Help with box design needed please....
 

I have an 8" sub, and I built a vented box for it today, using my Bass Box Pro program. The final volume was about .75 cubic feet internal, with a slot port 2" wide by 4" high by 18" long. Should be tuned around 35hz. Tested it out, good low end, but the bass does not have the punch I am looking for. I think the box might be too big. Here are the specs.


Z= 4 ohms
Re= 3.2 ohms
Pe= 160 watts
FS= 30.1hz
QMS= 7.13
Qts= .34
Vas= 23.27 liters
Le= 2.04 mh
Mms= 78.2 grams
Cms= .36 mm/N
Bl= 11.52 N/A
SPL= 84.7 dB/W/M
SD= 216 square cm
xmax= 2.3 cm


This is for a customer that listens to mainly metal, so he is looking for tight bass, for the double kick drums, etc. Bassbox recommended .33 cubes vented for the "High Fidelity" version, but that seems to small to me. It recommended .285 cubes sealed. If anyone can run the numbers, or make some suggestions it would be appreciated. Maybe tune it higher? I cannot get a hold of the manufacturer for specs, either. Thanks for the help, in advance!

Umm... the obvious answer to your question is to try what the Bassbox recommends. You trust the manufacturers specs, and the output of Bassbox otherwise, so why not trust the volume calc?

Tune higher for a little more punch...or just seal the darn thing and cover the whole spectrum :) Loose a little output, but much easier to control the sub.

Shawn

Thanks guys, my reason for not trusting the program is because that recommendation is smaller than any other one I have seen for an 8" sub before. I might actually try a sealed box as suggested, see how it works out.

Well, the "normal" spec for my ID v3 8" is .35 cubes...

I had no problem with the recommended sealed size, it was the vented box that seemed small to me. I did a sealed box, works fine.

Ahh.. good point! I looked at the wrong specs on the sheet there...

Good to hear that you got it working well in a sealed box. To me, ports always seemed like too much of a hassle in a small box.

As you said, This woofer call for a very small enclosure, about 0.2 cuft sealed for a Qtc of 0,7. Small woofers work the same as larges ones, so if you build a vented box 3-4 times larger than the optimal sealed it, for a car alignment, you know you'll be in trouble SQ-wize. According to your approx. volume and port mesurements, you're close to 40hz tuning, and the response is almost a flat in a anechoic chamber, wich is not desirable.

If the sealed box doesn't give the punch you're looking for, it's probably not loud enough, and i'd try next 0.3 cuft tuned to 32hz. You can also try 4th order bandpass, with 0.6cuft sealed and 0.3cuft vented, tuned at 70hz. You then loose any advantage of going with a small sub since the box get as large as for a sealed 12" (with about the efficiency of a sealed 12" too) but at least you don't have to change woofers, wich you know, can be tough on the ego for some people.