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Old 19th September 2006, 08:28 PM   #1
jmiyake is offline jmiyake  United States
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Location: San Jose, Ca.
Default vent by the speaker wall, or in a corner

Let's say you want to make a subwoofer 40" long.
To tune it correctly you need a 4" tube 36" long.
So the 4" tube end is 3" from the inside wall. Does this constrain the sound?

What if the tube is by a corner so 2 sides are close to or against it, and the inside wall is 3" away?

How would this affect the sound?
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Old 19th September 2006, 08:30 PM   #2
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I think the general rule of thumb is that the end of the port should be no closer than its own diameter from any other surface. I think.
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Old 19th September 2006, 11:08 PM   #3
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That is how I've heard it as well.

I know you did not ask or might not care but I'm curious why you cant use a shorter 3" port? Also, 40" is the quarter wave resonance of 83hz is there a reason the box is so long?
Since I know nothing about the design these q's sort of popped into my head. Is this a theoretical question, or is this an actual design, if so we all enjoy details.
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Old 19th September 2006, 11:57 PM   #4
jmiyake is offline jmiyake  United States
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Default Making it real

Project: Two 15" subwoofers, prefer ported.

Drivers: Dayton 15" reference series High Fidelity drivers. (Ordered expecting in a couple of days. )
Dayton 15" High Fidelity

Space available: Area under Front projection screen to left and right of center channel. Approximately 40" by 29" and 15" deep (need to be a bit shallow).

Materials: 1" think mdf. Well braced. 4" pvc pipe. Walls lined with convoluted foam. Bracing is routed out, details not shown in drawing.

Volume: 185L (approx, accounting for bracing, damping, speaker displacement... etc.)
Vents: Two 4"x 36" pvc tubes, tuning around 16-17hz.

Click the image to open in full size.

Room is 13' wide by 20' long. Dedicated theater with 108" front projection screen.
Subwoofers will be powered by a pro-amp QSC USA 370 with 185 watts per speaker. I could upgrade to a QSC RMX 1450 or 2450 in the future, if I feel I need it.
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