Room tests of the booth

I didn't feel like playing the guitar today; experimenting with microphones was the alternative activity. I had created a mini-booth for recording from the corner absorbers. This sounded good enough that I wanted to buy some more acoustic panels, but before I spent a lot of money, I wanted to take some pictures, to see if my ears were fooling me.


These pretty pictures above are spectrum diagrams of one click of the metronome (GTick). The top one is taken with the microphone and speaker in the 'booth', and the lower one is with the microphone and speaker in the middle of the same room, outside the booth. The vertical scale is frequency, the color is intensity, red being loud, blue not so loud. I guess the white sections are very loud. The horizontal scale is time.



You can see that the untreated sound, the lower image, lasts a little longer for all except the higher frequencies. This seems particular evident in the lower third of the frequencies, where the red in the untreated room image extends about 30% more.

This is clearer in this wave form image:


These are two snapshots of the metronome click. The time scale on the bottom shows a duration of about 0.70 seconds. The upper one is from the booth, the lower is in the center of the room. You can see how quickly the fuzziness is cleared up in the upper image and the click becomes fundamental. The lower image has lots of overtones that last almost .3 seconds. I'm not sure what the upper image is showing after .3 seconds. The frequency is 60 cycles; I'm not sure where it is coming from (see update, below). Perhaps it is the extra speaker cable I added to move it around the room.

So I'm psyched - 12 mineral wool panels and 12 Owens-corning 703 panels are now sitting in the carport. It should be interesting to hear, and see, what changes are in store.

Note: wave and spectrum diagrams are from Audacity.

Update, March 17th - the hum was probably from the Radon fan, as detailed here.