M-L shenanigans: Convex or concave ESL for center channel?

Martin Logan currently offers three ESL-hybrid center channel speakers: Matinee, Motif, and Stage. The first two are convex, like the rest of their speakers. 'Stage' is concave. Why?

My suspicion is that the curved ESL part of these hybrid centers is only a token gesture to their main ESL products, and that the electrodynamic tweeter and mid-bass drivers make most of the sound. In other words, the ESL panel provides only a visual family resemblance to help unify the appearance of the home cinema speakers. If this is true, then M-L has taken a big step toward being a marketing-bs driven company (no better than Bose) and away from being a technology leader.

http://www.us.martinlogan.com/speaker_intro/stage.html
 
a guess....

As the ML is only curved in one direction, a very short centre (but still high compared to the wavelengths of interest) would suffer from poor distribution in the height direction. My guess is they added a conventional tweeter to increase the sweetspot. The blend of dynamic with esl sound may not suit fanatics, but surround sound doesn't either. Matter of taste I suppose.
 
Hi,

I´m pretty shure that ML´s product line would look much better -in a technological way- if Mr. Sanders were still the head of the company. Yeah, fashion-bs just hits the point nowadays.
Conceptually ML is speeding back to the 80s as one can see or better said hear from e.g a Summit....good panel, very poor bass, bad integration of both.
The ´plasma-deposited PET-diaphragm´ is nothing special technologically. The ITO-films are industry standards used in TFT-displays. The drawback of these films is their thickness! No less than 12µm! This was ok in the 80s. Nowadays ESLs feature thinner membranes if they want to play in the first league.
What would be rather SotA could be a plasma treated film of just 3-4µm thickness, coated with a extremely thin conductive polymer!

jauu
Calvin
 
While the OP is right that the mid-bass drivers do a good bit of work, the panels are covering the key ranges up to 2.7K. The use of the Tweeter is a must for good vertical coverage, as a 12” high vertical flat-profile panel is not giving any vertical dispersion to speak of.

Now, regarding horizontal profiles, regardless of convex (bulging outward) or concave (bulging inward) there are a lot of rear-wave reflections coming back through the panel. The worst are the panels that are convex (as seen from the front) like the Theater, as they focus the energy at a point mid-way behind the panel and most of it will reflect right back through.

The concave designs, like the Stage, might do better in this regard, as the reflections will tend to angle away from the speaker. However, I bet one could still measure some significant bounce from rear-waves even with that design.

See this graph of the impulse response of a convex panel squarely in front of a wall: There is a huge spike from the rear wall bounce. I figure any convex radiator placed a few feet to a few inches will suffer from this in a major way.

One thing I’d say about a Stage is that you should put a really good absorber *behind* the speaker. Any wall reflections are magnified with an open panel center because it is not angled out like a L/R might be, and the rear wave will bounce off the wall behind the speaker and come right back through it, delayed, causing some nasty comb filtering. This destroys the mid-range and high ‘balance’ and of course is not as good as the L/R sound.

Note that I said open panel, models like the Motif might not be as susceptible (although they have it to a degree) due to their woofer box being behind the panel, and the factory design treats the box. The Logos had no treatment and comb-filtering was a serious problem on that model.

The front radiation pattern of a concave design will focus at some point and then broaden back out in a 30 degree arc. This owrks fine as long as listeners are not in the pre-focal point range.

Personally, I gave up on ML centers and designed my own hybrid (using a 4’ ML panel). This one actually works, and no need for dynamic tweeters ;)
 
Calvin said:
...
The ´plasma-deposited PET-diaphragm´ is nothing special technologically. The ITO-films are industry standards used in TFT-displays. The drawback of these films is their thickness! No less than 12µm! This was ok in the 80s. Nowadays ESLs feature thinner membranes if they want to play in the first league.
What would be rather SotA could be a plasma treated film of just 3-4µm thickness, coated with a extremely thin conductive polymer!

jauu
Calvin


Hi Calvin,

Intersting point, are there any other ESL vendors using less than 12µm thickness films?

Anyone done DIY with thinner and had sucess?
 
Hi,

Yes, I refurbished Audiostatic ES200 with 4 micron tensilized Mylar®. Quite a succes.


If you have touched the 12 micron and the 4 micron afterwards you will be shocked. 12 micron is like a package wrap, crispy! Does not belong in esls in my opnion. 6 micron feels more smooth and is much less crispy and the difference between 4 and 6 micron also is obvious. Remember, the relative differences are large.
 
Thanks for that info, Jonathan. It hadn't occurred to me that there would be appreciable differences in rear wave reflections based on convex or concave ESL panels. And your system with your custom center channel looks impressive! Sad to say, most of us that don't use a projector won't be able to try your set-up.

I have thought of using one narrow panel (Aerius or Aeon?) on its side adjusted downward toward the listening position height supplemented with a mid bass driver in the middle and directly above the ESL panel. (I don't care what it sounds like away from the middle seats.) But it wouldn't have occurred to me to use it concavely (or with the wings) as you theorized, Jonathan. Either way, the axis of curvature is horizontal.

But my original question is what is M-L up to by not settling on concave OR convex with their vertical axis curved center channels? Seems they should pick one over the other, presumably concave, if the rear refections are so bad.