Brief description

The phonograph is a device for the mechanical recording and reproduction of sound. It works by converting sound waves into physical vibrations that are etched into a rotating cylinder or disc, which can then be played back by tracing the grooves with a stylus.

Use / Function

• Primary use: Sound recording and playback.
• Secondary uses: Preserving oral history, entertainment (music), office dictation.
• Scale: Domestic and professional.

Operating principle

Acoustic-Mechanical Transduction:

1. Recording:
   • Sound waves enter a horn and strike a flexible diaphragm.
   • The diaphragm vibrates in sympathy with the sound waves.
   • A sharp stylus attached to the diaphragm cuts a varying groove into a rotating cylinder (covered in tin foil or wax).
2. Playback:
   • A stylus (connected to a diaphragm) traces the pre-cut grooves on the rotating cylinder.
   • The physical bumps in the groove cause the stylus and diaphragm to vibrate.
   • These vibrations move the air, which is amplified by the horn to recreate the original sound.

How to create it

1. The Rotating Mandrel

• Build a cylindrical drum (mandrel) that can be rotated smoothly by a hand crank or weight-driven motor.
• The mandrel should move laterally as it rotates (using a screw thread) so the stylus traces a spiral path.

2. The Recording Medium

• Tin Foil: Wrap a sheet of tin foil tightly around a grooved metal cylinder. The stylus indents the foil into the grooves.
• Wax Cylinder: A thick cylinder of hard wax is more durable and allows for deeper, clearer recording.

3. The Reproducer/Recorder

• Construct a shallow, circular chamber (the sound box) with a thin, flexible diaphragm (made of mica, thin metal, or treated paper).
• Attach a stylus (a sapphire or hard metal needle) to the center of the diaphragm.
• Connect a large conical horn to the sound box to concentrate sound during recording and amplify it during playback.

Materials needed

• Wood: For the base, frame, and horn.
• Metal (Brass, Iron, Steel): For the mandrel, screw threads, and stylus.
• Tin Foil or Wax (Beeswax/Paraffin mixture): For the recording surface.
• Mica or Thin Aluminum: For the diaphragm.

Variants and improvements

• Gramophone: Uses flat discs instead of cylinders, which are easier to mass-produce by stamping.
• Spring Motors: Replaced hand cranks for a more consistent rotation speed (essential for correct pitch).
• Electric Recording: Later versions used microphones and amplifiers to drive the stylus, vastly improving frequency response.

Limits and risks

• Sound Quality: Early mechanical versions have limited frequency range and significant background noise (surface hiss).
• Fragility: Wax cylinders are brittle and can mold. Tin foil recordings are ruined after only a few playbacks.
• Speed Consistency: Variations in rotation speed (wow and flutter) cause pitch distortion.

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