Effect of SDC body slots

[callgrlmusic]

does anyone have any good information about how body slots in SDCs affect performance? i read somewhere online about “opening up” the grille slots on SDC bodies doing something for the high end, but i have yet to build a test rig for these. i’m trying to find out if anyone has tried blocking them/different variations of the below/etc?

related question: why is there so much variation in this part of the design between manufacturers? has anyone here done a deep dive?

 

[pasarski]

They are essential in forming the polar pattern. Lots of information here if you search SDC vent/vents/venting etc. For a deep dive this is also gold for anything microphone related, including venting (EDIT: not true. The kind of venting that op is interested is not discussed in the paper) https://www.google.com/url?sa=t&sou...QQFnoECBIQAQ&usg=AOvVaw3ZO0fEsIX9q6-VZIQl8MkO

 

[callgrlmusic]

They are essential in forming the polar pattern. Lots of information here if you search SDC vent/vents/venting etc. For a deep dive this is also gold for anything microphone related, including venting. https://www.google.com/url?sa=t&sou...QQFnoECBIQAQ&usg=AOvVaw3ZO0fEsIX9q6-VZIQl8MkO

thank you! i wasn’t searching the right terms so nothing popped up for me initially. i’ll take a look at this and check back.

 

[kingkorg]

Changing the slots changes the sound in many ways, and not for the better necessarily. They have to be carefully engineered as they are the part of the equation. Just opening up for the sake of doing so doesn't make a mic sound better.

On the image you posted the body with larger holes doesn't improve things with that particular capsule because it relies on it's own slots. If the capsule is well engineered, it doesn't need any additional slots, and adding them like in the image is either detrimental, or doesn'tdo anything.

Some capsules, like kk105/104 (kms105/104) are engineered to "not care" what's behind them.

Conclusion is that it depends, and it's best to buy a reputable mic from a reputable source. The mod you ask about comes from dark ages of microphone modifications where different mic "gurus" performed mods like this without having any idea about what they were doing. And as a rule, whatever they did improved the sound and justified their guru title, and the price of specific mod.

Altering back vents could in theory change (not necessarily improve) high end, but that is by altering polar pattern. Which is the wrong way to do it, as it obviously - changes the pattern. No one can tell you what you will end up with.

 

[ricardo]

Some capsules, like kk105/104 (kms105/104) are engineered to "not care" what's behind them.

This isn't quite the case. The housing & slots have 'as much' effect as the capsule itself.

The Calrec cardioid capsule was much simpler than the AKG SDCs cos Clem Beaumont, my mike mentor, realised he could use the housing/slots (with far easier tolerances) to do much of what AKG did in the capsule. Bernhard Weingartner, a personal friend of Clem who designed many of the old AKG capsules including the CK12, was very impressed. But even the 'simple' Calrec capsule was a precision item as there was important stuff that the housing couldn't do.

The slots affect HF and pattern. Don't forget the cavity behind the capsule, it's shape, volume, bla bla too. Some of this stuff is non-intuitive.

Butchering the slots on a well designed mike will certainly change the sound. But as kingkorg says, usually not for the better.

BTW, the B&K Handbook says nothing about cardioid capsules or their venting ... which was the OP's interest.

 

[kingkorg]

This isn't quite the case. The housing & slots have 'as much' effect as the capsule itself.

We agree on most of the stuff as usual. In this particular case i think we might stumbled upon a confusion.

I was talking particularly about kk104 and kk105, the capsules found in Neumann KMS 104 and 105 HANDHELD STAGE mics.

They are different than say kk84, among other things, that the rear of the capsule is sealed, and the slots on the sides are the main part of the delay network, like the only vents the rear of the diaphragm "sees". KK105 doesn't have the second metal plate with the 8 holes, it's just a piece of metal with a "built in" spacer. The slots themselves are the missing 8 holes of the second backplate on kk84.

So the capsule is blint to what's behind it. It has insanely good rear rejection. It's kinda ingenious, newer design. Take a look at the images.

 

[pasarski]

BTW, the B&K Handbook says nothing about cardioid capsules or their venting ... which was the OP's interest.

Oops, true dat. Only pressure equalisation venting is discussed. Must have been thinking of some other paper.

 

[ricardo]

They are different than say kk84, among other things, that the rear of the capsule is sealed, and the slots on the sides are the main part of the delay network, like the only vents the rear of the diaphragm "sees". KK105 doesn't have the second metal plate with the 8 holes, it's just a piece of metal with a "built in" spacer. The slots themselves are the missing 8 holes of the second backplate on kk84.

That's sorta the Calrec capsule circa late 70s My Soundfield capsule also doesn't have 'holes' in the 'second plate' though that isn't a stick mike.

 

[kingkorg]

That's sorta the Calrec capsule circa late 70s My Soundfield capsule also doesn't have 'holes' in the 'second plate' though that isn't a stick mike.

I wish you wrote a book. So much knowledge scattered all over the web, it's not easy collecting everything you share and categorize it. Cheers!

 

[callgrlmusic]

thanks for the replies, everyone. lots to study (i’m early in both my mic modding and EE experience). i’ve got a ton of MXL 991s lying around so i’m actually trying a ton of different things.

once i have a decent test rig set up for everything, im sure i’ll document any interesting findings.

my main interest is in “cheaper” mics like those, because they’re so readily available for people like me (and for the average audio recording enthusiast). i love the alchemy of turning something decent into something good or great.

