Sub displacement

When building a box to spec, do you figure in the volume that the sub displaces.  For example, I'm building a new ported box for an Alpine R 12 giving it 1.90 cuft., the sub displaces .128 cuft, do I add that volume to the total size of the box  for a total of 2.02 cuft?  Also, can I use styrofoam or some other firm, lightweight filler to displace extra space in a box that is too big?

Yes, you need to add the amount of space the subwoofer takes, it is that much less volume the box will have. If you fill the box will something like foam, it actually tricks the subwoofer into thinking it is a bigger box, not smaller.

Keefe

Why would you add the subwoofer displacement to the internal volume of the box? The displacement is the space the woofer takes up, so you would subtract it from the internal box volume. As for something to eat up volume, maybe you'd want to just add some wood to the inside walls. Not only will eat up volume, but it'll act as braces making the walls stronger.

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Jon
Don't like rockford subs? Then don't look at my car =)

Lets just say that the sub need 2. cuft, the sub displaces .128 cuft inside the box.  Hence I add the .128cuft  to the outside dimensions when I build it, to compensate for the internal space the sub takes up.

If you add, that means it needs to be bigger, at least from my experience in Calculus... If the Sub takes up room, you need to add that much more size to how big you are going to build your box. If the box needs to be 1 ft3, and the sub takes up .128 ft3, your box needs to be 1.128 ft3... In other words add in the volume of the sub to how big the box needs to be to balance the equation.

As for putting wood in the box, you can't just randomly put wood in the box to take up space because that messes with the shape, sure it will be stronger, but how about just doing it right the first time, and forget having to go in a screw it up later.

Keefe

Sorry, I misunderstood your post, alex75. I didn't realize you were talking about the dimensions of the box.

I only recommended putting in wood because he wanted a way to eat up volume if the box he had was too big. I agree it should be done right the first time, but sometimes you experiment with different size volume boxes, and sometimes the box is too big. If the wood pieces are properly placed, the "new" shape inside the box shouldn't have any effect on the performance.

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Jon
Don't like rockford subs? Then don't look at my car =)

from what i remember not only is the wood good for bracing inside but the more irregular shape inside the box instead of cubes or rectangles the better you get rid of standing waves in the box giving the sub a better sound.

actually, the shape does matter, in sealed and ported. The way the air pushes the speaker back in an enclosure especially when dealing with larger enclosures, because the sound waves will indeed come back at different times and sometimes cause cancellations, as well as standing waves creating a boost in amplitude at certain frequencies.

Keefe

I was asking about adding something to eat up space not for the new ported box I'm going to build, but in an existing box I'd like to alter.  My new Type R needs 1 CUFT sealed, I allready have a small wedge that is 1.43 cuft.  I want to compare the SQ and SPL between both boxes.  I was simply going to add a few pieces of wood(3.5 x 3.5)  cut to lenght to take up the extra space.  I figure I'd add big pieces so I only have to add a few.  What would be the proper placement of the wood?