converting 4 ohms to 8 ohms how? [Archive] - Audio & Video Forums


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01-30-2005, 07:13 PM
I have a pair of speakers that have mismatched woofers, it's a long story and I will spare you all. The newer woofer is 8 ohms and the older woofer is 4. I'm planning to replace both, however in the mean time, if I add a 4 ohm resister to the + side of the 4 ohm speaker will my impedance become 8 ohms? My second question is whether I should even bother, my amp doesn't seem to have a problem running the two, I have one of those Yamaha 2500's, and it hasn't tripped the breaker... yet.

Any opinions appreciated.

01-30-2005, 10:31 PM
i think if you connect a resistor as you described, half of the watts are goign to go to that resistor as cause a lot of heat problems. might not be very safe, but then again, im not really sure either.

02-03-2005, 11:19 AM
ok. adding a 4 ohm resistor in series will give you an 8 ohm total load. the current will be the same in both the speaker and the resistor, but half the voltage will be dropped across the resistor and the other half across the speaker. power is found by the formula Power = Current x Voltage. this means that you would effectively have half your power dissipated in your resistor. there was another post about this sort of stuff, but based around lowering speaker resisitance. just as in that case, this is not a feasable approach. the only effective way would be to replace the woofer with an 8 ohm one.

so in other words, just run it the way it is.


N. Abstentia
02-03-2005, 11:57 AM
I did that once with a power resistor before I knew better...I just laid the resistor in the bottom of the enclosure. Lo and behold it got so hot that it burned a hole in the cabinet :)

Replace the woofers asap.

02-03-2005, 12:20 PM
I did that once with a power resistor before I knew better...I just laid the resistor in the bottom of the enclosure. Lo and behold it got so hot that it burned a hole in the cabinet :)

Replace the woofers asap.

That's okay, I fried a North Creek tweeter when I soldered it to the woofer output lugs on my crossover...The Peerless woofer seems fine though, coudn't figure out why I wasn't getting much sound out of the left speaker so I cranked up the volume a bit more and then shifted the balance left. Then a sound like a cap going off followed by ripped paper happened...pooof.

To make matters worse, when I took it apart, I had the polarities between the drivers matched, when in fact the tweeter should have been in reverse...

Moral of the story...some people have no business being inside speakers...lucky for me I ignored that lesson.

02-03-2005, 01:05 PM
indeed. its good to ask someone before messing with stuff like that and even better to leave it alone if you dont know what your doing!


09-27-2020, 10:01 PM
You need to put a 4 ohm high voltage resistor ( in series with the 4 ohm speaker you can. As a result, you will get a decrease in volume by about 2 times, but you will not burn anything. Only the resistor should be at least half the power of one amplifier channel. In our case, it is most likely ceramic. Well, he, of course, will warm up, so we carefully put it so that it does not melt anything. No practical degradation of sound due to a supposedly nonlinear change in frequency response from this resistor will not be in that system that you are modifying. So put it on and don't worry if lowering the volume does not bother you.

11-18-2020, 07:31 PM
Do you have more than two speakers? Do you have the amp manual, or some other way to see what it's rated at? Contact the manufasturer. Ask. Some amps have specs for either four ohm, or eight ohm. If so, the amp may be rated for more power output, at four ohms. I have a number of speakers, and prefer to have things matched. Yes, a four ohm (or even two ohm) resistor MAY help. Added IN SERIES. Speaker input impedances are NOT linear, and may decrease as the frequency decreases. If you use a resistor, please buy a larger size for heat dissipation, especially with more power. Or. a long spool of medium to small gage wire! Wire HAS resistance, usually insignificant for normal length runs. Heat dissipation shouldn't be a problem, as the heat is generated along the length of the wire. Make sure that any additions are IN SERIES, NOT parallel! Do you have another four ohm speaker? Adding this IN SERIES will give you the eight ohm impedance, that the amp will see. If you can run the amp with four ohm speakers, and do this carefully (ask for help, if you are not sure), placing an eight ohm resistor IN PARALLEL with the outputs to the eight ohm speaker, will 'match' the impedances that the amp 'sees,' at its outputs. (This should be OK, although this also 'wastes' some power, unless you're in a cold environment!) Unless you drive your amp hard, you may not hear the differences. Technically, since the amp power is going into a coil of wire, inside the speaker, the amp 'sees' an inductive load. A resistor, is just an ohm, resistance value! Not exactly the same as a speaker!