Proper enclosure size?

[pistolpete]

If I am building a sub or any speaker for that matter, how do I determine the proper size enclosure? Do I rely strictly on Vas? Why or why not. Also, without the enclosure type known(sealed or ported), is Vas the same? What happens to the sound when the enclosure is larger or smaller than Vas? Too small equals less bass and too large equals sloppy bass, yes?
I am just trying to pick the minds of experienced speaker builders because I plan to build so more speakers in the future and enclosure size seems to be a little art and science.
Thanks, Pete

[Rudy Jakubin]

Qts, Vas, Fs all factor in.
Here's a good read for beginners;

http://www.hometheaterhifi.com/volume_5_2/cmilleressayporting.html

Here's a small computer program that once you get a handle on how to use let's you play to your hearts content on how enclosure size and type of box and drivers parameters affects frequency response;

http://www.linearteam.dk/default.aspx?pageid=winisd

[cjd]

Enclosure is built based on a collection of T/S parameters (of which VAS is but one)

Programs like Unibox or M.J.King's Mathcad worksheets allow you to enter this data and evaluate likely low end response of just about any enclosure you can imagine (M.J.King has almost everything available now though they're perhaps a bit trickier to use).

Beyond that, bigger does not mean sloppy bass at all - the ultimate in subwoofers requires effectively infinite volume (this is technically true of both dipole and IB subs though, of course, there is no box for a dipole setup). Volume changes alter the transfer function of the box - smaller = higher order which *can* equate to less bass extension. If you're talking ported, it can also mean worse response - heavy peaking or other less than desireable behavior.

If you have MS Excel available, I would suggest checking out Unibox (available free at the FRD Consortium). Pick a driver (any driver) and start to experiment with some of the settings. There are a lot of information charts available that can be quite valuable in evaluating a particular alignment. Good stuff.

You could also look into WinISD though I don't like it nearly as much - it does most of the same stuff though (may be a bit more confusing to use).

C

[pistolpete]

Thanks guys. While I have been in the audio hobby for many years, I am new to the DIY and seem to have a lot to learn.
Pete

[cjd]

I am new to the DIY and seem to have a lot to learn.
Pete

That's the ticket!

I've been in DIY for a little while now, and still have a lot to learn! Sit back and enjoy the ride.

C