INFRASONIC
EXAMPLES OF ACOUSTIC DATA
COLLECTED DURING THE CONCERT

31 May 2003
Purcell Room, London

Data produced by the Dr Richard Lord and Dan Simmons
from the National Physical Laboratory UK

These graphs compare the sounds present in piece B, during Concert 1 and 2. They show a measurement that was taken over a 60 second period, around a minute after the start of the piece.

The horizontal axis shows frequency (pitch), measured in Hertz (Hz). Higher frequency sounds are on the right on the graph, lower frequency sounds on the left. The vertical scale shows the average sound pressure level over this time - this is known as the 60 second Leq. Sound pressure level in measured in decibels (dB). You can clearly see a peak in Concert 1, around 17Hz. This shows the infrasound, added to the music by our generator. This peak doesn't appear in the plot for Concert 2 as no infrasound is present.

Technical details: These plots show the Leq of the sound, five rows from the back of the auditorium, measured over a 60 second period.

SEE SPECTRAL PLOTS

SEE TIME HISTORIES

HEAR PIECE UNDER TEST(without infrasound!)
She goes back underwater (Sarah Angliss, 2003).

CONCERT 1 - INFRASOUND IS PRESENT IN PIECE B
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CONCERT 2- NO INFRASOUND PRESENT IN PIECE B
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Time histories

These graphs show you how the level of the sound varied during the 60 second period measured above.

The horizontal scale shows frequency (pitch), measured in Hertz (Hz). Higher-frequency sounds are on the right on the graph, lower-frequency sounds on the left. The vertical scale shows time from 0 to 60 seconds. The colours on the graph shows you how the sound pressure level (SPL) of the sound varies with time. Brighter colours show sounds with a higher SPL.

You can clearly see a bright line in Concert 1, around 17Hz. This is the infrasound, added to the music by our generator. This line doesn't appear in the plot for Concert 2 as no infrasound is present. You can also see wave-like bands in the plot. These show sounds in the music which gradually sweep between low and high pitches.

CONCERT 1 - INFRASOUND IS PRESENT IN PIECE B
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CONCERT 2 - NO INFRASOUND PRESENT IN PIECE B
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All images copyright The National Physical Laboratory.
Contact Dr Richard Lord, NPL

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