Does the screen seem to be moving when the speaker is playing? A signal generator and stroboscope can help highlight this.
I think the general trend would be for improved damping with more tightly adhered screen. How much improvement is hard to estimate from here. From bolserst's previous posts, seems like he's studied similar things, so hopefully he'll chime in.
I can't make out some of the construction details from your pictures. Is the diaphragm supported at any of your horizontal laths? Another way to ask this: what is the height and width of the diaphragm free area(s)?
I think the general trend would be for improved damping with more tightly adhered screen. How much improvement is hard to estimate from here. From bolserst's previous posts, seems like he's studied similar things, so hopefully he'll chime in.
I can't make out some of the construction details from your pictures. Is the diaphragm supported at any of your horizontal laths? Another way to ask this: what is the height and width of the diaphragm free area(s)?
Hi, I'm still not 100% satisfied with my newest stats, although it's still my best creation so far and plays without any problems 99% of the music I own. Only very dynamic recordings show the sensitivity / max volume limitation, and pieces with deep bass trigger resonance problems. For measurements see this topic below:
https://www.diyaudio.com/forums/planars-and-exotics/357561-stats-model-4-a-2.html#post6290403
Until recently I wasn't aware of acoustic impedance of damping screens: I just cheked the thread-count rather than checking the amount of rayles. The posts of Golfnut and Bolserst helped me understanding this.
In 2006, I first ordered damping screen, it was 64T / 160 mesh screen, not knowing the thread diameter or aperture, so actually not knowing the acoustic impedance. It could be something like 18 rayles according to some posts at this forum, but this is uncertain.
In 2019, because of limited effect on lowering Q of my diaphragm, I ordered 80T / 200 mesh screen. I assumed it to have a higher acoustic impedance, but with my current knowledge this is uncertain as the seller / advertisement doesn't specify thread diameter or aperture size.
This year, with my new awareness about rayles, targetting for at least about 50 rayles (this seemed to be a good number according to some posts here as I have a high Q large diaphragm), I ordered 140T / 355 mesh screen with a specified thread diameter of 34 um. According to the very helpful post / graph by Golfnut at:
https://www.diyaudio.com/forums/planars-and-exotics/152979-mechanical-sectioning-vs-silicon-dots-resonance-control-5.html#post5977154
... this screen would have an acoustic resistance of something in between 30 and 100 rayles - I guess it could be something around 50 - 60, unfortunately I don't have the formula.
So my assumption is that the newest damping mesh has a substantial higher acoustic resistance than my currently attached mesh screen. I glued the current screen in the inner side of the rear stator, just at the inner side of the wire stators. I only glued it on the wooden stator frame and glued the pvc spacers on top of the screen, using flexible glue which bonds well but is relatively easy to disassemble / remove. The stators use bolts to disassemble.
Right now, I'm wondering what would be wise: I'm curious about the effect of the new damping screen, but it will take some work to open the stators and replace 1 screen and compare it to the other (old) screen.
Any suggestions what would be wise? Test acoustic resistance of the different pieces of screen before replacing it in the stat itself? How? Or just replace and test it?
By the way - I'm also building my fifth set of stats, which will be hybrides, a combination of a smaller (40x150 cm panel dimensions, 22x120 diaphragm dimensions) stat panel with a ripole subwoofer. I could wait and use these new two panels to attach and compare two different mesh screens as well.
Difficult to make a good decision...
https://www.diyaudio.com/forums/planars-and-exotics/357561-stats-model-4-a-2.html#post6290403
Until recently I wasn't aware of acoustic impedance of damping screens: I just cheked the thread-count rather than checking the amount of rayles. The posts of Golfnut and Bolserst helped me understanding this.
In 2006, I first ordered damping screen, it was 64T / 160 mesh screen, not knowing the thread diameter or aperture, so actually not knowing the acoustic impedance. It could be something like 18 rayles according to some posts at this forum, but this is uncertain.
