Undertone sound

1. Undertone Sound

Problem №3
Undertone Sound
Allow a tuning fork or another simple
oscillator to vibrate against a sheet of paper
with a weak contact between them. The
frequency of the resulting sound can have a
lower frequency than the tuning fork’s
fundamental frequency. Investigate this
phenomenon.
Team Russia
Reporter: Andrey Shusharin

2.

Task analysis
Allow a tuning fork or another simple oscillator to
vibrate against a sheet of paper with a weak contact
between them. The frequency of the resulting sound
can have a lower frequency than the tuning fork’s
fundamental frequency. Investigate this phenomenon.
Contact which is
broken after
fork and paper
impact
Definition of the
undertone
Reasons for that
and critical
values
2

3.

Experimental setup
Tuning fork
f = 440 Hz
Vice
Electro
magnet
Electric
generator
3

4.

First observations
220 Hz
440 Hz
Undertone has frequency that is smaller
than the frequency of the original sound
4

5.

Sound appearance
Amplitude,
Amplitude, dB
dB
-30
-30
Tuning
fork Paper
spectrum:
Paper
hammering
the fork
White
producedand
Self noise
frequencies
-48
-48 No undertones
it’s harmonics
-60
-60 No undertones
-72
-72
-84
-84
1010
40
40
2000
400
Sound
is1100
created
by: Hz
2000 Frequency,
400 600800
Frequency, Hz
1.Tuning fork
2. Paper hammering the
mainfork
reason
3. Paper vibrations
100
100 200
200
-
5

6.

Qualitative explanation
Paper
f f tuning fork
No undertones
produced
Paper
f
f tuning fork
2
Half tuning fork
frequency
undertone
produced
6

7.

Different modes
Parallel:
0
Angle = 90°
Perpendicular:
Angle = 0° 7

8.

Undertone volume on angle
-16
Amplitude, dB
-18
- our main focus
α
-20
-22
-24
-26
-28
-30
-80 -60 -40 -20 0 20 40 60 80 100
Angle, deg
8

9.

Potential energy
Area moment 2
π