I built a closed enclosure with a 10-inch woofer. The enclosure volume is approximately 47 liters. External dimensions are 600 x 290 x 360 mm. The T/S parameters for the driver are as follows:
Fs = 16 Hz
Qts = 0.208
Qes = 0.217
Qms = 0.517
Vas = 8.1 cu.ft
Sd = 51.1 cu.in
Xmax = 0.23 in
Re = 3.6 Ohms
I ordered XPS foam and installed it in the enclosure. I expected the bass response to be boosted because the enclosure volume was reduced, and that the system's Q would be increased, resulting in a rise in bass response, with some trade-offs with deep bass.
However, the outcome has not been as predicted. The bass seemed to be softer. I kept adding foam to the enclosure, and it verified the result. So I took all of the foam out of the enclosure. Then, the bass was louder.
Why didn't my modification follow the theory?
Fs = 16 Hz
Qts = 0.208
Qes = 0.217
Qms = 0.517
Vas = 8.1 cu.ft
Sd = 51.1 cu.in
Xmax = 0.23 in
Re = 3.6 Ohms
I ordered XPS foam and installed it in the enclosure. I expected the bass response to be boosted because the enclosure volume was reduced, and that the system's Q would be increased, resulting in a rise in bass response, with some trade-offs with deep bass.
However, the outcome has not been as predicted. The bass seemed to be softer. I kept adding foam to the enclosure, and it verified the result. So I took all of the foam out of the enclosure. Then, the bass was louder.
Why didn't my modification follow the theory?
...
Quite the contrary.
System Q will lower because of increased damping.
Former higher Q gave you "more" apparent Bass, but low quality "single note" type.
A better damped cabinet will have lower but more even, more true Bass.
Your cabinet is actually tracking theory very well. 🙂
That's exactly what's expected
They did.
Read above.
The only time Q will rise in these cases is if you ram the cabinet with damping material to such an excessive extent that it will start to act as a solid (aka volume fill). Otherwise, as has been noted, adding damping material is doing what it should: damp.
XPS is a closed cell foam, so it should indeed reduce the volume "seen" by the driver.
But i suspect the closed cell foam is probably still soft enough to be compressed by loudspeaker pressure.
You could try some more rigid material in the box, bricks maybe?
But i suspect the closed cell foam is probably still soft enough to be compressed by loudspeaker pressure.
You could try some more rigid material in the box, bricks maybe?
XPS needs to be in a sandwich to be of any value. Once you skin it with something non stretch, trying to deflect the panel will try to stretch the outer skin over the thickness of the foam and the shear strength of the adhesive between the skin and the foam surface will prevent the panel from bending. This is what lets XPS be part of a better system than wood based boards, but it is not a complete material on its own. Look out for an upcoming tutorial on using XPS for speakers once my BR or TL question thread is sorted
Presscot did you try in simulator how small of a volume you'd need to have a peak? and the added enough XPS?
Intuitively XPS should reduce cabinet volume, but if it can move perhaps it danpens as well, or sometging. You could add resistor in series with the driver, or big capacitor, like 500uF, which would reduce electrical damping and get system Q up.
What you are doing is great way to learn how stuff sounds, but to really learn you should take measurements as well, to compare data and perceptual effects.
Intuitively XPS should reduce cabinet volume, but if it can move perhaps it danpens as well, or sometging. You could add resistor in series with the driver, or big capacitor, like 500uF, which would reduce electrical damping and get system Q up.
What you are doing is great way to learn how stuff sounds, but to really learn you should take measurements as well, to compare data and perceptual effects.