how much power to a REX 12D4

[maddmatt02 0]

I got one coming and have a rf 300.1

im going to wire it parallel for a 2 ohm load, so I can have around 300 watts available, but the subs only rated at 175rms, the box is about 2.4 cubes tuned to 28.

20V AC should be about 200 watts, where should I set it at, not sure if RE subs are tough and can handle a little extra or what?

Id be open to building a smaller box or similar sized tuned different if it will help in output. Im guessing tuned higher would be louder overall, but in winisd, the 1.5 @ 35Hz box they recommend doesnt look better than the box I built, at least not at anything under 45Hz, of course from there on up the scale it looks like the smaller box has the advantage but I dont really have anything about ~60hz to the sub, so which box route should I go with?

[KU40 173]

A sub in a larger box won't be able to handle as much power. So just remember that. The 2.4 @ 28 box will give you a much larger boost in probably the 25-40 hz range. If you want those kind of lows, go for that. That box will also have a more even frequency response. If you want output, though, don't tune so low. Tune to 35 or so.

[maddmatt02 0]

A sub in a larger box won't be able to handle as much power. So just remember that. The 2.4 @ 28 box will give you a much larger boost in probably the 25-40 hz range. If you want those kind of lows, go for that. That box will also have a more even frequency response. If you want output, though, don't tune so low. Tune to 35 or so.

so, I have 3 options I guess. I can run the box I have in her car now, build a smaller box tuned a little higher, or I can open the box thats in the car now(maybe, built with liquid nails construction adhesive) and cut a litte off the inside port wall to raise the tuning freq. but then of course the box volume goes up even more...

Im thinking Ill build a new one, what would you say about a 2 ft^3 tuned to about 33? or will an even higher tuned freq. have a significant output advantage while still sounding decent?

[sqjeep 9]

Your best bet is to build a new box, RE recommends an optimal tuning of 1.5ft^3 @35hz hope this helps

[maddmatt02 0]

alright, I need to get the figures more precise, but a real quick bit of math and this is about what I think Id need to do the the box I have now.

If I were to disassemble it and modify the port, I would be able to get the box down to somewhere between 1.5-1.7 ft^3, and the tuning around 33-35. but is one port better than 2 for any reason? is 35-40 in^2 too much port area(combined) for one 12 in a box this size?

also, the red line would be the port length, correct?

is it better to have a port without so many bends?

Edited August 30, 2009 by maddmatt02

[maddmatt02 0]

oh, and thats also if I can only find a scrap peice to finish the ports, if I have to buy a new 4x8 sheet then Ill just start over from scratch.

[KU40 173]

yes the red line would be your port length. I try not to have too many bends if possible as it adds a touch of delay. You won't need 40 sq. inches for that sub, but I suppose it wouldn't hurt anything. I assume you just did this to make the port longer, and thus eating up more net volume? If so, I'd recommend just building a new box. That way at least you save some space in your trunk. Or maybe even just cut down one side of your current box to make it less wide or something.

[maddmatt02 0]

alright, cutting off some of one side would be the easiest, but then it would still leave the same amount of space between the box and the rear of the trunk, where if I make it the same width now and make it shallower the leftover space in the trunk would be more usable. I guess I could just pop the front off the box, cut some off the top/bottom and sides and put the front back on, which would lower the internal volume and raisse the tuning a bit.

but after I built this box and started reading more, I think I got the port area on the smal side (was trying to get the most internal volume and lower tuning for the low end, which with more port area gave me a really long port).

its only about 16 in^2 of port area right now, I started thinking more would be better after reading some more stuff online.

lets say I start a new box, and go with RE's recommended 1.5 cubes at 35, how much port area, I know DD's philosophy is 16 in^2 per cube of volume, so would 24 in^2 be good or could I benefit from more?

thanks again?

