Woofer Replacement

[Guest iceman]

I am considering replacing the woofers in my AR9 and 3a, instead of re-foaming. Has anyone used the 12" woofers from AB Tech? They say that they are an exact replacment. Do they look and sound the same as the originals? Any information or opinions would be aprreciated. Thanks.

[ninohernes]

I would have them refoamed by Bill Miller. He does amazing work. Give him a call at 215-412-7700. He rebuilt my two AR-3 woofers for 120 bucks! The sound fantastic. A new woofer from AB tech costs around 160 for one! Have your AR woofers refoamed.

[Guest iceman]

I would definitely have Bill Miller re-foam my speakers if I were to re-foam them, however, there are some logistic issues; that's why I was curious about the quality of the AB Tech replacement speakers.

[ninohernes]

They are OK, but I feel that the originals are better. What are the logistical issues?

[Guest iceman]

I do not live near PA so delivering and picking up the speakers is an issue. Shipping would be expensive (I have 12 speakers) and I worry about potential damage. Also given the age of the woofers, if the replacements are just as good, I would probably prefer the new speakers.

[Guest Bret]

>Has anyone used the 12" woofers from AB Tech?<

Yes, and I am generally happy with the results. The only difference; I get the **impression** (might be my imagination) that the replacement drivers are less "thunderous" than the old were.

It is entirely possible that the "thunder" was caused by sloppiness in the old, worn, woofer which was cleaned-up by the new. It's also possible, even likely, that changed room placement is responsible.

To make my comparison even less meaningful, I've changed electronics.

Regardless, what would decide this for me is that the replacement woofers are no longer made. If you ever want some, now is a good time to get them.

If there are any differences, they aren't startling.

Unfortunately, I haven't had the opportunity to do any A/B listening yet, so I am not the voice of experience.

Did AB Tech recently quote you the $160 price? That's quite a price-jump from when I bought mine a year ago ($129/ea).

If you decide to buy new, I would still have my old ones worked-on, or sell them so someone else might have them worked-on, or store them to be restored in the future.

Bret

[ninohernes]

>

>Did AB Tech recently quote you the $160 price? That's quite a

>price-jump from when I bought mine a year ago ($129/ea).

>Bret

Sorry, my mistake, I was thinking of something else when I said $160, they are indeed $129 each. The difference between the Alnico AR-3a woofer and the AB replacement is pretty big. The Alnico woofers are indeed more thunderous. Mine have been rebuilt, but they still have that thunder.

[Guest Bret]

>The Alnico woofers are indeed more thunderous. Mine have been rebuilt, but they still have that thunder.<

What and why do you suppose that is? They'll simply "go lower?"

Look, I realize that imagination may have something to do with my thunder comment. "The mind" has a lot to do with why stereo works in the first place. (maybe that's why my speakers don't image as well as I remember. . . I'm losing my mind)

But I would bet big, big dollars on the following being fact even though I have no numbers to back me up: Some speakers recently resurrounded by Simply Speakers are too "tight," or restricted, or were rebuilt wrong, or something. I'm talking about an obvious thing with a friend's pair of CV speakers.

The resurrounded drivers look as good as new.

I used to sell these things to the kids who could afford a 45-watt receiver who were trying to knock-down walls with Judas Priest records. A distinguishing characteristic of the CVs was the throw on the woofer. They'd clear-up your chest and pulverize kidney stones.

These resurrounded ones won't and even at extreme volume with all sorts of boost the woofers are barely moving.

Resurrounded drivers, I'm thinking, are highly suspect.

If I can interpret the spreadsheet Ken posted, the SS woofers' free air resonance has been raised. By-product?

Bret

[ninohernes]

Bill Millers work is excelent. When I get a woofer back from him it is cabable full excursions without distortion. He is very skilled in what he does, especially AR speakers.

Here is why the alnicos are better.

