AR Woofers

[Guest dogmeninreno]

Does anyone know anything about these spendy woofers on eBay? http://cgi.ebay.com/ws/eBayISAPI.dll?ViewI...ssPageName=WDVW

Thanks, Dale

[soundminded]

I'm still puzzled about the AR9 woofers. If the Impedence is 4 ohms and they are in parallel, why is the impedence of the system still 4 ohms? Is there a 2 ohm drop in the series elements in the crossover network? The system is rated at 400 watts but the normal AR 12 inch woofers are rated at 100 watts each. Are the AR9 woofers different or is the crossover network able to dissipate an additional 200 watts? It doesn't seem that way. If I hadn't been told otherwise already here, I would have guessed that they were 8 ohms each and rated at 200 watts each but apparantly that's not true. Ken, Tom, somebody, could you clarify this mystery for me?

[tysontom]

>Does anyone know anything about these spendy woofers on eBay?

>http://cgi.ebay.com/ws/eBayISAPI.dll?ViewI...ssPageName=WDVW

>Thanks, Dale

Dale,

Those woofers are the Tonegen replacement woofers, #1210032, that were originally offered by AB Tech Services. This model woofer is basicallly identical to the original woofer, but the suspension is somewhat stiffer -- probably for reliability (power-handling) purposes. I recently sent one out to Ken to test, so at some point he can let us know the difference, if any, in that woofer and the original 200003-0 woofer. I do know that the magnet, voice coil and cone are almost identical to the original woofers. I suspect that the free-air resonance (fs) is somewhat higher on the tonegen woofer than on the earlier woofers.

--Tom Tyson

[tysontom]

>I'm still puzzled about the AR9 woofers. If the Impedence is

>4 ohms and they are in parallel, why is the impedence of the

>system still 4 ohms? Is there a 2 ohm drop in the series

>elements in the crossover network? The system is rated at 400

>watts but the normal AR 12 inch woofers are rated at 100 watts

>each. Are the AR9 woofers different or is the crossover

>network able to dissipate an additional 200 watts? It doesn't

>seem that way. If I hadn't been told otherwise already here,

>I would have guessed that they were 8 ohms each and rated at

>200 watts each but apparantly that's not true. Ken, Tom,

>somebody, could you clarify this mystery for me?

Soundminded,

The AR-9 woofers are indeed identical to the AR-11/AR-10Pi woofers, and they are connected in parallel. That would appear to make the impedance around 2 ohms, which would be true were it not for the novel crossover known to insiders as, "The Electronic Automatic Transmission," designed by Alex DeCosta, one of AR's engineers on Tim Holl's AR-9 design team.

At the AR-9’s system resonance of approximately 35 Hz, the impedance is at its (natural) highest point, well within normal operating range of nearly all amplifiers. The problem is the region above and below resonance at frequencies below the 200 Hz crossover. What AR did (Alex DeCosta) was to design a special circuit for the woofers. The crossover has the choke and series-capacitor bypassed by a resistor, and these are on one leg of the paralleled 1210003-0 woofers. It is a "tuned" circuit -- and at the speaker’s resonance frequency, the point where a speaker usually has its highest impedance anyway -- the capacitor and choke are essentially a short circuit and the resistor that bypasses them has no effect (path of least resistance). As the frequency rises, however, the impedance of these parallel woofers tends drops precipitously, and the system output tends to want to rise, but as the resistor is brought into the circuit in series, the impedance is raised to a safe area while at the same time reducing the output. This pulls down the output of the dual, parallel woofers above resonance so that the response is flat, and never allows the impedance to drop below 3.2 ohms rather than 2 ohms -- well within the safe-operating range for most all amplifiers. The brilliance of this whole thing is the AR-9's flat bass response, relatively easy impedance, and very low distortion.

This is a good example of why one should consider leaving the crossover of the AR-9 alone -- if everything is working properly. If crossover values are upset or modified, the speaker's response could be compromised, not to mention causing problems for most power amplifer.

--Tom Tyson

[Guest dogmeninreno]

Thanks Tom, I have a few (10) of the Tonegen woofers you refer to here but have never tried them in my 9's. I don't want to experiment with something that sounds so good! Dale

[soundminded]

Thank you for your response Tom. So if I understand you correctly, the driver's response at resonance is sufficiently above 4 ohms so that the parallel pair never drops below 3.2.

I'm still a little puzzled about the power handling capacity.