[lithium 358]

alright, cutting off some of one side would be the easiest, but then it would still leave the same amount of space between the box and the rear of the trunk, where if I make it the same width now and make it shallower the leftover space in the trunk would be more usable. I guess I could just pop the front off the box, cut some off the top/bottom and sides and put the front back on, which would lower the internal volume and raisse the tuning a bit.

but after I built this box and started reading more, I think I got the port area on the smal side (was trying to get the most internal volume and lower tuning for the low end, which with more port area gave me a really long port).

its only about 16 in^2 of port area right now, I started thinking more would be better after reading some more stuff online.

lets say I start a new box, and go with RE's recommended 1.5 cubes at 35, how much port area, I know DD's philosophy is 16 in^2 per cube of volume, so would 24 in^2 be good or could I benefit from more?

thanks again?

go with 24 in^2, there would be no real benefit of going with more port area because it would, most likely, not have be an audible increase in output (there is also a point of too much port area..)

good luck with the new box.

-lithim

[maddmatt02 0]

alright, thanks for the help. last question I got, fire it towards the rear? or toward the seat. Ive always built them rear firing but my friends got a couple 12s in a sealed box firing at the rear seat and its pretty loud and sounds good so I dont see any big downside, but I just dont know whats better. Ive seen plenty of subs firing up in hatches, what about in a sedan? the sub will be right under the rear deck (but Im not cutting the rear deck at all)

every search I try on google comes to home audio topics.

[maddmatt02 0]

alright, thanks for the help. last question I got, fire it towards the rear? or toward the seat. Ive always built them rear firing but my friends got a couple 12s in a sealed box firing at the rear seat and its pretty loud and sounds good so I dont see any big downside, but I just dont know whats better. Ive seen plenty of subs firing up in hatches, what about in a sedan? the sub will be right under the rear deck (but Im not cutting the rear deck at all)

every search I try on google comes to home audio topics.

oh, also, the trunk rattles REAL BAD!

I have taken care of the license plate, tightened the spoiler, removed the little plastic snap covers over the taillight bulbs. still rattles bad. I can stop it by just pushing in on the rear of the trunk lid. I thought maybe having the trunk close tighter might do it so I laid towels over the weatherstripping and shut the trunk on it and it still did it. I have no idea what it is rattling because every individual peice seems to be bolted tightly together.

would firing at the rear seat eliminate those rattles? of course the rear side cupholders will probably vibrate worse than before, but that should be easy.

[Duran 387]

Why do you care about the trunk rattle? Do you spent a lot of time listening to music outside your car or something?

[KU40 173]

If you face the sub forwards then seal off behind the front baffle of the enclosure, not only will the sub have less volume inside the cab to pressurize (likely increasing SPL), but it should also drastically reduce trunk vibration.

[lithium 358]

i've played around with spray foam (like great stuff from lowes or hd) in my brother's can and my own. helped kill some rattles in the truck lid. might be worth buying a can or 2. just be smart about using it.... dont let it fall on the carpet or get it on your hands lol. also dont spray too much at a time it expands a fair amount.

[maddmatt02 0]

huh, never thought of using the foam before, and they have different varieties that dont expand like crazy like the original stuff does, that could turn out bad if you fill a big area full of the stuff that really expands. actually not sure what it would do to sheet metal but I know it can bow/split window liners if you arent careful.

and no I dont frequently listen to the music outside the car, but I dont want to be the one at the light everyones looking at because it sounds like shit on the outside. I hate rattles. the rearview mirror rattles the worst of anything else in the car, I took it down to see if it could be opened up and filled with something to make it much heavier, but it doesnt.

and about sealing it off, its a possibility, but the amps location might have to change and the wiring is cut-to-fit right where it is now...

[maddmatt02 0]

heres the box.

and a graph of it in winisd.

the "doubled front" is just because I decided to put the sub flush again, and had already done a bunch of math to get it perfect, so I just have a square panel sitting behind the front panel to mount the sub to. thats why it isnt exactly 1.5@35.

its gonna save me 1.5" in depth over the box now, not much, but should be just enough to let me get to the spare without removing the box. figured out the old box was 2.45 @ 28 w/ 16.8 in^2 port area.