More 12" restoration questions

[Guest treblehit]

>Bill suggests some break in time before making final judgements.<

Don't say "break-in" too loudly around here. If your speakers are breaking-in, there are those who will report them to the authorities.

I think I can hear the results of "running-in" a vacuum tube or a capacitor, but maybe I'm hearing things and need medication.

I don't have 3a's so I can't do this, but I want to suggest it to you (which you probably would have done without my saying a word); if you unstrap the tweeter/midrange on the 3a's (if they are sitting side-by-side equal-distant from everything) you ought to be able to hear how the woofers compare pretty easily. That's so hard to really do, room acoustics being what they are.

I'm looking forward to hearing about your experiences. I was hoping you'd say there was no audible difference at all. But then, since the other side has been resurrounded (I'm assuming you didn't replace the spider) we still won't know which speaker, if either, is "right" without measurements.

We're trying to re-create something which had parameters that changed; no iteration of which we have all the numbers for; without measurements; for different speaker models; by ear.

Isn't this fun!?

At least we know that the Tonegens couldn't have been made less-suitable as drop-in replacements.

Bret

[Pete B]

Hi Roy,

Interesting experiment that your doing here and I'm also very curious to hear about the results. I'm also interested in measuring the T&S parameters for the stock Tonegen and one of those early "floppy" 11/12" woofers at some point.

Pete B.

>Hey Bret,

>

>They arrived this evening. I was told I was acting like a 5

>year old on Christmas morning as I attacked the boxes :-)

>

>Well, they certainly look good!

>

>I only had time to drop one of the late 70's woofers (they

>received the same treatment as the Tonegen's) into a '3a. I

>quickly compared it to another '3a containing a 1972 version

>that I re-foamed a few months ago and only listened for a very

>short while just to get a hint of what I was in for. My first

>impression was positive. The deep bass seems to be there

>(somewhat less mid-bass?) with the midrange actually seeming

>more defined than the old. Of course its early in the game.

>

>Bill suggests some break in time before making final

>judgements.

>

>Interestingly he also said he added some mass (just as Pete B.

>suggested) to the Tonegen cones under larger dust caps. Those

>will be the most fun to check out. I'll get down to busines

>this weekend.

>

>Stay Tuned...

>Roy

[Guest Bret]

Roy -

Digging around for nuggets of gold in them-thar old posts, I ran across what looks like the mother lode.

Tom Tyson described our spider failure in detail some time ago. He identified it as an affliction of certain vintages of the 20003 woofer. Our discoveries only confirm his observations about *the* way that this later iteration of 20003 will likely fail.

Since anecdotal evidence suggests continued confirmation of this, as a standard practice we should strongly caution all new-comers against solely re-foaming these particular drivers. They should be urged to examine the spider for signs of collapse more emphatically than “as a general rule” would suggest.

Hopefully, we can save them time and money; simultaneously preserving drivers and maybe entire systems.

In my case, these will be repaired twice to fix them once; the second repair will pose a risk to the cone due-to-the-new-glue (say that five times real fast; sounds like Dr. Seuss). My total cost in repairs will eclipse the cost of replacements.

Bret

[Guest Bret]

>Interesting experiment that your doing here and I'm also very curious to hear about the results. I'm also interested in measuring the T&S parameters for the stock Tonegen and one of those early "floppy" 11/12" woofers at some point.<

How will you do this, Pete? What equipment under what conditions, I mean.

(by the way, that isn't a "challenge," to your method; I'm just interested)

Bret

[Pete B]

I've been doing T&S parameter testing for over 20 years. I've stated here that I use LAUD (Liberty Audiosuite) for measurement, CALSOD for simulation, UNIBOX and my own programs for low frequency simulation, SPICE and more. I use a measurement mic with calibration curve. I do not have a precision calibrated acoustical laboratory but then these are only speakers not part of the space shuttle.

I've enjoyed this thread for the technical challenge. I've cloned at least two high end commercial designs, yet many insist, often professionals, that it can't be done. I had already done it when people ("experts") argued that it can't be done. Seems AR can't even make replacement parts for their own designs.

If I seem irritated it's not toward you Bret, just the general attitude on the net. This has been one of the better even enjoyable discussions.

Pete B.

>>Interesting experiment that your doing here and I'm also

>very curious to hear about the results. I'm also interested in

>measuring the T&S parameters for the stock Tonegen and one of

>those early "floppy" 11/12" woofers at some point.<

>

>How will you do this, Pete? What equipment under what

>conditions, I mean.

