Hi Everyone!
I'm going to build a pair of hybrid ESL speakers. I went to my local metal supermarket today and they have two types of perforated steel sheets.
The first one is a 16 gauge with 0.125" holes staggered on 3/16" centers. It has a 40% opening area.
The other sheet is 18 gauge and has 0.156" holes. It has a 63% opening area.
Will either of these be suitable? Or should I try for something more ideal from somewhere else?
I'm going to build a pair of hybrid ESL speakers. I went to my local metal supermarket today and they have two types of perforated steel sheets.
The first one is a 16 gauge with 0.125" holes staggered on 3/16" centers. It has a 40% opening area.
The other sheet is 18 gauge and has 0.156" holes. It has a 63% opening area.
Will either of these be suitable? Or should I try for something more ideal from somewhere else?
16 gauge equates to .063" or about 1.6 mm
The Cookbook recommends hole sizes should not be smaller than 2x the stator thickness so 16 gauge/.125 holes would be at the limit before coating the stators and the holes would get a bit smaller still after coating.
That's a tough call-- opinions, anyone?
Hi,
A second explanations is based on the behaviour of absorbants.
Punched metal sheets are useable as porous absorbers with a frequency dependant degree of transmittance.
The formula for a transmission degree of 50% reads:
f0.5~1.500*eta/I [Hz]
with:
eta the openness of the sheet in % and
I the acoustically effective thickness of the sheet, which depends on the sheet´s thickness X and the hole´s diameter D.
I=X+pi*D/2 [mm]
Example: eta=33%, X=1mm, D=3mm
I=1mm+3.14*3mm/2 --> 5.7mm
f0.5~1500*33/5.7 [Hz] --> 8.7kHz
This implies the choice of thin sheets, small holes and high openness and distinct rounding/tapering of the holes.
A calculation via the helmholtz-formula leads to similar but slightly lower results.
The calculations are not precise and include a high degree of tolerance .. in the dimensional values in... the air volumes.... in the shape of the holes etc. etc.
So regard it as a rule of thumb and only basic design guide.
jauu
Calvin
Yes thats true. If the hole wands are straight, every hole forms a small cylinder. The summed up volume of air trapped in all those tiny cylinders forms a Helmholtz resonator together with the air volume which is encapsulated between diaphragm and stator surface. As every Bassreflex system it performs a bandpass amplitude response which restricts the upper bandwidth limit. If the cylinder´s length is short compared to its diameter the effect is less pronounced and the upper bandwidth limit is high. Similarly rounded or tapered wands of the holes reduce the effect too. So with smaller hole diameters there goes a thinner sheet unless You are capable to round the holes´s wands.
A second explanations is based on the behaviour of absorbants.
Punched metal sheets are useable as porous absorbers with a frequency dependant degree of transmittance.
The formula for a transmission degree of 50% reads:
f0.5~1.500*eta/I [Hz]
with:
eta the openness of the sheet in % and
I the acoustically effective thickness of the sheet, which depends on the sheet´s thickness X and the hole´s diameter D.
I=X+pi*D/2 [mm]
Example: eta=33%, X=1mm, D=3mm
I=1mm+3.14*3mm/2 --> 5.7mm
f0.5~1500*33/5.7 [Hz] --> 8.7kHz
This implies the choice of thin sheets, small holes and high openness and distinct rounding/tapering of the holes.
A calculation via the helmholtz-formula leads to similar but slightly lower results.
The calculations are not precise and include a high degree of tolerance .. in the dimensional values in... the air volumes.... in the shape of the holes etc. etc.
So regard it as a rule of thumb and only basic design guide.
jauu
Calvin
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Freddy,
There you have it !
(I couldn't have said it myself, lol)
Choosing a stator material is a tough call for most of us-- you study all you can and go with your gut feeling on the hard calls and hope you made the right choices.
Thanks Calvin -- I was hoping you would jump in and bail me out on that question.
