Round VS Shelf port volume - diyAudio
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Old 19th November 2004, 09:54 PM   #1
Mick M is offline Mick M  United States
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Join Date: Nov 2004
Location: Puyallup WA
Default Round VS Shelf port volume

Hello;
I am new to designing speaker boxes, so these are probably a simple questions.

Given a calculated ported box volume with a round port:

Do you calculate the volume of the port to convert to a shelf port.?
As the shelf would be full internal width would it still be tuned?
What is the minimum distance from the back for a shelf?
Is it ok to bend the shelf into an "L"?

Then calculate the volume of the shelf to add to the volume of the box?
If you do this it will mess up a "golden ratio" box?
(I planned to make the shelf quite thick)

I want to use a shelf because its essentially free, and becomes a brace too.
What about angling the shelf to form a horn shape?

This is for a 15" subwoofer only.

Box size approx 17"W x 28"H x 10.5"D
Volume 2.77 ft3
Port size 6" dia x 27.3" (two 45 deg bends, 6" to stop any whistling)
Fs 18.8, Vas 319 ltrs, Qts .239
Port Fb 29.42 Hz, F3 37.86 Hz

The shelf would be 2x 5/8" sandwich.

I plan to use 5/8" board, then if it sounds ok double up the outsides with a sand center.
So a triple sandwich of 5/8".
Hopefully this should minimize internal bracing.

Thanks
Mick M.

( I happen to have 3 sheets of 5/8 board and the driver already)
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Old 20th November 2004, 05:44 AM   #2
Volenti is offline Volenti  Australia
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Join Date: Aug 2003
Location: Australia
You can safely ignore the need for a golden ratio box for subwoofer use, the wavelengths are too long for standing waves to occur. Concentrate instead on making the box as strong as practically possible.

Regarding the shelf port, try to keep the ratio under 10:1, really thin slit vents can alter the tuning frequency in unexpected ways and can have reduced output (as far as pure resonance is concerned a round port is superior)
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