background image

50

60

70

80

90

100

110

120

130

140

150

Distance from centre of disc to stylus (mm)

150

200

250

300

350

400

450

500

550

Rotational velocity (mm/sec)

12" 33 1/3 RPM
7" 45 RPM

Figure 3.11: The relative speed of the

stylus to the surface of the vinyl as it

tracks from the outside to the inside ra-

dius of the record.

50

60

70

80

90

100

110

120

130

140

150

Stylus distance from centre of disc (mm)

0.001

0.01

0.1

1

10

100

Wavelength (mm)

20 Hz
100 Hz
1 kHz
20 kHz

Figure 3.12: The wavelengths measured

in the groove, as a function of the sty-

lus’s distance to the centre of a disc.

The shorter lines are for 45 RPM 7“discs,

the longer lines are for 33 1/3 RPM 12“

LPs.

However, now we have a problem. If
the “wiggles” in the groove have a
total wavelength of 11

µ

m, but the tip

of the stylus has a diameter of about
36

µ

m, then the stylus will not be able

to track the groove because it’s simply
too big (just like the tires of your car do
not sink into every small crack in the
road). Figure

3.13

shows to-scale

representations of a conical stylus with
a diameter of 36

µ

m in a 70

µ

m-wide

groove on the inside radius of a 33 1/3
RPM LP (60 mm from the centre of the
disc), viewed from above. The red lines
show the bottom of the groove and the
black lines show the edge where the
groove meets the surface of the disc.
The blue lines show the point where
the stylus meets the groove walls. The
top plot is a 1 kHz sine wave and the
bottom plot is a 20 kHz sine wave, both
with a lateral modulation velocity of 70
mm/sec. Notice that the stylus is

simply too big to accurately track the
20 kHz tone.

-100

-50

0

50

100

Groove length (µm)

-50

0

50

Lateral Position (µ

m)

-100

-50

0

50

100

Groove length (µm)

-50

0

50

Lateral Position (µ

m)

Figure 3.13: Scale representations of a

conical stylus with a diameter of 36

µ

m

in a 70

µ

m-wide groove on the inside

radius of a 33 1/3 RPM LP, looking di-

rectly downwards into the groove. See

the text for more information.

One simple solution was to “sharpen”
the stylus; to make the diameter of the
spherical tip smaller. However, this can
cause two possible side e

ects. The

first is that the tip will sink 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
can result in more wear on the groove
itself because the “footprint” of the tip
is smaller. However, since the problem
is in tracking the small wavelength of
high-frequency signals, it is only
necessary to reduce the diameter of
the stylus in one dimension, thus
making the stylus tip

elliptical

instead

of conical. In this design, the tip of the
stylus is wide, to sit across the groove,
but narrow along the groove’s length,
making it small enough to accurately
track high frequencies. An example
showing a 0.2 mil x 0.7 mil (10 x 36

µ

m) stylus is shown in Figure

3.14

.

Notice that this shape can track the 20
kHz tone more easily, while sitting at
the same height in the groove as the

conical stylus in Figure

3.13

.

-100

-50

0

50

100

Groove length (µm)

-50

0

50

Lateral Position (µ

m)

-100

-50

0

50

100

Groove length (µm)

-50

0

50

Lateral Position (µ

m)

Figure 3.14: Scale representations of an

elliptical stylus with diameters of 10 x

36

µ

m in a 70

µ

m-wide groove on the

inside radius of a 33 1/3 RPM LP, look-

ing directly downwards into the groove.

See the text for more information.

Both the conical and the elliptical
stylus designs have a common
drawback in that the point of contact
between the tip and the groove wall is
extremely small. This can be seen in
Figure

3.15

, which shows various stylus

shapes from the front. Notice the
length of the contact between the red
and black lines (the stylus and the
groove wall). As a result, both the
groove of the record and the stylus tip
will wear over time, generally resulting
in an increasing loss of high frequency
output. This was particularly a problem
when the CD-4 Quadradisc format was
introduced, since it relies on signals as
high as 45 kHz being played from the
disc. In order to solve this problem, a
new stylus shape was invented by
Norio Shibata at JVC in 1973. The idea
behind this new design is that the
sides of the stylus are shaped to follow
a much larger-radius circle than is
possible to fit into the groove,
however, the tip has a small radius like
a conical stylus. An example showing
this general concept can be seen on
the right side of Figure

3.15

.

11

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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