>

>(by the way, that isn't a "challenge," to your method; I'm

>just interested)

>

>Bret

[Guest Bret]

>I've stated here that I use LAUD (Liberty Audiosuite) for measurement, CALSOD for simulation, UNIBOX and my own programs for low frequency simulation, SPICE and more. I use a measurement mic with calibration curve.<

Yes, you have said that. What I was really wondering is if you were using any of the various methods to derive these numbers and then insert them for further analysis, or if you were measuring them directly. A calibrated lab would be nice, but I don't think I can afford to create one. I'm sorry if the question reminded you of something that irritates you.

I understood how it might have "come across" so that's why I included the explanation for the question.

And then again, look at it this way: Even the derived numbers would be better than guessing (which is all I can do).

And on the third-hand look at it this way: Although Ken made reference to offset error in all the numbers he reported from a calibrated lab situation, at no time did someone say "Hey! Bret, these spiders are so shot that measuring these drivers is a waste of our time!" I suspect Ken did not know this. Once again, careful evalutation and expert analysis is made moot by the curse of all second-hand analysis; a problem with the premise.

On the other hand we DID learn a partial answer to the question Ken first proposed we investigate; what kind of job reconers were doing.

Let me ask you something: Do you think there is any merit to the argument that small signal parameters are inadequate for predicting performance in a dynamic situation (the argument made by Short et al for not designing from the small signal numbers).

This "makes sense" to me, but then I believed that 16 bit digital was enough; and a 1-bit decoder could not be improved-upon, and the tooth fairy flies around. Enough is supposedly enough; and the tooth fairy does have wings.

Now I find that what may be mathematically provable doesn't necessarily mean that it holds-up in practical application. Obviously, math shows that my parents were sticking the coins under my pillow because the tooth fairy can't possibly fly with those wings. It's also useful to note that there is no Creator or he wouldn't have designed the tooth fairy with so little lift.

In my own work I find Nobel-prize winning theory and complex predictive analysis usually falls-victim to a single, simple, unpredicted "ugly fact" (whatever it might be).

Bret

[RoyC]

Hi Bret and Pete,

I'm reporting from AR woofer overload land. The collective magnetic fields of these beasts have created a black hole over my residence into which my abilty to discern what I'm listening to has been sucked!

The bottom line is that the re-spidered woofers are more alike than different from the old. I doubt you will be disappointed, Bret. The Tonegens are now AR worthy, and the 70's versions are easily functioning as drop in '3a replacements as I type this.

I finally decided to install the retreads in two systems and live with them awhile.

The Tonegens are in a custom cabinet (slightly larger than the '3a) with the more efficient AR-3a replacement drivers and AR-3a "limited" crossovers from the early 90's. They sound great! Bret, I'm hoping your 10pi's will sound like this system.

I installed the late 70's woofers in the '72 vintage AR-3a pair and at this point feel that they are AR-3a in every way.

From both systems, I'm getting the bass response I've always enjoyed in '3a's with the mids quite possibly cleaner than before.

Pete, I no longer have original Tonegens with which to compare.

Its only been a couple of days, but feel the surgery was a success. The re-foam work on all drivers is flawless as well.

Bill called Sat to see how the new "more aggressive" spiders were doing. I told him they were still attacking after 3 cans of Raid. Nice guy!

Roy

[Guest Bret]

>I'm reporting from AR woofer overload land.<

I originally mis-read that as “AR woofer overlord land.” Woofer Overlord. . . nice title.

> The collective magnetic fields of these beasts have created a black hole over my residence into which my abilty to discern what I'm listening to has been sucked!<

I hate when that happens.

>The bottom line is<

Pun intended?

> that the re-spidered woofers are more alike than different from the old. I doubt you will be disappointed, Bret.<

I hope you’re right. I’m trying to have faith; really I am.

> The Tonegens are now AR worthy, and the 70's versions are easily functioning as drop in '3a replacements as I type this.<

That’s certainly encouraging.

> I'm hoping your 10pi's will sound like this system.<

I hope your system sounds terrific and I hope the 10pi’s sound even better than that ! ! ! ;-) Weeelll. . . (Ohmygosh, I suddenly sound like Elizabeth Montgomery. Help Me.)

