Kach said;
“I'm a stat guy (or flat panel guy) and know it.”
It might not seem like it but actually, while doing “the job” a different way, a proper horn and an electrostatic speaker can have some similar features.
By that I mean the result can be more similar than to a direct radiator system.
For example, if you put in a sine wave at any frequency and measure the result with a microphone and then compare the phases, one is confused. If one removes the phase shift which is present due to the time it took for the sound to get to the microphone, one is left with the acoustic phase of the transducer. That with the amplitude curve describe the speakers response in amplitude AND where in time with respect to the input, the signal emerges.
With an electrostatic speaker, the thing producing the ‘force” which moves the diaphragm is the voltage thus the attractive force is always “in phase” with the input voltage.
In that case, put a square wave in and a square wave comes out, or anything else you put in.
The fly swimming in the beer is the speaker requires a high voltage signal which is supplied by something like a tube output transformer connected backwards.
That is fine, the issue though is that the stators have a capacitance between them and what you are doing with the signal is changing that voltage which being a capacitor resists until you have put current into it.
Reflected back through the transformer, the electrostatic can look pretty different than a ‘normal” speaker to the amplifier, in that is has significant capacitive reactance. While Tube amplifiers (being a very wide band device individually) had entirely different limitations. Solid state amplifiers, especially early on, had safe operating area “protection’ which could easily intrude into operation driving some electrostats at even a modest level. Tube amps like the Mcintosh m-60’s and 240’s I used to have would laugh at my electrostats even my big homemade ones.
Part B of the large element in general is they have a radiation null 90 degrees off axis and this means much less reflected sound from the walls and that allows the recording’s stereo image to be heard most clearly farther from the speakers (the near field zone, dominated by direct sound).
A direct radiator when it is “small” compared to wavelength is a constant acceleration device where the excursion increases by four when the frequency is halved. This is needed because the woofer is a fixed physical size BUT the sound it is producing has different wavelengths. As the frequency falls, the radiator is getting smaller acoustically and so less and less efficient as a radiator. The up shot is the excursion has to increase by four for each octave you go down to have flat response which the radiator is small compared to the wavelength.
It is a woofers mass that is being accelerated back and forth but in an electrodynamic motor (a DC motor like a voice coil) it is current that produces force. When the motor converts the electrical to mechanical domain, it reflects the mass back as a capacitance. As the signal here (sound) is the voltage across the capacitor, one finds the acoustic phase of this source generally lags over the mid part of it’s range and only reaches “zero” somewhere around Rmin in the impedance curve.
The result here is the drivers acoustic phase is not the same as the voltage and depending on frequency it may lag or even lead the voltage signal phase.
Thus, this device generally cannot reproduce a complex signal like a square wave because the different frequencies emerge at the speakers acoustic phase shift which re-arranges the signal ie; no preservation of complex signal waveshape.
The problem with all loudspeakers is the problems they have increase faster than the rate of the input signal.
By that I mean in addition to the real signal, it also produces distortion at X multiples and some noise and if you increase the signal 20dB (100X), the loudness may not increase 20dB 100X.
At some point, the problems are loud enough for the subjective judgment that sounds bad”.
I probably would still have electrostats except this is where they didn’t do it for me.
Horns use an electrodynamic driver but in a different way, they attempt to grab a hold of a large slab of the air and connect it to the tiny radiator.
A horn can be as high as 50% efficiency (for an omni directional speaker a sensitivity of 109dB for 1 Watt) or even more but only over a bandwidth.
A horn can also preserve the signal wave shape keeping in mind the bandwidth limitations.
Horns can also have high directivity and they can be made so that the radiation angle is nearly constant over a wide band so they are the only solution in large spaces and bad rooms where the room issues are much worse.
The hard part is they do not cover the “whole range”, they require equalization which while it exactly compliments what the driver needs, it only does so if you know what that is and can design it. Bottom line, they are much more difficult to design and align.
While the first part can be accomplished with DSP, the physical spacing between sources is not fixable electronically so horn systems made of discrete horns produces polar patterns which are not potential customer friendly and so are not discussed.
The original uses for horns took advantage of the high sensitivity, these types of horns from the old days are mostly what is used in the high efficiency hifi area.
The most recent horns like what I do at work use the most modern drivers and approaches I can think of etc, focusing on high quality sound at high acoustic power, with constant directivity used in large spaces.
Here when used in a living room instead, a speaker like the sh-50 radiates a portion of a sphere just like an ESL-63, it radiates in time like a single source, like an ESL-63 and can reproduce a square wave too but goes lower in frequency, is about 15dB more efficient and can go also can go about 30dB louder if asked.
See if you can guess what electrostatic speaker has a special spot in my heart and shaped my efforts haha.
Best,
Tom Danley
Danley Sound Labs
