PDA

View Full Version : rec. a box size for my brahma...



d audio 450
06-13-2003, 01:27 AM
anyone have any recommendations on what size my box should be for a 15" brahma? im planning on going sealed, and i want real clean tight-hard-hittin bass. i really dont want to go ported cuz to be honest i dont think id be able to pull of constructing a box thats tuned to a specific freq. Adire recs like 2.5cuft, and in general anywhere from 1.3-3.5 i think it said.
well, any suggestions or advice greatly appreciated
thanks
-pat

mgaidica
06-13-2003, 01:30 AM
ide say anything they recomend is fine.. dont be intimidated by ported box's, way to many people are and theres no reason to be.. but u said tight clean, so maybe sealed is best. I must say though, from what i hear that thing will stay tight and clean in a good ported box..

Trixter
06-13-2003, 11:59 AM
Using WinISD....

2.5cu' = 42Hz
3cu' = 40Hz
3.5cu' = 38Hz

I would go with the 3.5 because of the lower freq. response.

Although I plan on putting mine in a 6cu' ported box tuned to 26Hz;)

d audio 450
06-13-2003, 12:02 PM
thanks a lot guys- trixter- how would i go about bring the tuning freq down? would it be hard to get it down to like 25Hz?
thanks again
-pat

Trixter
06-13-2003, 12:06 PM
The lowest freq. you can go with a sealed box is 26Hz...and that's in an 60cu' box!!

d audio 450
06-13-2003, 12:18 PM
wait...holy carp i thought u were talkin about ported boxes...i didnt even know you could tune sealed boxes...
what about a 5cuft box...whats that?
-pat

Trixter
06-13-2003, 12:22 PM
5cu' - 35Hz

The only tuning you have for a sealed box is it's size...the bigger the box the lower the freq. (that's why people cheat and use poly-fil.)

slipknot87420
06-13-2003, 12:31 PM
i thought after you went so big that it was like IB because i dont think a sub in a sealed 10cube box would work to well

Trixter
06-13-2003, 12:35 PM
Depends on the sub. A 15" Brahma in a 10cu' box has a flat response tuned to 30Hz...looks like it would sound good. But if I was looking for this effect, I would just port it in a reasonable sized box.

d audio 450
06-13-2003, 02:05 PM
so what if a i made a 5 cuft box and loaded it with poly fill? any idea?
thanks again
-pat

Trixter
06-13-2003, 02:58 PM
You are only supposed to use something like 1/2lb of poly per cu'. At that rate, you may make it seem somewhere closer to a 6cu' box and get it down around 33Hz. If you are concerned about getting a lower freq., why don't you go ported? A 5cu' ported box tuned to 24-26Hz would sound awsome. If your concerned about it being difficult, just go with a round port. If you can cut a hole, you can make a round port.
(I'm going with a round one so I can change it at comps.)

d audio 450
06-13-2003, 03:33 PM
ok. but does where the port is placed affect the tune freq?
could i port a box like this? with plexi galss? (blue)

thanks
-pat

Trixter
06-13-2003, 07:25 PM
You can put the port anywhere you want w/o the tuning being effected. With something like that, I would put it in the top. Just make sure that you leave as much room between the end of the port and the opposite side of the box. What I mean is, let's say your using a 4" diameter port. When it goes into the box, it needs to be at least 4" away from the opposite side of the box. (If you don't understand, let me know and I'll draw up a pic.) You say your concerned about it being hard to make a box w/ a port, but you making a plexi window? How is this sealed and kept from flexing? If your doing this, a port should be a piece of cake.

d audio 450
06-15-2003, 07:03 PM
as for the plexi glass- i drew it in that pic way to big, with the brahma and a 1200.1 it would blast it apart unless i used reeeal thick pglass. , i want to have a little window, maybe even as small as 6x6 cuz i wanna throw a neon inside (i just like the effect) and have the sub glow blue or whatever color. I just got home 20mins ago from home depot and i bought 2 4x4 sheets of mdf, 3/4" , tee nuts, and bolts and screws... i really appreciaste the help and all- i just have one last question:
if i put it in a big box, and say its sealed tuned to 33hz or whatever, does this mean that its freq-response graph will be spiked at 33? is this spike smaller than if i ported it?
thanks again
-pat

Trixter
06-16-2003, 11:05 AM
Actually, the 33Hz is at -3.5db in a 6cu' box (or a 5cu' box w/ poly-fil) It hits 0 db at 84Hz and flat lines from there. There is no "spike". I think the only way to achieve that is to go ported.

With my box, 6cu' ported to 26Hz, I get a +3db spike from 30-34Hz. I like this set up because it will produce a strong low end.

d audio 450
06-16-2003, 12:08 PM
ok, u said earlier you could have a 5cu ft box tuned to like 23HZ...right? to build this, i can have any 5 cu ft box in any shape, and i just need to know the necessary diameter of the port, and the length of the port?
thanks again
-pat

Trixter
06-16-2003, 12:39 PM
Yes, that's right. The size of the box (as far as length width and depth go) and the kind of port you want (round or slot) determines the kind/size your port will be. The box shape can be anything, as long as it's air tight. The tuned freq. of the port comes from the ports internal surface area, not the diameter or length. That's why I say, depending on the sizes/shape of you box, you can make a port however you want as long as you have it's area correct.

d audio 450
06-16-2003, 12:41 PM
oh ok- i understand now- thanks a lot
-pat

Trixter
06-16-2003, 12:46 PM
Need anything else let me know.

If you haven't DL'd WinISD yet here:http://www.linearteam.dk/ (make sure to get the pro version. The Brahma 15" is already in it's data base.)