Polk Recommends Minimal Polyfill, How much?

phil65

Im adding a second sheet of mdf to the top of my box for my mm1040 svc. Just wondering how much polyfill I need? Should the box be half full, full to the top, bursting with polyfill?

pentoncm

How does it sound? Keep in mind that there are different density poly fill products out there. I bought the cheap bag at Michael's and i had to compress the pieces by hand because I could only fit a tenth of a pound in the box which did nothing. I filled my 1 cu.ft box (before displacement) about half way with poly fill that i mashed together so it was dense. Ended up with 1/2 a pound in my box and it made a significant difference with low end extension. You can buy the slightly more expensive stuff which is easier to work with because its already dense.

I would try filling it 1/3 to half way with densely packed fill.

pentoncm

Keep in mind that where you have your sub is going to change the sound in a big way.

In my car

(1) corner loaded - firing towards back of trunk in the back corner results in lower bass but bad integration with mids.
(2) Firing rear - midway between seat and trunk lid is ok
(3) Back corner side firing to opposite side of trunk sounds best to me because there is really good low extension but I can get good upper end response to integrate well.

phil65

I have it firing straight up under the rear passenger side seat of my sierra ext cab, it can also be fired towards the front when the rear seat is folded up. The box is yet to be covered with dynamat and carpet and im also going to add a second layer of mdf to the top panel, sounds like the box is resonating a bit and sounds like the bass is missing something, dynamat and carpet should fix the resonance, hopefully polyfill adds some more to the bass.
Its mounted where its at due to lack of mounting options, still need my rear seat and leg room.

Vital

How exactly are you going to dynamat your enclosure?

pentoncm

don't fire up and don't fire forward

Up pulls attention to the rear, and for some weird reason firing forward is usually the worst sound.

Polyfill won't give you more bass, it will actually reduce your efficiency. I suspect what you are lacking is more due to location and phase issues. Try reversing phase of sub if you haven't already

phil65

Ive tried reversing the phase and It didnt seem to do much, still have to get some time to play with the system as a whole since everything is installed now. Like I said up firing is almost the only option since im lacking space, down firing is possible but I would need a better woodshop to build it. All I have now is a friends small table saw, a jig saw, and a circular saw.
Vital, im not really sure, ive heard of people doing it and that It helps reduce resonancies. Might just add the second sheet of 3/4 mdf to the top panel and be done with it.
If polyfill reduces efficiency what exactly is it used for? My understanding is that it makes the speaker think there is more volume in the box than what there really is? What does that do?

pentoncm

By making the sub think its in a bigger box it shifts the response a little bit giving the sub more low end extension. You need to find the right balance. As you add more and more your efficiency decreases thus being counterproductive. Also, after a point the effect reverses and the sub thinks its in a smaller box if you put too much in. A common practice is to use .5 to 1 pound of poly fill per cu.ft. of airspace, this is an acceptable range.

How much airspace do you have in your box?

Where do you have your gain on the amp set? What LPF are you using for the sub?
Is there not enough bass or is the bass muddy? What type of EQ do you have on the headunit? Are you sure its sealed properly? Leaks will kill the bass and cause noise.

Vital

^^^ +1 on this

Dynamat isn't going to do jack to make 3/4 mdf enclosure stronger. It's just not made to be stronger then wood or add strength to it.
Adding another piece of wood will help with resonating since it'll make your box (or at least one side of it) stronger but sounds to me like your problem is something else. Answer questions asked by pentoncm, this should give us something to start with.

Where did you get this box from?? How much airspace does it have? Custom built? Got it from Best Buy? New/used???....

phil65

I just found a little leak in the box on the mounting ring of the sub, one of the screws didnt hold in the mdf, adding a second sheet and re mounting should fix that issue. I'll see what happens when I do that, and will probably throw in a little polyfill, box is .67 cu ft internal volume, polk lists .66 as recommended with minimal polyfill.

After installing my speakers im pretty sure im going to have to dynamat my doors to fill in the 4x6" hole directly below the speaker, and the other holes around the speaker allowing the waves off the back of the speaker to come through, the mid bass definitely isnt there. Thanks for the help guys, you've really improved the install, as has some other members on this site, pretty awsome.