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From: bill@vrdxhq.verdix.com (William Spencer)
Newsgroups: rec.audio.high-end
Subject: Re: Crossover design
Message-ID: <9272@uwm.edu>
Date: 1 Feb 91 14:43:47 GMT
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in article <9226@uwm.edu>, jj@alice.att.com (jj, like it or not) says:
> In article <9172@uwm.edu> dlin@prodigal.psych.rochester.edu (Daniel Lin) writes:

>>	The
>>	literature suggests that equations used to determine low and high
>>	pass filter componenets cannot be applied to design the bandpass
>>	filter due to interactions between components.

> This is quite true, unless you figure the (complex) impedence of the
> driver into your equation.  You will find out very quickly that
> you will then have no first-order functions anyhow. 
[etc.]

I believe you are answering a different question here. He (and Bullock)
are saying a 3-way is not the same as two 2-ways in cascade. The crossovers
interact with each other. (I'd like an explaination of why this happens,
I don't get it, partially because I've stuck with 2-ways.)
Anyway, good explaination of the need for impedance compensation or other 
techniques.

Cookbook techniques for impedance compensation are availiable. With 
an oscilloscope and a sine wave generator you can experiment to further
flatten impedance magnitude and phase. Connect a resistor, say 50 ohms, 10W
between amp and the driver/compensation load. Changes in the load impedance 
will change the voltage response.

>You'll be better off measuring SPL individually 
> at each driver and then in sum, and making a guess as to
> what's happening, I suspect.

It's also a good idea to check your transfer function at the driver terminals
with that sine wave and 'scope.
You will need to know what rolloff rate and phase characteristic to expect.


> I've been predicting for years that people will start making
> integrated amplifier/speakers, with all the filtering done passively.

Not biamped? And you have to plug the speakers into the wall? Humm.
I do think that for bi-amping to catch on some kind of standard is needed.
Maybe amps with slots for crossover cards or something. Or ROM cards and 
digital crossovers! I can't believe I just wrote that :-). Digital does 
seem more illuminating when it replaces as much of the analog as possible.
Even digital amps, but coming up with an amp that really uses digital
to advantage requires some new approach. The digital could be used as an
input to the power supply to intelligently prepare for transients, for example.

Bill Spencer