Ahh; YES.
No speaker is perfect but I do wish everyone could hear some the the better ESL designs. I'm sure many would find their sound addictive.
I must first disclose my bias favoring ESLs, which I've championed for years, and in particular my latest DIY design 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. Not that it's less work (the labor is horrendous)-- but 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 the cons are not terribly hard to remedy in a good design. Some manufacturers mitigate the cons quite well.
Pros:
1. The ultra-low moving mass diaphragm is so effectively dampened by the greater air mass it's coupled to, that it simply doesn't ring.
2. Line-source configuration gives really good imaging.
3. Contrary to popular belief and commercial offerings, the traditionally narrow dispersion pattern can be DIY-tailored to your desire, or even configured with switch-selectable wide & narrow dispersion modes (costly but do-able).
4. No crossover in full range designs, or hybrids can use a single crossover set below the ear-sensitive midrange.
5. Typically excellent/superior coherence, resolution & transient response.
Cons:
1. The diaphragm's drum-head resonance is a nasty-loud distortion that's difficult to mask.
2. Anemic bass unless the panel is huge, and drum-head resonance can render it boomy & sluggish.
3. Hybrids add the bass but few achieve a seamless blending of the woofer & stat panel.
4. 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 iffy, especially in DIY versions.
Mitigating the drum head resonance:
An ESL diaphragm is remarkably resonance-free across the audio bandwidth except for its single fundamental "drum-head" resonance peak 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) and is likewise undesirable.
Acoustat and some other full range designs apply a felt strip or mesh fabric on the rear stator which partially absorbs 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 uses a similar approach but with higher diaphragm tension / higher resonance frequency, and distributes its energy to boost the upper bass / lower midrange. This mitigates the dipole roll off without having to use EQ boost (which isn't available anyway with a passive crossover). The accompanying distortion remains but it's fairly we'll masked, without sacrificing much efficiency so --- smartly done in my opinion.
Mitigating the narrow dispersion:
Narrow dispersion is not necessarily a flaw. In fact, the Sanders/InnerSound speakers are purposely designed or narrow dispersion because it gives the most precise imaging at their tightly focused sweet spot. Some prefer the narrow sweet spot but it's not so good for entertaining guests, and most other designers opt for wider dispersion.
Some designs (ML & Soundlab) curve the stat panel to about 30 degrees of arc, which curves its projected wave-front. The small curvature is still a bit beamy but retains much of the magical imaging.
Some designs use a separate, narrow treble panel to spread the highs.
The Quad 63 and similar designs use separate bass panels plus 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 now produce reliable speakers, although 20 years seems to be the best-case limit (except for Acoustats which are seemingly 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.
The weakest link in any ESL panel is the diaphragm coating degrading over time. So; a good design goal would allow for easy disassembly without damaging the stators, and preferably leaving the diaphragm intact. If so accessible; the diaphragm could be easily and cheaply re-coated or replaced.
The most robust designs use insulated wire stators because of their superior 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 perfectly smooth-over the cut metal edges and apply the insulating coatings with the margins needed to prevent arcing.
The old Acoustat ESLs are bullet-proof reliable because they used superbly insulated wire stators and a simple carbon black diaphragm coating that remained stable over time-- these continue to play happily for decades!
So; if you want a super reliable ESL design; choose one similar to an Acoustat, or at least one than can be easily disassembled to access the diaphragm.
*********************************************************************************************************************
My hybrid ESL design (the Jazzman MkIII):
The drum head resonance:
Because my speaker is a hybrid, and bi-amp'd using a digital crossover with parametric EQ's and ample amp power, I don't need to use the nasty drum head resonance energy to offset the dipole roll-off, and so I've opted to work around it. That is; I simply avoid it 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:
Tailoring the dispersion requires choosing either a narrow sweet spot with very precise imaging or a wide sweet spot with less precise imaging or something in-between (physics forces this choice-- you can't have it all).
I chose the latter option and tailored the segmentation scheme accordingly.
The stat panel employs symmetrical multi-segmented wire stators driven sequentially from the panel centerline outward to function as a line source projecting a cylindrical wave-front. This works amazingly well; giving wide, smooth-trending dispersion.
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 scheme also reduces the phase angle offset back to the amp (whatever that means), which helps keep the amp stable (from ultrasonic oscillations).
Woofer/Panel Integration:
The matching dipole radiation patterns of the excellent OB mounted Eminence KappaLite 3012LF woofer and the stat panel merge seamlessly to sound like a single, coherent driver-- the best integration I've heard in a hybrid ESL.
Reliability:
The wood lattice supported wire stators are less impact-tolerant than perf metal stators and must be handled accordingly. Otherwise; they are highly arc resistant resistant and therefore unlikely to be harmed by even crazy-loud volume levels. Even with no protection 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.
The stators can be either bond bonded together or mechanically mated in this design. If mechanically mated; the stators can be easily separated to access the diaphragms, should servicing them ever be needed.
