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Old 6th August 2012, 08:36 PM   #11
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Quote:
Originally Posted by madtecchy View Post
isit not true that woofers designd for in car use are of the spec range to suit a small enclosure ???????
Small but lossy
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Old 6th August 2012, 09:52 PM   #12
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On WinISD (pro), key in the driver's T/S parameters, add a Linkwitz Transform, then look at the Amplifier apparent load Power (VA). This'll give you an idea of how much power is being pumped into the drivers to do what's needed.
A Linkwitz Transform forces excursion by increasing power input. The smaller the sealed cabinet, the more amplifier power needed to move the cone around.
The maximum SPL of the system is the same for infinite baffle (mounted in-wall) as a tiny sealed cabinet, so long as the driver's power ratings are not exceeded.

You have a pair of 12" drivers, so I'd expect 30Hz to be a reasonable target. You could go for lower, but the maximum overall SPL available drops further.
You could use a tiny cabinet, and throw loads of power in (this is what most commercial subwoofers do) - this is why I mentioned the Amplifier Apparent Load on WinISD - you can find out how much power is going in, and then pick a compromise between extension, SPL, and driver safety.

Chris
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Old 7th August 2012, 04:45 PM   #13
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Quote:
Originally Posted by chris661 View Post
On WinISD (pro), key in the driver's T/S parameters, add a Linkwitz Transform, then look at the Amplifier apparent load Power (VA). This'll give you an idea of how much power is being pumped into the drivers to do what's needed.
A Linkwitz Transform forces excursion by increasing power input. The smaller the sealed cabinet, the more amplifier power needed to move the cone around.
The maximum SPL of the system is the same for infinite baffle (mounted in-wall) as a tiny sealed cabinet, so long as the driver's power ratings are not exceeded.

You have a pair of 12" drivers, so I'd expect 30Hz to be a reasonable target. You could go for lower, but the maximum overall SPL available drops further.
You could use a tiny cabinet, and throw loads of power in (this is what most commercial subwoofers do) - this is why I mentioned the Amplifier Apparent Load on WinISD - you can find out how much power is going in, and then pick a compromise between extension, SPL, and driver safety.

Chris
After doing a little more research into the Linkwitz Transform, I'm starting to think that this may be the way to go. I can keep the enclosure sealed and consiquently small, which was the main goal of the project. I'm not clear on something though, is the circuit essentially a pre-amp eq or is it a line level filter/booster? Also, what do they typically cost to build? I didn't state my design goals in the beginning, but the secondary consideration was minimum cost. Since I have the drivers and the amp on hand, all I need is some MDF, (which I can get for free from my cabinet maker),a port will be required if I go ported, some ancillary materials for finishing and such, and some grill cloth. So I'm looking at maybe $50 in the end. Probably more like $30 for total project. I'm willing to spend more to get a better product in the end, but I'm diverging from my original goals by doing so.
Thanks again!
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Old 7th August 2012, 07:34 PM   #14
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Download the spreadsheet and have a play around.
Linkwitz Transform Subwoofer Equaliser
It's likely better to use WinISD to figure out the right Qp and Fp WRT excursion, power handling etc, but the spreadsheet will tell you the values.

I could make the circuit (completely from scratch) for ~ 10.
It's a TL072, a couple of resistors and capacitors, and some stripboard (see below - you guys in the USA might call it something different)

Click the image to open in full size.

You'll need a split power supply. For a test, you could use say 8x AA batteries, giving a +/- 6v supply. The current draws for the chip will be tiny, so they'll last for a long time.
For more long-term use, you could use a 12v wall-wart, but you'll need to split the supply using some resistors, and add caps to block the DC on the input and output (the whole thing would sit at +6v to stay half-way up the supply).

Chris
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