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Alnico vs. Ceramic Version of AR-3a Woofer


Rich W
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Guest matty g

Hi Rich

The older alnico drivers have a cast aluminum basket with AR in raised lettering (part of the casting). The magnet structure is a smaller diameter, deeper unit without the ring around outside of it. Generally speaking, the alnico units have a cloth surround, although I have heard of transitional units having foam from around 1970.

The ceramic magnet style has a stamped steel basket and the magnet is a larger diameter but short, squat magnet with a ring around the middle of the outside circumference. These units, afaik, have foam surrounds. Electrically I don't know if there is any difference, but I doubt it. I have heard of speakers purchased as pairs that had one of each, so go figure.

Hope this helps -

Matt

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>A very rudimentary question . . . how does one tell the

>difference between the Alnico and Ceramic versions of the

>AR-3a woofer?

>

>Thanks,

>

>Rich W

Rich,

From the front:

http://www.classicspeakerpages.net/dc/user_files/2663.jpg

Fig. 1. AR-3/AR-3a Alnico Woofer

http://www.classicspeakerpages.net/dc/user_files/2664.jpg

Fig. 2 AR-3a Ceramic-Ferrite Woofer

--Tom Tyson

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Thanks, gentlemen.

Looks like my latest acquisition has one of the transition woofers - everything about it is "Ceramic" except for the cone which is "Alnico" (with a foam surround, no less).

Rich W

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Tom, here are the images of the transitional AR-3a woofer. Note that it's been prepped for a refoam.

Serial number is 35724. Although there's no date stamp on the woofer, the midrange and tweeter are dated 1/6/70 and 1/12/70 respectively.

Rich

post-101134-1189084016.jpg

post-3-1189084016.jpg

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>Tom, here are the images of the transitional AR-3a woofer.

>Note that it's been prepped for a refoam.

>

>Serial number is 35724. Although there's no date stamp on the

>woofer, the midrange and tweeter are dated 1/6/70 and 1/12/70

>respectively.

>

>Rich

Thanks, Rich, for the image of your woofer. I am still not sure if the foam damping ring shown is factory-original or not; there was really no reason for Acoustic Research to add the damping ring to that cone insofar as it was a very low-loss cone anyway, and the fact that the ceramic woofer was intended to be used with the lower-AR-3a crossover frequency, 575 Hz vs. 1000 Hz in the AR-3. Perhaps some of these woofer were to be used as AR-3 service replacement units, but that is only conjecture. In fact, the 200003 woofer (the ceramic version with the low-loss cone) was smoother up to 800 or so Hz than the earlier Alnico woofer which originally used the damping ring. In addition, adding the damping ring would add a little mass to the woofer cone, already optimized in weight to be used in the AR-3a enclosure. Another mystery.

--Tom Tyson

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Tom,

From your post, it seems that the dampening ring is completely superfluous for the ceramic woofer when installed with an AR-3a crossover configuration. The only adverse effect of leaving it attached (and correct me if I'm wrong) would seem to be the increase in woofer mass. I dare not remove it, for fear of damaging the cone, as it seems very securely attached with the same aggressive adhesive as the original surround.

Would this increase in woofer mass have any theoretical significance?

Thanks,

Rich

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>Tom,

>

>From your post, it seems that the dampening ring is completely

>superfluous for the ceramic woofer when installed with an

>AR-3a crossover configuration. The only adverse effect of

>leaving it attached (and correct me if I'm wrong) would seem

>to be the increase in woofer mass. I dare not remove it, for

>fear of damaging the cone, as it seems very securely attached

>with the same aggressive adhesive as the original surround.

>

>Would this increase in woofer mass have any theoretical

>significance?

>

>Thanks,

>

>Rich

Rich,

I know that ultimately the damping ring was unnecessary on the ceramic woofer, but Roy Allison, who designed the AR-3a, told me once that although he was unaware of the damping ring for that woofer, it might have been used initially in order to get the BL (motor strength, basically) properties correct on the new woofer. Often there were adjustments to be made in these new products, so perhaps the damping ring was placed for additional mass on the earliest cones. There is also the issue of the AR-3 with its higher crossover: the damping rings might have been helpful with the upper-response of that woofer when used as a factory-service replacement woofer for the AR-3.

That said, the damping ring I have seen on several of the woofers, with AR-3a serial numbers being in the early 1970 timeframe, would be consistent with the very early introduction of the ceramic woofer in AR-3as. But by all means, leave it in place. The installation looks to be factory, for sure, as those AR damping rings would not be available from any source, and to get one on that woofer would have required removing one from an Alnico woofer, and that is highly unlikely.

--Tom Tyson

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>This damping ring in another "transitional" ceramic

>magnet woofer (June, 1970) sure looks original to me. AR

>probably had some old cones to use up.

>

>Roy

>

>http://www.classicspeakerpages.net/dc/user_files/2678.jpg

>

Roy,

That cone is definitely the "low-loss," felted-paper cone that was designed for the ceramic-magnet woofer, not the Alnico-woofer cone, which is quite different in addition to having corrugation ribs running around the circumference. I suspect that the early cones were too light and didn't meet the design criteria initially, and AR engineers (probably Chuck McShane) had to make adjustments. Roy Allison thinks this is the case, but he did not remember the damping rings being used on the ceramic woofer. Those woofers definitely look factory-original, in any case.

--Tom Tyson

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