AR-3a Fiberglass Weight

[Pete B]

It's important to keep in mind that some parameters, take Bl for example do not change at all when say cone, spider, and edge repairs are made, even when different parts are used. One would have to change the field strength, B, or the length of wire in the gap l to change Bl. Bl could be altered for example if the voice coil is replaced with an incorrect new one that provides a different l in the gap. My theory is different magnet material or magnet structure geometry as is supported by the marketing literature. My view is that it's fairly clear that AR made at least two versions with different Bl's and that they may have used both of them in the 10pi, 11, 9s and others at different points in time since the marketing literature indicates the state of the design at the time of printing. As I said more samples will help firm up these theories.

I don't see any reason to assume overhang when the factory indicated different magnet strengths and the lab data supports the claim.

Pete B.

>We will never, ever know because now that the "odd" drivers

>have been repaired there is no way to get new T/S parameters

>on them.

>

>Bret

[tysontom]

>It's important to keep in mind that some parameters, take Bl

>for example do not change at all when say cone, spider, and

>edge repairs are made, even when different parts are used.

>One would have to change the field strength, B, or the length

>of wire in the gap l to change Bl. Bl could be altered for

>example if the voice coil is replaced with an incorrect new

>one that provides a different l in the gap. My theory is

>different magnet material or magnet structure geometry as is

>supported by the marketing literature. My view is that it's

>fairly clear that AR made at least two versions with different

>Bl's and that they may have used both of them in the 10pi, 11,

>9s and others at different points in time since the marketing

>literature indicates the state of the design at the time of

>printing. As I said more samples will help firm up these

>theories.

>

>I don't see any reason to assume overhang when the factory

>indicated different magnet strengths and the lab data supports

>the claim.

>

>Pete B.

I won't say that what you imply is not possible, but it is highly unlikely and certainly impractical that AR would have had specified different magnets or magnetic strengths for that particular woofer. There might be several reasons, but the most obvious is that the flat-side 2000003 woofer was considered a "universal" 12-inch woofer, interchangeable with virtually all AR speakers that would accept it. Having woofers with significantly differenent motor strength would pose problems if that woofer was considered to be used as a "standard." It is also possible that some woofers will measure different BL based on the tolerances of the voice coil and top plate, such that wider tolerances create slightly less flux density.

If the circuits had different motor strengths -- and as many as two as you suggest -- it's also likely that there would have been a change in the physical appearance and weight of the magnetic circuit, and I have never seen anything to support that idea. Incidentally, the 2000003 woofer is very hard to find "center" position, so measurement of BL can sometimes be tricky on this woofer. It far more likely that the literature and ad copy was erroneous -- common practice.

I do think that compliance was altered on this woofer over time, but not the BL, and fs always stayed about the same at 18 Hz, +/- 1 Hz.

--Tom Tyson