Has any one tried stators with countersunk holes

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I plan to use 3 mm thick aluminium stator panels with 4 mm countersunk holes to reduce the tunneling effect. Has any one tired it?

I have built ESLs with thin perforated stators but have always found them resonating at some frequency or other.

Here is the image of the hole configuration on the panel.

Thanks

tjjohn
 

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What exactly do you mean by tunneling? If you are trying to minimize the acoustic impact of the mass of the air in the holes on the HF response your best option is to use half-thickness radius on both sides of the stator. Hole separation distance may limit you to smaller radius.
 

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Thanks Bolserst for your comments. I am sorry for the delayed reply. I was away from home.

Yes I do mean the impact of the mass of air trapped inside the hole and I do agree about drilling half thickness radius on both sides as a better option.

However I was wondering whether the conical profile of the hole that looks like a hand held megaphone can in any way amplify the sound waves.

Also if a rear stator is made identical to the front and mounted with the cone facing the diaphragm will the sound from the rear be attenuated?.

My knowledge of acoustic physics is limited and any comments on this will be helpful.

Thanks

tjjohn
 
AX tech editor
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The 'shaping' effect on sound directivity will only come in effect at frequencies where the wavelength gets on the order of the hole and chamfer dimensions. From the top of my head with these dimensions that only happens in ultrasonics land.

Edit: the wavelength for 70kHz is 5mm...

Jan
 
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Hi Jan

The end effects on the holes increase the air mass too, pushing the frequency a bit lower than you might expect, especially for larger holes. The rounding of the holes reduces the end effects. Bolserst might be able to offer a more quantitative comment on this point.

The largest effect is due to the acoustic reflectance of the perforated plates, which is increased, and that means the pair of stators form a better resonant cavity. The result is a peak in the ESL output barely above the audio band and accompanied by a low-pass like response affecting the upper audio band, usually by several dB.

Bolserst and I published paper on this effect - send PM with email if you want a copy

regards, Rod
 
...Bolserst might be able to offer a more quantitative comment on this point.

I only have experimental results for half-thickness round over of holes. It essentially removed the entire contribution from the end effect.
For example the proposed stator with 3mm physical thickness and 4mm holes:
- Without round over, the stator would be acoustically ~4mm thick
- With half-thickness round overs, the stator would be acoustically ~3mm thick (same as physical thickness)

The proposed countersink hole shape would likely reduce the acoustic thickness to something in between the two extremes. It won't amplify sound in the audio band, and may actually reduce the sensitivity(SPL for given voltage input) of the ESL especially if the countersink is oriented toward the diaphragm. This is because it would reduce the strength of the static electric field between the stators. More info here: First time ESL builder

..Thanks for the excellent article...
A thread had been started last year on the article. I had intended to post an Excel spreadsheet that would perform the transparency calculations but there didn't seem to be much interest at the time and I forgot about it. Perhaps people found it easy to just run the LTSpice circuit as shown in the AES paper.
Superb article on HF ESL phenomena (IMHO)
 
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