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PostPosted: 10 Jul 2014, 20:41 
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Joined: 06 Apr 2014, 03:15
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Hi, I am a nube to all of this, so forgive me if this is a dumb question. I have two speaker boxes, each with an 8" 8 ohm speaker and tweeter, which I drive with a 20w class D stereo amplifier. This system does a great job with music from my ipod or computer, but I want to add a subwoofer. The amp just has the two output channels, but is there a way to send a mono signal from the amp to the sub? Do I need a different amp with a sub output or can I use a filter/crossover?

Any advice would be welcome

Thanks


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PostPosted: 12 Jul 2014, 08:49 
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Joined: 26 Oct 2012, 21:00
Posts: 201
Location: ontario canada
mono summing at speaker level is not practical or advisable and with only 20 watts available you would better off looking into a passive line level crossover(google "PLLXO") and an amp (mono or stereo bridgeable) to drive your sub.
perhaps a "plate amp" with a diy box with a decent driver would fit the bill or are you looking to "make it so" with what you have?


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PostPosted: 12 Jul 2014, 20:43 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
I would go for a plate amp as well. Parts Express carries on that would work for you at $35. Part number 300-782. With it and a cheap woofer in a box you would be good to go....at the same time there are many powered subs on the market now for under $100 and you don't have to build anything.

Good listening
Bruce

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PostPosted: 14 Jul 2014, 15:02 
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Joined: 06 Apr 2014, 03:15
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gofar99 wrote:
I would go for a plate amp as well. Parts Express carries on that would work for you at $35. Part number 300-782. With it and a cheap woofer in a box you would be good to go....at the same time there are many powered subs on the market now for under $100 and you don't have to build anything.

That was another question I had. I was looking at powered subs on Parts Express and was wondering if that means they are amplified or if you still need to amplify them. Sounds like powered means they have a built in amplifier, but correct me if i'm wrong.


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PostPosted: 14 Jul 2014, 18:42 
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Joined: 09 Oct 2012, 19:43
Posts: 338
Location: Vancouver Canada
You are right in thinking powered subs have their own amp built in. Also most of them have the necessary cross-over built in as do the plate amps and powered- sub units already suggested in this thread.
So if you wish to build your own box and buy separate spkr for a DIY spkr project buy the plate amp, If on the other hand you want an all in one unit but the ready made powered subs available and all that is needed is to hook up the wires and enjoy.


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PostPosted: 30 Jul 2014, 17:14 
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Joined: 30 Jul 2014, 02:00
Posts: 5
Location: New York City, USA
I was planning to power my subwoofer project (a 6x9 Tang Band in a 0.2 cu ft box for my computer) with one of the LM3886 chipamps fed from a summed L/R input (preamp level, not amplified) with a high-pass cut filter so I only get 10Hz to 150Hz. Granted, I have power because I'm piggybacking on the same (beefed up, though) power supply as for the speakers, so I don't need to buy a separate one.

I ran various power output numbers through modeling software and discovered about a 10db difference between 5W and 50W, and 20db between 5W and 100W. In practice, this means @ 100Hz I get 90db vs 75db, but more like 20db difference below 100Hz. This is fine for my computer, but not so fine for your outdoors project. You'll need a LOT of power, and that means, as was noted by others, a plate amp of some sort.


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