8ohm receiver to 4ohm questions

Posted by: jimmydj

8ohm receiver to 4ohm questions - 12/09/13 12:58 PM

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
Posted by: tomtuttle

Re: 8ohm receiver to 4ohm questions - 12/09/13 02:26 PM

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.
Posted by: Ken.C

Re: 8ohm receiver to 4ohm questions - 12/09/13 02:53 PM

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.
Posted by: jimmydj

Re: 8ohm receiver to 4ohm questions - 12/09/13 03:37 PM

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
Posted by: Murph

Re: 8ohm receiver to 4ohm questions - 12/10/13 07:54 AM

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.
Posted by: jimmydj

Re: 8ohm receiver to 4ohm questions - 12/10/13 10:38 AM

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
Posted by: Murph

Re: 8ohm receiver to 4ohm questions - 12/10/13 12:14 PM

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.
Posted by: jimmydj

Re: 8ohm receiver to 4ohm questions - 12/10/13 01:12 PM

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
Posted by: jimmydj

Re: 8ohm receiver to 4ohm questions - 12/10/13 01:14 PM

Basically i Jus wanna know if running huge wire to the sub will compensate some for the 4ohm resistance
Posted by: alan

Re: 8ohm receiver to 4ohm questions - 12/10/13 01:55 PM

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
Posted by: jimmydj

Re: 8ohm receiver to 4ohm questions - 12/10/13 03:04 PM

Thx a lot maybe ill try running a crossover ,great info to know
Posted by: ClubNeon

Re: 8ohm receiver to 4ohm questions - 12/10/13 05:29 PM

Instead of a crossover, get an amp. That's really how home systems are designed to run. The receiver powers the 5 or 7 channels of speakers, but the subwoofer is fed a line-level signal, and is expected to have its own dedicated amp.
Posted by: tomtuttle

Re: 8ohm receiver to 4ohm questions - 12/10/13 06:01 PM

I'm really worried that you're going to end up frying your receiver by cobbling all this together.

If you REALLY want to make the sub driver and enclosure "work" with a home theater receiver, your best approach - by far - is to use a separate, dedicated subwoofer amplifier that would be connected to your receiver with an RCA cable.

Parts Express has all kinds of stuff.
Posted by: SirQuack

Re: 8ohm receiver to 4ohm questions - 12/10/13 07:12 PM

ditto what Tom said
Posted by: jimmydj

Re: 8ohm receiver to 4ohm questions - 12/11/13 11:28 AM

Yeah I'm probably gonna gobdown that road Amd I.need new speakers anyway