Divided boxes?

neomagus00

this came up in the miata thread... why is it that a divided box is better for multiple subs (barring bracing)? I'd think that shared air would help cancel any minor non-linearities across the 2 or more drivers; as well, this could save precious space, if that's a concern, and of course this is assuming that there's appropriate bracing all the way round (even across the interior of the box if necessary.

LittleCar_w/12s

I guess you are correct, however the center brace itself is very important for preventing flexing. If you were to cut large circles in the divider it might help eat up some of those 'non-linearities' but it will also ineveitably cause some resonance sideways in the box (reduced more by size and placement randomness of the holes). In the end you havent saved any hassle, and if one sub stops, you can imagine what will happen inside the box... with a full divider you will not have any problem with just one working.

neomagus00

hmm... this is true, i didn't think about the work-to-benefit ratio... however, it's be interesting to have an undivided box with one working and one nonfunctional sub... you'd get almost no volume (as one sub goes out it pulls the other one in at almost the same speed and time, then pushes it back out... you'd set up inverse waves that were a fraction of a second out of phase...) wonder what it'd sound like?

LittleCar_w/12s

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exalted512

the only reason why divided chambers is good b/c if one sub stops working for whatever reason...youre more likely to blow the other sub in the box since you just doubled its air space
-Cody

neomagus00

good point... oh! i think i get it! why a smaller box is louder, at least for higher frequencies - volume is based upon the pressure differential... that is, if the difference in pressure from the pushing part of a wave and the pulling part of a wave is higher, the volume is louder. so, in a small box, the air suspension will push and pull harder on the cone, creating a higher differential for a given excursion... now, this doesn't explain why, for a given power, the smaller box is louder...

LethalLee

louder not lower

neomagus00

Originally posted by neomagus00
a smaller box is louder, at least for higher frequencies

LittleCar_w/12s

for larger drivers (subs) the larger box allows the cone to move further than designed for, which increases the needed recovery or turn-around of the cone after it's input changes direction... This means the cone cannot reproduce higher frequencies in a larger box without terrible distortion or even total elimination of the higher frequencies. This is very true with heavier cones... a smaller box will definitely decrease the turn-around of the cone's response, but for those lower frequencies, you will have to compensate with more power...
So it's a trade-off smaller box - more efficient and accurate for a wider spectrum, or a larger box for more efficient use of power at lower frequencies at a significant loss of higer ones.

Please note, home audio 12" speakers will have a great spectrum because they are made of lightweight but sturdy paper/resin. And they almost always need to be supplemented with a heavy sub-box for that low-end. SDo pick your battle, or both if you want to.

-Jerry