[Trevor]

On 1/04/2017 7:27 PM, Don Pearce wrote:

HOW did you calibrate your system to provide "absolute SPL' then?
Bet it doesn't! Relative is a lot easier.


I used an SPL meter and a fixture. Stax headphones make this a
reliable method because the sound generating area is so large. You can
move the measuring mic around by tens of millimetres and the level
doesn't change.


Is your SPL meter calibrated? How do you calculate the difference
between the SPL at microphone position and ear drum? Why do you care
anyway? Relative SPL is all that matters for a frequency plot.

Trevor.

[Trevor]

On 1/04/2017 7:29 PM, Don Pearce wrote:
On Sat, 1 Apr 2017 19:13:20 +1100, Trevor wrote:
My calibration is pretty good. I reckon I'm within 2 or 3dB of the
right level.


And you know this how exactly?


I'm used to measurement. I spent several years as chief engineer of
Marconi Instruments. I know how to make root-sum-square calculations
of the effects of the various uncertainties in any system. And more
importantly, I know how to tell the difference between good
measurements and unreliable ones.

OK What calibration certificates do you have?
What is your uncertainty and confidence level of those measurements?
How did you determine the sources of error?
Pure guess right?

Trevor.

[Trevor]

On 2/04/2017 7:06 AM, geoff wrote:
Today I am doing a function where they have specified a SM57 for violin
- yuk ! Or "Ouch'.

Most specs I see usually state : Instruments SM57 *or better*, Vox SM58
*or better*. Obviously you can do better. :-)

Trevor.

[Don Pearce[_3_]]

On Mon, 3 Apr 2017 14:13:51 +1000, Trevor wrote:

On 1/04/2017 7:27 PM, Don Pearce wrote:

HOW did you calibrate your system to provide "absolute SPL' then?
Bet it doesn't! Relative is a lot easier.


I used an SPL meter and a fixture. Stax headphones make this a
reliable method because the sound generating area is so large. You can
move the measuring mic around by tens of millimetres and the level
doesn't change.


Is your SPL meter calibrated? How do you calculate the difference
between the SPL at microphone position and ear drum? Why do you care
anyway? Relative SPL is all that matters for a frequency plot.

Trevor.


Calibrated? Yes. I still have access to Marconi's NAMAS standards lab.
And SPL at the ear drum is not the parameter that matters. The SPL
presented to the ear is what matters. And obviously I care what the
absolute level is - I'm assessing my hearing, not drawing pretty
pictures.

Look, can we stop here? Your attempts to pull apart my measurement are
getting increasingly desperate and stupid.

d

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[Don Pearce[_3_]]

On Mon, 3 Apr 2017 14:19:24 +1000, Trevor wrote:

On 1/04/2017 7:29 PM, Don Pearce wrote:
On Sat, 1 Apr 2017 19:13:20 +1100, Trevor wrote:
My calibration is pretty good. I reckon I'm within 2 or 3dB of the
right level.


And you know this how exactly?


I'm used to measurement. I spent several years as chief engineer of
Marconi Instruments. I know how to make root-sum-square calculations
of the effects of the various uncertainties in any system. And more
importantly, I know how to tell the difference between good
measurements and unreliable ones.

OK What calibration certificates do you have?
What is your uncertainty and confidence level of those measurements?
How did you determine the sources of error?
Pure guess right?

Trevor.


See my other post. And I don't need certificates as I am doing this
for myself. And I'm not supplying you a tutorial on metrology. I'm
done.

d

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[Trevor]

On 3/04/2017 4:46 PM, Don Pearce wrote:
On Mon, 3 Apr 2017 14:13:51 +1000, Trevor wrote:

On 1/04/2017 7:27 PM, Don Pearce wrote:

HOW did you calibrate your system to provide "absolute SPL' then?
Bet it doesn't! Relative is a lot easier.


I used an SPL meter and a fixture. Stax headphones make this a
reliable method because the sound generating area is so large. You can
move the measuring mic around by tens of millimetres and the level
doesn't change.


Is your SPL meter calibrated? How do you calculate the difference
between the SPL at microphone position and ear drum? Why do you care
anyway? Relative SPL is all that matters for a frequency plot.


Calibrated? Yes. I still have access to Marconi's NAMAS standards lab.
And SPL at the ear drum is not the parameter that matters. The SPL
presented to the ear is what matters. And obviously I care what the
absolute level is - I'm assessing my hearing, not drawing pretty
pictures.

Keep telling yourself that! :-)


Look, can we stop here? Your attempts to pull apart my measurement are
getting increasingly desperate and stupid.


In fact all I said was that absolute SPL is not important for a
frequency plot, something you still seem to dispute?
Your unsupported claims that you have a calibrated system at home
because you have access to one with unknown capability somewhere else is
what looks desperate and stupid IMO.
But I do agree it is NOT important to me what you do, so yes let's stop.

Trevor.

[Scott Dorsey]

In article , Trevor wrote:
On 2/04/2017 7:06 AM, geoff wrote:
Today I am doing a function where they have specified a SM57 for violin
- yuk ! Or "Ouch'.

Most specs I see usually state : Instruments SM57 *or better*, Vox SM58
*or better*. Obviously you can do better. :-)

Oh, I get plenty of folks who absolutely have to have an SM58 on their vocal,
and can't abide anything else. I have one SM58 with an AKG element inside,
another with a B&K element inside, and usually one of those two will do it.

That said, in a small room with something like a dance band, the fiddle usually
is mostly heard acoustically anyway, and only needs a little punching up in
the PA to bring it out. An SM-57 with about 6dB pulled out centered around
3 or 4 kc can do the job in a pinch if that's all you have.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."