>I installed the late 70's woofers in the '72 vintage AR-3a pair and at this point feel that they are AR-3a in every way.<

Excellent. You know, the two fixed by Tri-State impressed me that way in the 10pi’s - mean that they "fit", not that they sounded like 3a's. When they are in one of the 9s, I get thunder. Thor is jealous. When both 9s get fixed, I think I’ll throw open the windows and play some eerie pipe organ music, or maybe something really frightening; like rap, Loren Green singing "Bonanza," or a modern political speech.

>From both systems, I'm getting the bass response I've always enjoyed in '3a's with the mids quite possibly cleaner than before.<

Do you suppose that’s because the 12" isn’t overbearing in the crossover frequency area anymore? That settles it, I’m going to Radio Shack and buy a cheap SPL meter and finally get a test recording of some sort; something with lots of sustained warbled frequencies and other auditory oddities - like a Streisand record.

>Pete, I no longer have original Tonegens with which to compare. <

Yes, but I know someone with four of them. They are smelly.

>Bill called Sat to see how the new "more aggressive" spiders were doing. I told him they were still attacking after 3 cans of Raid.<

lol

He called me today to get my permission to fix something “extra.” Yes, he seems to be a very nice guy. But he just don’t tawk lack us-all down heah in the lil’ ol’ sowweth. You know we always depend on the kindness of strangers.

I’ve sent email (local forum email) to Pete. Depending on how he answers (and if he answers) we may be in for some more fun.

I’m really glad you are pleased with the results. I’m sure I will be also, and REALLY APPRECIATE the heck out of your not leaving me hanging all weekend or anything, Roy . . . I held my breath from Friday until Saturday night. I was beginning to enjoy it, but a small child walked-up to me outside a BBQ restaurant and asked, “Elvis?” so I quit,thank you. Thankyouveramuch.

It’s late, I’m tired, and my public-discourse inhibitions got sucked into the hole over your house. I know you all must really hate when that happens. I hoped that your silence was rapture and not, "Uh oh, how can I say something bad after all Mr. Miller's tried to do for me?" Considering the glowing reports he's been getting here for quite a long time, I suspected Mr. Miller would not disappoint, but with Tonegens, well, I wasn't sure you could trust 'em to cooperate.

Bret

[Pete B]

>I’ve sent email (local forum email) to Pete. Depending on how

>he answers (and if he answers) we may be in for some more

>fun.

>Bret

Hi Bret,

I'm not ignoring you I never got that email. I've used the forum mail before the url changed and it worked so I don't know what's going on now? Feel free to visit my professional page (listed here in my profile) and use the contact link which brings up the email address. I don't want to list it here to avoid bots picking it up.

Pete B.

[Pete B]

I've seen this type of failure before and it seems to happen when the driver sits for a long time, usually in storage facing up, or down, and the center shifts due to what we call cone sag. Really the spider becomes deformed but it is the cone that sags. I know people who flip their speakers in storage to avoid this. I've seen situations where it seems to sag all the way to one end which is what I understood you to be saying if I followed you correctly.

>Tom Tyson described our spider failure in detail some time

>ago. He identified it as an affliction of certain vintages of

>the 20003 woofer. Our discoveries only confirm his

>observations about *the* way that this later iteration of

>20003 will likely fail.

>

>Since anecdotal evidence suggests continued confirmation of

>this, as a standard practice we should strongly caution all

>new-comers against solely re-foaming these particular drivers.

> They should be urged to examine the spider for signs of

>collapse more emphatically than “as a general rule” would

>suggest.

>

>Bret

[Pete B]

Hi Roy,

Good to hear that these are finally working to your satisfaction. No problem about the Tonegens, I'm in no rush and it would be better to find some close by to me. I'm also wondering if you have the driver part numbers handy for your AR-3a Limited, just to know which ones work well together? I think what you've got then are all the right parts for an AR-3a Limited but with the deeper bass extension of the early 3a if I'm following correctly? They're also probably a bit more efficient than the originals.

>The Tonegens are in a custom cabinet (slightly larger than the

>'3a) with the more efficient AR-3a replacement drivers and

>AR-3a "limited" crossovers from the early 90's. They sound

>great! Bret, I'm hoping your 10pi's will sound like this

>system.

>I installed the late 70's woofers in the '72 vintage AR-3a

>pair and at this point feel that they are AR-3a in every way.

>

>

>From both systems, I'm getting the bass response I've always

>enjoyed in '3a's with the mids quite possibly cleaner than

>before.

>

>Pete, I no longer have original Tonegens with which to

>compare.

>

>Its only been a couple of days, but feel the surgery was a

>success. The re-foam work on all drivers is flawless as well.

