Back to Basics

Audio Minus 80

Books on audio weren’t plentiful 80 years ago, but the 1940 edition of Audels New Radioman’s Guide gives a glimpse of everyday audio back then. As the title suggests, the book is basically devoted to the theory, construction, and servicing of radios, including aircraft and marine radio, and even television.  Many of its 34 chapters cover such fundamentals as power supplies, vacuum tubes, coil calculations, test instruments, and batteries. Only four directly concern audio: Physics of Sound, Loud Speakers, Phonograph Pick-Ups, and Public Address Systems. Skimming the radio chapters, I see no mention of FM except for one FM radio schematic in the chapter of radio schematic diagrams. (FM broadcasting had already begun, but FM radios weren’t very common.)

It’s an interesting look into the state of audio back then, parts of it surprisingly modern and other parts emphatically not. Here are some highlights:

Speakers: I was surprised to discover that the book covered electrostatic as well as magnetic speakers—and even more surprised that it covered five other types little known today. Most common of those was the electrodynamic type, basically the same as the magnetic, but using electromagnets rather than permanent magnets.

Balanced-armature construction (now found on many earbuds), said author E.P. Anderson, completely eliminated “chattering on loud signals, usually encountered in the magnetic type.” However, making it sensitive required such small air gaps between the voice coil and magnet that the coil might strike the magnet on loud bass notes, “emitting a rattling sound.” This is probably not a problem for earbuds, due to the much lower signal levels they handle.

Piezoelectric speakers used crystals that expanded and contracted with the signal’s fluctuations. They were “often used in connection with high-frequency reproduction.” “Metal strip” speakers (presumably what we’d call “ribbon” speakers now) and “induction” speakers were merely described.

The book explains why baffles are needed and how to calculate their size, but doesn’t discuss anything but flat-plane and backless baffles – no sealed or ported enclosures.

Phonographs: This being a “radioman’s” handbook, it considers a phonograph as a device converting needle vibrations into audio “for reproduction through a radio receiver.” The “modern phonograph pick-up unit” illustrated looks clunky by today’s standards, but not much more so than the Webcor changer my Dad bought in the early ‘50s.

Of the four pickup cartridge types mentioned (condenser, carbon resistance, magnetic, and crystal), I’d expected piezoelectric crystal pickups to be emphasized. Crystal and, later, ceramic piezo cartridges predominated on simple phonographs for decades (our 1956 Webcor had one) because they were inexpensive and produced reasonably musical results without equalization. However, moving-coil magnetic pickups were covered in more depth; I guess moving-magnet types had to await stronger magnetic materials than were then available.

Styli were straight needles, held in by a set-screw for easy replacement. They must have needed replacement often: needles weren’t diamond-tipped, back then, and records were “made of hard materials, and . . . possess abrasive qualities sufficient to grind the needle point at the beginning of its travel in order to reduce the pressure of the needle.” More expensive radio-phonographs also had scratch filters.

Most records were 78 rpm, with 10-inch discs playing for 2-1/2 minutes and 12-inch discs playing 4 minutes. But some turntables also played at 33-1/3 rpm for 16-inch discs (“employed in sound picture work,”) that played for about 14 minutes.

Fidelity? What’s that? Nowhere did I see any mention of distortion—even push-pull amplifiers are touted as producing higher power, not cleaner sound. The lone frequency-response graph, for “a typical radio receiver,” shows audio response down about 15 dB at 5 kHz for the upper reaches of the AM radio band, and -25 dB at a station frequency of 600 kHz. (Not that “kHz” wasn’t in use, yet—they said “kilocycles per second,” back then.)

But though the Guide doesn’t mention it, progress toward higher fidelity had been going on for years. Stromberg-Carlson, for example, offered console radios with acoustical labyrinth speaker enclosures, essentially bass-reflex designs partitioned to form a long, folded tube that delayed the rear-wave from the speaker to prevent low-frequency cancellation. The U.S. Radio model 10-C was “equipped with 2 dynamic speakers (one tuned for bass—one for treble)”; both speakers were the same size, though, which would have restricted off-axis treble propagation. E.H. Scott Radio Laboratories (no relation to H.H. Scott) boasted “high-fidelity reproduction,” adding “you will hear tones you did not realize were there . . . . music . . . can now be heard with a faithfulness that will thrill every fibre of your being.” Companies such as E.H. Scott and Capehart were predecessors of today’s audio high-end, with exacting attention paid to audio, radio performance and (in Capehart’s case) exquisite cabinets.

Interest in improved home audio didn’t become widespread until after World War II, when thousands of people educated in electronics by the military came home, and war-surplus electronics were on sale all over. Soon, there was a hi-fi industry, based on specialized components rather than console systems. By the 1950s, the term was so well-known that Max Factor brought out a “Hi-Fi Lipstick.”

She wore her new Max Factor!