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Description
Musical instruments rely upon vibrating elements to produce their musical notes. Stuart Freake takes this theme and points out that the programme will concentrate on the phenomena of resonance and... forced vibration, using principally the violin as illustration. But to start, a number of musical instruments are reviewed to show the role of strings, air columns, plates and membranes, and the nature of the restoring force involved when each is displaced The factors controlling the frequency of vibration are reviewed, with special emphasis on vibrating strings. Using a mute violin, Keith Hodgkinson shows that there is more to a violin than just the strings, the sound needs amplification. A sound board can help and some sound boards appear better than others. A laser doppler system developed by Rola-Celestion Ltd is employed to show the effect of forcing a thin sound board to vibrate over a range of frequencies and the effect of resonance is apparent. The effect is demonstrated again using a series of driven pendulums of varying length. But what determines the width of resonance? Keith gives two simple demonstrations, and hypothosises that it is controlled by the amount of damping in the system. This hypothesis is borne out by comparing a set of damped pendulums with the earlier undamped ones. But a violin needs to amplify frequencies over a wide range. The laser doppler demo demonstrates that a simple plate can vibrate in a number of modes and so will amplify at these frequencies. Keith explains how the more complex shaped violin plate will have yet more natural modes and that when a violin is assembled the resulting system of plates and air cavity have a large number of resonances distributed through the audio range. However, the relation between the complex pattern of resonance and the subjective judgment of tonal quality is not yet fully understood, but scientists are working on it and may be able to help the craftsman in the future.
Musical instruments rely upon vibrating elements to produce their musical notes. Stuart Freake takes this theme and points out that the programme will concentrate on the phenomena of resonance and... forced vibration, using principally the violin as illustration. But to start, a number of musical instruments are reviewed to show the role of strings, air columns, plates and membranes, and the nature of the restoring force involved when each is displaced The factors controlling the frequency of vibration are reviewed, with special emphasis on vibrating strings. Using a mute violin, Keith Hodgkinson shows that there is more to a violin than just the strings, the sound needs amplification. A sound board can help and some sound boards appear better than others. A laser doppler system developed by Rola-Celestion Ltd is employed to show the effect of forcing a thin sound board to vibrate over a range of frequencies and the effect of resonance is apparent. The effect is demonstrated again using a series of driven pendulums of varying length. But what determines the width of resonance? Keith gives two simple demonstrations, and hypothosises that it is controlled by the amount of damping in the system. This hypothesis is borne out by comparing a set of damped pendulums with the earlier undamped ones. But a violin needs to amplify frequencies over a wide range. The laser doppler demo demonstrates that a simple plate can vibrate in a number of modes and so will amplify at these frequencies. Keith explains how the more complex shaped violin plate will have yet more natural modes and that when a violin is assembled the resulting system of plates and air cavity have a large number of resonances distributed through the audio range. However, the relation between the complex pattern of resonance and the subjective judgment of tonal quality is not yet fully understood, but scientists are working on it and may be able to help the craftsman in the future.
| Module code and title: | S271, Discovering physics |
|---|---|
| Item code: | S271; 09 |
| First transmission date: | 16-06-1982 |
| Published: | 1982 |
| Rights Statement: | |
| Restrictions on use: | |
| Duration: | 00:25:00 |
| + Show more... | |
| Producer: | John Stratford |
| Contributors: | Stuart Freake; Keith Hodgkinson |
| Publisher: | BBC Open University |
| Keyword(s): | Air columns; Laser doppler system; Membranes; Musical instruments; Pendulums; Plates; Resonance; Rola-Celestion Ltd.; Sound board; Violin strings |
| Production number: | FOUS234D |
| Videofinder number: | 1788 |
| Available to public: | no |
