Yesterday I mentioned that I would attempt to find out how much power I can get from my cheap Denon receiver into a pair of M80s.
A few words about my receiver: it's the Denon AVR-2105 rated at 90W/channel into 8 Ohms with 0.08% distortion and 125W/channel into 6 Ohms with 0.7% distortion. Dynamic power is 200W x 2 channels into 2 Ohms. The receiver cost me $350 a couple of years ago brand new.
So a few words about what I did: I wanted to use the worst possible load the M80s could present to the amp. As shown on the graphs below, this load presents itself at about 50 Hz and is 4 Ohms. At this frequency, the speaker has a resistance of 2.83 Ohms and an inductive reactance of 2.83 Ohms due to the 45 degree phase angle (R=4*cos45, XL=4*sin45). So I injected a 50Hz test tone from the Realtraps CD (thanks again Randy
) and measured the RMS voltage across the speaker terminals. I had both M80s going but I only measured one of them. The real power is ((V^2)/4)*cos(45), the reactive power is the same formula but substitute sin instead of cos. The complex power is the square root of the sum of the squares of the real and reactive. The data below (see blue column) shows that I could source as much as 306 Volt-Amps (Watts) from the Denon at maximum volume.
As I indicate on my notes on the graph, I only applied the test tone for about 5 seconds (long enough to get a reading) because frankly I was scared I might do some damage
I did not do any distortion measurements as I don't have any equipment to do that. I can tell you though that up to +3 on my main gain knob, the 50Hz tone sounded "good" to me. After +3, I had to stop and put in earplugs. But I watched the M80 drivers a few times after +3 and they looked to be travelling linearly to me.
This tells me a few things:
1. Denon amps deliver! If my bottom-of-the-line unit can do this, I am sure the rest of them can do more.
2. I would certainly not hesitate to run this unit continously at the +3 level. As I've mentioned before, I have left it turned on continously for an hour at maximum volume with music while I left the house with no shut-down (come to think of it now maybe it did shut down and then re-start but it was certainly playing when I got home).
3. This was a test tone at the worst possible frequency. For real music and with a sub, the receiver would never experience these kinds of torturous conditions.
4. I don't know how anyone, in a room that is 4,000 cubic feet or less can possibly listen to any levels approaching 0 on the gain knob. I've listened to some classical at +7 but absolutely no more.
5. If this is the capability of my cheap Denon, what does that say about Odyssey, Emotiva and other more "esoteric" brands? Be careful that you don't fry your M80s!!!
I hope this is helpful to anyone out there looking for an amp. I am sure that the discussions about power will rage on but at least this is some quantitative data that we can draw on.