background image

vinyl and the tip of the stylus. In
general terms, as we’re already seen,
there is a groove with two walls that
vary in height, almost independently
and the tip of the stylus traces that
movement accordingly. However, it is
necessary to get down to the
microscopic level to consider this
behaviour in more detail.

When a record is mastered (meaning,
when the master disc is created on a
lathe) the groove is cut by a heated
stylus that has a specific shape, shown
in Figure

3.9

The depth of the groove

can range from a minimum of 25

µ

m to

a maximum of 127

µ

m, which, in turn

varies the width of the groove.

5

Flat face

Burninshing

facet

Cutting

edge

Direction of

cutting action

Figure 3.9: The cutting stylus used to

create the groove in the master disc.

150 µm

Goove depth and radii

33 1/3 RPM microgroove LP

130 µm

13 µm

Minimum depth

1 mil = 25 µm

Typical depth 

~

38 µm

Maximum  depth

5 mil = 127 µm

~

70 µm

~

250 µm

~

50 µm

0.036 mm

0.7 mil

0.5 mil

Conical

(Spherical)

Elliptical

0.2 x 0.7 mil

0.026 mm

0.036 mm

78 RPM

75 µm radius

0.15 mm

Line Contact

78 RPM

Figure 3.10: Dimensions of record grooves, drawn to scale. The figure on the left is typical for a 78 RPM shellac disc. The three grooves

on the right show the possible variation in a 33 1/3 “microgroove” LP.

The result is a groove with a varying
width and depth that are dependent on
the decisions made by the mastering
engineer, and a modulation
displacement (the left/right size of the
“wiggle”) that is dependent on the
level of the audio signal that is being
reproduced.

In a perfect situation, the stylus that is
used to play that signal back on a
turntable would have exactly the same
shape as the cutting stylus, since this
would mean that the groove is traced
in exactly the same way that it was
cut. This, however, is not practical for
a number of reasons. As a result, there
are a number of options when choosing
the shape of the playback stylus.

3.3 Tip shape

The earliest styli were the needles that
were used on 78 RPM gramophone
players. These were typically made
from steel wire that was tapered to a
conical shape, and then the tip was

rounded to a radius of about 150

µ

m,

by tumbling them in an abrasive
powder.

6

. This rounded curve at the tip

of the needle had a hemispherical
form, and so styli with this shape are
known as either

conical

or

spherical

.

The first styli made for “microgroove”
LP’s had the same basic shape as the
steel predecessor, but were tipped with
sapphire or diamond. The
conical/spherical shape was a good
choice due to the relative ease of
manufacture, and a typical size of that
spherical tip was about 36

µ

m in

diameter. However, as recording
techniques and equipment improved, it
was realised that there are possible
disadvantages to this design.

Remember that the side-to-side shape
of the groove is a physical
representation of the audio signal: the
higher the frequency, the smaller the
wave on the disc. However, since the
disc has a constant speed of rotation,
the speed of the stylus relative to the
groove is dependent on how far away it

is from the centre of the disc. The
closer the stylus gets to the centre, the
smaller the circumference, so the
slower the groove speed.

If we look at a 12” LP, the smallest
allowable diameter for the modulated
groove is about 120 mm, which gives
us a circumference of about 377 mm
(or 120 *

π

). The disc is rotating 33 1/3

times every minute which means that
it is making 0.56 of a rotation per
second. This, in turn

7

, means that the

stylus has a groove speed of 209 mm
per second. If the audio signal is a
20,000 Hz tone at the end of the
recording, then there must be 20,000
waves carved into every 209 mm on
the disc, which means that each wave
in the groove is about 0.011 mm or 11

µ

m long.

5

“The High-fidelity Phonograph Transducer” B.B. Bauer, JAES 1977 Vol 25, Number 10/11, Oct/Nov 1977

6

ibid.

7

pun intended

10

Содержание Beogram 4000c

Страница 1: ...Beogram 4000c Technical Sound Guide Bang Olufsen A S This manual is for information purposes only and is not legally binding November 27 2020...

Страница 2: ...ross 7 3 2 Signal Levels 8 3 3 Tip shape 10 3 4 Bonded vs Nude 12 3 5 Tracking force 12 3 6 E ective Tip Mass 12 3 7 Compliance 13 3 8 Soundsmith SMMC20CL 13 4 Audio Specifications 14 4 0 1 Magnitude...

Страница 3: ...Emil Berliner was awarded a patent for a sound recording and reproducing system that was based on a groove in a rotating disc rather than Edison s cylinder the original version of the system that we k...

Страница 4: ...are the same at Time 0 ms However it is also evident that when this is true they have very di erent amplitudes in fact the amplitude would have to double for every halving of frequency a drop of 1 oc...

Страница 5: ...ns of the RIAA equalisation filter define the transition points as time constants instead of frequencies So instead of 50 Hz 500 Hz and 2122 Hz as shown in the response plots the points are listed as...

Страница 6: ...down left up right for example This means that signals that are identical in both channels move the stylus laterally exactly as in earlier monophonic discs 4 Figure 2 10 An over simplified depic tion...

Страница 7: ...eophonic Transducer Cartridge In 1963 Erik R rbaek Madsen of Bang Olufsen filed a patent for a cartridge based on the Moving Iron principle In it a cross made of Mu metal is mounted on the stylus Each...

Страница 8: ...be encoded without incurring additional distortion that is inherent in the encoding system itself is when the maximum or minimum value in the audio signal reaches the highest possible signal value of...

Страница 9: ...here is a relationship between the total playing time of a vinyl disc and the modulation velocity In order to have 20 minutes of music on a 12 LP spinning at 33 1 3 RPM then it the standard method was...

Страница 10: ...here are a number of options when choosing the shape of the playback stylus 3 3 Tip shape The earliest styli were the needles that were used on 78 RPM gramophone players These were typically made from...

Страница 11: ...k deeper into the groove making it more di cult for it to move independently on the two audio channels The second is that the point of contact between the stylus and the vinyl becomes smaller which ca...

Страница 12: ...pin which is in turn connected to the cantilever the long arm that connects back to the cartridge housing This bonded design is cheaper to manufacture but it results in a high mass at the stylus tip...

Страница 13: ...the compliance of the stylus suspension Compliance is the opposite of spring sti ness the more compliant a spring is the easier it is to compress and the less it pushes back Like many other stylus pa...

Страница 14: ...of 70 7 mm sec 4 0 3 Rotational speed Every recording playback system whether for audio or for video signals is based on the fundamental principle that the recording and the playback happen at the sam...

Страница 15: ...changes in the speed that are higher than 100 Hz This is typically only a problem with analogue tape decks caused by the magnetic tape sticking and slipping on components in its path and is not often...

Страница 16: ...nal relative to the average frequency however the e ect of very slow and very fast changes have been reduced by the filter Finally the standard deviation of the variation from the average is calculate...

Страница 17: ...mith SMMC20CL Stylus Nude 0 12 mm square Radius of curvature Contact Line Recommended tracking force 1 3 g Compliance 28 m mN E ective tip mass 0 32 mg General information Automatic speed selection Ye...

Страница 18: ...nditions in the Cutting and Playing of Stereo Disk C R Bastiaans Vol 11 Issue 1 Jan 1963 Factors A ecting the Stylus Groove Relationship in Phonograph Playback Systems C R Bastiaans Vol 15 Issue 4 Oct...

Страница 19: ...commendations for Lateral Cut Commercial and Transcription Disk Recordings 98 Processed Disk Records and Reproducing Equipment 386 Method of Measurement of Speed Fluctuations in Sound Recording and Re...

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