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Old 10th July 2012, 04:34 PM   #21
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Quote:
Originally Posted by Legis View Post
Yes, maybe on some ESL's but not in these with the Plitrons. They make normal cone floorstanders green from the low THD numbers at the bass.
Congrats on the successful rebuild.
Like Calvin, I am used to seeing THD rise significantly at lower frequencies approaching and below resonance where there is significant diaphragm excursion. Had you done similar distortion measurements on your dynamic dipole woofers for comparison? Do you know what the resistance is of your diaphragm coating?

Have you done any near field measurements to see the behavior of the resonances of the different sections? Perhaps this would give some insight in to the admirable distortion performance.

Attached are some sectional near field measurements I took of a Sound Lab A-1 full range ESL.
Attached Images
File Type: gif SL_A1_NF.gif (57.1 KB, 123 views)
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Old 10th July 2012, 05:24 PM   #22
Legis is offline Legis  Finland
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Quote:
Originally Posted by bolserst View Post
Congrats on the successful rebuild.
Like Calvin, I am used to seeing THD rise significantly at lower frequencies approaching and below resonance where there is significant diaphragm excursion. Had you done similar distortion measurements on your dynamic dipole woofers for comparison? Do you know what the resistance is of your diaphragm coating?

Have you done any near field measurements to see the behavior of the resonances of the different sections? Perhaps this would give some insight in to the admirable distortion performance.

Attached are some sectional near field measurements I took of a Sound Lab A-1 full range ESL.
Thanks.

Yes I have measured the woofers, one of them plays at approx 0,3% at 95dB at the upper bass and 1% at 105dB if i rememeber correctly. The one model with linear xmax of 8mm, can throw +/- ~10mm before 10% THD at Fs of higher frequencies when measured near field free air. The wooders are BMS 18S430v2, 18N850 and 18N860. The motor is pretty high tech, but the spider suspensions are little too progressive for home use imo. I have seen Klippel measurements of two of their lesser 15" models, both Le(x) and Bl(x) are top notch, but Cms(x) is average due to the high progression. I will do THD measurement for the whole system after I get to remembrane the other panel also.

I will measure the sections of the panel soon. I have listened to them near the panel, the smaller sections (13-15cm) definitely have a higher resonance to them judged by the ear. The membrane has not settled yet though, It will take at least 200hrs I think.

Last edited by Legis; 10th July 2012 at 05:28 PM.
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Old 10th July 2012, 06:20 PM   #23
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It's quite hard to get the resonances to show as my mic is omni and the room has concrete walls (room modes).

Panle widthwise in the room:

Click the image to open in full size.

Panmel lenghtwise in the room:

Click the image to open in full size.
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Old 10th July 2012, 06:27 PM   #24
Calvin is offline Calvin  Germany
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Hi,

Legis, the response looks fine. I assume that to be a farfield measurement at 4m(? or what) distance.
Obviously the 20dB difference in SPL falling from 500Hz to ~150Hz is only in part due to acoustic phase cancellation. Itīd be interesting how much of the drop is left in a nearfield measurement. If thereīd also a be distinct drop in SPL it could explain the surprising absence of THD-increase below 200hz.

I also tried the BMS 18N850. The build and design look exceptional well. But same as You Legis, I disliked the all too progressive suspension, which hinders the driver to reach the specified excursions values. The spider is way too small in diameter to allow for the claimed stroke capability.
Besides that, BMS couldnīt supply for these drivers for several months (because of probs with the spiders, as I was told).
So I finally turned these drivers down and used some different.
Still have one 18N850 lying around, apart from some measurements unused and in mint condition. If anybody wants to make an offer, Iīll listen

jauu
Calvin
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Old 10th July 2012, 06:42 PM   #25
Legis is offline Legis  Finland
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Quote:
Originally Posted by Calvin View Post
Hi,

Legis, the response looks fine. I assume that to be a farfield measurement at 4m(? or what) distance.
Obviously the 20dB difference in SPL falling from 500Hz to ~150Hz is only in part due to acoustic phase cancellation. Itīd be interesting how much of the drop is left in a nearfield measurement. If thereīd also a be distinct drop in SPL it could explain the surprising absence of THD-increase below 200hz.

I also tried the BMS 18N850. The build and design look exceptional well. But same as You Legis, I disliked the all too progressive suspension, which hinders the driver to reach the specified excursions values. The spider is way too small in diameter to allow for the claimed stroke capability.
Besides that, BMS couldnīt supply for these drivers for several months (because of probs with the spiders, as I was told).
So I finally turned these drivers down and used some different.
Still have one 18N850 lying around, apart from some measurements unused and in mint condition. If anybody wants to make an offer, Iīll listen

jauu
Calvin
Yes the upper bass drop is due phase cancellation/room interaction since I cannot measure it near field.

