Dynamic mics and noise

[Tobiah]

Are there any self noise issues to consider when choosing
a dynamic microphone? I could imagine that sensitivity would
be something to consider, in that if one needs to crank the
pre-amp up, the preamp noise would be more prevalent. Other
than that, are dynamic mics as self-noise free as they come?

Thanks,

Tobiah

[PStamler]

Nope. they have internal resistance, which will generate Johnson noise and will cause the preamp to generate noise based on the input devices' current noise if they're bipolar transistors.

A good preamp won't add appreciably to the mic's own Johnson noise, so you're on target that the way to maximize signal-to-noise is to look for dynamic mics with higher sensitivities. Consistent with the response you want, of course.

Peace,
Paul

[Scott Dorsey]

No, dynamic mikes tend to be fairly noisy because of the thermal noise
of all of those windings. Add more turns, you get more signal, and you
get a heavier coil that reduces your high frequency response. Make the
wire smaller to reduce the mass, you get higher resistance and more noise.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Mike Rivers]

On 5/24/2013 11:03 AM, Tobiah wrote:
> Are there any self noise issues to consider when choosing
> a dynamic microphone?

Microphone self noise is really only a problem if you're trying to
record something very quiet. Singers at a reasonable distance? No
problem. A fly's footsteps? Problem with any mic.




--
For a good time, call http://mikeriversaudio.wordpress.com

[Don Pearce]

On Sat, 25 May 2013 07:24:32 -0400, Mike Rivers <mm1...@yahoo.com>
wrote:

>On 5/24/2013 11:03 AM, Tobiah wrote:
>> Are there any self noise issues to consider when choosing
>> a dynamic microphone?
>
>Microphone self noise is really only a problem if you're trying to
>record something very quiet. Singers at a reasonable distance? No
>problem. A fly's footsteps? Problem with any mic.

Not a problem if you can persuade the fly to walk on the diaphragm.

d

[Peter Larsen]

I don't know how valid the equivalent self noise data can be assumed to be,
but based on them a quiet condensermicrophone, like the MKH 406 is some 10
dB less noisy than a MD 421 and a cheap one is about the same as a MD 421
and some electret stage microphones are more noisy than a MD421, based on
testing one I was offered to try and refusing it 20 years ago. And then
there is the "how does the noise sound" issue ...

> d

Kind regards

Peter Larsen

[hank alrich]

Dynamic mics are like all other mics. It's down to what it is and the
shape it's in.

Some have high sensitivity, some have low sensitivity, and many work
well with some preamps and not so well with others.

That said, any good dynamic, one with a solid rep, and a decent pre and
you're good to go.

--
shut up and play your guitar * http://hankalrich.com/
http://hankandshaidrimusic.com/
http://www.youtube.com/walkinaymusic

[geoff]

"hank alrich" <walk...@nv.net> wrote in message
news:1l3dbbt.jw3sfz1pagx0eN%walk...@nv.net...

> Tobiah <to...@tobiah.org> wrote:
> Dynamic mics are like all other mics. It's down to what it is and the
> shape it's in.
>
> Some have high sensitivity, some have low sensitivity, and many work
> well with some preamps and not so well with others.
>
> That said, any good dynamic, one with a solid rep, and a decent pre and
> you're good to go.

Given the generally low output of dynamic mics compared to condensor/active,
I would think that external noise factors (from cable interference and mic
pre front ends) would totally swamp any self-noise.

geoff

[Mike Rivers]

On 5/27/2013 2:57 AM, geoff wrote:

> Given the generally low output of dynamic mics compared to condensor/active,

. . . . .

Is this still true for today's mics? Used to be (when there weren't so
many mics available) that that for a given SPL, for example, a U-47 put
out about 10 dB more than an RE-15. There are some moderately popular
dynamic mics that have a lower than average sensitivity, such as the
Shure SM7, and the Neumann KM84 is about 10 dB hotter than average. But
when comparing modern condenser mics with common dynamics such as the
Shure SM57, I've found that that the condenser mics seem to be only
about 3 dB hotter than the dynamics.

Some (or maybe all) of this "normalization" seems to have stemmed from
the early days of the "affordable" condenser mics. Early novice users
complained that their new brilliant mic was too hot for their mixer or
preamp, forcing them to commit the unpardonable sin of turning down the
gain. So mic manufacturers adjusted. So did mixer manufacturers, forcing
the next generation of users to commit the other unpardonable sin of
turning the gain up.

You can't win unless you understand and accept gain structure and
recognize that the microphone is part of the system.

[Peter Larsen]

geoff wrote:

> Given the generally low output of dynamic mics compared to
> condensor/active, I would think that external noise factors (from
> cable interference and mic pre front ends) would totally swamp any
> self-noise.

Dynamic mics are good at high spl and can then deliver line level output.

