So my mesh arrived and I measured it at 030 so that converts to about 76um. So I guess about 20 rayl.
Front, middle, and back amounts to 60 so probably a good median?
Front, middle, and back amounts to 60 so probably a good median?
I second bolserst & golfnut's recommendations for tightly stretched fine mesh cloth for 'pure' acoustic resistance.
I've used tightly stretched cloth glued to the chassis of EML units. By plotting the Impedance before & after, you can get the 'EXACT' [1] acoustic resistance introduced. I'm sure the Constant Charge ELS has a similar relation but my 1 remaining brain cell is inadequate to work out how to determine this from Impedance measurements.
[1] 'EXACT' for its effect on frequency response.
I've used tightly stretched cloth glued to the chassis of EML units. By plotting the Impedance before & after, you can get the 'EXACT' [1] acoustic resistance introduced. I'm sure the Constant Charge ELS has a similar relation but my 1 remaining brain cell is inadequate to work out how to determine this from Impedance measurements.
[1] 'EXACT' for its effect on frequency response.
Still not sure of the advantages of Isobarik ELS. As an ex-EML guru, I'm sure that EML Isobarik has NO ADVANTAGE to compensate for its many faults.
For ELS, the force coeff nearly doubles but as you have 2 panels in parallel, efficiency actually goes down slightly cos you are taking twice the power from the amp.
Max spl does go up cos when flashover happens, you have nearly twice the force.
But if you accept the hassle of another panel, why not have them side by side. This gives you twice the efficiency, better LF bla bla to go with twice max spl ... as opposed to the Isobarik which has worse efficiency, worse LF bla bla to go with max spl.
For ELS, the force coeff nearly doubles but as you have 2 panels in parallel, efficiency actually goes down slightly cos you are taking twice the power from the amp.
Max spl does go up cos when flashover happens, you have nearly twice the force.
But if you accept the hassle of another panel, why not have them side by side. This gives you twice the efficiency, better LF bla bla to go with twice max spl ... as opposed to the Isobarik which has worse efficiency, worse LF bla bla to go with max spl.
Okay, in my case I've doubled the amplifiers as well. But efficiency aside, the main difference I hear is the increased dynamic quality. Decay is extended and it sounds more full. The single panels sound thin in comparison.
Were you measuring thread diameter? or thickness of the mesh cloth.
By 030, did you mean 0.030 inches? or 0.003 inches.
If you did get 160Count mesh with 76um thread diameter, 20 Rayl is a reasonable estimate.
Using one layer on front and another on back of Acoustat panels will give you almost the same damping as stock, but without the reflections in the mids/highs normally caused by the thick felt.
If by "front, middle, and back" you mean you are thinking of using it in your isobaric configuration without the thick felt layer in between the panels, you will have issues with several frequency response notches or dips in the mids/highs since the rear panel will now be projecting its high frequency information straight thru the front panel without getting mostly filtered out by the felt.
Glad to hear you have a measurement setup, this should help you better understand what you have and why you are hearing the differences you are.
For ESLs where size is generally already bordering on unacceptably large, there are a couple reasons (related to size) for placing the panels one behind the other rather than side by side.
- For mid-twt or full range ESLs, you get the increased output without messing up polar response. Of course to take full advantage of this you need to keep the distance between the diaphragms to an absolute minimum.
- For ESLs intended as woofers only, this allows increasing output using stacks of diaphragms without significantly increasing the footprint.
Yea, 0.030" thread dia. IYO would it be better to not have a layer between panels?
Are you comparing your Isobarik with a single panel? The fair comparison would be with 2 single panels side by side.
Were these bass panels?
What did the main resonance move up to when you added the 'Isobark panel' If it moved from 50Hz to 70Hz, it would likely have sounded more tuneful, foot tapping, more musical bass bla bla ...
... gotta be careful extrapolating from extensive DBLTs on EMLs to CCESL but that's what I expect you will hear ... 🙂
Are yus ESL gurs (hint hint golfnut & bolserst) going to do the maths for this ? 🙂
Thanks for this Pete. I see you are comparing your Isobarik with a single panel so not apples with apples.
