Electrostatic Loudspeaker Attributes, the Mythic and the Mythical

February 12, 2021 3 Comments

Over the decades, there’s been a mix of wonders and flaws claimed for this interesting and surprisingly ancient type of loudspeaker. In this posting, I address a range of electrostatic attributes. Naturally, in the process, I keep in mind our 2008 version of the first practical design -- the one that started it all in 1955 -- namely the original JansZen Wide Range Tweeter. This was developed by my father, Arthur A. Janszen, a few years before several others began working on their own embodiments.

You’re probably hoping this posting won’t entail a continual hyperbolic slant in our own favor, which I've tried to avoid, despite this being me writing for the JansZen blog.

TLDR: Every company making electrostatics has its own approach, so each design in this category is a mixed bag of attributes -- mostly positive, some negative, and rarely indifferent.

To begin with, and probably why you’re interested in electrostatics, all offer exceptional clarity, immediacy, smoothness, low distortion, and transparency, especially in the midrange and treble. Various criticisms, however, have accumulated over the decades, spread out among a number of makers, past and present.

The upshot of the lengthy comparative notes below is that, although not perfect for every situation or taste in sound, JansZen electrostatic hybrids defy the usual criticisms. They’re as compact, setup-friendly, punchy, bass-rich, and trouble-free as any conventional loudspeaker, yet embody all the mythic sonic attributes that have always drawn people to electrostatics.

They’re also unique in two important ways: they’re the only monopole electrostatics, and also the only ones with controlled dispersion. This minimizes the influence of the listening room, so if you’re fond of attending live performances, you’ll like how a JansZen releases you from your listening room and transports you to each individual recording venue.

If you'd like a refresher first about how electrostatics work and what makes them better, you can start here.

Alrighty, then, on to the mythical and semi-mythical aspects and discussions thereof:

Amplifier requirements

Electrostatics need special amplifiers. There’s one type of full range electrostatic loudspeaker that presents an amplifier with such low impedances at treble frequencies and highly reactive loads that not all amplifiers can deal with them. There are a couple of such electrostatics currently made right here in the USA. One even makes its own special amplifier for its loudspeakers. These drive the entire area full range, rather than dividing it up into regions that have been designed for specific frequency ranges.

Those that are divided up are easy to drive; well known examples are QUADs and the venerable KLH Nine.

Hybrid electrostatics, such as JansZens, can also be easy to drive, because they have relatively low capacitance. In our case, this is because our electrostatic drivers are small, and we use cone woofers for the bass and midrange below 500 Hz. Our Carmelita stand-mount is a 6 Ohm loudspeaker, and our Valentina floor-stander is 4 Ohms, and neither one's impedance drops below 3.5 Ohms at any frequency, so they’re a normal load for any amplifier.

Electrostatics need powerful amplifiers. Depending on what you consider a powerful amplifier, this one is true for most electrostatics to some extent, mainly because most aren’t very sensitive, being in the mid 80 dB range. Single area full rangers as mentioned just above tend to need very powerful amplifiers, though, in addition to having to handle a 1 Ohm load in the treble and high capacitive reactivity.

Our Carmelita and Valentina have 84 dB and 87 dB sensitivity, respectively, and can handle 120W continuous power. 240W is a good number for headroom purposes, though, for reproducing high level drum, cymbal, piano hammer, and string pluck transients on top of loud musical passages. I think most people would consider us busted on this one.

On the other hand, because electrostatics are exceptional for having proper tonality at any volume level, if you listen at relatively low volumes in a quiet room, you’ll be perfectly happy with low powered amplifiers. In our case, if you’ve got a 25W/ch amplifier driving a pair of Valentinas, you’ll get 100 dB peak levels in a medium sized room, which is fine for handling crescendos and transients at a 75 dB average listening level. There are JansZen owners who gush about the sound with amplifiers in the 25W – 40W range (Decware, LT Audio, etc.).

Electrostatics need tube amplifiers. Some electrostatics eliminate the possibility of using tube amps at the outset because of their high power requirements. Others, like QUADs, the KLH Nine, and JansZens can go either way.

In these cases, because amplifiers can impart a tonal influence, deciding which type to use is just the usual matter of personal taste/opinion. One caveat might be that, since JansZen loudspeakers use cone woofers, the bass tends to be tighter and better controlled with solid state amplifiers, but of course, not everyone likes that.

At any rate, what goes into an electrostatic is what comes out, so whatever an amplifier’s sonic signature or lack thereof, its tonal influence will be perfectly evident.

Reliability

Electrostatics are unreliable. There are weaknesses in some designs that can lead to reliability issues:

Inadequate protection against the formation of unintended high voltage pathways. This can lead to clicking, popping, hissing, or squeaking sounds. Soot and dust from the air can collect on surfaces due to the presence of static electricity. Our design prevents dust collection as much as possible, and prevents whatever debris is inevitably attracted from coming into contact with any of the high voltage parts. Also, the polarization voltages are relatively low, so the tendency to attract particulates is commensurately low.

