From: chrisc@gold.gvg.tek.com (Chris Christensen)
Newsgroups: rec.audio
Subject: Re: How are speaker impedences specified?
Date: 3 Sep 92 21:58:22 GMT
Article-I.D.: gold.5140
Organization: Grass Valley Group, Grass Valley, CA

In article <1992Sep02.171943.7402@bmerh85.bnr.ca> shiv@bnr.ca 
(Shiv Naimpally) writes:

NOTE:  The original poster was asking a much simpler question than
this discussion has diverted to but,  Sinca I have a specific end goal
I have decided to jump in!

>I should have also pointed out that the impedance charts are impedance
>vs frequency - they go in the lab, squirt frequencies in and measure
>the impedance. Meanwhile back at home you are playing music which has
>many frequencies - who knows what the impedance is !

While you are right about the test process I would be inclined to
believe that the swept impedance plot on a speaker,  while done with a
swept sine ware (or other suitable test signal) the impedance graph
will represent the load that the amplifier will see when music is
applied,  or a reasonable facsimile.  The electro mechanical factors
that create the delta impedance are still there weather it is sine
waves or music.  The only thing that I am unsure of is if there is a
significant change in the characteristic impedance when the motor is
excited with music.  There is probably some mathmatical equation that
will predict this effect.

I am very interested in this topic as I intend to design 
Zobels for some of my own speaker systems.  I only have swept sine
and pink noise to do this impedance compensation testing so I am
concerned that I will be able to get it right!  I would hope that Dick
Pierce may be able to shed some additional light on this derivation of the
thread,  please?  Also is the LMS product really as good as ATI thinks
it is?  I have been seriously considering it's purchase as a companion
to LEAP  to avoid the drudgery of manual speaker parameter measurements.

I  was also woudering just how important the size and overhang of the VC is
in the cabinet design equation.  The speakers I am using allow be to dissamble
the driver and get directly at the VC.....

>My point is that impedance figures are just numbers the manufacturer
>conjures up based on some data (data that is arrived at under
>conditions you will never have in your home). Its a 'guide' and should
>not be taken to be absolute.

I agree with your ststement in general and  I do (now) believe that
loudspeaker manufacturers don't tell the truth about their products,
but the term "conjures" seems a bit extreme :-) 

The impedance plot is simple and easily repeatable,  not like
some of the ways they measure frequency response!

>If you are matching speakers to an amp, hook them and listen to them
>and trust your ears and not some data the manufacturers give you !

That is the final test, after you have done all of the rest of the
tests!

I have a lot of people come to me and say "What speakers should I buy"
I have a fool proof answer that has never had a client come back to me
disappointed  or upset!  I say "Buy the speakers that sound the
best to you and within the budget that you have to spend" 

-- 
Chris Christensen                  The opinions I express are my own,
chrisc@gold.gvg.tek.com            and sometimes they are wrong!
916-478-3419 FAX 916-478-3887      After all, I *AM* only human.
Newsgroups: rec.audio