bigbird said:
as far as i know, the bigger the box the better the sound resonance. i think its ur no names that are the problem. i had some no names that i got for about 50 bucks a piece. they SUCKED.
Um. No. No. No. No. If you look up the specifications for any respectable sub, they will list the size the box should be. They will usually give both sealed and ported sizes (as they is a big difference between the two styles). For instance, here's a website that lists the requirements for the sub I'm running:
http://www.cardomain.com/item/ROCRFR3110
Look at the bottom:
Subwoofer Specifications
Size: 10 inch
Sealed Box Dims: 0.63 - 0.63 cu. ft.
Ported Box Dims: 0.75 - 1.75 cu. ft.
Free Air Usage: not recommended
Sensitivity: 83 dB
Now, my box is ported, and is 22"x11.5"x11.5". So, using LxWxH=2909.5 cubic inches. Multiply that by 0.0005787, and we get 1.68 cubic feet. Right in the specifications for my sub.
Now, let's look at yours, We'll use the 12" numbers from the 12" version of my sub:
Sealed Box Volume 1.00 cubic ft.
Ported Box Volume 1.75 - 4.0 cubic ft.
20x18x22 = 7,920 Cubic inches, multiply that and we get, 4.58 cubic feet. Since you've got some generic 12" and not a 1000Watt RMS sub, we can safely assume your box is too large (especially if it's a SEALED box). However, there are multitudes of things that could make it sound worse.
1) Cheap Sub. Face it, it's cheap, it's a no name, it's probably not going to be fantastic.
2) Cheap Amp. Could also be underpowered, or just not suited to the task. Bridged? Mono? Class D? etc.
3) Resistance. What's the stable load the amp is built for? Is the sub correct? or is it 8ohm and your 4ohm steady amp is having issues?
4) Crossover. Are you feeding all the frequencies to the sub? or do you have it limited to a certain range? You don't want to feed 20khz to a sub.
You do not just want to build a box as big as possible. It just doesn't work that way. Then you throw in the location, size, and depth of the port and it becomes even more complex. Then comes in little things, like batting, and how well it's sealed.