Microphone material differences?

[Spencerleehorton]

Hi All,
I wondered what the differences would be with using different metals for mic bodies.
Brass, copper, bronze, aluminium, steel, permalloy.
Disadvantages and advantages, a nice list would be good to make.
Anyone want to pitch in with for instance shielding, ease of cutting, strength, braising, coating, price.
What on paper without worrying about price would be the best material to use?

Regards

Spence.

 

[Matt Nolan]

Not an "expert" opinion, but my opinions:

Copper - a little too soft to build a rugged mic from
Brass - stronger, traditionally used, easily machined
Bronze - more rugged than Brass (generally), slightly less easily machined, generally more expensive and less widely available in convenient sizes

All the above can be left as-is - they will tarnish/patinate but not corrode. Or they can be plated with Nickel or Chrome, or painted, powder coated, enamelled, whatever.

Aluminium - some newer mics using this, using thicker walls, of course, than you would with brass - easily machined only with the right tools and cutting lubricants, but ok to drill, file, etc. Better finished result if anodised at the end (either for hardness and scratch resistance or for colour) - can also be chromed.

Steel - strongest, cheapest, easy enough to work - has issues with corrosion though. You need good finishing like enamelling or a good clean, copper plate, then nickel plate, (then chrome too if you want).
Permalloy - overkill frankly - use only for screening transformers. Beware that after any working that causes stresses, its magnetic properties are severely degraded and it has to be accurately re-annealed. The same would be true of knocks and bangs it might receive if used as an outer casing.

All the metals will screen you from electric fields. Only the steel and permalloy will also screen you from magnetic fields. But that is rarely an issue unless you are right on top of a power transformer or a CRT.

 

[gyraf]

Good rundown of materials.

Want to add; Brass and Bronze solders easily - aluminum and steel not at all. This important for headbasket mounting/fixing.

Jakob E.

 

[hodad]

Not to veer too far off topic, but would conductive epoxy be good for securing a headbasket to a steel (in this case, stainless) mic body? 

 

[kooma]

Good rundown of materials.

Want to add; Brass and Bronze solders easily - aluminum and steel not at all. This important for headbasket mounting/fixing.

Jakob E.

I've been soldering aluminum with "alusol"
apparently it can solder stainles steel etc.
http://www.farnell.com/datasheets/1683972.pdf

but it takes more heat than normal solder.

 

[Matt Nolan]

Good point! I forgot that.

Good rundown of materials.

Want to add; Brass and Bronze solders easily - aluminum and steel not at all. This important for headbasket mounting/fixing.

Jakob E.

 

[Matt Nolan]

Good rundown of materials.

Want to add; Brass and Bronze solders easily - aluminum and steel not at all. This important for headbasket mounting/fixing.

Jakob E.

I've been soldering aluminum with "alusol"
apparently it can solder stainles steel etc.
http://www.farnell.com/datasheets/1683972.pdf

but it takes more heat than normal solder.

Yes, I've used this for structural purposes before, but not for electrical. No electrical reason why it won't work though. The high heat can soften certain aluminium alloys which may or may not be a problem. If used to join Alu and brass or bronze, the high heat will soften the latter two also. Possibly not enough to cause problems unless it is something thin - ha - like a headbasket frame...

 

[ln76d]

Not to veer too far off topic, but would conductive epoxy be good for securing a headbasket to a steel (in this case, stainless) mic body?

I had problem with conduction using conductive epoxy  (three different) i had to solder it anyway. Epoxy is ok for support but not conduction. In my case i was changing "grills" in lollipop style head of donor for my new G7.
BTW. i used steel pipe for that mike - 2mm thick - microphone weight is 1,1kg
Try to find cheap shockmount for it

 

[MicDaddy]

There is an adhesive that we used at EV for gluing in the mesh to the bodies. I cannot for the life of me remember what it was called but it was a grey paste.

I believe it was possible a 3M product,.

Perhaps metal filled, it looked almost like solder paste, but it was not.

It had to bake to cure.

I will try to dig around and see if I can recall what it was.

 

[Matador]

It almost sounds like JB Weld epoxy putty, which can be heat-cured.

 

[Spencerleehorton]

This is all great info, thanks guys, I've been using copper mostly for bodies and headbasket structure, brass for mesh, all braises well.
Someone brought round a fairly big sheet of brass which I will work into something in the summer.
Up the road is a company which makes some really decent bronze pipes, two of my M49 are made from bronze, great finish and really solid, but really heavy!!!!
I'm definitely going to look into some of these other ideas.

Regards

Spence.

 

[john12ax7]

Interesting topic. Most of the responses seem to be electrical and mechanical. But what about acoustics? I would imagine there would be some effect, although it might be swamped by other factors.

 

[abbey road d enfer]

Interesting topic. Most of the responses seem to be electrical and mechanical. But what about acoustics? I would imagine there would be some effect, although it might be swamped by other factors.

You want the body to be dead as can be acoustically; however, many mic builders use brass, which is one of the most resonant metals, because it is easy to mill and drill, so they make sure the construction and filling will damp the resonances (typically a combination of putty and foam).
Ease of machining is definitely the most important parameter. There are some alternatives; injection-moulded plastic is becoming more and more accepted, even for high-quality mics, wood has been used with success (the only reason being esthetic), and plumbing steel tube is favored by some DIYers for its cheapness and not requiring a lathe.

 

[ln76d]

Definately thicker pipe is always better. My 2mm steel is quite acoustically dead.
Other thing is that mostly am using textolit and teflon boards inside tube microphones and these (especially textolit) have really good damping properties. For chinese condensers am using for damping silicone paste - it works very well. Sometimes technical foam to fill empty spaces on the main construction with pcb.

 

[zephyrmic]

With the mics I  have built, I have found bonded acetate fibre that is used in pillows, in speaker enclosures, or around heating ducts, works very well to deaden any ringing in the mic bodies. I just keep it away from any sensitive areas, such as the very high impedance front ends of circuits, etc. Just a piece either side of the circuit board/s contacting the inside of the tube is all that is needed. Doesn't need to be tightly stuffed in.

Kindest regards,

zephyrmic