>

>Bill called Sat to see how the new "more aggressive" spiders

>were doing. I told him they were still attacking after 3 cans

>of Raid. Nice guy!

>

>Roy

>

>

>

>

>

[Pete B]

You ask some good questions Bret. I'm not sure I follow exactly what your asking about T&S parameters but i'll give it a try. There are two methods used for measuring the T&S parameters, both involve measuring the input impedance but we need to alter a parameter since there are many combinations of mass and compliance that will provide the same Fs. There's the delta mass method (free air with and without additional mass) and the delta compliance method (free air then in a test box). I use the delta mass method, LAUD will do either type. LAUD does all the calculations for this measurement, and all the driver parameters can be calculated from these two runs of impedance measurement. You do need to compute the surface area of the cone, a ruler usually works fine for this and it helps to measure the DC resistance. Yes I've often checked the design with the actual measured parameters if that's what your asking. It's also well known and has been verified by many with calibrated laboratories that T&S based simulation programs such as Unibox are highly accurate.

It's true that a driver manufacturer can for example actually weigh the moving assembly to determine moving mass, but how do you account for part of the edge, and part of the spider? I'm sure they have approximations for this. Certainly driver design starts this way but they use similar methods to measure T&S parameters for the final driver.

Ah the small signal, large signal question, I was going to bring this up. I've been talking here about adding resistance and all our calculations here are for a cold voice coil. The voice coil resistance goes up as it is heated, and you probably noticed that these drivers are about .3 to .5% efficient. The voice coils do get very hot and this shifts RDC, and thus motor strength and Qtc. I've never designed for hot and prefer to use large coils, even multiple woofers, to handle the heat and provide more consistent performance. Moving mass plays a large part in setting system performance and luckily this is one of the few things that doesn't change with level. If a drivers mid to large signal performance changes drastically from small signal, then it's probably not a very good driver and I wouldn't use it. Large signal performance is a high priority and I design from the outset for the best performance rather than worrying about it later. I design vented systems weighing large signal performance at least as much as small signal.

You've probably seen the measured performance of the AR3 woofer and you might notice that it agrees quite well with UNIBOX with the drivers that have the correct parameters.

I think that this has been a good learning experience. Driver repair seems very straight-forward however we've seen how important it is to use a top notch reconer.

As far as cloning goes, what I've suggested here are cloning methods and it's interesting that they're needed for parts claimed to be drop in replacements.

Pete B.

>>I've stated here that I use LAUD (Liberty Audiosuite) for

>measurement, CALSOD for simulation, UNIBOX and my own programs

>for low frequency simulation, SPICE and more. I use a

>measurement mic with calibration curve.<

>

>Yes, you have said that. What I was really wondering is if

>you were using any of the various methods to derive these

>numbers and then insert them for further analysis, or if you

>were measuring them directly. A calibrated lab would be nice,

>but I don't think I can afford to create one. I'm sorry if

>the question reminded you of something that irritates you.

>

>I understood how it might have "come across" so that's why I

>included the explanation for the question.

>

>And then again, look at it this way: Even the derived numbers

>would be better than guessing (which is all I can do).

>

>And on the third-hand look at it this way: Although Ken made

>reference to offset error in all the numbers he reported from

>a calibrated lab situation, at no time did someone say "Hey!

>Bret, these spiders are so shot that measuring these drivers

>is a waste of our time!" I suspect Ken did not know this.

>Once again, careful evalutation and expert analysis is made

>moot by the curse of all second-hand analysis; a problem with

>the premise.

>

>On the other hand we DID learn a partial answer to the

>question Ken first proposed we investigate; what kind of job

>reconers were doing.

>

>Let me ask you something: Do you think there is any merit to

>the argument that small signal parameters are inadequate for

>predicting performance in a dynamic situation (the argument

>made by Short et al for not designing from the small signal

>numbers).

>

>This "makes sense" to me, but then I believed that 16 bit

>digital was enough; and a 1-bit decoder could not be

>improved-upon, and the tooth fairy flies around. Enough is

>supposedly enough; and the tooth fairy does have wings.

>

>Now I find that what may be mathematically provable doesn't

>necessarily mean that it holds-up in practical application.

>Obviously, math shows that my parents were sticking the coins

>under my pillow because the tooth fairy can't possibly fly

>with those wings. It's also useful to note that there is no

>Creator or he wouldn't have designed the tooth fairy with so

>little lift.

