Mechanical improvement of mic build.

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KrIVIUM2323

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Ok so now we have most of the weakest points for our purpose listed.

What could we do with that: first i think that for the parts by themself (not the overall structure) we should try to damp them individually.

For the headbasket plate i've already given what i would like to try (the cld) to isolate the capsule mount from the rest of the body but to selfdamp itself too.

For the headbasket and the grid/mesh Frederic gave a nice idea about the 'tennis racket' damper. Other things could be done to try to dampen the whole headbasket (like a sorbothane washer between the haedbasket and the plate or body) but this may face some contradictory requirement as we must keep an electrical continuity for capsule shielding).

For the body tube we could try to dampen it, maybe using some spring loaded sorbothane pad (a bit like in the Elam but with damping pad at the end of the sping). Some coating could be used too (same for rails below) but in some case this will be impossible because of thickness constraints.
If we had someone with software and knowledge to model the tube including material i'm pretty sure this could be effective to determine the best place/spot where to apply damping too!

About that, MSVienna could you describe how you damped the body tube for the mic you described? 

For the rails we could try to aplly some coating to them to damp them. The kind of coating used in automotive to damp the large metal parts. This may proove tricky and messy in practice but could work effectively.

For the end bell same thing, should be easier.

The other effort could be in the point of contact, using some kind of pad to isolate each parts from each others. This may be difficult and contractidory requirement about electrical shielding.

Then we could use some damping/isolator to mount the electronic parts (pcb,boards,..). This may be difficult too, i don't know for the moment.

This could deal with the solid transmission of vibration inside the mic and help damp the whole thing to a maximum.
So we could have the most 'inert' mechanical structure possible.

What do you think about that?
 

granger.frederic

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KrIVIUM2323 said:
I was aware of the felt dampers, not from the mechanical articulation. Could you explain how it perform?

https://www.gearslutz.com/board/geekslutz-forum/821064-telefunken-ela-m-251-pattern-switch-assembly-photo-timeline.html

this pictures should give you an idea of how it works  ;)

they have chosen felt to damp the capsule...
felt has a great damping ability.
they probably looked inside a piano before designing the mount...  ;)

personally, i prefer this mount to the rubber one. the rubber absorb a force then restitute almost the same force, thus oscillate.
or it's stiff then it damps nothing ...
imagine a piano with dancing rubber dampers  ;D

we must keep in mind that every tiny movements of the capsule or HiZ parts are highly unwanted at such impedance.
each tiny capsule movement or oscillation will degrade the impulse response of the mic.
we don't want that.

that's why i dont like elastic shockmounts neither.

i would use only elastic material for self damping elements,  like "dampers" for the headbasket mesh...

for the capsule we have the Aputis mount...

it may be wise to hard mount the mic on a very stable stand, to transmit elsewhere (maybe to the floor via decoupling spikes, or into a damping mechanism...) the vibrations absorbed by the mic ...
or we could use some felt also for the shockmount or even for the stand feets...
no?






 

MS Vienna

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KrIVIUM2323 said:
About that, MSVienna could you describe how you damped the body tube for the mic you described? 

I applied a layer of felt on the inside of the tube with doublestick tape.


granger.frederic said:
they probably looked inside a piano before designing the mount...  ;)

That´s quite likely. Felt was easily available in many variations at that time. There were lots of piano makers in Vienna as well as hat makers . In Nobilegasse (road where AKG was located) there´s a big pianoworkshop  just a few blocks away that still exists today.

 

KrIVIUM2323

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they have chosen felt to damp the capsule...
felt has a great damping ability.
they probably looked inside a piano before designing the mount...  ;)

Yes felt have damping ability but i would'nt say this is great. Most recents material do have greater damping.
If it was choosen in a piano this is because it does give some nuance when you use mute pedal: it don't stop vibration immediately and gives possible variation to the player.
This is not to say engineers did a wrong choice about that in capsule mount, just they did what they felt to be adapted within the situation, materials easy to source and the application in production.

personally, i prefer this mount to the rubber one. the rubber absorb a force then restitute almost the same force, thus oscillate.
or it's stiff then it damps nothing ...
imagine a piano with dancing rubber dampers

