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[Marik]

danlavry wrote on Fri, 10 March 2006 21:07

Hi mark My comments are regarding the very basic fundamental principles. My understanding of how a condenser works is that air motion is "translated" to variation in capacitance...

Dear Dan,

I was hoping some folks would take it more seriously, but since I did not see much cooperation and like to check any theory in real life, I went ahead and made a little test.
I took a matched pair of microphones I designed myself, built with B&K 4133 measurement mics capsules and a cascode FET/tube based head preamp.

I left one mic unchanged and put a 330pf (the smallest value I could find in my dror) in parallel with the capsule.
I don't have special equipment for measuring capsule distortions and relied on my ears.
The sound change was quite significant. It was absolutely obvious the capsule in the microphone with added
capacitance had much less distortions (and we are talking about high precision, low capacitance, industry standart measurement capsule).
Of course, the microphone is not usable due to poor S/N ratio, but as you repeated many times, this is about basic
principle of operation.
I think this little test confirmes that your theory is right.

Best regards, Mark Fuksman

[danlavry]

Marik wrote on Sat, 11 March 2006 20:20

danlavry wrote on Fri, 10 March 2006 21:07 Hi mark My comments are regarding the very basic fundamental principles. My understanding of how a condenser works is that air motion is "translated" to variation in capacitance... Dear Dan, I was hoping some folks would take it more seriously, but since I did not see much cooperation and like to check any theory in real life, I went ahead and made a little test. I took a matched pair of microphones I designed myself, built with B&K 4133 measurement mics capsules and a cascode FET/tube based head preamp. I left one mic unchanged and put a 330pf (the smallest value I could find in my dror) in parallel with the capsule. I don't have special equipment for measuring capsule distortions and relied on my ears. The sound change was quite significant. It was absolutely obvious the capsule in the microphone with added capacitance had much less distortions (and we are talking about high precision, low capacitance, industry standart measurement capsule). Of course, the microphone is not usable due to poor S/N ratio, but as you repeated many times, this is about basic principle of operation. I think this little test confirmes that your theory is right. Best regards, Mark Fuksman

Thanks for posting the above.

Regards
Dan Lavry
www.lavryengineering.com

[Terry Demol]

Marik wrote on Fri, 10 March 2006 03:16

Dan, Thank you for taking your time to do the graph. I am confused, though. Is it for push pull or single ended operation? If you don't mind and have time could you post both FFTs, please. Also, what happens if we increase the cartridge capacitance to 40pf? Best regards, Mark Fuksman

Hi Mark,

What Dan has desribed is for single ended operation, ie; diaphram
and 1 charged plate.

-If- your meaning of push pull is that the diaphragm moves
between 2 charged plates and the OP's are configured balanced,
then the result will almost certainly be that 2nd / 4th etc
harmonics are largely cancelled, depending on symmetry of
circuit.

As such, generally, the distortion can be up to 20dB lower but
the spectrum is changed having dominant 3rd with even H's
supressed.

The same thing happens in electronic circuits and there is much
discussion about which sounds better.

Cheers,

Terry

[danlavry]

Terry Demol wrote on Sun, 12 March 2006 11:49

Marik wrote on Fri, 10 March 2006 03:16 Dan, Thank you for taking your time to do the graph. I am confused, though. Is it for push pull or single ended operation? If you don't mind and have time could you post both FFTs, please. Also, what happens if we increase the cartridge capacitance to 40pf? Best regards, Mark Fuksman Hi Mark, What Dan has desribed is for single ended operation, ie; diaphram and 1 charged plate. -If- your meaning of push pull is that the diaphragm moves between 2 charged plates and the OP's are configured balanced, then the result will almost certainly be that 2nd / 4th etc harmonics are largely cancelled, depending on symmetry of circuit. As such, generally, the distortion can be up to 20dB lower but the spectrum is changed having dominant 3rd with even H's supressed. The same thing happens in electronic circuits and there is much discussion about which sounds better. Cheers, Terry

Hi Terry

Thanks for the help.
I certainly find it less then easy to explain in non technical terms the effects of non linearity due to addition of fixed cap in parallel to the "variable cap".

I assume that the mic designers figure out the optimum point in term of the ideal input capacitance as well as all other parameters, and I am certainly not suggesting that people will add a bunch of pF's to their mics.  

Clearly one can not have 0pf, and even a few pf is enough to raise some serious harmonics in the context of real capsules (say 20-100pF?)

My guess is that there is an optimum point and the mic designers know where it is. But I was told by a "mic guy" that in some mics, when the attenuation switch is "on", they in fact added a parallel fixed cap and that is all they do. The reason is to limit the level, but I would think the result be sonic as well.

Your comment regarding even only in a push pull is very interesting. It would suggest that push pull has a different sonic signature then single ended. That is good to note!

