# Relationship between subwoofer box volume and sound?



## Kerpal (Jan 27, 2009)

Very basic question. With a sealed sub box, what effect does the internal volume have on the sound characteristics? Generally you have an ideal volume for a given driver, but which qualities of the sound will change if you go above or below this number? 

I've heard statements such as small boxes sound tighter and larger ones typically boomier, and that small boxes can increase the power handling of the driver. Is any of that true or are those just generalizations?

The reason I ask is I put my sub in a larger box than it was in before and it sounds different, as in not as tight, and seems to not play certain frequency ranges as well. However this is also a totally new install (different car, different amp). I'm trying to figure out what's to blame, but I assume it could be the slightly oversized box?


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## zoomer (Aug 2, 2009)

Kerpal said:


> Very basic question. With a sealed sub box, what effect does the internal volume have on the sound characteristics? Generally you have an ideal volume for a given driver, but which qualities of the sound will change if you go above or below this number?
> 
> I've heard statements such as small boxes sound tighter and larger ones typically boomier, and that small boxes can increase the power handling of the driver. Is any of that true or are those just generalizations?
> 
> The reason I ask is I put my sub in a larger box than it was in before and it sounds different, as in not as tight, and seems to not play certain frequency ranges as well. However this is also a totally new install (different car, different amp). I'm trying to figure out what's to blame, but I assume it could be the slightly oversized box?


you are basically correct... a given sub has an optimum box size that is usually given in teh specs or on the manufactured web site. A smaller box increases the Q of the system and causes a peek in the resonance. It may sound boomier at that frequency. A smaller box also provides more air spring and controlls the woofer more at other freqeuncies, thus sounding tighter and reducing the cone excursion and increasing power handling.

A larger may give you a bit more bass but at the expense of sounding floppy/less controlled and with less airspring it causes more cone excursion and reduced power handling. 

optimum box size can also be calculated with sub design programs.. 

Think of a sub like a car with springs and shocks.. increase the spring stiffness and it is a harsher ride and wont bottom out.. but may resonate.. decrease the spring stiffness and it will wallow down the road like an old big american car. Shocks (damping) will also affect the performance. Just like in a car, there is an optimum balance of spring, damping, and mass for a given desired performance.


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## Lanson (Jan 9, 2007)

zoomer said:


> you are basically correct... a given sub has an optimum box size that is usually given in teh specs or on the manufactured web site. A smaller box increases the Q of the system and causes a peek in the resonance. It may sound boomier at that frequency. A smaller box also provides more air spring and controlls the woofer more at other freqeuncies, thus sounding tighter and reducing the cone excursion and increasing power handling.
> 
> A larger may give you a bit more bass but at the expense of sounding floppy/less controlled and with less airspring it causes more cone excursion and reduced power handling.
> 
> ...



Close, but a larger box provides a bigger air spring. At least according to Andy's posts.

With any box, I always shoot for the "magic" .707 Qtc. At least within 10% of it.


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## aztec1 (Jun 13, 2008)

A bigger box will generally let the speaker get lower on the same power. Sometimes the box itself can resonate at certain frequencies and color the sound. You may also try pointing it in a different direction and/or moving it around...placement makes a huge difference.


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## zoomer (Aug 2, 2009)

fourthmeal said:


> Close, but a larger box provides a bigger air spring. At least according to Andy's posts.
> 
> With any box, I always shoot for the "magic" .707 Qtc. At least within 10% of it.


Perhaps its just semantics... A larger box has more air and is easier to compress.. like a small spring...
A smaller box has less air and is harder to compress... like a larger spring.


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## Lanson (Jan 9, 2007)

Nope, this is the ultimate post for answers like this. Look for Andy's answers (he's the guy from Harmon.)

http://www.diymobileaudio.com/forum...ven-cabin-gain-reality-do-we-need-low-fs.html


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## Lanson (Jan 9, 2007)

In fact here's the ultimate post in that ultimate thread:



> Consider the following Thiele and Small parameters:
> 
> Cms = The compliance of the suspension--how easily it's moved
> Vas = Cms expressed as a volume of air that has the same compliance
> ...


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