I was very much aware from Tim Holl's excellent writeup that changing any of the components in the crossover network would be extremely risky because the circuit is so carefully tuned. Bass response from my pair has been the best I've ever heard. Unfortunately, after more than 20 years of reliable service, my AR9s took out my Dyanco Stereo 120. The exact culprit was DG 419 603-2 Prokofiev's Alexander Nevsky cut 5 The Battle on the ice. In this battle the AR9s won and the Dynaco amp lost. Fortunately, its replacement and probably lineal decendant Klaus/Peterson Mosfet 120 has been completely reliable and has had no difficulty driving the AR9s to very loud undistorted levels at very low frequencies despite its modest (by today's standards) 60 wpc rating.

[Guest dogmeninreno]

Tom, I am also following your thread with Ken, Thanks, Dale

[tysontom]

>Thank you for your response Tom. So if I understand you

>correctly, the driver's response at resonance is sufficiently

>above 4 ohms so that the parallel pair never drops below 3.2.

At resonance, the velocity of the cone is greatest, and thus the *back EMF* from the motor circuit is also greatest and will raise the impedance by a factor of 3 to 6, while the dc resistance remains constant. With a very low impedance for the two parallel woofers, at resonance the impedance would still be quite high. This is the part of the AR-9 that is so clever: the impedance of a driver at resonance is always at its highest point (for example, the impedance of a four-ohm AR-3a at resonance is about 20 ohms or so, whereas it drops to four ohms an octave or so higher), so if they could control the impedance above and below resonance in the AR-9, there would be no problems driving the speaker.

>

>I'm still a little puzzled about the power handling capacity.

>

To my knowledge there is no universal standard for rating the power-handling capability of a speaker. And the standards today are probably quite different from 1978 when the AR-9 was introduced. For all practical purposes, the question that has to be asked is whether the input to the speaker is steady-state sine-wave power into a woofer, or peak power or average power or what? A 20 Hz sine wave applied to an AR-9 with as little as 70 or 80 watts rms (or possibly less) would very likely cause it to distort. Yet it could easily handle 400 watts rms or more at 200 Hz. On normal music (with peak-to-average ratios of 15 to 20 dB or more) the AR-9 could probably handle >1000-watt peaks with no problem.

>I was very much aware from Tim Holl's excellent writeup that

>changing any of the components in the crossover network would

>be extremely risky because the circuit is so carefully tuned.

>Bass response from my pair has been the best I've ever heard.

>Unfortunately, after more than 20 years of reliable service,

>my AR9s took out my Dyanco Stereo 120. The exact culprit was

>DG 419 603-2 Prokofiev's Alexander Nevsky cut 5 The Battle on

>the ice. In this battle the AR9s won and the Dynaco amp lost.

> Fortunately, its replacement and probably lineal decendant

>Klaus/Peterson Mosfet 120 has been completely reliable and has

>had no difficulty driving the AR9s to very loud undistorted

>levels at very low frequencies despite its modest (by today's

>standards) 60 wpc rating.

When I purchased my AR-9s in 1978, I drove them with a McIntosh MC2200, and this proved to be excellent. Never satisfied, I traded the 2200 for a McIntosh MC2500 -- brash overkill. These amplifiers, of course, never wavered. Prior to these MACs I had a series of amps that died on me, most noteworty my Dynaco Stereo 400 driving into a pair of LSTs. The next to go was a Marantz 250. In each case I was playing the speakers at high levels, usually after a few scotch & sodas, showing off to friends. I think it was *Switched On Bach* that took out the Dyna, and this same music also caused a failure in my first AR Amplifier.

--Tom Tyson

[kkantor]

That was Alex De Koster, who eventually became VP Engineering. (At the same time, Ercilio Costa was VP Manufacturing...)

In my opinion, the main reason why the woofer suspension was stiffened was that the automated lines in Japan just could not cope with the kind of ultra-floppy parts that very low resonances required. I think the Tonegen is an excellent woofer, and it is a testament to its inherent linearity that there is no distortion penalty to be paid when using it to replace an older (more acoustically suspended)12".

[tysontom]

>That was Alex De Koster, who eventually became VP

>Engineering. (At the same time, Ercilio Costa was VP

>Manufacturing...)

Ken,

Thanks for the correction on the spelling of Alex De Koster! It just goes to prove that you can never trust your memory on things such as that, and I should have looked back through some files to get it correct. Accuracy is always the most important thing when relating historical facts.

