Phono EQ Origins and Design Elements:
Phono playback has come a long way from wind-up phonographs/gramophones. Before 1925, all shellac discs, whether 78, 80 RPM, faster or slower, the cylinders or discs were recorded acoustically. The musicians would gather around the bell of the horn, used as the only studio recording microphone, while the truncated throat of the horn housed a semi-flexible membrane with a centered, cutting stylus used to “cut” the foil, wax, or later lacquer discs in this "direct to disc" fashion. With the pre-1925 discs, the membrane/cutting needle was the “transducer” converting acoustical energy to mechanical energy, cutting a continuous groove onto the master disc. In acoustic record manufacturing, this wax disc was first coated, electroplated metallically, becoming the mother disc with a “negative” of the grooves, thus bulging, squiggly hills, processed to create one of the disc stampers. Two metal stampers were used to “press” a biscuit of shellac, and later vinylite, into the two sides of 78s, hydraulic pressure sandwiched together, for a “single” disc. As the record companies needed more copies to sell, their first or second generation master disc was used again to create fresh stampers, since the stampers do wear out. The above description is an over-simplification of quite the manufacturing wizardry.
During playback in the home, in essence the acoustic wind-up phonograph horn was an “acoustical equalizer” for the acoustically recorded discs, hopefully recreating all of the recorded sounds of all the instruments/performers surrounding the horn during the recording session. That was a bit too much to ask. During recording, there was no volume control, no equalizer, no audio electronics. Many early disc collectors treasure their acoustical reproducer, horn equipped phonographs. Some shellac collectors even shun the idea of playing these discs through more modern playback systems.
Let us explore some more mono disc chronology. Then, we can realize how we can reproduce these pre-1925 discs, electronically, yielding an even higher fidelity than using acoustic reproducer equipment, as well as increasing our enjoyment with later, electrically recorded discs.
Figure 1, below is a very informative frequency response graph of an early Victor acoustic phonograph, recorded with a 500 cps Turnover:
allegedly recorded at a state of the art sound studio, circa 1953, as seen in Audio Engineering, Vol. 37 #7, July 1953, pages 19-22 and 53-54 in author R.C. Moyer’s famous “Evolution of a Playback Curve” composition on behalf of RCA engineering, almost one year after RCA introduces the “New Orthophonic” EQ curve.
Note that there is very little “flat frequency response” indicated in this “musical snap shot” looking graph. In fact, this is a dismal, jagged response. The recording used had a wider response pressed onto the shellac disc, but the Fig. 1 graph represents the response of the wind-up, acoustical horn equipped phonograph “system.”
Before the recording studios converted to electrically recorded discs in 1925, disc response was presumed to have little or no extreme bass below 150Hz and rarely anything above 5000 Hz. Considering that later era Bell Telephones had a response of 300 to 3000 Hz, designed for intelligibility of the spoken words and recognition/identification of the speaker’s voice, acoustic phonographs could still present even higher fidelity, acoustically.
Phono playback has come a long way from wind-up phonographs/gramophones. Before 1925, all shellac discs, whether 78, 80 RPM, faster or slower, the cylinders or discs were recorded acoustically. The musicians would gather around the bell of the horn, used as the only studio recording microphone, while the truncated throat of the horn housed a semi-flexible membrane with a centered, cutting stylus used to “cut” the foil, wax, or later lacquer discs in this "direct to disc" fashion. With the pre-1925 discs, the membrane/cutting needle was the “transducer” converting acoustical energy to mechanical energy, cutting a continuous groove onto the master disc. In acoustic record manufacturing, this wax disc was first coated, electroplated metallically, becoming the mother disc with a “negative” of the grooves, thus bulging, squiggly hills, processed to create one of the disc stampers. Two metal stampers were used to “press” a biscuit of shellac, and later vinylite, into the two sides of 78s, hydraulic pressure sandwiched together, for a “single” disc. As the record companies needed more copies to sell, their first or second generation master disc was used again to create fresh stampers, since the stampers do wear out. The above description is an over-simplification of quite the manufacturing wizardry.
During playback in the home, in essence the acoustic wind-up phonograph horn was an “acoustical equalizer” for the acoustically recorded discs, hopefully recreating all of the recorded sounds of all the instruments/performers surrounding the horn during the recording session. That was a bit too much to ask. During recording, there was no volume control, no equalizer, no audio electronics. Many early disc collectors treasure their acoustical reproducer, horn equipped phonographs. Some shellac collectors even shun the idea of playing these discs through more modern playback systems.
Let us explore some more mono disc chronology. Then, we can realize how we can reproduce these pre-1925 discs, electronically, yielding an even higher fidelity than using acoustic reproducer equipment, as well as increasing our enjoyment with later, electrically recorded discs.
Figure 1, below is a very informative frequency response graph of an early Victor acoustic phonograph, recorded with a 500 cps Turnover:
allegedly recorded at a state of the art sound studio, circa 1953, as seen in Audio Engineering, Vol. 37 #7, July 1953, pages 19-22 and 53-54 in author R.C. Moyer’s famous “Evolution of a Playback Curve” composition on behalf of RCA engineering, almost one year after RCA introduces the “New Orthophonic” EQ curve.
Note that there is very little “flat frequency response” indicated in this “musical snap shot” looking graph. In fact, this is a dismal, jagged response. The recording used had a wider response pressed onto the shellac disc, but the Fig. 1 graph represents the response of the wind-up, acoustical horn equipped phonograph “system.”
Before the recording studios converted to electrically recorded discs in 1925, disc response was presumed to have little or no extreme bass below 150Hz and rarely anything above 5000 Hz. Considering that later era Bell Telephones had a response of 300 to 3000 Hz, designed for intelligibility of the spoken words and recognition/identification of the speaker’s voice, acoustic phonographs could still present even higher fidelity, acoustically.
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