Do you owe it to yourself to try electrostatic speakers?
Ahh; YES.
All speaker designs have trade-offs but I do wish everyone could hear some the the better ESL designs. Many find their sound quite addictive.
I confess my bias for ESLs, which I've championed for years, and in particular my personal speaker referenced below.
In my experience, it's far easier for a DIY'er to build a world-class ESL than a world-class conventional speaker. It's not less work (believe me; it isn't), it's just that a good result is more certain because you start with less baggage.
I can list as many cons as pros for ESLs but the pros are really good and and the cons are not so hard to remedy.
Pros:
1. Ultra-low mass diaphragm is so effectively dampened by the greater coupled air mass that it simply doesn't *ring.
2. Line-source configuration gives magical imaging at the focal sweet spot.
3. Contrary to popular belief and most commercial designs, the dispersion pattern can actually be tailored to suit your desire, or even configured with switch-selectable wide & narrow dispersion modes.
4. No crossover for a full-range, or a hybrid can use a single crossover set below the ear-sensitive midrange region.
5. Typically excellent/superior coherence, resolution & transient response.
*An ESL diaphragm is remarkably resonance-free across the entire audio bandwidth except for its single fundamental "drum-head" resonance which typically occurs in the bass region at a frequency determined by its tension. This resonance is analogous to a woofer's free-air resonance (f/s).
Cons:
1. The diaphragm's drum-head resonance is a nasty-loud distortion that's difficult to mask.
2. Anemic bass unless panel is huge, and drum-head resonance renders it boomy & sluggish.
3. Hybrids add bass but rarely achieve a seamless blend between the woofer and stat panel.
4. The narrow dispersion which some listeners find objectionable (i.e. "head-in-a-vise" effect).
5. Capacitive load & impedance as low 1 Ohm in treble band requires a strong, stable amp.
6. Long-term reliability is historically questionable, especially for DIY versions.
Mitigating the drum head resonance:
Acoustat and some other full range designs apply a felt strip or mesh fabric on the rear stator to absorb some of the resonance energy.
Soundlab uses the drum-head resonance to boost bass output by dividing the diaphragm into multiple different-width sections which break up the single/loud/narrow resonance peak into multiple softer resonances spread over a wider bandwidth (i.e. "distributed resonance"). It's an innovative solution that mitigates the booming effect and boosts bass output, but it's not a perfect solution because the the drum head resonance is by definition a distortion, so using it must include its distortion.
Martin Logan, even though a hybrid design, tensions the diaphragm quite high, and likewise uses distributed resonance to enhance the upper bass/lower midrange, so that less EQ'ing is required to offset the panel's dipole roll off and flatten the response curve.
Mitigating the narrow dispersion:
Some describe the narrow dispersion as the "head-in-a-vice" effect but it does give very precise (almost magical) imaging at the tightly focused sweet spot. In fact, the Sanders/Innersound speakers are specifically designed with narrow dispersion. Some prefer it for solo listening but most agree it's not so good for entertaining guests.
Some designs curve the stat panel to about 30 degrees of arc, which curves its projected wave-front.
Some designs use a separate, narrow treble panel to spread the highs.
The Quad 63 and similar designs use separate bass panels and a center mid/treble panel with concentric ring conductors sequentially driven thru an LC delay line to function as a point source projecting a spherical wave front.
Mitigating the load capcitance:
Most designs add low value resistors in front of the transformers which renders the load partially-resistive (although still mostly capacitive).
Reliability:
Most manufactures have achieved significant improvements in recent years; although 20 years seems to be the best-case limit (except for Acoustats which are practically immortal). I would not advise purchasing a DIY ESL unless you do your homework on the specific design, and you and trust the builder to stand behind it.
Even with well designed panels, the weak link is the diaphragm coating degrading over time. So; the best designs would have panel that can be easily disassembled without damaging the stators, and preferably also leaving the diaphragm intact. If so accessible; the diaphragm can be easily re-coated if needed.
By far the most robust designs use insulated wire stators because of their higher resistance to arcing.
Perf metal stators can be reliable if made by a manufacturer like ML who has mastered the specialized processes required to prevent arcing.
I would no longer build or purchase a DIY ESL with perf metal stators because it's so difficult to smooth-over the cut metal edges and of the apply the insulating coatings to the high level of skill and margin required to prevent arcing.
The old Acoustat ESLs are practically bullet proof because they used superbly insulated wire stators and a simple carbon black diaphragm coating that remained stable over time-- they continue to play happily for decades!
So; if you want a reliable ESL; buy or build one similar to the Acoustat design. Or at least with stators than can be disassembled to re-coat or replace the diaphragms, should that ever become necessary.
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My DIY design (the Jazzman MkIII):
The drum head resonance:
Because my speaker is bi-amp'd using a digital crossover with parametric EQ's and plenty of amp power, I don't need to use the nasty drum head resonance energy to offset the dipole roll-off, so I've opted to work around it. That is; I simply avoid exciting the resonance by tensioning the diaphragm to resonate <100Hz and crossing the panel out to the woofer at least one octave above the resonance using a steep-sloped digital crossover (250Hz @48db/oct). Hence; the panel is not being energized/excited near the diaphragm's resonance frequency.
Dispersion:
The stat panel employs mutli-segment wire stators driven sequentially from the panel centerline outward, and function as a line source projecting a cylindrical wave-front. This works amazingly well; giving wider, smoother-trending dispersion than a 30-deg curved panel. Tailoring the dispersion requires choosing either a small sweet spot with more precise imaging or a wide sweet spot with less precise imaging or something in between those two extremes. I opted for the latter and tailored the segmentation scheme accordingly.
Load/Impedance:
The RC line which curves the wave front also linearizes the impedance and renders it predominantly resistive, as only the capacitance of the first two wire groups is reflected back to the amp. I'm told by a respected ESL mentor that this segmentation scheme also reduces the phase angle offset back to the amp (whatever that means), which helps to keep the amp stable (from ultrasonic oscillation).
Woofer/Panel Integration:
The matching dipole radiation patterns of the open baffle woofer and stat panel merge seamlessly and sound like a single driver; giving the best integration I've heard in a hybrid ESL.
Reliability:
The stat panels can be easily damaged by physical impacts to the wires or supporting lattice. Otherwise; they are highly arc resistant resistant and therefore unlikely to be harmed by even very loud music. Even without any kind of clamp-down or fusing circuitry, the electronics interface has also proven to be reliable. Over the past five years I've built seven pairs for myself and audio pals, and none have failed. How long will the diaphragm coating last? I can vouch for 5 years so far-- but I'll get back to you on that in about 10 years if I'm blessed to still be here.
Website with build photos & write-ups:
http://jazzman-esl-page.blogspot.com/?m=0Photo:
