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Old 10th June 2005, 01:11 AM   #1
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Default Couple of fundamental questions....

In a box, when you add stuff or acoustic foam, what relationship does it have with volume? (I assume it reduces it)
Is there a downside to stuffing in terms of sound quality?

Also in relation to this, if you lengthen a port generally what is the result? What if a port is too long, what is the result? Too short result?

Thanks for any help.
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Old 10th June 2005, 01:42 AM   #2
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Sorry, forgot to add, vented box, approx .25 cubic feet in size.
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Old 10th June 2005, 02:05 AM   #3
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When you add something like polyfill it actually slows the sound waves and increases the effective size of the enclosure by up to 25%. In a vented enclosure this also alters the tuning frequency btw.

When you lengthen the port, decrease the port area, or increase the box size (or any combination of the 3) you lower the tuning frequency. The effect this or its reverse will have on the sound depends on the specific driver being used.
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Old 10th June 2005, 06:54 AM   #4
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Thanks for the info. Does the slowing of the waves have any negative effect on sound quality, or perception of the sound?
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Old 10th June 2005, 07:05 PM   #5
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Not that I'm aware of, it's used quite extensively in car audio so people can get away with smaller-than-spec sub boxes, I haven't heard of any negatives thus far.
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Old 11th June 2005, 01:44 AM   #6
Volenti is offline Volenti  Australia
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Just the clarify the enclosure fill effect;

Fill damps the oscillation of the driver at resonance, this results in a reduction of the impedance rise at resonance (usually by around half) and a reduction of the "hump" in amplitude response at resonance (by around 3db)

It's the reduction of these 2 things that makes a smaller filled enclosure "sound" like a larger one, however you don't get something for nothing, the larger enclosure will have more bass extension and greater efficiency than the smaller one.

Think of fill as a way to make a driver "behave" nicely in a smaller than optimal enclosure, rather than making the enclosure volume appear larger to the driver (which it doesn't really do)
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Old 11th June 2005, 04:47 AM   #7
mike.e is offline mike.e  New Zealand
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Larger enclosure,lower F3, Greater efficiency you say?
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Old 11th June 2005, 07:02 AM   #8
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fill generally accepted to reduce standing waves from the sides of the enclosure. The wavelengths of low frequencies are much longer (56.74ft for 20Hz at 24deg c , 25.22ft at 24deg c) so it doesnt really come into play in the same respect unless your box is room sized. My understanding is its normally used for midranges though.
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Old 11th June 2005, 08:05 AM   #9
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Quote:
Originally posted by ocool_15
The wavelengths of low frequencies are much longer (56.74ft for 20Hz at 24deg c , 25.22ft at 24deg c) .
??????????
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Old 11th June 2005, 04:44 PM   #10
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RE : Bill
The wavelengths of low frequencies are much longer (56.74ft for 20Hz at 24deg c , 25.22ft at 24deg c).


If a box has a dimension of a 1/2(i think thats correct) wavelength
you get a standing wave.
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