What Class D amps will drive a 2 ohm load

Atmasphere,
You said, "But I don't agree about the 'best speaker you can afford' thing! The reason is simple- you may find that you have a preference for an amplifier technology- tubes for example- and if that is the case buying an incompatible speaker will simply be money down the loo. So- if you know what kind of amp you prefer, then get the best **compatible** speaker you can for it."

I say that no speaker is "incompatible" with any amplifier.  A 5 watt tube amp may make great music up to 105 dB with an efficient horn speaker.  But driving a 75 dB efficient electrostatic with small panels, it can make beautiful chamber music at SPL of 75 dB, which is the natural level of a string quartet, for instance.  Suppose the listener wants to hear sweet mellow sound from the string quartet, then the more "compatible" higher powered neutral/accurate SS amp is not for him.  

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.  Any of them are much closer to theoretical perfection than any speaker available today, all of which sound hopelessly veiled compared to the real thing, although I come much closer with my electrostatic and EQ.    The real advances in high fidelity should be in speaker design rather than amp design.  Produce better electrostatic designs, rather than inferior huge curved panels of Sound Lab and Martin Logan which smear HF and bloat images.  It is interesting how the new smaller Maggie LRS is creating a sensation.  I haven't heard it yet, but the size is right.  How about plasma drivers crossed over to electrostatic panels for lower freq.   I heard the Plasmatronics speaker by Dr. Alan Hill in the early 80's.  Too bad most of the market cares about big dynamics instead of accuracy and finesse, which is why these plasma and stat transducers are largely ignored.  

How about plasma drivers crossed over to electrostatic panels for lower freq.

Funny you should bring them up.
Which is what I use, ACI SV12's in 5cuft IB enclosures xover at 130hz to big esl's, xover at 10khz to MP-02 plamsa's  https://www.ebay.com.au/itm/Magnat-Plasma-MP-02-ion-tweeter-massless-air-plasma-speaker-Plasmahochtoner/272894087984?hash=item3f89c15330:g:V5sAAOSwCJxZ6PXy&frcectupt=true

Cheers George

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