AR 3a woofers

[ironlake]

Has any research been done to see if the alnico woofers with cloth surrounds, molded in ripples on cone, and little foam inserts by dust cap to sound or perform any different to the the next style with same cones but foam surrounds and cermanic magnets? Thanks for any answers.

[RoyC]

Has any research been done to see if the alnico woofers with cloth surrounds, molded in ripples on cone, and little foam inserts by dust cap to sound or perform any different to the the next style with same cones but foam surrounds and cermanic magnets? Thanks for any answers.

I have, and there are differences...most notably, "Q" measurements were higher in the foam surround/ceramic magnet woofer. All evidence suggests that AR replaced the #7 1.88mh woofer inductor with the #9 2.85mh woofer inductor when the cloth surround/alnico woofer was replaced with the ceramic magnet version. This should be taken into consideration when woofer replacement is part of a restoration or repair.

Roy

[ligs]

This is very interesting. Do you have the Qts of foam vs cloth AR woofer, alone and in system.

If AR 12-inch cloth woofer has lower Q than the foam version , the system Qts may also be lower. Typically DCR of the inductor will increase the Qts.

[ironlake]

I restored them and the speaker with the foam surround and small cone in center of woofer still had the number 7 inductor from the factory. I left the inductor in and just changed the caps and refoamed the woofer.

Sorry but not familiar with the term DCR and Qts. My other speaker has the cloth surround speaker with alnico magnet . and both are from the 1969 era.

[ligs]

Qts is from

http://diyaudioproje...all-Parameters/

DCR is essentially the resistance of an inductor.

Qtc usually refers to the total resonance of the speaker system (including crossover, stuffing and in-box)

http://www.carstereo...icles.cfm?id=29

I am interested in the low bass performance of cloth surrounded AR 3 woofer vs foam surrounded AR3a. I seem to remember one of the reviewers said, "comparing to AR 3 , AR 3a has a touch of more rosin on the lower strings" or something to that effect.

[RoyC]

I restored them and the speaker with the foam surround and small cone in center of woofer still had the number 7 inductor from the factory. I left the inductor in and just changed the caps and refoamed the woofer.

Sorry but not familiar with the term DCR and Qts. My other speaker has the cloth surround speaker with alnico magnet . and both are from the 1969 era.

ironlake,

As we discussed previously, your foam surround woofer was a transitional driver, and appears original to the "#7 inductor" cabinet it is in. I am not aware of any testing done on your version of the woofer.

The #9 coil along with the typical foam surround/ceramic magent woofer showed up within months of the manufacture of your relatively rare specimen. If you ever switch to the later, more conventional foam surround woofer, you should consider switching to the #9 inductor. If your speakers sound good to you as is, I would not change anything. You would have to take some rather sophisticated measurements to determine otherwise.

Roy

[RoyC]

This is very interesting. Do you have the Qts of foam vs cloth AR woofer, alone and in system.

If AR 12-inch cloth woofer has lower Q than the foam version , the system Qts may also be lower. Typically DCR of the inductor will increase the Qts.

ligs,

We conducted many measurements using S&L Woofer Tester 2 software when we were putting the AR-3a restoration guide together. I don't have the data readily available, but Qts in and out of the system, was consistently lower for the cloth surround/alnico magnet woofer. As I recall, system Q with the alnico woofer ranged from .7 to .75. The foam surround/ceramic woofer was around .9 for earlier serial numbers, and around .8 for later serial numbers.

We did much experimentation with stuffing amounts, as well as inductors, and the trend remained the same.

Roy

[ligs]

Thanks for the reply. I don't know people can detect the difference between Qtc of 0.8 vs 0.7 or not . However, I have not seen any proposal on replacing the 2.85 mH(17 gauge magnet wire with about 0.8 ohm DCR) in the AR 3a woofer crossover with a larger gauge wire air-core inductor (hence with a lower DCR). Theoretically it will lower the Qtc and increase the efficiency a little bit, I think the difference will be quite audible. AR limited Model 3 speaker uses a 12 gauge(about 4 mH) inductor in the woofer crossover.

[RoyC]

I have not seen any proposal on replacing the 2.85 mH(17 gauge magnet wire with about 0.8 ohm DCR) in the AR 3a woofer crossover with a larger gauge wire air-core inductor (hence with a lower DCR). Theoretically it will lower the Qtc and increase the efficiency a little bit, I think the difference will be quite audible. AR limited Model 3 speaker uses a 12 gauge(about 4 mH) inductor in the woofer crossover.

The difference would be audible, but probably not for the better.

Resisitive properties of the crossover components are critical to maintaining original design parameters. Significantly lowering inductor resistance is not an improvement for a proven, well engineered design. The early AR models, like the 3a, were unusual in that the woofers were given much midrange duty, so significant changes to the original woofer inductor's resistive properties will also change the character of the whole system....not just the bass response. Making the woofer circuit "more efficient" will also increase the woofer's output in the troublesome big woofer-to-dome midrange crossover region...and the 3a already has a rolled off upper frequency response relative to many speakers. When AR stopped using 17ga wire for the #9, #7, etc, in the late 70's/early 80's, those same parts were wound with smaller 18ga wire.

