Mechanical improvement of mic build.

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KrIVIUM2323

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I had'nt thought about the wire from capsule. You are probably right Fred.
The technique used by MsVienna is probably way better to limit transmission of structural vibration.

Last night i though about a possible way to dampen the headbasket supporting plate in chinese mic.
It could not be used with every mic body type but could be worth a try... use of CLD technique.

I ll try to find time these evening to draw something and publish here.
 

KrIVIUM2323

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instinctively, if the mesh is ringing when i tap on it with my nail, i imagine it will ring when i put it in front of my fender deluxe reverb, playing some notes near the resonance frequency of the mesh...
i always wanted to record/mesure that but how ???
silicon rings will reduce ringing somewhat like a silicon damper on the strings of a tennis racket...

Ok got it, the damper of tennis racket is nice idea, should be easy to do.

It should be possible to record/measure using an accelerometer and expose the headbasket to high spl source using a sweep to find frequency of resonnance.

B&K have nice accelerometers.
This one could do but find someone who own it would'nt be easy, this is very dedicated tool :

https://www.bksv.com/en/products/transducers/vibration/Vibration-transducers/accelerometers/4516

One of my friend own an older one much bigger than this one, he once used it to record a piano, to add some attack to the regular microphone. Worked nice, and interesting to think about... you record sound which doesn't exist yet! ;)
Nice paradox.
 

12afael

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maybe we can use a piezo? it is used on acoustic guitars a lot.
even maybe a ceramic cap, smd would be small enough provably to not add to much damping to the mesh.

great thread!
 

granger.frederic

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i would talk about the HiZ wires again...

i recently built  a mic and i tried to  stuck the capsule wires on the rubber part of the capsule suspension ( with a colson ring)

the result was awful, lifeless and colored  :mad:

it sounded like if the vibrations (from were? headbasket, capsule?...) were incorporated with the signal...

also, i always had the feeling that placing teflon pins (or mechanical decoupling)  between headbasket and body, was really cleaning the sound.

AFAIC, it is such an obviousness for me that i sadly never recorded a mic with and without...

i would also say something about the wire diameter and stiffness...
Ben (beezneez) chooses larger diameter/stiff, Neumann medium but soft/resilient, the same for Flea/Thiersch, TFK use small Teflon wires, AKG use standard PVC wires...
Teflon wires are stiffer... maybe more resonnant...
however teflon isolates...
why not using Litz wires (tonearm)...?
i think we should take care and think about it...

the mounting could be important as well.
i wouldn't apply too much tension here, excessive length, nor making loops...
i would also avoid (as much as possible) physical contacts between HiZ wires and headbasket or body.

Please share your opinions...


PS: if Tim is reading, i would be nice if he could place the CT12 backplate connectors lower, to reduce wire length...or move the mounting holes...
 

Khron

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Teflon indeed is a great electrical isolator, but i'm not so sure about its mechanical isolation properties. It does have a really low friction factor, but that doesn't have much to do with vibrations...
 

KrIVIUM2323

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This is something i wonder too.

In my experiments with pcb spacers as i said before i thought of because of the low friction and different mechanical properties (it is really soft material) than metal, the end compound structure could offer better damping because of the different 'impedance' of each layers.

But i m really not an expert... All this from my part is trial and errors and i m open to be corrected! This is the 'reason d etre' of this thread.

Sharing our experience and find what works and if possible why it works (and how to implement it in real life). ;)

To come back to ptfe, in the industry it is often used where there is high mechanical constraints and movement.
I ve seen it used in interface (kind of washer i don t know the name in english) between ball bearing and metal tube. The original piece used to make a lot of noise when in use. Once changed for ptfe equivalent it was dead silent.

Constraints are quite different here but maybe there is a gain, as i already said i don t have data to back this up.

This is the material with the lowest friction coef you could find ever (at the moment and afaik). It could help just by this fact as it slip at the contact point with other material?
 

ln76d

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Simple solution for most of chinese microphones.
Usual size fits exactly most of headbaskets.
Dampening resonance of the base, extra dampening for capsule saddle/holder, keeps wires isolated from the base.
Same material can be used for internal headbasket frame resonance dampening.
 

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Banzai

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Teflon wires can be super microphonic. In a 251 they're unusable for the backplate to grid connection. In comparison, 26 AWG or smaller PVC is dead quiet.

