Dayton Audio OmniMic V2 Precision Measurement System - Manual (Page 13)

13 | P a g e
Frequency Response: Waterfalls
Index
Waterfall plots are used by driver and loudspeaker designers for driver selection, to identify resonances or reflections, and
to view driver and waveguide behavior.
The Waterfall feature becomes available when you click the Waterfall button (above the Frequency Response graph, next
to the Smoothing control). Waterfalls are calculated from the impulse response.
What does a Waterfall mean?
A waterfall is an attempt to illustrate on a 3-D graph how the energy decays or is radiated over a range of frequencies.
OmniMic includes three different styles of waterfall processes, selectable via the "Waterfall Type" menu.
A "
Cumulative Spectral Decay ", or "CSD" waterfall shows a series of time slices approximately indicating the
contribution to the total response that is made after the time instant shown in the axis going into the screen. When a
loudspeaker is driven with an electrical impulse, the pressure it creates should ideally also represent a pressure impulse.
But loudspeaker drivers aren't ideal so they also generate resonances -- pressure waves that decay more slowly at
various frequencies. The effects of echoes can hide the resonances in a CSD waterfall, but at higher frequencies the
echoes can be removed by "Windowing" the calculation to only include the part of the Impulse Response that occurs
before the first reflection (from a surface such as a wall or furniture) reaches the OmniMic. Careful choice of positioning
within the Impulse Response is critical, because the effects of any reflections included within the selected portion will
contaminate all regions of the graph up to that point on the time axis. Below some frequency determined by where the
Impulse Response is clicked and how far along on the time (depth) axis a trace exists, meaningful calculation cannot be
done. The graph curve is chopped off at those points on the waterfall display.
The CSD waterfall calculation process introduces some spurious side effects, so the graph should be viewed in general
terms. Exact values along the curves of waterfalls are not usually reliable, rather, the positions and sizes of decaying
forward-approaching ridges on the graph indicate frequency and relative intensities of resonances.
CSD waterfall curves can now be shown with different degrees of smoothing, and can also be use with long time lengths
(to 250 milliseconds) for viewing effects of room reflections.