What can happen adding additional ring on the LDC capsule diaphragm ring?

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ln76d

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Aug 11, 2012
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I wonder what could happen if i would add additional ring on the capsule.
Or to simplify my weird question - if the diaphragm ring would be double thick?
Could this change directivity, sensitivity or other ...vity?
 
It depends on the type of capsule.

But one effect that applies to all types is that the cavity in front of the diaphragm(s) is increased and the resonant peak this gives will move down and be higher.  You get this in all condensor mikes and the real mike designers use it to flatten & extend the HF response.

If it is a single diaphragm cardioid or fig-8, it also increases the path length between front & back.  I'm too tired to remember what happens for a double diaphragm.

Have you got a copy of the Neumann PDF book on mike design on their website?  It will explain the significance of greater path length.
_____________________

ln76d, I think it is high time you looked seriously at how to do quasi-anechoic measurements of microphones at home.  ;)

Chapter 10.4.3 ACOUSTIC FREQUENCY RESPONSE

of the Clio 8 manual is the best explanation of this. http://www.audiomatica.com/wp/?page_id=34

I highly recommend Clio as an inexpensive R&D tool.  The calibration of their inexpensive measurement mikes are one of the few I believe.  ClioQC is THE system for production testing.

Eric Benjamin’s Extending Quasi-Anechoic Measurements to Low Frequencies
http://www.aes.org/e-lib/browse.cfm?elib=12875
explains some advanced methods to extend useful measurements to lower frequencies.

These methods measure an impulse response and use FFTs to get the (complex) frequency response.  The comparison is done by (complex) dividing the response of the DUT by the response of the reference in the Frequency Domain.

There’s only a few free programs that allow this to be done conveniently.

- Prof. Angelo Farina developed the Log Sweep method that is now the favoured method from Clio to the latest Audio Precision to yours truly.  If you have Audition, try his Aurora plugins.  There is a version for a special version of Audacity.
- Our own Les Watts uses & recommends the full version of ARTA.  There is a free version.

Read the Clio manual regardless of what you use.    It is the ONLY clear & accurate explanation of quasi-anechoic that I know of.  If you find a better one ... or even another .. please let me know.

I haven’t used any of these methods but have my own version of Angelo’s method in DOS.

If you do use them, please consider writing a little report on how they can present graphs with 25dB/decade aspect ratio.
 
Thanks ricardo as always!

As always great, valuable informations!

Yes, i  have Neumann book, i will read at the evening.
For now i'm unable to make any measurements (as many other different things related to diy) , first i need to finish building studio, then i will have a place for this. I also had a plan to make some setup for simplified or even  indirect methods measurements.
In this case am not sure right now do i use double ring or find another soulution.
I need to separate connection between metal diaphragm ring and backplate.
Plastic shims do the job in case of surface, but still there's a need to separate connection by screws.
Additional plastic ring above metal ring would make 70% of job, but as i suspected it will affect capsule properties.
There's no option to find plastic screws in this size :)
 
ln76d said:
I need to separate connection between metal diaphragm ring and backplate.
Plastic shims do the job in case of surface, but still there's a need to separate connection by screws.
Additional plastic ring above metal ring would make 70% of job, but as i suspected it will affect capsule properties.
There's no option to find plastic screws in this size :)

You could try to make a corresponding ring out of thick plastic foil (> 100µm) for insulation. To prevent the screw threads from touching the metal ring I´d pierce through the plastic ring with a needle or fine center punch roughly in the midde of each hole and push the screws through. That way the foil should form kind of a collar around the  screw and prevent it from touching  the ring.
If that doesn´t work try to coat the clear thread portion of screws with laquer (polyurethane preferably) to prevent electrical contact with metal diaphragm ring. If the holes in the rings are way oversized even thin heat shrink tubing might work.
Of course you can additionally coat the inner surface of the holes too.  All quite delicate work though.

The thin plastic foil ring would not have a significant acoustical effect (if that´s what you´re looking for).
 
Thanks MS Vienna!

I considered similar options, but still had no time to try.
I wanted to try small teflon pipes (i can't find it currently in my mess) or exactly try to paint both - ring holes and screws.
Yes i'm looking for most acoustical transparent solutions :)
 
If it is a LDC, even 1mm washer will be difficult to measure, let alone hear, difference.  I think the fig-8 response is most likely to be affected but even then, I think the effect will be small.

But beware of listening to beach bums on the internet  8)

If it is a 12mm capsule, it would be much more of a problem.
 
ricardo said:
If it is a LDC, even 1mm washer will be difficult to measure, let alone hear, difference.  I think the fig-8 response is most likely to be affected but even then, I think the effect will be small.

But beware of listening to beach bums on the internet  8)

If it is a 12mm capsule, it would be much more of a problem.

FIrst ide was to use double ring, so it's 2mm of original ring and 2mm of additional.
Then diaphragm sits pretty deep. I think here effect could be noticeable.
For now probably i will try to use paint or if i find teflon tubing and it will fit the i will use both. I have no option for now to use foil or washer.
I
 
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