BRUEL & KJAER BEAT FREQUENCY OSCILLATOR 1022. FREQUENCY RESPONSE TRACER 4709 & LEVEL RECORDER 2305., 1960's

The Bruel & Kjaer Beat Frequency Oscillator (back left) is part of a system known as the 'Electroacoustic Telephone Measuring system'. The Manual reads: - ''Covering the range 20 to 20000 Hz (cycles). The Apparatus is designed to meet the numerous requirements of a signal source for audio frequency work. It is excellently suited both for electrical and electroacoustical measurements as well as for acoustic research''. The system basically has two oscillators one at a fixed frequency the other variable, the two signals are then mixed, the required frequency is then obtained as the difference between the two frequencies and can be read off a large illuminated scale. This unit is used with the Frequency Response Tracer and the Level Recorder. The whole system was used with the Microphones Item A1864.
The Frequency Response Tracer (back right) is part of a system known as the 'Electroacoustic Telephone Measuring system'. This s a Visual Display Unit for use with other equipment such as the Beat Frequency Oscillator Item A1882. It has nine valves, a graticule on the screen as well as a plastic overlay for tracing the curve produced. This item would have been used with the microphones Item A1864.
The Level Recorder (front right) is part of a system known as the 'Electroacoustic Telephone Measuring system'. Its primary purpose is to print the results of equipment such as the Beat Frequency Oscillator. This item would have been used with the microphones Item A1864.

Donated by John Barnes

A1882