My amplifier is rated at 8ohms for my surround sound but my speakers are 6 ohms. The owners manual says that if the speaker resistance is too low the power protector will blow and that is exactly what happens when I raise the volume on my amp. I want to increase the resistance on my 5 surround sound speakers and my subwoofer by 2 ohms from 6 to 8. I was thinking about inline resistors. My question is do I use 2 ohm resistors to take 6 to 8 and do I put them on both the positive and negative speaker lead or just one of them. If both would I put 1 ohm on each lead to get 2 ohms total?
Figure 1. Series connection of resistor.
Since you are increasing resistance in a series circuit the amplifier won't know or care where in the circuit the resistance is. Convention would be to put it in the red or '+' wire.
Figure 2. Simplified equivalent circuit.
The problem is that your speaker isn't just a resistor. It is largely an inductive load and since it has mechanical resonance (favourite frequencies to vibrate at) the situation becomes more complex. A good amplifier will have a strong drive to force the speaker to the correct position at any instant and overcome the inductance. Low resistance speaker cables are part of this equation. Adding your 2 Ω series resistance will affect how well the amplifier is able to control the speaker and some loss of fidelity will result.
Try it and see if you notice. The resistors will need to be rated to handle the power. Start with ones rated for at least 1/4 of the nominal amplifier output power rating.
Adding a single, \$2\Omega\$ resistor in series with each speaker will work.
Make sure to get appropriate resistors, they will dissipate one fourth of the maximum power your amplifier can output, per channel. If you have 50W per channel your resistors can dissipate up to 12.5W, so you need to get at least this wattage.
Using series resistors is not something I would recommend though. The best option would be to change the speakers, but this of course come at a price, the new speakers' price. But you can just keep your volume low enough. Keep in mind that adding resistors will let you rise the volume up to the maximum, but you will not hear a difference in actual volume since the excess power is dissipated on the resistors, which usually do not emit sounds.
I am guessing you are using the system with a TV set that includes some 5.1 source: maybe you can rise all the volumes, and regulate your amp volume so that the protection does not blow, then you do not touch this volume anymore and just regulate the source.
The resistor option is the safest anyway, since an unaware person can (and will) stop by, rise the volume and blow the protections.
Hey consider this: your objective is to be able crank your amp harder so you can get more SPL before your amp trips, right? Well there's kind of an Achilles heel with this exact problem. ... See, the extra 'loudness' that you're expecting to gain from your modification might very well be unobtainable because now instead of the amp working too hard and getting hot and tripping (not allowing you to use your amp to its full hardware potential, your old problem) ...
The problem you'll have once you do the modification is that now roughly 25% of your amplifiers pushing power will be tapped off all the time... resistors don't emit sound or move but what they do do, is get hot. So essentially your amp will now be running your 6 Ohm speakers fine but you'll not have any more loudness then previously cause now your amp is driving a heater also.
- lots of energy just goes to waste - heating up the environment.
Food for thought. Happy tweaking, yo! :)
Great info going on here. I can see a scenario where this would be rather ideal.
In the guitar amp world, 4"x12" speaker cabinets are quite common. Since some vintage speakers are becoming more and more rare, picking them up in pairs, or even singles at a time, might be the only option for procurement. So you might end up with a pair of 8 Ω and a pair of 16 Ω.
A couple of 8 Ω resistors in series with the 8 Ω speakers will enable our cab to be wired to 16 Ω (typical series/parallel wiring) for the amp head set at 16 Ω. And since tube guitar amps are about 199 % too damn loud, this serves to properly match speakers and cut a few dBs. And actually put less load on the 8 Ω speakers since the power to them is divided between the speakers and the resistor. Like a win/win/win.
I kind of wonder however, how the change in the cone excursions for the 8 ohm pair, might, or even would affect the other pair. Certainly not like an out of phase thing but if there would be anything noticeable about it. Hmmm.