure rather than the old...?

There is a tech report on the ferrite mag that I read somewhere that is slightly different than the one posted in the "technical reference" forum. It might of been a "not for release" memo or something since at the time I had access to the reps entire JBL paperwork stash...closest thing to the internet was his floor / filing cabinet.

I have a fewf shifted / cracked 2225 (35 ) frames to look at but no longer have any gray magnets. I will look around and see if I can find one since I might acquire a pair of 2231H's in about a month and this issue might creep up here..

I agree with giskard - spend the money in a more modern direction if the '35 isn't doing it for you.

sub

boputnam
09-30-2007, 08:06 PM
There was a lot of data and Dave said it would take a few days to crunch the numbers.Oh, OK. Not trying to be a pest. I was just interested in the raw plots/traces...

grumpy
10-01-2007, 08:27 AM
Well... I don't pay attention for a few days and :spin:

An interesting and enjoyable time was had over at Todd and Linda's (most can stop reading now):)

I think we adjusted the speaker locations and driver levels to where the Yamaha EQ
should have a pretty easy time of it (no major corrections if used), and to where there
was a noticeable improvment in the listenability of Todd's system (only referring to the
stereo pair of 2235(Alnico mag)/L175/075 in L200 cabinets).

With my admittedly limited experience in the particular area of acoustics, I still feel
fairly sure that what we were seeing as a low midrange dropout was a combo of floor,
rear, and sidewall delayed reflections; pushing the speaker toward the wall (inches)
brought up the middle of the dropout, putting pillows on the floor modified the response
in the dropout area, sideways adjustment (toward sidewall) moved one low-Q null in
frequency.

What I -do- know, is these are things we have to live with in most non-purpose-built
sound rooms, e.g., living rooms. To the extent that one can make reasonable
adjustments in speaker placement, listening geometry, and reflection control,
it's quite possible to improve the listening experience, hopefully making it more enjoyable.

I think that was accomplished at Todd's. :) If anything technical is further resolved,
I'm sure it will get posted. It appeared the conjugate network was off (we discussed
that while I was there, I suggested a much smaller cap based on imp vs freq plots)...
WT2 also indicated a box Q-factor of 12... understuffed? more than I know. I'm
learning too :D -dave/grumpy

P.S., I'll try to edit down the far too many plots and get anything interesting annotated.
The more interesting (to me) plots were done with WT2 on Todd's laptop... woo files
were stored. Maybe Todd could email 'em to me.

Steve Schell
10-01-2007, 10:17 AM
Toddalin said:

"Steve, another possible effect of the resistor in series with the woofer is in raising the crossover frequency that is obviously dependant on the woofer impedience. This may be why these crossovers work so well with the 12 ohm load of the W##GTI series too."

I had forgotten to consider this, but doubling the impedance of a speaker would also double the frequency of a first order low pass filter used with it. Not sure what would happen with a higher order filter! If your crossover was cutting off the woofer too low and creating the response hole, then moving the crossover point up an octave would surely help.

As for room reflections creating the hole, for a response dip centered at 750Hz. the reflection would have to have an additional path length of about 9" to the mic compared to the direct sound. If the speakers are located really close to the side walls this could be the culprit.

toddalin
10-01-2007, 10:55 AM
Toddalin said:

"Steve, another possible effect of the resistor in series with the woofer is in raising the crossover frequency that is obviously dependant on the woofer impedience. This may be why these crossovers work so well with the 12 ohm load of the W##GTI series too."

I had forgotten to consider this, but doubling the impedance of a speaker would also double the frequency of a first order low pass filter used with it. Not sure what would happen with a higher order filter! If your crossover was cutting off the woofer too low and creating the response hole, then moving the crossover point up an octave would surely help.

As for room reflections creating the hole, for a response dip centered at 750Hz. the reflection would have to have an additional path length of about 9" to the mic compared to the direct sound. If the speakers are located really close to the side walls this could be the culprit.

Speakers are about 5 feet from the side walls.

http://www.largescaleonline.com/eimages/lsolpics/Team_Member_Pics/toddalin/room1.jpg

http://www.largescaleonline.com/eimages/lsolpics/Team_Member_Pics/toddalin/room2.jpg

grumpy
10-01-2007, 11:15 AM
Hi Steve,

Yes, I was thinking sub-foot delay differential would do it... the sidewall distance is quite
a bit larger, and I thought we might be seeing N-cycles + sub-foot delay, as there were
lumps in the response lower (unfortunately I wasn't keeping track if they moved as well).

(note: we also ended up with the speakers closer to the rear wall than shown in the above pics
Todd just posted).

