speakers: was AW: [sdiy] DIY help needed

[Czech Martin]

Well, this is another can of worms ;->

on one hand you want to divide the audio spectrum in a lot of bands, usually
up to 4, since you want to avoid these problems:

-partial resonances in membranes (@1kHz the wavelength is about 30cm,
 so standing waves can fit into a woofer cone as large as that)
-focussed radiation beam if wavelength comes close to cone diameter
-large low frequency excursion (2kHz is LOW for a tweeter)
-doppler FM distortion due to large velocity

OTOH you want a single system for the complete audio band, because
of phase problems, crossover problems, wave geometric problems.

It is funny that some people still believe that phase is not audible.
Someone played a couple of partials to test individuals, and
he changed the relative phase. The people could not really
tell, and so it was printed: "human ear phase insensitive".
Do you like spinach? It is good for your health, an incredible
amount of iron in there ;->

Now, this was back in 1930 or so, in the meantime people found out
that music is a little bit different from listening to 
10s of constant sine partials. Because there are transients.
This is where the phase comes into play. A short transient
like rim shot, castanet etc. changes it's sound when no
linear phase, ie. phase distortion comes into play.
This is also called diffusion.

It is simple to show that a three way speaker can never
have linear phase @ all points of the listening room.

And there are other problems, because usual speakers are a mass, 
damping and spring device, so this makes a bandpass with a distinct
resonance,
with additional phase distortion. Crossover networks
will make all this worse, regardless what manufacturers claim.

There are a couple of people who try to avoid this all:

http://www.pfleid.de
http://www.manger-msw.com

they claim to have found a resistive real load device
that avoid resonances and is useable for a wide frequency
range. Some of them write religiously, only THEIR solution
is worth knowing off, etc.
They all have one problem: limited power, especially
in the lower bass regions.

Funny enough that all these inventions come from 1970 or so.
These years seem to be very innovative for audio.
Hey, isn't there any progress today?

The question is of course if all this matters, if we
have the reproduction of pure electronic music in mind.


m.c.







> -----Ursprüngliche Nachricht-----
> Von: John L Marshall [mailto:john.l.marshall at gte.net]
> Gesendet: Donnerstag, 1. November 2001 08:51
> An: synth-diy at dropmix.xs4all.nl
> Betreff: Re: [sdiy] DIY help needed
> 
> 
> Don,
> 
> Don't you agree that a three-way sounds better than a 
> two-way? (Yea, too
> many issues to say one way or the other.) At what frequency 
> does a 15 inch
> woofer run out of gas? There is just too much mass and too 
> much inertia to
> get very high. And, where does the horn kick in? It takes a pretty big
> (horn) mouth and long throat to get down to 1kHz. I think 
> there is a giant
> muddy hole in the middle frequencies of these sound 
> reinforcement two-ways
> and I  can hear it. B&O clearly out classes the speakers that I was
> referring to and they are designed for a different 
> application and more
> critical ears.
> 
> Yes, the moron DJ may have had the Bass and the Treble 
> cranked up. Thump and
> sizzle. He also had the speakers mounted too close to the 
> floor and only the
> bass reached the back of the dance floor.
> 
> John
> 
> 
> ----- Original Message -----
> From: Don Tillman <don at till.com>
> To: <john.l.marshall at gte.net>
> Cc: <synth-diy at dropmix.xs4all.nl>
> Sent: Wednesday, October 31, 2001 10:37 PM
> Subject: Re: [sdiy] DIY help needed
> 
> 
> >    From: "John L Marshall" <john.l.marshall at gte.net>
> >    Date: Tue, 30 Oct 2001 21:36:03 -0800
> >
> >    I'm getting crankier as I get older. Another peeve. I 
> was at a dance
> >    Saturday night. The DJ was using a pair of popular 2-way powered
> >    speakers (made in the Seattle area) with a 15 inch 
> woofer and a horn
> >    tweeter. The sound was awful. The light went on. Those 
> two ways with
> >    giant woofer and horn seldom sound good. What is the 
> most important
> >    range of frequencies for clear voice and instrument 
> fundamentals? The
> >    mids. At what frequency range is the crossover from 15 
> inch woofer to
> >    the horn? Right in the middle of voice frequencies. Do 
> filters shift
> >    phase at crossover? Use a three way any day.
> >
> > Actually there are a lot of two way speakers that are considered
> > excellent.  I think the taste of the DJ is far more suspect. :-)
> >
> > And besides, there are a number of ways to build crossovers with no
> > total phase shift: use a 6dB/oct crossover, use an algebraic
> > crossover, use a biquad style active filter and mix in a 
> little of the
> > bandpass signal to both sides, the B&O speakers with the bandpass
> > midrange (same thing, really), and digital filters.
> >
> >   -- Don
> >
> > --
> > Don Tillman
> > Palo Alto, California, USA
> > don at till.com
> > http://www.till.com
> >
>