SDC capsulses-ring tension, capacitance and frequency response

Hi folks,

I've recently been experimenting with many of the small diaphragm condenser capsules that are being tested in other current threads, searching for a flatter frequency response from MXL type capsules.  I've had pretty good luck making mods that have flattened things out quite a bit, but want to fine tune what I'm doing a bit more.  I have some questions for those who are familiar with taking these things apart.

How does the tension of the brass ring that holds the components of the capsule affect the capsules capacitance?

Also, how does capacitance affect the frequency response of the capsule?

Any help on this would be appreciated.

Craig

Rabbit's hole you want to enter only if you are serving a life sentence and capsule modifying is all you can do for fun. Or if you just don't want to use an EQ for whatever reason.
 
Yes it does affect the tone. But there is no recipe. Unfortunately. For example changing capacitance will change the sensitivity of the capsule, so while you are potentially changing the frequency response, you get more noise, or you tighten diaphragm so slose to the backplate that it sticks to it at larger spl. I noticed that  it mostly affects amplitude of lower frequencies, never the shape.

It is more like trial and error, and once you get it right, if you get it right, it is almost impossible to replicate.

I don't think there is any part of those capsules i haven't  modified. And the rule is if you change one thing it will affect the other you never wanted to change. For example: Do something to make it flatter, than it changes pickup pattern. Lower the highs, it loses lows as well, or gets noisier. Get rid of 7-8k peak, the peak appears at 800hz, or creates -10db dip at 4k. Change spacer, or rotate backplate and turn it into telephone effect.

I even reskined them with different tensions/tunings and aluminium sputtered mylar, and introduced central termination screw.

I came to conclusion that it simply isn't worth it. Dr. Marik came to the same conclusion and in the end he changed the whole construction of the capsule for AKG type with whole different backplates that allow precise tuning.

I find the 603 capsule to be completely unusable as-is.  No amount of EQ has ever fixed their innate harshness to my satisfaction. 

I modified two of the capsules, and the first one sounds great-super flat response, and I noticed the capacitance was very close to the stock version.  The second one I modified was better, but not as smooth as the first one, and noticed the capacitance was about 15pf less than the stock capsule and the one I modified.

I trust that you've fought this battle and lost.  I remember when Marik was offering modification services on these capsules several years ago, and I didn't have the cash to send them in to him.

Do you think construction of the KM84 type capsule from scratch is too difficult?  I have several CK series capsules in my mic locker, and while I love them, they are an entirely different beast.

Anything is possible, but KM84 capsule is something else, very different construction.

How did you mod the capsule to make it super flat?

Here's km84 capsule backplate. It is very sensitive to tightening, reacts in a whole different way than mxl capsules.

Right, I guess the MXL's are their own thing, but at the same time, there usually isn't a lot of creativity in the cheap designs coming from there.

I took the capsule apart, making sure not to separate the thick plastic disc with the holes in it from the brass backplate, removed the ring that holds the mesh grill in place, and used a grinder to get rid of the extra space at the front of the capsule.  Then inserted the mesh from the inside of the capsule , and glued it where it would rest on the ring that it was in front of before.  I stuffed everything back in as closely as it was before as possible.

If you and Marik spent time trying to make these capsules better and weren't satisfied, if I had success it was probably luck.

Now that you said that, it gave me an idea.  Even though i did grind off excess from the front of the capsule, i never tried to grind off the excess from the back of the capsule, and make it shallower behind the backplate. It needs maybe two turns just to sit in place. I would need to shave off the screw as well.

I might try that these days, and if i get anywhere i will post the results.

I would love to hear the results!

craigmorris74 said:

How does the tension of the brass ring that holds the components of the capsule affect the capsules capacitance?

Click to expand...

Changing the tension does not change the capacitance. It changes the dominant resonant frequency, so increasing tension may enhance highs and decrease lows. This is within certain limits; if the tension is reduced so that the diaphragm collapses, the capacitance would indeed increase, but it would not be functional.

Also, how does capacitance affect the frequency response of the capsule?

Click to expand...

It just does not. It changes marginally the LF response of the high-pass filter constituted by the capsule's capacitance and the input resistance of the head amp. Typically this HPF is set at a few Hz. For example an LDC with a capacitance of 68pF, in conjunction with a FET head amp with 1Gigaohm input impedance results in LF -3dB point at 2.3 Hz. An SDC with a capacitance of 18pF paired with the same headamp would see its -3dB point shifting to about 9Hz.
In both cases, low enough to make no audible difference; however this has an effect on the noise performance of the head amp; the lower the -3dB point, the lower the noise, at a rate of 6dB/octave. The head amp, paired with the LDC would be quieter by about 12dB than with the SDC.
However, the LDC's intrinsic noise (due to the electroacoustic radiation resistance) would generally also be quieter than the SDC.

