DCR Double Chamber Reflex Subwoofer

[gpsmithii]

I’ll start out by thanking you all in advance for your input and suggestions.

I’m going to build a double chamber reflex subwoofer. I would like some verification as to my interpretation of how to approach the design. The David Weems book states:

To start out with an standard “optimum” design.

The subwoofer I’m using has the following Thiele/Small parameters.

Qts 0.41
Vas 8.10 cubic feet
Fs 32

Calculated Vb 8.53 cubic feet
Calculated Fb 31.47 Hz

The basic directions as I interpret them result in division of the total Vb into two chambers of 66.66% and 33.33% after having determined the size requirements of two ducts needed to tune the total initially calculated Vb.

The driver is an 18” Selenium 18SWS800 subwoofer. Using two 4” vents 4.93” in length will tune the 8.53 cubic foot enclosure to the 31Hz Fb. I may go with 2 larger i.e. 6” ducts but they get real long @ 13.29”, to make sure vent noise and compression are very low.

The enclosure would consist of two chambers. One being 5.68 cubic feet and the other at 2.85 cubic feet. Each chamber would have a 4X4.93” duct and be interconnected via the same.

Then Weems goes on to say the more accurate way to do it would be to multiply Fb by .89 (27Hz) and use a duct that would tune the larger volume (5.68 cubic feet) to the new Fb of 27Hz. The new duct dimensions for each chamber would now be 4”X13.11” and be interconnected via the same.

Comments/Suggestions?