What would I see in this hyphothetical scenario?

[PitterWaffle]

What would I see in a waterfall graph if I had just one speaker and a mic, floating in an infinitely large room? Assume that those are the only things you need to make a measurement so no computer, no mic stand, no cable, no nothing; just empty space, the sound source and the mic.

My assumptions would be that:

1. I would see one slice only since there would be no reflections at all (infinite room).
2. In terms of frequencies, I would see a smooth-ish curve that represents what my speaker can reproduce combined with what my mic can capture. If both mic and speaker were absolutely perfectly flat -remember, hypothetical scenario-, I would see a straight horizontal line.

Am I right?

 

[Matthew J Poes]

What would I see in a waterfall graph if I had just one speaker and a mic, floating in an infinitely large room? Assume that those are the only things you need to make a measurement so no computer, no mic stand, no cable, no nothing; just empty space, the sound source and the mic.

My assumptions would be that:

1. I would see one slice only since there would be no reflections at all (infinite room).
2. In terms of frequencies, I would see a smooth-ish curve that represents what my speaker can reproduce combined with what my mic can capture. If both mic and speaker were absolutely perfectly flat -remember, hypothetical scenario-, I would see a straight horizontal line.

Am I right?

No sorry, the first point is not correct. The decay isn't a measure of reflections. It's a measure of decay. A speaker does not start and stop instantly. You would see decay in a free space measurement as well because the speaker itself decays.

Your second point is correct however. You see no contribution from the room. The measurement mics we use are all very accurate between 20hz and 20khz but have some issues above and below that, and some rise in the high frequencies that a correction file usually adjusts for. The response itself is normally fairly flat.


Here is a reflection free waterfall measurement. The ripples toward the front of the graph are probably noise and not a part of the actual response. You see perfect minimum phase behavior of a woofer. This was taken using ground plane.

 

[John Mulcahy]

The help also has information about the waterfall plot and its appearance.