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In Reply to: RE: So, what's the down side, if any? nt posted by arend-jan on July 04, 2009 at 04:40:56
Hi arend-jan,
Before I answer your present post let me state that I regard you as being
one of the most valuable inmate of our beloved Asylum. I have been reading
every one of your contributions and I fully agree with all of them. The onlyone that I do not agree with is your statement in your inmate profile
("Feedback arend-jan") when in "Music Preferences and Comments" section
in "System Weakness" you wrote "NARROW SWEETSPOT". And in "System Goals/
Comments" your answer was "YOU-ARE-THERE/THEY-ARE-HERE EXPERIENCE". And why would you have this wonderful experience? Please make sure that you are safely seated before I tell you why. BECAUSE OF THE SWEETSPOT. To regard it as a weakness is a misconception shared by almost everybody. One noted person who explains this so eloquently is no other than Mr. Roger Sanders, himself a highly regarded electrostatic loudspeaker manufacturer, who saw the light and tells you about it at last year's CES.
Please click on the link below.
http://www.youtube.com/watch?v=Vdf3VA06iSA
I will complete my post in a new message.
Hi David,
I had seen the Sanders video before. I must say my alarm bells immediately start ringing when I see someone single out one aspect of speaker design and put's that much emphasis on it. Especially when it is accompanied by pseudo science (which by my definition is the presentation of claims as facts without the supporting evidence, nor any pointers to previously scientific work to support the claims). It almost always is a sales pitch and nothing new under the sun. What amazes me even further is that there are no polar plots to be found on Sanders website. So he talks a lot about directivity, but does not show the measurements for his own speakers. Sorry if I sound so harsh towards Sanders, but this is the way I see it.
I could go into the claims that he makes in the video one by one, but I chose not to do so mostly because this forum is not a technical forum and probably 99% of the readers would be bored to death. Note that I do not necessarily disagree with his point of view, but I do disagree with the way he presents and over emphasises it.
Directivity is nothing new. Let me quote a piece written by Baxandall on this subject from circa 1988. Baxandall is a true genius when it comes to electrostatic loudspeaker theory, acoustics and electronics.
"Taking all aspects into account, it is evident that some loudspeaker directivity is always desirable, but that the nature of this directivity needs to be rather carefully controlled, both for good stereo imaging, and to avoid an unpleasant or unnatural quality in the overall sound received by listeners.
The directivity of a loudspeaker at very low frequencies cannot in practice be made very great, for any totally enclosed cabinet design has substantially zero low-frequency directivity, and a doublet design has a theoretical directivity index of 4.8dB. At higher frequencies, more directivity is desirable, so that the directivity must in practice be allowed to increase with rising frequency, but it is m,ost important that this increase should be achieved in a smooth and continuous manner. It is also important that the off-axis frequency responses which accompany this increase in directivity should not have exaggerated and unnatural features, such as pronounced peaks or dips, nor be if a shelving or step-like form (ref 13 = D.E.L. Shorter, 'A survey of performance criteria and design considerations for high quality monitoring loudspeakers' - Nov 1958)
Gently falling high-frequency responses are frequently met in natural circumstances, for example when listening to sounds that have travelled round corners (ref 13) so it is hardly surprising to find that the off-axis sound from loudspeakers should be arranged to have this kind of characteristic of the overall results is to be interpreted as natural sounding.
Not only should the directivity increase smoothly and continuously with frequency above a certain frequency, but also the magnitude of the increase should be appropriately optimized - sufficient to give good stereo conditions, but not so great that listening positions become unduly critical. If any large increase in directivity is allowed to occur by 1000 Hz, the reverberant sound will appear to be bass-heavy and dull, and yet, for good stereo, some directivity at 1000 Hz is desirable. In this respect a doublet system has a real advantage, for directivity at 10000 Hz is then obtainable without having to suffer a variation in directivity below this frequency."
Note that Baxandall is discussing directivity in the light of electrostatic speakers, which by nature have an increasing directivity with frequency, but one that is far too much when no measures have been taken to prevent this. The original Quad ESL also has a number of mechanisms in place to control directivity.
Let me finish with another quote from Baxandall:
"No single recipe can be confidently stated to be universally right, partly because personal preferences are inherently involved, but also because the optimum directional characteristcs are very considerably influenced by the acoustics of the room in which the loudspeakers will be used (ref 35, P.J. Walker, 'The sound of the room', August 1991)"
Thank you for this post. I did not want to post with this great of detail regarding directivity and directivity idex. It can be a complex subject for some to understand.
