Shure SM-81 modification

[ofajen]

A few days ago, I received a pair of modded Shure SM-81s that I bought from Scott Dorsey. I bought them mainly to use with my SM-80 omni capsules, but the modded SM-81 capsules sound excellent, too. The issue of Recording magazine that is just now hitting the streets has his article on this mod.

In brief, the SM-81 uses a slotted disc in front of the diaphragm that creates a very small, resonant chamber that helps make the frequency plot flat up to 20KHz. However, that resonant chamber inevitably results in inferior transient response. Removing the slotted disc improves the transient response, while high frequency response is still a respectable -3dB at 18 KHz. I find the modded capsule to have a very natural sound, more so than the unmodded capsule (which certainly has its uses). I tend not to like "crispy" so much, so this mod suits me quite nicely.

Cheers,

Otto

 

[Gamelan]

I'd like to try this on my SM81's, but how does one go about opening up the capsule?

 

[tdukex]

From the post above:

The issue of Recording magazine that is just now hitting the streets has his article on this mod.

 

[ofajen]

I'd like to try this on my SM81's, but how does one go about opening up the capsule?

Please bear in mind a few things:

1) While little used and essentially like new, the SM-81s I bought from Scott are about 25 years old and obviously no longer under a manufacturer's warranty. He actually did the mod on these mikes 20 years ago and sent them to David Josephson for response testing, since he didn't have the gear for that back then.

2) Modifying your own mike would almost certainly violate any warranty you might still have in effect.

3) Scott has written an article detailing how the mod is done and it is in the issue of Recording magazine that is just hitting the streets.

4) I asked him and he suggests that while it's not hard to do, you would be well served by reading the article first.

5) He's waiting for an angry letter from Shure to arrive any minute!

Cheers,

Otto

 

[mshilarious]

It will be interesting to see the article. While not precisely the same thing, what is a 20kHz signal but a very fast transient? I suspect this mod will make the mic different, but everything's a tradeoff. As an example, with the SM57 mod, it might sound better sans transformer, but a transformerless dynamic will distort badly in the presence of phantom power. That might not matter to many modders, but I didn't see it mentioned in too many of the threads about it.

Why not sell the mic and buy something more suited to what you want? I'm all for modding cheap mics, but an SM81 isn't exactly cheap, and for a similar price there are alternatives . . . this mod, unless it catches on big time, could greatly reduce the resale value. Is it reversible?

 

[ofajen]

It will be interesting to see the article. While not precisely the same thing, what is a 20kHz signal but a very fast transient? I suspect this mod will make the mic different, but everything's a tradeoff. As an example, with the SM57 mod, it might sound better sans transformer, but a transformerless dynamic will distort badly in the presence of phantom power. That might not matter to many modders, but I didn't see it mentioned in too many of the threads about it.

Why not sell the mic and buy something more suited to what you want? I'm all for modding cheap mics, but an SM81 isn't exactly cheap, and for a similar price there are alternatives . . . this mod, unless it catches on big time, could greatly reduce the resale value. Is it reversible?

1) I'm sure you understand that there is a difference between the steady state response to a single tone versus the dynamic impulse response and the inevitable physical result of resonance resulting in ringing. Just because two mikes have the same steady state response does not mean they have the same impulse response.

2) I guess you missed the part about how I really bought the SM-81s for their bodies to use with my SM-80 omni capsules. So they would have been suited to my purpose even if the capsules were broken. The fact that I will also use the modded SM-81s is just a bonus score.

3) The modded SM-81 capsule is more in line with my sonic tastes than the original.

4) The mod is reversible, you simply remove a slotted disc that fits in front of the diaphragm.

5) Resale value is a non-issue for me. I will never sell the SM-80s so I will never sell the SM-81 bodies. I have no plan to ever sell the SM-81 capsules, either, and they wouldn't fetch much anyway, modded or unmodded.

6) Scott will be glad to buy them back at the same price anytime I decide I don't want them. He has better, but can use them as backup mikes or when recording multiple events.

Cheers,

Otto

 

[mshilarious]

1) I'm sure you understand that there is a difference between the steady state response to a single tone versus the dynamic impulse response and the inevitable physical result of resonance resulting in ringing. Just because two mikes have the same steady state response does not mean they have the same impulse response.

Yes, that's why I said "not precisely". However there is generally a correlation between the two features, in terms of capsule characteristics. The introduction of grids, mesh, plates, etc. in front of a diaphragm alter that somewhat. So I don't presume that the Shure engineers didn't realize this as well, after all, they had to add the component in the first place.

As for the rest of your comments, I am talking to everyone else reading this thread as well as the respondents. Lurkers generally outnumber posters by at least 10 to 1.

Anyway, I sold my SM81s last year because I bought KSM141s. Really, the SM81 is a thirty year old design, and I think the Shure engineers did a substantial improvement in the KSM series. And you don't even need to hunt down omni capsules

 

[ofajen]

Really, the SM81 is a thirty year old design, and I think the Shure engineers did a substantial improvement in the KSM series. And you don't even need to hunt down omni capsules

That's a good point. In general, readers will not find any SM-80s nor even any SM-80 capsules. I just happened to find two. They only sold about 10 per year.

I like the looks of the KSM 141 very much. However, a pair would cost me almost twice as much as I spent on the SM-80s and SM-81s. The self noise appears to be 2 or 3 dB lower, which is an improvement. They also handle higher SPLs, but what little high SPL stuff I do can be handled with my RE-55s. Hmmm, maybe I'll buy a KSM141 someday and compare.

Cheers,

Otto

 

[mshilarious]

Hmmm, maybe I'll buy a KSM141 someday and compare.

Anybody that got a deal on SM80 capsules, I envy. I looked for a while but gave up. I suspect if you pick up a KSM141, you'll keep the SM81s, they are different--the KSM isn't flat response at all, neither cardioid nor omni. I preferred the KSM on most things, but not everything, but I don't have the budget to keep all the mics.

 

[ofajen]

Anybody that got a deal on SM80 capsules, I envy. I looked for a while but gave up. I suspect if you pick up a KSM141, you'll keep the SM81s, they are different--the KSM isn't flat response at all, neither cardioid nor omni. I preferred the KSM on most things, but not everything, but I don't have the budget to keep all the mics.

Maybe I can help you out there. I'm thinking a pair of your omni mikes will be my next purchase. I just have to figure out whether I want to start with the -1M or the -1O.

Cheers,

Otto

 

[mshilarious]

Maybe I can help you out there. I'm thinking a pair of your omni mikes will be my next purchase. I just have to figure out whether I want to start with the -1M or the -1O.

Yeah I have trouble figuring that out too. I will say that things will change a little next year, so if you're not in a hurry you could look then

 

[ofajen]

I suspect if you pick up a KSM141, you'll keep the SM81s, they are different--the KSM isn't flat response at all, neither cardioid nor omni. I preferred the KSM on most things, but not everything, but I don't have the budget to keep all the mics.

I'll wager you are right that I would keep the others, given my strange preference for accurate, natural sounding mikes. The flat response was the other factor that tilted me in favor of the SM-80s over the KSM-141, along with the cost factor. The modded SM-81 allows the very top end to sag a little in exchange for better transient response and less "crispy" or harsh sound on the top end. I really like that sound. The KSM-141 looks to have a low, broad high end peak in both settings, which I would expect to sound very good with a little bit of brightness that helps tracks stand out. I'm sure I'll find uses for that if I pick one up. I have a local dealer that will probably let me try one out before I commit to buying (he's sold me a fair amount of gear that way over the last couple of decades).

Cheers,

Otto