If you make the poor assumption that the speaker load is not reactive (R only) then
adding 20 ohms in series should produce a roughly 10dB loss (blue = voltage across
speaker without 20 ohms in seried, red = same, but with 20 ohms in series). Plot
freq range is 10Hz-10KHz.

Although the peaking would pump up the response in Todd's hole (so to speak), the
simulation doesn't explain why the overall response didn't drop as much when
measured. Some info is missing :)

pos
10-01-2007, 12:00 PM
I was buying a LOT of JBL frames during the intial ferrite crossover and the first gen 2205"H" frames used a gray magnet that was bolted thru the frame to the magnet assembly's back plate and *that* one had a different design than the later black magnet 2225H ( which also had a longer voice coil ).
Is it possible to recognized these first generation frames on a photo?

For example this one, a 2205H frame:
http://i10.ebayimg.com/06/i/000/b9/9c/0548_12.JPG
It seems to be grey. Could it be a first generatin frame that could led to different T/S parameters than a stock 2235H when reconed with a C8R2235?

boputnam
10-01-2007, 12:19 PM
...adding 20 ohms in series should produce a roughly 10dB loss (blue = voltage across
speaker without 20 ohms in seried, red = same, but with 20 ohms in series). Right - you've merely worsened the sensitivity of the woofer. That's why I wonder whether in-addition to the reflections issues (real), there is a better EQ solution, too.

Can you tell what the room response is?
Can you know what corrections Yammie applied, and how these "fit" with those needed?

grumpy
10-01-2007, 01:00 PM
POS: Think the one in your frame picture started out black,
the gray I've seen is more obviously gray (not charcoal)...
Magnet appears (to me) to be identical in form to all of my
various 2225/2234/2235 frames.

Bo: I'm sure there is a better solution. The conjugate and crossover both
appear to be coming in too low... just exacerbating the environmental issue
as well as the weak magnet 2235's.

Next time Todd and I both have copious free time, I'd be happy to attempt a
room response (actually tried for an RT30 plot, but I'm still learning how to
pilot the software)... manual's a bit vague there. There's a room resonance in the
male vocal range that's apparent, and probably in the main problem area.
Suggestions, experience, pointers to material ... all welcome :)

The correction plots I saw from the Yamaha were too tiny (and unlabeled)
to be of much use other than as a gross indicator. Todd may have more info.

toddalin
10-01-2007, 01:28 PM
Right - you've merely worsened the sensitivity of the woofer. That's why I wonder whether in-addition to the reflections issues (real), there is a better EQ solution, too.

Can you tell what the room response is?
Can you know what corrections Yammie applied, and how these "fit" with those needed?

Other than the general patterns, it is too hard to see all eight channel plots on a 7" monitor. And even though the Yamaha shows 1/3 octave tick marks, it does not provide the center frequencies or dB levels, though based on 1/3 octave, "pert nears" should be fairly obvious.

When I fire up the projector tonight, I'll try to remember to photogragh the screen and post the pics. I've not re-eqed to the new speaker postions yet, so this should provide a before and after. However, we did some crossover adjustments and these too will affect the plots and a little adjustment can go a long way.

Even though the Yamaha provides eq, maybe my ears are just extremely sensitive to coloration in that region.

boputnam
10-01-2007, 01:40 PM
When I fire up the projector tonight, I'll try to remember to photogragh the screen and post the pics. I've not re-eqed to the new speaker postions yet, so this should provide a before and after. Cool.


Next time Todd and I both have copious free time, I'd be happy to attempt a room response Very cool...


There's a room resonance in the male vocal range that's apparent, and probably in the main problem area. Actually, probably a combined room + cabinet resonance. Need to know the FR characteristics of the room and what frequency you're referring to. There are some boy sopranos (and castratos, too...) who are confused by what "male vocal range" means... :p

Anyway, in seriousness, my grab is this is dominantly a cabinet resonance issue. That room looks hella easy, compared to most I get to try and "tame"...


Suggestions, experience, pointers to material ... all welcome :)Cooler, still. We are all learning here...


The correction plots I saw from the Yamaha were too tiny (and unlabeled) to be of much use other than as a gross indicator. Very non-cool...

grumpy
10-01-2007, 02:37 PM
...confused by what "male vocal range" means...Why did I -know- someone would take a poke at that... :p

What I meant was you can hear a room resonance with the speakers off...
but good point about the cabinet.

Should be able to pick up gross cabinet panel resonances... some sort of
poor man's accelerometer (I don't have access to real ones & charge amps
any more)...

pos
10-01-2007, 03:28 PM
POS: Think the one in your frame picture started out black,
the gray I've seen is more obviously gray (not charcoal)...
Magnet appears (to me) to be identical in form to all of my
various 2225/2234/2235 frames.
thanks a lot grumpy.

toddalin
10-01-2007, 07:23 PM
Room eq Settings

OK, I've let the Yamaha re-eq to the new crossover settings/speaker positions.

