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Old 23rd September 2006, 12:59 PM   #11
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Hi Calvin,

Adjusting a capacitor in the amp is what I thought about

You're right about +10 dB resonance peak in esls. But I 've read that this depends on the mechanical tension. With tightly stretched mylar, the amplitude of the resonance should decrease. The reason I think could be that the higher pitched resonance frequence is more effctively damped by the air (acoustic resistance increases with higher frequency). I am not sure if the article I read was right about this, but it came from the philips lab.
Did you measure a strong resonance mode without notch?
ML uses differently sized segments with different resonance freq.
I want to do the same with my next panel. If using a notch, to what freq. must it be tuned if there are two resonance modes?
Can the notch cause some ringing, phase problems or other negative side effects? I'am rather puristic, so I want to keep things simple.

I've seen a lot of hybrid designs without notch. Is there some reason ML is forced to use a notch while others can get away without any?

Best regards, MartinJan
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Old 23rd September 2006, 07:16 PM   #12
Calvin is offline Calvin  Germany
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Hi,

segmenting mechanically with different sized segments doesnīt decrease the Q of the resonance significantely, neithert does the reduction of mechanical tension. With rising tension the resonance-Q gets a bit smaller, but not much. To get rid of it You need some mechanical damping like a piece of fine meshed cloth etc. but that has serious disadvantages on other fields. The reason for high mechanical tension is high efficiency and stable working conditions. As a result the fs is quite high and so is the crossover point. Only when the crossover point is far enough away You might omit the notch. But as long as the fs is in the range of just 2...3 octaves below the crossover point You have to use the notch. The only other possibility would be to use just a high-Q 2nd order filter with a electrical crossover point app. 1.5 to 2 octaves above fs. The acoustical crossover point will then be just below the fs, because the filter will fill up the suck-out above fs and the high Q of the fs fills up below the electrical crossover point (I measured up to 95dB!!) . Efficiency and linearity can be very high, but the long decay of the fs is imho always audible. AfakML did this with their Prodigy.

jauu
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Old 23rd September 2006, 08:18 PM   #13
Bazukaz is offline Bazukaz  Lithuania
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Hi Calvin,
What are the serious disadvantages of mechanical damping ?

Regards,
Lukas.
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Old 24th September 2006, 06:49 AM   #14
Calvin is offline Calvin  Germany
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Hi,

external mechanical damping like a piece of cloth has some disadvantages

- it looks bad, or at least You loose the transparent looks
- it never works linear over level (excursion or SPL)
- it never works linear over frequency or exactly just on the specially desired frequency
- itīll make up some kind of acoustical resonant circuit (cavity between damper and membrane), i.e energy storing
- it might lead to reflexions of HF --> interference and distortion of the first wave front (clarity)
- its not necessary to damp the complete diaphragm area, but just damping a part of it could lead to standing waves (break up) because of the twisting the membrane.
- mostly its just used on one side of the diaphragm, therefore introducing some slight asymmetry.

The notch filter also forms a resonant circuit and energy storing mechanism, but it doesnīt spoil the rest of the performance since it can be tuned easily to the desired frequency leaving everything else untouched (since an ESL is a minimum phase system, the notch actually can correct not only for the frequency response but for the phase response, which could be very helpful in the crossover design too).

Since You canīt get away with the ground resonance of the ESl panel by principle You have to deal with it mechanically or electrically . The electrical way beeing the easier and more precise with lesser negative side effects.

jauu
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Old 24th September 2006, 04:00 PM   #15
Bazukaz is offline Bazukaz  Lithuania
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Hi Calvin,
Thanks for your explanations. I understood that , if mechanical damping is used , it should provide relatively small amount of acoustical resistance.I have made some measurements with a small ESL fully damped with batting(back side).The damping only increased non-linearities in frequency response and THD. BTW , for some strange reason i measured quite high levels of intermodulation distortion of panel.With 250:8020 Hz tone frequencies , IMD was ~0.5%. For a comparison , the same test with a dynamic loadspeaker system shew only <0.1% IMD. THD of panel at 1 kHz was 0.2-0.3% , while THD of a dynamic speaker system was ~0.7%@1Khz. I am not sure if my measurements are accurate and it may be influenced by microphone or other devices.
It would be interesting if anybody else here tried to do distortion measurements of ESLs.

Best regards,
Lukas.
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Old 6th November 2006, 05:35 PM   #16
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Question:

I have read the post from Calvin that the ML Sequel II has about 1kV bias. Does that mean that the max level signal voltage is limited to 1kV as well? If not, how much voltage is required to fully drive those panels?

Thanks,

Jan Didden
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Old 13th November 2011, 07:46 AM   #17
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Hi Calvin !
I'm from Viet Nam.
I'm using Martin logan Sequel II
Can you give me schematic for the sequel II, speakers are in a state of failure, I need it to repair.
Please send it to my mail : hailedinh80@gmail.com
Thanks,
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Old 14th November 2011, 01:20 PM   #18
tyu is online now tyu  United States
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I have read the post from Calvin that the ML Sequel II has about 1kV bias. Does that mean that the max level signal voltage is limited to 1kV as well? If not, how much voltage is required to fully drive those panels?

As far as i no,Info from Jim Powers at ML the Sequel2 was the same panel used in the SL3,Ascent,i....
An from what jim told me all the bias boards were the same...An at 3400-3700-V on the panels in the twoway set up....CLS were higher at first but that drop the back to 3700-4000-V...
I have a pr of SL3 here now that i have redone the panels with a bias feed on left an right side... all stock ML panels are only feed from the right side...good for saleing more panels but not good for geting all that these great panels can give....
i have just set up a new bias feed for the SL3s... an it at about 4k an sounds the best i have ever got out of the panels.....so looks to be a little low to me....

Here what i think about the logans i have had 4pr of the twoway,an 1pr of CLSs

Retail...
The panes $$1k-1500....ea

The Bass drivers $$200-300....ea

That Box or frame$$200.300...ea

Bias Board $$30....each...in all...

I think there a lot of room for inporvment in the bias set In any ESL it has just as much to do with the sound as any mylar....or setup tranfourmers....But gets over look like just any thing well work....the bias tranfourmers in the ML $$3.maybe...
Just my 2cents
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Old 14th November 2011, 08:31 PM   #19
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Quote:
Originally Posted by Calvin View Post
Hi,

here it is ;-)
Click the image to open in full size.

Calvin
Calvin, a request.
For some reason that attachment (S II xover & bias) doesn't increase in size when clicked and when saved and blown up loses all resolution.
Is it possible to have a better resolution version - this one is hard to read.
Could you send one via PM to jan AT linearaudio DOT nl ?

jan didden
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