Path: utzoo!attcan!uunet!samsung!zaphod.mps.ohio-state.edu!uwm.edu!csd4.csd.uwm.edu!info-high-audio-request
From: bill@vrdxhq.verdix.com (William Spencer)
Newsgroups: rec.audio.high-end
Subject: Re: making woofers: part 1 (getting information)
Message-ID: <6355@uwm.edu>
Date: 17 Sep 90 12:59:36 GMT
Sender: news@uwm.edu
Lines: 52
Approved: tjk@csd4.csd.uwm.edu


in article <6313@uwm.edu>, sbhattac@rnd.gba.nyu.edu (Shankar Bhattacharyya) says:
> Some time ago I said on rec.audio that those of us who had built
> woofers could probably be persuaded to post designs with budgets in the
> $100-200 range.

I have one.

Sealed box approx. 2.5 cu. ft. 10" woofer (Qts .4 to .5  Free air 19-24 Hz.)
Most likely with varivent ("aperiodic loading") & choice of stuffing, wall
damping, heavy braced construction.

Result is a system Q less than .7 for a less boomy sound. Useful to about 30
Hz. 

Possible woofers are Carboneau rubber surround models and Audio Concepts AC-10.
These drivers have an efficiency of 88-89 dB which speaks volumes on their 
orientation compared to higher output types: they're oriented towards depth
instead of false boom.

Design methods include experience and Cookbook calculations. I've tweaked my
12" system as far as it will go and it went from obnoxious bass to acceptable.
Cabinet volume is 2.8 cu. ft., response is to 40 Hz. Cone excursion is almost
nil. The smaller woofer in a relatively larger enclosure (lower Q) will have
much higher excursion and should still stay within acceptable limits. 

A 12" could be used in a larger enclosure. Crossover frequencies recommended
are lower however with a 12. My crossover is 300 Hz, 6 dB/octave. Frequency 
could be higher with a higher slope. Generally, the lower the better, but
that transfers responsibilty to the other drivers. 

The sealed box design provides better infrasonic control than vented types
although the excursion is higher at the lower limits of the passband.

> If there is any interest, perhaps a hint or two on practical woodworking
> for novices can follow.

The simplest box is overlapping (butt) joints using Liquid Nails. Use 2-3
finishing nails per side to increase strength and hold it together until the
glue dries. You will have to figure out which sides overlap and the size of the
pieces to correct for the overlaps. Fiber or particle board, 3/4" thick or
better.

finish such as Texturelac for my next project -- tough and fills in
imperfections.

Don't forget prefab boxes. Parts Express has one less than $30, 1.9 cu. ft.
(?), walnut veneer, requires assembly, although it's sure to need reinforcement.McGee Radio carries some unfinished car boxes that can be used as satellites
that are very reasonable. 


bill S.