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BAM 22nd October 2003 04:31 AM

Acoustic Suspension Designs
 
What are the criteria for a sealed box enclosure to qualify as an "acoustic suspension" enclosure? How would the 15" Dayton Quatro woofer work as an Acoustic Suspension subwoofer?

15" Dayton Quatro: PE #295-560

If I use the 250-watt PE plate amplifier (which can be modified to incorporate various levels of Bass Boost up to 5dB centered at a certain frequency), should I use a bass boost on an acoustic suspension enclosure? This will be purely a music subwoofer.

roddyama 22nd October 2003 11:45 AM

Bam,

Sorry, but my Bass Box Pro doesn't have the parameters for the 295-560 so I couldn't run a box for it.

An "Acoustically Suspended" enclosure is the name used for sealed box systems before the T/S alignments became the norm in the '70's. The early sealed box designs like the AR speakers had relatively good success in sounding good vs the ported designs because the ported designs were harder tune correctly without the benefit of the T/S alignments.

kelticwizard 22nd October 2003 12:59 PM

BAM:

I have some articles here that define the Acoustic Suspension Design. As I recall, the classic Acoustic Suspension is:
Qts = 0.38
Box Volume = 1/3 Vas

This yields an Fc, (resonance in closed box) an octave above Fs, (free air resonance), and a Qtc double Qts. At the time, it was understood that you could make an Acousitic Suspension design with a box smaller than 1/3 Vas, but not larger.

All this is according to the formula:

Fc=(VasVb) X Fs
Qtc=(VasVb) X Qts

The reason they called it Acoustic Supension, (or air suspension), is becasue when Vb is much less than Vas, the springiness of the air in the enclosure had a much greater effect on the woofer than the woofer's own mechanical suspension. So the woofer cone is essentially suspended by the enclosure's air.

Nowadays, the terms have loosened up a little and an Acoustic Suspension enclosure is a closed box where the box volume is significantly smaller than the Vas.

By contrast, an Infinite Baffle is a closed box enclosure where the box volume is near or greater than the Vas. That is because the greater the volume of the box as regards the Vas, the less the speaker is affected by the air in the box, and the more it is affected by it's own suspension.

The Acoustic Suspension design was really dominant in the mid sixties through the seventies. It coincided with the coming of affordable transistor recievers of 20 watts or more, and played a big part in transforming hi fi from the concern of a few people to the point where most everyone had a well designed high fidelity system. Before that, most people had these large stereo all-in-one "consoles" that were designed as furniture first and where the sound was secondary, to the point where the speakers were just added on as an afterthought-there really was no "enclosure" as we know it on those. The speaker cabinets in the "consoles" frequently had cardboard backs!

GM 23rd October 2003 12:12 AM

Sealed cabs become a ~ IB equivalent at 4*Vas if stuffed to yield a Qtc = Qts, and 10*Vas if not. Above 10*Vas, the mass of air in the cab begins to mass load the driver, lowering its Qts.

Strictly a nit-pick: Qts = 0.383. ;)

GM

kelticwizard 23rd October 2003 03:38 PM

2 Attachment(s)
Please note that the formulas I gave in post #3 are incorrect.

The correct formulas are given below.

Thanks to the people who Emailed me about the error. :)


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