Benchmark ABH2 amp and full range electrostatics, e.g. CLX or Soundlab

Soundhound:
Go to PS Audio website, "Copper Magazine," and read the series of articles by Galen Gareis. (Something like issues 53 or 54-56 or 57. Alternatively, you could just go to the Iconoclast website and read their white papers. Galen Gareis is a former Belden engineer. The level of time and effort he appears to have put into researching and developing cables impressed me. Now sold under brand name Iconoclast, these include a speaker cable with both low capacitance and low inductance. Each model they make has three price options, depending on the grade of metal one chooses. The top of their line wires are not cheap (to me, anyway), but they make Nordost's silly pricing look like lunch money. Best of all, everything they sell has a 30-day, no questions asked return policy and no restocking fees. I just discovered this option quite recently and do not yet have any myself, but how can you go wrong? After all the half-million dollar record players and speakers we've seen in recent times (e.g., Mr. Fremer's recent fave $50,000+ tonearms), isn't it time for just a little bit of common sense in high-end audio? I am as obsessive as any audiophile and more than most, but one of the smartest things I've done is use my own ears more and worry less what high-end fashion dictates. YMMV

soundhound
Benchmark ABH2 amp and full range electrostatics, e.g. CLX or Soundlab

Should be fine, but I would not use a "bridged ABH2’s" (mono’ed) into these sort of ESL 1ohm loads, as the stability won’t be as good and the current ability to drive into low impedance will be halved.
If you have two ABH2’s and the speakers have two sets of speaker terminals then you could vertically bi-amp the stereo ones.
http://www.classicspeakerpages.net/IP.Board/uploads/monthly_2016_03/7_Vertical_Bi-Amp.thumb.jpg.672f...

Cheers George

George,

The CLX is not an easy speaker to optimize.  I had concerns regarding whether a single AHB2 amp could properly drive the CLX and like you whether the doubling of output impedance would pose a problem in regards to the very low impedance the CLX has above 8 kilohertz.  I have ordered an AHB2 amp will compare to my Coda 15.5 amp which is an excellent match.  Martin Logan has used bridged AHB2 amps to drive their hybrid speakers at various shows and apparently has not had a problem with bridged amps.  Nor has kstaken who in an earlier post on this thread communicated that bridged AHB2 amps are an excellent match with his CLX's.

Thanks for your thoughts.

jeffreyfranz,

I appreciate your suggestion.  I have done a little investigation regarding the optimal electrical parameters for full range electrostatics most of which behave like a large capacitor.  Roger West and Roger Sanders who know a bit about full range electrostatics have both advocated speaker cables with both very low inductance and low capacitance.  This is not easy to achieve.  Roger Sanders used to sell a dual coax speaker cable with such characteristics.  The Nordost cables published specs also have both low inductance and capacitance; I was curious about Nordost 2 cables and tried a combination of Heimdall 2 speaker cables and interconnects together in my system.  I selected the Heimdall 2 as a midlevel Nordost cable which would give me an idea of the signature of this brand.  They are excellent cables but have a distinct sonic signature.  I am aware of the Iconoclast cables but have not tried them.  They use Belden wire to fabricate their cables.  I looked at the Belden catalog and noticed that Belden Coax 8268 has 13 gauge central silver coated copper conductors and also very low inductance (0.077 microH/ ft) and low capacitance (30.8 pF/ft).  It is gotten expensive for raw cable, $6.90/ft from RF Parts.  I used xhadow spades for terminations.  It works surprisingly well and I found no advantage to the considerably more expensive Nordost and is perhaps slightly more transparent.  I cannot tell anyone else whether this cable will work in a given system but for full range electrostatics you might give it a try if you can properly terminate the cables and can deal with the stiffness of this cable. 

This is the problem you are up against.

Most ESLs have an impedance that ranges from whatever peak they have in the bass to about 1/9th to 1/10th of that at 20KHz.


Now imagine a well built solid state amp that can double power as impedance is halved.


Now comes the tricky bit- ESLs don't follow the same rules that box speakers do. To start with, there's no box :)  To further complicate things, their impedance curve is based on a capacitance (hence the falling impedance at higher frequencies). What isn't obvious is that in a box speaker, the expectation is that the impedance curve is also a map (to a certain degree) of its efficiency. For example, the woofer has a resonance in the box; this resonance is represented by an impedance peak. Into that peak the amp has to throttle back its power, which a solid state amp does because if it doubles power as impedance is halved, that means that it also halves its power as impedance is doubled. That works out nicely for flat frequency response when dealing with many box speakers.

But ESLs are different as I pointed out. Their impedance curve is not a map of efficiency; to reproduce a 100Hz tone at 90dB takes about the same amount of power as it does to reproduce a 10KHz tone at 90dB. You can see what will happen: an amplifier that can double power as impedance is halved will be too bright because the impedance is much lower at 10KHz as it is at 500Hz.


Martin-Logan has been sort of getting around this problem by making the impedances of their speakers very low; starting at 4 ohms in the bass and going down to a fraction of an ohm from there. Since many solid state amps (their intended market, since there are more solid state amps on the market than there are tube amps) can't continue doubling power into such low impedances, they sort of get away with it.

But with a Sound Lab, which is arguably the state of the art in ESLs, the 20KHz impedance is between 1.5 and 3 ohms depending on the position of the Brilliance control. A lot of solid state amps can drive impedances like that- but on the flip side, the Sound Lab is typically about 30 ohms in the bass, which means that solid state amps can't make power. So on a Sound Lab, a 200 watt tube amp can usually keep up easily with a 600 watt solid state amp on this account!

To further complicate matters, the human ear/brain system detects sound pressure by listening for higher ordered harmonics of any sound. For this reason the ear is keenly sensitive to higher ordered harmonics as it has to have a range of over 120dB. Both solid state and tube amps make distortion, but if you look at measurements you will see that the fundamental test frequency is usually only 60 to 100Hz, so we don't get to see what the amp is doing at 5-7KHz, which is where the ear is most sensitive  (the Fletcher-Munson curve, if you're still reading this far). So the higher ordered harmonics aren't shown. But if you are wondering why tubes are still around its because they sound smoother, and the higher ordered harmonic structure is why (not bandwidth!).


The ear converts all forms of distortion into tonality. The higher orders are treated as brightness and harshness. If you've been paying attention, then you know where I'm going with this- in addition to a brightness caused by a frequency response error on the part of most solid state amps on an ESL, you also get higher ordered harmonic content which the ear will also treat as brightness. Its a double whammy.


This is why ESLs and tubes have had a very friendly relationship going back to the very first ESL.  For more on this topic see
http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php