How do vinyl records and record players work?

Vinyl records fell out of use following the introduction of Compact Discs. However, they are still made in limited numbers, as are record players.

A vinyl record contains a long spiral groove on each side. The sound is encoded into this groove by “wiggling” the groove from side to side in proportion to the sound wave, starting at the outside edge of the record and working inwards.

When the record is played, a pickup transforms the lateral wiggles into an electrical signal which is amplified and played back through headphones or loudspeakers. Inexpensive pickups consist of a sapphire stylus which tracks the groove and is connected to a ceramic piezoelectric material which turns the movement into a tiny electrical voltage.

Because the contact area of the stylus tip is very small, there is massive pressure at the point of contact and a diamond stylus can be used to obtain a longer life than a sapphire stylus will provide. Even a diamond stylus is considered a consumable item which must be replaced from time to time to maintain sound quality, and to avoid damaging the records.

More expensive pickups attach a magnet to the stylus and surround it with a coil which has an electric current induced into it by the movement of the magnet. It’s also possible to reverse this arrangement and use a moving coil pickup, where the coil is attached to the stylus and the magnet is fixed.

The pickup is attached to the tone arm, which carries it along the spiral of the grooves. This arm can be connected to a mechanism which can lower it into position at the start of the record, and return it to its rest stand at the end of playback.

Records come in various sizes, and are designed to rotate at different speeds. A single holds a few minutes of music on each side, and is commonly 7 inches diameter and must be spun at 45 revolutions per minute (rpm). An LP, or “long playing album”, holds 20 or 30 minutes of music on each side, and is 12 inches diameter. An LP is played at 33 and 1/3 rpm. Most record players have a speed selector switch.

Other combinations exist, such as 12 inch 45 rpm records for disco use, and also 10 inch records. A small number of spoken voice records were produced at 16 and 2/3 rpm.

Older records (pre-1960) played at 78 r.p.m. and were made from shellac instead of vinyl. they were usually 10 inches (3 minutes per side) or 12 inches (5 minutes per side)

To avoid loud bass notes causing one groove to “cut across” the next, the bass was de-emphasized and the treble was enhanced. This equalization needed to be reversed after playback. The standard equalization curve was known as “RIAA equalization“.

Stereophonic records (containing two audio channels) were encoded by modulating each side of the groove separately, and at 45 degrees to the vertical. One side of the groove carried the left channel and the other side carried the right channel. In this way, the sum of the channels produces horizontal movement which can be reproduced on monaural (mono) equipment, while stereo equipment has a pickup with two piezoelectric strips or coils (at right angles to each other) so that each channel can be decoded and amplified separately.

Record players were available that could play a stack of up to six sides in sequence; these were known as record changers.

Records suffered from being easily scratched, which could render them unplayable. They also attracted dust into the grooves which produced “clicks” and “pops” on playback. Slight misalignment between the left and right channels in the pickup could lead to crosstalk (the signal from one channel also appearing to some extent on the other channel), and the whole process of mechanical reproduction introduced various kinds of distortion.

The record player could introduce additional artifacts, such as “wow” (variation in rotational speed due to changes in the belt drive tension), “flutter” (faster variations due to motor irregularities), and “rumble” (vibrations from the motor being transferred to the pickup). The stylus could also “jump” from one groove to another if the record player was bumped (or even if someone jumped on the floor nearby), and a damaged groove could cause the record player to “skip”, playing the same groove over and over again.

So it was not surprising that the compact disc rapidly replaced the vinyl record. A few people still collect vinyl because they like its distinctive soft distortion (”analog sound”) as opposed to the sometimes-harsh clarity of the CD, but it’s a niche market.

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