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Siemens Stiftung

The Ear, Hearing and Hearing Impairment: Refraction

Graphic:
The wave front model of refraction on an interface makes it clear why the direction of the sound propagation changes.

When waves cross over from one medium to another, the speed at which the waves spread changes. Consequently, the wave normals of the incident and broken waves have different directions. With light waves, the change in the index of refraction at the boundary is the cause; with sound waves, it is the change in the density.
The graphic illustrates the case when the speed of propagation becomes slower at the transition from the first to the second medium: The wave is broken at the perpendicular of the boundary surface.
An explanation of this phenomenon is provided by the Huygens' Principle: Every point on a wave front is the starting point for a new wave, known as an "elementary wave". The enclosing end of the elementary wave creates the new wave front.

Information and ideas:
Refraction at boundaries also occurs with sound waves (for example, in the atmosphere at the transition from warm to cold layers of air).

Relevant for teaching:
Sound/acoustics: parameters
Vibrations and waves

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Siemens Stiftung

The Ear, Hearing and Hearing Impairment: Diffraction

Graphic:
Diffraction of waves on encountering an obstacle.

The graphic shows possible diffraction effects according to aperture and wave length.

Information and ideas:
Diffraction arises in sound waves as well, for example at corners of buildings.
Further information regarding this graphic is available as information sheet on the media portal of the Siemens Stiftung.

Relevant for teaching:
Sound/acoustics: parameters
Vibrations and waves

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Siemens Stiftung

Speech signal - individual word

Chart:
Screenshot of the oscillographic curve of the spoken word "dogs".

Speech sounds are fluctuating sound signals where the composition of frequencies changes all the time.
Aperiodical overlap periodical parts. Unlike noises, some of which have similar frequency curves, sound in speech is always the carrier of meaning or of messages sent out by the speaker. Other noises like smacking of lips, hissing, rhythms, basic pitch are typical of the individual (acoustic fingerprint) but not essential for the speech content!

Information and ideas:
Supplementary to worksheets and transparencies.

Relevant for teaching:
Sound/acoustics: parameters
Vibrations and waves
Communication and understanding

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Siemens Stiftung

The Ear, Hearing and Hearing Impairment: Sound absorption

Graphic:
If sound waves strike an obstacle with a corresponding material structure, they are absorbed, i.e. the entire mechanical energy of the sound is converted into thermal energy.

This effect is enhanced by sound barrier walls made of porous materials. By means of multireflection and dispersion, the passage of sound in such materials is extended considerably. The sound peters out.

Information and ideas:
Reference to students' everyday world: silence after snowfall.
Can be checked with the students in an experiment.

Relevant for teaching:
Sound/acoustics: parameters
Vibrations and waves

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Siemens Stiftung

Microphone - transparent

Graphic:
With a moving coil microphone (dynamic microphone), the coil moves in "time" with the sound and produces a tone-frequency current.

In a microphone the mechanical energy of the sound waves is transduced into electric energy. From the mechanical vibrations the microphone produces an electric signal of the same frequency and amplitude.

Information and ideas:
Explanation of the process of sound transduction as it occurs in the inner ear of a human being using a technical device familiar to the students.

Relevant for teaching:
Sound/acoustics: parameters
Communication and understanding
Vibrations and waves

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Siemens Stiftung

Guitar, a classical string instrument

Photo:
Sound is produced by plucking strings and their vibrations are reflected by the resonance of the guitar body.

The vibration of the strings is transmitted to the body (soundboard) of the guitar which in turn vibrates and stimulates the air in the hollow body to vibrate itself. Finally a much bigger volume of air is now vibrating, the sound of the strings is much more clearly audible.

Information and ideas:
Guitar, violin and piano are good examples to illustrate the production of sound through vibrating objects on the one hand and, on the other hand, to show the importance and function of resonance bodies.

Relevant for teaching:
Acoustic phenomena
Sound/acoustics: parameters
Vibrations and waves

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Siemens Stiftung

The Ear, Hearing and Hearing Impairment: Differentiated frequency ranges in the cochlea

Labeled graphic:
Position of the receptors for tones of varying frequencies in the spiral canal of the human cochlea.

Frequencies between 16 hertz (hertz = vibrations per second, abbr.: Hz) and 20,000 Hz can be heard by the human ear.
To differentiate these frequencies, the receptors for high tones are at the beginning of the canal, those for the low tones at the apex of the cochlea.

Information and ideas:
The illustration is suitable for explaining or revising fundamentals of Physics like sound, frequency and vibrations.
Usable in a worksheet, for work together on the digital projector, or as an overhead transparency.

Further information regarding this graphic is available on the media portal of the Siemens Stiftung.

Relevant for teaching:
The human body
Structure and function of a sense organ
Perception of sound
Human hearing ability
Communication and understanding

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Siemens Stiftung

The singing wine glass

Photo:
Rubbing a wine glass can produce tones.

If you rub along the rim of a wineglass with a wet finger this produces a tone. As soon as the glass produces a tone, short-wave marginal waves appear in the liquid. The glass oscillates back and forth at those places at which the waves occur. Between them it is still. The oscillation of the glass is not only transferred to the liquid but also to the air and in this way reaches our ear in the form of a fine tone.

Information and ideas:
This experiment can be done easily in class - the class might even make a glass harmonica on their own?
Further information on this photo is available as information sheet on the media portal of the Siemens Stiftung.

Relevant for teaching:
Acoustic phenomena
Sound/acoustics: parameters
Vibrations and waves

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Siemens Stiftung

Frequency differentiation in the uncurled cochlea

Labeled graphic:
High-pitched tones are heard in the front part of the cochlea, low tones are heard in the back part.

As the sense of hearing is able to differentiate locations of the nerves, it is able to recognize the frequencies.

Information and ideas:
This graphic is good for creating a link between the topics of "Sound? and "Hearing?.
Further information regarding this graphic is available as information sheet on the media portal of the Siemens Stiftung.

Relevant for teaching:
Perception of sound
Human hearing ability
Communication and understanding
The human body
Structure and functions of a sensory organ

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Siemens Stiftung

The Ear, Hearing and Hearing Impairment; Teaching unit: From the drum to the eardrum: Resonance body piano

Photo:
Grand piano and piano are good examples of the great significance of resonance bodies with regard to volume and sound.

The frame and the air in the piano vibrate in resonance with the string that has just been struck. Whereas the more modern grand piano "fills" whole concert halls, its historical predecessor, the spinet, is just loud enough for the living-room. Apart from the volume the tone colour of the spinet is also much thinner. This comparison makes the importance of the resonance body very clear - both generally in the production of sound and specifically in music.

Information and ideas:
A practical example from the field of music shows how important the subjects of Physics and Acoustics are for the world of art and communication.

Relevant for teaching:
Sound/acoustics: parameters
Vibrations and waves