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=0
Photo of the Jazzman MkIII ESL:
No speaker is perfect but I do wish everyone could hear some the the better ESL designs. I'm sure many would find their sound addictive.
I must first disclose my bias favoring ESLs, which I've championed for years, and in particular my latest DIY design 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. Not that it's less work (the labor is horrendous)-- but 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 the cons are not terribly hard to remedy in a good design. Some manufacturers mitigate the cons quite well.
Pros:
1. The ultra-low moving mass diaphragm is so effectively dampened by the greater air mass it's coupled to, that it simply doesn't ring.
2. Line-source configuration gives really good imaging.
3. Contrary to popular belief and commercial offerings, the traditionally narrow dispersion pattern can be DIY-tailored to your desire, or even configured with switch-selectable wide & narrow dispersion modes (costly but do-able).
4. No crossover in full range designs, or hybrids can use a single crossover set below the ear-sensitive midrange.
5. Typically excellent/superior coherence, resolution & transient response.
Cons:
1. The diaphragm's drum-head resonance is a nasty-loud distortion that's difficult to mask.
2. Anemic bass unless the panel is huge, and drum-head resonance can render it boomy & sluggish.
3. Hybrids add the bass but few achieve a seamless blending of the woofer & stat panel.
4. 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 iffy, especially in DIY versions.
Mitigating the drum head resonance:
An ESL diaphragm is remarkably resonance-free across the audio bandwidth except for its single fundamental "drum-head" resonance peak 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) and is likewise undesirable.
Acoustat and some other full range designs apply a felt strip or mesh fabric on the rear stator which partially absorbs 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 uses a similar approach but with higher diaphragm tension / higher resonance frequency, and distributes its energy to boost the upper bass / lower midrange. This mitigates the dipole roll off without having to use EQ boost (which isn't available anyway with a passive crossover). The accompanying distortion remains but it's fairly we'll masked, without sacrificing much efficiency so --- smartly done in my opinion.
Mitigating the narrow dispersion:
Narrow dispersion is not necessarily a flaw. In fact, the Sanders/InnerSound speakers are purposely designed or narrow dispersion because it gives the most precise imaging at their tightly focused sweet spot. Some prefer the narrow sweet spot but it's not so good for entertaining guests, and most other designers opt for wider dispersion.
Some designs (ML & Soundlab) curve the stat panel to about 30 degrees of arc, which curves its projected wave-front. The small curvature is still a bit beamy but retains much of the magical imaging.
Some designs use a separate, narrow treble panel to spread the highs.
The Quad 63 and similar designs use separate bass panels plus 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 now produce reliable speakers, although 20 years seems to be the best-case limit (except for Acoustats which are seemingly 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.
The weakest link in any ESL panel is the diaphragm coating degrading over time. So; a good design goal would allow for easy disassembly without damaging the stators, and preferably leaving the diaphragm intact. If so accessible; the diaphragm could be easily and cheaply re-coated or replaced.
The most robust designs use insulated wire stators because of their superior 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 perfectly smooth-over the cut metal edges and apply the insulating coatings with the margins needed to prevent arcing.
The old Acoustat ESLs are bullet-proof reliable because they used superbly insulated wire stators and a simple carbon black diaphragm coating that remained stable over time-- these continue to play happily for decades!
So; if you want a super reliable ESL design; choose one similar to an Acoustat, or at least one than can be easily disassembled to access the diaphragm.
*********************************************************************************************************************
My hybrid ESL design (the Jazzman MkIII):
The drum head resonance:
Because my speaker is a hybrid, and bi-amp'd using a digital crossover with parametric EQ's and ample amp power, I don't need to use the nasty drum head resonance energy to offset the dipole roll-off, and so I've opted to work around it. That is; I simply avoid it 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:
Tailoring the dispersion requires choosing either a narrow sweet spot with very precise imaging or a wide sweet spot with less precise imaging or something in-between (physics forces this choice-- you can't have it all).
I chose the latter option and tailored the segmentation scheme accordingly.
The stat panel employs symmetrical multi-segmented wire stators driven sequentially from the panel centerline outward to function as a line source projecting a cylindrical wave-front. This works amazingly well; giving wide, smooth-trending dispersion.
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 scheme also reduces the phase angle offset back to the amp (whatever that means), which helps keep the amp stable (from ultrasonic oscillations).
Woofer/Panel Integration:
The matching dipole radiation patterns of the excellent OB mounted Eminence KappaLite 3012LF woofer and the stat panel merge seamlessly to sound like a single, coherent driver-- the best integration I've heard in a hybrid ESL.
Reliability:
The wood lattice supported wire stators are less impact-tolerant than perf metal stators and must be handled accordingly. Otherwise; they are highly arc resistant resistant and therefore unlikely to be harmed by even crazy-loud volume levels. Even with no protection 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.
The stators can be either bond bonded together or mechanically mated in this design. If mechanically mated; the stators can be easily separated to access the diaphragms, should servicing them ever be needed.
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=0
Photo of the Jazzman MkIII ESL:
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