 

[Icantthinkofaname]

Anybody know what MXLs those are with the vents on the capsule? Or are those aftermarket capsules?

 

[Icantthinkofaname]

thanks for the replies, everyone. lots to study (i’m early in both my mic modding and EE experience). i’ve got a ton of MXL 991s lying around so i’m actually trying a ton of different things.

once i have a decent test rig set up for everything, im sure i’ll document any interesting findings.

my main interest is in “cheaper” mics like those, because they’re so readily available for people like me (and for the average audio recording enthusiast). i love the alchemy of turning something decent into something good or great.

Honestly when it comes to small diaphragm mics, there are some great ones for around $100.

You have the Line Audio CM4 for something like $120 last time I checked.

Then you've got the AKG Blueline mics which are something like that used, maybe a little closer to $150 now.

Solid little mic though I really hated the hypercardiod capsule. Mine was super thin sounding.

If you can get one that hasn't been abused the Sennheiser K6 system can be good. I sent mine back to the seller because it had a considerably low output.

If you don't need swappable capsules I highly recommend the Line Audio.

 

[callgrlmusic]

Anybody know what MXLs those are with the vents on the capsule? Or are those aftermarket capsules?

those are aftermarket cardioids from 3u. really gorgeous capsules, but i haven’t had the chance to do any testing on those versus the stock capsules. at this point i have stock boards, boards with signal caps replaced, bodies with bigger holes, stock bodies, etc etc etc so i plan to do a ton of a/b testing For Science

 

[jp8]

Anybody know what MXLs those are with the vents on the capsule? Or are those aftermarket capsules?

I guess you are referring to the MXL 606. I had one to see if it was compatible with 3U 22mm capsules. The center pin interface was different, as far as I remember. And it was impossible to remove the head amp PCBA and swap with a DIY version. The nose cone was stuck. Don't know how they ever got it in. Maybe by heating up the tube so it expands?

Now that I mentioned the 3U capsules, this is what they say (quote): "We designed the cardioid capsules to match the vents on slotted mic bodies as below pictures. Please do NOT close the vents on the mic bodies." So what they actually say is that slot and back chamber design affect the FR of their capsules, so it doesn't have its own closed back chamber. Unfortunately, they don't mention which body they took as a reference. I measured the 3U cardioid capsule on the MXL991, Takstar CM-60 and CM-63 and on the Alctron T-02A and all FR charts differed by a few dBs in the top end. On my FR measurement setup, the T-02A measured best (flattest) and the CM-63 with the large slots and back chamber was the worst of all (~2 dB lower @ 8KHz and up or so).

Jan

 

[Icantthinkofaname]

those are aftermarket cardioids from 3u. really gorgeous capsules, but i haven’t had the chance to do any testing on those versus the stock capsules. at this point i have stock boards, boards with signal caps replaced, bodies with bigger holes, stock bodies, etc etc etc so i plan to do a ton of a/b testing For Science

Okay, that's what I thought. The only MXL I know of with a capsule like that is the 606 but that's clearly not a 606 body.

I guess you are referring to the MXL 606. I had one to see if it was compatible with 3U 22mm capsules. The center pin interface was different, as far as I remember. And it was impossible to remove the head amp PCBA and swap with a DIY version. The nose cone was stuck. Don't know how they ever got it in. Maybe by heating up the tube so it expands?

Now that I mentioned the 3U capsules, this is what they say (quote): "We designed the cardioid capsules to match the vents on slotted mic bodies as below pictures. Please do NOT close the vents on the mic bodies." So what they actually say is that slot and back chamber design affect the FR of their capsules, so it doesn't have its own closed back chamber. Unfortunately, they don't mention which body they took as a reference. I measured the 3U cardioid capsule on the MXL991, Takstar CM-60 and CM-63 and on the Alctron T-02A and all FR charts differed by a few dBs in the top end. On my FR measurement setup, the T-02A measured best (flattest) and the CM-63 with the large slots and back chamber was the worst of all (~2 dB lower @ 8KHz and up or so).

Jan

I was wondering if MXL did another mic with a vented capsule, cause that looks like a 991 body.

The lack of a back chamber is what keeps me away from the capsules. It makes me think the capsules will sound very different on different bodies, which it sounds like you're experiencing.

 

[jp8]

I'm afraid I misinterpreted @Icantthinkofaname 's question in post #11 and took it more as a general question, rather than referring to the picture from OP's post #1. Anyway, the mics on the picture are not 606 models, that's for sure. I too would think these are 991 or 603 models with 3U cardioid capsules.

Btw, my measurements confirm @pasarski 's post #2 and @kingkorg 's post #4. I've seen posts (don't remember where) stating that the bigger the vents, the better. For sure you'll get a different on- and off-axis FR, but any better...?

Btw, I tried to improve (flatten) the top-end of the CM-63 with 3U capsule by 3D printing a longer nose-cone, filling up the back chamber cavity to more or less the volume of the CM-60 cavity. It was also blocking the bottom two rows of vents. It did help somewhat, but not as much as I had hoped. I guess the dimensions of the remaing vents are just not right. Small back chamber with narrow vents like the CM-60, MXL991 and particularly the T-02A seems to work best for the 3U cardioid capsule, at least if a flat FR is your goal.

Jan