In 2019, because of limited effect on lowering Q of my diaphragm, I ordered 80T / 200 mesh screen. I assumed it to have a higher acoustic impedance, but with my current knowledge this is uncertain as the seller / advertisement doesn't specify thread diameter or aperture size.
This year, with my new awareness about rayles, targetting for at least about 50 rayles (this seemed to be a good number according to some posts here as I have a high Q large diaphragm), I ordered 140T / 355 mesh screen with a specified thread diameter of 34 um. According to the very helpful post / graph by Golfnut at:
https://www.diyaudio.com/forums/planars-and-exotics/152979-mechanical-sectioning-vs-silicon-dots-resonance-control-5.html#post5977154
... this screen would have an acoustic resistance of something in between 30 and 100 rayles - I guess it could be something around 50 - 60, unfortunately I don't have the formula.
So my assumption is that the newest damping mesh has a substantial higher acoustic resistance than my currently attached mesh screen. I glued the current screen in the inner side of the rear stator, just at the inner side of the wire stators. I only glued it on the wooden stator frame and glued the pvc spacers on top of the screen, using flexible glue which bonds well but is relatively easy to disassemble / remove. The stators use bolts to disassemble.
Right now, I'm wondering what would be wise: I'm curious about the effect of the new damping screen, but it will take some work to open the stators and replace 1 screen and compare it to the other (old) screen.
Any suggestions what would be wise? Test acoustic resistance of the different pieces of screen before replacing it in the stat itself? How? Or just replace and test it?
By the way - I'm also building my fifth set of stats, which will be hybrides, a combination of a smaller (40x150 cm panel dimensions, 22x120 diaphragm dimensions) stat panel with a ripole subwoofer. I could wait and use these new two panels to attach and compare two different mesh screens as well.
Difficult to make a good decision...
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If you want to document and optimize, measuring the acoustic resistance is probably the way to go. Something similar to this method, I suspect:
"Internal Document: How to use ASTM C-522"
www.frazierinstrument.com/internal/reference/standards/organizations/astm/guide-astm-c-522.html
Another approach is to build a test ESL panel you can swap different damping material into easily and gather data that way.
One thing I was always curious about with your current design is the diaphragm free span vs. spacing. I can't tell if your diaphragm has no internal support (free span is the whole diaphragm area) or if the wire supports also trap the diaphragm and divide it into 18 smaller areas (or some other number). Your resonance is quite low, which also suggests a panel that may have less inherent stability than one with a higher resonance.
"Internal Document: How to use ASTM C-522"
www.frazierinstrument.com/internal/reference/standards/organizations/astm/guide-astm-c-522.html
Another approach is to build a test ESL panel you can swap different damping material into easily and gather data that way.
One thing I was always curious about with your current design is the diaphragm free span vs. spacing. I can't tell if your diaphragm has no internal support (free span is the whole diaphragm area) or if the wire supports also trap the diaphragm and divide it into 18 smaller areas (or some other number). Your resonance is quite low, which also suggests a panel that may have less inherent stability than one with a higher resonance.
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In my damped "full-range" designs with similar spacing, I've typically found a smaller free span in one direction beneficial. For long, narrow panels something around 50x spacing for the narrow dimension has worked better for me, and still allowed diaphragm resonance in the 40 Hz range (heat shrinking for tension).
In addition to basic stability potentially being reduced with larger free spans, it also becomes increasingly difficult to keep the diaphragm centered, as flatness in the overall construction is hard to maintain over larger areas. The longer, narrow panels give you very good spacing control in one axis at least. I don't normally use spacer dots on large panels for the same reason. A full perimeter of support helps keep everything in line and gives more mounting points.
In addition to basic stability potentially being reduced with larger free spans, it also becomes increasingly difficult to keep the diaphragm centered, as flatness in the overall construction is hard to maintain over larger areas. The longer, narrow panels give you very good spacing control in one axis at least. I don't normally use spacer dots on large panels for the same reason. A full perimeter of support helps keep everything in line and gives more mounting points.
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