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Planars & Exotics ESL's, planars, and alternative technologies 

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31st December 2018, 06:26 PM  #1 
diyAudio Member
Join Date: Jul 2016

Optimizing my DIY full range esl
Hi all,
I've built both a "small" (40x120 cm) and big (68x178 cm) electrostatic loudspeaker. Currently I use the big panels as they go lower in frequency, although the small panels still perform quite good given theire relative small size. I will post some nearfield and farfield frequency repsonse measurements, but it turns out there is a very steep high (Q) resonance at 25 Hz on both panels. I used small rectangular spacers, two vertical rows, similar to silocone dots, so I guess the membrane have multiple resonance frequencies, but at 25 Hz there is a very clear resonance. Fortunately, only in very specific recordings this is audible  the membrane starts to rattle. I used the esl_seg_ui software by Edo Huzlebos to simulate and design the ladder segmentation. I have 9 wire groups of different widths  the middle is about 1 cm width and the groups get wider towards the sides of the panel. I have a few questions about frequency response, especially about low frequency repsonse. My first question: does the esl_seg_ui software take into account dipole acoustic cancellation? My second question: at what frequency starts acoustic cancellation? At Wikipedia (link) I read: "The bass rolloff 3db point occurs when the narrowest panel dimension equals a quarter wavelength of the radiated frequency for dipole radiators, so for a Quad ESL63, which is 0.66 meters wide, this occurs at around 129 Hz, comparable to many box speakers (calculated with the speed of sound taken as 343 m/s)." Bass rolloff of my 68 cm wide panels would then start at 343 / (0.68 * 4) = 126 Hz at 6 dB/oct. Last edited by silvershadelynx; 1st January 2019 at 10:19 AM. 
2nd January 2019, 01:27 AM  #2  
diyAudio Member
Join Date: Jun 2005
Location: Fort Worth, Texas

Quote:
Here is an example measurement of an unsegmented ESL line source showing the +3dB/oct slope. Current vs voltage drive ESL? Here is another example measurement of a nearly massless dipole ribbon showing the constant slopes and slight step offset from baffle edges. (Note the slopes are +6dB/oct since it is small and behaving like a point source. If it would tall, it would be have had a +3dB/oct slope of a line source) DIY ribbon dipole tweeter, reductio ad minimum More details on line source assumptions here: Segmented Wire Stator ESL simulator (esl_seg_ui) Example measurementsvsmodeling of what happens if your ESL is too short to act like a line source and transitions to a point source: First ESL build  Full Range . Quote:
More details here: Dipole phasecancellation in ESL speakers 

2nd January 2019, 08:25 PM  #3 
diyAudio Member
Join Date: Jul 2016

Hi Bolsert, thanks for your extensive and excellent reply. If I'm correct the slope rate depends on differnt facors. A few factors are (taken from your links)
* (far field) 3 dB/oct. for line source voltage driven esl's * (far field) 6 dB/oct. for point source voltage driven esl's * current drive (by placing a resistor at primary or secondary of the audio transfomer) changes contant voltage to constant current drive and flattens frequency response * stator segmentation and ladder nresistor etwork adds area with decreasing frequency and flattens frequency repsonse My esl doesn't reach the ceiling, there's at least 1 meter free space between the top of my els and the ceiling. And my listening position is bigger than the height of my esl. So I would think my esl is somehtng "in between" a point and line source  or at least not a true line source? That would mean that the slope would be in between 3 and 6 dB/oct (far field, voltage driven)? Last edited by silvershadelynx; 2nd January 2019 at 08:33 PM. 
4th January 2019, 12:27 AM  #4  
diyAudio Member
Join Date: Jun 2005
Location: Fort Worth, Texas

Quote:
F = c * r / d^2 where: c = speed of sound r = listening distance d = panel dimension (height) You can use the latest version of the segmented ESL spreadsheet(experiences with ESL directivity?) to plot this be choosing Line Source = Finite, setting the number of segments to n=1, the low frequency break point fL = 100000, and the diaphragm resonance frequency Fs=0. The solid green line would be the response for an infinite line. The dashed green line shows the response for the finite line. The ESL spreadsheet uses an average trend line of the response. If rigorous calculations are performed you will see the response has ripples superimposed on the response, with a hump at the transition from line source to point source behavior. An example calculation of this is attached. (taken from here: Help with esl simulator) An example measurementvstheory can be found here: Vertical dispersion on planars. How much? 

12th January 2019, 12:18 PM  #5 
diyAudio Member
Join Date: Jul 2016

Hi Bolsert,
again, thans for your helpful reply and example calculations, this is really appreciated. If I'm correct my stator simulated by Edo Hulzebos his eslsegui software, is calculated with the assumption of an infinite linesource whereas my esl that has a height of 180 cm that is smaller than the ceiling height of 280 cm is a pointsource for lowest frequencies (below (343 * 3) / 1.8^2 = 318 Hz at 3 m listening distance). If I'm correct Edo's software compensates for a +3dB slope whereas my slope below 318 Hz is a +6dB slope, so the final result after calculated segmentation / correction by the eslsegui software would be +0 dB/oct above 318 Hz and +3dB/oct slope below 318 Hz? If my statement is correct, I could use a lowshelving filter of +3dB/oct. I tried that using my MiniDSP 2x4HD, but although there was a subtle audible boost at low frequencies, it was unlcear to me whether this was an improvement or not. So I decided to leave it as it is. 
17th January 2019, 09:40 PM  #6 
diyAudio Member
Join Date: Jun 2005
Location: Fort Worth, Texas

Your understanding is correct concerning the compensation of the ESL itself. Of course, there may be room mode related problems below 300Hz that might need to be addressed as well. One other important thing is to handle the diaphragm resonance, which may be complicating the LF behavior. I forget if you are using acoustic mesh damping or not, but since you have a miniDSP, you could measure the resonance with nearfield mic placement and then use a Linkwitz Transform to modify the resonance Q to something around 2.
Linkwitz Transform Set f(0) and f(p) equal to the diaphragm resonance frequency. Set Q(0) to match the diaphragm resonance Q Set Q(p) = 2 This along with the shelving compensation will improve the fidelity of low frequency reproduction. 
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