Re-foaming the AR-9

[ar_pro]

There's been some question regarding the pros & cons of re-foaming original woofers, or replacing them with new drivers. Over the course of restoring four pairs of AR-9s, I've had experience with both sides of this issue, having purchased new drivers from AB Tech (absolutely first-rate people!), and having had original woofers re-foamed by a qualified professional. To be honest, I cannot hear ANY difference between the repaired woofers and the brand-new ones, and it's my opinion that an ACCURATE evaluation of the original driver's condition, and a SKILLFUL replacement of the foam surround are at the center of the matter. That said, here is an unsolicited suggestion: Millersound Labs, located at 1422 Taylor Road, Lansdale, PA 19446. Their telephone # is 215-412-7700. Bill Miller is perhaps the most knowledgeable and conscientious person that you'll ever meet in this field - he loves loudspeakers, and is an absolute wizard when it comes to repairing the air-suspension driver. Anyone who has had the opportunity to chat with him on the phone or in person, will be reminded of why they enjoy this hobby in the first place!

[ToastedAlmond]

I think that's right across the river from here. Good tip. Thanks.

Toasted Almond

[Guest]

>To be honest, I cannot hear ANY difference between the repaired woofers and the brand-new ones<

Did you refoam or replace the 8" drivers?

Bret

[ToastedAlmond]

I had the 8 inchers re-foamed, as well as all four 12 inchers. Total price was $220.

Toasted Almond

[ar_pro]

Two 8" drivers were replaced (the cones had water damage), and the others were re-foamed. The new drivers were purchased ten years ago, and sound identical to the re-foamed speakers...I'm not sure if the current supply is an exact match for the original, though.

[Guest Sean]

I have a pair of 9's and a pair of 90's. The 12's, 10's and 8's have all been refoamed. I was previously driving the 9's with 500 wpc on 12's and 400 wpc on the 8's and top end with no problems. Believe me, i do stand on the throttle quite a bit. Believe it or not, i could still drive the amps into compression even with this much power on hand. I ended up switching to a single full range amp to drive the 9's, but it is rated at 1200 wpc. This sounds much cleaner and will play louder but lacks the bottom end impact that the woofer amp used to deliver. Such is life.

I currently have the 9's running as the mains in my HT system. The 90's are being run as the rears with a custom built center channel. The center use two re-foamed AR 8's with the "dual dome" 9LS / 9LSI upper midrange / tweeter mounted on a plate. I have two subs, each of which consists of re-foamed AR 12's ( from AR 9's ) mounted in sealed and stuffed cabinets. As mentioned, the mains are being fed 1200+ wpc and the center, surrounds and two subs each see 800+ wpc. In case you were wondering, this totals up to 6000+ watts rms for my HT system. I have had NO problems with any of the woofers. Now the upper midrange domes, that is another story :-( As such, i would not worry about re-foaming the drivers so long as the spider is still solid and you can center the coil in the gap. Sean

>

[tysontom]

This brings up a great topic: re-foaming vs. replacing with new.

The replacement Tonegen 12-inch, service-replacement woofer is essentially the same as the original, but there are differences. For example, the voice coil diameter and overhang are virtually identical on all the 12-inch woofers all the way from the original 1954 AR-1 up to the latest 12-inch replacement woofer. The original AR woofers can move one-half inch peak-to-peak in a completely linear fashion, and up to nearly one inch before distorting heavily. The cone mass and diaphram diameter, etc. are virtually all the same. Also fortunate -- and by sheer necessity -- AR truncated the edges on two sides of the famous woofer so it could be properly dropped into the cabinet and clear the wide cabinet-edge molding. This is indeed fortunate, because it demands that one uses an authentic AR woofer as a replacement, rather than something unsuitable, and results in consistent performance in that group of AR speakers.

If you examine the woofers from the earliest AR Alnico 12-inch woofer (PN#3700) used in the early AR-1's, AR-3's and earliest AR-3a's, the cone in free air was extremely compliant, and had a free-air resonance of 17-19 Hz., which gave the mounted speaker a 41-43 Hz. resonance. (Some have even lower resonance: when AR/NHT tested my AR-3a's for Julian Hirsch's review of the AR-303, the measured resonance was 37 Hz. on one and 38 Hz. on the other). When the first 12-inch ferrite woofer was introduced around 1969, it became the most compliant woofer ever made by AR -- almost too much so. The reason for the extreme compliance was to rely on approximately 90% elasticity of the air in the box itself, and 10% elasticity in the mechanical springs, for lowest-possible harmonic distortion. The downside of this was that the bottom plate on this new ferrite woofer did not have the recessed bottom plate, so common in today's high-quality woofers, to prevent prevent damage from over-excursion. The Alnico woofer had a much deeper bottom plate, and the voice coil was never close to bottoming; but under extreme excursion, the spider could bottom against the top plate and cause damage. This feature of very high-compliance suspensions in the earliest AR-1's, AR-3's and AR-3a's/LST's earned the reputation of extremely low distortion.

By 1975, AR had done a minor re-design to this woofer, stiffening the suspension slightly (in the spider, not the surround), modifying and improving the cone composition. While the woofer had the same basic parameters such as mass, voice-coil properties, etc., the suspension was made intentionally less compliant, especially at excursion extremes, in order to increase power-handling capability, and to reduce over-excursion and flattening of the nomex voice-coil former. The end result were speakers such as the AR-10Pi, AR-11 and later iterations, that had almost identical performance to the AR-3a and AR-LST, yet had greater low-frequency power-handling capability. By 1978 in the AR-9, there were several other minor changes to this original woofer to improve its performance and durability.

By the time the Tonegen driver was made available a few years ago, it was stiffer yet. The end-result is a woofer that sounds almost identical, yet is the most durable by a good margin of any of the woofers. If you measure its free-air resonance, however, it is slightly higher than the early AR-built woofers, and I think the distortion is slightly higher, but not audible for all intents and purpposes.

What all this means is that it is completely worthwhile to rebuild the early woofers with new surrounds if you play a lot of deep-bass music, and want to retain the original, low-distortion performance. But for durability, higher-stress conditions, the new woofer can't be beat.

--Tom Tyson

[Steve F]

>What all this means is that it is completely worthwhile to rebuild >the early woofers with new surrounds if you play a lot of >deep-bass music, and want to retain the original, low-distortion >performance. But for durability, higher-stress conditions, the >new woofer can't be beat.

>--Tom Tyson

I agree with Tom on this completely. I replaced my AR-11's woofers with service units from AR when they were still in Canton, MA in 1989. Those were Tonegen woofers. (I was the NE Sales Manager for Panasonic--Telecommunications Division--at the time, so for a swap of a nice cordless phone, the woofers were free.)

I replaced my 3a woofers with Tonegen service units from A-B Tech Services in 2001, and those seem fine also, although maybe with just a tick less extension than the originals.

Steve F