Converting 4 ohm speaks to 8 ohm

 

Does anyone know the proper method of adding resistance to speakers so my 4 ohm speakers will be compatible with my 8 ohm receiver? My Sony str-d711 goes into "PROTECTOR" mode when I turn volume up to approx. 1/3. Sony says since we have eliminated other possible problems thru their trouble-shoot guide, it probably is the lack of proper resistance in the speakers which the receiver interprets as a short in the system. Anyway, Radio Shack guy says a simple in-line resistor won't do it, it is some "very complicated" and expensive endeavor, & that only a "technician" could do it prpoerly. Any ideas???
 

John Allen
When I did school Physics, two resistances in series gave a combined resisitance that was their sum. I don't think this has changed. Connect a 4 Ohm resistor anywhere between one speaker terminal and the corresponding terminal on the amp, and you add 4 Ohms to what the amp sees. The amp doesn't know, or care, whether the load is a speaker or a lump of wood.
 

Kar
How does the changing frequency affect the total impedence? If at all
 

John Allen
I cannot see where frequency comes in. That is just the number of times the current changes direction each second. The speaker may offer a different impedance at different frequencies, because it is using the current to drive something mechanical, with different resonances and different loads at different frequencies. But put a blind 4 Ohm resistor in the way, and you just add 4 to whatever the impedance was before, at any frequency you choose.

My electronics is very simple minded, I admit.

I would try it. A pair of 4 Ohm resistors is not a big outlay.

The worst that can happen is that it doesn't sound so good, like having very long or very thin speaker cables. You will be able to tell.
 

John, your logic concurs with my own. I went in to the local radio shack and found that the resistors were rated for ohms and watts. I couldn't find a 4 ohm resistor that came close to my watt needs. Was I looking at the wrong section of resistors?? Like I said before, the clerk in the store shot my idea down and wasn't very helpful, unless he was correct in that a simple resistor would not work. In that case I guess he was helpful, but I can't understand why it would be so complicated...
 

John Allen
TCS on another thread agrees with us, Terry. But you will need a resistor that will take the power in Watts. If Radio Shack does not have one, you will have to find an electronic components supplier.

Here is the thread:-

http://www.ecoustics.com/electronics/forum/home-audio/5654.html
 

Thanks, that sounds great. I'll check with a larger Radio Shack and hopefully find a bettor selection of resistors. If that fails, surely I'll be able to find a supply house on the net...
 

John A.
I think it has to work OK. You will need a higher volume control setting for the same real volume. It is just possible it will play louder, though, in the end, because you will be able to turn the control way beyond one third without the receiver thinking there is a short. Please report back!
 

We'll do. It'll take a few days to get the supplies...
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