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AXPONA 2017: JansZen Electrostatic Headphones

amirm

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#2
By request, I visited this suite in the marketplace. David JansZen explained that his father had invented the electrostatic speaker! To do something new, he decided to create a portable electrostatic headphone. That is, a headphone that includes its own power source and high voltage transformers built right into the cans. That way you can plug them into any source and enjoy the sound without lugging around an external box.

The unit on hand was pretty bulky size wise but weight was fine. He said these were 3-D printed prototypes. Pretty neat approach. They sell for less money than the new Sonoma and he said they should sound better.
 

RayDunzl

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#3
David JansZen explained that his father had invented the electrostatic speaker!
Hmm...

http://www.aes.org/aeshc/docs/recording.technology.history/loudspeaker.html

"1929 - E. W. Kellogg filed patent No. 1,983,377 on September 17, 1929, granted December 4, 1934, that described an electrostatic speaker composed of many small sections able to radiate sound with out magnets or cones or baffles. This patent, as well as the 1932 British patents of Hans Vogt, influenced Peter Walker to build the Quad ESL flat panel speaker in 1957."

"1953 - Arthur Janszen was granted patent No. 2,631,196 on March 10, 1953, for an electrostatic high-frequency speaker"

http://www.janszenaudio.com/brand-history

"Arthur Janszen is an example of what was once known as an applied physicist, someone who later would be called an engineer. He invented many things in his life, but is known in audio for inventing the first practical electrostatic hi-fi speaker, a wide-range tweeter that covered midrange through ultrasonic frequencies (800 Hz - 30 kHz)."
 

ztatic

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#4
Yep, the very first ones were made in the 1800's, and were actually the first means of transducing sound from an electrical signal, but Arthur Janszen invented the first commercially practical one, i.e., manufacturable, reliable and durable, high sensitivity, and not an ozone generator, a distinction that tends to get lost when jotting down notes from a quick verbal conversation at an audio show.
 

ztatic

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Someone might find this video interesting. I walked around town for a couple of hours on a Saturday afternoon with a videographer, and we asked random strangers to try the next generation Lotus prototype on camera. Friendly town -- most said okay.
 

amirm

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Someone might find this video interesting. I walked around town for a couple of hours on a Saturday afternoon with a videographer, and we asked random strangers to try the next generation Lotus prototype on camera. Friendly town -- most said okay.
Very nicely done!
 

andreasmaaan

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#12
I'm curious as someone who's never used electrostatic headphones: what are the claimed advantages over dynamic headphones?
 
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ztatic

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As with electrostatic speakers, the main difference is fidelity. To be clear, by fidelity, I mean less change to the recorded sound.

TLDR: It’s impossible for any other means of making sound to alter the sound less than electrostatics do. The result is the most convincing, detailed, natural, clear music possible. The knock-on result of that is you'll be drawn into the music more so than with any other type of headphone. In short, electrostatics have the greatest potential for making you feel directly connected to the musicians and singers, like being a witness to each actual performances.

Now for a technical explanation of the differences and the effects they have.

Dynamic drivers are asked to do the impossible, namely act as pistons, when they're really a diaphragm being pushed from the middle by a much smaller, non-linear motor. The diaphragm thus moves in many ways, but not quite like a piston.

For one thing, it develops multiple resonances, and different areas move at different speeds and in different directions. This is true for the surround, the part that suspends the edges of the cone, moving quite differently than the diaphragm, yet far enough to make sound, and the diaphragm breaking up at certain frequencies into separately resonating areas. This causes unnatural ripples in the frequency response, meaning the sound levels of some tones are not the same as when they were recorded.

The combination of motor and diaphragm also has substantial mass that has to be accelerated. That causes the sound to be emitted with a delay relative to the signal, and this delay is proportional to the frequency. This misaligns the fundamental and harmonic content of the signal to various extents.

Also, most of the energy goes into accelerating the mass and only a little into making sound. Not that this is very important under most conditions, but when a dynamic driver is playing loudly, its coil heats up and thus develops additional electrical resistance, and this reduces the sound level out of proportion to the signal level, a form of distortion called power compression that reduces the naturalness of the musical dynamics.

Lastly, the non-linearity of the system causes harmonic and intermodulation distortion. There are two sources of non-linearity. One is the variation in diaphragm force vs. position. This causes both kinds of distortion, but mostly harmonic distortion, namely adding harmonics that are not present in the signal, but are at least harmonically related to the signal. The other is the variation in inductance with diaphragm position, which causes the phase of the sound to vary with movement of the diaphragm. This causes intermodulation distortion, that is, the development of sounds that are not harmonically related to the signal, and these are particularly harmful to the naturalness of the sound.

In a high quality, over-ear, dynamic headphone, the driver is usually 40 mm in diameter, sometimes 50 mm, and the opening of the headphone can is usually in the range of 600 x 800 mm. This means the sound can vary substantially depending on how the headphones are placed on the head, because the alignment of the driver with the ear canals and pinnae can vary. There are other influences on the sound with position, but this is the big one.

