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Audio Design Handbook by H. A. Hartley (1958)

“AUDIO DESIGN HANDBOOK” by H.A. Hartley (1958, 226 pages, Gernsback Library No. 71).


The aim of this book is to bring together in compact form all the material necessary for designing an audio installation of the type known as high fidelity. Within the limitations of one volume it is impossible for it to be complete; nor is it necessary that it should be so.

There is a vast amount of matter available for reference and study. Apart from the numerous books treating high fidelity as a separate branch of audio engineering, there is the whole range of standard textbooks and innumerable articles in the technical magazines. Some of these are of very great value and the student, engineer and purely amateur enthusiast should not fail to refer to the various indexes published annually listing what has been written. Yet it has to be said that there is an even vaster accumulation of writing on the subject that, while having technical integrity, does not seem to have much practical value.

What value has this book, then, when so much has already been written? The answer to that stems from a conversation I had with the publisher some three years ago. We were discussing various books and scientific papers and he said that he found it very difficult to steer a steady course through so much material-and so many shoals. I said that I, too, had sometimes had to hunt through masses of stuff to get hold of some fact I wanted and very often didnt find it. There and then we resolved to compile a book which would be a handy data book for those interested in audio.

The work was started but before very long we came, independently, to the conclusion that what was wanted was not so much a data book as a guide book, something that would describe how the job was done, with emphasis on the need for the designer to have a clear idea in his mind what he wanted to do before he started in to do it.

This meant that a good deal of the material already got together had to be scrapped and other material fashioned into the new approach. This accounts for the long delay between the original announcement of the book and its actual appearance. While apologizing to those who have been so patient, I think I can fairly say that the book will be more useful to them in its present form.

I describe how my more than 30 years experience in audio engineering suggests a problem in design should be tackled. I also add from time to time some comments on blind alleys I have explored, and I conclude with a wholly personal chapter on where I think we are all going and why we shouldnt go there! These past 8 years have been exciting years for all audio workers, but because, in the continual search for novelty, certain ideas are being exploited which were tried and rejected thirty years ago (but which are unknown to younger readers), a good-natured word of warning here and there seems desirable.

I have not attempted a thorough treatise on speakers and enclosures. The subject is far too vast even for a whole volume. Meanwhile I offer this book as, I hope, a dependable guide through the intricacies of audio, and where it fails I shall be grateful for comment and criticism and suggestions for its improvement.


Chapter 1: Perception of Sound

Characteristics of musical instruments. Harmonic range of various sound sources. Harmonics. The frequency range of the chief musical instruments. Characteristics of the human ear. Loudness and intensity. Ear response vs. volume level. Phonic level. Interference. Standing waves. Masking effect. Combination or Subjective tones. Reaction of the ear to complex sounds. Basic requirements for fidelity of reproduction. The listening room. The music room.

Chapter 2: Audio Amplifiers: The Output Stage

Design considerations. Power output stages. Triodes vs tetrodes Tube transconductance. Power supply stabilization Single-triode output stages Single-tetrode output stages. Power output and harmonic distortion. Push-pull triode output stages. Matching tubes. Push-pull tetrode output stages. Class B and class AB output stages. Output triodes in class A. Push-pull operating conditions of output triodes. Push-pull operating conditions of output tetrodes.

Chapter 3: Audio Amplifiers: Inverters and Drivers

Inductive phase splitters. Stage gain. High permeability cores. Center-tapped choke. Vacuum-tube phase splitters. Self-balancing inverter. Schmitt inverter. Split-load phase inverter. Balancing circuit components. Split-load inverter with direct-coupled amplifier. Size of components in plate and grid circuits of the direct-coupled amplifier. Cathode-coupled phase inverter. Drivers. Transformer coupling. Overall gain. Instability. Push-pull drivers. Design sequence.

