ESLs have bad decay plots

[MJ Dijkstra]

Hello all,

During time I've collected all kind of information about esls.
What strikes me is that all cumulative spectrum decay plots (CSD) from ESLs I've seen sofar, all show resonances at mid and high frequencies. Not very bad, but very good (dynamic) tweeters are able to exceed the ESL on this excercise and show CSD plots with a more rapid decay.
This is somewhat against the popular belief that the ultralight esl-film is effectively damped by the surrounding air and immediately stops with no ringing.
In a dutch book (Fikier) it is stated that the delays shown on a CSD plot can not be heard as they are 'masked' in case of an ESL. But I couldn't find any theory supporting or explainig this. The only thing I can think of is that the several resonances will cancel at a longer distance as they travel across the film while the CSD plot is closed miked and shows a small area only.
Does anyone have some opinions about this masking effect?
( it may help to explain the subjectively experience of micro-resolution in ESLs)

Martin-Jan

[Few]

Have you seen this thread? I inserted a discussion of the CSD measurements of panel speakers in post #31 and followed up with a few others. Perhaps it'll be useful.

Few

[MJ Dijkstra]

Hi Few,

Thanks for the link!
It seems from the comments of Atkinson about a decay-plot, that there might indeed be a possibility of canceling out of the resonances in case of large flexible membrane.

All the decay plots shown in the thread are worse than top-tweeters like scan speak....

[Capaciti]

Hi,

the quality of CSD of ESL is depending on the design of the ESL.

Curved designs with highly tensioned membrane show worse CSD. This is obvious since multiple resonances caused by bended shape and high tension of small areas wont enable fast decay.

Best CSD is possible using nonsegmented flat panels with optimized width-height ratio and very important optimized membrane tensioning.

Segmented ESL panels can have a very good CSD, but it is a long way of trial and error to find out appropriate segment areas and segment filtering. Segmented areas and depending filters will store energy.

Capaciti

[Capaciti]

Here is CSD of flat and segemented panel

Distance 1 meter, grey area is limited feedback due to reflections

Capaciti

[a.wayne]

Nice graph capacity , fast and clear decay ............. yours ?

[Capaciti]

Hi a.wayne,

yes that CSD is from my segmented fullrange panel. Membrane width is 20 cm, having 17 segments.

Capaciti

[a.wayne]

17 segments with only 20 cm width ......... ..Nice !

[Few]

Capaciti,
Based on your experience would it be accurate to say that some of the "hash" in the CSD when using segmented panels comes from having neighboring regions of the diaphragm driven by different signals? Your 17 segment, 20 cm wide panel would presumably drive neighboring segments of the panel with quite similar signals (because there are so many segments), and a non-segmented panel will, of course, have the entire diaphragm driven by the same signal.

Also, can you say a little more about what you've found regarding diaphragm tension? As you progress from low tension through the best tension to too much tension, is there a trend in the CSD that you've observed? This is the first I've heard of a connection between tension and energy storage, apart from the fundamental resonance, so I'm very interested to know what you've observed.

Finally (sorry to have so many questions!) have you seen any clear trends associated with the number or pattern of diaphragm clamping points, such as silicone dots between the diaphragm and stators?

Thanks for your helpful posts.
Few

[Capaciti]

Hi Few,

1. you are right, if segmentation is not optimized adjacent areas will interact with each other in a negative way.
2. My experience shows that a just mechanical strechted membrane even can take years until remaining resonances due to stretching are gone. Be aware that any resonance of the membrane will disturb CSD. E.g. a resonance at 200 Hz will show up as a multitude at e.g. 1000 and 2000 Hz where its critical to the ears
3. Thats why i perform a mixture of mechanical stretching and thermal treatment.
4. Silicone dots can have negative impact to CSD when distributed wrong. This cannot be calculated, just try different positions and measure. symmetrical is worse than nonsymmetric distribution of dots.
5. Most critical to CSD is the surrounding frame where the membrane is glued to. Often this is just some rectangular spacer material with a sharp edge. i am adding a damping layer at the outer edges of the membran area to minimize longitudinal resonance modes.