>

>In my own work I find Nobel-prize winning theory and complex

>predictive analysis usually falls-victim to a single, simple,

>unpredicted "ugly fact" (whatever it might be).

>

>Bret

[tysontom]

>I've seen this type of failure before and it seems to happen

>when the driver sits for a long time, usually in storage

>facing up, or down, and the center shifts due to what we call

>cone sag. Really the spider becomes deformed but it is the

>cone that sags. I know people who flip their speakers in

>storage to avoid this. I've seen situations where it seems to

>sag all the way to one end which is what I understood you to

>be saying if I followed you correctly.

>

I think Pete is exactly right. It is the spider that sags under the weight of the "moving system," and it settles up or down, depending on how the driver is stored. This is particularly true of the earlier, highly compliant, drivers. From the beginning AR warned against storing speakers in a face-up or face-down position for extended periods. Once the speaker has sagged, the spider is stretched and cannot be repaired without replacing the spider assembly. This condition used to be called, "collapsed skiver," but in truth it is the spider that deforms under the weight.

When I store any spare driver, I always brace the cone in the center position with foam blocks or rolled-up KimPac or similar material. This physically prevents the cone sag.

--Tom Tyson

[Guest Bret]

>When I store any spare driver, I always brace the cone in the center position with foam blocks or rolled-up KimPac or similar material. This physically prevents the cone sag.<

Makes perfect sense.

Bret

[Guest Bret]

>There are two methods used for measuring the T&S parameters, both involve measuring the input impedance but we need to alter a parameter since there are many combinations of mass and compliance that will provide the same Fs. There's the delta mass method (free air with and without additional mass) and the delta compliance method (free air then in a test box). I use the delta mass method, LAUD will do either type. LAUD does all the calculations for this measurement, and all the driver parameters can be calculated from these two runs of impedance measurement.<

I do appreciate this and the other explanations you gave me. I learn something new all the time and while it might not qualify me to be an engineer, I am always getting a better and better idea of the issues and grasp of the important concepts.

Bret

Bret

[Guest Bret]

I thought since I shared the "before" photo that someone might want to see the "after" shot.

Bret

[Guest Bret]

Dear Woofer Overlord -

Although I'm sure I'll only illicit the same response Ed McMahon got when telling Carnac "I hold in my hand, the LAST envelope;" this will be my final posting in this thread.

I did receive the Millersound repaired drivers yesterday and, of course, could not wait to drop them into my 10pi's to see what there was to see. It was very late (early) by the time I got them installed and got down to the business of listening. Admittedly, I was too tired to listen long - I probably only had an hour with them, possibly less; far too little time to come to any final, minutia-filled conclusions about anything.

The Millersound repair job is a beautiful thing to look-at. Even if they had sounded awful you have to appreciate the care and skill applied to their finished appearance; much like we used to admire DeLoreans. Even if their performance was awful, it was still fun to look.

Fortunately for me, the Tri-State repaired "DUT 5 & DUT 6" were in their cabinets and so I had a fair opportunity to do a little comparison on bass extension which, until the brightness issue gets resolved, is all I'm prepared to talk about.

The Millersound speaker did require 15-30 minutes of play before it began reaching for the low notes; but it got there. I feel safe saying that both repairs are so far superior to using replacement drivers that they are worth twice as much as a replacement driver, yet cost less than half as much.

As much as I'm comfortable saying this moment is that the Millersound pair are gorgeous AND sound as though they belong. Bill is not the sort to muck-about, either. He got them one Wednesday and shipped them to me the following Monday or Tuesday.

What I've seen and heard is good-enough that the Simply Speakers drivers are already in the box ready to be sent to Mr. Miller for correction.

Bret

[Pete B]

I just noticed that the driver motor flux densities are given in the AR literature for several models and there are at least two different values:

11/12" woofer:

AR-10pi 9,800 gauss

AR-9 9,800

AR-11 8,200

It's clear that some are upset by many of my posts, so I'll just point out that I don't expect anyone to accept my theory below until it is tested. I will measure a Tonegen someday, and one of the first things I'm going to check is Bl. I want to get to the facts but this won't happen until we theorize and measure. People will not be able to maintain their classic "gems" unless we determine the parameters for the stock AR drivers and determine how to duplicate the target response for each system with new, old, or substitute drivers. People are welcome to their opinion as to the best way to repair a system but it is just that an opinion, take it for what it's worth.

Pete B.

