Mechanical improvement of mic build.

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KrIVIUM2323

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Hi,

following message in  this thread:

https://groupdiy.com/index.php?topic=67343.40

it is worth to have one dedicated entirely to the subject of microphone body and mechanical issues and possible answer.
There is now a lot of knowledge about electronic design, choice of components, acoustical properties of headbasket, capsule, etc,etc, but not many things about body and related issues.

With the offer of medium priced chinese body we have really nice looking body to house our circuit and this is really nice.

But there is differences to the classic mic we try to clone most of the time.

Thanks to internet this is easy to spot and it is interesting to take a look at classic mic to see how things was done in the 'glorious old days'.  ;D

Let's start with the grandfather of classic German mic, U47:

http://www.jogis-roehrenbude.de/Roehren-Geschichtliches/Neumann-Mikro/U47/U47.htm

Then, the Elam 251:

https://scontent-sea1-1.cdninstagram.com/t51.2885-15/s480x480/e35/14515633_357879077935382_2219332665541132288_n.jpg?ig_cache_key=MTM1MzYwMDY1MDk0ODQxMzMzMQ%3D%3D.2

http://www.coutant.org/akgc12/251-3.jpg

http://www.saturn-sound.com/images%20-%20microphones/telefunken%20elam%20251%20microphone%20-%20inside.jpg

http://www.klemm-music.de/telefunken/ela_m_251e_stereo/photo/ela-m251-stereo05.jpg

http://www.klemm-music.de/telefunken/ela_m_251e_stereo/photo/ela-m251-stereo12.jpg

Then Neumann m367 (special version of m269c with u67 headbasket build for ORTF):

http://www.infernalemachine.com/DATAPANIK/Neumann_M367_SN8324_0.jpg

http://www.infernalemachine.com/DATAPANIK/Neumann_M367_SN8324_8.jpg

https://medias.audiofanzine.com/images/normal/neumann-m-367-479503.jpg

Ok i think this is ok for now...

So what do they have in common from a mechanical/architectural point of view?

_First thing which strike me is that All this classic mic have a complete headbasket which is "closed" and don't have holes or other entry to the body tube.

_the u47 and the Elam are point to point using turret board and acrylic/perspex to mount components. The m367 too but it use pcb too.

_All tubes are 'decoupled' from mechanical structure: using rubber mount and elastic in u47, rubber mount for Elam and using 'coiled' wire for the m367.

Well... not what we have in most of our build using chinese body and pcb...






 

KrIVIUM2323

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This is more or less what Fred stated in the previous thread:

the critical elements (for vibrations) are (no order) :
- capsule mounting
- tube mounting and tube
- headbasket and body resonances
- HiZ wirings
- microphonic components (caps, hiZ resistors...)
- shockmount

About capsule mount there is some possible technique to apply:
Take a look at how the capsules wire are done in this most impressive modification of MSVIENNA's Brauner Vm1 and how headbasket acoustical issues are taken care of... just MARVELOUS!

https://groupdiy.com/index.php?topic=63305.20
 

Khron

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You'll want to correct the link to the thread :) Right now the link is for the "Microphones" sub-forum.
 

KrIVIUM2323

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So, why to have a closed/separated headbasket is important? Maybe because if you take a bottle and blow in it you'll have a nice note being produced...

Nasty potential acoustical resonnance you surely don't want to record.

Why to have point to point is important ( you probably already know why it is important from an electrical point of view)?
I do think this is because each component will have it's own self resonnant frequency and not one overall common frequency. This can be easier to damp (capacitor for example can be really microphonic! Using same technique to mount them as ac701k tube in m367 with coiled wire can help).
The turret are mounted on perspex/acrylic board which should help too as they probably have better self damping properties than metal. Could be even better to use PTFE board.

Decoupling of tube is important too: tubes can be (sometimes highly) microphonic and this can help to manage a mildly problematic one or really make wonder for a quiet one improving it even further.

Ok all this is just starting point and ideas dumped to have strting point about discussion.

