Mechanical decoupling of microphones and their capsules and tubes.

[rock soderstrom]

Also silicone O rings around the tube are effective.

Really? I think they have less effect because the internal structure of the tube is microphonic, not the glass.

Check these out, good for mounting the tube socket or anything that needs vibrational loss.

Yes, they look good.

 

[MicMaven]

I wonder whether anyone has investigated Sorbothane or other such materials that are sometimes used in structures to isolate from vibration?

Yes. The HEIL PR35 micrphone and HEIL Handi Mic are both supposed to have sorbothane internal mounts to reduce handling noise. ... or so they say! Ham radio operators have used these for years. James

 

[Cqwet Dbdfte]

There is no magic bullet for vibration damping, some thinking and experimentation is needed. Adding mass to a spring will lower the resonant frequency. Making the spring (including elastomeric parts) harder will increase the resonant frequency. Power transformers are noisy, to some degree, and potting them in wax, tar, and dry sand have been used to reduce that effect.
The original 47 condenser mike from the 1930's made by Western Electric had a cast 6lb. brass body. We can guess the reason.
( that mike also had a separate heater lead and 200V plate supply, plate current ran thru the output transformer).

 

[Tubetec]

In my experience an O ring or two around the tube does help brace the internal structure a little better ,
I think the red silicone O rings are best , there made for higher temps , the black is only rated to 150C .

 

[Cqwet Dbdfte]

Tube sockets with shields add mass and may help.

 

[Tubetec]

A sheilding can around the tube will make a difference to the incidental capacitance ,
Heat dissipation and air flow may also be effected by the presence of a tube shield .

In one mic I made I used aluminium tube with an ID very close to the tube diameter I was using , it turned out some versions of the EF86 wont fit in , the Mullards fit , the later East German/Russian varieties dont .
The aluminium part the tube fits into is bolted to the the frame ,so has a chance to dissipate heat by conduction .

You do see some better domestic tube gear with very close fitting mu metal tube sheilds , they have a short lenght of braided wire making the 0V bond at the appropriate point in the circuit .
Tube reel to reel players from Tandberg have it , the reason is that both a motor and power transformer are in close proximity in a tape machine ,so extra precautions need to be taken to exclude the AC feild .

Anyway in the context of a hi-z tube mic the proximity of the tube screen will have an effect on the tone , it might be favourable or not depending on what your trying to achieve .

 

[Cqwet Dbdfte]

Added capacitance yes, main use for shields is for RF, but the actual numbers do not add up to much. Mike tubes are often metal cans anyway. Correct with sizes, Russian Noval tubes I've seen have a larger diameter.
Metal cans do add mechanical rigidity to the tube.

 

[metalockpick]

I wonder whether anyone has investigated Sorbothane

 

[rock soderstrom]

There is no magic bullet for vibration damping, some thinking and experimentation is needed. Adding mass to a spring will lower the resonant frequency. Making the spring (including elastomeric parts) harder will increase the resonant frequency.

True. My impression is that mechanical decoupling at several points with different materials (-->resonant frequencies) improves the result. I'm still experimenting...

 

[Cqwet Dbdfte]

Sorbothane is a great material, but do not expect miracles.

 

[Olioli]

Interesting discussion , I'm just starting a mic build and I was wondering about the way the capsule could be /should be fixed. For suspension I was thinking of using a silicone sealant mixed with cornflour , the amount of powder can be adjusted to give the amount of flexibility you want and it also causes the silicone to cure fast even when it is thick.
But then I was also thinking that a capsule diaphragm is like a speaker cone , and those require a very rigid framework to operate against , and we add weight and stiffness to the baffle and the box to maximise that. So maybe a lead ring to add weight around the capsule and then a silicone support...
But if the best tube mics ever made do without anything like that , perhaps it's overthinking. And if capsules are made / tuned to give an appropriate frequency response with a normal mounting , some other kind of mounting may simply induce distortion.
I guess experimentation is the only way to know.

 

[Khron]

But then I was also thinking that a capsule diaphragm is like a speaker cone , and those require a very rigid framework to operate against , and we add weight and stiffness to the baffle and the box to maximise that.

Well, despite some of the principles by which they work being similar, the goal is a bit different.

In the case of a speaker, the point is to transfer as much of the electrical energy / signal into the air outside of the speaker box. If the baffle flexes (and/or the rest of the box), that's just cancelling out some of that air motion which does NOT get transferred towards the listener, thereby wasting energy (ie. reducing efficiency). Plus panel resonances could add sounds that are not in the electrical signal being applied, etc-etc-etc.

The point in shockmounting capsules is "only" minimizing the amount of (mostly low-frequency) noise getting mechanically conducted to the capsule, and/or cutting down the resonances of the microphone body.

 

[MicMaven]

wondering about the way the capsule could be /should be fixed. For suspension I was thinking of using a silicone sealant mixed with cornflour

Interesting Serving Suggestion, although it sounds more like a rue to thicken a gravy or sauce than a capsule support!

But if the best tube mics ever made do without anything like that , perhaps it's overthinking. And if capsules are made / tuned to give an appropriate frequency response with a normal mounting , some other kind of mounting may simply induce distortion.
I guess experimentation is the only way to know.

As another novice mic builder, I think this is a good question. I, too, wonder whether different support materials will alter the sound. Should it be rigid or flexible, or be comprised of a mixture of both qualities in some way? While I may dampen deleterious microphonic vibrations, I do not want to make it sound unduly dull or brittle by selecting the wrong material.

And, yes, I suspect experimentation may be the best way to determine the matter. James

 

[MicMaven]

wondering about the way the capsule could be /should be fixed. For suspension I was thinking of using a silicone sealant mixed with cornflour ,

I occasionally use self-amalgamating (self-fusing) rubber tape (e.g. Tremflex 2155) that remains pliable and squishy and is easy to apply and remove at will. Use only as much as necessary to fill the gap between cartridge/capsule and holder/mic body. Peels off at will leaving no residue. It is also good for water sealing coaxial cable connections. James

 

[Emmathom]

What about that ?

https://a.aliexpress.com/_Ez5N7oF

 

[MicMaven]

The point in shock mounting capsules is "only" minimizing the amount of (mostly low-frequency) noise getting mechanically conducted to the capsule, and/or cutting down the resonances of the microphone body.

Silly Novice Question No. 28973 -

Um ... er ... so how do we KNOW suspending the capsule in a mushy, squishy, flexible silicone-rubber mount does not have a deleterious impact on overall sound capture?

I get the point about mechanically decoupling the capsule to minimize low frequency rumble and handling noise, but could mounting the capsule on a jiggly, wiggly, squishy support produce an even worse negative affect for other reasons?

I ask, because so many capsule mounts are quite rigid and inflexible. That suggests manufacturers make stiff, rigid mounts for OTHER GOOD reasons. Perhaps manufacturers rely on external shock mounts (and high pass filters) to minimize low frequency interference, while mounting the capsules on relatively sturdy, rigid mounts, because capsules capture sound across the rest of their frequency response curves that way.

Um ... just thinking aloud.

(... he typed, donning his Teflon(F) suit ...) / James /