There you have it !
(I couldn't have said it myself, lol)
Choosing a stator material is a tough call for most of us-- you study all you can and go with your gut feeling on the hard calls and hope you made the right choices.
Thanks Calvin -- I was hoping you would jump in and bail me out on that question.
Hi,
I just copied the formulas from my notes. Rethinking about I wonder if they can be right though. It´s the formula for effective thickness which seems a bit weird to me, because larger diametered holes would lead to a lower transmittance factor. This can´t be right. Thinking in extrems...a single huge hole would show a lower transmittance than a myriad of tiny holes with same openness!?!? Too, a smaller hole increase losses, which allows for microperforated film absorbers to omit with additional damping material alltogether, which larger holed absorbers still need.
jauu
Calvin
I just copied the formulas from my notes. Rethinking about I wonder if they can be right though. It´s the formula for effective thickness which seems a bit weird to me, because larger diametered holes would lead to a lower transmittance factor. This can´t be right. Thinking in extrems...a single huge hole would show a lower transmittance than a myriad of tiny holes with same openness!?!? Too, a smaller hole increase losses, which allows for microperforated film absorbers to omit with additional damping material alltogether, which larger holed absorbers still need.
jauu
Calvin
Calvin,
Sorry, I don't understand what these numbers mean. Is this a European gauge system?
Ah OK, smart! Simple and direct terminology
Jonas, your avatar is freaking me out...LOL, I see it out of the corner of my eye and just about swat my screen.
What is the effect of the diaphragm's thickness? I see 6 micron film from TAC and also 3 micron on ebay. Is it simply a matter of thinner is better because of less mass up to a certain point where structural integrity gets compromised? In other words, if it's too thin then it could break too easily?
kindly check this
Kindly check this thread on page six, "start to finish esl" by mavric. I had alot and i mean alot of help here. CharlieM, Gerald, Chinsettawong,Calvin, and many others. I took alot of pictures and tried my best to show details and where the material came from., CharlieM has a blog page that will save you alot of time and money on the electronics and engineering, he helped me through the whole thing hands on.
>mine are 51% open area
>1/16 perf steel, .171 holes i believe
>panels are 16" by 40"
>tl is a pretty neat desighn, check out the pics, there is a diagram for the build, 8" carbon fiber driver per panel.
>The system is by amped, one amp runs one esl and sub.
>Diaghphram came from some place CharlieM allready had and i cannot remember. but it .0005 micron, coated with Licron Tec Spray part #1756-8S(techspray.com).
I am using a crossover as impiedence drops sharply with esl's, so i went hybrid.
I hope this helps, my amps are only 100rms per channel, and I am so happy with this as it was my first build.
I am not a very technical person, so please check my post, a picture is worth a thousand words. page 6, start to finish esl, Mavric.
good luck, your gonna love it.
Kindly check this thread on page six, "start to finish esl" by mavric. I had alot and i mean alot of help here. CharlieM, Gerald, Chinsettawong,Calvin, and many others. I took alot of pictures and tried my best to show details and where the material came from., CharlieM has a blog page that will save you alot of time and money on the electronics and engineering, he helped me through the whole thing hands on.
>mine are 51% open area
>1/16 perf steel, .171 holes i believe
>panels are 16" by 40"
>tl is a pretty neat desighn, check out the pics, there is a diagram for the build, 8" carbon fiber driver per panel.
>The system is by amped, one amp runs one esl and sub.
>Diaghphram came from some place CharlieM allready had and i cannot remember. but it .0005 micron, coated with Licron Tec Spray part #1756-8S(techspray.com).
I am using a crossover as impiedence drops sharply with esl's, so i went hybrid.
I hope this helps, my amps are only 100rms per channel, and I am so happy with this as it was my first build.
I am not a very technical person, so please check my post, a picture is worth a thousand words. page 6, start to finish esl, Mavric.
good luck, your gonna love it.
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