Phonographic - Styli

Styli

In the sound recording industry, a stylus or needle is a phonograph or gramophone needle used to play back sound on gramophone records, as well as to record the sound indentations on the master record.

The stylus is subject to increased wear as it is the only part of the phonograph that comes into direct contact with the spinning record. There are three desired qualities in a stylus: first, that it faithfully follows the contours of the recorded groove and transfers the vibration to the system, second, that it does not damage the recorded disc, and third, its resistance to wear.

Different materials for the stylus have been used over time. Thomas Edison introduced the use of sapphire in 1892 and the use of diamond in 1910 for his cylinder phonographs. The Edison diamond disc players (1912–1929), when properly played, hardly ever required the stylus to be changed. The latter stylus for vinyl records were also made out of sapphire or diamond. A specific case is the specific stylus type of Bang & Olufsen's (B&O) moving magnet cartridge MMC 20CL, mostly used in parallel arm B&O turntables in the 4002/6000 series. It uses a sapphire stem on which a diamond tip is fixed by a special adhesive. A stylus tip mass as low as 0.3 milligram is the result and full tracking only requires 1 gram of stylus force, reducing record wear even further. Maximum distortion (2nd harmonic) fell below 0.6%.

Other than the Edison models, early disc players (such as external horn phonographs or internal horn "Victrola" style models) required the use of exchangeable needles. The most common material was steel, although other materials such as copper, tungsten, fibre, and cactus needles were used. These needles needed to be replaced often due to the forces exerted by the record. Early advertisements implored customers to replace their steel needles after each record side. Steel needles were sold in packets that varied due to their thickness and length. Thick, shorter needles produced strong loud tones while thinner, longer needles produces softer, muted tones. In 1916, Victor introduced their tungsten-tipped "Tungs-Tone" brand extra longplay needle which was advertised to play between 100 and 300 records. At the end of acoustic 78 rpm, "longplay" hardened steel needles came on the market, which were advertised to play 10-20 sides on a single disc.

When sapphires were introduced for the 78 rpm disk and the LP, they were made by tapering a stem and polishing the end into sphere of around 70 and 25 micrometers respectively. A sphere is not equal to the form of the cutting stylus and by the time diamond needles came to the market, a whole discussion was started on the effect of circular forms moving through a non-circular cut groove. It can be easily shown that vertical, so called "pinching" movements were a result and when the stereophonic LPs were introduced, unwanted vertical modulation was recognized as a problem. Also the needle started its life touching the groove on a very small surface, giving extra wear on the walls.

Another problem is in the tapering along a straight line, while the side of the groove is far from straight. Both problems were attacked together: by polishing the diamond in a certain way that it could be made doubly elliptic. 1) the side was made into one ellipse as seen from behind, meaning the groove touched along a short line and 2) the ellipse form was also polished as seen from above and curvature in the direction of the groove became much smaller than 25 micrometers e.g. 13 micrometers. With this approach a number of irregularities were eliminated. Furthermore, the angle of the stylus which used to be always sloping backwards, was changed into the forward direction, in line with the slope the original cutting stylus possessed. These styli were expensive to produce, but purists accepted these costs all the more, because by now stylus life was much higher than before.

The next development in stylus form came about by the attention to the CD-4 quadraphonic sound modulation process, which requires up to 50 kHz frequency response, with cartridges like Technics EPC-100CMK4 capable of playback on frequencies up to 100 kHz. This requires a stylus with a narrow side radius, such as 5 µm (or 0.2 mil). A narrow-profile elliptical stylus is able to read the higher frequencies (greater than 20 kHz), but at an increased wear, since the contact surface is narrower. For overcoming this problem, the Shibata stylus was invented around 1972 in Japan by Norio Shibata of JVC, fitted as standard on quadraphonic cartridges, and marketed as an extra on some high-end cartridges.

The Shibata-designed stylus offers a greater contact surface with the groove, which in turn means less pressure over the vinyl surface and thus less wear. A positive side effect is that the greater contact surface also means the stylus will read sections of the vinyl which were not touched (or "worn") by the common spherical stylus. In a demonstration by JVC records "worn" after 500 plays at a relatively very high 4.5 gf tracking force with a spherical stylus, played "as new" with the Shibata profile.

Other advanced stylus shapes appeared following the same goal of increasing contact surface, improving on the Shibata. Chronologically: "Hughes" Shibata variant (1975), "Ogura" (1978), Van den Hul (1982). These styli are marketed as "Hyperelliptical" (Shure), "Alliptic", "Fine Line" (Ortofon), "Line contact" (Audio Technica), "Polyhedron", "LAC", and "Stereohedron" (Stanton).

A keel-shaped diamond stylus appeared as a byproduct of the invention of the CED Videodisc. This, together with laser-diamond-cutting technologies, made possible "ridge" shaped styli such as the Namiki (1985) design, and Fritz Gyger (1989) design. These styli are marketed as "MicroLine" (Audio technica), "Micro-Ridge" (Shure), "Replicant" (Ortofon).

It is important to point out that most of those stylus profiles are still being manufactured and sold, together with the more common spherical and elliptical profiles, despite the CD4 quadraphonic system being a marketing flop.