Understanding Mcintosh Meters?

First, the meters are logarithmic, not linear; so 1/2 way between two marked points is not a value arrived at by taking the linear mid value. In other words, 1/2 way between '40' and '400' is not 220, rather it works out to about 125. There are a couple sites that can explain how to make the calculation or look it up in a math text. Second, clipping refers to distortion of the waveform from hitting the rails. I believe that the amplifiers determine clipping by comparing the 'input' waveform to the 'output' waveform and turning on a light when clipping occurs, simultaneously reducing gain - in other words, you cannot really clip, for other than a few milliseconds, with a mac amp. However, you can fry speakers with a mac amp by simply providing too much current to the speaker. In short, if you are worried about damaging your speakers, find out from the manufacturer the maximum wattage your speaker can handle, then keep your gain set so you don't exceed that wattage, as properly read from the meter. Trying to base your analysis on the impedance of your speakers vs the taps on the amp is not fruitful because the impedance spec'd for your speakers is nominal - no speaker has the same impedance over the frequency range of interest. So the method I have suggested is general. There are a host of other issues that I am sure other responders will mention - including, but not limited to, the accuracy of the meter reading at any one point, and the duration of the signal at a given wattage.

As to the last post - I am not familiar with the model amp you mentioned, my explanation was based on current amps sold by the company - you may want to look at the manual, or call the company, to find out if the clipping protection I described is in your model.

“You said that as long as I am supplying less wattage than my speakers can handle I am fine. So does that mean if my amp is say 50-100 wpc (depending on speaker impedance) and my speakers are rated at 350w power handling, I dont have to worry about frying them with my amp? But then why does everyone say an underpowered amp is more dangerous”

The theory as to why an underpowered amplifier is potentially more damaging to your speakers than an adequatly powered amp is that the amp will tend to clip when "overdriven", and this will occur at lower volumes than for an adequatly powered amp. Clipped waveforms are waveforms that sit at the rail voltage of the amp (not an intended aspect of the signal). For example, consider a sine wave with a peak of 10 volts as opposed to a clipped sine wave with a peak of 10 volts. The greater clipping, the longer per cycle the waveform sits at 10 volts. In the extreme, the waveform becomes a square wave. Impressed across the same load, more power is dissipated by the clipped waveform than the unclipped waveform. More power means more heat dissipated , and at some point, damage may occur. However, that does not mean that an adequately powered amplifier cannot cause damage just because it does not clip. If the speaker draws more current than it can handle, damage can result.

If you want to see what the meters are measuring and at what point, the schematics for all of the currently sold amplifiers are available from Mcintosh for a very nominal feel. Suggest buying the schematics and studying them - which will dispel the idea that the meters measure nothing.