Alnico

AlNiCo is a type of alloy magnet which was used extensively in loudspeakers between 1930 and 1960. As its name suggests this family of alloy magnets employ Aluminum, Nickel, and Cobalt. The most common ones are with marks 2, 5, and 8. Each has its own unique characteristics which generally has to do with how strong they are when magnetized, and how easily the magnet can be demagnetized. For speaker applications, AlNiCo 5 is the best choice in the AlNiCo family of alloy magnets. Its peak energy product is just right for loudspeakers where we need to concentrate high densities of magnetic flux in the gap around the voice coil. AlNiCo 5 is an alloy made up of 8% Aluminum, 14% Nickel, 24% Cobalt, and 3% Copper. AlNiCo 5 is almost universally chosen for loudspeaker use because it has a high flux, and under normal circumstances of use, the speaker wasn't intended to be driven hard enough to affect the magnetism of the magnet by the voice coil magnetism. The price of cobalt began to skyrocket, so the industry was forced to develop other types of magnets. It currently sells for about US $64 a kilo. Most of the worlds supply comes from Zaire. Besides that country controlling the market, cobalt is also a strategic metal used in missles and other weapons systems and cobalt magnets are still the most widely used magnets in the world, being employed in everything from weapons systems to analog meter movements, to debris separator grates in manufacturing processes.

Many people, who don't take AlNiCo cult for granted, ask themself why it should be better than ferrite with the same magnetic strenght. The answer lays in Alnico's smooth compression at high average levels. This effects sound simmilar to tube's soft clipping at high outpout powers. Alnico is an alloy magnet and all alloy magnets are easier to demagnetize than comparable ceramic (Strontium Ferrite) magnets. As the voice coil starts moving in response to the input signal, it generates a magnetic field of its own that tries to demagnetize the magnet. As its effect lowers the available magnetic field of the alnico magnet, the speaker becomes less efficient, the voice coil moves less, etc. The physics of it is that the magnet domains near the surface of the magnet poles begin to change state, or flip directions. The result is smooth compression, the same kind of operating curve compression that occurs in a tube amplifier. The ceramic magnet, on the other hand, doesn't compress or demagnetize as easily, so the voice coil moves to its mechanical limit and won't go any farther. This is why many say ceramic magnets sound a little edgey at high average levels as opposed to alnico. If we continue with tube/solid state comparison, then alnico behaves tube-amp like and louder average volumes can be achieved but with smooth compression. The compressing or demagnetization that occurs with the AlNiCo is not permanent. It's domains spring back to their initial state.

[tysontom]

>>The Alnico woofers are indeed more thunderous. Mine have

>been rebuilt, but they still have that thunder.<

>

>What and why do you suppose that is? They'll simply "go

>lower?"

>

>Look, I realize that imagination may have something to do with

>my thunder comment. "The mind" has a lot to do with why

>stereo works in the first place. (maybe that's why my speakers

>don't image as well as I remember. . . I'm losing my mind)

>

>But I would bet big, big dollars on the following being fact

>even though I have no numbers to back me up: Some speakers

>recently resurrounded by Simply Speakers are too "tight," or

>restricted, or were rebuilt wrong, or something. I'm talking

>about an obvious thing with a friend's pair of CV speakers.

>

>The resurrounded drivers look as good as new.

>

>I used to sell these things to the kids who could afford a

>45-watt receiver who were trying to knock-down walls with

>Judas Priest records. A distinguishing characteristic of the

>CVs was the throw on the woofer. They'd clear-up your chest

>and pulverize kidney stones.

>

>These resurrounded ones won't and even at extreme volume with

>all sorts of boost the woofers are barely moving.

>

>Resurrounded drivers, I'm thinking, are highly suspect.

>

>If I can interpret the spreadsheet Ken posted, the SS woofers'

>free air resonance has been raised. By-product?

>Bret

Bret,

The reason for the subjective description, "more thunderous," regarding the Alnico woofers has very little to do with the Alnico magnet itself, but more to do with the compliance of that woofer and its free-air resonance. Also consider that the old woofer may also have become somewhat underdamped for one reason or another, but this is unlikely. The newer ceramic-ferrite woofers, with the exception of the 1969 AR-3a ceramic woofer, are less compliant than the original AR-3-style, Alnico, cast-aluminum woofer. On the other hand, the Tonegen 12-inch replacement woofer also has a higher resonance than any of the older woofers due to its significantly stiffer suspension, and it would sound dryer in the bass. Some of the rebuilt woofers may also have a higher resonance also due to a stiffer surround or other changes.

--Tom Tyson

[soundminded]

"On the other hand, the Tonegen 12-inch replacement woofer also has a higher resonance than any of the older woofers due to its significantly stiffer suspension, and it would sound dryer in the bass."

