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From: klein@ucbvax.ARPA (Mike Klein)
Newsgroups: net.audio
Subject: Re: RAW SPEAKERS
Message-ID: <9570@ucbvax.ARPA>
Date: Thu, 1-Aug-85 21:37:34 EDT
Article-I.D.: ucbvax.9570
Posted: Thu Aug  1 21:37:34 1985
Date-Received: Sat, 3-Aug-85 02:47:38 EDT
References: <3177@decwrl.UUCP> <28400013@smu> <1036@teddy.UUCP>
Reply-To: klein@ucbvax.UUCP (Mike Klein)
Organization: UC Berkeley CAD/CAM Group
Lines: 57

It is generally recognized that smaller woofers have more distortion
than larger ones, all other things being equal.  And this is indeed why:

> This would then imply that the smaller drivers have higher levels
> of mechanically (due to non-linearities in the suspension) and electromagnetic
> (due to the size of the linear protion of the magnetic field, the LENGTH
> of the voice coil) induced distortions. 

And on to some other interesting things about woofers...

> Also, because of there lower masses, smaller cones have higher fundamental
> resonances than larger ones.

Fundamental resonance is determined mainly by the cone and voice coil mass
and the suspension compliance.  Note that small woofers usually have very soft
suspensions and larger ones usually have stiffer suspensions.  On the whole,
smaller woofers have a higher fundamental resonance, but the difference may
not be nearly as much as you'd expect.

> Smaller woofers tend to be severely electro-magnetically
> overdamped, resulting in over-controlled and, as a result, relatively
> reduced bass performance. This requires either tailoring the response
> of the input signal, further exacerbating the excursion problem, or
> wieghting the cone to make it more massive (the "Mortite" syndrom)
> reducing efficiency, etc., etc., etc.,.....

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.
This is not a design defect!  It is also not the real reason why efficiency
suffers.  Efficiency, system cutoff frequency,  and box volume are the three
fundamental factors that must be traded off, and it's not very fair to
the frequency:

	best efficiency = (constant) * (box volume) * (cutoff frequency ^ 3)

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.  (this equation holds for free-field
radiation.)

> It might be argued that smaller cones have less breakup problems at
> higher frequencies. ALl things being equal, this is true, but much
> of this is controllable by appropriate materials technology. It turns
> out that the most commonly used cone material, paper, is markedly
> unsuited for loudspeaker use (more on this if anybody is interested)

This is really true!  Recent research has shown that newfangled materials
can actually behave very well through the breakup region.  Paper is not
one of them.  Bextrene and polypropylene are very good.

Also -- The "tightness" of the bass has nothing to do with size of the
woofer, but with the overall damping of the woofer system.  However,
some people may assign the word "tightness" to a frequency response that
emphasizes the 60-100 Hz range, because that's the frequency range that
hits your gut hardest.  The typical smaller woofer in a smaller box
may very well have this kind of frequency response, and may appear
to have a "tight" bass.