Yes it is thru for rubber and most elastic only materials. Your example of the piano would not be thru because you in the mute pedal you have mechanical force applied to the dampers and this translate in mass applied to the string, those being stopped vibrating by the application of both together (force+damper). ;)

In fact you omit some parameters in the analyse you make of 'suspended' system: as already said those system are tuned and if weight, shore hardness of material and stiffeness are wisely choosen this system absolutely works*. The issue of oscillation may indeed be not ideal but if this is done with low enough frequency this should not be a problem as big as it seems.
And don't forget the rubber mount serve multiple purpose as one, the need to protect the capsule in case of schock being one of them.
Oh and if you use viscoelastic materials you don't have that oscillation as with elastic only material. That is the whole point of it in CLD principle. There is an hysteresis behavior about that where energy is dissipated in heat by deformation.

As always this is all about trade off and balance between the needs, you gain somewhere, you'll loose somewhere else... ;)

*the real issue i see is more in the fact that under the fc there is amplification and a bounce with loss of efficiency higher up in frequency. I'll try to find some graph showing both effects i've already seen them in datasheets somewhere... just have to found where... :)

we must keep in mind that every tiny movements of the capsule or HiZ parts are highly unwanted at such impedance.
each tiny capsule movement or oscillation will degrade the impulse response of the mic.
we don't want that.

I agree but there is a point where you have to draw a line and make trade off
For me this line is with the protection of the capsule as i can't buy a new one each time a mic fall down (which sadly happen).
It's a bit like with cars... The absolute concept to go fast and be precise in drive capability is a F1. But if you need to go off road or bring your familly somewhere this isn't going to be practical to use a F1, as it won't be confortable, won't have the place nescessary to move more than one person or is economic as you must change the engine every 4/5 hours.

For me and what i 've seen of professionnal use of mic i accept to invest in an hybrid SUV/F1 kind of car not a F1... this too much compromise on the economic side for me.
Though, this won't stop me to help and think about your needs (if i can)! After all this is really interesting and i'm a curious mind. :D

it may be wise to hard mount the mic on a very stable stand, to transmit elsewhere (maybe to the floor via decoupling spikes, or into a damping mechanism...) the vibrations absorbed by the mic ...
or we could use some felt also for the shockmount or even for the stand feets...
no?

I agree 100% about the isostatic condition (stable reference mount) but... spikes or not decoupling gear! In fact this is the inverse they are coupling mechanism! There is a misunderstanding of the principle at work...

Let me explain it: if you take a thumbtack and apply to it your thumb with a force of 10kg, at the upper part (if the thumbtack is big enough!) wher you apply your thumb you'll have say 1cm² so you have a 10kg/cm² force applied.
If you look at the lower side of the thumbtack there is a spike with let's say 0.1cm². Same force of 10kg is still applied so you'll have a 10t/cm2 force at apex of spike!

The thumbtack will act as a mechanical amplifier of the force applied. If you put this spike on a soft floor (let's say some wood), it will then 'enter' a little bit in the matter and with a 10t/cm² force applied on it it will be a very effective coupling mechanism.

In fact this is seen as being a decoupling tool because most tends to think the tiny point of contact will block the vibration transmission but as it is a mechanical amplifier it just increase the coupling to the floor!

This is not a problem in practice as this create an isostatic condition (and if you use 3 points of contact you have the most stable
condition you'll find because it deals with issue of non flatness surface) and in the case of loudspeakers or ours mic it is desirable. Well, i think this is desirable. ;)

to transmit elsewhere (maybe to the floor via decoupling spikes, or into a damping mechanism...) the vibrations absorbed by the mic ...
or we could use some felt also for the shockmount or even for the stand feets...

I do agree but this raise some contradictory needs. If you try to damp you'll most likely use a viscoelastic material so it will have the ability to move in x,y,z axis. If you make a very stiff system then vibration from ground (solid transmission) will go either way from the mic to ground and from the ground to mic.

As always you'll have to make trade off... Then you'll have to choose where you define the line versus a very stiff system or a damped one.

There is a large variation of possible trade off... depends of what you want to highlight and how you want that to happen! :D

For example the idea given by MSVienna don't fullfill the requirement for isostatic condition in my view. But that won't say this can't work... quite the opposite it can be very effective!