In the thread which started this one i talked about techniques used in loudspeaker build to damp vibration. I think this is an interesting starting point about the body resonnance too (the body tube).  There is analogy between a loudspeaker and a microphone: both are transducer, and both probably suffer from same issues (more or less and of different amplitude).

 

kingkorg

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Great thread. Since we are there, does anyone know what is this material Shure uses in their mics as pop filter. It is very effective, did winders in one room where i had AC. Stops pops incredibly well, even though i use  pop filter with it. Some people just remove it blindly. By the way construction of KSM44 is amazing. I felt like i was dismantling some king of extraterrestrial capsule.
 

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Khron

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Some sort of really fine-mesh gauze?

kingkorg said:
Great thread. Since we are there, does anyone know what is this material Shure uses in their mics as pop filter. It is very effective, did winders in one room where i had AC. Stops pops incredibly well, even though i use  pop filter with it. Some people just remove it blindly. By the way construction of KSM44 is amazing. I felt like i was dismantling some king of extraterrestrial capsule.
 

granger.frederic

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KrIVIUM2323, thank you for the topic... :)

i have a lot to say, i will try to find some time...

Neumann did make some attempts to reduce the internal resonances, where it's critical : in the high impedance parts...
look at U67 internal picture :  the foam (with time: infamous because of the disintegration) !

they also greatly encapsulated (+/- sealed)  the HiZ microphonic parts.
their famous asymmetrical headbasket was also an (great) success.

But for me, the Elam 251/250 is a piece of art, the most "processed" with all its molded enclosed stuctures , its short HiZ wirings, its efficient capsule holder, and other ingenious designs...

the "side" effect is to protect also from the moisture on long term...

the first thing to check is the air sealing of the body, we don't want sound resonances inside. Most (all?) chinese bodies are awful in the domain... truly leaky sieves!

my opinion is there's room to vastly improve our mic creations, or our clones, by understanding, studying , copying (and maybe improving... ;)) the mechanical designs of classical mics created between the 50's and the 70's  :eek: ...

regards
Fred
 

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ln76d

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Some quotes from peluso topic ;)

granger.frederic said:
the headbascket has less resonnances, the body has less resonnances

Don't agree here - original headbasket of ela m250/251 is pretty resonant - i tested it - don't believe test it with headbasket and without.
C12 headbasket have better mesh, single layer, but diameter is a little bit smaller and when we add to this capsule saddle (which have impact on the resonance inside headbasket) then it isn't truly better than M251.
Body - the pipes of both M251 and C12 are pretty sh*tty (thin brass) but in M251 plexi cage works as a damper pretty good.
In fact both designs makes frequency colorations but this fits nicely original CK12 repsonse.

granger.frederic said:
the metal body is damped with two lateral springs

MS Vienna said:
The actual purpose of these springs is the grounding of the body tube to archieve proper shielding.

Not really. In fact  use of the springs in M251 is much simpler than you think.
It doesn't improve grounding and it doesn't improve dampening (at least it wasn't intention).
It's just to keep removable head in its place and keep whole internal construction in proper position.  When you install pipe it just press and stabilise side bars.

U67 just have improved removable head mounting system so there's no side springs.

 

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granger.frederic

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U67 has side springs (a bit different yes), they're fixing the head also
the original elam headbasket is less resonant than chinese clones i tested, but more than a U47
the C12 has an issue with magnetic fields, the mesh is too opened
lateral springs shouldn't stabilise the head, as the head is already placed when you insert the body
those mysterious springs could :
-transmit ground
-damp the resonances
-stabilise the internal parts
-all that in the same time... 8)
 

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KrIVIUM2323

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U67 just have improved removable head mounting system so there's no side springs.

I second Fred comment, there is spring in u67 as well in u87. There are integral part of the rail system.
About there purpose... well they may serve multiple at once yes.

The comment from MSVienna in the previous thread does make sense and as you can find same thing in other Akg mic it is not there just for fun.  ;)

In fact both designs makes frequency colorations but this fits nicely original CK12 repsonse.

In fact most headbasket induce coloration. The fact that they were probably 'tuned' to capsule response is highly possible. As regularly stated by 'expert' engineer from this area was serious about their work.