Inadequate or nonexistent protection against arcing. When the stator electrodes are not insulated, or are insufficiently insulated, sparks can puncture the working diaphragm, eventually accumulating to the point of causing driver failure. Our electrodes can withstand extreme voltages without allowing a spark. In fact, our electrodes glow blue with plasma and generate ozone without arcing as part of our tweeter Q/C test regimen, so should be alright with amplifiers that are much more powerful than recommended. But still, we recommend against trying that at home.

Loss or alteration of membrane tension. To work properly, the diaphragm that vibrates to make the sound must be not too tight or too loose. There are several ways that it can change, such as being over-stretched when the speaker expands thermally from high temperatures during transport, but then not recovering completely, or losing adhesion at its edges, or a phenomenon called "creep," where a polymer gradually relaxes on its own over time.

There is a particular problem with one well known design, where to work properly, all the tension has to be applied in the vertical direction, and none in the horizontal. Over time, however, tension can accumulate in the horizontal direction, usually due to polymer aging and chain creep that gradually adds horizontal tension. The result is that the membrane gradually saddles back toward the rear stator and eventually collapses onto it.

Failed bias supplies. Electrostatic loudspeakers require a constant electrostatic charge on their diaphragms. Because our electrostatics are not handling low frequencies, they do not need such high charge voltages, so our bias supply can have a minimal number of components -- no power transformer, no oscillator, no active circuitry. This makes it inherently reliable, as well as not being a source of any type of radiated emissions.
Failed signal step-up transformers. Electrostatic loudspeakers need high voltages to vibrate the membrane. As with the low diaphragm charge voltage situation, our electrostatics do not need very high drive voltages, and this means that the signal transformers endure relatively low stress.
Loss of membrane coating. Electrostatic loudspeakers require a microscopically thin, semi-conductive coating on the membrane to distribute the bias charge. There have been designs that inherently allow the coating to gradually disappear. Our coating is not only stable, but is protected by an additional membrane that is laid over it, which to our knowledge is unique.

Our warranty is 5 years. There are original JansZen Laboratory tweeter arrays from the 1950’s that are still in service.

Electrostatics make noise at idle. True for some, no doubt, but not ours, although malfunctions can occur over time. Please refer to item (1) in the section just above about unintended high voltage pathways.

Bass depth

Electrostatics have to be large to make bass. This is true for full range electrostatics. To get full, deep bass from a purely electrostatic speaker requires a lot of surface area.There are two reasons for this:

One is that to make loud bass, you've got to displace a lot of air. To do that, you can use a small diaphragm and displace it by a lot or a large diaphragm and displace it by a little. Electrostatic diaphragms can only be displaced by a little, and consequently must be large to make bass.

The other reason is that at low frequencies, an electrostatic must be operated as a dipole, namely open at the back. This is because it generates just enough force to make sound, and not enough to pressurize the air in an enclosure. Another way of putting it is that an electrostatic’s acoustical impedance is well matched to the air, which has a very low impedance, but the pressure inside an enclosure has a high impedance that it can’t possible match.

The reason an open back is an issue for bass is that, since bass is omnidirectional, it gets short circuited between the front and back. Basically, bass that leaves the edges of the front gets sucked in the back and vice versa. This is called dipole cancellation.

Dipole cancellation does have a benefit: the bass is emitted mostly to the front and rear, and not much to the sides. This reduces room mode excitation, which makes the bass more natural in most rooms. On the other hand, it restricts the bass depth. The wider the panel, the lower the bass it can reach. In the case of the KLH Nine, its 24” [61 cm] width creates a -3 dB point at 40 Hz. This corresponds to its natural bass resonance and thus performs a secondary duty of completing the damping of that resonance.

Electrostatics are all dipoles. Not to constantly harp on JansZen electrostatics, but this raises an important point – of all electrostatics, ours are the only ones that are not dipoles. This has three advantages:

without the back wave, room excitation is reduced, which improves the ratio of recorded sound to room sound. This improves realism and better conserves recorded ambiance by not swamping it with room reverberancy
omitting the back wave also eliminates comb filtering coloration created when a back wave reflects from the front wall and recombines after a short transit delay with the direct sound
reduces space requirements by allowing placement close to the front wall

Hybrid Shortcomings

Electrostatics mated to cone woofers have a noticeable tonal discontinuity. There are two aspects to this part of the story. One is that, at one time, woofers were not good enough to reproduce sound as well as electrostatics, which was a strong reason for making large electrostatic loudspeakers.

Although electrostatic loudspeakers still outshine all other types for midrange and treble clarity, distortion, and effortlessness, the best woofers have advanced to the point that those aspects are comparable. In addition, of the two types, dynamic woofers are much better at delivering punch and deep bass.

