Help with Diy Sub

Riaad · 07-29-2003, 02:21 AM

Hi

I am very keen in building a Diy sub.My dad is a cabinet maker by trade so the skills and tools needed are definitely there.I have read that DIY subs will out perform $ for $ compared to over the counter subs.

The problem I have is that I live In South Africa and there is nothing available in regards to drivers, plate amps etc.
for home theater.
Could I maybe use some car drivers that will work well for home theater as well?

Please advise on what my options are.Would purchasing online be worth it in terms of price and what about warranty?.If so could you suggest who to buy from?

Please help.

Riaad

Derek*k · 07-30-2003, 09:50 AM

Well, car subs are often ill-suited to the task, but every once and a while you'll find one that fits the bill. Here are a few things to look for:

First off, if you can't find the T/S parameters for the sub (or the manufacturer doesn't make them available), run, don't walk, away from the driver.

2nd, make sure the Qts of the driver is .28-.45 and that the Fs is less than about 30hz. Good excursion is also neccisary, so 8-10mm is just about the minimum. Likewise, those excursion numbers are one-way, so if the manufacturer lists the Xmax as "peak to peak", double the numbers I listed above.

Vas is something else to look for. For a 10" driver, Vas should be in the 60L range, 12" no more than 120L, and 15" no more than 180L. If the Vas is higher, then you'll have a real hard time building anything but a sealed box for it. Smaller Vas numbers are rarely a bad thing.

D.

Geoff L · 07-30-2003, 10:36 AM

Riaad

Can you list some of the driver brands, home or car available in your area...??

Regards
Geoff

Brian Fellmeth · 07-30-2003, 10:53 AM

Don't sweat trying to find a "plate amp". Any audio amplifier works fine as a substitute (assuming you plan on using a HT receiver as a source). Just install speaker wire binding posts and position the amp out of the enclosure. Monoblocks, Integrated, pro gear or even old audio receivers all work fine so long as they have enough power.

Ryan Schnacke · 07-30-2003, 10:25 PM

"Smaller Vas numbers are rarely a bad thing."

Actually if Vas is small enough it can cause you some headaches when trying to build a vented subwoofer. In order to keep vent airspeeds down you might need a 3" or 4" or larger port. But as the diameter of the port increases, you must make the port longer to reach the same tuning point for a given box size.

At some point the Vas can get small enough that you cannot fit the required port into an enclosure that meets your alignment. You'd be forced to use passive radiators, which greatly increase the cost of the subwoofer, or go with a sealed sub.

The Vas values listed above are good for most DIY home subs.

**HTF Ads**

Derek*k · 07-30-2003, 11:19 PM

Quote:

At some point the Vas can get small enough that you cannot fit the required port into an enclosure that meets your alignment. You'd be forced to use passive radiators, which greatly increase the cost of the subwoofer, or go with a sealed sub.

...or you build a slot port.

Frank Carter · 07-30-2003, 11:26 PM

I thought I Adire Audio had a dealer in South Africa.

Riaad · 07-31-2003, 04:05 AM

Hi Frank

I just checked out Adire Audio's website and they do have a listing for Africa. However they don't specify which part.I have emailed them and hopefully I will get some good news .

Thanks guys for all the info. Ill do some searching for drivers which match the suggested criteria and let you guys know.

Riaad

JoeFish · 07-31-2003, 10:12 AM

Quote:

2nd, make sure the Qts of the driver is .28-.45 and that the Fs is less than about 30hz. Good excursion is also neccisary, so 8-10mm is just about the minimum. Likewise, those excursion numbers are one-way, so if the manufacturer lists the Xmax as "peak to peak", double the numbers I listed above.

I have an automotive sub (MTX 7000 series 12") that mostly fits the bill, except for the Qts. What effect will a higher Qts have on a home theater subwoofer? I'm planning a sealed box. Here's the T/S params:

Fs 26.4 Hz
Vas 3.18 Ft^3 (90.1 l)
Qts .55
Qes .59
Qms 9.20
Re 3.61 §Ù
(One Way) Xmax .50¡± (12.7 mm)
D 10.125¡± (.2572 m)
RMS 400 Watts
Total 1000 Watts
Sensitivity 1W/1m SPLo 86.8 dB

Thanks,

-Joe

Derek*k · 07-31-2003, 10:23 AM

That's actually not too bad. A 3.5ft^3 box with about 3lbs of stuffing would give you a sealed F3 of around 36hz and usable output down into the 20hz range. 4ft^3 would give you a few more hz of extention, but at the expense of power handling. Because of the size of the box (the higher Qts is what did ya in), I wouldn't power it with more than about a 120W amp in any event. That's still plenty to get you up around 100db in your average living room.

I think it's worth doing. It should sound great with music (not boomy or flabby at all), and respectable with HT.

Oh, and it's pretty unsuitable for a ported box.

JoeFish · 07-31-2003, 12:31 PM

I just plotted out the freq response, and it looks good. It looks real smooth - I plotted it against the Adire Shiva, and it looks like a carbon copy, except it's 3db higher, and starts to fall off about 10hz lower. Nice!

The only thing is, using Unibox with heavy fill and a Qtc of 0.707, Vb for the Adire if 45.6l, and the MTX is a whopping 183.0l!! That's over 6 cu ft.

Let's see...if I drop Vb to 100l (just over 3.5cu ft)...Qtc goes to 0.770...Fb is 34.75hz. The graph still looks pretty favorable, with a little hump around 80hz. hmmm...

-Joe

Derek*k · 07-31-2003, 01:02 PM

...hence the reason I said for the 3lbs of stuffing to bring the Q back in line. Still a little high, but not unfavorable, especially for music where a little better damping will get ya a bit more bump (but we're still talking a LOT less than your average >1 Qtc car audio box).