attenuators for dynamic mics

  • Thread starter Thread starter rob aylestone
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rob aylestone

rob aylestone

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In my quest for usable Chinese products I've found some radio mics - handhelds with dynamic capsules, that actually sound quite nice and RF wise on the test gear seem pretty decent. For those kinds of scary projects, like the ones near water where you know some idiot will drop one in, or those where you know somebody will slam one into the stage floor doing a Freddy Mercury - I don't want to use my expensive sennheisers, so the ones I'm looking at will be ideal. However, they don't have an attenuator built in - -10 or -20dB is pretty vital when going from a person speaking to a singer bellowing away. They do have screw on capsules, so I was thinking maybe I could knock up a resistor pad and hide it in the capsule. Then I could always swap out a capsule (assuming I can get a few spares) to cope with the singers. A few resistors isn't too big a thing to conceal inside? Any comments? Have any of you every put a pad between mic and a pre-amp section like this?
 
I would think for a dynamic mic, an inline attenuator would be just about the same as using the pad in a mixer. You don't have an amplifier inside the mic to overload. You're talking about 3 resistors since you don't need to worry about phantom power. You can buy them already encased with male and female connectors for less than it costs to buy the connectors themselves.

If you can fit a switch to the mic, it should be a simple deal. Dave can probably give you the exact resistor values.
 
Dave bloody can't give you the exact resistor values because the decibabbles depend on the source impedance (not accurately known) and the load resistance of the pre, an equally imprecise beast!

But yes, buy inline XLR 'slugs' but caveat bloody emptor! I bought a cheap 20dB attenuator a few years ago and it was NOT balanced! Could have caused all sorts of hum issues.

N.B. If inserting attenuation between a capacitor mic capsule and the impedance converter you need to use a CAPACITOR network, not resistors or you will eff up the response mightily.

Dave.
 
I think a simple Lpad will work and if the values are a bit adrift, then my 10dB might be 6 or 15? Might not matter as if it works it works. I'd just put it in a bit of heatshrink and hide it inside. It's just that overdriving the wireless mics preamp sounds rotten but so does adding gain at the far end if I add too much. The capsules screw on, so if I can remove the transmitter wipe plate, I might just be able to add the components on the reverse side.
 
OK, best to keep things balanced so, back of envelope? Assuming a mic Z of 150R a 560R in each 'leg' followed by a 1k shunt gives 9.85dB of loss. Call it 10dB for jazz? That also assumes a mic pre Zin of 1.5k

Dave.
 
Dave - that's good enough for me - thanks. I'll try dismantling it and seeing how easy it is?
 
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