gday. jst wondering, iv noticed that some sub boxes iv seen are lined on the inside with a foam material, and others are fiberglassed to make it smooth on the inside (better air flow i gess). Is the idea that if the box is ported , you make the inner smooth with fiberglass.

and with the sealed boxes, they are lined on the inside with foam material..

sorry if this has already been covered, i cant seem to find it.

i would like to see some technical info on this subject as well.

Nathan

at sub bass freqs, lining a box cannot make a diff according to the laws of physics, but some ppl think it can so they use filling. If you just want a warm fuzzy feeling then line your box.

peace
Cyberpunky

The idea is that the filling slows the airspeed inside the box down, making the sub think its in a bigger box than it actually is. Not a real solution, the proper solution is making the box the correct size.

ohk then, i jst kinda assumed maybe they used fiberglass to line the ported sub boxes to improve air flow, to make it sound louder

all the fibreglass lining does is seal the box...

ok thanks for the input

Adding stuffing to ported boxes generally decreases output, it does however smooth out the response.

Adding stuffing to sealed boxes generally lowers the F3 frequency, not much difference in output.

Adding FG to improve airflow in ported boxes really isn't needed, unless you're using it to seal the box.

i was aware of what youve said here, but do you know if how much you put and how thick or compact it is makes any diffrence. should it be stapled to the wall or just thrown in etc.. also, what about lining it with acoustic/convoluted foam, any use...make any diffrence you reckon compared to using fill.....any elaberation on this topic would be great...thanks..

I'd also be keen to find out about this! Someone said to half "stuff" the box - but unsure on this and if it meant to fill it half way or staple round the outside etc etc

staple it to the walls, no need to pack it in.

A ported box should have the walls lined a few inches thick. Dacron or Tontene (polyester pillow stuffing etc) is good as it won't break apart and is nice and dense.
A sealed box should be loosely stuffed with the same stuff.

Speaker boxes that don't use damping material can sound loud due to peaky response. The damping material absorbs sound that would otherwise bounce around the box and back to the cone. Such reflections onto the cone either reinforce or interfere with it's output, causing peaks and dips in the speakers response.
Reflections from the back wall are the worst, so extra should be used there.
Damping also helps suppress modal behaviour (tuned resonance etc), Ideally the damping material should be located at points of highest velocity. For axial modes, this is a few inches from the walls. In reality, stuffing a sealed box, or adding extra thickness to a ported box is fine.
Putting the damping on the walls will help suppress tangential and oblique modes.

As already stated, the damping material will also make the box appear larger without increasing the air mass inside the box. The air has to weave around the fibres, so it's path to the walls of the box end up longer than if there was no damping. This helps extend low end frequency response (f3), without lowering the Q of the speaker, which would lead to a boomy sound.


Most of the above about damping reflections is more applicable to full-range speaker boxes (Ie. home stereo), but it also somewhat applies to subwoofer design. Although the damping of axial modes etc. isn't so critical, seeing as the wavelengths are often much longer than the dimensions of the box.

spongy stuff increased NRC why would you want that in a sub box?