> geoff

Kind regards

Peter Larsen

[Scott Dorsey]

geoff <ge...@nospampaf.co.nz> wrote:
>"hank alrich" <walk...@nv.net> wrote in message

>> Tobiah <to...@tobiah.org> wrote:
>> Dynamic mics are like all other mics. It's down to what it is and the
>> shape it's in.
>>
>> Some have high sensitivity, some have low sensitivity, and many work
>> well with some preamps and not so well with others.
>>
>> That said, any good dynamic, one with a solid rep, and a decent pre and
>> you're good to go.
>
>Given the generally low output of dynamic mics compared to condensor/active,
>I would think that external noise factors (from cable interference and mic
>pre front ends) would totally swamp any self-noise.

In the real world it often can. But with a modern low-noise preamp when
you're not in crazy conditions with stage dimmers all over the place, you
can easily get to the point where the thermal noise of the coil is the
limiting factor on a 421. With an SM-57, I am not sure if the thermal noise
of the coil or the transformer is dominant but I can tell you it's a lot
higher than that of a 421.

[PStamler]

You may be seeing the effect of the SM57's inductive reactance, which is quite substantial if the graph published by Ballou is any indication. The rise in impedance created by inductive reactance doesn't create Johnson noise, but if the preamp's input stage uses bipolar transistors, their current noise may make for a worse equivalent input noise when the source impedance is inductive. It's like the difference I see in input noise when I plug a high-inductance phono cartridge like a Stanton into my preamp (which uses a bipolar-input NE-5534a in the front end) instead of a low-inductance cartridge like a Grado.

[Scott Dorsey]

PStamler <psta...@pobox.com> wrote:
>
>You may be seeing the effect of the SM57's inductive reactance, which is qu=
>ite substantial if the graph published by Ballou is any indication. The ris=
>e in impedance created by inductive reactance doesn't create Johnson noise,=
> but if the preamp's input stage uses bipolar transistors, their current no=
>ise may make for a worse equivalent input noise when the source impedance i=
>s inductive. It's like the difference I see in input noise when I plug a hi=
>gh-inductance phono cartridge like a Stanton into my preamp (which uses a b=
>ipolar-input NE-5534a in the front end) instead of a low-inductance cartrid=
>ge like a Grado.=20

That would make sense... the SM57 is definitely quieter into a transformer
input preamp, which would follow reasonably.

[Ty Ford]

On Fri, 24 May 2013 11:03:45 -0400, Tobiah wrote
(in article <OiLnt.20007$cs.1...@newsfe03.iad>):

Just had to help a friend with a RE20 and a small cheapish board because the
preamp didn't have enough gain before noise. I lent him an AKG C414.

Not all preamps are created equal.

Regards,

Ty Ford



Try my blog; http://tyfordaudiovideo.blogspot.com/
Try my audio sample archive: http://tinyurl.com/796z25d
Try my gear reviews: http://tinyurl.com/79q797r

[S. King]

On Thu, 30 May 2013 21:06:53 -0400, Ty Ford wrote:

> On Fri, 24 May 2013 11:03:45 -0400, Tobiah wrote (in article
> <OiLnt.20007$cs.1...@newsfe03.iad>):
>
>> Are there any self noise issues to consider when choosing a dynamic
>> microphone? I could imagine that sensitivity would be something to
>> consider, in that if one needs to crank the pre-amp up, the preamp
>> noise would be more prevalent. Other than that, are dynamic mics as
>> self-noise free as they come?
>>
>> Thanks,
>>
>> Tobiah
>
> Just had to help a friend with a RE20 and a small cheapish board because
> the preamp didn't have enough gain before noise. I lent him an AKG C414.
>
> Not all preamps are created equal.
>
> Regards,
>
> Ty Ford
>
>

Expect the same from a Shure Sm7. Small Mackie board preamps (VLZ) are
too noisy, when you turn up the gain pot for these mics. IMO

Steve King

[geoff]

"S. King" <steveSP...@steveNOSPAMking.net> wrote in message
news:koa8vt$4el$1...@dont-email.me...

>>
> Expect the same from a Shure Sm7. Small Mackie board preamps (VLZ) are
> too noisy, when you turn up the gain pot for these mics. IMO

Dunno is it's just my SM7, but very low output level,especially with voice.

geoff

[PStamler]

On Friday, May 31, 2013 8:38:26 PM UTC-5, geoff wrote:

> > Expect the same from a Shure Sm7. Small Mackie board preamps (VLZ) are
>
> > too noisy, when you turn up the gain pot for these mics. IMO
>
>
>
> Dunno is it's just my SM7, but very low output level,especially with voice.

It's not your mic; they're all that way. The SM7 is just a low-output mic.

Peace,
Paul

[Peter Larsen]

It officially needs a preamp with 60 dB gain, my lil' soundcraft does that
beautifully.

[hank alrich]

+1

[S. King]

When you have the right preamp, it is a great mic. It is thought of as a
radio announcer or narrator mic, but I've used it on baritone sax, cello,
a number of things. It probably wasn't my first choice for those, but
when you get to the back of the mic locker...

Steve King

[LAB]

A state of the art mic preamp has an input self noise of about 400nV
(-128dBV), that is the same of a 480 Ohm resistor: en [nV]=18.2 SQR (R).
Adding a 480 Ohm noise to such a preamp, noise increases of 3dB (the double
noise power)

[Mike Rivers]

You can't win (that's the First Law of Thermodynamics). Might as well
quit worrying about it and just use the mic.