From: chrisc@gold.gvg.tek.com (Chris Christensen)
Newsgroups: rec.audio
Subject: Re: Designing Crossovers
Date: 27 Sep 92 23:49:12 GMT
Organization: Grass Valley Group, Grass Valley, CA

In article <1992Sep25.180917.10332@en.ecn.purdue.edu> lauson@en.ecn.purdue.edu (Patrick W Lauson) writes:
>Just a quick question for those of you out there that have designed your
>own home speakers (excluding 'kits').

Not a quick question!  I have put out a couple of comments and
suggestions.  But bu no means a complete answer to your questions.

>Exactly how do you design the Crossover for your box without an anechoic
>chamber and measuring equipment?  Do you just Calculate the theoretical
>values of the components or what? Do you calculate, and then change the
>parts after listening to the system?  It just seems pretty hard to me
>to design a very good system without the proper test equipment.  Besides,
>how would you know the freq response of your drivers without measuring
>them (and the paramters for that matter).  Do you just trust the
>published data for them??  

Speaking from my experience the answers to all of your questions is
YES.  The science and engineering must be done up front that assemble
the rig and do the final tests.  

As far as test equipment I have 1/2 octave spectrum analyzer, spectrum
analyzer.  This equipment isn't sufficent to detect the absolute
frequenct response of the system but it is a starting point and
indicates trends.

I have/am seriously thinking about the LMS susyem to bring my test
methods into the 90's.  I am soliciting advice from the real experts.

Dick,  have you sen or used the LMS system?

One thing I as well as others has done is to caculate the crossover
based, blindly,  on the "nominal' impedance of the speaker.  I learned
better a long time ago but for non-"critical" applications I have
still done it and they sounded fine.....  

For the most part the designs that I have done in the past several
years have bee actively crossover bi-amp and tri-amp systems.  I am
currently working on a combination bi-amp and passive xover system.
Where I will crossover the woofer at 200 Hz active and crossover
between the 12" mid and the HF driver with a passive network.

The design compromise here is quantity and weight of amplifiers.  And
for the record I strongly believe that this concept is one of the best
for basic home and audiophile audio systems.  The sub-woofer and amp
can be a basic solid state power house and the expensive tube mono
blocks to drive the mid and high end of the system.  Or however you
want to drive it.  The basic principal is to seperate the really power
hungry bottom end from the less demanding mid-n-high end.

Locate the amplifiers as close to the speakers as possible because the
electronic crossover should be able to drive the interconnect cables
with minimum loss.  The speaker leads will be short and if you choose,
the mid-high cables can be a bit lighter in guage......

>This isn't for a current design project I am doing or anything, its just
>out of curiosity.  After building my own set of speakers for about
>$300 that sound better than anything I can find under $2000 it seems
>like a waste to me for people to BUY speakers....

I am not surprised with your results.   A large part of commercial
speaker cost is labor, markup (manufacturers profit) and markup
(retail sales profit).  And that doesn't touch shipping at all!  If
the speakers are large and shipped by truck there could be $100-200 in
shipping alone!

Just my thoughts.
-- 
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.