Most 'invisible' headbasket i've encountered is this one:

https://www.google.fr/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwilz4r21MXXAhWC0hoKHWWyBtIQjRwIBw&url=https%3A%2F%2Fvintageking.com%2Fjosephson-c725&psig=AOvVaw1o4bbC8lfCoLyh3MVNTY3N&ust=1511009963115396

https://i.ytimg.com/vi/ivelRgQYKbk/maxresdefault.jpg

The whole mic have a stunning 'transparent' yet 'solid' sound. Difficult to say if this is capsule, headbasket or circuit related (or the whole enchilada) but it is really one of the most impressive 'modern'* mic you can find. From Josephson this is not a surprise.

But for us this almost impossible to have access to this kind of headbasket anyway... Aluminium foam is not a cheap material, it is difficult to source and i have difficulties to see how it could be machined easily. Not to mention this is patented by Josephson.

* it coud be argued than it is not this 'modern'.  After all this is a very c37 inspired mic, same kind of capsule, overall shape,low output...
At least this is a very nice 'hommage' and the electronic is very different (jfet cascode transformer coupled versus cathode follower).

he original elam headbasket is less resonant than chinese clones i tested

Which one have you tried Fred? The one from Chunger?

This bring us back to the original subject: how to improve our chinese mic?

First thing is to close all unwanted holes which gave entry to the body in the headbasket.

That could be done using some plastic sheet glued to the plate of the headbasket. I've never done it for now but this will proabbly happen in my next build using Equinox u47 body.

This will bring us closer to the goal to have different cavities for the differents parts of the body (headbasket/body tube). But this will probably not be enough as the tolerance in parts and machining is a little bit loose in chinese mic (compared to 'boutique' jewels like Flea's kit for example).

Maybe a skirt made from some elastomer material could help to improve sealing?

The other obvious improvement will be in decoupling/damping of pcb/mounting plate for internal electronic components.

I've done some experiment about that as i didn't have easy acces to dedicated washers. I've used silicon (the one used for aquarium) to do some pads in hope to dampen ef14 and socket at the time. To make a long story short it proved to have some efficiency but i won't do it again as this a real mess to do the pads and this is not convenient as you have to play a lot with torque of bolts/screw to find sweet spot and i can't say this is consistant in results.

This is really time consuming from my experience...

I've got a company dedicated to elastomer parts for decoupling/vibration management near where i live and i'll probably ask them if they could do something more convenient and with consistant results.  ;)

Meanwhile i played a bit with some PTFE standoff and parts (Yes i'm a bit obsessive about PTFE, i like this material).
The stand off are convenient, but difficult to find in the dimension i was looking for. I had to make some by myself. It is easy (even if the material is so slippery it is sometime frustrating). 

I used some to space pcb from rails. The idea i had about that is that it as so low friction coefficient it should make a 'barrier' in the propagation of vibration and as it is soft material (stiffeness is low) is must have self dampening effect.
I don't have data to back this up but i think it work... 





 

ln76d

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granger.frederic said:
U67 has side springs (a bit different yes), they're fixing the head also
the original elam headbasket is less resonant than chinese clones i tested, but more than a U47
the C12 has an issue with magnetic fields, the mesh is too opened
lateral springs shouldn't stabilise the head, as the head is already placed when you insert the body
those mysterious springs could :
-transmit ground
-damp the resonances
-stabilise the internal parts
-all that in the same time... 8)

In both u67 and m251 springs stabilise connection of the side bars to not jump out from the removable head. In both case the side bars are to keep whole construction in place. Without it you will have only electrical connection pins as mounting system which isn't blocked. Imagine when mic falls or it's mounted upside down and pins connection isn't stable ;)
Note that in m251 side bars are only screwed on the bottom part. Springs are only parts which holds them tighter in the upper part. Otherwise it can jump out easily.
Didn't had the problem with magnetic field in C12 but i've read that some folks had. Maybe problem is elswhere?
I think that the hundreds of records where C12 was used also don't shows any magnetic field problem ;)

For headbaskets coloration - it all depends. U47headbasket have also coloration and note that capsule is mounted in a specific way which also boost a lttle bit some frequencies. 
With chinese headbaskets (as also classic mikes) it all depends.
Most capsules with thinner diaphragms will shows you more coloration (pretty unwanted in most cases), most multippatern cardioids also in comparison to pure cardioid. There's a lot of factors. Not every headbasket fit well every capsule.
Main advantage of U47 headbasket over m251 is diameter - "size does matter after all " :D
It's 5mm wider per side.  Overall 10mm. It's pretty big difference.
From the cheap headbaskets, single layer, MXL 770 is pretty good (still not every capsule). Mesh density is pretty small but diameter works here.

