What Class D amps will drive a 2 ohm load

The more general point is that the sound character is largely determined by the speaker, closely followed by the recording.  Most good amps today have superb specs and sound fairly close to each other.  

@viber6  Actually this isn't true. It is true that speakers have a lot of sound character (as does the room) but amps don't sound the same at all, nor do all amps interface correctly with all speakers.


One example is how solid state generally doesn't work well with full range ESLs. Full range ESLs have about a 9 or 10:1 range of impedance from the bass to 20KHz. For example a Sound Lab is 30 ohms in the bass and between 1.5 to 3 ohms at 20KHz depending on the position of the Brilliance control (if the control were removed it would simply be 3 ohms). (BTW, Sound Lab solves this issue to some degree by having a bit of adjustability to their speakers- bass settings, midrange settings (IIRC) and the Brilliance control.)


Now most solid state amps are designed to work as a voltage source, which is to say they maintain the same voltage regardless of load. This is the idea of doubling power as impedance is halved or halving power as impedance is doubled. So If the solid state amp makes 100 watts into 8 ohms, On a Sound Lab ESL with 30 ohms in the bass it will make only about 26 watts but with the same level signal applied at 20KHz will make 300 watts- over a 10:1 difference! The problem here is that unlike a box speaker with a driver in it, the ESL's impedance curve is based on capacitance rather than a base impedance influenced by resonance. Put more simply, it **has the same efficiency regardless of impedance**. This causes solid state amps to be bright on top and unable to make power in the bass. Martin Logan gets around this by simply having a super low impedance at high frequencies and most solid state amps (tube amps to a greater degree) can't make power into that impedance and so they tone down the brightness. In a nutshell, ESLs are not Voltage driven; they are Power driven. For more on this see http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php

Conversely a B&W 802 is designed for a voltage source amp (solid state) and so tube amps have a very difficult time making bass on this speaker.


But put even more simply, we've been getting spec sheets from amplifier manufacturers for 60 years, but we can't tell what the amp sounds like. So we have to audition the amp on our speakers to see if it satisfies! This simple fact is common knowledge with all audiophiles.


Of course we have to examine what is considered 'superb specs'; the simple fact of low THD doesn't mean the amp will sound uncolored or musical to the human ear- in many cases quite the opposite! This is why tubes are still around 55 years after being declared 'obsolete'. Its complex, due to how the human hearing perceptual rules work; how we perceive sound pressure (the presence of higher ordered harmonics, FWIW), how the ear converts distortion into tonality and the masking principle all play a role.


Because some manufacturers want their amplifier to conform more closely to the human perceptual rules, they are willing also to have 'inferior' specs. Its a simple fact that as our current regime of test and measurement goes, we're not always measuring the right things.

Atmasphere,
I follow what you are saying about how a voltage source SS amp invariant to impedance theoretically would sound bright driving an electrostatic speaker.  But in practice I don't find this to be the case.  Years ago, for fun, I put my tonearm leads into the line stage, bypassing the RIAA curve of the phone stage.  Of course, that produced very bright sound due to the 30 dB boost at HF compared to low freq.  With the stat speaker, impedances can be as high as 30-100 ohms in the upper/lower bass, and 1 ohm or less in HF.  This is more than the 10:1 ratio you cite, but still nowhere near as much as the inverse RIAA curve.  Still, according to your theory, the stat speaker should sound like a less drastic inverted RIAA curve, which I didn't find in the listening.  Also, all dynamic speakers have marked variations in their impedances, and your theory would predict that a SS amp would produce markedly different sound from different speakers in relation to each speaker's impedance curve.  But I have found similar tonal differences A/B'ing 2 amps on different speakers.  For example, SS amps generally sound brighter than tube amps, which I have found to be true regardless of whether I used dynamic or stat speakers.  I am puzzled by my different listening findings compared to your theory.

I wasn't saying that amps don't make much difference, because obviously I pursue finding amps that offer more clarity, etc.  But it is clear that whatever sonic differences there are among amps, the sonic differences among transducers like speakers are vastly greater.  This is also true of transducers like cartridges which are really inverse speakers.  

@ georgehifi

All the amplifiers in the world double when drop in ohm to half, but when you reach their current limit then you will not see the doubling when you drop in ohm

With the stat speaker, impedances can be as high as 30-100 ohms in the upper/lower bass, and 1 ohm or less in HF.  This is more than the 10:1 ratio you cite, but still nowhere near as much as the inverse RIAA curve.  Still, according to your theory, the stat speaker should sound like a less drastic inverted RIAA curve, which I didn't find in the listening.  Also, all dynamic speakers have marked variations in their impedances, and your theory would predict that a SS amp would produce markedly different sound from different speakers in relation to each speaker's impedance curve.

@viber6  this isn't correct. (BTW what I'm talking about here isn't theory, its more like audio history. The Power Paradigm is what was around before MacIntosh and ElectroVoice developed the Voltage rules in the late 1950s.) With most dynamic speakers (there are exceptions in high end audio) the speaker is meant to be 'voltage driven' so variable power output is what you're looking for in the amplifier in order to get flat frequency response. The idea is plug and play, no need to adjust any midrange or treble controls (like you see on older speakers, stuff from the 50s and 60s). Of course like anything else, this approach solves one problem while introducing others.


The brightness of an unequalized RIAA curve would **not** have been compensated by the way the ESL and solid state amps work together.  I think you will find though that the 10:1 ratio I described is generally pretty close- that describes Quads, Martin Logans, Accoustats and Sound Labs which are the ESLs with which I have the most experience. If you can find one that is outside of that (for example: 100:1) I'd be very interested in knowing about it!