DIY subwoofer

N

Nick_Black

Mirthmaker
yeas this is kinda one of those questions where I have little knowledge of what Im talking about... ok here we go.

I would like to build a subwoofer, diy websites tell me that closed/air tight enclosures are best, but how come most of the subwoofer enclosures you see have a sound hole?

and also, is there a way to "tune" a subwoofer? or is that best done via the software? (this subwoofer will be hooked up to my recording pc)

any sugestions/links will be greatly apreciated
 
The sound hole (port) is to allow air displacement from within the enclosure. The back side of a speaker moves air too.
 
thanks for the reply.

what kind of dimentions should the subwoofer box be then, becouse I don't want the "blow hole (I think that's what it's called) to phaze out some of the frequencies, and raise others... or is that how you would tune a subwoofer, by calculating what freq. you need, and boosting those parts?
 
Check out partsexpress.com. I got a lot of good info in the forums over there when I built my speakers.
 
Do you want to build an active subwoofer or a Passive one that will be powered by a external amp??

If doing the active route you will probably have to build some sort of Electronic crossover to limit the frequencies going to the Subwoofer from say 20hz to 400hz, A Salen Key Filter should be good for this Pluss electronicly they are easy to build:

You can use the "Filter Pro" software by TI to design your Filter....

http://focus.ti.com/lit/an/sbfa001a/sbfa001a.pdf

http://www.ecircuitcenter.com/Circuits/opsalkey1/opsalkey1.htm

For powering the Subwoofer Class D amps are popular but they have a pretty high distortion rate (10% THD) and are 1 Bit digital amps which makes they harder to build and they usually use a SMPS which isn"t very appealing when dealing with pro audio......
You could use a simple Chipamp topology useing something like a LM3886 IC which can put out up to 68w into 4 ohms or you can Bridge/Paralell multiple chips to output more power at different loads....I have built a few amps like these and they sound extremely good and are Very LOUD!!!

Here is some design software for designing Subwoofer enclosures.....

http://www.mobiledynamics.ca/resources/software.php


Hope this helps....

Cheers
 
A sub isn't going to help you record or mix unless you set it up VERY carefully - so take it easy & match its projection to a know music source.
 
Nick_Black said:
thanks for the reply.

what kind of dimentions should the subwoofer box be then, becouse I don't want the "blow hole (I think that's what it's called) to phaze out some of the frequencies, and raise others... or is that how you would tune a subwoofer, by calculating what freq. you need, and boosting those parts?
Click to expand...

It's called a port, and you can tune a subwoofer by changing the length of the port.

But at that point, you've already made most of the important decisions, which include the driver size and cabinet volume. Pay special attention to cabinet volume, because generally bigger is better. All the clever engineering that goes into subs is often a result of wanting lower frequency performance out of a smaller box, but there are tradeoffs involved. If you have space for a big box, you'll enjoy a much smoother bass response.

Once you select a driver (I would recommend 10" or 12"), try this tool here:

http://www.mhsoft.nl/SpeakerCalculator/index.html
 
been awhile since i screwed with this but IIRC you can get the box too big for a given driver... the air inside to some degree supports the driver and if too large it will unload as they call it... sounds like a fart... when you choose your driver the spec should tell you what size box the woofer likes best,,, generally given as quarts of displacement...
 
dementedchord said:
been awhile since i screwed with this but IIRC you can get the box too big for a given driver... the air inside to some degree supports the driver and if too large it will unload as they call it... sounds like a fart... when you choose your driver the spec should tell you what size box the woofer likes best,,, generally given as quarts of displacement...
Click to expand...

Oh yeah . . . but for a 10" woofer, that is a giant box size. Most people aren't thinking anything that large. It's hard enough to get them to build a box bigger than 12x12x12 . . .

The speaker design calculator I linked (and others out there too) will tell you the ideal volume for ported and sealed designs, based on the driver parameters. Most people doing a sub won't used a sealed design, but I like them for mains . . . my mains are sealed boxes with 10" woofers :)
 
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