For my builds I've settled on PTFE for board to mic connectors in the PSU, and for front and rear capsule wires. Everything else including backplates, I use Eco-wire by Alpha (mppe insulation). Non-microphonic, and very thin and lightweight. Perfect for tube grid connections. Cheap too.
 

granger.frederic

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i would say that too thin and soft wires can vibrate or oscillate too easily
too thick and rigid wires could transmit vibrations of the body to the capsule, or could resonate
for the capsule, i would abandon Teflon for wires (too rigid) and the too thin, too thick and too long wires , i'd choose 27-28 AWG PVC

i think that the teflon pins between headbasket and body are canceling any contact/any friction between the wires and the metal.
it "breaks" the transmission.
it seems also that Teflon has a high absorbance in the medium range (between 400hz and 1,3khz)...

we should have the same analysis with the capsule holder/suspension and its rubber (or equivalent) material...

we need someone with solid knowledge about mechanical vibrations analysis and simulations...

i think we underestimate the capsule micro-movements/vibrations on loud sources...

 

Banzai

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granger.frederic said:
i would say that too thin and soft wires can vibrate or oscillate too easily

They can't vibrate at all. That's the point of being non-microphonic  ;)

Same as Kynar wire. Ultra thin, but non-microphonic. Great wire for mics.
 

granger.frederic

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i wouldn't be affirmative on this point ...
could you explain the non microphonic properties of that wire ?
i'm a bit lost... :-\
PVC has an elasticity modulus around 3200 MPa.
if mppe is the same as PVDF (between 350 and 1100 MPa)... it's near the PTFE that you qualified "super-microphonic" (PTFe between 300 and 800 MPa)
 

Banzai

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I'll turn into a salesman for Alpha, but use your ears. If you hit ecowire or kynar connected to a capsule or tube, you'll hear nothing. Vibrations aren't being transmitted through the wire or insulation jacket.

To make sense of it, you need to take into account insulation thickness. Because these are much stronger materials with better dielectric properties, the jackets are ultra-thin for similar properties to PVC.

But the non-microphonic properties of wirewrap builds are very well known. Makes it a great technique for mic building that pretty much no-one uses.
 

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granger.frederic

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insulator thickness is important...
maybe it's the right wire...but...
how do you measure that "you hear nothing" ?  did you make some tests ?

electrical insulation of PVC is between 10°14 and 10°16 ohms/cm, it seems enough...
i'm still not convinced that a thinner and harder material is the most suitable for capsule connection...
other opinions?
someone?
 

KrIVIUM2323

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Dampening resonance of the base, extra dampening for capsule saddle/holder, keeps wires isolated from the base.

Piotr, there is many kind of 'technical foam' so could you provide a link to the specific one you use  please (or define the material more precisely) ?

i think that the teflon pins between headbasket and body are canceling any contact/any friction between the wires and the metal.
it "breaks" the transmission.

I don't know if it break the transmission but i think it lessen it. It follow the thought i had about the spacers stand off. But we may be wrong.

we need someone with solid knowledge about mechanical vibrations analysis and simulations...

I do agree.  Simulation could be great! It could be of great help to dampen the body tube for example. We probably will come back to this latter. ;)

i think we underestimate the capsule micro-movements/vibrations on loud sources...

Maybe not underestimate but like you i think this is a major point. With the analogy about loudspeaker, it is well known that parasitic vibration of the whole structure do induce coloration but at the same time 'smear', 'mask' (or both at the same time!) low level information in loudspeaker box.
I think i've already read some serious analysis about that and iirc, differences of up to 1/1.5db have been recorded between the same hp in differents enclosure with different build techniques... I'll try to fin that in my hdd i may have kept this.
This thread makes me digg deep into my hdd's... and rise the need for a better organisation of info to find them again...  ::)

I'll turn into a salesman for Alpha,

You are not Banzai! This is really interesting and of great help. And it will not break the bank to try it.

But the non-microphonic properties of wirewrap builds are very well known. Makes it a great technique for mic building that pretty much no-one uses.

I've already seen it mentionned a few time from different sources in the 'audiophile' world. Problem being that it is from audiophile world most do think this is pure BS.

Ok so i've got a bit of time last night to make some rendering about a possible way to limit vibration transmission to headbasket baseplate and 'isolate' capsule mount/saddle from the one for the body using CLD.

This use two baseplate. The lower one being attached to rails and rest of the body, the second upper one see the capsule mount attached to it. It is fairly simple and should be easy to do in practice, two aluminium disc 1/2mm thick used as baseplate.

