The quest for a good Measurement Microphone

[IamJF]

The SM58 info. was interesting for sure, but was extremely close 'micing' with a cardioid mic.
As I understand it, the most common form of measurement mic. is omnidirectional.
IS THIS CORRECT !

ALL measurement microphones are omni!

https://www.diyaudio.com/community/threads/full-size-3-way-project.389962/page-11#post-7492875
"You don't understand the difference between a pressure mic and velocity microphone. Look it up for details.
A velocity microphone (everything but omni) changes it's frequency response when comming in the nearfield of a speaker. The closer, the more bass. And not a little - that's 20-30dB. Nearfield depends on the frequency - it's a mess all over."

Extreme nearfiel measurements with an SM58/57 ... I'm sorry but this proves lack of understanding of fundamental acoustic principles. You don't even measure sound pressure in this situation. And the mic will have a frequency response of about +-10-15dB.

1/8" microphones don't have any directivity at 20kHz. 1/4" start at about 10kHz (if you take it serious, about 1dB at 20kHz and keeps that until 40kHz - without protection grid. With grid 1dB worse) and with 1/2" positioning is important.

Behringer - you simply have no idea if you get a good or horrible one. It's pure luck, not measurement.
And mic in with some tinkered P48 ... don't come back and complain that doesn't work well - it doesn't work well. 🤓 Something like the Presonus 1 channel interface starts at €60, 2 channel (for impedance measurements) under 100 bucks. That will work.

 

[Pano]

For years I used the Behringer mic with decent results. I didn’t expect it to be super accurate at the top end. When it broke I bought the Dayton measurement mic which is basically the same thing, but it comes with a calibration file. I trust it a little more than the Behringer. 🙂

I wanted to experiment with far field room EQ using a cardioid mic so I bought an AT2020 and compared it to a couple of Shure SM81. The resulting curves obtained were so close to the factory published response that I just used the factory curve.

Why cardioid? Because the human ear is not omnidirectional. In a room omni mics pick up too much room tone, they don’t sound natural. So I used the cardioid mic to “sort of “ imitate my ears at the listening position. I was much happier with my room EQ when using the cardioid vs the omni. For very large rooms or work outside, I still use an omni measurement mic. Same for close measurements, like 1m or less.

 

[Pano]

I will build my own little phantom power box and use PC mic. in.

Remember that the PC mic input has its own DC bias, called Plug In Power. It is low current and usually around 3V. You’ll want to DC block that voltage at the audio output of your phantom supply.

 

[Audio>X]

Remember that the PC mic input has its own DC bias, called Plug In Power. It is low current and usually around 3V. You’ll want to DC block that voltage at the audio output of your phantom supp

The phantom power box already has the obligatory DC blocking capacitor on its output.

 

[Audio>X]

And mic in with some tinkered P48 ... don't come back and complain that doesn't work well - it doesn't work well.

For unbalanced use, phantom power IS simply 48 volts DC supplied via a 6.8Kohm current limiting resistor
and a 10uF DC blocking capacitor on the output. NOTHING CAN GO WRONG - you silly tut tut .

 

[Audio>X]

Re. my phantom power box >

This could be of interest to some readers:
I was 'surfing about' on the net and found this bargain.
It became clear (given the AUD) that to build using a good metal box, P.S. & XLR connectors etc.
I might as well buy one of these. I have ordered one.
https://www.aliexpress.com/item/32811869432.html

 

[IamJF]

These units are very common and you should get one at your (local) music shop for the same price.
https://www.thomann.de/at/millenium_pocket_phantom.htm
https://www.thomann.de/at/millenium_pp2b.htm

I use a more expensive one but with proper power supply cause these switched ones sometimes add some noise.
https://www.thomann.de/at/palmer_pan_48.htm
Here is one with rechargeable battery to avoid ground loops with the computer: https://www.thomann.de/at/xvive_p1_portable_phantom_power_sup.htm

Btw - you also could just get a M-Audio M-Track Solo and use the instrument input for loopback ... €44,-. I remember some wise guy here told you ... 😎
https://www.m-audio.com/m-track-solo
Or the duo for 10 bucks more and 2 identical inputs.

 

[keantoken]

I got an ECM8000 from a friend. I expected it to be terrible. Testing showed it had popcorn noise. I cracked it open with vise-grips and was able to replace a faulty SMD ceramic capacitor with a tiny NP lytic I had laying around. The housing was totally caked on the inside with brown grit! It made no sense. When I was able to test it against multiple calibrated mics I discovered it actually had the flattest response of all of them without calibration, which shocked me. I must have been lucky to get one with a good capsule. The main downside is that it's not a low-noise mic.

 

[IamJF]

I must have been lucky to get one with a good capsule.

There ARE good ones out there, in fact most are useable.
But you only know when you compare to a good and calibrated microphone with a good and controlled setup ... which defeats somehow the reasonableness of a cheap measurement microphone 🤓