Before we get to electrostatics, I should mention another type of driver, the large area, planar magnetic. This is a special type of dynamic that solves many of the problems. It has conductors bonded to a thin diaphragm, and current through those conductors causes the diaphragm to move in a magnetic field.

The large area makes the sound more independent of position on the head, and the membrane gets more or less even force over its area, so it moves more as one, and it’s far less prone to breakup. Their inductance is nearly constant, so intermodulation distortion is minimal. These are the technical reasons why good ones sound better than standard dynamics, at least to people who recognize and appreciate high fidelity.

There is still significant mass on the diaphragm, however, because of the metallic electrical conductors on the diaphragm. The diaphragm itself must be thick enough to support those conductors and withstand the heating that occurs as current flows through those conductors. The heating varies the tension of the diaphragm, because the plastic expands when heated, and this varies its sound, so in addition to power compression, the frequency response is somewhat loudness dependent.

Finally, we get to electrostatics. There are two kinds: those with the diaphragm charge embedded into the diaphragm, called electrets, and those that have an external polarizing supply, called true electrostatics.

Electrets are impractical, mainly because they are inefficient. They are inefficient for two reasons. 1) The highest voltage charge that can be embedded is about 600VDC, which is quite low, and efficiency is proportional to voltage. 2) The membrane materials that can hold embedded charge are thick, and this causes the sound to roll off within the audio band.

Also, it’s impossible for the materials that can hold embedded charge to maintain the tension needed for reproducing a wide range of frequencies. They consequently don’t start adding sound until above about 8000 Hz.

As a result, makers claiming that their electret headphones have “electrostatic technology” in them are technically correct, but at best, they are selling dynamic headphones with the very top octave or two supplemented by the electret. An increase in the fidelity of the upper harmonics makes very little difference in the sound we hear, so even if an electret were loud enough to keep up with a dynamic driver, it still wouldn’t matter.

True electrostatics offer many advantages over dynamics.

There are two most important aspects. One is that the diaphragm material is so thin and light that it presents no mass loading within the audio band. All energy applied goes into making sound. The diaphragm acts as a virtual air barrier and vibrates to make sound without adding any voice of its own. The other aspect is that the force is spread evenly across its surface. Put together, these aspects mean a true electrostatic has no choice but reproduce the signal with the highest fidelity possible -- no breakup, no resonances, no frequency-dependent inductance.

A true electrostatic is also quite efficient. The diaphragm in a true electrostatic is polarized to the limit of what the air can support. This makes them at least 9 dB more sensitive/efficient than an electret, all else being equal, and they can keep up with a dynamic driver.

The diaphragm material can maintain tension indefinitely, and can thus be arranged to reproduce many octaves, even from a headphone sized transducer.

Since ours are or will be the only true electrostatic hybrid, I hope no one will mind that I phrase the rest of this with our headphones in mind.

Ours cross over to the woofer at about 800 Hz, meaning the range of sound that requires the highest fidelity is produced by the highest fidelity transducer possible. Running the woofer only below the frequencies where its diaphragm would break up means its fidelity is also quite high within the range it is being asked to run.

The area of our electrostatic transducers is nearly the entire aperture of the headphone, so they are relatively immune to variation in sound from differences in how they fit to the head.

The crossover from electrostatic to dynamic must not create an evident disjunction in sound, and we have accomplished a seamless transition. In fact, compared to full range electrostatic headphones, ours go deeper and have a richer sound in the bass, thanks to the use of a dynamic woofer.

One main reason we use a dynamic woofer is to be able to build everything into the headphones, namely the polarization supply and step-up transformers. Because full range electrostatics have large step-up transformers to cover the bass, these items must reside in an external box that gets plugged into wall power. This makes ours the only true electrostatic that's portable. The other main reason is to make them sensitive enough to drive from a phone or portable player at levels loud enough to use outdoors, so unlike full range electrostatics, they don't need an amplifier.

I hope this was helpful and not overly self-promotional.
 

andreasmaaan

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#14
Thanks for the extremely detailed response @ztatic :)

My question arose after looking at Innerfidelity measurements of various vintage Stax headphones and the current flagship SR-009, and comparing these to better-quality dynamic headphones, e.g. my everyday studio headphones, the NAD Viso HP50. I couldn't find any appreciable differences in measured performance (other than poor LF response and high THD in the older Stax models - although certainly not in the SR-009). For example, THD levels across the various Stax models seem similar to THD levels in typical dynamic headphones, and the SR-009 and HP50 measure similarly in this regard.

However, detecting any cone breakup in the dynamic drivers would no doubt require a CSD measurement, which Innerfidelity does not provide. It's also ofc possible that Innerfidelity's measurement methodology is flawed.

Another point: I understand that (AFAIK) the Stax models don't use a LF dynamic driver like yours do. So I'm not suggesting the Stax measurements are comparable to how yours may measure. I'm just taking Stax as a reference because of its primacy in the industry and the high regard it's held in.

Anyway, on the basis of what you've written, I take the absence of cone breakup to be the main advantage of electrostatics.