Here's an example pic from AKG M251 (yeap AKG) ;)
 

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granger.frederic

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yes for example : http://store.studio939.com/product/custom-headbasket-for-c12-clone-microphone
it rings a bit too much
i though about placing some fine silicon or rubber rings, tensioned, outside or preferably inside (for aesthetics), to damp it...
 

MS Vienna

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ln76d said:
Note that in m251 side bars are only screwed on the bottom part. Springs are only parts which holds them tighter in the upper part. Otherwise it can jump out easily.

You´re right, I stand corrected. That flimsy construction would not work without the pressure from the springs, so clearly that´s the primary purpose.
Anyway electrical connection is almost as important since the housing is painted with a fairly thick layer, and especially in combination with the painted screw base there would be quite a risk for hum problems. And the bit of extra damping doesn´t hurt.
It´s funny how cheap this thing feels and how well it works.

I attached a picture that shows the thourough paintjob even inside the switch cutout  on an NOS ELA M 250 (not replica) - just for the record.
 

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MS Vienna

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This is a very nice - and necessary - thread!

I have a little present for you. That´s a photo of the original blueprint of the ELA M 250/251 capsule head assembly from early 1959.

Though this pic might raise the desire for more,  please don´t ask. I gave my word not to spread this stuff. Since this one doesn´t contain any measurements I think it should be ok to show. It´s the most beautiful anyway.
 

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KrIVIUM2323

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Kingkorg,
I don t know which kind of material is used by Shure to screen the capsule. As Khron suggested this is very probably some fine mesh synthetic gauze. Synthetic because natural material may damage with time and pollute the headbasket.
Audio Technica use a disk of open cell coarse foam inside the headbasket of my 4033 to protect the capsule from projection. Maybe it act as a pop filter too, i don't know i always use one for vocals anyway (and rarely use the 4033 for vocals).

Fred, i m curious about the way you would damp the c12 clone headbasket: i don t really figure where and how you want to apply the silicon, could you make a sketch or describe it more precisely please (and when you have time alowed;) ).

I think we should give explanation of which kind of vibration/resonnance we try to adress. This is not always obvious (for me anyway).

Until now, what i described was to try dampen/limit structural/architectural born source of resonnance.
Obviously, trying to seal the headbasket/body junction is to deal with acoustical resonnance in the body itself.
About that, i wonder if Neumann didn't tryed to have multiple cells in the u47 structure. When looking at the pictures linked in the first post the plate supporting capacitor is plain which is not mandatory from a pure structural strength point of view. I don t know?

What MSVienna did in his Vm1 mod adress multiple things too: the new capsule support deals with headbasket acoustic issues (relocating capsule higher, geometry of the holder), the braided junction between electronics and capsule's wire deal with structural vibration transmission.

It is to be noted that moding anything located inside the headbasket will induce modication of final sound of mic which may or may not be 'better'. Please refer to Msvienna thread this is selfexplanatory.

The u67 foam ring deal with acoustic of headbasket, not damping.

We didn t talked about wiring inside the body for point to point realisation, but it is to be noted that they can be microphonic too. It had been pointed many times but it is worth repeating it: don t overtight them, having them a bit loose help to damp them (think about guitar strings), material used for sleeve of cable help too (ptfe help). There is some pictures about that in the tlm to m49 conversion page at Tab/Funkenwerk website.

 

granger.frederic

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the U67 foam damps internal acoustic resonances for sure, but also damps the capsule wires and prevent (+/-) their vibrations.
but i don't like that method, because it disintegrate with time and the moisture goes inside...
we should think about better methods...

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...
 
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