And cheap to try and very practical if you record some drums for example. But if you want 'ultimate' details for voice tracking for example it could be bettered in my point of view ( in including a chassis and spike to induce isostatic condition for example. ;) ).

I've got others ideas about the mic stands and the mic holder... but i think some me think i'm crazy or an audiophool so i don't know if i will publicly share them...  ::)  ;D

But maybe at first we should concentrate on the mechanical structure of body don't you think?
 

MS Vienna

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KrIVIUM2323 said:
I've got others ideas about the mic stands and the mic holder... but i think some me think i'm crazy or an audiophool so i don't know if i will publicly share them...  ::)  ;D

But maybe at first we should concentrate on the mechanical structure of body don't you think?

Effective shock isolation methods for mic stands and holders are beneficial for all microphones not just for selfmade ones ;-)

Don´t be afraid. Just try out your ideas first and share the ones that worked out well for you.
 

KrIVIUM2323

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Don´t be afraid. Just try out your ideas first and share the ones that worked out well for you.

You are right MSVienna. First will be test of the CLD idea for the headbasket plate then dampening...

And as i am fearless here is a clue about what i have in mind...

https://www.youtube.com/watch?v=HuSiRRoz72Y

https://www.youtube.com/watch?v=Fk_3zjTDKm4&t=3s

Not so easy to diy but... well you get the idea! (second link is long but show some interesting properties if you look at it long enough, from 2'25 to 3'10 for example ...and many differents approach to explore). :D

And this is not esoteric approach very very science driven with real life proof of effectiveness. Just at a larger scale than the one we are interested in.

;)
 

granger.frederic

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KrIVIUM,
thanks for your ideas... :)
i think we shouldn't focus, and get lost in very technical considerations, on the mechanical structure of the body without a global thinking.
we should consider a mic as an assembly of multiple elements from the capsule to the mic stand.
after, we should evaluate from where the main vibrations are coming into this assembly, depending of the most probable LDC mic uses, in front of moderate and loud sources.
we also have to analyse the type (frequency, intensity) of the most commun unwanted and detrimental vibrations.
then we have to choose if we want to transmit and/or absorb those vibrations, and how.
and during all that time, we have to keep in mind the feasibility for DIYers.
waow ! so much things to do !  :'(
i humbly admit that i haven't all the answers yet...
like you said it's a question of compromises.

the mic fall...
it shouldn't but yes, it happens.
we could ask capsule builders for the resistance to shocks, i suspect that edge terminated  are more resistant than center terminated.
rubber protects nothing: U47 users can us give testimonies...for example: a wrinkled diaphragms (despite a flexible mount)... :(
however it is not relevant for me.
a studio mic shouldn't fall, especially with expensive capsules and tubes.
i think that this is mostly the capsule impact on the headbasket, that damage it most of the time.

capsule mount...
like i said before, for me, elastic materials are delicate to use .like rubber.
viscoelastic are more suitable and could be performant materials in this application, but are harder to source.
felt is easy to source, and perform still well today.
after all, there no actual piano or pool table with viscoelastic materials.
for me, elam mount style is efficient and less resonant.
it seems to me a good compromise.

coupling/decoupling...
you didn't understand me because i wasn't clear.
i know the needles principle but i was wondering if we consider that the air transmitted vibrations are paramount, thus we should dissipate to the floor with needles, OR absorb the vibrations with some other damping elements...Or, the contrary and we want some coupling elements against the vibrations from the floor...
for the frequencies, let's say from subsonics to max 500hz...after the energy is negligible...
for me, i'd say mostly from the floor thus decoupling (like ms vienna's pads)...
i'd choose non elastic materials for that  ...
i'd choose the most flexible cable to connect the mic, to avoid vibration transmission through it.
and i'd manage the rest of the directly absorbed vibrations, with the mic internal structure and the shockmount.
i'd use the heaviest mic stand.
i'd use felt isolation for the mic shockmount. It must damp but not let move or vibrate...
For the mic, i'd check first the air sealing of the mic body.
then i'd enclose the hiZ parts (u67/87 like) or all the electronics (Elam) for a better vibrations isolation.
with chinese mic body donnors (chunger), i would use an ELAM type (Aputis...) capsule mount, then i would build a sealed and non resonant (3D printed parts with PVC,ABS...) round box placed near the capsule mount, under the top metal plate, and i could include the hiz components inside (point2point),including the tube, and even a mechanical directivity selector if i can...
i'd use viscoelastic decoupling glue to attach it to the body.
but i admit i haven't designed yet such a thing...and i'm not comfortable with sketchup...

sorry to be redundant, but it seems important to me.
i don't want to make things more complicated, but if we focus on one element after another, it could be possible to make choices that, in fine, could be in contradiction between them...



