Can I build a ported box with these t/s specs?

These are the specs I have: DCR 6.2 OHMS, Fo, 38.4Hz, Zmax 90 ohms, Sd, 0.0211 sq/m , SPL 1W/1M 91db, Qms 5.3748, Qes 0.3538, Qts 0.3320, Vas, 42.2266 litres, Motor parameters, 1kHz 0.7082mH, Krm 5.1393ohms, Kxm 4.9212mH, Erm 0.6091, Exm 0.7850. I'm missing the Xmax spec and therefore the
Vd spec and every box building program out there that I've tried needs at least one of the 2 to find the proper volume and port lengths. What can I do about this missing spec? If it's relavent it's an 8" midwoofer/woofer and I'm using the exact drivers and crossover that are in this speaker

Ron E

2002-06-27 10:41 pm
Xmax helps figure out power handling and port diameter, but it isn't all that critical. Nothing wrong with putting a guess value in for Xmax - just say it's 4-6mm...

It has nothing to do with volume, and you should always use the biggest port that's convenient.

Vent 3" dia x 8.44 in long - use a flared port
Oh okay, I didn't know Ron E's box was for the woofer I got. I though those specs were use an example of something that I didn't pick up on. Where can I get flared ports on the internet? The port stays the same length and I just put the flared ports on right? I was going to use a rectangulat port, is flared better?

One last thing before I start building is how do you find out how much voume your x-over components take up. About how precise does a ported box have to be to sound right? My lasted (sealed) box that I build was suppose to be .90 cu. ft. and it turned out .85 cu. ft. I don't have any power tools except for a drill and jigsaw and as of last week I bought a sander, so it's hard for me to make perfectly straight and at 90 degrees cuts in MDF by myself. When they cut the MDF into the pieces I need at the lumber yard they never get it that precise.
Jimmy154 said:
One last thing before I start building is how do you find out how much voume your x-over components take up.

If you leave it outside the box it won't take up any volume, and should be less microphonic.

If you want to find out exactly, put the XO into a zip-lock, suck all the air out. Then fill a bowl or pitcher to overflowing with water, careful put the XO in. Water will overflow to exactly the volume of the XO. You can measure the volume of water lost by carefully filling up the water container with a measuring cup.

The parameters of the driver generally indicate whether it is intended for a sealed vs. vented enclosure.

I forget where I originally came across these parameters, but here they are:

Drivers for Sealed Boxes generally have Qts > 0.40, Fs < 35Hz, and Xmax > 4mm or an (Fs/Qes) close to 50.

Drivers for Vented Boxes generally have Qts < 0.40, Fs < 45Hz, Vas < 4cu ft, or an (Fs/Qes) close to 100.

Note that these are not absolutes, but rather general guidelines. My vented subwoofer violates one of those parameters, yet still measures well.