If you ever wanted more bass to your sub woofer bandpass box? Now you can on the cheap instead of buying poly fill.
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I think my subwoofer`s skeakers are too small. Can I just change them for two bigger ones without damaging the subwoofer ? What detail should I take into account before doing it ?
pillow stuffing is polyfill
That aside, yes, polyfill is much less expensive when you get it from pillows. =)
Now, if the box is ported, as they often are for greater efficiency, then the air does move in and out through the port, and we are talking a completely different thing. Typically, a cheap ported speaker has a big peak right at the bottom just above a very sharp cutoff, to get maximum efficiency and maximum low frequency. This accounts for the whump whump whump one- note-only sound of a cheap ported box. If you stuff the port with something, you do impede the movement of the air, and the more you plug it the closer it comes to a sealed box with no port, obviously. The comparison is, that a ported box theoretically goes down an octave lower but falls off twice as fast below that, compared to the same box with the port plugged. Cheaper ones tend to be designed with a big hump at the bottom to make it louder and bassier, but, as i said, without the ability to distinguish the various notes very well. More seriously designed speaker will be smoother down that end. In any event, the effect of plugging the port partially is, like you might expect, the more you plug it the more it tends to sound like a sealed box until it's completely plugged; which means, the dropoff starts an octave higher but is shallower, so there is still some response way down at the bottom, where the ported is down to nothing. The graph here is great http://www.ajdesigner.com/fl_subwoofer/subwoofer.php
Me, I've got a lot of those cheap speaker systems with subwoofers, like they sell for computers, etc, and I just stuff the port with old socks until I'm satisfied with the sound. I don't have any of them running unplugged; and although it's not serious home theater quality, even with their cheap little amplifiers, there's still enough oomph to do a good job on the TV movie effects, while at the same time music on tv shows is a lot more listenable.
you can play around with the amount of stuffing too.
Adding stuffing to any subwoofer will slow down the air flow in side of the subwoofer resulting in am bigger box.