Waterfall help?

[golfman]

Just started using the rew software. I was hoping to get a little help on this waterfall graph. I am not sure exactly what I am looking at? Can I get your thought on how to read this please? I have also posted a corrected subs only graph that the waterfall came from.

[Wayne A. Pflughaupt]

I am not sure exactly what I am looking at? Can I get your thought on how to read this please?

Waterfall graphs show the length of time it takes the REW sweep to decay or “fade out” – or at least attenuate to the lowest level you’ve designated on the graph (45 dB in this case).

Waterfalls can reveal room modes (which are peaks that are slow to decay).

What the graph displays as the length of time it takes the signal to fade away is highly level dependent. For instance, if you took two sweeps, one at 72 dB and the other at 80 dB, the latter would show a noticeably longer decay time, making it look “worse” than the former.

In your graph, it doesn’t appear that you have any significant room modes. Above ~50 Hz the signal is falling off the graph faster than 300 ms. Not bad for a reading averaging between 75-80 dB SPL, especially if your room is untreated.

Below 50 Hz things don’t look as good, but that’s not unusual. Note in places where the level has fallen below ~ 70 dB that the signal kinda “goes its own way” and is no longer tracking with the higher level signal. And at 20 Hz, where the signal seems to level off and remain constant. Both of these things could be an indication that there was background noise in the room when the REW sweep was taken. You might regenerate the graph in a longer 600 or 1000ms window to see what happens below 50 Hz “long term.”

As you can see, if you want to examine waterfalls in any meaningful way, it’s imperative that all sources of background noise, such as furnaces, refrigerators, washing machines, and so forth, are turned off before you make the sweep. Even outdoor noises such as lawnmowers and leaf blowers and maybe your next door neighbor’s air conditioner can be picked up as well.

Regards,
Wayne

[RastusW]

Golfman,
Thanks for creating this post.

Wayne,
Thanks for the succinct answer. I think I now understand. Maybe.

The goal is to have a short decay time. Correct?
Would a good waterfall plot show all the levels decaying at a pretty consistent rate?

Rastus