Regards
Dan Lavry
www.lavryengineering.com

[Marik]

Terry Demol wrote on Sun, 12 March 2006 11:49

Marik wrote on Fri, 10 March 2006 03:16 Dan, Thank you for taking your time to do the graph. I am confused, though. Is it for push pull or single ended operation? If you don't mind and have time could you post both FFTs, please. Also, what happens if we increase the cartridge capacitance to 40pf? Best regards, Mark Fuksman Hi Mark, What Dan has desribed is for single ended operation, ie; diaphram and 1 charged plate. -If- your meaning of push pull is that the diaphragm moves between 2 charged plates and the OP's are configured balanced, then the result will almost certainly be that 2nd / 4th etc harmonics are largely cancelled, depending on symmetry of circuit.

Terry,

Thank you. Yes, I should've thought about it looking at the FFT.

BTW, yes, I refer to push-pull operation as a diaphragm symmetrically placed in between 2 charged plates. Here should be noticed that there are some capsules with a front plate which is not charged, and is a "dummy" one, creating acoustical enviroment.
Pearl microphones have a "true" PP arrangement. Although they definitely have different sonic signature, it is pretty hard to base judgement on those, as they use rectangular shape.

Another question. There is an effect well known in electrostatic speakers, called charge migration, where with diaphragm getting closer to the stator the charge moves to that place. That's the reason the diaphragm is coated with low conductivity material in order to minimize this effect.

Any idea how and if this effect takes place in the microphone capsules?

Best, Mark

[danlavry]

[quote
Your comment regarding even only in a push pull is very interesting. It would suggest that push pull has a different sonic signature then single ended. That is good to note!
Dan Lavry
[/quote]


I have not fully analysed it yet. Someone outside the forum mentioned to me that symmetry eliminates the even distortions, not the odd. I do not yet know the answer (even or odd), it would be good to read good comments.

I did look for information about the push pull mics, and I see Sennhiser has some. Some of the explanations are different then what I expected, they are about having the air both push and pull the diaphragm. I thought it was about 2 charged plates and a diaphragm between them. I was trying to see how the signal is "tapped" (wondering if there is a differential amp used, and how it is connected....).

Regards
Dan Lavry
www.lavryengineering.com

[Marik]

danlavry wrote on Mon, 20 March 2006 18:56

I did look for information about the push pull mics, and I see Sennhiser has some. Some of the explanations are different then what I expected, they are about having the air both push and pull the diaphragm. I thought it was about 2 charged plates and a diaphragm between them. I was trying to see how the signal is "tapped" (wondering if there is a differential amp used, and how it is connected....).

Dan,

The Sennheiser is a RF mic, where the capsule is a part of the resonant countour (is it the term in English?). There is no hi-Z part there.
Have a look at the schematics here:

     http://www.waltzingbear.com/Schematics/Sennheiser/MKH-405.ht m

To my knowledge, the Pearl is a "conventional" design.

Best, Mark Fuksman

[danlavry]

Marik wrote on Mon, 20 March 2006 19:03

danlavry wrote on Mon, 20 March 2006 18:56 I did look for information about the push pull mics, and I see Sennhiser has some. Some of the explanations are different then what I expected, they are about having the air both push and pull the diaphragm. I thought it was about 2 charged plates and a diaphragm between them. I was trying to see how the signal is "tapped" (wondering if there is a differential amp used, and how it is connected....). Dan, The Sennheiser is a RF mic, where the capsule is a part of the resonant countour (is it the term in English?). There is no hi-Z part there. Have a look at the schematics here:       http://www.waltzingbear.com/Schematics/Sennheiser/MKH-405.ht m To my knowledge, the Pearl is a "conventional" design. Best, Mark Fuksman

I thought they had other mics based on the the principle. I really can not find much data about a push pull mic principle of operation.

Regards
Dan Lavry
www.lavryengineeing.com

[Marik]

danlavry wrote on Mon, 20 March 2006 18:56

(wondering if there is a differential amp used, and how it is connected....).

Never saw schematics, but would imagine instead of phase splitter in case of SE front end, it will be fully balanced all the way through. The diaphragm would be grounded.

Regards, Mark Fuksman

[Gunnar Hellquist]

Please,
    maybe we should keep the RF mics outside the discussion here? They are very interesting subject. But perhaps we could run it in a separate forum or a separate thread. I cannot stop from entering though.

I believe the Sennheiser involvment stems back to early transistor days, before the FET. Not having a high impedance transistor they had to resolve going with an RF circuit instead in order to make a solid-state mic. Typical early schematic might be seen here:
http://www.waltzingbear.com/Schematics/Sennheiser/MKH-405.ht m

The 405 as shown is one example of an older generation, single sided capsule.

The newer generation MKH20-30-40 were introduced about 25 years ago and has a double plate constructiaon (ie push-pull plate), one plate on each side of the membrane. According to some the push-pull construction greatly reduces intermodulation distortion.

(Actually, the RF principle goes back much later but was then made with tubes).

Gunnar