The other aspect is that there can be a compatibility challenge. While electrostatics are exceptional in terms of speed and group delay, not all hybrid makers have decided that making woofers behave commensurately is the best approach. Where a noticeable discontinuity exists, despite using decent woofers, the usual cause is the use of ported woofers, or signal processing that mimics the effect of ported woofers.

I have to believe that this happens when market research indicates that resonant bass is what a majority of people in its target market want, probably because they’re used to it. FWIW, when someone who is accustomed to ported woofers first receives a pair of JansZens, they may take a week or two to grow accustomed to the sound, and then attribute it to a break-in effect.

At any rate, as long as a loudspeaker system is implemented in a way that provides electrostatic-like responsiveness from the woofers, the transition can be made seamless and undetectable, and thus the days are long past when a full range electrostatic speaker is justifiable on sonic merits. Set up properly, JansZen loudspeakers will be down only 3 dB at 30 Hz in small and medium sized rooms, yet the bass remains tight and punchy. This gives the impression that the entire speaker is electrostatic.

Wimpiness and Delicacy

Electrostatics aren’t dynamic. This one depends on what the term dynamic is supposed to mean, but a pair of Valentinas can produce 108 dB peaks, and even at moderate loudness, when called for, their sound hits you in the chest with plenty of punch. Most people find our loudspeakers are dynamic, and of course some are surprised, given the reputation of electrostatics as too delicate to convey bombast.

Another form of being dynamic is to sound as clear, full, and revealing at low volume as at high, which all electrostatics excel at, having no need to be cranked up to "come alive."

JansZen loudspeakers can convey the subtlest nuance, yet can also rock, and even give you a trance club experience.

Electrostatics are unsuitable for popular music. Please refer back to the part about not being dynamic and the other part about not having enough bass.

Setup and Listening Area

Electrostatics need a lot of space and are hard to set up. As mentioned above, most electrostatic loudspeakers are dipoles, with just as much sound coming out the back as the front. Unless the loudspeakers are at least six feet [2m] out into the room, this causes comb filtering coloration as the reflected back-wave interacts with the direct sound. The back-wave also creates other challenging setup issues. For some, the sense of envelopment from extra sound bouncing throughout the room is worth the added coloration and degraded imaging, but this is not how we see things.

Our loudspeakers are monopoles, i.e., the sound comes only from the front. Their set up is pretty much the same as usual for conventional loudspeakers. In fact, because the tweeters are planar, and have a controlled directivity aspect designed into them, there’s a big reduction in wall, floor, and ceiling splash. This lets them go near walls without creating excessive brightness or degrading the spectacular imaging. It also reduces the impact of overly reverberant and asymmetrical rooms.

Electrostatics are "beamy." This refers to the need to stay within a very tight sweet spot to hear the full audio spectrum. The larger the speaker area, the tighter the beam, and the less latitude one has for listening position. The general solution is to use a small transducer, but that reduces loudness.

In our case, we make the area that produces the treble narrower than the area that produces the midrange. We can do this without losing loudness, because an electrostatic speaker gets louder as the frequency goes up. The sound from the treble and midrange areas overlaps and combines to provide about a 20° width at 10 kHz, and then drops off quickly farther to one side or the other.

This is called controlled dispersion, and creates a fairly wide sweet area, while restricting wall splash. It also means we do not have to add an intrusive electrical network to compensate for the increased loudness at higher frequencies. As with any stereo setup, there is one place where the imaging is centered and most convincing, but the tonal quality is maintained over an area that's wide enough for two or three people.

Electrostatics sound like headphones. When people say JansZen loudspeakers sound like headphones, it kills me for just a second, because what I think of first is how headphones create a center image in the interior of the head, which is weird, but then I realize they’re just referring to the immediacy of headphone sound.

Just to be clear, a JansZen’s stereo image is very convincingly three dimensional, out and away from you, with height, width, and depth, floating in the air. As is one of the usual goals in high end audio, the loudspeakers become difficult to locate with eyes closed.

Planar magnetic (magnetostatic) vs. electrostatic loudspeakers. It's easy to mistake a planar magnetic for an electrostatic, because they look about the same. Examples of magnetostatic planars are AMTs, isodynamic or quasi-ribbon tweeters, true ribbon tweeters, and full range implementations, such as made by Magnepan or Apogee. Both types vibrate planar membranes to make sound, but the operating principles could not be more different.

The most common planar magnetic, the quasi-ribbon, makes sound by vibrating a relatively thick plastic membrane that's loaded down by a serpentine track of metal foil bonded to it. The foil is needed to conduct the current that generates the dynamic magnetic force that makes it vibrate.