Sorry, but i can't agree with couple of things mentioned above. We are talking about SDC MXL603 capsules.

Decreasing tension of tightening ring will not cause collapsing, tightening might as it brings mylar closer to the backplate.  And it will change capacitance somewhat, as over tightening  and loosening will compress/expand ca.10um thick pvc spacer between diaphragm and backplate. Tightening of the ring doesn't change the tension of the diaphragm.

I think you are referring to k67 type of capsules, in that case it would make sense.

Kingkorg is correct in regards to the MXL SDC capsule.  I've just taken measurements and can confirm that tightening the brass ring increased capacitance.

kingkorg said:

Sorry, but i can't agree with couple of things mentioned above. We are talking about SDC MXL603 capsules.

Decreasing tension of tightening ring will not cause collapsing, tightening might as it brings mylar closer to the backplate.  And it will change capacitance somewhat, as over tightening  and loosening will compress/expand ca.10um thick pvc spacer between diaphragm and backplate. Tightening of the ring doesn't change the tension of the diaphragm.

I think you are referring to k67 type of capsules, in that case it would make sense.

Click to expand...

OK, my answer was based on the notion of tension, that usually refers to the diaphragm's tension.
Now, changing the distance between diaphragm and backplate indeed changes the capacitance, with the effects I mentioned earlier about electrical LF roll-off and noise. However, the most noticeable effect of tightening would be that of increasing the diaphragm's damping, which would extend the frequency response both ways (LF and HF) without any significant change in sensitivity. That may also tame the secondary resonances in the upper region of the spectrum and somewhat limit the max SPL.

Hi, you guys seem to have a lot of experience with those 603  capsules. Do you know if there are different  iterations of that capsule? Because the two I have and use unmodified  in royer modded  bodies are pretty ok to my ears. Even with the original electronics  they sound different and  have a rather sloppy cardioid pattern, compared to my km84, but they still have their qualities with the right sources. Now  with the cathode follower electronics those mics are my goto tom microphones. Very deep and clean with tons of headroom. Great capsules for that. Not bass shy at all and no  harsh or peaky treble.

There are several different versions. Most of stock ones i have measured have a peak between 7k and 8k. And i still can't find the exact cause.

Grinding off the front of the capsule, and enlarging vents at the back of it flattens the area above the peak, but not the peak itself. This is confirmed, documented and measured by several people.

I still find stock capsules fine for a lot of things, and knowing they have a peak there i have never had a problem taming that area with an eq.

Hypercardioid versions have by the nature a bit flatter high end response.  I attach the image cardioid vs hypercardioid. Hypercardioid is the one with larger holes in the plastic backplate.

I recently bought a 3U Warbler 127 with their Cardioid Flat capsule, and have been putting it through its paces on sources where I usually use SDC's (acoutic guitars, drum overheads).  I can say that this mic is the flattest sounding SDC I've heard outside of a KM84.  Flat with roboust lows and mids.

That said, my two modified MXL capsules on the MXL V67N (the transformer balanced model) with vent modification are a significant improvement to my ears over the stock.  I've got two capsules both with the brass rings tensioned so that I get about 35pf capacitance on each.  There is still a rise around 7k, but rise is flat, like a high shelf.  The dip before the 7k rise is gone.  Up until 7k, the sound is very similar to the 3U mic. 

Of course, if you have use for the stock MXL capsules, that's great.  I don't mic toms, so I they're not particularly useful to me as-is. 

The 3U mic almost makes the search for something else irrelevant for me.  I still would like to try one of the  Banzai type capsules, though.

I converted one of my capsules to hypercardioid yesterday, and that knocked off 7k peak. It sounds marvelous now, however that caused a dip at 4K, so i can't call it flat.

If anyone wants to try it, the diameter of holes in plastic backplate is 2mm for hyper capsule.

craigmorris74 said:

  I don't mic toms, so I they're not particularly useful to me as-is. 

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I don't get this; do you imply that the 8kHz lift is good for toms but not other elements?

I don't.  But  if you're following these SDC threads, but toms are the only thing that I've seen anyone mention the MXL style SDC's are good for.

One thing that can radically affect the sound is the thickness of spacers betwen the backplates. You could try to mod these.

If you have two spacers, try removing one. Or try adding a layer of tape on one of them, or paper.

One more thing i can confirm is that these capsules perform way better when placed inside a LDC body.

Resonances created behing capsules in stock 603 bodies cause various dips and spikes depending on capsule type.

I believe Steve Albini (Josephson) style of body would be perfect for these.

Yes, the Josephson style body probably would help out.  Just getting rid of the first bar of the vents gets rid of the 4-5k dip.