Mechanical decoupling of microphones and their capsules and tubes.

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rock soderstrom

Tour de France
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I think everyone who has been involved in building (and modifying) microphones knows the problem.

Microphones and their components react to low-frequency structure-borne sound much better than you would like.

Some microphones are so sensitive that unrestricted use (on stage, for example) is almost impossible.

Accordingly, a lot of effort is put into this area and more or less successful measures are taken, which is what this thread is about.

Everyone knows the typical microphone shockmounts (in Germany we call them colloquially "Spinne" => spider), an effective protection against rumble sound based on the elastic suspension of the microphone in rubber bands.

spinne.jpg

This is where the first questions arise. What characterises a good shockmount? How elastic must the suspension be and what is its relationship to the weight of the microphone? What is better, a rather soft or tight suspension?

The idea of the "spider" can also be used successfully in other places; it may be sufficient to simply suspend the capsule elastically. What are your experiences?

For example, I have modified this microphone and I love it but it is extremely sensitive to rumble, the microphone thinks it is an earthquake detector with incredible sensitivity, unfortunately not so good for my application.

schumann.gif
Simple solutions like this one do very little to nothing. How can I optimize this?

What would be the best way to successfully suspend the capsule? Rubber bands or metal springs? Soft or tight suspension? Lightly dampen the suspended capsule with a felt damper? Does this help or should the capsule be able to swing freely (in the rubber bands)? Do I need to "tune" the damping system?

Not only capsules need physical isolation, tubes can also benefit from it. These mechanically rather delicate constructions also tend to resonate. That is one of the reasons why they are selected or even produced for this purpose.

Nevertheless, all tubes in microphones can benefit from mechanical decoupling. Which way do you go here?

I'm currently trying something like this, two DIY shock absorbers cut from the insulation of an XLR cable. It lasts forever, we'll see if it really works. What are your experiences?

absorber1.jpg
absorber2.jpg
In this context, it is also interesting to ask what is the benefit of a layer of rubber between the capsule and the holder? What would an additional layer of rubber between the holder and the body achieve?
Should the distance holder be designed as a shock absorber (as above)?
20231203_115541.jpg
I've also noticed that the wire to sensitive components such as capsules and tubes should be flexible and light rather than heavy and rigid, as this seems to reduce the transmission of mechanical energy? What do you think?

There is another thing to consider from my point of view. High pass filters in the head amp circuit of the microphone should be dimensioned accordingly. It makes no sense to extend the corresponding filters excessively downwards (anode to xformer cap, 1G grid resistor...) because this only amplifies the existing problems. Of course, it is better to counter structure-borne noise events mechanically, but the electrical side is also part of the game.

What do you think? I appreciate any input.
 

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What you are posting about brings up something I don't understand with posts I have read on the web over the years

Why do people remove the U67 HPF? You can build or buy another microphone without the HPF

Reducing the input resistor with a tube changes the HPF and interacts with the grid current and...

I have built microphones with and without second order HPFs IMO if they are low enough in frequency (so what they do is not very audible) they help a lot with removing low frequencies however, you need to think about how the different filters in the complete circuit(this can be the cable and preamp input as well) interact.
First order HPFs have to be set higher for about the same rumble reduction
 
Spider shock mounts with the sprung felt lined band add considerable damping and stops the mic body from ringing , the kind that screw into the thread on the XLR stub dont provide any .

I think you need to match the shock mounting system to approximately the right mass to load it ,
I often find a spider type shock mount will only hold a mic properly in the upright position , if you place it at an angle then it droops to one side ,possibly making contact with the frame , which nullifies any anti vibration. Placing an extra turn of the bungee cord around the mounting hooks can improve a slightly sloppy spider . spider.jpg

Drone style soft anti vibe mounts are just about perfect for use in microphones , there usually speced by the mass they support , normally in compression .
https://www.flyingtech.co.uk/frames...ibration-soft-mount-kit-flight-controller-pdb
 
You could try mounting up that 58 capsule in a standard Shure shockmount and place it inside the old style mic housing . That old rubber thing your using probably doesnt work the way its supposed anymore as its become brittle and hard over time .
 

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..think of those trittschallfilters / shockmounts as simple mechanical lowpass filters that isolates mic capsule from the environment. To metaphor to a RC-filter, holder tension is like the resistance part - softer/lower tension equals higher resistance, mic total mass equals capacitance. Felt parts soak energy, reduce Q.

Thinking of it this way, it's clear that you are also allowed to make notch filtes.. :)
 
Cathode follower mics Ive found to be very good at rejecting physical vibrations in the tube itself.
couple that with internal shockmounting of the tube , damping of the mic body and finally the spidermount to deal with vibrations from the floor ,it makes a big difference .

