Enclosure volume allowances

[sweatepz]

I am no totally sure, but am I correct in assuming that if a speaker was to require an internal vented box volume of 0.75cu.ft, that I should add extra volume for the displacement of the speaker, plus the port, plus any bracing material, plus a factor allowance for damping materials used to the 0.75cu.ft?

Also if the above is the case, I am not sure as to how much should be added for the damping material. If I was to use one inch thick 85% - 100% wool lining on the enclosure walls what percentage should be added. I can easily work out the volume of the material but it is comprised of air and wool and but am not sure how much to add. It mentions on the PE site that 10% - 25% can be added. If you could please offer me some guidance as to how to allow for damping materials for a vented box volume and how much damping material to use that would be great.

[johninCR]

Yes the driver, bracing, and ports decrease the volume in computing Vb. Damping like wool and fiberfill do not.

[Paradise_Ice]

You cant just say 10% air space for the drive unit, its not accurate at all, i have subwoofers that remove 8 litres of air with just the magnet assemble, you would be best to measure your drive units air displacement with a good air tight bag and a big bucket of water

[sweatepz]

Thanks for your help!!!!!

[mltaunt]

It would be nice if speaker manufacturers would supply this info. I would assume they all have 3D cad models that would make this a piece of cake. Maybe the big resellers like PE could talk them into supplying this data.

[Paradise_Ice]

Your right! i never though about that really,
Its simple to measure the volume when you have the drive unit in modular form.

Nice one Guys

[Ron E]

Or you could guesstimate:

Take the measured diameter of the cone or the mounting diameter - call it D
Take the depth of the system from the back of the mounting frame to the back of the magnet - call it d

Approximate displacement volume is V = 0.25 * 0.33 * pi * D^2 * d This is the formula for a cone with base diameter D and height d. You can visualise this as a cone with diameter D with the point at the back of the magnet structure. The cone is taller than the actual driver cone, and the extra volume compensates for the volume of the magnet system.

For a Shiva, which has a diameter of 10 inches and a depth of 5.125 inches, you get 0.25*0.33*pi*100*5.125 = 133 cubic inches

Using mounting hole diameter (11 inches) for D, you get:
0.25*0.33*pi*121*5.125 = 161 cubic inches

Advertised displacement is 183 cubic inches.

As you can see, this gets you quite close without dunking your driver in water. I don't think your box design will be altered much by about 20-50 cubic inches......

[rnoble]

Originally posted by Paradise_Ice
Your right! i never though about that really,
Its simple to measure the volume when you have the drive unit in modular form.

Nice one Guys

If you are lucky enough they will have that fixed foam padding in the box for transport. I just used the imprint of the padding to test litreage, beats worring about waterproofing your driver.

Mltaunt they did with my tempest sub driver. I guess this is because the displacement is so large so I agree it should come with all driver TS paremeters!

[Mark25]

the area that a drive unit consumes from within an enclosure depends upon the thickness of your front baffle.

EDIT: and whether or not you rebate the mounting flange. (prob why manufacturers don't supply the data)