Xref: utzoo rec.audio:30324 comp.dsp:1493
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From: ulfl@kuling.UUCP (Ulf Lagerstedt)
Newsgroups: rec.audio,comp.dsp
Subject: Re: Good speaker + DSP == perfect speaker?
Message-ID: <2005@kuling.UUCP>
Date: 30 Mar 91 19:52:33 GMT
References: <1991Mar22.171203.8665@sco.COM>
Reply-To: ulfl@kuling.UUCP (Ulf Lagerstedt)
Organization: Dept. of Computer Systems, Uppsala University, Sweden
Lines: 40

In article <1991Mar22.171203.8665@sco.COM> jfischer@sco.COM (Jonathan A. Fischer) writes:
>	So you buy a programmable DSP "package," containing the DSP
>unit (which also performs as a frequency generator), and a mike or
>Sound Pressure Level meter.  You set up the SPL meter in your
>listening spot, press the "setup" button on the DSP unit, and it
>commences to send frequency sweeps through your sound system, reads
>the levels and the phase response.  Finally, using these variables, it
>sets up a digital equalization + phase doctoring DSP program which
>will transform your sound system, no matter what your room's or your
>speaker's acoustical properties, into one with a completely flat
>frequency response curve, and with zero phase shift across the entire
>spectrum.

It seems to me that this procedure would not be enough. The imperfectness
of your speaker/system might not correspond simply to single frequencies,
but instead, say, a loud bass pulse X following a midrange pulse Y. 
I suppose you would have to analyse each musical piece individually.
Furthermore, since your speaker is less than perfect, the corrections you
apply will need counter-corrections and counter-counter corrections. It is
not obvious that subsequent results will be closer to the original, or
even that a given speaker of good quality is theoretically capable of
emitting a certain signal given *any* possible input.

I recall the motional feedback (MFB) speakers made by Philips in the
early 1970's, which had a built-in amp and a piezo crystal placed on
the moving bass cone. The crystal would sense the acceleration, and
information of the motion of the bass cone would be compared to the
input signal and corrected by the amp. The speakers had unusually good
low bass response, but that was about it. I don't think the speakers
were commercially successful, since they were a bit expensive. Besides, 
most people already had paid for their own power amps.

As a side note, the model I examined had a rather dangerous mains
connection for the built-in amp. One speaker was connected to the wall
socket, and the other speaker to the first one with a male-to-male cable...

-- 
 "Television - a medium. So called because              Ulf Lagerstedt
 it is neither rare nor well done"                      ZYX Sweden AB
                                                        ulf@zyx.se