>>>Is it well known among AR people that early and late

>>production AR-9s sound different as far as deep bass goes?<

>>

>>Not that I'm aware of. In fact, I don't understand the

>reason

>>for the question.

>It would support my theory that the early and late 200003s are

>different. My latest theory is that there are old and new

>magnets and old and new voice coils:

>Old magnet, old coil Bl = 10 DUT5 and 6

>New magnet, old coil Bl = 11.75 DUT2, 3, 4

>New magnet, new coil Bl = 13 DUT 7, AR303, probably

>Tonegen

>

>>>Do we think that the Tonegens are a direct replacement for

>>the late 200003?<

>>

>>They are sold that way, but I no longer consider them a

>>suitable "drop-in" replacement.

>

>Looks like we have 3 drivers, 200003 old and new and Tonegen,

>I bet the Tonegen has a Bl of 13 like the 303 and DUT7 but a

>lighter cone like the 200003, DUT 7 has the motor of a Tonegen

>but with mass added as you point out. Again, we can add mass

>to make up for the stiff suspension and add resistance/remove

>damping to make up for the high Bl.

>

>It's interesting that Roy noted that AR used less damping with

>the newer drivers, just as I've been suggesting for some time

>on here.

>

>Pete B.

[Pete B]

Your welcome Bret, your polite way makes the discussion enjoyable.

Pete B.

>I do appreciate this and the other explanations you gave me.

>I learn something new all the time and while it might not

>qualify me to be an engineer, I am always getting a better and

>better idea of the issues and grasp of the important

>concepts.

>

>Bret

[Pete B]

Tom Tyson wrote:

> I think the spider was cut or modified, and ultimately a

>longer voice coil was used to allow for the longer excursions.

> To my knowledge, no mass was added to the original woofer,

>although the cone used in the production model was

>considerably heavier than the prototype, I believe.

I read about the cut spider here, where it is indicated to be a quote from Villchur. Refer to the second block of text:

http://history.acusd.edu/gen/recording/villchur.html

I was told the acoustic suspension story, many years ago, by the audio engineering professor who I studied under. I had already read about it but it was also interesting to get his perspective and critique of the design. There is no doubt that it is one of the greatest and revolutionary inventions in loudspeaker design. Added mass was speculation on my part since it would be required to get a low Fc in the original prototype. Does anyone know the Fc of the original prototype?

I was aware that some older amplifiers had variable output impedance and wondered if this was how he got the damping factor of 1 in the AR-1 as published in the AES, then I noticed the series resistor. I looked at pictures of the back of the AR-1 in the library and saw the suggestion for strapping the resistor in or out depending on placement after I posted the question above. Thanks also for your input Tom.

I'd been assuming a target Qtc of 1 in this discussion based on what was published in the original AES article, however the damping factor of 1 as stated in that article made it seem incorrect for the woofer and crossover inductor system alone.

I recently noticed that Qtc values of .7 and .75 are given for the AR-10pi and AR-11. A Qtc of about .7 is probably right for the AR woofer when a low source impedance or high damping factor is used.

It should be noted that tube amplifiers typically have an output impedance of one ohm or more and this discussion shows how much it effects the low frequency response by raising the effective Qtc.

Pete B.

[Pete B]

Hi Roy,

I'm wondering how these Tonegens modified by Miller turned out?

Any comments?

Pete B.

>Hi Pete,

>Coincidentally I called Millersound this afternoon and thats

>essentially what I was told. The stiffer spider saved AR "alot

>of hassles" as amplifier power grew and listening levels

>increased. It unfortunately altered the bass response when

>used in older systems designed with the soft spider.

>He suggested replacing the spider as well. I will be

>delivering some woofers to him soon and will have him install

>spiders equivalent to the early 12 inchers in the Tonegens. We

>shall see ("hear" I should say).

>

>Roy C.

>

>

>

[RoyC]

Hi Pete,

Well, the bass response did (subjectively) improve with the slightly softer spiders and the added cone mass. The spiders were not as soft as the old ones, and he added the mass under rather large new dust caps.

The down side is that the woofers' midrange contribution was altered resulting in less "warmth" in the 3a sound. I prefer them over the original Tonegen's for use in the AR-3a, but would still choose an alnico/cloth surround or early 70's version for that speaker system.

Roy

[Pete B]

Hi Roy,

Thanks for the update. Now you've got me wondering if the cone, spider, voice coil and edge replacement parts for the early 70's woofer would fit in the Tonegen frame. I wonder if the top plate thickness is the same in the Tonegen magnet structure.

Pete B.