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I decided to measure my speakers today, Pi 4 mains with Pi 3 subs. I used a Pyle Pro PDMIC58 (Shure SM58 clone) that I have laying around the house for drunken karaoke nights, so I knew going in that these measurements may not be accurate. They ended up having a slope to them that I haven't seen on other Pi speaker measurements. After doing a little reading, I found this chart for the SM58 (bottom) that looks quite familiar... So as someone who does not measure speakers very often (I'm actually only measuring them now because I plan to rebuild my cabinets in the next couple of months and would like before/after measurements) I'd like to know what microphone(s) I should be looking at. I've seen several units that claim to be measurement microphones starting around $40 online. Or am I barking up the wrong tree?
You can definitely see the influence of the microphone superimposed on the measurements. Your charts look right considering the microphone response curve has rolloff down low, up high and a peak between 3kHz and 5kHz. If you were to account for the microphone chart with a conjugate curve, and then apply that curve to the measurement charts, you'd have a chart that accurately showed loudspeaker response.
I found the following SM58.cal file out on the internet, and loaded it. 20 -15 50 -7 100 -1 120 0 1000 0 2000 +1 4000 +4 5000 +5 7000 +3 7500 +2 9000 +3 10000 +4 15000 -5 20000 -15 My microphone is knockoff, so I don't expect those figures to be exact. And my room is terrible: 16' ceilings, ceramic tile floors, very few treatments. I think the measurements look pretty good all considered, but I'm not entirely sure what they're expected to look like in my case.
There you go! That's what I'd expect to see.