Heres an interesting article on a related subject I thought people might like , its more about preventing physical vibrations from the monitors getting into the structure of the building and causing frequency responce anomylies .

https://www.audiotechnology.com/features/name-behind-the-name-tom-hidley
 
I wonder whether anyone has investigated Sorbothane or other such materials that are sometimes used in structures to isolate from vibration? I also thought of Sylomer but I assume its compliance would be far too low

As mentioned above, if creating a mass-spring system it has to be tuned in order to really do anything. If the spring is too stiff relative to the mass, it won’t act as a spring (and won’t suspend). If it has too much compliance relative to the mass load, it’ll compress fully and likewise stop acting as a spring/stop suspending
 
Thanks for the good information!
Spider shock mounts with the sprung felt lined band add considerable damping and stops the mic body from ringing , the kind that screw into the thread on the XLR stub dont provide any .
Thats true, the damping directly on the body significantly reduces the ringing of the shell.
Drone style soft anti vibe mounts are just about perfect for use in microphones , there usually speced by the mass they support , normally in compression .
Looks promising. (y)
You could try mounting up that 58 capsule in a standard Shure shockmount and place it inside the old style mic housing . That old rubber thing your using probably doesnt work the way its supposed anymore as its become brittle and hard over time .
interesting, but I think I will try a inbody spider construction. Four metal springs and ring mount for the cartridge could work..
..think of those trittschallfilters / shockmounts as simple mechanical lowpass filters that isolates mic capsule from the environment. To metaphor to a RC-filter, holder tension is like the resistance part - softer/lower tension equals higher resistance, mic total mass equals capacitance. Felt parts soak energy, reduce Q.

Thinking of it this way, it's clear that you are also allowed to make notch filtes..
That helps (y)
a mechanical vibrator/variable oscillator could be useful to sweep the system
just like measuring an eq:unsure:
I need one for further experimentation.
Heres an interesting article on a related subject I thought people might like , its more about preventing physical vibrations from the monitors getting into the structure of the building and causing frequency responce anomylies .
Thanks!
I wonder whether anyone has investigated Sorbothane or other such materials that are sometimes used in structures to isolate from vibration? I also thought of Sylomer but I assume its compliance would be far too low
Yep, interesting how modern materials will work in this application.
As mentioned above, if creating a mass-spring system it has to be tuned in order to really do anything. If the spring is too stiff relative to the mass, it won’t act as a spring (and won’t suspend). If it has too much compliance relative to the mass load, it’ll compress fully and likewise stop acting as a spring/stop suspending
This also corresponds to my expectations. Where is the sweet spot? I would like more information on this topic. Can anyone say more about this or has a good link?
 
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I wonder whether anyone has investigated Sorbothane or other such materials that are sometimes used in structures to isolate from vibration? I also thought of Sylomer but I assume its compliance would be far too low

As mentioned above, if creating a mass-spring system it has to be tuned in order to really do anything. If the spring is too stiff relative to the mass, it won’t act as a spring (and won’t suspend). If it has too much compliance relative to the mass load, it’ll compress fully and likewise stop acting as a spring/stop suspending

I thought making a capsule post of Sorbothane would be the simplest solution. Ha!
I'd have to pull up spreadsheets, but IIRC I stopped because of a few things:

Primary show stopper: Sorbothane's catalog / stock items had few options for proper loading. What @soapfoot says is key. I even considered adding weight to the capsule holder. Then you need to ensure the Shore / stiffness rating will not interfere with decoupling but also confer decent rigidity so the capsule doesn't move around enough to result in a change on/off axis sound. Of course you'd also need to decouple the screws and threads on both sides of the capsule post as well. For my humble brain, trying to get into the right ballpark felt like trying to square a circle; made my decoupling of soffit-mounted KH420s seem like a cakewalk!
 
Drone style soft anti vibe mounts are just about perfect for use in microphones , there usually speced by the mass they support , normally in compression .
Thanks for this, I've been looking for exactly these kinds of mounts to suspend a tube socket inside a microphone.
 
I have a large Grampian moving coil mic dating back to the 30's
Its has a square metal frame on the outside , the mic body itself is suspended by 4 springs ,
inside each of the four springs in a piece of felt , that helps with damping any movement or noises from the springs .
 

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That looks good. That's roughly what I had in mind for my modified Schumann mic. Small metal springs are easier for me to mount than rubber bands.
 
I believe Oliver Archut developed a shockmounted pedestal for the capsules in the Lucas CS1 and CS4. I can’t remember if he used sorbothane or something similar. I may have notes on it somewhere, or there may be info buried on the Lucas message board, if it’s still up.
 
Some manufacturers take the extra step of adding shock absorption of some sort between the headbasket and body, or additional under the capsule mount, aside from the common rubber capsule pedestal. Adding shock absorption via rubber or similar to handle vibration around the output connector is another thing you will run across.
 
I'm pretty convinced the springs on 1930'es era carbon-dust microphones were NOT there to prevent acoustic-mechanical coupling to the environment like today: 1) These have close to no low-frequencies to mess with, and 2) the springs are usually tuned waay too high (tense) to make any sense for this. I think that system is more about mechanically protecting the mic capsule, that tends to get quite fragile if you want high-sensitivity out of carbon dust (or -dot).

(I haven't been able to verify this independently, but was told so many years ago by an already-old radio engineer)
 
One might consider soft silicon O-rings under low tension for vibration isolation, loaded against a heavy mass.
 

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