The membrane is thick to support the foil and withstand the heat generated when current flows through the metal track. One of the drawbacks to quasi-ribbons is that the heat causes the diaphragm tension to change with loudness, because the membrane material expands and contracts quickly with temperature, so the tonality isn’t entirely stable with loudness.

A true ribbon has a continuous metal foil and no supporting plastic membrane, so it’s far more stable with loudness than a quasi-ribbon. Its main potential pitfall is metal fatigue where the diaphragm is supported at its edges, which can cause the ribbon to fail at some point.

For both ribbon and quasi-ribbon, the weight of the metal foil presents a mechanical load much greater than the air, and this significantly influences its motion, creating a frequency-dependent delay between when the signal arrives and when the diaphragm moves. The weight also makes it quite hard to arrange things so that the diaphragm stops when it’s supposed to, so the transient response typically shows not only some delay, but also significant ringing.

The prime advantage of planar magnetic drivers is a big one, and it's the planar construction itself. This lets them operate as true pistons, and thus produce essentially uncolored sound. I'm sure that you who are fans of Maggies and Apogees can attest to the smooth, clear sound they make.

As the electrostatic moniker indicates, an electrostatic loudspeaker relies on electrostatic force, rather than magnetism. This type of driver applies a static electrical charge to an extremely much lighter diaphragm than those found in magnetostatic planars, and vibrates it by way of an alternating electrical field pushing and pulling that layer of charge. One advantage is that this makes no heat, so the performance is perfectly stable with loudness.

The big advantage, however, is the extreme lightness of the electrostatic diaphragm, which means its load is almost purely acoustical, i.e., it’s just the air itself. No energy is consumed accelerating its own weight, and thus no delay occurs after the signal arrives asking it to move. This lightness not only makes it able to respond instantly to transients, but also makes it easy to arrange for it to stop moving instantly when it’s supposed to.

Another difference is that the sound from planar magnetics has to penetrate a bulky magnet structure, at least on the back side, and in some cases both sides, whereas an electrostatic is fully open to its surroundings and thus unencumbered by surrounding structures.

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Thanks for your attention. I hope I’ve left you with a new appreciation for what electrostatic loudspeakers can and can’t do. I also hope that, if you’re not now nor ever have been an electrostatic loudspeaker owner, you've gained a sense that they’re worth considering.

All the best,

David Janszen

3 Responses

David

August 05, 2022

David, do electrostatics show a rising response anechoically on axis ?

AV

August 05, 2022

I enjoyed the blog, I hope others did too. I do agree with most of it. The true ribbon speaker has more qualities than mentioned here, though the mechanical fragility is indeed, and in due course, an issue. However, given the ease and low cost with which a membrane can be replaced – especially if the speaker has been built by oneself – mitigates the problem.

To say that “planar magnetics has to penetrate a bulky magnet structure” is a bit inaccurate. First, the sound only propagates through the slits in-between the magnet rows (like in the Magnepan example), but do not “penetrate” the magnetic strips themselves. In fact, they (air molecules) bounce off them and hit back on the membrane (admittedly, with some diminished energy). A true dipole ribbon doesn’t not suffer from this phenomenon. Second, the same is true for an electrostatic membrane, whether sandwiched between perforated plates (ML), wires, cast electrodes (Beveridge), etc. Third, it is not quite accurate to claim that an electrostatic membrane will “stop on a penny”, or instantly, although it will do so much much quicker than a dynamic driver, due to its low mass/accumulated energy. But in physics, once a mass is excited it will not truly stop instantly. Still, save for plasma speakers, that’s the closest we can get to instant stop.

All planar membranes obviously suffer to a degree from displacement non-linearity the closer it gets to its frame (and center spacers/dampers, if any) – at which point it cannot move at all. Some compensation can be had by judiciously increasing the magnetic/electrostatic force progressively nearer the frame – but the phenomenon cannot be entirely resolved. It is more pronounced with full range planar membranes, less of a problem with high frequency ones. The late Harry Pearson famously – or infamously – called it the “credit card” effect/sound.

In my opinion, no matter how much the dynamic drivers improve (and they certainly do) they will never equal the speed and transparency of electrostatic speakers, due to the former’s manyfold greater mass. As we know, it is “difficult” to bend the laws of physics. Dynamic drivers (woofers) can progressively eliminate more and more nasty distortions as technology advances – but cannot emulate the speed. My own compromise on this is to employ dynamic drivers at a tiny fraction of their max. potential displacement, thus making them move as little as, and accumulate as little energy as, possible. The price for that is (greatly) increased radiating acreage and judicious choice of driver size.

Hopefully we can enjoy more blogs here.

AV.

william lawhorn

August 05, 2022

A very informative and easy to comprehend article. I now have a greater appreciation for your speakers and company. .

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Electrostatic Loudspeaker Attributes, the Mythic and the Mythical

3 Responses

David

AV

william lawhorn

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