This first shot shows the before.

http://www.largescaleonline.com/eimages/lsolpics/Team_Member_Pics/toddalin/Pre-eq.jpg

And this shot shows the post-adjustment eq levels. Looks like we are a little less hot on the right mid-horn, thus the receiver boosting this range.

http://www.largescaleonline.com/eimages/lsolpics/Team_Member_Pics/toddalin/post-eq.jpg

Note that these calibrations were taken with the mic placed about 15" high over the center of the couch.

boputnam
10-01-2007, 07:54 PM
Wow, as useless as those images are (not your fault - there are no scales on either axis... :bs:), the "after" clearly shows (to me... :wave: ) that the autoEQ is trying to compensate for the loss of LF response related to your DIY in-line resistor.

Check it out...

L (after) - LF has a spike where there was a gentle peak, and also a flat-line (200Hz...?) correction (boost) where there was a swale. The MF and HF are mostly unchanged.

R (after) - LF, ibid. A pronounced peak is now introduced where before there was a mostly flat correction; and, the swale (around 200-400Hz...? ) is replaced by a flat-line correction (boost).

What is the non-attributed bottom window below the two channels - is that the overall reading, before-correction? If so, you can sure see the compromised LF response (probably...) relating to that DIY in-line resistor... :hmm:

grumpy
10-01-2007, 08:01 PM
pretty sure the resistor didn't stay in, but :dont-know

this (not knowing exactly what the Yamaha would do)
is part of why all of the testing (and listening) was with the auto-EQ off.

I'll get some FR plots up after I switch computer types...

toddalin
10-01-2007, 08:43 PM
Wow, as useless as those images are (not your fault - there are no scales on either axis... :bs:), the "after" clearly shows (to me... :wave: ) that the autoEQ is trying to compensate for the loss of LF response related to your DIY in-line resistor.

Check it out...

L (after) - LF has a spike where there was a gentle peak, and also a flat-line (200Hz...?) correction (boost) where there was a swale. The MF and HF are mostly unchanged.

R (after) - LF, ibid. A pronounced peak is now introduced where before there was a mostly flat correction; and, the swale (around 200-400Hz...? ) is replaced by a flat-line correction (boost).

What is the non-attributed bottom window below the two channels - is that the overall reading, before-correction? If so, you can sure see the compromised LF response (probably...) relating to that DIY in-line resistor... :hmm:


No resistor in place in any of the pics. This is simply the result of minor crossover adjustments and placement and toe-in relative to the rear wall.

Actually, if you look close, the second set are better in the bass area. The "spike" you note represents an increase in just one band whereas the "gentle slope" shows that the correction is actually over a wider range of bands.

The center one below the pair represents the eq for the center channel, below that are the four surrounds and two presence channels. All channels get the eq treatment. I was focusing on the L/R as that's where we're working.

boputnam
10-02-2007, 06:54 AM
No resistor in place in any of the pics.OK.


Actually, if you look close, the second set are better in the bass area.Yes, I thought so, too.

But are these the corrections, or the response?


The center one below the pair represents the eq for the center channel, Again, are these the corrections, or the measured response?

toddalin
10-02-2007, 09:40 AM
OK.

Yes, I thought so, too.

But are these the corrections, or the response?

Again, are these the corrections, or the measured response?

The graphics show the applied corrections, so it stands to reason that the actual frequency response is the conjugate of what you see.

The resistor on the woofer came about as a matter of experimentation and I don't actually run them this way.

Initially I put a 16-ohm L-pad on the woofer to dial in its volume and noticed that as I increased the resistance, the mid-range volume came up smoothing out the dip. I reported this and most said I was crazy. :blink:

When I sent Zilch one of the crossovers I asked that he also perform this test. He said that he did and could not confirm my findings. He reported that it only made the woofer quietier.

This was merely a test to show that I am in fact sane and the speakers behaved just as I had reported.

grumpy
10-02-2007, 10:22 AM
This was merely a test to show that I am in fact sane and the speakers behaved just as I had reported.

This is just too weird. We're missing something. The impedance run showed that there
was a bad assumption somewhere. I ran a few sim plots that we should be able to
roughly replicate looking at WT2 output again and measuring voltage drives at each
driver.

Note that the last plot below, has the impedance scale moved up 20 ohms...
which is exactly what we saw w/WT2 when we thought the hook-up was ok (nominal
shifted up 20 ohms across the band). What I expected was a rise in the impedance of
the low-end only (4th plot), and a drop in low-end level (3rd plot).

