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andychamp

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Posts: 279 Member Since: 01/02/2011

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Feb 24 16 7:42 PM

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Some older RE20s have the option of setting their output impedance to 50, 150 or 250 Ohms.
What's the best setting for standard studio use?
I bought the mic off a P.A. company that usually deals with VERY long cable runs, so it's probably been set accordingly.

Also, I'd be very grateful for a comprehensive explanation of the whole impedance-matching thing, how the respective Z of source and destination affect each other, especially how the preamp can affect a mic capsule.

 

André Champaloux 

"The biggest question this thread has actually raised is: When do we start to serve the artist more than our insecurities?" - Fletcher

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seth

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Posts: 5,532 Member Since:26/01/2011

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Feb 24 16 9:15 PM

That's something I would like to know as well. I think I sort of understand it, but a real explanation would be very helpful.

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mikerivers

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Feb 25 16 7:42 AM

andychamp wrote:
Some older RE20s have the option of setting their output impedance to 50, 150 or 250 Ohms.
What's the best setting for standard studio use?
I bought the mic off a P.A. company that usually deals with VERY long cable runs, so it's probably been set accordingly.

Also, I'd be very grateful for a comprehensive explanation of the whole impedance-matching thing, how the respective Z of source and destination affect each other, especially how the preamp can affect a mic capsule.


 

This can can have either simple or complicated answer. The simple answer to just not worry about it. If you have a preamp that has a selection of input impedances, just listen to how the mic sounds at each setting and use what seems to work best for whatever you're recording. If you have a good quality preamp, just use it. If you want to buy "the best preamp to use with the RE-20," that probably doesn't have a real answer, though there may be a concensus of a few models that make a good companion for the mic for the kind of work where it's conventionally used. But a broadcast studio, a voice-over artist, an acoustic guitarist, and a drummer all have good uses for the RE-20 and each one might have a favorite preamp for his own application.

I'm working on an article about microphone specifications at the moment, and there's a couple of paragraphs in there about impedance. The impedance quoted for your mic is the source impedance, but sometimes you'll see a spec sheet that lists impedance somewhere in the ballpark of 1500 to 2500 ohms. That's what the manufacturer recommends as the minimum load impedance (preamp input impedance) for the mic to perform within its specifications. If the load impedance is too low, it will reduce the output level of the mic, which means that it won't meet its sensitivity specification. It may also alter the frequency response (or not) depending on what other components are inside the mic. To further complicate things, if the preamp has an input transformer, its reactance can interact with an output transformer in the mic, sometimes in a good way, sometimes in a bad (but usually not too bad) way, mostly in a "color" way. The rule of thumb is that the input impedance of the preamp should be at least 10 times the source impedance of the mic. This is the same rule of thumb for any "voltage source" interconnections like line output to line input for most modern studio equipment.

Transformerless mics are usually not very fussy about load impedance other than how it affects the sensitivity, and if the mic has an output transformer (tube, solid state, or dynamic) and the preamp has an input transformer, or vice versa, you have a case-by-case basis for what the combination sounds like. Sometimes, using a lower load impedance can smooth out a resonance peak built into the mic (by design or just by gosh), with the tradeoff of somewhat reduced sensitivity. An SM57 sounds better with a 600 ohm load than with the typical 2000-3000 ohm load of a modern mic preamp. Try it some time.

Is that enough for now? If not, there's a general article about most things impedance on my web page:
https://mikeriversaudio.files.wordpress.com/2010/10/catching_some_zs_revised.pdf



For a good time, call mikeriversaudio.wordpress.com

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andychamp

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Posts: 279 Member Since:01/02/2011

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Feb 25 16 9:26 AM

Thank you, Mike!

I also found this article in the meantime:

http://www.recordingmag.com/resources/resourceDetail/330.html

Especially the 2nd paragraph "carry that load".



So, this "10 to 1 rule" would suggest that setting the mic to 50 Ohms would give the strongest output level and be adaptable to the greatest variety of preamps.

OTOH, it would run the greatest risk of undesirable artifacts.

The 250 Ohms setting in turn would have the best chances of sounding good, but this would come at the cost of lower level ( = more noise from the preamp).



Current RE20s are factory set to 150, which would suggest the best compromise.

I'll try setting mine to 250, seeing as it's usually picking up loud sources, anyway.

André Champaloux 

"The biggest question this thread has actually raised is: When do we start to serve the artist more than our insecurities?" - Fletcher

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klaus

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Feb 25 16 10:25 AM

The interplay between transformer-coupled mic output impedance and mic pre input impedance is an issue where practical experience comes in handy, sometimes beating theoretical computation.


