Hooking up 4ohm speaker into amplifier rate at 8ohm impedance?

[MinusTheBear]

What is the difference between speakers that are specified at 4ohms and at 8ohms. My reciever is specified at 8 ohms impedance on all channels (front, centre, rear etc) but the speakers that i want to put in the rear channel are rated at 4 ohms (all my other speakers are rated at 8 ohms). My question is can i do this and what are the consequences on the amplifier if a 4 ohm speakers is hooked up to an amp rated at 8 ohms.

 

[Davemcc]

Which reciever? It matters.

 

[MinusTheBear]

The Amp is an Onkyo A-SV620...it is an older model back in the early 1990's.

Front L/R - 120 watts per channel at 8 ohms (Stereo mode)
Coninous power ouput 2x140 watts at 8 ohms

Surround Mode

Front L/R, Centre = 75w each at 8ohms
Rear Channel - 25W each at 8 ohms

 

[Rickster71]

One option I've used in the past:
In your case, add a 4ohm resistor in series,
to the + terminal of the speaker.
It has to be rated wattage of your receiver.
You could solder it, and put shrink wrap over it.
It's a cheaper option than getting a new receiver or speakers.

 

[MinusTheBear]

Thanks for your response. I do not quite understand how that works and i have no soldering equipment available. Are there any other options I have or am i just out of luck.

 

[annunaki]

Crimp caps would work instead fo soldering. The resistor option should work but will soak up a bit of power. Make sure the resistor can handle at least 25 watts rms.

 

[fmw]

Thanks for your response. I do not quite understand how that works and i have no soldering equipment available. Are there any other options I have or am i just out of luck.

Neither do I because it doesn't work. Adding a resistor in series with your speakers will change the resistance of the load, causing it to require more power to drive but not the impedance. Impedance is not the same thing as resistance. It is an AC measurement. Some people get confused because the ohm is unit of measure for both of them.

The simple solution for you is to try it. The problem is that 4 ohm speakers draw more current than 8 ohm speakers. So it is possible that you could exhaust the power supply's ability to feed the amplifer enough current. So keep the volume under control and, if it starts sounding even slightly bad, then turn it down because you've gone past where you should. Hope this helps.

 

[j_garcia]

Even if you get the impedance down, the amount of current it draws is not going to drop dramatically...it will still draw a fair amount of current. I agree with FMW, give it a try and see how it does since it could go either way with early Onkyo stuff.

 

[j_garcia]

Quite possibly. My speakers are all 4 Ohm also, and my 120wpc receiver wasn't happy driving 5 of them.

 

[MinusTheBear]

Thanks for everyone that has taken the time to post in this topic.

I am still a bit confused and if someone could clarify this for me. So what i got so far is that the 4 ohm resistor would work and somehow trick the amp into thinking it is a the right impedance, however this would degrade power to the speakers as well as sound quality so adding the resistor is not worth doing, but in theory would work???

 

[mtrycrafts]

The Amp is an Onkyo A-SV620...it is an older model back in the early 1990's.
Surround Mode

Front L/R, Centre = 75w each at 8ohms
Rear Channel - 25W each at 8 ohms

With that power limit, you may have a problem, but I you could test it as the rears usually don't demand lots of power. Just be careful with the volume.
You may need to get a different speaker back there or a new receiver.

 

[deedubb]

I suspect you'll be able to play those speakers at moderate volumes. The amp will probably shut down on you when you try to crank it up though.

 

[Rickster71]

I don't mean to imply it's a perfect solution.
I've used a resistor on speakers in a spare listening room, where I read the paper. So it's never really very loud. (for about 15 years)
Also with a pair of Niles outdoor rock speakers, for about three years.
No ill effects so far, albeit I've never tested with instruments.
I don't want to recommend anything that may damage their equipment.

 

[MinusTheBear]

My new question now is what reciever (7.1) in the price range between 400 - 700 dollars would handle mixing 8 ohm fronts and 4 ohm rears.

 

[PENG]

I don't mean to imply it's a perfect solution.
I've used a resistor on speakers in a spare listening room, where I read the paper. So it's never really very loud. (for about 15 years)
Also with a pair of Niles outdoor rock speakers, for about three years.
No ill effects so far, albeit I've never tested with instruments.
I don't want to recommend anything that may damage their equipment.

No it won't increase the likelihood of damaging equipment but it is a power waster because that resistor will dissipate power according to Power=CurrentXCurrentXResistance. Looking at it another way it drops the voltage. So the problem is it reduces performance. One will be much better off to, like mtrycrafts said, be careful with the volume and everything will be fine.

 

[mtrycrafts]

My new question now is what reciever (7.1) in the price range between 400 - 700 dollars would handle mixing 8 ohm fronts and 4 ohm rears.

One of the upper end Onkyo close to your upper limit should. They have more power all around, hence, it should handle that 4 Ohm speaker better back there.
As Peng indicated, a resistor will drop the voltage in half or so to the back speakers, that will reduce the volume. Then, trying to turn up the volume will just hinder the whole operation

If you like those rear speakers, a better receiver is the way to go and you will have one with modern features in sound processing.

 

[j_garcia]

With them set to small, they will also draw less current, so the load is a bit easier to handle. As has already been said a few times, just be careful with the volume knob and you should be OK.

 

[deedubb]

My new question now is what reciever (7.1) in the price range between 400 - 700 dollars would handle mixing 8 ohm fronts and 4 ohm rears.

harmon kardon receivers are reasonably high current and should be able to handle 4 ohms.

 

[MinusTheBear]

Thanks for the suggestions so far, keep them coming !

I was looking at the Onkyo recievers online and I know for sure the 805 will handle it but i do not want to spend that much if i dont have to, are there any other Onkyo models below the 805 model that could handle it. I was also looking at the Denon website and am not sure if the models in the price range of 400 -700 can handle it also.
I just got off the Yamaha website but found it very confusing for A/V recievers because i do not know what is the difference between each of the 3 models they have.

If anyone has any clarity on this that would be great

 

[PENG]

harmon kardon receivers are reasonably high current and should be able to handle 4 ohms.

Not according to the bench tests I have seen. They seem to have large power supplies in them but the amps do not seem all that strong.