# Non Powered Sub Vs. Power Sub



## jjharmon (May 5, 2007)

My question is home theater related.

I have an Insigina surround sound system. It is a piece of crap, the speakers are fine but the receiver is trash. (Won't power on)

I have bought a new receiver to replace it. (Harman Kardon AVR 140)

The new Receiver needs a powered sub. 
Now I planed on using my existing speakers; but my current sub is not powered
Can I convert it to a power sub some how?

2nd question on the same subject

What is an OHM and how does it effect my speakers if the rating doesn't match the receiver...
Are we talking sound quality issue or a FIRE issue here?


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## kiwiguy (Aug 17, 2003)

If you have a non-powered sub you need a sub amp that is powered to drive it.

An Ohm is a unit of resistance, if the Ohm rating of the speaker is lower than that of the amp, the amp can overload and cook the output, it will try and deliver too much current into the lower ohm rated resisance of the speakers. E.g if the amp is 8 ohms and the speaker is 4 ohms, damage to the amp could result.

If the Ohms rating of the speaker is higher than the amp, the volume will be lower but all will be safe.


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## jjharmon (May 5, 2007)

Where can I get a sub amp... or would it be cheaper to get a new powered sub?


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## kiwiguy (Aug 17, 2003)

No idea, you should ask at your local audio store, armed with the specs of the speakers and the receiver. I doubt it will always be an "in stock" item and may be hard to locate.


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## ioTus (Sep 26, 2005)

The Ohm thing is in relation to speaker "impedance". impedance=resistance, so more resistance, tells the amplifier it doesn't need/want as much power. It /resists/ the power flow.

An amplifier works by charging capacitors up with power, which it then feeds to your speakers as they call for it (based on the amount of impedence at the time, it fluctuates w/ frequency depending on the speaker), if the impedence of the speaker is too low, it calls for ALL of the power from the capacitors, and more, and so you start getting power directly from the wall. yikes! bad things happen here.

Powered subs are rather common. But if you dont want to go out and purchase a new sub ($350 for a really nice one), or a new amplifier for the sub you have (which you could probably get for under $100), you could wire the sub inline w/ the speakers (say, maybe the front channels). This would only be advisable if the sub is meant to do this, though (as in, it has a passthrough, or a set of both "audio in" and "audio out" connections). This method also requires that your sub have what's called a built-in crossover, which is something that will strip off the low frequencies to the sub and pass on the rest to your mid/high pair.

If you want to investigate this further, read up in your manual for your sub, or message me and we can figure out what will work best.

Hope this helps!


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## bdimag (Apr 8, 2001)

ioTus, you seem to know your stuff - and this has just been a curiousity of mine for a while...

Maybe its bridging? But, for example, can you have 2 speakers on 1 channel, the positive of the amp going to the positive of the first speaker, the neg of that speaker going to the positive of the other speaker, and the negative of that going back to the amp?

Or is that what you were talking about, and do speakers need to be made specifically to do this?


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## ioTus (Sep 26, 2005)

OK, what' you're referring to is a bit different than what I mentioned above. First, to explain what you described:

*What you described is two speakers wired in "series"*
Using one channel of an amp, wiring the + of the amp to the + of the 1st speaker, the - of the first speaker to the + of the 2nd, the - of the 2nd back to the - of the original channel on the amp. This is called "Series" wiring, and will actually make the sound quieter. The reason why is that it will take the impedence rating of the two speakers and add them together, so if you have two 4 Ohm speakers wired in Series, the resulting circuit will have an 8ohm load and will hence draw LESS power from the amplifier, and be quieter. Most aplifiers will be fine with this, as it doesn't tax them much more, in fact runs them at half power.
*A pair of speakers wired in series off one amp channel:*









*The alternative would be wiring them in "Parrallel."* In a parrallel circuit, the + of one channel has two wires coming out of it, each going to the + of each speaker, as well as two - wires, one to each speaker's - connection. In this circuit, there is an overall impedence of HALF of the speaker's impedence, so if you have two 4 Ohm speakers, they will register as (a single) 2 Ohm load, thus demanding DOUBLE the power from the amp. Don't do this unless your amp specifically says it can handle the load. Here you run the risk of overpowering and damaging the amp, and bottoming out and physically damaging your speakers (as the cone will move so much it will hit the chassis).
*Speakers wired in parrallel:*









*Bridging is where you take two channels of an amp and "bridge" them with a circuit.* It requires two channels, (presumably a Left and Right channel), taking the - of one channel and the + of the other, and wiring a speaker (or series/parrallel set of speakers) in between. This has the same result as wiring two speakers in Parrallel, so this will halve the power rating of the speaker, and deliver DOUBLE the power from the amp. Again, I wouldn't recommend doing this unless it is suggested by the amp manufacturer, as you can overheat the amp or damage the speakers.









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*Crossovers*
What I was referring to above is called a "crossover" circuit. This takes your two speaker cords (input of left + and -, right + and -) and peels off the low frequencies (say, 200Hz and lower), and delivers them directly to the sub. The rest it spits back out (output of left + and -, right + and -) w/ the rest of the frequency range (perhaps 200Hz to 22kHz) to be delivered to your front two speakers.
*An "active" type crossover in a powered subwoofer:*








Note that in the above picture, there are 4 red and 4 black connectors on the back. the left 2 red and 2 black are the input, the right 2 red and 2 black are the optimized output.

There are also "passive" crossovers that don't require power, which appear in non-powered speakers and utilize various circuitry and transistors and such to filter out frequencies.

Hehe, I realize that can be a bit much all at once. Did any of it make sense?

Hope that helps some!


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## bdimag (Apr 8, 2001)

Best read of the day.. i love audio equiptment.. 

I knew what "bridging" was, its just that I asked somebody the same question and they reffered to it as bridging for whatever reason... and didnt know a damn about the ohm situation... 

and same with crossover - im sure that helps the OP though..

---

also helps explain a situation that occured recently - I helped my friend install his amp (speakers were installed by previous car owner).. He got his amp 2nd hand and free (which is good in hindsight) - it was a 2 channel and he needed 4.. so I parralleled them - then all of the sudden they stopped working (?).. so i put them in a series and noticed they were much quieter.. and now I know..


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## ioTus (Sep 26, 2005)

Hahah, nice!! Yeah I learned much of this as I went, as well. I did a few car installs, then realized that as fun as the outcome was, it wasn't worth tearing the entire car apart and customizing it (and sacrificing half of my skin and blood to the speaker gods), and all the money spent just to drive around a car.

So now I'm into home theater hi-fi, heheh!


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## bdimag (Apr 8, 2001)

you get down with vintage hi-fi?


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## ineedhelp890 (Jun 23, 2004)

I would probably recommend just buying a cheap powered subwoofer as you will get a much better result. On another topic good choice with the Harman / Kardon receiver. They make, in my opinion, the best home theater receiver on the market. If you do decide to power the sub with an external amp, the cheapest solution would be to find a cheaper pro amp, as most home theater amps are higher end and will cost you a lot more than a cheaper pro audio amp. In the end it will be cheaper and probably better to buy a power sub though.


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