making sealed box smaller-long (1 Viewer)

[Tim Brewers]

hey people, sorry this is kinda off topic, but I can't seem to find the answer and was hoping all your collective knowledge could help me out.
Ok, I built a sub box for under the back seat of my truck.Pics here
I plan on putting two IDQ10's v2 in there. Specs Ok, the subs are recomended in a .25 to.50cu' box. My box has two seperate chambers, both are .85cu'. So how would I make the air space smaller? One way we discussed was adding some 2x4's in there to make it smaller. There are two problems with that, 1. It would take almost 10' worth of 2x4 to get me to the .50cu' range, and 2. this would be adding a lot of weight.
BUT, someone recomended putting some of that blow in Polyurethane Foam insulation, like that is used around a window in a home. This brought up a couple questions, would this actually act like polyfill and add to the cu', or would it work to lower the air space?? This also brought up the question of why polyfill works as it does? Is it the air space in the material, or does it have to do with the "spring" effect of the material. So when the sub pushes against the air space in the box, plus the polyfill, the polyfill springs back, thus creating the illusion of more air pushing back??????
Ok, so after all this, my main question remains, will this expanding foam work to lower the air space in the box? Plus I am pretty much stuck with these speakers, so I would appreciate not having a bunch of replies to use other speakers, it is just not in the budget right now. :frowning: Thanks much for the help.
Brew

 

[Jon Torres]

Why don't you try out the subs in the box first before thinking of filling it up. You might want to check with a box program too. I have a DEI10 which has a recommendation of 0.5cu minimum. I tried that out, but it doesn't sound so great. Bigger box sounds better in my case. Try it out in the box you built and see if you like it.

 

[Dave Crigna]

Hey Tim,
The best thing to do is call or email matt at id. He is there tech guy and is great to deal with. [email protected] He usually will get back with you within a day.
Tell him what you have and what type of sound you are looking for and he will be more than willing to help you out. Depending on you music taste .8cf after driver displacment may work great for you. But I think talking with matt first is a good starting point.

 

[Tim Brewers]

Ya, I tried that, but he never really gave me the time of day. I even chatted with him on ICQ for a while, and he never answered my question. He even said he had a prefab box for my truck, and offered to sell it to me, when I told him I would be interested he never gave me any more info? Maybe I caught him at a bad time.

That was the recomendation of a few people, just leave it as it is. I know the power becomes a concern as you add more space, but I will be only pushing about 200 watts rms to each so that is not a big concern. I guess my whole thing is, I am quite new to the whole thing and didn't want make a mistake or when someone says to try it and if is sounds good leave it. My problem is I honestly wouldn't know the difference between a $100 sub like mine and a $10,000 competition setup. I mean, I wouldn't know if it sounded good or not. So I was hoping I could get near spec and not have to use my own judgement. Does that make sense?? Thanks for the quick replies. I will most likely try it the way it is, but does the foam sound like it would work if needed? The box already is quite heavy and I would hate to add 25lbs more lumber. Thanks again,

Brew

 

[Dave Crigna]

Hey tim
I am surprised matt acted like that. Everytime I delt with him, he was great. I did some quick calc on your driver and with .8cf enclosure you will have very "tight" bass that drop really low but not get as loud in the mid-band as the other enclosures they recommend. You can use the expanding foam. The only problem I have is, it is very hard to calc how much room the stuff is taking up. Using 2x4 to me is better. You will add more strength to your box and it is easily to calc how much you need. Also, on the 2x4, I would use 3 2x4x10" strips ( .046 cf per strip) per box and that will drop you volume down to .7cf before driver and .65 after driver disp which is so close to there max rec. spec of .6cf that there is hardly any difference. This adds up to 5ft of 2x4 and only add 12lbs total to your box. Just make sure you secure the 2x4 down so they add to your box strength and not rattle around. Hope this helps

 

[Tim Brewers]

Ok, I just plugged in your measurements and there is kinda a problem. A 2x4 is actually 1.5" x 3.5", but that is not that big of a deal, I can use a 2x6 or something larger. It should be fairly easy to get into the .65 range before I add the sub. Taking 1.5 x 5.5 x 10" (size of a 2x6 ten inches long) I get .047cu' So That would work out fine too. I am pretty sure I can get 3 in there, might end up being 6 chunks, but should work.

Brew

 

[Brian Bunge]

Tim,

OK, I ran a quick simulation in WinISD with a .5ft^3 enclosure and a .8ft^3 enclosure. In the .5ft^3 enclosure you end up with a Qtc around .76 which is just above the max flat response of .707. IIRC, .707 gives you the lowest possible F3. Then I ran the .8ft^3 which gives you a Qtc around .63. While you will end up loosing around .5-.7dB above 50Hz with the larger enclosure, you actually gain a few dB of output below 50Hz with the larger enclosure.

Also, the lower Qtc is considered to be a more musical alignment since it gives you better transient response. I imagine whatever power handling you lose with the larger enclosure will be minimal. One guy that works at a local car audio shop used to design drivers for one manufacturer (sorry I can't remember who) and said that in general he always thought a larger sealed enclosure that what the manufacturers recommend gives better SQ. It's just that in car audio one of the biggest issues is using the smallest enclosure possible.

So what this all boils down to is leave the enclosure as is. You should have a more musical sub and because you're in the auto environment you'll get plenty of cabin gain anyway. Let us know what you think of it when you've got it all installed!

Brian

 

[Tim Brewers]

Ok, I will probably wait till I listen to them. I can always add some filler if they don't sound too great. Thanks for all the help everyone.

Brew