using polyfil in a ported enclosure?

[mat3833 10+ year member]

ok, so i am in the process of designing 2 enclosures for my HT settup. aiming for a 25-28hz tuning or so with a SA-8 or a TC sounds Epic-8(still havent decided). the problem is since i am using 2 subs i dont have quite enough room to make the enclosures as large as required/suggested. i have used polyfil in the past in sealed enclosures with fantastic results.

my question is can i use the polyfil to make up for the lost volume and acheive the tuning i want? from what i was told, making the enclosure larger with lower tuning(up to a point) will yeild better response than a smaller enclosure with the same tuning. TC sounds said that since i will be tuning so low that i should make the box~30% larger than their recomendations to help with woofer excursion control at such a low frequency. i am waiting to hear back from sundown for their thoughts but TC sounds' thoughts seem wrong.

i am hopeing that i can use polyfil to end up with ~1ft^3 effective volume out of a ~.75-.8ft^3 enclosure. but i only want to use polyfil IF it will yeild a beneficial response increace/SQ increace. if not i will simply not use it and make the enclosure as large as i can. the enclosures will be completley externaly ported(external slot port is looking like the best option, but i may end up using 4" pvc for its flexability) with woofers fireing forwards to the couch and ports fireing into each corner. this leaves essentially 5 walls of the enclosure that can be completley polyfilled with a partial 6th due to the port placement. if i use a pvc port i wil be using a molded "velocity stack" aproximitly 1.5" tall inside of the box with the rest of the port outside of the box for beter airflow into and out of the port.

can anyone confirm tc sounds' recomendations on box size/tuning? it has been a week and i have not heard from sundown yet and with fathers day comming up in a couple weeks i need to have all of the designs finalized so that i can get my fathers day present installed and functioning on time.\

Matt

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[PurpleDiesel 10+ year member]

Over at DIYMA.COM search polyfill there are many many threads about this.

IIRC polyfill is almost noneffective in a ported enclosure.

My suggestion is to go as big as you can.

 

[mat3833 10+ year member]

well aparently using polyfil in a ported enclosure just smooths out the "peak" in response at the tuning frequency. and i cant find ANYTHING on smaller box volume vs larger box volume for low tuned settups. with sealed larger is better for low end but you loose some of the "punch" and some power handeling. but i think the opposite would be true for vented. looks like ill be doing ALOT more research.

Matt

 

[snoopdan 5,000+ posts]

well aparently using polyfil in a ported enclosure just smooths out the "peak" in response at the tuning frequency. and i cant find ANYTHING on smaller box volume vs larger box volume for low tuned settups. with sealed larger is better for low end but you loose some of the "punch" and some power handeling. but i think the opposite would be true for vented. looks like ill be doing ALOT more research.
Matt

Sealed enclosures always can take more power then vented, no matter what the size of the enclosure is. Adding polyfill to a vented enclosure just changes tuning because of the added displacement of the material. Brah.

 

[slim2fattycake 10+ year member]

Yeah it does change your volume and tuning. It also does smooth out peaks.

 

[BrownVanMan 10+ year member]

doesnt help at all in ported ive tried, just makes it quiet. with that much air space, depending on the power, either use the 2 8's sealed or go with 1 in the right ported box

 

[mat3833 10+ year member]

Sealed enclosures always can take more power then vented, no matter what the size of the enclosure is. Adding polyfill to a vented enclosure just changes tuning because of the added displacement of the material. Brah.

"Brah" sealed can take more overall power than vented. but at or around the tuning frequency vented can handle much more power than sealed. but more power doesnt mean more sound, if i go sealed i need about 500W more power to get the same output as the vended enclosures. and adding polyfill doesnt change the tuning very much at all, adding 2lbs to my ~.75 ft^3 enclosure only drops the tuning by .5hz if im tuned for 25. over at diyma the guys said adding some polyfill and adding a bit of port length will keep the tuning the same but increace overall output by 1 ~db across the board with less of a peak at the tuning. since this will be a HT enclosure i want that peak, so polyfil is out.

and since i wont be able to horribly overpower the SA's or TC's i dont want to go sealed. if i do the 2 smaller ported boxes i can get the output i want without having to buy a new amp. and with some Winisd modeling making the box larger will do hardly anything besides make the port longer and make the peak at tuning a bit higher.

i may end up making a simgle box to go behind the couch. i will have more space, but it might end up sounding not as good.

Matt