Cheers,
Andreas
 

Sal1950

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#15
That is, a headphone that includes its own power source and high voltage transformers built right into the cans. That way you can plug them into any source and enjoy the sound without lugging around an external box.
Sorry but I don't see that as a positive. I would never consider anything so glomous. Anything that could be done to reduce the size and weight should be approached.
 

ztatic

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Sorry but I don't see that as a positive. I would never consider anything so glomous. Anything that could be done to reduce the size and weight should be approached.
Likely will do so in another model someday, and for those for whom size and weight are primary, hopefully the trade-off 's will be worthwhile, e.g., bass not as deep, higher crossover frequency, lower impedance (the Lotus is 32 Ohms), and less isolation from ambient noise. The Lotus optimizes the benefits of the electrostatic against a trade off in size, although they are quite comfortable.
 

SIY

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#17
Zero experience with the JansZens, but my subjective impression of Stax ESL was that they were ultra clean and detailed. THD doesn't tell the whole tale- I'd be interested in comparisons to dynamics using things like Geddes-Lee metrics, POLQA, ABC-MRT, and multitone, all of which I'm equipped for.

Just in case you want to send me a pair for review. ;)
 

andreasmaaan

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#18
Zero experience with the JansZens, but my subjective impression of Stax ESL was that they were ultra clean and detailed. THD doesn't tell the whole tale- I'd be interested in comparisons to dynamics using things like Geddes-Lee metrics, POLQA, ABC-MRT, and multitone, all of which I'm equipped for.

Just in case you want to send me a pair for review. ;)
Yes of course, wasn't trying to suggest THD gives the full picture. It's just I don't have more detailed measurements to go by at this stage. Wish I had a pair to send you ;)
 

ztatic

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Thanks for the extremely detailed response @ztatic :)

My question arose after looking at Innerfidelity measurements of various vintage Stax headphones and the current flagship SR-009, and comparing these to better-quality dynamic headphones, e.g. my everyday studio headphones, the NAD Viso HP50. I couldn't find any appreciable differences in measured performance (other than poor LF response and high THD in the older Stax models - although certainly not in the SR-009). For example, THD levels across the various Stax models seem similar to THD levels in typical dynamic headphones, and the SR-009 and HP50 measure similarly in this regard.

However, detecting any cone breakup in the dynamic drivers would no doubt require a CSD measurement, which Innerfidelity does not provide. It's also ofc possible that Innerfidelity's measurement methodology is flawed.

Another point: I understand that (AFAIK) the Stax models don't use a LF dynamic driver like yours do. So I'm not suggesting the Stax measurements are comparable to how yours may measure. I'm just taking Stax as a reference because of its primacy in the industry and the high regard it's held in.

Anyway, on the basis of what you've written, I take the absence of cone breakup to be the main advantage of electrostatics.

Cheers,
Andreas
IMO, standard headphone measurements are fatally flawed.

It seems to me that placing a microphone at the bottom of a tube that's supposed to represent the ear canal and surrounding the exit of the tube with an artificial ear is a wrongheaded convention, so to speak, that sells expensive test equipment but makes no sense.

The tube makes no sense, because the part of the ear that's struck by sound is on the outside. The artificial ear makes no sense because the pinnae are effectively rendered non-functional with headphones -- the in-your-head sound is proof of that.

Measuring all those wiggles in the frequency response caused by cavity resonances inside an over-the-ear headphone makes no sense because those are compensated by the way we hear things -- the ear interprets them as a static sound source position as if they'd been created by the pinnae in a free field situation.

Those wiggles are strongly dependent on how the headphones are positioned on the artificial head, and one of them is just an artifact of the resonance of the tubular ear canal model. In other words, they are dependent of the measurement apparatus, and your results on your head, artificial or real, will vary.

I think headphones should be measured in the free field at midrange and treble frequencies, and closed at bass frequencies, then the two plots stitched together. This not only well represents the way sound is presented to actual ears, but is reproducible and independent of the apparatus, so measurements can be easily and clearly compared.

About the main advantage of electrostatics, while the lack of breakup is the key aspect for you, the lack of HD and IMD are also very noticeable. Amplifier companies make a big deal about low distortion, but most dynamic drivers have orders of magnitude more distortion than most amplifiers, on the order of 0.2% - 1.0% and sometimes much more, whereas a good electrostatic can have THD as low as 0.01%, making low distortion in the signal from the source electronics worthwhile.
 

andreasmaaan

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#20
Hmm actually it seems that Soundstage does do spectral decay measurements on dynamic headphones. Doesn't appear to be any measured cone breakup in the audible band with the NADs I mentioned for example, but instead a couple of narrow-band resonances in the low treble. These use a 40mm driver so cone breakup couldn't be occurring that low down, although something sub-optimal is clearly going on here.

They also give a very helpful distortion spectrum, which does show some -75dB high order harmonics at 100dB SPL. These might be audible I guess, although it seems quite unlikely. I could run these figures through a GedLee calculator if anyone's interested, although I don't believe the GedLee metric is the final word on distortion audibility and I don't know of calculators for the more sophisticated metrics.
 

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