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Old 5th December 2003, 07:23 PM   #1
Lusso5 is offline Lusso5  United States
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Location: Houston, TX
Default Need help with enclosure design

I'm going to attempt to put a sub under the front seat of one of my cars this weekend. I've got roughly a 1/3 cu. ft of space for an enclosure - give or take. 13x13x3.5h

The driver im using is an 8" Dynaudio 97W49 (4ohm).

Specs:
Fs: 41
Qts: 0.52
Vas: 31.8 L / 1.1 cu. ft

My two approaches are -

1. Make the largest sealed enclosure I can fit, and overstuff it with polyfill, but this still may only get me roughly halfway to the optimum size. But with the small size and ease of build I could do it in 30 min or so, so why not give it a shot.

2. Make a baffle, open-ended on two sides (basically take the bottom and two sides off the box above), and down-fire it.

I used two of these drivers, as subs, in the rear hat shelf in a previous car with terrific results, so I'm optimistic about using a baffle, but with as small as space as I've got, I dont know if I can even refer to it as that.

I really want to get this to work, so any and all advice would be much appreciated.
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Old 5th December 2003, 07:50 PM   #2
sreten is offline sreten  United Kingdom
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JMO but the open baffle simply won't work - at all,
well it might rattle your seat a bit but bass ? NIMO.

Resistive loading might work ?

Basically build the box as big as you can.

Then you add a resistive layers to the front of the drive unit
opening. This reduces efficiency, i.e. kills volume but if its
resistive it will reduce the Q.
Given the state of tune of the box it will need to be seriously
resistive - chair foam wedged between the box and the seat ?
Just adjust how much ?
A metal grille for the driver would be a very good idea.

Long time ago that I read this regarding controlling port Q
and the book was written in the sixties so i can't remember
what the material was - and it was a port.

/sreten.
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Old 5th December 2003, 08:25 PM   #3
Lusso5 is offline Lusso5  United States
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Quote:
Originally posted by sreten
JMO but the open baffle simply won't work - at all,
well it might rattle your seat a bit but bass ? NIMO.
I kind of figured that as well.

Quote:


Resistive loading might work ?

Basically build the box as big as you can.

Then you add a resistive layers to the front of the drive unit
opening. This reduces efficiency, i.e. kills volume but if its
resistive it will reduce the Q.
Given the state of tune of the box it will need to be seriously
resistive - chair foam wedged between the box and the seat ?
Just adjust how much ?
A metal grille for the driver would be a very good idea.

/sreten.
What about approaching it by adding some feet/spikes to the box and down-firing the woofer into the floorboard/carpet? Getting as close as I can - considering the 9mm Xmax.

Quick question on the polyfill: From searching the board I get a 15% increase factor (for box size). But how full do you stuff? How full CAN you stuff?

Thanks for the reply.
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Old 5th December 2003, 09:20 PM   #4
sreten is offline sreten  United Kingdom
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Sorry for being amused but I'd suggest overfilling is not
going to be your problem !
Overfilling can lead to reduced system efficiency and Q !

Max increase possible I think in effective box V is 25%

Its quite possible a normally bad filling - such as chair
foam - will help you on your quest !

Come to think of it I did my little bass practice amplifier
like this when I replaced the driver with a hi-fi bass unit,
Its stuffed full with softer foam - upholstery foam - the
sort you lean back against rather than actually sit on.

I did stuff a speaker once with chair seat foam - the
stiffer stuff - the results were awful - no bass - but
there wasn't much wrong with the bass with polyfill -
I was trying to improve the midrange and the bass a bit.

Upholstery foam is definitely going to help IMO.

If your still going to try front resistive loading then any
small airspace will totally bypass the effect - if you don't
like the idea of the metal grille then rear mounting the
unit in the baffle is the only other option.

Try really stuffing it with upholstery foam first. If this
doesn't work enough then change the unit mounting
from front to rear and try resistive additionally on the
front.

You'll need a screw-on front baffle that you can glue
if your happy with a front mounted arrangement.

/sreten.
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