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SM81 tweak Recorders, Players & Tape Machines
Old 20th May 2016
  #1
Lives for gear
SM81 tweak

I know quite a few Remotesters use the Shure SM81, but might not be aware that top end can be improved by removal of a capsule windscreen plate ?
It's a reversible physical mod, but the risk is all yours....

- Modifying the Shure SM81 : Recording Magazine -

It's a Scott Dorsey procedure, and he's no hack..he also contributed to one for modifying the impedance of the Shure SM57 for better preamp matching:

- Shure SM57 Impedance Modification : Recording Magazine -
Old 20th May 2016
  #2
RPC
Gear Addict
 

Scott's modification is not usually reversible - the guard usually comes out in several pieces. I haven't tried it myself, but it sounds intriguing. I have modified the electronics, giving 6dB less noise, reduced distortion, and 1dB more level, albeit at the cost of the bass rolloff filter. As Scott points out in his article, the SM81 electronics have been through several iterations; my mod only works on the first two.
Old 25th February 2018
  #3
RPC
Gear Addict
 

Update (for both of you who care): in looking at the AES paper Shure published when they released the SM81, it appeared that the grille and slotted disk were both attached to the front of the capsule. Sure enough, you can VERY carefully pry off the grille and the slotted disk, then glue the grille back in place. Note that it's critically important that the grille make electrical contact with the capsule body or the hum will be tremendous. (I used conductive epoxy.)
Attached Thumbnails
SM81 tweak-r104.jpg  
Old 25th February 2018
  #4
Hi studer, RPC,

Thanks for bringing this to our attention -- sounds interesting but the link posted back in 2016 appears now to be broken. I'd be curious to hear a little more about what is meant by "improving" the top end -- not out of any skepticism, but simply based on the fact that the mic's frequency response is specified as being rather flat. Does the mod result in something "smoother" or otherwise desirable while being (as so often) difficult to precisely quantify?

Cheers,
Luke
Attached Files
Old 25th February 2018
  #5
Lives for gear
If you can't purchase the back issue from 'Recording' magazine, do a Google search for Scott and contact him directly...I'm sure he'll be helpful. He also hangs out on rec.audio.pro newsgroup
Old 25th February 2018
  #6
OK, good to know -- thanks!
Old 25th February 2018
  #7
RPC
Gear Addict
 

Here's a perhaps somewhat more honest frequency response from Shure's European Web site. I just kludged a test rig together; so far as I can tell the slotted disk causes a broad mild resonance (about 2dB) from 8-16kHz. I'm not going to say whether removing this makes the microphone more "accurate" - you could argue it either way. I've yet to listen to them on anything but my voice; once I get them pointed at some real sounds I'll post the results.
Attached Thumbnails
SM81 tweak-frequency-response_sm81.gif  
Old 2nd June 2018
  #8
RPC
Gear Addict
 

As promised, some audio from the modified SM81s. This is a youth orchestra in a lecture hall, ORTF into a Mixpre-6.

EDIT: I can't see the attachment, so go over to https://www.dropbox.com/s/qwt7i1bl81...1PLUS.wav?dl=0.
Old 2 weeks ago
  #9
RPC
Gear Addict
 

And here (finally) is a direct comparison of the straight versus modded SM81. This is an ORTF pair, same hall as previous, but a different band. The two pairs were on the same stand within 3 inches or so of each other, so i think this is a fair comparison.

EDIT: Apparently even these snippets are too big to attach, so you can get them from

Dropbox - SM81M.wav

and

Dropbox - SM81P.wav.
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