To pollyfill or not to pollyfill?

**sansoo24** · 04-19-2005, 02:24 AM

Ok ive built and installed plenty of subs in the past. The vast majority in Sealed enclosures built to exact specs. Ive used pollyfill in the past but never more than just sheeting the inside of the sealed enclosure with it. But i recently built a ported enclosure and dont really understand pollyfill enough to know how to use it properly. Or if i even needed it for a ported box.

The box inside measurements are 15x15x13 and tuned to around 40hz. The sub performs freaking awsome in this box. No distortion and it really pounds. I have a little port velocity noise but nothing really noticable. The problem is the box sounds sort of hollow. It sounds like it has an echo or something in it. All joints are screwed, glued, and sealed so i know the box is very sound in construction.

It just doesnt have that low deep clean bass to it. I know a ported box isnt going to sound super clean but i thought they still sounded good.

Sorry for the long post. But i could really use some help with this. As im sure others on here could. thanks

**WhiteRabbit** · 04-19-2005, 11:48 AM

polyfill isnt used too often in ported applications. Ive heard talk about people gluing sheets of polyfill to the walls, but at that point you may as well purchase eggcrate foam. I'm not so sure the difference would be noticible considering the noise floor in a car anyways.

I'd err on the lazy side myself, and not bother.

however, a hollow sound might be caused by box vibration. how well is your box braced? would it be very difficult to cut some wood and glue pieces inside the box now that its already together?

**sansoo24** · 04-19-2005, 08:14 PM

I can try bracing. But its not a very big box so i didnt even think to worry about it.

**WhiteRabbit** · 04-19-2005, 10:33 PM

what did you do for the port? maybe it isnt resonance. I could see some major issues if you used schedule 125 3 or 4 inch PVC as your port, flush mounted and installed wih woodglue or something....

**sansoo24** · 04-20-2005, 12:13 AM

The port is a new design im trying out using a design off of a JL box. The port is actually a right angle port or L shaped port. Which may or may not prove to be a good idea. Its basically 13in long by 1.25 in wide and is in an L shape. Hope this makes sense. Ive thought of using some liquid sound dampener i have left over and lightly coating the inside of the box just to slow down the sound waves in the box itself.

Like i said im a little new to the ported boxes. So im just experimenting at this point.
thanks a lot for the help

**WhiteRabbit** · 04-20-2005, 12:46 AM

well, if htat port is made of .75 inch mdf, then I dont see why that would resonate, either.

wait, after re reading your post a few times, how low is low? are you trying to get sub 35 Hz with a 1 cubic foot box tuned to 40 Hz?

**sansoo24** · 04-20-2005, 12:51 AM

that might bit it rabbit. I thought i tuned the crossover to 40hz but i have yet to double check all that. thanks

**WhiteRabbit** · 04-20-2005, 01:57 AM

40 Hz lowpass filter? or 40 Hz subsonic filter?

and at what slope?

**sansoo24** · 04-20-2005, 11:08 PM

40 Hz lowpass and 12db slope on the external crossover.

Amp is set to nothing. Not using its gain or crossover

**WhiteRabbit** · 04-21-2005, 01:20 AM

I think we have a culprit. your box isnt designed to play much more below 40 Hz. In fact, starting half or a full octave below tuning (around 30ish Hz) the subwoofer will have realistically zero suspension. talk about an easy way to blow a subwoofer with practically no power!

turn the crossove rup to at least 60, the box is designed to play more in that range anyways!

40 and below as an exclusive range is really the realm of larger diameter speakers....