--Tom Tyson

[Guest dogmeninreno]

>>Does anyone know anything about these spendy woofers on

>eBay?

>>http://cgi.ebay.com/ws/eBayISAPI.dll?ViewI...ssPageName=WDVW

>>Thanks, Dale

>

>Dale,

>

>Those woofers are the Tonegen replacement woofers, #1210032,

>that were originally offered by AB Tech Services. This model

>woofer is basicallly identical to the original woofer, but the

>suspension is somewhat stiffer -- probably for reliability

>(power-handling) purposes. I recently sent one out to Ken to

>test, so at some point he can let us know the difference, if

>any, in that woofer and the original 200003-0 woofer. I do

>know that the magnet, voice coil and cone are almost identical

>to the original woofers. I suspect that the free-air

>resonance (fs) is somewhat higher on the tonegen woofer than

>on the earlier woofers.

>This is the response I received...

AR has sourced them to China. Like everything else, oh well.

Please give us a call or e-mail if you need more information.

We will be happy to help you.

Regards,

Sean Ryan, Tom Ryan, and the Crew at Simply Speakers

http://www.simplyspeakers.com

Store Address:

Simply Speakers

6625 35th St. N.

Pinellas Park, FL 33781

>--Tom Tyson

[Guest ToddBurger]

I have a pair of reconditioned AR-10pi's (replaced with AR woofers designed for these speakers, purchased from AR parts house about 10 years ago). The speakers work fine, but ...

My Yamaha 140 W RMS per channel amp, to which the AR-10pi's were connected, finally bit the dust. I blew something on one channel, which I figure is not worth repairing (not XM-ready, no surround sound, etc)... The new Yamaha amps I am looking at (XM-ready, 7 channel) are only 100, 120 and 130 watt RMS at 8 ohms. Are they powerful enough to properly drive my AR 10 pi's?

I occasionally like to crank them up...

-Todd

[RoyC]

I recently measured the fs of a couple of Tonegen "replacement" woofers (thanks Bret!). They both measured 25hz+/-. These are not new drivers by any means, so one would have to assume the fs was higher earlier on.

Mr Villchur's patent document states that "the natural frequency of said transducer in free air is in the subsonic region below 20 cycles per second". I believe the AR-3a documentation states that the woofer should measure 18hz +/-10 or 20%. I have measured NO original AR 12 inch woofer to be over 21hz with a new foam surround, and 19hz or below when broken in. Further, cloth surround woofers always dial in safely under 20hz (typically below 18hz).

The difference between the "replacement" and the original is significant. The replacement woofer will never sound the same unless some changes are made to its design; a big problem since bass response is one of the most endearing qualities of these old beasts. In my opinion, at nearly $300 a pair, the replacement woofers are overpriced and inadequate for any model prior to, and including, the AR-11.

Roy

[dynaco_dan]

Hi Roy;

Thank you for your commentary on the 12" AR woofer, Roy.

Your insight and valuable ability to write here certainly adds to wealth of total AR knowledge.

We are all still learning about the 1950's AR, all these many years later.

You and so many other members that add to this site are a real pleasure for me to read and enjoy.

[KlausDK]

Hi Roy

I have a set of Tonegan 11" woofers, I took out of my LST's. I wonder what they would sound like/measure if you replace the stiffer tonegan surround with replacement surround designed for the "real" AR woofer. If coil and cone are very close to the original, could this bring them up to a useable standard, do you think?

Best Regards

Klaus

[RoyC]

>I wonder what they would sound like/measure if you

>replace the stiffer tonegan surround with replacement surround

>designed for the "real" AR woofer.

Hi Klaus,

I gave that a try a couple of years ago with another pair of Tonegens. Unforunately it wasn't until I had the spiders replaced that any appreciable difference could be noticed.

Roy

[KlausDK]

Hi Roy

Thank you for your answer. When you changed the spider in the 11/12" woofer, was that for a softer or stiffer one?

I have refoamed three pairs of original AR woofers from 1970'ies speakers, and they have had quite some differences in spider stiffness between the different pairs. They were from a set of 3a, LST and a set of 10Pi respectively.

Best regards Klaus

[RoyC]

Klaus,

I had softer spiders installed.

Roy

[frankmarsi]

>Klaus,

>

>I had softer spiders installed.

>

>Roy

From where?

FM

[RoyC]

Hi Frank,

Millersound in Lansdale, PA...Bill can be reached at (215)412-7700 or millerspkr@aol.com

He does excellent work.

Roy