Home Theater Forum and Systems banner

1 - 3 of 3 Posts

1 Posts
Discussion Starter #1
1 lb. of pollyfil to 1 cu. ft. box size.
Polyfil tricks your sub into thinking it's in a bigger box by about 30%.
What this process really does is higher your Q.

Qtc - value for the damping provided for a driver in a sealed enclosure. Denotes the enclosures ability to
control the driver response at resonance. Qtc = 0.707 is the optimum value for sealed enclosures, providing
flattest response and highest SPL for deep bass extension. Enclosures for this value are often rather large.
Lower Qtc can give even better transient response, down to a Qtc of 0.577 for the best damping and
transients, but the enclosure is usually huge and SPL's are down. A Qtc of 1.0 is a compromise between deep
bass and transient response vs. smaller sized enclosure. Larger subs can go with an even higher Qtc, as their
resonant frequency is often very low, but Qtc's above 1.5 can begin to sound very muddled and boomy, and
sacrifice deep bass extension and transient response for enhanced mid-bass peaks (louder).

I have a 3 cu. ft. sealed box with 2 12 in. subs in it. The exact size these subs call for. The inner volume of the box is slightly smaller because of the space the magnet of the subs take up. I added about 2.7 lbs. of pollyfil on all sides of the box. I cut 2 pillows and used the pollyfil from inside them. It was like sheets instead of a messy fluff (easy to work with). A pillow is about 2 ft. by 18 in. and 4 in. thick. I ripped the 4 in. thick part in half which gave me about 4 ft. by 18 in. and 2 in. thick. Put it in as loose as possible with staples.

I notice a tighter bass sound. I don't know why, but this process caused my subs to hit way harder at a much lower amp gain. Before the pollyfil my amp gain was turned up 3/4's the way, almost full power from the amp. Now that the pollyfil is in I have to put my gain at less than half. I guess the positive side of this, is my amp only pushes half the wattage to slam the subs at their best. I may have gained a db. or 2 louder. It gave the subs more of a tight mid bass sound that is clean, rather than boomy (very punchy). It made a noticeable difference that I'm very happy with.

3,069 Posts

I have just bought this stuff in the UK. I bought a 5kg bag as Scott from FI suggested that 10lb of fill is what I needed.


I presume this is ok to use. I take it I just chuck it in the areas between the braces inside the box.

FI have worked out I currently have a QTC of 0.95 but with the wadding this should bring it down.


1 - 3 of 3 Posts