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In Reply to: RE: On the subject of directivity posted by arend-jan on July 05, 2009 at 05:05:54
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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