I was thinking, If curved panels have more trouble with bass and flat panels are bad off axis. way not curve the last 3-8 inch's of the panel with the center still flat? I searched the forum and was shocked i found nothing as this seems like an easy idea.
a curved part in the middle and straight ´ears´ was the concept of the old ML CLS. A planar part in the middle doesn´t make much sense i.m.h.o, because of manufacturing probs. When the metal sheet is bowed, there will always be some inches of straightness at the edges left. Apart from that, I don´t think, that a combination of curvature and straightness is useful in generating a fullrange system. The easiest and best is still to use a curved panel together with a dipolar dynamic bass.
Curving the panels a-la ML doesn't do much for dispersing highs. Look at polar plots of the things. The curve is there to make the assembly mechanically rigid, and maybe for asthetic reasons. If the panel width is greater than a wavelength (and it is at the upper end of the audio range) it's going to beam, slightly curved or not.
If you want high frequency horizontal dispersion you can segment the stators into narrow vertical strips. Drive the center from the full bandwidth signal, and then use resistors to connect to the strips as you go outward from the center. You will flatten the response at the same time you're broadening dispersion. Look at the Malme patent.
Quad does something similar in the ESL-63, though they use inductors instead of resistors to connect circular segments so that dispersion is increased in both horizontal and vertical directions. They say some some stuff about delay lines, and pulsating spheres, etc., but whatever you want to call it, the ultimate effect is increased dispersion in both horizontal and vertical dimensions.
No matter what you do to the radiation pattern, speakers will always sound best to the one person who is sitting in the "sweet-spot".
Just take a look at the way a CLS (ML) is constructed. This is probably what you want. I have auditioned the CLS1 and it can sound very good.
Martin Logan talks about controlled dispersion. Although high frequences are still radiated across a limited angle, it doesn't sound 'beamy' to my ears. It is also better than electrical segmentation which is a step backwards to a multiple drivers design.
Acoustat used two, three or four cells in a small radius, the effect is/was to spread the HF dispersion. It does work to some extent borne out by simple experiments with Acoustat cells set up flat and compared to the radiusing they used.
This approximates your idea pretty closely.
Which imaged "better" is a horse race on several levels.
Sound Labs did the same trick but with many smaller size cells positioned over a 1/4 cylinder...
The original Quad design tried to overcome this problem with a narrow strip for the highs, wider for the mids and widest for the bass - separate cells.
Beveridge overcomes this with a complex acoustic lens, acheiving supposedly a 180 deg dispersion across the spectrum!
I doubt that Your concept sounds best. The reason is the strongly differing directivity of the three drivers. The big prob with bad sounding hybrid-ESLs is mainly the change in directivity between the globally distributing woofer and the dipolar and beaming ESL. Adding a third driver (which is wholely unnacessary with ESLs) just adds probs without solving one (btw. get rid of the illusion that a plasma is massless! Indeed is a ESL -with regard to membrane area- equally light or even lighter than the volume of the tiny flame! And the ESL´s distortion is much lower at higher levels).
Quote Calvin: The big prob with bad sounding hybrid-ESLs is mainly the change in directivity between the globally distributing woofer and the dipolar and beaming ESL.
Calvin: interesting that you bring up this topic. I am concerned about this very problem in two very different systems that are on my drawing board at the moment. The first is trying to match dispersion characteristics between a Lambda Unity horn and a suitable bass driver at the crossover point of about 350 Hz., and the second is in an ESL/dynamic hybrid project.
It would seem to me that if you look at most of the hybrids out there (comercial) they attempt to run the bass driver up as as far as they can to minimize panel excersion (a good idea). In most cases they (the comercial dsigners) will run the bass driver up to just below the point where the driver begins to loose its pistonic operation. Roger Sanders designs are like this I think.
