Feeler K50 capsule For M50 Mic

[mics]

Hi All.

Well we are getting close now! 

Over the coming days/week, I will be testing substrates for the diaphragm. 

Pictured is Platinum, i will also be testing Gold, Aluminium and an amalgum of these in various combinations.

 

[GeorgeToledo]

After noticing this thread, I thought I would add this comment from Neumann about the early PVC M50 capsule.

Seems like a very interesting project, hopefully successful!

 

[mics]

After noticing this thread, I thought I would add this comment from Neumann about the early PVC M50 capsule.

Seems like a very interesting project, hopefully successful!

Hi George, thanks for your post re the early k50.  Martin is certainly correct regarding the first version of the k50.  Interestingly, there was actually more differences than merely the diaphragm here is a basic list.

1/ diaphragm was pvc and glued like the m7
2/ backplate was mechanically very different
3/diaphragm support mechanism was bakerlite.

I have decided to make the second version of the k50 also known as the K53.  Originally this version had an Aluminium diaphragm.  This diaphragm when working well sounds beautiful but is also plagued with problems as it has no insulator from the backplate. 

The mechanical preparation for this capsule is now complete  and now we will be testing different substrates as well as metals.  Ideally I would love to settle with a metal diaphragm that has a half to one micron insulator as this will be a best of both worlds scenario.

On another note, don’t you just hate it when you miss a hole!!!! Lol. 

 

[rmburrow]

Ben..
Have you tried nickel (1 micron or less)?  Aluminum doesn't seem to hold tension long term.  I have some old Capps CM2250 mics I use as a "test bed" and nickel seems to work the best.  The nickel can be tensioned (carefully) to 0.5 kg or so before clamping and seems to hold.  (BTW the tension in the Capps mic is predetermined since the backplate is spring loaded, but nickel works very well...)

 

[Recording Engineer]

Oh my goodness! So crazily excited! Glad I saved my pair of Beesneez 49 bodies for these! Ben, it could be great if you could compare your BV11-type to a toroidal for this! I’m also extremely curious of  any difference of using the M50 circuit vs the KM53 circuit.

 

[mics]

Ben..
Have you tried nickel (1 micron or less)?  Aluminum doesn't seem to hold tension long term.  I have some old Capps CM2250 mics I use as a "test bed" and nickel seems to work the best.  The nickel can be tensioned (carefully) to 0.5 kg or so before clamping and seems to hold.  (BTW the tension in the Capps mic is predetermined since the backplate is spring loaded, but nickel works very well...)

I have actually tried nickel and to me, it is just a little stiff.  Even a less than 1 micron it is quite stiff and brittle to work with. 

I do love platinum and gold mixed as a metal as it has excellent oxidisation resistance and not too brittle.  I think i will though use an insulator (probably 1/2 micron) as it will prevent so many issues down the track.

Growing metal on glass to mount is relatively easy, even easier when using a substrate insulator so I’ll keep you all posted!

 

[Delta Sigma]

Oh my goodness! So crazily excited!...

Read your M50 comments recently; I was wondering when you'd see this!

 

[mics]

I thought i’d share this with you all here.

This picture gives you an idea of really how small the backplate for the M50 is.

This type of intricate small work is a really enjoyable  challenge.

I can see why the M50 is so loved.  It sounds beautiful.

 

[bremusound]

Looks promising!

 

[bremusound]

I thought i’d share this with you all here.

This picture gives you an idea of really how small the backplate for the M50 is.

This type of intricate small work is a really enjoyable  challenge.

I can see why the M50 is so loved.  It sounds beautiful.

Which membrane materials have you been testing ?

 

[mics]

Which membrane materials have you been testing ?

Platinum, Titanium and Aluminium.

Sonic differences are very small between the different metals..  Tuning and pocket depth  are the primary focus when tuning a capsule of this type.

 

[Recording Engineer]

I’m curious what pocket depth is?

My understanding is the ridiculously tiny gap between the diaphragm and backplate and tighter-than-usual diaphragm tension, as to not slap the backplate, is what makes the biggest difference with these types of capsules. I’m curious if that ends up being your experience or not, Ben.

 

[GeorgeToledo]

If you change the distance of the gap, the capacitance ends up changing too, and the frequency response as well.  With a different air mass inside, the damping factor against the diaphragm would change too...maybe that could effect transient response at some level, maybe basically imperceptible with moderate changes?

