I think you did. Thanks for your analysis. With a 12 dB/octave upper roll-off on the woofers, there is a slight effect on the frequency response from the woofer interaction in some positions, which no one has found objectionable or apparently noticeable. Response uniformity and image height invariance with frequency are certainly better than for the case of a single woofer in floor-effect, mated to a line source.
FWIW, at the RMAF, the front chair was about 9 feet from each speaker. Seemed closer to some people, I guess because the speakers are so tall.
A legitimate concern -- not good to have a cabinet bonking around with ESL membranes acting as sails or kites. The need for lots of reaction mass may be a reason why this arrangement is not seen from other ESL companies.
The cabinets weigh 150 lbs. each. The moving mass is pretty low on both woofers. It's about 20g on the upper one, which including the air by an approximate rule of thumb comes to about 26g of moving mass. I would estimate that about 65 out of the 150 lbs provide reaction mass/moment to the upper woofer, for about an 1100:1 mass ratio. The cone's Xmax p-p is about 0.5", so the cabinet will be moving about half a thousandth of an inch p-p. Even if the membranes sail this entire distance, it is a fraction of what would matter. We have not measured the actual cabinet displacements, but vibration can hardly be felt, and there is no evident modulation of a high frequency tone by a low frequency tone.
I hope it is okay for me to mention here that there is a full review in the October Dagogo, and before a change was made that improved the bass response, HP made it the topic of his March "HP's Workshop".
Thanks for the detailed specifications on the woofer/cabinet mass ratio.
Wow! 150 lbs!!!
That is a good deal of mass for the 20g - 30g woofer to attempt to shake around.
I see now that the base is extended back for improved stability.
I located the one detailed review David mentioned online here:
Ed Momkus reflects on the validity of electrostatic speakers via the $27,560 Janszen Model One - Equipment Reviews - Dagogo
I certainly don't expect Mr. Janszen to share all his trade secrets, so....
Has anybody else every attempted to use an ESL in a monopole(box) configuration?
This is intriguing to me as I have always dismissed the idea as compromised at best.
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Yes, of course. Can't sound spacious, etc. without the back wave. The back wave can't be soaked up completely in a box. Sounds less realistic without the extra room ambience. Well, actually, all seem to be well known yet incorrect, although it can be a matter of taste and of degree. At the risk of being accused somewhat rightly of blatant self-promotion, here are a few of my thoughts on the subject, simplified for brevity:
Interference: Not that I disagree categorically with Herr Linkwitz's basic thesis that the sense of realism can under some circumstances be improved by increasing the local room ambience and adding it to the recorded ambience, but this arrangement can be a compromise. Mainly, the frequency response is roughened, because it undergoes comb filtering due to interference, especially when the relatively coherent back wave from a large area dipole (or bipole), or even a tall line interacts with its own reflection from the walls behind the speaker and with the front wave. Only a strongly beaming tweeter would be able to completely avoid interference effects by entirely missing any part of the first rear reflection of its own beam. Point sources are not too bad, either, for the opposite reason, because their spherical sound fronts are inherently more dispersive. FWIW, I believe the Linkwitz designs minimize the interference drawback. Of course, much can be solved by judicious use of diffusers and absorbers, or at least moving the speakers out a considerable distance from the back wall, but that is IMHO a bucket of ugly compared to just eliminating the back wave, not to mention that it probably counteracts some of the hard won ambience benefits.
Back wave absorption: It is possible to completely absorb the back wave from an ESL in a box, at least down to the upper bass region. A side benefit is the opportunity to damp the fundamental membrane resonance.
Local ambience: I share with many the belief that realism is improved by restricting although certainly not eliminating local ambience. Take this too far, and you have external headphones, or an outdoor venue effect. Go too far the other way, and you are listening to speakers playing in a room, and not the performers playing in the original venue. There is a happy medium, and I think it is not going to far to start with avoiding dipoles, at least for the mids and treble. Dipole woofers are another topic for another time.
Spaciousness: People who were previously convinced that only dipoles can produce a sense of spaciousness are amazed when they hear the Model One. With the right material in a reasonably lively room, it seems like the sound is coming from everywhere. One visitor to the RMAF exhibit, who brought his own discs, remarked that the effect was strong enough that he could not resist a couple of times looking over his shoulder and off to the side, this in a hotel room with no treatments at all. (Are you out there? Please blog about it.) This happens largely because of wide dispersion, and a quite uniform spectrum off axis, so the room reflections have about the same spectral content as the original, minus wall absorbency. The goals of dipole radiation, as I understand them, are thus achieved without the drawbacks.
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