After many a try with all three settings, I keep coming back to strapping the RE20 for 250 Ohms for the beefiest, most robust and satisfying sound. 

 Give all three options a try, and report back whether you can hear a difference, and what that difference might be to your ears.

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spiritwalker

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Feb 25 16 5:50 PM

I just purchased one, so I look forward to strapping it for 250Ω and having a go with this mic on my 24 " 1947 WFL kick drum.

Fun fun fun.

OK it's cold here

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mikerivers

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Feb 25 16 9:02 PM

andychamp wrote:

So, this "10 to 1 rule" would suggest that setting the mic to 50 Ohms would give the strongest output level and be adaptable to the greatest variety of preamps.
OTOH, it would run the greatest risk of undesirable artifacts.
The 250 Ohms setting in turn would have the best chances of sounding good, but this would come at the cost of lower level ( = more noise from the preamp).


Actually, you have that backwards. For a given SPL, you get a higher voltage out from the 250 ohm tap than with the 50 ohm tap. It "steps up" the impedance, and in the process, steps up the voltage. So as long as your mic preamp's input impedance is 2500 ohms or greater (most of them are, these days), the mic will appear to be more sensitive when set for 250 ohms than for 50 ohms. Since the RE20 has a fairly low sensitivity compared to other dynamic mics, that may be an advantage if you're recording quiet things.

On the other hand, if you're recording loud things and need to reduce the mic's output level so it doesn't overload the front end of the preamp, doing it by changing the transformer tap to a lower output impedance may be better than using a pad. A pad maintains the same dynamic range of the mic and just shifts it to a different nominal output voltage. A transformer can potentially increase the dynamic range because when you reduce the level with a lower impedance tap, if the mic's distortion doesn't increase due to mechanical overload of the capsule, you can scream louder and push it to the same output level as with the 250 ohm tap.

In practice, what you'll notice most about changing the transformer tap is just a change in sensitivity.



For a good time, call mikeriversaudio.wordpress.com

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andychamp

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Feb 25 16 9:52 PM

So, into a given preamp input impedance (let's say 2.5kOhm), the 250 tap would yield a higher output AND stronger damping of the membrane?

André Champaloux 

"The biggest question this thread has actually raised is: When do we start to serve the artist more than our insecurities?" - Fletcher

Last Edited By: andychamp Feb 25 16 9:55 PM. Edited 1 time.

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mikerivers

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Feb 26 16 8:23 AM

andychamp wrote:
So, into a given preamp input impedance (let's say 2.5kOhm), the 250 tap would yield a higher output AND stronger damping of the membrane?

The 250Ω tap will give you a higher output than the 50Ω tap. Damping is really dependent on the individual microphone. You can't really predict it without knowing details about the microphone itself that you really can't tell from any published specification. It's something that you need to experiment with, if you care. For many mics, it's irrelevant. Not to say that you won't hear the sound of the mic change as you change its load impedance, but you have to be really careful with your listening tests to be sure that you're not just hearing a change in level. Loading will definitely change that.

The article that you saw on the Recording Magazine web site is about a specific microphone, the Shure SM57. Their listening tests led to the conclusion that this mic sounded best when loaded with (as I recall) 600Ω. And that doesn't mean using a preamp with a 600Ω input impedance, assuming you could find one. It means that for a given preamp, for which you know the input impedance, you add a resistor which, when connected in parallel with the known input impedance, gives you a 600Ω load.

This is certainly something you can experiment with yourself if you care to do so. It's not that hard. But the RE20 is already a good sounding mic that people use because they like its sound.  In the case of the SM57, the 600Ω load smooths out some peaks which, at least in the opinion of the test group, makes it sound better for certain things like vocals and maybe acoustic guitars - if you're looking for a natural sound. But the SM57 has wide applications as a go-to mic for snare drums and guitar amplifiers. Those who use it for those sources may prefer the normal SM57 sound to one that's smoothed out.

 



For a good time, call mikeriversaudio.wordpress.com

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andychamp

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Posts: 279 Member Since:01/02/2011

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Feb 26 16 9:28 AM

Rest assured, I will definitely try and not solely rely on theoretical knowledge.
The mic is due for a foam replacement, anyway, and while it's open, might as well check the Z, especially since it was used with very long cable runs before I owned it (I originally learned of the impedance options from a tech working at that exact same company who advised I check this.)
I just figured It'd be nice to know the underlying principles and which way to look for a possible improvement of my mic for its current use.

André Champaloux 

"The biggest question this thread has actually raised is: When do we start to serve the artist more than our insecurities?" - Fletcher

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