[zareliman]

I've had this conundrum in my mind for a long time. It's kind of the problem of "What was first, the egg or the chicken" (In that case the egg was first since that egg was given birth by a close relative of chickens at some point).

We all know microphones don't read frequencies in a flat frequency response kind of way. We also know that no device can produce a completely clean flat frequency response unless calibrated.

But how do you calibrate the speaker you use to then calibrate the microphones ? You will never ever know what a flat frequency response really is because even if someone claims to have the perfect waveform emmiter and the perfect microphone perfectly calibrated, there isn't any way to determine if that is true or not. There could be 2 companies claiming to have flat FR equipment, yet if they differ in measurements, who do you believe ?

 

[NeoG]

It's not about who you believe, it's about understanding what references are being used to determine what a graph/plot is telling you. Once the signal is turned into electricity we have a very good idea of how it changes through a system, and those measurements are fairly trivial to do nowadays.
 
You are looking is at the electro-mechanical interface step on the inwards or outwards direction. What is actually happening is that a three dimensional volume is being flattened into a point in space. There is really no standard that captures the entirety of this transformation process (due to the complexity and size of the task) - and so you are only really ever getting a small slice of the whole picture.
 
A 2D FR response plot is the smallest amount of information - two identically plotted microphones can sound wildly different if this is the only reference.
A response polar at one frequency in addition to the FR gives you a better understanding but still leaves a lot of unkowns.
1/2 octave polars start to give you an idea of how it really works in 3 dimensional space. This is already way more information than most would provide with equipment.
H/V directivity plots gets you most of the way there, but is rarely done on account of expense and time (plus not many people can intuitively read them)
Full volumetric measurements would capture pretty much all of the possible variations - but this is so over the top (Harman does this for new JBL pro gear IIRC) that it's really a design tool meant for professionals.
 
The more information you capture, the less chance that two similar devices will diverge in actual usage. Most will only give you the first or second level of information leaving a huge area that can change between two devices while not affecting the measurements much.
 
So, I'd say the takeaway is, understand what you are not getting when you look at measurements, and understand that it's not that one is true and the other is a lie, but that you didn't get told enough to understand why they differ in usage vs measured performance.

 

[spruce music]

https://en.wikipedia.org/wiki/Measurement_microphone_calibration
 
This explains it.

 

[NeoG]

I actually misread the original post so my response is actually just a bunch of irrelevant tangent. Whoops.

 

[Speedskater]

It takes calibration equipment and trained technicians to calibrate a microphone (that's why it costs money).
 
You might check a mic's cal only after reading this Earthworks paper:
 
"How Earthworks Measures Microphones"
How to measure microphones and the implications relating to measuring loudspeakers. 
 
http://www.earthworksaudio.com/support/technical-articles/

 

[RRod]

Quote:

  https://en.wikipedia.org/wiki/Measurement_microphone_calibration
 
This explains it.

 
And to go as far down the rabbit hole as we can go:
SI base unit