Acoustic Testing Equipment

Principle

Investigate the spectra of different musical instruments. Show that the acoustic spectrum can be influenced by thetype of excitation. Different musicalinstruments supply different spectra:even when the same note is played.

Principle:

When a sound wave of a particular frequency is divided into two coherent components (like, for example, light waves in an interferometer experiment), and if the path of one of the component waves is altered, it is possible to calculate the wavelength of the sound wave and its frequency from the interference phenomena recorded with a microphone.

Tasks:

1. Record the extension of a Quincke tube for given frequencies in the range 2000 Hz to 6000 Hz.
2. Calculate the frequencies from the wavelengths determined and compare them with the given

What you can learn about:

• Transverse and longitudinal waves
• Wavelength
• Amplitude
• Frequency
• Phase shift
• Interference
• Velocity of sound in air
• Loudness
• Weber-Fechner law

Principle

Sounds are generated by oscillations. The sound volume is influenced by their relative amplitude, while the sound pitch depends on their frequency. This relationship is examined based on three examples: oscillating ruler, tuning fork, string of a monochord.

Tasks

Try to generate sounds with a ruler, tuning fork, or a taut string. Examine the factors that the pitch and sound volume depend on.

Principle

This experiment demonstrates, particularly clearly, the propagation of sound waves in air and, thereby,
the working principle of the eardrum that is caused to oscillate by pressure waves.

The movement of the membrane is transferred to the neighbouring air molecules, which in turn transfer it to their respective neighbouring molecules. All of the molecules oscillate around their position of rest, since - just like springs - they are joined by cohesive forces. This leads to pressure variations that propagate through space in the form of a sound wave (pressure wave). If a second drum is held precisely in parallel to the first one, the wave can cause the membrane of the drum to oscillate.

Tasks

The sound is generated by striking a frame drum or the bottom of a tray vigorously with a striking hammer. The "sound receiver" is a (second) frame drum. Its movement is visualised with the aid of a styrofoamsphere pendulum. Try this method of detection out and try to optimise it.

Principle

The transmission (or conduction) of sound through a solid body means: One end of the solid body is caused to oscillate (e.g. by placing a tuning fork on it). This oscillation propagates through the solid body to the other end of the solid body. The transmission through the solid body can be heard directly as an oscillation of the other end (experiment 2) or through the air (experiments 1 and 3).

Tasks

Examine, with the aid of several examples (a plastic ruler, the human head, a thin thread), as to whether sound cannot only propagate in air but also in solid bodies. Show that the sound of the tuning fork can no longer be heard, or that it can only
be slightly heard, through the air at a greater distance (approximately 20 cm). Demonstrate that the conduction through solid bodies over comparable distances ensures that the sound can be heard clearly.

Principle

The aim of this experiment is to enable the students to find out that sound can also propagate in other media, e.g. liquids. For this purpose, they study the propagation of the sound of a tuning fork in a tube that can be filled with air or water. For comparison, the sound propagation via the tube itself (solid body) is also observed. The students learn that the quality of the sound propagation depends on the density of the transferring medium.

Tasks

Normally, we hear sound that is emitted by a source when it reaches our ear through the air. Examine in this experiment whether sound can also propagate in water. To do so, try to hear the sound of a tuning fork through the air as well as through water. Does the tuning fork sound different?

Principle

In this experiment, the students determine the velocity of sound in air. For this purpose, they measure the difference in the propagation time of a sound signal of two spatially offset stereo loudspeakers with the "measure Acoustics" software.

Tasks

We all know that during a thunderstorm, sound propagates with a limited velocity. We see the flash of lightning but the thunder does not follow until several seconds later, depending on the distance. In this experiment, determine the velocity of sound in air with the aid of stereo loudspeakers and a microphone.