Rotel RB 1080 and 4 ohms

[yanies]

I have a set of Magnepan MMG 4 ohms and a Rotel RB 1080 Power amp that supports 4 and 8 ohms
Theoretically I read that 4 ohms multiply the power level
Comparing to what I hear that doesnt happen in my case.
Should I hear a bit more louder or double in this case?
Or there is a way to make the amplifier to work on 4 ohms?

The manual of my amplifier doesnt say anything about this.

Thanks in advance

[Kevin D]

I'll try my best to keep this simple as this can get complicated pretty quickly.

There's several factors at work here. As the ohm load goes down, the power of an amp will go up (to a point). The ratings on speakers are averages, based on all frequencies. So some frequencies may be real low some may be real high. A class A/B amp won't double power, but can come close. I believe the 1080 will produce about 360 watts into a 4ohm load.

Anytime you double the power to a speaker, you'll be able to get about 3db more output. That's just about the minimum increase for a human to acknowledge an increase in volume. In order to double the volume, you would need 10 times as much power. So if your speakers were 8ohm and your 1080 was pushing 200 watts, you would need 2000 watts to double the volume.

So that's half the story.

The other side is the efficiency of the speaker. That's basically how much volume a speaker will have based on the power applied. An inefficient speaker will require more power to produce the same volume as another efficient speaker (You Magnepan's are pretty inefficient at 88dB).

Since you can't dynamically change the ohm load of a speaker, you seem to be comparing what your 1080 did on an 8ohm speaker versus what they do now on a 4ohm speaker. If you take into account the differences in efficiency, the Magnepan's could sound just as loud or even quieter then your old speakers.

In the end let's pretend your Magnepans are as efficient as your old speakers. Your 1080 will not produce twice as much power into a 4ohm load, so your volume will be less than 3dB higher then your old speakers, and that's less then the minimum required to notice a difference.

Hope that clears it up.

Kevin D.

[miner]

Great explanation Kevin D. I am expereinceing the same with my Dynaudio 4 ohm speakers with my Rotel RB-1092 amp.

Kevin G.