Audio Range Research Articles

Light Modulation by P-Type Crystals

A means of modulating a light beam with a flat response which greatly exceeds the audio range is described utilizing the linear electrooptic effect in P-type <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">**</sup> crystals. The unit uses parallel polarized light and although it requires relatively high voltages, it draws essentially no current and has no moving parts. From the basic aspects it seems very promising for an efficient yet sturdy variable-density recording system.

Noise Spectrum of Crystal Rectifiers

Studies of the noise spectrum of crystal rectifiers were made over a frequency range of 50 cycles to 1 megacycle. The circuits used in the analysis are described. It was found throughout the range that, regardless of the type of power applied to the crystal, the noise temperature varies inversely with the frequency. The noise in the audio range is always large; a noise temperature ratio of 106is not uncommon. A mechanism responsible for the observed noise has not yet been suggested.

Detection of Resonances in Vibratile Members by Measurement of Electro-Magnetically Induced Voltages

An instrument is described by which the velocity versus frequency characteristics of a conducting filament or similar vibratile member may be detected, regardless of the inaccessibility of the member. The assembly to be studied is submerged in a known magnetic field and subjected to vibration over the audio range. The voltage generated in the vibratile member is amplified and this indicates the integrated vibration velocity of the member.

A New Type of Practical Distortion Meter

This paper gives a description of a distortion meter embodying circuits which differ somewhat from the types previously employed for this type of instrument. It consists essentially of a bridged-T audio-frequency bridge circuit, in which the inductance element is replaced by a reactance-tube circuit. Because of the flexibility obtainable in vacuum-tube circuits, it is a relatively simple matter to vary the effective inductance continuously over a fairly wide range, and thus allow the distortion meter to be used at any frequency in the audio range. Certain precautions must be taken in a circuit of this type in order to avoid difficulties due to nonlinear action of the reactance-tube circuit. Application of negative feedback to the reactance-tube circuit effectively reduces the nonlinearity, increases stability, and at the same time keeps tube noise and hum at a minimum level. An analysis of the reactance part of this circuit, together with formulas for calculating the effective Q and the optimum operating conditions are included. Although the study of the properties of the reactance-tube circuit with negative feedback was limited to features applicable to the problem at hand, some of the information obtained may be of use in other fields.

A System of Frequency Modulation in Audio Range and its Application to the Picture Tnansmission by Radio

A System of Frequency Modulation in Audio Range and its Application to the Picture Tnansmission by Radio

STABILIZED OSCILLOSCOPE WITH AMPLIFIED STABILIZATION

One stage of amplification included in the stabilizing circuit of the Bedell-Reich oscilloscope, which comprises a cathode-ray tube with linear time-axis for observation of periodically varying quantities, extends the frequency range of the instrument and permits stabilization without disturbance to the circuit under test. Although not primarily intended for use beyond the audio range, the instrument has in this way been stabilized above 100,000 cycles. Curves are given showing the use of the instrument for the study of non-electrical quantities (as sound and light) as well as of electrical quantities (as in the study of modulation and rectification).

A Direct Reading Frequency Bridge for the Audio Range, Based on Hay's Bridge Circuit

This paper describes the construction and operation of a direct reading bridge for measuring audio frequencies in the range from 50 to 5000 cycles per second and upwards. The circuit used is a modification of Hay's bridge for the measurement of inductance, and is obtained from it by the insertion of a variable resistance in the inductive arm. This resistance and another in the condenser arm are varied for balance. For the design as given, the frequency in cycles per second is determined by the number of ohms in the variable resistance plus that of the internal resistance of the coil in series with it. The bridge is portable, simple to construct, and makes use of external connection for the variable resistances to two standard decade non-inductive resistance boxes. Its operation is convenient and permits of a precision of balance of 0.1 per cent with a probable error of less than about 0.25 per cent.

The frequency characteristics of telephone systems and audio-frequency apparatus, and their measurement

The value is demonstrated of the frequency/amplitude characteristics of telephone systems or apparatus in determining the transmission efficiency, including volume and articulation efficiency. The audio-frequency ranges of importance for speech and music are then considered.Methods are described for the direct and indirect production of constant acoustic output over the audio range, and the calibration of acoustic measuring instruments is dealt with.The next section of the paper deals with the production of electrical energy of constant value over the required frequency range, and a description is given of a special form of oscillator, together with associated apparatus for the direct recording of frequency characteristics.The concluding part of the paper gives frequency characteristics of each part of the apparatus used in a telephone connection, and also of audio-frequency amplifiers and loud-speakers. For the purely electrical portions of the circuit, current or voltage characteristics are given, whilst for apparatus such as transmitters and receivers the characteristics are given in terms of acoustic pressures on the diaphragm. The characteristics of some commercial types of granular transmitters are first given, then under the heading of receivers will be found the characteristics of both the Bell pattern and some typical loud-speakers of the horn and hornless types. Particulars are given of apparatus designed to measure diaphragm motion, some results obtained by an aural balancing method being included.In the section dealing with lines will be found characteristics for unloaded open wires and cables and for loaded cables. An impedance/frequency characteristic is also given and its application to fault location illustrated.Some notes on telephone line repeater characteristics are included, and the next section deals with exchange cord circuits and subscriber&apos;s instrument characteristics.Under audio-frequency amplifiers some typical intervalve transformers of the type used for broadcast reception are characterized, and an extension is given of the theory of this type of transformer covering the effects of resistance and capacity loads.

The frequency characteristics of telephone systems and audio-frequency apparatus, and their measurement

The value is demonstrated of the frequency/amplitude characteristics of telephone systems or apparatus in determining the transmission efficiency, including volume and articulation efficiency. The audio-frequency ranges of importance for speech and music are then considered.Methods are described for the direct and indirect production of constant acoustic output over the audio range, and the calibration of acoustic measuring instruments is dealt with.The next section of the paper deals with the production of electrical energy of constant value over the required frequency range, and a description is given of a special form of oscillator, together with associated apparatus for the direct recording of frequency characteristics.The concluding part of the paper gives frequency characteristics of each part of the apparatus used in a telephone connection, and also of audio-frequency amplifiers and loudspeakers. For the purely electrical portions of the circuit, current or voltage characteristics are given, whilst for apparatus such as transmitters and receivers the characteristics are given in terms of acoustic pressures on the diaphragm. The characteristics of some commercial types of granular transmitters are first given, then under the heading of receivers will be found the characteristics of both the Bell pattern and some typical loud-speakers of the horn and hornless types. Particulars are given of apparatus designed to measure diaphragm motion, some results obtained by an aural balancing method being included.In the section dealing with lines will be found characteristics for unloaded open wires and cables and for loaded cables. An impedance/frequency characteristic is also given and its application to fault location illustrated.Some notes on telephone line repeater characteristics are included, and the next section deals with exchange cord circuits and subscriber's instrument characteristics.Under audio-frequency amplifiers some typical intervalve transformers of the type used for broadcast reception are characterized, and an extension is given of the theory of this type of transformer covering the effects of resistance and capacity loads.