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Old 4th April 2010, 12:47 AM   #1
diyAudio Member
Join Date: Apr 2010
Default Newb - Effects of Vb on enclosure design

Hey guys im a brand new member and have recently really gotten into elclosure design. focusing mostly on auto aplications but i have already built a few full range speakers.

I have been using Bass Box for help calculating port lenghts and port velocities. For my most recent bulid i have calculated a Vb of 2.793 sqft with a port length of 24.88" . My question is what effect does Vb have on an enclosure and sound quality. Seems like a pretty big box for a single 12 subwoofer. (trying to hit an Fb=32hz)

thanks for all the help guys.
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Old 5th April 2010, 12:04 AM   #2
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Join Date: Sep 2008
Originally Posted by duckywitbigfeetz View Post
what effect does Vb have on an enclosure affects the size of the enclosure. Can you be a little more specific?

and sound quality.
All things being equal, a properly built enclosure should not affect "sound quality" what so ever, except for obvious elements like phase and group delay. The driver is designed to operate (mostly) linearly within its usable passband, and is unaffected by the enclosure itself.
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Old 5th April 2010, 02:16 AM   #3
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Join Date: Apr 2010
Im sorry i know what Vb means. What i ment to say was how can the size of the box affect the sound of the speaker.

ie.. if i have two boxes..

box one:
vb=2.5sqft with port tuned to fb=32hz

Box 2:
vb=3.5sqft with port tuned to fb=32Hz
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Old 6th April 2010, 12:41 AM   #4
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Join Date: Feb 2002
Location: Western Sydney
The Vb chosen depends on both the Vas of the driver, and the tuning of the box Fb.
The best way to see the effects of a change in Vb is to input the parameters of your driver into Unibox or Winisd, and vary Vb only, leaving the tuning fixed. (In a real design, they interact, so you need to tweak both).
Generally, too large a Vb and you'll get a hump in bass response, too small and you'll get a falling off of bass response
Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 6th April 2010, 12:51 AM   #5
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Join Date: Sep 2008
There is one thing I should've mentioned too.. a box that's tuned too low, and perhaps even too big for a given Fs target, will be very boomy and have a loose sound. One that's more constricted in the Vb and port size will sound tighter.
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