The AR Limited Model 3 speaker (not to be confused with the AR-3a Limited:-)) is a completely different design.

Roy

[ligs]

"The difference would be audible, but probably not for the better"

I totally agree with you on this statement.

When voicing a speaker design the crossover parts are chosen for a reason--they sound good.

Having listened to many good vintage speakers, I begin to appreciate the efforts and different "personality" behind them. Good old Advent Loudspeaker, Boston Acoustics A 150, many AR models and even the bold/over bright Pioneer HPM 100 all have qualities that I like to enjoy.

[ironlake]

Just what will the foam surround do to the speaker that is different than the cloth. As the foam breaks in I notice it is way more floppy when producing low bass, more like the cloth surround. Also what difference does the magnet have on sound. The cones are identical so no sound change should be there.

Thanks again for any answeres.

[soundminded]

IMO the sound of the original cloth woofer was different and superior to the later foam version. It seems to play deeper with lower distortion and has an indescribable quality the foam woofers can't match even if that doesn't show up in the measurements. I think the decision to change the design was an unfortunate one for more reasons than just the limited longevity of the foam surrounds.

For all of Henry Kloss's skill as a speaker designer he was a very poor manufacturing engineer as I see it. The decision to install the crossover network inside a sealed box and to use mineral wool instead of fiberglass led to failures that were unnecessarily costly to repair. The absurdity of it became most evident in the original version of KLH Model 6 where you practically have to destroy the speaker to fix an inevitable failure in it. Nevertheless this arrangement set the pattern for almost all speakers to come. The indifference paid in design to eventual ease of repair is common even today in many products and always has been. It often doesn't become evident until services is required. For example, mMy HP Presario computer came with a defective main audio output jack that wasn't discovered until much software had been loaded. To repair it would have entailed replacing the motherboard and then remapping the hard drive wiping out all of the software. HP offered this for free under warranty but it was unacceptable. They did not offer to supply me with a better idea, an $8 USB sound card instead, I had to buy that myself.

[RoyC]

Just what will the foam surround do to the speaker that is different than the cloth. As the foam breaks in I notice it is way more floppy when producing low bass, more like the cloth surround. Also what difference does the magnet have on sound. The cones are identical so no sound change should be there.

Thanks again for any answeres.

ironlake,

We have been using the surround and magnet type to identify the era and version of the AR-3a woofers. Differences in suspension (surround and spider), cone mass, cone material, compliance, voice coil inductance, voice coil resistance, magnet strength, etc, are some of the things that will affect the response and differences between drivers. The web links posted above by ligs apply to this post as well. The foam and cloth surrounds have different properties, but serve the same function. The woofer's overall response, however, is intimately tied to many other aspects of the woofer's design.

There really are no simple, non-technical answers to your questions in this thread, nor would the answers have any practical application to the ownership of your AR-3a speakers. The various versions of the 12 inch AR woofer used in the 3a have some differences, but they are relatively minor in the overall scheme of things...and are not likley to detract from the experience of their use.

Roy

[RoyC]

IMO the sound of the original cloth woofer was different and superior to the later foam version. It seems to play deeper with lower distortion and has an indescribable quality the foam woofers can't match even if that doesn't show up in the measurements. I think the decision to change the design was an unfortunate one for more reasons than just the limited longevity of the foam surrounds.

For all of Henry Kloss's skill as a speaker designer he was a very poor manufacturing engineer as I see it. The decision to install the crossover network inside a sealed box and to use mineral wool instead of fiberglass led to failures that were unnecessarily costly to repair. The absurdity of it became most evident in the original version of KLH Model 6 where you practically have to destroy the speaker to fix an inevitable failure in it. Nevertheless this arrangement set the pattern for almost all speakers to come. The indifference paid in design to eventual ease of repair is common even today in many products and always has been. It often doesn't become evident until services is required. For example, mMy HP Presario computer came with a defective main audio output jack that wasn't discovered until much software had been loaded. To repair it would have entailed replacing the motherboard and then remapping the hard drive wiping out all of the software. HP offered this for free under warranty but it was unacceptable. They did not offer to supply me with a better idea, an $8 USB sound card instead, I had to buy that myself.

Hi Soundminded,

Henry Kloss left AR before AR went to foam surrounds. His era of KLH speakers all had cloth surrounds, and it wasn't until he founded Advent that he switched to foam. I have to agree with you about the dreaded early KLH 6 cabinet.

Deterioration of foam surrounds is a big drawback. The response characteristics are gradually, constantly changing, and the need to periodically replace the surrounds with aftermarket products adds to the variables. I believe the original reason for the move to foam had something to do with damping properties. Come to think of it, the damping ring on the cones of early AR woofers was also foam (and typically deteriorated). AR's extensive use of foam as a suspension material, and as an under-the-dome damping material, of its early tweeters also proved to be troublesome.

Roy