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From: klein@ucbvax.ARPA (Mike Klein)
Newsgroups: net.audio
Subject: Re: RAW SPEAKERS
Message-ID: <9709@ucbvax.ARPA>
Date: Tue, 6-Aug-85 16:09:00 EDT
Article-I.D.: ucbvax.9709
Posted: Tue Aug  6 16:09:00 1985
Date-Received: Sat, 10-Aug-85 04:51:28 EDT
References: <3177@decwrl.UUCP> <28400013@smu> <1036@teddy.UUCP> <9570@ucbvax.ARPA> <1098@teddy.UUCP>
Reply-To: klein@ucbvax.UUCP (Mike Klein)
Organization: University of California at Berkeley
Lines: 76

>One way of measuring true effective compliance is to specify what is refered
>to as the "equivalent volume of compliance". This is the restorative force
>presented by an enclosed vloume of air that is the same as the mechanical
>stiffness of the woofer.

This volume (Vas) takes the area of the diaphragm into account and
plain suspension compliance does not.  This is because an equal
movement of a larger diaphragm displaces more air; a larger value of
Vas is required to simulate the same suspension stiffness.  Your
example of the two KEF drivers with identical suspensions bears this
out.  Fundamental resonance is calculated from suspension compliance
and moving mass and does not depend on Vas.  Vas is a useful
abstraction for calculating enclosure volume later on.

>Low and behold, it turns out the the mass becomes the more important
>term. Interestingly enough, the manufacturers product data supports this
>fully. I have this data for about 45 manufacturers, and have confirmed it for
>most, have you?

Yes I have.  It does not invalidate anything I said, though...

>>Small woofers are massively overdamped because they are designed to go
>>in a small box which raises the system's overall Q more than a larger box would.
>Wrong, small woofers, in the vast majority of cases, are overdamped because
>it is more economical for a driver assembler to stock fewer diverse magnet
>assemblies. This I know because I once was intimately involved with several
>of them.

A few years ago, I evaluated a large number of different drivers for
woofer applications.  I limited my evaluation to drivers that were good
candidates for woofers.  An interesting thing I noticed is that older product
lines tend to consist of all the combinations of a few components (suspensions,
magnets, voice coils, cones) and this is where you get some pretty bizarre
parameter combinations.  Newer product lines have evolved with Thiele's and
Small's work and tend to consist of fewer drivers that are optimized for
specific applications.  These are overdamped because their application
demands it.

>In practice, I have found
>through manufaterers data sheets and my own extensive testing, that small, 
>high quality woofers are far to overdamped to be usable as bass drivers.

Depends on the requirements!  If you want a tiny woofer in a tiny box,
you must settle for either low efficiency or a high bass cutoff frequency,
or both.  The KEF B110 is great down to 60-70 Hz.  If this satisfies your
requirements then this is the woofer you should use (it *is* an excellent
unit).

>>A woofer in a small box trying to have a low cutoff frequency is
>>*fundamentally* constrained to have a low efficiency.  It actually
>>does not depend on the woofer size.
>Why is it independent of diameter? Because your asking this little tiny
>woofer to do far more excursing to produce a given sound level, thus
>driving it farther into it's non-linear operating regions!

This gets us back to my statement in the very beginning, that it is
generall accepted that smaller woofers distort more than larger ones,
all other things being equal (the other things being efficiency and
cutoff frequency).

>>Also -- The "tightness" of the bass has nothing to do with size of the
>>woofer, but with the overall damping of the woofer system.
>Gee, I hope your not accusing ME of saying that!!! :-)

No, I'm not; it was in reference to the original article that started this.

>The upshot of all of this is that is seems that a lot of so-called
>information seems to be rumor, guessing and so forth. I am not necessarily
>accusing the above respondant of such...

Good!
-- 

		-Mike Klein
		...!ucbsim:klein@ucbvax.uucp
		klein%ucbsim@berkeley.arpa