I have noticed that there are a decent amount of sdc capsules that don’t have nearly as good off axis response as Neumann SDCs generally do, which I am thinking is probably more about the backplate design?

Curious about Ben’s perspective!

—

That is a very interesting fact earlier in the thread that the Capps mic had a spring loaded backplate!

 

[shabtek]

interested

 

[rmburrow]

If you change the distance of the gap, the capacitance ends up changing too, and the frequency response as well.  With a different air mass inside, the damping factor against the diaphragm would change too...maybe that could effect transient response at some level, maybe basically imperceptible with moderate changes?

I have noticed that there are a decent amount of sdc capsules that don’t have nearly as good off axis response as Neumann SDCs generally do, which I am thinking is probably more about the backplate design?

Curious about Ben’s perspective!

—

That is a very interesting fact earlier in the thread that the Capps mic had a spring loaded backplate!

George, there is a lot of physics behind any microphone; the condenser mic is often most studied.  Think about the microphone membrane when impacted with sound; the membrane movement is measured in angstrom units.  The spacing between the back plate and the membrane may be 0.1 mm or less.  Obviously, the spacing between back plate and membrane limits the polarizing voltage.  The thickness of the membrane can affect the transient response of the microphone.  I suggest looking up the chapter on the condenser microphone in Dr. Philip Morse's text "Vibration and Sound".  The mathematics is explained there.  The tension of the membrane directly affects the HF response of the mic.  The hole pattern in the back plate affects the membrane damping.

The old Capps CM2250 mic used a 6AK4 or a 5703 subminiature triode..the capsule was polarized through a 100 meg resistor from B plus, and the cathode was elevated above ground for self bias.  A UTC type O-8 was used for the output transformer.  The back plate was spring loaded to get the membrane tension.  That mic sounds good with 0.7 micron nickel membrane...nickel seems to hold tension better than aluminum...

 

[GeorgeToledo]

rm - yes, I own it and have read it !

What I was getting at, is that the diaphragm has to push against the air mass inside. So, changing the gap, though not the same as changing diaphragm thickness, changes the relation between the internal air pressure and the mass of the diaphragm.

I am curious what air pressure release works like in an M50 capsule...is there a little vent hole somewhere?

 

[mics]

rm - yes, I own it and have read it !

What I was getting at, is that the diaphragm has to push against the air mass inside. So, changing the gap, though not the same as changing diaphragm thickness, changes the relation between the internal air pressure and the mass of the diaphragm.

I am curious what air pressure release works like in an M50 capsule...is there a little vent hole somewhere?

Hi George, hi to all you guys too!

Last things first; the pressure release in an omni is not specifically planned but does happen.  It would be very difficult to completely seal a sdc.  Think of it this way; each screw thread has play so pressure would fluctuate there, the rear electrode screw would also naturally allow for pressure change. 

What is the pocket?  It is actually the air gap behind the drilled surface of the backplate.  This pocket gently controls overall frequency response.  There are of course other factors that make huge changes ie; diaphragm tension and capacitance spacing but these two are either nice or just plain nasty!  So once you get this right, the magic happens in the pocket!

Here is a picture of the parts needed to make a single m50 (k53-M50) capsule.

 

[benqbasic]

I thought i’d share this with you all here.

This picture gives you an idea of really how small the backplate for the M50 is.

This type of intricate small work is a really enjoyable  challenge.

I can see why the M50 is so loved.  It sounds beautiful.

That small intricate work sounds like my nightmare.  ;D

 

[mics]

Hi All.

These are ready to go if there is any interest.  They sound amazing and the capsule really stable.  We have 3 on a tree in a sound stage doing famously as well as a few kicking around the factory being tested each day.

We also have a neat little circuit board that s a pick design for the m49 oem bodies.  It has two circuits on the same board, one for transformer balanced the other for transformerless.  If that is interesting for you we can make arrangements there also.

Let me know.

 

[Phrazemaster]

Hi All.

These are ready to go if there is any interest.  They sound amazing and the capsule really stable.  We have 3 on a tree in a sound stage doing famously as well as a few kicking around the factory being tested each day.

We also have a neat little circuit board that s a pick design for the m49 oem bodies.  It has two circuits on the same board, one for transformer balanced the other for transformerless.  If that is interesting for you we can make arrangements there also.

Let me know.

Looks really great Ben! Sorry if I missed it, but how much for the capsule? And are you still making the M49/50 bodies? Will there be a kit since you mentioned a circuit board?

Thx,

Mike