While this tact is sucessful in allowing tight stator spaceing in the panel and so higher sensitivity. This then creates the problem with major differences in the dispersion of the two driver elements at the crossover frequency. Seems that I remember reading on the Altec Heritage site about a dynamic/horn system where the designer was concerned about this. To solve the problem he chose to use a 10 inch mid driver and ran it up to the point where it actually started to become directional enough so that its dispersion then matched that of the horn. This was then the determining factor for setting the crossover point. A smaller midrange driver could have done the job in terms of output but would have had to be run up much higher in frequency to attempt to match the horns directivity pattern.
So without the benefit of measurements to go by (I am just guessing here) I would think that the ESL panel with its figure of eight polar pattern would make a better match to a substantially larger bass/mid driver than is normally seen on commercial systems (which are attempting to be domestically acceptable). A 12 or even 15 inch bass/mid driver would begin to become much more directional far sooner than a smaller driver. I am just going from memory (probably bad) so please jump in and correct me here but I thought that a 10 inch driver would be still operating in pistonic mode (omnidirectional) up to about 800 Hz. Matching dispersion at crossover is a very inportant consideration. If I am to make a hybrid system work then this issue must be addressed.
Anyone care to shed some experience on this issue? Do you think that smaller dynamic drivers (say 6.5 inch or smaller) could be run in tandem in a way to intentionally create the desired directivity pattern at the chosen crossover point? I look forward to your thoughts on this. Best regards Moray James.
You can not hear differences in radiation patterns when fixed to one listening position in an anechoic room.
In normal listening room you have reflections to walls and different radiation patterns will suffer from them in a different way.
The woofer of a hybrid esl may suffer from another radiation/reflection pattern, but since it produces only very low freq, I am not afraid that it will have a different spatial character. Also, most esls are not that directive at these low freqencies.
well it´s my experience over the years that a combination of a dipolar bass and a ESL (crossed over between 100 and 250Hz, depending on ESL size) always worked very well and never gave the probs other concepts had. Maybe it was just due to the imo superiority of dipolar bass, but stacking dipolar basses to get even closer to the dipolar-cylindrical character of the (strip-size) ESL always improved sonics. Maybe it depends on the different coupling of energy into the room (velocity/pressure transducer) that the typically best position for a dipolar transducer differs from that of a global transducer (CB, BR, etc.),maybe it depends on the differing soundpressure level over distance, or maybe nothing of that at all, but since the dipolar basses can be built extremly small and blend in best with the ESL, it´s my prime choice
KF: your idea of leaving a gap around the edge of the stator so that there is a section of undriven diaphragm is exactly what Jim Strickland of Acoustat did. Perhaps he had the same idea that this would allow for a more pistonic motion of the diaphragm.
Roger Sanders did a lot of research into diaphragm motion. I think that I recall him saying that if you took a lamp and watched a reflection in the diaphragm while the speaker was playing that you could clearly see that the reflection was not distorted so the diaphragm motion had to be pistonic. Regards Moray James.
I'll try this, I think it should be an easy test for a small set "6 by 9 inch or so" who knows i may get new computer speakers out of this. I will make two sets keeping every thing the same but the driven area. Give me 5 weeks for the money to gather and I'll post back what i found.
An ESL diaphragm will move as a flat planar piston with all bending taking place at the edge – but only above the low-end resonance. Near or below fundamental resonance, the stiffness or stretch of the plastic dominates over the air load and you get a drum head shape (probably a catenary curve). In the vicinity of resonance, you’ll probably see a blending of planar with catenary – talk about tough math! High above resonance, where most of the action is anyway, the air load dominates over the plastic stretch, except at the constrained edges. Here is an opportunity for further research. Since so much bending is taking place across such small dimensions near the edge, are there better ways to build a trampoline-like suspension? Is the stretching producing any chaotic behavior (tiny crinkling noises) at -80, -90 or -100dB? John Atkinson commented on this chaotic behavior after measuring ESLs but didn't understand the source of it. Maybe I’m making a mountain out of a mole hill; I don’t know. By the way, cones generate all kinds of chaotic noises (scrapes, cone bending noises, turbulence, etc), and probably a lot more than ESLs.