Vintage Griffin & George Sonometer

£ 18.00
This Griffin & George Sonometer is ideal for demonstrating the effect of length, tension, diameter, and material on the pitch of a vibrating string. At its core, the sonometer is a 1.14 metre long hollow wooden box with metre rules, support struts and fastenings on either end. Strings can be rigidly attached to the fastenings, with provisions to changing the tension.
Several experiments are possible with this;
1) Show that the frequency varies inversely as the length of the vibrating string: The length of each string can be changed by moving a bridge under it. If the string is plucked near one end and stopped at 1/2, 1/3, 1/4, 1/5, etc, of its length, the 2nd, 3rd, 4th, 5th, etc. harmonics will be sounded. If a sharp-edged piece of soft rubber (an eraser) is used to stop the string, it is possible to make 10 or more harmonics audible.
2) Intervals: If you make the string 2/3 of its original length, the pitch rises exactly a perfect fifth, a fraction 3/2 above its original frequency. If you make the length 3/4 as long, the pitch rises a perfect fourth, or a fraction 4/3 above what it was.
3) The frequency varies directly as the square root of the tension: The string passes over a pulley and the tension is provided by hanging a weight from the end of the string ... quadruple the weight to secure twice the frequency.
4) Finally, the frequency varies inversely as the square root of the mass per unit length of the string. We have a small selection of wire sizes to show this.
This Griffin & George Sonometer is ideal for demonstrating the effect of length, tension, diameter, and material on the pitch of a vibrating string. At its core, the sonometer is a 1.14 metre long hollow wooden box with metre rules, support struts and fastenings on either end. Strings can be rigidly attached to the fastenings, with provisions to changing the tension.
Several experiments are possible with this;
1) Show that the frequency varies inversely as the length of the vibrating string: The length of each string can be changed by moving a bridge under it. If the string is plucked near one end and stopped at 1/2, 1/3, 1/4, 1/5, etc, of its length, the 2nd, 3rd, 4th, 5th, etc. harmonics will be sounded. If a sharp-edged piece of soft rubber (an eraser) is used to stop the string, it is possible to make 10 or more harmonics audible.
2) Intervals: If you make the string 2/3 of its original length, the pitch rises exactly a perfect fifth, a fraction 3/2 above its original frequency. If you make the length 3/4 as long, the pitch rises a perfect fourth, or a fraction 4/3 above what it was.
3) The frequency varies directly as the square root of the tension: The string passes over a pulley and the tension is provided by hanging a weight from the end of the string ... quadruple the weight to secure twice the frequency.
4) Finally, the frequency varies inversely as the square root of the mass per unit length of the string. We have a small selection of wire sizes to show this.