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Discussion Starter · #1 ·
I'm trying to understand the use of acoustic fiberglass in the overall design of my subwoofer. I think it is used to reduce internal reflections but my concern is about the internal volume. The design I'm copying uses this material and I haven't been able to determine if an allowance was made for the volume occupied by this insulation. I know it won't be 100% but it obviously does occupy some space. My design is a sonotube and it has about 2 inches of this material in the top held in by a baffle.

Thanks,

John
 

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However it does change the performance of the enclosure since fill material lengthens the effective pathways for sound waves inside the enclosure, making it function as if it were physically larger...
 

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Discussion Starter · #4 ·
Not acoustically, the sound waves penetrate the insulation, therefore it doesn't affect the internal volume of the cabinet.
However it does change the performance of the enclosure since fill material lengthens the effective pathways for sound waves inside the enclosure, making it function as if it were physically larger...
Does it affect the performance enough that I need to adjust the volume of the enclosure?

I'm preparing to cut my sonotube so there's no turning back at that point.

Thanks for your response.

John
 

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It could make the tube appear as if it is up to 10% larger, depending on the amount of fill you use. In most cases though the effect is minimal.
 

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4" should be used on the rear wall of your sub. Everything else is unnecessary.

You can't really calculate the effect which is negligible anyway.
 

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I was wondering about sonotubes as well. So you're saying you shouldn't worry about treating the sides of the tube, just the top cap?

I've seen previous builds where they've used egg crate foam on the sides, etc. This is not necessary?
 

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Discussion Starter · #10 ·
10% larger is what one pound of polyfill per cu.ft. would do. I'm not sure what the effect of 2" of 703 would be. I suspect it would be minimal as stated above.
4" should be used on the rear wall of your sub. Everything else is unnecessary.
You can't really calculate the effect which is negligible anyway.
Thanks again for your input. I'll treat it as negligible

Here's a screen shot of my design.

 

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Discussion Starter · #12 ·
The port brace isn't really necessary. What sub are you going to use?
That 39 inch port sure seems long without support. It also has a radius on it to prevent wind noise. If you are sure it's not needed it would eliminate one of the more complex parts.

Also, is the port length measured from the top of the sub, that is, do I include the thickness of the flaired top in the length or just the length of the tube?

I will use the CSS SDX-15.

Thanks for you comments Mike.

John
 

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In a tube you just treat the wall with 2" Not sure why a flare is needed in a sonotube design. The whole point of a sonotube is that it allows you to get a large enough port where turbulence isn't an issue.
 

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You measure the port from the top of the tube, it includes the thickness of the top cap.

Not sure why a flare is needed in a sonotube design.
It depends on the design, if tuning to 15 hz or lower there is no need for a hi pass filter and port air speeds can get extreme.
 
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