What is clear is Roger Sanders and Peter Walker/Peter Baxandall had completely different ideas about the importance of directivity. While I have not heard the Sanders speaker and the designer gives little if any details about his speaker, it is clear by the geometry of the electrostatic element, at some frequency, there will be a rapid and dramatic change in the directitivity index of the speaker. This change in directivity will be neither smooth or gradual in nature. PJW/PB would claim this sort of rapid change will produce an unnatural overall balance and unpredictable off-axis response(in-room).
PJW commented about this type of approach, i.e. rapid change in directivity 'Of course, out in the open that sounds fine, directivity doesn't come into it. And if the loudspeaker is raised up off the floor fairly close to the listener so that he hears mostly direct sound anyway, it makes practically no difference what you do with directivity. But when you move the speaker to different rooms and try them the reproduction varies from room to room more than you would like.'
'This is because the after-sound, if you like to call it that, has got the characteristic of the power output firmly attached to it, and so it's all bassy. That won't do. Neither is it any good to make the power response level and have the directivity jump up 6dB around 200-500 cycles - that would sound most unnatural.'
'So we tried about a dozen directivities and found that the best thing to do is to change the directivity gradually, never by more than a decibal in an octave, preferably less than that. The trouble with most loudspeakers is that where you change from the woofer to squawker or squawker to tweeter the diameter of the speaker changes sharply and so does the directivity.'
Nothing new or exciting about PJW comments, just science. Few loudspeaker designers pay any attention to directivity and power response. The focus is on flat on-axis frequency response. But without flat power response any given speakers performance will change dramatically from room to room. This is not the case with ESL63. It sounds remarkable predictable/similiar in various room.
I would be careful to draw any conclusions about directivity from the looks of the thing. As I understand it he's using circuit board for the stators with the copper layers in between. Or at least that is what his patent was about IIRC. So it would be possible to control directivity by means of an electrically segmented stator.
Then again, the only thing we can do is guess since there is no data available, just that it is "highly directional".
I'd be interested to get a copy of the piece that you quote P.J. Walker from. Can you tell me what it is? Or send me an e-mail if you can share a copy.
If you are interested in 'new' developments on the area of directivity, there is/has been a lively discussion going on on diyaudio about waveguides, dipoles, cardioid's and controlling directivity. Unfortunately it is a bit scattered across multiple threads (Geddes on waveguides, beyond the ariel, and some others). There are some goodies to be found though.
Another interesting source is the writings of "John Kreskovsky" on http://www.musicanddesign.com/ Lot's of good info there!
Agreed. But since I can't find any detailed information on the speaker, and I don't wish to purchase a pair for experimenting, the best one can do is guess as to what is going on.The quote from Peter Walker is from the interview he gave to The Absolute Sound issue 23, 1981. I have scanned the entire interview and have it one file. Drop me a private email and I will be happy to send you a copy.
Edits: 07/06/09
and here's some more on Sander's speakers since you said you could not find more information
If you genuinely want to help us, give us some real information. Where are the whitepapers on directivity? Where are the measurements? Polar plots? Full frequency response? Burst decay?The one's you link to classify as promotional material in my book, not as whitepapers.
Edits: 07/06/09
sorry if this did not meet your needs
maybe these articles will better meet your needs
here's some information you may find interesting, written by Sanders
I actually have a copy of that book.When I bought it many moons ago, I was hoping that it would help me understand how electrostatic loudspeakers work. It did not. This book is about following a fixed strategy to put together your own speaker, not about gaining any insight in how it works. I suppose 'cookbook' does say it all.
In that light, I don't see how mentioning this book is helping the discussion. It seems to me that you are more eager to take any opportunity to promote your husbands products, than to genuinely contribute to the discussion. Now I can understand this, but this forum is not the right place.
Regarding the cookbook, it has been of no use to me. If anyone wants to have it for shipping cost, send me a message.
Edits: 07/06/09
Arend-Jan, I have no idea who you are, but you've just come across as a nasty little bully, a sad waste of space internet-commando. Grow up.
wow......You don't know me and I find it very unfair for you to judge me. I have sincerely attempted to provide information that many others have said were very helpful to them.
have a super fantastic day,
Angela
.
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