The THD measurement was done at 2m with 1st order high pass at 150hz (Plitron would have saturated otherwise). I forgot to mention it. From this picture you can see the responses with and without XO.

Last edited by Legis; 10th July 2012 at 06:45 PM.
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Old 10th July 2012, 07:16 PM   #26
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I made some full range* THD measurement at near field (15cm away from the membrane) as high level as Plitron takes (*with only the 60ĩF series capacitor, xo-point at ~40Hz). The drive level is the same in both bias settings.

Low bias (~2,3kV):

Click the image to open in full size.


High bias (~4,6kV):

Click the image to open in full size.


THD from high bias setting:

60Hz: 0,303%
100Hz: 0,131%
200Hz: 0,178%
300Hz: 0,106%
400Hz: 0,100%

By the way, any idea why the THD rises towards the high frequencien (I mean this measurement)? Because of the voltage driven stat and the radiating area gets (from which the signal sums up to mic) smaller as the frequency increases?

Last edited by Legis; 10th July 2012 at 07:19 PM.
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Old 11th July 2012, 07:01 PM   #27
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Quote:
Originally Posted by Legis View Post
I made some full range* THD measurement at near field (15cm away from the membrane)
Very nice measurement set. Still puts dynamic drivers to shame
Distortion rising trend at LF is what I am used to seeing.

The distortion rise at HF you mention is often due to limits of driving & measurement electronics.
Have you tried a loop back test from output of amplifier while driving ESL to see what the best case distortion/noise levels you could expect?

How far away from the panel sections was the microphone placed when taking the sectional measurements shown in post#23?
If I remember correctly, the section heights varied by nearly a factor of 2.
I would have expected to see greater variation in the fundamental resonance between the smallest and largest sections.
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Old 11th July 2012, 07:35 PM   #28
Legis is offline Legis  Finland
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Quote:
Originally Posted by bolserst View Post
Very nice measurement set. Still puts dynamic drivers to shame
Distortion rising trend at LF is what I am used to seeing.

The distortion rise at HF you mention is often due to limits of driving & measurement electronics.
Have you tried a loop back test from output of amplifier while driving ESL to see what the best case distortion/noise levels you could expect?

How far away from the panel sections was the microphone placed when taking the sectional measurements shown in post#23?
If I remember correctly, the section heights varied by nearly a factor of 2.
I would have expected to see greater variation in the fundamental resonance between the smallest and largest sections.
Yes the measuring and driving equipment could explain some. Here's a the measurement of the driving monos, 10V into 4R load made from wirewound power resistors: http://i817.photobucket.com/albums/z...4R-lowbias.png I quess the THD at the HF rises quite a bit with an ESL load but the amps should be quite adequate for low impedances with their 12 pairs of BJTs. I will measure the THD with the ESLs as the load once I get new low-thd soundcard (the prevous broke), current measuring equipment cannot measure 0,000x thd levels of these balanced Class A monos.

The mic almost touched the front stator during the sweeps. Maybe the crosstalk between the sections with an omnipolar mic or the room messes my measurements. How did you measure the Soundlabs?

Last edited by Legis; 11th July 2012 at 07:38 PM.
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Old 11th July 2012, 08:43 PM   #29
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Originally Posted by Legis View Post
The mic almost touched the front stator during the sweeps. Maybe the crosstalk between the sections with an omnipolar mic or the room messes my measurements. How did you measure the Soundlabs?
The omni mic will certainly pic up some crosstalk from adjacent sections, but it drops off pretty quickly with distance.
Measurements for the Soundlabs were with omni mic 1" away from diaphragm.
I used FFT analysis of pulsed pink noise excitation and no smoothing.
This seems to give the best visualization of exactly what the diaphragm resonance modes are.
Measuring with steady tones results in a more damped looking response, I'm not exactly sure why.

Your plotted curves appear to have smoothing applied.
Do you have non-smoothed versions available?
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Old 11th July 2012, 10:41 PM   #30
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Here are unsmoothed REW sweeps (I made them again):

Click the image to open in full size.

... and 1/24oct smoothed, ungated made with periodic noise with ARTA (cannot overlay unsmoothed):

Click the image to open in full size.


I had forgotten that I had put 5dB/3,2Q parametric eq at 62Hz, it affected the last measurements but not these.

Last edited by Legis; 11th July 2012 at 10:44 PM.
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