Various measurements on audio equipment. by jimmy67music. A classic reprint of the famous Norman Crowhurst book that is a complete compendium of measurement and testing techniques for audio equipment including. AUDIO MEASUREMENTS. by Crowhurst, Norman H. Edition: First Edition; First Printing. Book Description. New York: Gernsback Library, Inc.. First Edition .

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What is a cathode follower?

Not only does the loudspeaker impedance have to be matched to the amplifier output impedance, but the output impedance of the amplifier affects the operation of the speaker.

Other supplies are sometimes used ; for example, in aircraft, where the frequency is not 60 cycles, but cycles, and in automobiles, where the supply is not measurrements but d-c, at 6 or 12 volts from a battery. This means the gain and distortion will ajdio divided by 5.

A.R.C. Marketplace: Audio Measurements by Norman Crowhurst

Search the history of over billion web pages on the Internet. As a practical amplifier has frequency limitations and eventually loses gain completely at extreme frequencies, it cannot fol- low any of these constant-gain lines circles all the way. It is all possible due to the form that individual hearing perception takes in its transmission from the individual ears to the brain. The choke has to have a fluctuating current, however small, to pro- duce the fluctuating voltage across its terminals.

To overcome the fact that the extremely small movement, above, say 10, cycles, would mean that the surface noise would be louder than the audio, constant amplitude is also applied above a fre- quency of 2, cycles. Again horman an input resistance ofohms and an input current of 0.

If one sound is stronger at one ear than the other, the apparent direction is toward the side where it normwn received the strongest.

Hence, the gain margin is probably measurments the most value in asses- sing the performance of an amplifier. Two kinds of rectifier are used for audio amplifier circuits: It has an internal resistance due to the plate resistance of the output tubes of 5 ohms. How can it be avoided?

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If, however, the response is uniform up to the highest frequency in which we are interested, say 10, or 20, cycles, and then at some frequency after that rises up to a peak, ringing occurs. Shielding prevents what three kinds of induction? A low source resistance will prevent the voice coil overshooting, while a high source resistance will allow the voice coil to move erratically and affect the transient response of the loudspeaker.

It may be a record of the vibrations that occur in different parts of a supersonic missile in flight or a record of the progress of a certain in- dustrial process that requires careful comparison of the results of the pro- cess in successive hour periods.

Why make it difficult? This results in a double-frequency current in the cathode resistor, because of the asym- metrical current waveforms in the tubes. Any transformer will radiate some magnetic field. What are the essential features and characteristics of a magnetic, b electromagnetic, and c electric shielding?

Describe the action of a special type of tube that is used to provide automatic volume control electronically. If the rectifier is fed straight into a resistance load, the output waveform will be either a succession of half-waves, with a gap for each alternate half-wave, or if full-wave rectification is used, a succession of half-waves end to end.

This means we get a rising response all the way up to a certain frequency which is dependent on the width of the air gap and the speed of tape travelwhich falls off very suddenly to zero. In a smaller room, where reverberation is almost absent and by the very size of the room, intensity must equalize somewhatthe hearing faculty gets extra critical about time differences.

Without feedback, the internal resistance was 5 ohms; with feedback it is 1 ohm. Ringing can cause other crkwhurst in an amplifier in addition to unwanted oscillation on the corners of a square wave. This attention is not necessary at the output stage, where there may be volts or more audio, so we can use the simple smoothing circuit there.

They will need a basic education in audio to enable them to add horman contribution to progress and to earn themselves a living! If the voltage fluctuation fed back caused the cathode of the first tube to move negative by as much as the positive initial fluctuation at its grid, oscil- lation would take place. The usual cause of distortion to square waves is the way in which amplifica- tion varies at high frequencies.


Turning a phonograph record faster raises all the frequencies by the same ratio, and the pitch steps up by a constant tone interval. Unfortunately, we cannot solve this problem by using a smaller cathode re- sistor because it would result in too high a current in the tubes when no signal was passing.

The measurement circuit is here and the measurements are here. Hence borman need further smoothing action to get an adequately smooth or steady d-c and to avoid producing hum in the amplifier. Current in plate circuit used to maintain, induced current in tuned grid circuit.

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Audio Measurements, by Norman H. Crowhurst | The Online Books Page

It has, however, the disadvantage that the whole of the current drain has to be passed through the rectifier in a small fraction of one half of the cycle.

This, to some extent, recreates the original time and phase differences that set up the directional effect in the sound waves. This impedance is only a small fraction of the total impedance of the loudspeaker, most of which is due to the resistance and inductance of the voice coil. It is, of course, good to use a consistent impedance in any particular system. Unless a very heavy gage is used, the line will have a resistance of about one ohm crowhhrst every 50 feet.

All amplifiers possess some reactance, such as coupling capacitors, which aiFFect the low-frequency response, and stray capacitances, which affect the high-frequency response.

The disadvantage is that, if the screen current should vary which it audo under certain conditionsthe screen potential will also vary, because of the change in voltage drop across the feed resistor.