 

maq3396

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Yes... I do have several 3D printers. Both of the FDM and SLA variety.

I am also proficient at SolidWorks CAD design.

Therefore prototypes can be turned out quickly!

Cheers
Mac
 

Murdock

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very interesting discussion! even though I don't understand everything  ::)
I'm in the planing stages of a C12 type (Siemens SM204) build and will also build the body mostly myself. I noticed that in the original, that the body tube is only hold in place at the bottom with 3 Allen screws, right? So to not rattle or anything at the other end of the mic it has to be build with very tight tolerances so that there is no room for the body tube to "shake". I hope you understand what I'm trying to say :p
I never held a real C12 in my hands, so can somebody tell me How tight it is? Or is there something I'm not seeing on the pictures?
I'm thinking about leaving some space between mic rails and the body tube and applying some kind of dampening material so that the metal parts don't really touch each other.
What do you guys think?
 

MS Vienna

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It is a pretty precise fit - no rattle possible.
Materials are straight forward, just regular off the shelf brass tubes. 40x1mm for the frame, 42x1mm for the shell.
Note that thin brass tubes rarely are perfectly round as they come. You might need to correct slightly oval cross-section by applying pressure. If it still doesn´t fit sand the diameter of the inner tube slightly smaller. Turning it smaller on the lathe is not ideal since this brass alloy (Ms63) is not well suited for this type of machining and will give a fairly rough finish.
Don´t take off too much.  Sliding the tube over the frame should need some very gentle force.  It should not be loose.

 

Murdock

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Wow, wanted to ask you about some measurements anyway, so thanks alot for the extra info! Wasn't quite sure about the thickness of the shell. That's good to know. Luckily the C12 is mechanicly not really complicated.
Don't want to hijack the thread, but could you maybe tell me one last measurement, the length of the frame? Without the top and bottom base.
::)
 

KrIVIUM2323

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Hi,

i think we shouldn't focus, and get lost in very technical considerations, on the mechanical structure of the body without a global thinking.

Ok i haven't been clear enough on the strategy i think we should apply about vibration management:

_for the microphone body:
_ we should try to make the whole thing the most inert possible. This mean damp everything that is possible: the body tube, the end bell, the rail, the headbasket plate and the headbasket.  This mean seal the body tube the most that is possible too.

The most important thing to do imho is body tube related. This is the most exposed part to both aerial and solid vibration transmission. Aerial by exposure to SPL, solid because in most of the case this is where coupling occurs to shockmount.
As the endbell cap and the rail system couple to the body tube i think they should be damped too.
The Headbasket is more an issue because mechanical/electrical constraint may render impossible to have them damped too. We should try to damp the grill too.
The headbasket plate/capsule holder plate should be damped too.

_we should try to isolate the electronic and capsule from the solid vibration transmission too. I do think this is as important as damping the whole body.

Once this is done we should focus on airborn vibration and how to deal with it. But i suppose once the solid vibration transmission has been treated not many things will still be in needs except for capsule.
  But as i already said i don't know how you could manage that for the capsule/holder.

I think  your approach to have electronic parts 'encapsulated' is the way to go. Maybe not all parts?
I don't know if issues with heat could arise?

Anyway if all the parts are encapsulated AND decoupled from body vibration this is conditions close to the box into the box principle used in acoustic for isophony. But we'll have to find a material/ way  to decouple at low resonnant frequency  for this to be effective.   

I don't know for whole electronics parts but the high Z parts this is sure would benefit from this treatment. This could help on more front than only vibration isolation and could make the build have consistent reliable operation for long time by protecting components from dust, etc, etc...

About materials to damp, i think sorbothane could well be all that is needed to damp the body parts. It is widely availlable, exist in different thickness and sheets, some are already glued on one face, this is a viscoelastic material, it is easy to cut using a knife... not messy like glue or coating to apply.