Chapter 4: Audio Amplifiers: Voltage Amplification

Resistance-capacitance-coupled triodes. Source impedance. Grid-to-cathode impedance. Input resistance. Coupling capacitors. Motorboating. Signal and supply voltage requirements. Resistance-capacitance-coupled pentodes. High-frequency attenuation. Value of the plate load. Bass amplification. Techniques for applying screen voltage. Decoupling. Resistance-capacitance-coupled phase inverters.

Chapter 5: Amplifier Design

Selecting a phase inverter. Checking performance. Checking stage gain. Component tolerance. Use of additional stages. Using negative feedback. Full development of the design for a high-grade 20-watt amplifier. Choosing the output stage. Tube characteristics. Triode vs. tetrode output. Eliminating distortion. Ultra-Linear operation. Positioning the transformer screen-grid taps. Driving voltage required. Power and distortion. The Ultra-Linear transformer.

Chapter 6: Audio Transformers

Iron-cored transformers. Transformer characteristics. Self-capacitance and leakage inductance. Transformer efficiency. Transformer ratios. Design characteristics. Power transformers. Core size. Core materials. Interstage transformers. Output transformers. Methods of winding. Testing and measuring audio transformers. Testing transformer frequency response. Checking interstage transformers. Distortion due to a transformer. Parasitic oscillation. Miller effect.

Chapter 7: Negative Feedback

Positive and negative feedback. Amplifier stability. Phase shift and time constants. Application of negative feedback. Simple current feedback. Cathode-circuit arrangements. Triode-connected tetrodes and pentodes. Single-stage feedback. Feedback across a push-pull stage. Two-stage feedback. Ultrasonic oscillation. Amount of feedback. Bass cut filter. Staggered response. Stabilized feedback amplifier. Bass attenuation and phase-shift nomogram.

Chapter 8: Filters and Tone-Controls

Network components. Active and passive networks. Two- and four terminal networks. Transducers. Low-pass filter. High-pass filter. Bandpass filter. Trap filter. Basic tone control circuit. Attenuation and boosting. Bass cut control. Treble cut control. Circuit Q. Attenuation curves. Rate of attenuation. Simple tone-control amplifier. Terminal impedance. Bass boosting. Amount of boost. Response curves of the tone-control amplifier.

Chapter 9: Amplifier Power Supplies

Half-wave rectifier. Thermionic rectifier. Metal rectifier. Capacitive load. Waveform at the output of the rectifier. Bridge rectifier. Full wave rectifiers and their output waveforms. Voltage doubler. Capacitor input filter. Rectifier output voltage. Choke input filter. Two-stage choke-input filter. Decoupling network using a V-R tube. Decoupling filter. Stabilizing supply using a triode. Iron-cored inductor characteristics. Transformer and choke construction.

Chapter 10: Speakers and Enclosures

Limitations of frequency response curves. Polar curves. Distortion arising from cone deformation. Speaker damping. Loose vs. tight suspension. Power-handling capacity of speakers. Cone materials. Visual appraisal of a speaker. Speaker impedance. Impedance curves of speakers. The baffle and speaker impedance. Summary of design features for baffle-loaded speakers. Bass-reflex enclosure. Dividing networks. Constant-resistance network. Horn-loaded speakers.

Chapter 11: Measurements and Testing

Meters for voltage, current and resistance. Moving coil meter. AC meter. Measuring resistance. Bridges. Vacuum-tube voltmeters. Oscillators and oscilloscopes. Frequency response. Measurement techniques. Interpretation of waveforms. Second harmonic distortion. Third harmonic distortion. Fourth harmonic distortion. Fifth harmonic distortion. Second plus third harmonic distortion. Third plus fifth harmonic distortion. Square wave testing. Phase measurement.

Chapter 12: High Fidelity - Hail and Farewell

High fidelity. Some thoughts on frequency range. Undistorted range. More about speakers. Types of spiders. Tangential arm spider. Free edge suspension. Channels of purity. Speaker coloration. The cone, the coil and distortion. Introducing a compliance into a voice coil. Audio furniture problems. Planned layouts. Possible speaker locations. Bass and baffles. Bass loss with finite baffles. Enclosure resce. Nodal lines in a flat baffle. The Baffle.


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