Have you any measurements of before and after?
Max spl isn't usually a problem with ESL mid & HF. The smaller sensitivity of single panels is easily managed with a different transformer ratio. The actual efficiency of an Isobarik is slightly less once you have taken into account the load to the amp. Mid & HF is also where the Isobarik faults are most obvious.
For LF ... Shock Horror! You mean size & WAF are important considerations even in Texas?!? 😱
More seriously, the advantages of larger single panels at LF are many ... increased efficiency, more extended bass, greater max spl bla bla ... only offset by a poorer WAF.
Something that is hardly ever mentioned is with large panels/dipoles, you can often operate in the near field ... even in large rooms to further advantage.
I've done some theoretical work on the interaction of dipoles in rooms and even designed a commercial speaker to make use of this. EML based though.
I have no measurements yet. I will measure them as is first, then in stock form, and finally with mesh. But I'm waiting for insight from bolserst whether to bother sandwiching a layer of mesh between panels as that would take an extra step for comparison. Not sure if that would be worthwhile.
0.03" thread would indicate at maximum you could have 33 threads per inch. Are you sure it isn't 0.003" thread?
Sorry for belaboring this, I just want to make sure we know what type of mesh you have.
If you are planning to use the mesh in isobaric configuration with 2 Acoustat panels, I would definitely include a layer between the panels.
You may even consider putting mesh on both sides of each panel before stacking them together.
If you are taking measurements, I'd suggest a step-by step approach as you add mesh.
For example you might consider measuring each(or just some) of these configurations
- 1 panel, no mesh
- 2 panels(isobaric), no mesh
- 1 panel with 1 layer of mesh (measure on mesh side)
- 1 panel with 1 layer or mesh (measure on opposite side to mesh)
- 2 panels(isobaric), each panel with one layer of mesh
- 1 panel with 2 layers of mesh
- 2 panels(isobaric), one of the panels has 2 layers of mesh, the other 1 layer of mesh ***this would be your layer in between case
If measuring near-field, you will want the mic in the exact same location each time.
The math can be done easily enough, although there is some approximation because of the radiation impedance. Best case would be to have the EML in a wall where the radiation impedance is well defined.
My preference is to either measure acoustic transmission at HF in open air, or LF in a tube where the acoustic impedance is well defined and purely resistive.
To be clear, I am not talking about increasing sensitivity(SPL out for voltage in) but rather increasing maximum SPL output capability. For mid-HF range, the on-axis sensitivity of two panels will be essentially the same whether they are side-by-side, or stacked one behind the other.(again with the caveat that you need to keep spacing between the diaphragms to a minimum. For mid-HF you can adjust transformer design and gap to get most any sensitivity you are after. But, the max SPL is fixed by the area of the panels used since the available driving force per unit area is a fixed quantity for ESLs. Also, efficiency is kind of irrelevant with ESLs since it is so high that essentially all the power dissipated by the driving amplifier is due to the transformer and any crossover parts. In my experience, it is becomes difficult to get max SPL > 100dB unless you start narrowing the dispersion. Even segmenting the panel and using RC or LC transmission lines, you are still left with conflicting requirements resulting in compromises between max SPL and polar response. The Quad ESL63 is a case in point with a central disk of about 14cm diameter to reach 105dB.
I agree that(if domestically acceptable) the best path for woofing with dipole ESLs is increase the area as much as possible. But you may still reach the limit of your room size before target SPL. See example SoundLab ESLs with extra woofer panels. Even those used double diaphragms.
- Driving force per unit area is a fixed and limited quantity for ESL (50-60 N/m^2) due to air breakdown limit, but for EML (Planer Magnetic or Dynamic coil drivers) is the limit of the maximum Force determine by the amount of current the conductor trace or voice coil can take through it (power compression or damage) and also its linearity region of operation?
- In order to achieve more SPL (120dB) how bad is the dispersion narrowing (beaming) gets?