Some dedicated viscoelatsic coatings exist too like these one:

http://www.kineticsnoise.com/industrial/kdc.html

https://www.google.fr/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&ved=0ahUKEwjA2K6siOnXAhXIPxoKHWB4AeoQFghBMAM&url=https%3A%2F%2Fwww.pyroteknc.com%2Fdmsdocument%2F94%2FDECIDAMP-SP150-TDS-113IP.pdf&usg=AOvVaw3k78JJQmsBe25J6lExFJmM

But this is usually dedicated to boat/marine industry  or cars modders so this is usually not easy to source in small package and must be sprayed over the parts you want to treat (for most efficiency). Not so easy to use than sorbothane. But this is effective.

https://youtu.be/X-szLg-WG_8

I'm still looking for a possible solution/material like that for dampening of rail and endbell cap.

About the source of vibration: i do think we are dealing with something like 90% solid transmission 10% aerial. The frequency in question range from subaudio to audiorange ( let's say 5hz to something like 5khz) for structural born vibration (solid) and more something in  the range 50hz to 10khz for aerial.
The lower the most energy we must deal with, so the more issue to treat.
Typical isophony situation i would say.

Coupling, decoupling... Well, this will depend of what you want to achieve...

I don't fully agree with your view of 'transmitting' vibration to others parts which will damp things because 'mechanical diode' materials doesn't exist to my knowledge, and vibration doesn't have a direction path: either a part (or an assembly of part) vibrate and damp at a defined frequency either it vibrate and damp at an other one frequency... You can not escape law of physics.

The use of spring/load isolator is neither a yes or no situation, the use of it is more: is it dedicated to the situation or not?
What do you try to damp and why? Is the system designed to fullfill requirements?

So here is an article which deal with sping/load isolators and there design:

http://www.kineticsnoise.com/industrial/pdf/shock.pdf

This is for industrial purpose but it is clear, well explained and give very interesting graph of spring/load behavior and what to expect from possible solution.


Back to the global thinking:
so for the mic stand i think we should have a stable point of reference (coupled) then decoupling (the lower the frequency resonnance the better and if possible in the X,Y,Z axis), then a very stiff (but damped) system which hold the mic (tube and mic shockmount).
In fact something like a good quality mic stand mounted on an effective decoupling system.
Like MSVienna system. But i would prefer with defined and constrainened axys deplacement (X,Y,Z) and known resonant frequency of the decoupling process (i would like it to be around 1hz or lower).   
 

granger.frederic

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Hello KrIVIUM,

I began some tests with a sensor piezzo of fortune and several points of measurement: capsule, body,  microphone stand, etc…
I must find a smaller and light sensor to review other measurement.
I seek…
and the results are very astonishing in front of an amplifier guitar and bass amp…
I must improve my measurements (and to check them on several microphones) but it seems that the direct vibrations are more important than envisaged, which I had suspected intuitively… and until frequencies a little higher than envisaged…
for me, in my concept, the capsule must be fixed and is used as mechanical point of reference in space, if it is wanted that the transitory answer is the best possible one…
After all the music is primarily made up of transients…
the least movement within the space of the capsule will degrade its answer in impulse mode, with these very high impedances.


The only part moving must be the diaphragm.


it must thus be mounted “rigid” and the vibration boxed by this one must be transmitted (transmission of the vibrations in solid systems…) towards a system of viscoelastic evacuation/damping, but with a very low resonance frequency  until strong modes.
your system seems promising… to test …
the sorbothan seems to me too elastic for the use.
it would be necessary to find a paste, an adhesive or a viscoelastic gel not too flexible but effective with fine thicknesses.
not easy…
the surface of contact between the support and the capsule must be maximum as a result, for a maximum of transmission. By example, a ring metal, without internal damping, tight with the backplate.
in the event of fall the capsule will resist even better, because I think that the movement is worse…
one will be able to also envisage a hollow capsule tube mount to make pass the wires of the capsule, and include viscoelastic material in his center (without contact with the walls). That will limit the transmission direct by these wires and will decrease the exposed length.
the body vibrates too.
I haven't the same opinion that Msvienna, the body should be rather thick and heavy , and/or receive a damping coating…
it is also necessary, as we suspected it, to uncouple all internal electronics, including the output transformer .
the encapsulation avoids wet pollution but allows also a sound insulation (elam), a little like a double glazing…
the tube does not heat enough not to consider that.
here is my opinion on some points…

cheers
Fred
 

KrIVIUM2323

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Hi,

Murdock:

I'm thinking about leaving some space between mic rails and the body tube and applying some kind of dampening material so that the metal parts don't really touch each other.
What do you guys think?

