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Old 28th January 2008, 12:04 AM   #1
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Default Budget T-amp system sub?

I recently acquired a gen2 Sonic Impact T-amp, which I am running in using the TV lineout into a couple of 40-year-old Wharfedale Dalesmans. The sound is great (apart from the TV which buzzes faintly through the supplied interconnect). Anyway it kind of rekindled my interest in budget hi-fi.

I have a pair of Audio Nirvana Super 8's coming whch I intend to build into the Commomsense Audio 2.8 cft enclosure. I figure this is a restrained and efficient way to spend money, considering the anticipated spl. The amp cost ~$100 US shipped and the drivers $250. Hmmm... budget.

For music listening I intend to run a T-amp into these speakers using an M-audio 2496 souindcard which I've got in a desktop computer. This soundcard has a good reputation as an entry-level tool for digital recording studios. I got a 4-channel Behringer mixer I can always interpose if I feel I need some EQ.

Now I'm thinking about building a subwoofer to complement this arrangement. It needs to be a genuine musical asset, and cost should be proportional to the rest of the system. I can build pretty much anything. The room is about 6x7x3 metres and fairly live.

I also need to connect it to the existing system and I'm not quite sure about how best to go about that.

I like efficient, I don't want to expend a lot of watts. I don't want to spend a lot of personal energy redesigning the wheel.

Any suggestions as to where to start?

w
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Old 20th February 2008, 12:59 AM   #2
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Hi wakibaki,
Efficient = largish box. I doubt you want a high order box, so a B4 would seem to be reasonable unless you stick with a smallish woofer and high cutoff frequency. Some 8" Peerless woofers will get you into the 35 +- Hz range. One older Peerless 8" ran about 28Hz, -3dB. Impressive. Vifa might get into the low 40s. Much higher than this and I would be thinking a damped port / sealed box. A 6.5" pretty much requires a sealed box and maybe a damped port.

If you want to reach lower, a good 10" woofer would work well. Again, I'd be thinking a B4 type box and expect a little over 20 Hz -3dB. That's lower than your room would support I think. You would really feel that.

Run it with something like an LM4780. I'm not into class D technology, and a chip amp would probably run less money and complexity.

Did you define your requirement beyond what you posted originally? I'm sure box size may dictate changes (possibly). A box built to the optimal size will be more efficient, higher order boxes are more difficult to get and keep tuned. Especially as the voice coil temp goes up.

-Chris
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Old 20th February 2008, 02:42 AM   #3
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As Chris says, higher efficiency usually means a big box.
A driver I was looking at a while ago might suit your needs. It's a Peerless 830668 and it's fairly cheap ($60.00 here).
Put this in a 60 litre ported box, and you'll have an F3 of 30Hz.

Output with 50 watts max would be ~106db. An LM3886 chip amp could be enough power for moderate use.

Response is slightly peaked, but this is the trade off for the smaller box. If you can accommodate a bigger box, lower F3 and a flatter response would result.
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Old 20th February 2008, 02:53 AM   #4
anatech is offline anatech  Canada
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Hi John,
That's what I had in mind. Also, the LM4780 is a stereo chip that can be bridged for higher power. Two mono type ICs would spread the heat out a little better if needed.

Thank you for doing the homework. ;-)

-Chris
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Old 20th February 2008, 11:13 PM   #5
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Quote:
Originally posted by anatech


Thank you for doing the homework. ;-)

I had this driver modeled already, plus a number of other ones, so not much work.

The LM4780 bridged would be the perfect choice for a mid sized sub like this - possible to get about 120 watts into an 8 ohm load with a +/-30 V supply. Not sure if wakibaki is into doing his own electronics though.
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Old 20th February 2008, 11:31 PM   #6
anatech is offline anatech  Canada
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Hi wakibaki,
Comments?
How close are we to your mark?

Hi John,
You know what? I suspect this would be a decent sub woofer. A front firing woofer would have impact that tends to get lost firing into the floor. I might be interested in this or some variation.

-Chris

Edit: John, I don't think you've had enough time to actually read much, but did anything in those books strike your curiosity?
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Old 21st February 2008, 04:05 AM   #7
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Quote:
Originally posted by anatech


Edit: John, I don't think you've had enough time to actually read much, but did anything in those books strike your curiosity?

They have been light bedtime reading . You're right though, I haven't had much opportunity to sit down with them for any amount of time.
Scimming through them, I can see that I really should have had these about 3 years ago when I seriously started in this hobby. Research on the internet has given me much of what is in those books, from one source or the other.
Great reference though.

PS: I've sent you a email.
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Old 21st February 2008, 08:13 AM   #8
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Sorry guys, I have a heavy workload at the moment, and limited spare attention.

I very much appreciate what seem on a quick scan to be some helpful and thoughtful replies. I will have a response when I get a chance to absorb them.

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Old 21st February 2008, 08:31 AM   #9
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If you find a reasonably efficient low-impedance driver, you can use this Class-D amp, 41Hz Amp9:

http://41hz.com/main.aspx?pageID=130

Sounds great, and you can parallel the outputs for quite a bit of power into 1-2 Ohm loads. Energy efficient and small.
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Old 21st February 2008, 03:41 PM   #10
anatech is offline anatech  Canada
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Hi John,
Thanks.

Now you have mail!

-Chris
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