Dayton Audio OmniMic V2 Precision Measurement System User Manual
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show impulse responses, and you can select how much of an impulse reponse you want to
analyzer to look at when forming a frequency response. Click on the impulse response
graph at the latest part of the impulse response you want OmniMic to include when it
computes frequency response. The selected portion will appear as a red trace, the rest
will remain black.
Reflections of sound in a room will appear as abrupt features in later parts of the
impulse response (usually after about 3 to10 milliseconds from the main impulse response.).
The response of the speaker without room reflections is smoother and less varied than when
room reflections are included. Removal of room reflections is possible only at higher
frequencies -- at lower frequencies, the reflections happen before even one full cycle of longer
low frequency waves.
Because all audio frequencies are played at once in the pseudo noise signal, you cannot
determine that the speaker is playing at any specific sound level at any individual frequency,
so measurements with the psuedo noise show only relative response flatness. The curves are
shown as values given in units of "dB". Also, minute variations in clock frequencies of different
players can cause the response at higher frequencies can appear to vary when using pseudo
noise. When high frequency accuracy is important, use the sine sweep signal.
To evaluate loudspeaker how frequency response changes at specific levels and for best
accuracy at high frequencies, use the sine sweep to display curve values as "dBSPL" (sound
pressure level).
In most cases, it is best to measure the frequency response of each speaker individually (i.e.,
have only one speaker at a time playing the Test Track signals). This will avoid interference
effects from the two speakers complicating the graphs. However, in "all" (full room)
responses, you may want to also measure with all speakers playing together.
Frequency Response Options:
"all": this setting shows a frequency response that includes all room echoes and reflections.
In other words, the entire impulse response. In this view, impulse response itself is not shown.
"only to": for suppressing reflections. This is calculated only from the impulse response within
the time selected. To select a different ending time, click the mouse at the desired time point
within the impulse response graph. Impulse response information after the selected time will
be excluded from the frequency response calculation. Select this time to exclude later
reflections visible on the impulse response plot. Lower frequencies can't be measured using
this option, limited by the length of the time selected. This mode works best when the
OmniMic is relatively close to the loudspeakers.
"blended": blends from the "only to" calculation at higher frequencies, to the "all" calculation at
lower frequencies. In other words, this mode removes echoes when it can, and doesn't when it
can't.
smoothing: You can choose to smooth the frequency response graphs over 1 octave to
1/96th octave regions, to vary the amount of detail shown. An unsmoothed frequency
response will be very ragged except when echoes are windowed or the measurement is taken
very close to the loudspeakers.
Frequency Response measurement curves can be saved as "Added Curves" in FRD
format using the
You can save either or both of the current "live" curve
(currently produced by the microphone) or any displayed average curve. These can then be
reloaded using the "Added Curves" menu so that multiple Added Curves can be shown on
the same graph along with the "live" curve and the average curve. When Frequency
Response files that contain these files are printed or saved in a "Snapshot", a list of legends