I believe that my AR9s have the Tonegen woofers. They were replaced by the factory in 1984 shipped directly to me and have square magnets and butyl surrounds. I am happy to report that with proper placement and equalization they can produce the chest thumping, window rattling, wall shaking bass I expect from AR9. This is confirmed by such recordings as Virgil Fox (Laser Light 15 313) which was originally recorded by Bert Whyte as a direct to disc and was transferd to cd from the master lacquer. Also Dixieland Hymns (Green Hill Productions GHD5019) is quite impressive. One big advantage that acoustic suspension woofers have over ported designs is that you can effectively equalize them including below their in-box resonant frequency due to their predictable, linear, and relatively gradual 6 db per octave falloff.

[tysontom]

>

>I believe that my AR9s have the Tonegen woofers. They were

>replaced by the factory in 1984 shipped directly to me and

>have square magnets and butyl surrounds.

The Tonegen 12-inch replacement woofers, such as sold by AB Tech, have round magnets and foam surrounds. AR actually had production 12W woofers back in the 70s and 80s with square magnets, so your units might be in that category. The butyl surrounds are a question to me, though. I wasn't aware of any of the factory 12W woofers with butyl-rubber surrounds, but you learn something new every day.

>One big advantage that acoustic suspension woofers have over ported designs is that you can effectively equalize them including below their in-box resonant frequency due to their predictable, linear,

>and relatively gradual 6 db per octave falloff.

Actually, acoustic-suspension designs roll off at the rate of 12dB/octave below resonance, but this is measured in the traditional 2-Pi Steradians, or a 180-degree solid angle.

--Tom Tyson

[soundminded]

If you look at Ken's data, you'll see for example that on nf.pdf a typical curve, the violet line for instance intersects 20 hz at about minus 14 db and 40 hz at about minus 8 db or 6 db per octave. Above that region, the falloff is even more gradual. This is about what I expected. What am I missing here?

BTW, the 8 inch lower midranges supplied with my AR9s also had butyl rubber surrounds. There has been absolutely no sign of deterioration in 19 1/2 years.

[tysontom]

>If you look at Ken's data, you'll see for example that on

>nf.pdf a typical curve, the violet line for instance

>intersects 20 hz at about minus 14 db and 40 hz at about minus

>8 db or 6 db per octave. Above that region, the falloff is

>even more gradual. This is about what I expected. What am I

>missing here?

Soundminded,

There are some basic principles of direct-radiator loudspeaker operation that date back to the work of Rice and Kellog in 1925, described in great detail in Beranek’s *Acoustics,* and later clearly described by Villchur, Small and others. I will try to paraphrase a small portion of that here.

This applies to all direct-radiator loudspeakers, not just acoustic-suspension designs, and it all relates to “air-load resistance,” and it determines how much energy a speaker will transfer to the air for a given cone velocity. Air-load, or radiation, resistance increases with the square of the frequency up to the point of ultimate air-load resistance, or about 900 Hz for a 12-inch speaker. Above that frequency that resistance remains constant; and above the primary mechanical-resonance of the speaker’s moving system, the system is mass controlled. For each octave above resonance, the cone velocity is cut in half (again, up to the point of ultimate air-load resistance). Therefore, within the frequency region from resonance (e.g., 43 Hz. in an AR-3a) up to the frequency of ultimate air-load resistance, cone velocity and radiation resistance are changing in opposite directions. And since the power varies with the square of the velocity, all things being equal, the speaker should have theoretically uniform acoustic output within this frequency region.

Below resonance, however, the cone is compliance-controlled. Velocity is cut in half for each lower octave, and since the radiation resistance is still falling, the *total* drop in speaker output below resonance is at the rate of 12 dB/octave, not 6-dB/octave. Remember, too, that cone velocity for a given power output doubles with each lower octave down to resonance, and the excursion of the cone is quadrupled for each lower octave down to system resonance.

For verification of this, look at the many frequency-response curves run by AR on the AR-1, AR-2, AR-3 so forth. These were calibrated, automatically run curves of AR speakers measured on a flat, 180-degree solid-angle baffle (usually the speaker buried in the ground flush with the surface) and facing into free space. A good study can be made here of the speaker’s “Q” to see how it affects response at resonance, but also it can be plainly seen that the bass response of these woofers falls at the rate of 12-dB/octave below system resonance.

--Tom Tyson