DJ SprinklesNJO

im building a box, and i have a question....
the specs for the internal volume of air is 1.25 per speaker. but im putting in two subs. so can i just double the internal volume needed (so it would be 2.5) or is there another way to caculate the internal volume. by the way im not making the box into seperate chambers for each sub. jsut one big box for the two subs.
unless other wise stated (and really recommeded) i prefer not to put in a support in the middle, which would also make the box into two chambers. ill explain why....

it is a real small system and the subs are not powerful at all. already what i put in there is good enough. (a single 12 in a tube was all i could fit) (89 mustang convertible GT 5.0 ughh soo nice) but anway so i figured 2 12's in a made box would sound and give a little more bass than the tube.

wow this is gettting long, one more thing. does it make a difference if the box is made real awkard. i mean like from the side it will look like an "L" the total height will be 9inches and depth of the top part is 15" then when it gets to the bottom of the L piece it will be another 5'' longer and have a height of 5''s

thanks for any advice. i know the last part got real confusing so dont worry about that so much. thanks

postrin

there are 2 problems with going with a mono chamber for 2 subs, 1 is support, but since you aren't looking for makor bass, isn't too much of a concern. The other problem is that if for some reason you blow one of the subs, you now have a 2.5 cubic foot box for one sub, which would be way too much, and if not caught pretty quickly could easily blow the other one. To find internal volume, multiply inside length, by inside width, by inside height, and divide by 1728

DJ SprinklesNJO

2 good valid points. i appreciate it. thanks

biggie27

Im not good with box building but if you do it that way wouldnt your subs kinda cancel each other out this way yould actually get less bass out of the 2 12"'s than you should?

stevie

>so can i just double the internal volume needed (so it would be 2.5)

Yes. If the box is ported, you will also need to double the number of ports. It is advisable to separate the two chambers but, if you can't, try to put some kind of reinforcement between the center of the front baffle and rear wall. The shape of a subwoofer cabinet isn't critical. Most subs are better off without internal wadding as well, but that's another story.

Stevie

DJ SprinklesNJO

thanks stevie, but the box will be sealed. so can it still be doubled. lol. also just for everyones info plans are in effect to make two chambers. ill try to do it that way.
ps whats internal wadding?

stevie

Jimmy - it's the soft, fluffy stuff (or foam) that you find inside speaker boxes, usually stuck against the walls.

Stevie

DJ SprinklesNJO

oh ok thanks. i guess i call it somethng different, but i know what ur talking about. let me ask you this. is there a difference when that stuff is added and when it is not in the box. i know it can be used to correct boxes that have been built too small but for perfect dimension boxes, does it make the sub sound better. or more bass etc.

stevie

>does it make the sub sound better. or more bass etc.

It depends on the passband and size of your sub. Under 80 Hz, you might as well leave it out, as it can do more harm than good by moving about.
The main thing wadding does is dampen internal resonances that can escape through the ports or the cone - even through the cabinet itself. The internal resonant frequency of a 3 foot long cabinet is somewhere around 160 Hz (from memory). That would require damping unless you are using a 24 dB per octave crossover.
If you have a cabinet whose main dimension is 1.5 feet, your main standing wave is going to occur at 320 Hz, which will be about 24 dB down even with a 12dB per octave crossover and well out of harm's way.

Stevie

stevie

The above also explains one of the disadvantages of free-air sub installation and why treating the trunk acoustically is beneficial.

Stevie

stevie

Biggie,

You don't get cancellation with two drivers; if the drivers are the same, you get addition.

What you don't get is lower bass (a common misconception). You get greater efficiency, higher maximum output, and lower distortion for a given sound pressure level, which should equate to a cleaner sound. But anyone doubling up on drivers to get lower bass is in for a disappointment.

Steve

Mean Gene

Jimmy - To give ya a little less technical opinion ( maybe we should let Stevie & Percy handle the technobabble 'cause it's WAY over my head!! ) the wadding is commonly referred to as polyfill & it not only reduces the internal resonance but slows down the backwave ( making the woofer "think" it's in a larger enclosure ). Does it work? Based on some playing around years ago I'd say "Yes", but only to a degree. It won't raise your SPL by a full dB but I did get an average increase of almost .5 dB. The rule of thumb is to start with about a pound of polyfill ( easily available from Crutchfield & relatively cheap ) & go from there. Of course, U'll need a meter to register any improvement ( if there is any ). U can always remove it. This is assuming U're using a box w/o plexiglass - it'd be really ugly to see the polyfill thru the glass!! U could also try Percy's Deflex material - totally different animal ( looks sharp in a sub enclosure, though ).

DJ SprinklesNJO

uhm ok wow thats a lot of info. all great stuff. but what ive come to learn is building a box is extremely technical. and im sure it takes many tries and many boxes to get a nice sounding one. ohwell. i want to try anyway. thats the whole fun of it.

stevie

>the wadding is commonly referred to as polyfill

Gene and Jimmy

Hey - I'm doing my best here. It's not known as polyfill where I live- You may not have noticed, but I am spelling centre 'center' and calling a boot a 'trunk' and the rear parcel shelf the 'rear deck'.

Just don't ask me to sing the Star Spangled Banner, 'cos I don't know the words-

Stevie

DJ SprinklesNJO

stevie, ur doin fine, its not ur words its jsut some things we dont understand yet. all this techincal talk.