Both are glued together using a VERY THIN layer of VISCOELASTIC glue or dedicated viscoelastic material. No other form of contact should exist between the baseplate than the viscoelastic material or the effect is defeated or largely attenuated.

It can seem counter intuitive (at least for me) but the viscoelastic glue layer must be very thin for it to work as a CLD.
And the glue must be viscoelastic not only elastic.

CLD do work by transmitting vibration to the intermediate layer and transform them in heat by means of SHEAR DEFORMATION, not mass increasing.

As the name implies it does damp the structure but not by the more intuitive 'increase of mass' to achieve it.
This is really a situation where there is mismatch of 'mechanic impedance' between layers.

Base material could be other than aluminium, steel works no problem. 
This technique i widely used in the industry (a lot in the marine industry where vessels induce problematic behavior of sound transmission because of the all metal stuctures) but as well in the pure studio acoustic field.

In the studio this is often build using two plasterboard from same thickness (in France it is BA13 - 13mm, or BA18- 18mm thick) separated by some form of bituminem materials sheets (4mm thick).

It can be argued that this is so form of mass damping in this case and yes for some kind of frequencies this is it, but as you move away this does indeed become a CLD and shear deformation is at play.

Ok back to the base plate, as seen in the sketch clearance must be allowed to have rail bolts not to touch the upper plate, and the bolt to mount the capsule holder not touching the lower plate. I have not drawn holes to have the wire go through but same principle apply.

The upper plate should be a little bit smaller than the lower one to be sure not to have contact with body or headbasket.

The sketch does more or less copy the arrangement that you can find in most chinese U47 body style.

Ok now the difficult part... Where to find some viscoelastic glue or material?

Well, 3M has some dedicated tape for that kind of things: 'Ultra Pure Viscoelastic Damping Polymer 242f01'
It is convenient as it is a double sided tape so no mess with glue... It is used to damp HDD noise by the way... But i do not know if the glue used will be enough for the weight it'll face. It is very likely yes.

https://www.google.fr/url?sa=t&rct=j&q=&esrc=s&source=web&cd=8&cad=rja&uact=8&ved=0ahUKEwjCyfqRls3XAhWIFuwKHe-6B0EQFghbMAc&url=https%3A%2F%2Fcdn2.hubspot.net%2Fhubfs%2F99603%2F3M_Ultra-Pure_Viscoelastic_Damping_Polymer_242F01_242F02_sales%40gleicher.com_distributor_converter.pdf%3Ft%3D1493911022522&usg=AOvVaw0G_b2ni_f_SF8ctZGRGPC6



I've found glue from Permabond that could be used too: something like their TA4246 should work.
http://www.permabond.com/wp-content/uploads/2016/05/TA4246_TDS.pdf



 

Khron

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Since, in essence, that's basically shockmounting the capsule, are there really no easier ways to achieve that?

Something like, say, an oversized saddle and the capsule mounting screws going through some very compliant bushings?

By "bushings" i mean like those insulators for TO220 heatsink mounting, for instance (but bigger, and made out of silicone or something nice and gummy-soft).

https://www.google.fi/search?q=to220+bushing&num=20&client=firefox-b-ab&dcr=0&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiukMavoM3XAhVjOJoKHV9pC28Q_AUICigB&biw=1599&bih=788
 

KrIVIUM2323

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Since, in essence, that's basically shockmounting the capsule, are there really no easier ways to achieve that?

Yes very probably! :)
But i see other advantage thru this: you'll defacto protect from body vibration mounting teflon pin (if you use it too) and it is not 'bulky' maybe at worst 2mm higher than regular plate.

There is something that bother me too with typical decoupling technique (use of resilient and soft material): when you see graph of efficiency of attenuation there is always 'bouncing' (lost of efficiency) higher up than the decoupling frequency in the frequency response. This can be audible.

I think that it is easily seen in the m600 suspension comparaison pointed in the previous thread (but it is different strategy once again so it may not be relevant, the point being in the graph the elastic mount behavior not the behavior of the shift of resonnance frequency).

I'll look for cld but i don't remember to have seen that behavior for this technique.

Anyway i don't think this is a cure for all disease.  ;D
One possible answer to add to multiple other.

I don't think this is difficult to realise too (except for the glue part which can be an issue to source).
A little bit of 'faceplate designer' a little bit of wait (and money spent i agree!) and Schaeffer deliver the plate to you. ;)
 
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