I think this is wise.
As you are building the body from scratch you'll have more freedom if you want to damp things than doing it for something already done.

One thing about damping, it should not be more than approximately 30% of weight of existing part, once you go over this there is diminishing return and could in some case be worst.

I've digged in my HDD and found more info about all this, i will post some documents and links in the next coming days. There is some interesting infos.


Fred,
I began some tests with a sensor piezzo of fortune and several points of measurement: capsule, body,  microphone stand, etc…

but it seems that the direct vibrations are more important than envisaged, which I had suspected intuitively… and until frequencies a little higher than envisaged…

I've done some too. But different from yours: i suspended parts of an Equinox47 body (rails, plate, headbasket, body tube and end bell) and i hit them with a screwdriver and recorded the results.

This is not astounding that each part does ring! For me they obviously need damping.
I won't give any of my result for the moment, this was done very roughly and most results are not really usable like this ( my test rig was really questionable. :D ).

I don't have made the test with sub assemblies (eg end bell+ rail+ plate, bodytube+rail+headbasket, the whole assembled thing,etc,etc,...) but this is on the list.

All in all i would say than once all this things will be dampened, we may be in right direction... or not! Maybe it could change the whole behavior and induce some other issues.  Only real test could tell i think.

I bet you've found some ringing in the 1K/3k range within your own test?
In my (very non professional) test this is where some metal parts ringed the most...



for me, in my concept, the capsule must be fixed and is used as mechanical point of reference in space, if it is wanted that the transitory answer is the best possible one…

After all the music is primarily made up of transients…

I agree, but in practice this may be very difficult to achieve using passive way (capsule as a reference point). We may approach that however. Or take it as a theorical ideal condition.



the sorbothan seems to me too elastic for the use.

Well, it depends of many factors... What you want to use it (damping OR isolating), the hardness shore (it exist in diferent kinds),etc,etc... and you must remember this is a non newtonian material: it's own nature does evolve in time depending on pressure applied and how it is applied. 
I'll post a document and video link about that latter.

the surface of contact between the support and the capsule must be maximum as a result, for a maximum of transmission. By example, a ring metal, without internal damping, tight with the backplate.
in the event of fall the capsule will resist even better, because I think that the movement is worse…
one will be able to also envisage a hollow capsule tube mount to make pass the wires of the capsule, and include viscoelastic material in his center (without contact with the walls). That will limit the transmission direct by these wires and will decrease the exposed length.

Wow.. nice ideas, not so easy to implement! We will have to think about all that... ;)

the body vibrates too.

HELL YES! From my test this is the part (body tube) which have the longer decay of all, second being the endbell...  About the body tube this may be shape related too. I was surprised from my prelimary test (eq47 tube body is made of aluminium and i didn't expected it to ring this much i have to admit).


I haven't the same opinion that Msvienna, the body should be rather thick and heavy , and/or receive a damping coating…

It may well be situation dependent. Like i already stated, an heavier one maybe resonate lower in frequency and be in need of much more damping than a lighter one... And it is possible than once fully assembled (body+electronics) things be more difficult to predict or impredictable...


it is also necessary, as we suspected it, to uncouple all internal electronics, including the output transformer .

Yes definitely and especially for tube electronics. There is lot of small mechanical parts more or less allowed to move in a tube... microphony!
I agree about the transformer as well. Some of them do have treatment (varnish) to keep cois from moving under electrical stress, mechanical stress should have an effect too but probably smaller... anyway as we are going in a direction we should take that into account too.

the tube does not heat enough not to consider that.

In which circuit with which tube? And with what kind of material for the housing? All this should be taken into account... But yes the more i think about it the more i would like to have everything encapsulated AND decoupled. This isn't going to be easy i think though...

More latter...
 

granger.frederic

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we are  mostly on the same wavelength. :)
we should try to make sketches/drawings
pen and paper for me... :(
 

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