93 lines
5.8 KiB
Plaintext
93 lines
5.8 KiB
Plaintext
This project was done in for the West Orange High School Science Exposition
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by Dan Rosenstark. As any good paper submitted to a school teacher who knows
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nothing of the subject, some of this pure bullshit. But, for the most part,
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the information contained herein is factual. The graphs containing the testing
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information are coming soon. Please don't critisize this now - it's already
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the end of school by the time most of you will read this.
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This project was done to test the differences in different magnetic materials
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used in audio tapes. It was a very interesting project, and answered many long
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standing questions many of my classmates, as well as myself, have had about the
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differences between audio tapes.
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When a manufacturer chooses an audio tape material, he has only one thing in
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mind. He wishes to increase the frequency response. The general rule for
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increasing the frequency response of a tape is this: The more magnetic
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material that be put onto one inch of tape, the better the sound quality. This
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can be translated into another idea, which in the past was for the most part
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true. The smaller the size of the magnetic particle, the better the sound
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quality (and the frequency response). And a good way of estimating size is to
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look at the molecular weight; the lower, the smaller. But, regardless of how
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one goes about obtaining higher density of particles, the principle of 'the
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more particles the better' holds true always.
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There are basically three types of audio tapes: "Metal" or "Metaxial",
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"Chrome" or "High Bias", and "Normal." These tapes are basically the same
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throughout the many manufacturers in terms of frequency response, as well as
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(for the most part), the mater- ials used.
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"Metal" tapes are made of what most companies refer to as a "pure" metal
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particle as the basic magnetic material. To retain their trade secrets of
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exactly what particles are used, none of the companies would reveal what the
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particle was. They all used trade names: Phinavinx, Stabilized Pure, etc.
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These substances had very strange frequency responses. At some frequencies,
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such as 4 kilohertz, the metal tape fell of short of even normal tapes. At
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others, it was comparable to the Chrome. It was impossible to find out why
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this occured, because there was no way to find out what the magnetic material
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on the tapes was.
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The "Chrome" tapes are not really made of chrome. At one time, these tapes
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were made out of Chromium Dioxide, or CrO2. This is a relatively small
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particle, with a molecular weight of 81.994 grams per mole. But now, they use
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a completely different substance - actually a combination of two: Cobalt Oxide
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(CoO) adsorb (on the surface of) Ferric Oxide (Fe2O3). Ferric Oxide is not a
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particularly small particle; it has a weight of 159.69 grams per mole. Cobalt
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Oxide, on the other hand, is a compari- tively tiny particle; it has a weight
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of 74.93 grams per mole. As one is on the surface of the other, they can
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seemingly occupy the same space on the tape. In this sort of stacking effect,
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a very high number of particles on the tape may be achieved. Where as Chromium
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Dioxide is a fairly small particle, these two combined give the same effect as
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one tiny particle. This is why this tape was superior to any of the others
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tested.
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"Normal" Tapes contain Ferric Oxide (Fe2O3) as their mag- netic material.
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With a molecular weight of 159.69 grams per mole, it is a much larger particle
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than even the Cobalt Oxide alone in the chrome tapes. This accounts for its
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loss of sound in many of the frequencies, particularly the higher ones.
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Testing the tapes was a simple process. We recorded pink noise onto each
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tape. Pink noise a signal that is equal throughout every octave - unlike white
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noise, in which there is a three decibel increase every octave. After we
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recorded the signal, we played it back and viewed the result through a spectrum
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analyzer. Ideally, a tape would have reproduced the pink noise exactly; an
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even signal throughout every octave. None of the tapes tested was good enough
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to have ideal readings. Some came very close, while some fell short
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completely.
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Tapes are made of different substances after much thought from the
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manufacturers. In recent years, the process for picking the materials has
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changed. While it is still for the most part "The smallest particle is the
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best sound," that isn't always the case. The manufacturer' are realizing that
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there are many ways to manufacture a better tape.
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In any case, the tapes are definitely different, and some are better than
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others. But, the difference in the tapes was never more than two or three
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decibels. To most people, a two or three decibel difference is inaudible. So,
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to most people's ears, the differences in the tapes will be none, or a very
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trivial one. But the difference, although subtle, still exists.
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