Tube Amp for Martin Logan Speakers
An amp like say a Krell or similar, will remain almost flat in it's response across the frequency spectrum. All you need to do is look at the simulated speaker load graphs of amps at 1/3 power on Stereophile to see what happens to them if they have, high'ish output impedance or can't deliver current, many tube amps exhibit this, and even many Mosfets, they are far from the ideal flat. And the simulated speaker load that Stereophile uses is not as savage as what we're talking about here with the ML's, and things like Wilson Watt/puppy, Alexandria etc. Cheers George |
Here is an Audio Research Reference 150 considered by many to be a tube amp with better drive than most. It's only being asked to drive 2.83v hardly taxing. Look at the black trace in the link, this is Sterophile's simulated (rather easy speaker load), the 150 is having a hard time staying flat.(I can show you an impedance graph of their simulated speaker load, I have it somewhere it's not as nasty as the ML's) Then look what happens to it when it has to drive a straight 2ohm load (green trace) it's really starting to take a dive in the upper mids/highs. What do you think will happen to the highs into a 1ohm capacitive load of the ML's http://www.stereophile.com/content/audio-research-reference-150-power-amplifier-measurements#dgk5iym3Akuwqg5H.97 Cheers George |
Here is a link to those Stereophile simulated speaker loads, as I said hardly as taxing as the ML's loads. http://www.stereophile.com/content/real-life-measurements-page-2#GhGr6lrCxHfPYcsl.97 Cheers George |
Again, though, as I indicated in my previous post George's comments mainly address frequency response at the amplifier output/speaker input. And flat frequency response at those points does not necessarily mean that the acoustic output of the speaker will have flat frequency response. Ralph (Atmasphere) stated above that "in an ESL, the efficiency is fairly constant despite the impedance." ("Efficiency" referring to acoustic power out vs. electrical power in). I believe that is generally true. But even if we assume that the efficiency of a given ESL is just a little bit closer to being constant across the frequency range than it is to mirroring the impedance curve, then the minimal variation of amplifier output voltage as a function of load impedance that is characteristic of almost all solid state amps (assuming they are operated within the limits of their voltage, current, power, and thermal capabilities), and hence the increase in power delivery that will occur as impedance decreases, will result in greater frequency response variation in the acoustic output of that ESL than would result with a tube amplifier (operated within its capabilities) whose output impedance is some relatively high value, and whose output voltage therefore varies significantly as a function of varying load impedance. Apologies for the long sentence :-) Regards, -- Al |
