From: demetri@cgrg.ohio-state.edu 
Subject: band pass box design
Organization: OSU Advanced Computing Center for the Arts and Design
Distribution: usa
Date: Wed, 27 Jan 1993 02:15:19 GMT

     I want to add a subwoofer to the system I have in a Nissan Sentra.
The bass I get from 4 - 6" woofers is "ok" but I really want to fill
out the bottom (below ~100 Hz).  I had a pair of Legagy (by Pyramid)
8" subs in a box in the trunk.  They sounded ok, but they 
and the amp running them were stolen.  I have since had an alarm installed
and I am plotting revenge against the *&^&^%$^&*& *&^%%$^^&*%$$# who broke 
into my car.  (Maybe not today, maybe not tomorrow, maybe not even soon!
but for the rest of his life he is going to regret this!!!!!!!)  ...
     Any way... I want to build a box that will be a little (a LOT) less accessible
-inside the car, inside the rear seat cushion, secured from beneath the car with 
whatever it takes to make it not worth a thief's while...
This design means the box has to be flat (a maximum of 7" high, a possible 
12 - 16" deep and 48 - 52" wide) to fit the space.  Another consideration is the
already limited space in the trunk of the Sentra (I still want to be able
to carry groceries or luggage).
     I've been looking at band pass designs for JL subs (that's the major brand 
carried by the shop I've been going to for advice).  If I build a band-pass box, 
the driver would need to fire into a small chamber that connects to a larger
sealed chamber (and radiate into a ported chamber next to it...) like this...

              
                   ______________________________________
                  |--------------------------------------|                  
                  ||_               ______            __||  
                  |---              ------            ---|         
                  ||  \            /  ||                ||
                  ||   \          /   ||                ||
                  ||    \        /    ||                ||
                  =====  \      /     ||                ||
                        |========|    ||                ||
                  ===== |========|    ||                ||
                  ||__________________||________________|| 
                  ---------------------------------------- 


I know this will work.  I've seen a few installs that used this method.  My questions 
are... 

How narrow can this passage be without adversely affecting the performance of the 
speaker?  

How does this kind of configuration affect the size requirements for the 
sealed and ported chambers?  

Am I going to get bad effects from the broad expanses 
of flat wood on the top (and possibly bottom) of the box (this is a front view)?

Would it help to have another driver mounted in an isobaric configuration (wired
180 out of phase) on the far end of the passage (to help control the flow of air in 
the passage...)?  

And, finally, how "portable" are the box specs I got from JL?
Could I use a different driver with the same box and get good results?

... I will surely have more questions about band-pass boxes once I have hammered 
out more of the design requirements.  I look forward to any words of wisdom you can 
lay on me.

-Demetri