Also note that no cabinet tuning or LF speaker resonance is modelled here. The effects
should still be grossly similar.

-grumpy

toddalin
10-02-2007, 11:09 AM
This is just too weird. We're missing something. The impedance run showed that there
was a bad assumption somewhere. I ran a few sim plots that we should be able to
roughly replicate looking at WT2 output again and measuring voltage drives at each
driver.

Note that the last plot below, has the impedance scale moved up 20 ohms...
which is exactly what we saw w/WT2 when we thought the hook-up was ok (nominal
shifted up 20 ohms across the band). What I expected was a rise in the impedance of
the low-end only (4th plot), and a drop in low-end level (3rd plot).

Also note that no cabinet tuning or LF speaker resonance is modelled here. The effects
should still be grossly similar.

-grumpy

"The impedance run showed that there was a bad assumption somewhere."

I think that the "bad assumption" is that the mid and tweeter determine the overall speaker impedience for signals in their range. I think that because the woofer is directly coupled to the amp (albiet through a coil of wire), it's impedience is the primary speaker impedience regardless of the frequency.

The mid and tweeter are only indirectly coupled to the amp through a capacitor, so while their impedience affect their crossover frequencies, it doesn't do so much for the overall speaker impedience.

Recognize that even though we can't hear the woofer over a couple thousand Hz, your impedience plots clearly show woofer resistance (impedience) at the upper frequencies.

Of course I could be totally wrong. :o:

grumpy
10-02-2007, 11:57 AM
Heh... well, I'm cool with you disagreeing :), but that's part of what a crossover
normally does. LPF section with resistive/simulated 2235 is about 50 ohms at
3KHz (almost all due to the 2.2mH coil). From about 1KHz up, its all high-passed
components/drivers.
-grumpy

toddalin
10-02-2007, 12:14 PM
Heh... well, I'm cool with you disagreeing :), but that's part of what a crossover
normally does. LPF section with resistive/simulated 2235 is about 50 ohms at
3KHz (almost all due to the 2.2mH coil). From about 1KHz up, its all high-passed
components/drivers.
-grumpy

Yes..., until you add the Zobel network, then as WT2 demonstated, the impedience of the woofer stays pretty flat throughout the audio range even though the frequency is rolled off.

I imagine that without the Zobal, we would see something like the plot that you expected (i.e., the resistor primarily adds to the woofer load at low frequencies).

But I could certainly be wrong. :o:

grumpy
10-02-2007, 12:25 PM
Plot above -is- with the zobel (which is where the shallow dip below 1KHz comes from).
The zobel can't reduce the viewed impedance of the 2.2mH inductor... it's in series.
The impedance equalization (zobel) occurs -after- the 2.2mH inductor, so that the inductor
will see a mostly resistive load and the crossover will behave a bit more predictably.

If you take out the 2.2mH, you're right, the impedance "curve" should more
or less look flat, if the speaker/zobel combination is implemented well.

If I scaled the WT2 network impedance curve more usefully, I think this would be
easier to see... perhaps. :) It would take a re-run, as the resolution was set low.
-grumpy

WTPRO
10-02-2007, 02:00 PM
Hi Grumpy

I see you are using the new WT2 software. If you look in the options pull down, you will find that you can now select the pulse, MLS, noise and chirp real time modes for generating fast impedance plots with lots of resolution. The TS tests themselves will revert back to sine mode for maximum precision and noise rejection. We enabled these modes for our customers that needed ZMA data for the ICD crossover designer. If you look at the WT2 simulator you will also find that you can specify a series cable resistance and see the modified response. However, I just found the software clips the cable resistance value at 5 ohms, and you wanted 20!

Best regards,
WTPro

grumpy
10-02-2007, 02:12 PM
Yep... Just downloaded the update a few days ago :) Cool features!
Just got a brief taste at home. Looking forward to exercising 'em further.

Didn't bring a copy of the new s/w with me to Todd's,
only the original CD (so what you're seeing was old .woo files, collected
at Todd's place, then imported into the newer version for display). -grumpy

subwoof
10-02-2007, 07:53 PM
The gray magnet is the older one. It was only used for about a year until the engineering changes and new coil ( to become the 2225 ) were introduced. The magnets ARE identical from the outside but the internal configuration was alluded to be different in one ( or more ) of the MANY "debates" ( happy searching ) posted on this site.

A sure way to check is to remove the foilcal and look at the recessed casting number that is on the back plate. As far as I know, NO listing of these numbers is available anywhere from any source other than a call to JBL and even then it would be a head-scratcher to anyone NOT employed in magnet design 25+ years ago.

sub