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8ohm receiver to 4ohm questions
#399167 12/09/13 05:58 PM
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Hi in new to the forum and just have a question about impediance ,I have a 7.1 home receiver and a polk audio 4ohm sub,I want to know if there is anyway to use two sepreate 8ohm channels to power a 4ohm sub, I don't want to over heat my receiver. Thx

Last edited by jimmydj; 12/09/13 06:08 PM.
Re: 8ohm receiver to 4ohm questions
jimmydj #399171 12/09/13 07:26 PM
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Are you saying the sub doesn't have it's own amplifier?

The answer depends on your receiver, but most aren't set up to output the main LCR signal to more than one channel.


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Re: 8ohm receiver to 4ohm questions
jimmydj #399173 12/09/13 07:53 PM
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In any case, you cannot connect two channels to one speaker without risking extreme damage to the amp--there's nothing to stop the output from one channel from just going on into the other channel.


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Re: 8ohm receiver to 4ohm questions
jimmydj #399174 12/09/13 08:37 PM
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Wow even if their both output channels some of that power can come back into the receiver? It is not a powered sub, basically its a "car sub" Thx BTW I have a Denon act 95 hard to find a manual for it so I'm not sure if it could even handle 4ohm by itself, which I doubt ,so many conflicting facts and answers online

Last edited by jimmydj; 12/09/13 08:51 PM.
Re: 8ohm receiver to 4ohm questions
jimmydj #399180 12/10/13 12:54 PM
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Hi there.

Is it still in a car shaped enclosure? It would be interesting to hear this in a room environment. Very different designs.

Basically, the safe thing to do would be to purchase a separate amp for it. Then you can hook it up 'properly' to you receiver and have control the low frequencies it receives.

If you try to hook it to even just a single channel (say assigned as a front) on you Denon, it's going to receive the full frequency range instead of just the low frequencies that it would be limited to if it were attached to the proper sub output.

That means, whomever built your sub better have included a built in crossover component to block those higher frequencies, as the Polk driver by itself, just wasn't built for that and it will sound awful, at best.

So if your going to the trouble of building a sub enclosure with a crossover, might as well add the built in amp as well and do it right.

Note: This isn't meant to discourage you. Building and experimenting is fun.


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Re: 8ohm receiver to 4ohm questions
Murph #399183 12/10/13 03:38 PM
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Yes it is in a car enclosure its a single VC woofer I have an amp as well ,I thought about taking a power source from a desktop pc and dedicating it to the amp but that's a bit of a process, I've seen it done, I guess there's no way to hook it up to the sub out on the receiver ,I think there's Jus too much resistance 4ohm,I

Re: 8ohm receiver to 4ohm questions
jimmydj #399186 12/10/13 05:14 PM
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If you hook it up to the sub-out and use an external amp, the resistance is irrelevant to the sub out on your receiver. The 4 ohms will be a factor between the sub and the amp.

I assume you are mentioning a PC PSU to the amp cause the amp is also an auto variety.

I would suggest that you do a bit of Googling on home made sub building. There is a lot of good info out there on building subs and connecting them properly in a simple manner.

It's not that you can't make all this work in the end with auto parts if that is your goal but, respectfully, I think it's adding a bit of extra complexity for a first project.


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Re: 8ohm receiver to 4ohm questions
jimmydj #399188 12/10/13 06:12 PM
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What If the sub is within 10 feet of the receiver using larger12ga wire will that lessen the resistance and be acceptable? Jus a thought

Last edited by jimmydj; 12/10/13 06:12 PM.
Re: 8ohm receiver to 4ohm questions
jimmydj #399189 12/10/13 06:14 PM
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Basically i Jus wanna know if running huge wire to the sub will compensate some for the 4ohm resistance

Re: 8ohm receiver to 4ohm questions
jimmydj #399190 12/10/13 06:55 PM
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Hi Jimmyd,

Using a 12-gauge speaker cable to your sub won't lower the resistance presented by the subwoofer to the amplifier. The impedance of a speaker is largely determined by the voice-coil windings of the driver in the sub, and the crossover, if you decide to build one or buy a simple analog crossover.

Of course, it's always good to use a 12-gauge speaker cable so you don't raise the resistance (and waste power) presented to the amplifier. For short runs, you could even use thinner cable like 14-gauge or 16-gauge, which would not significantly increase resistance.

Regards,
Alan


Alan Lofft,
Axiom Resident Expert (Retired)
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