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The size of a playback tape head gap must be small enough so as to contain no more than one half of a cycle of a signal within the width as it passes by. Using general intuition, you can imagine that if the gap only needed to be the width of one cycle of the highest frequency signal of interest, then the positive and negative portions of that signal would cancel out as it passed through.
The following formula pertains:
Wg = V / 2F
wherein -
Wg = Playback head gap Width (in inches)
V = Tape Velocity (in Inches per Second or ips)
F = Frequency in Hz
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For example, assume that we need a playback head for a professional tape deck that must record up to 20 KHz (20,000 Hz) and operate at a speed of 15 ips. The minimum gap size for the playback head would be:
15 / 2 x (20,000) = 0.000375 inches in width (or 0.375 mils)
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Note 1: These rules do not apply to the recording head of a tape deck; this is due to the AC bias signal imposed on the audio and the fringing that occurs at the edge of the tape recording head gap. Recording head gaps, as a rule, are wider than playback head gaps.
Note 2: The colloidal magnetic tape particle size, as a rule of thumb, should be about 1/10th the size of the playback head gap.
Note 3: A similar principle applies to the size of a stylus riding on a mechanical record, except that the Velocity term is "Tangential Velocity" not constant linear Velocity.
keywords: wavelength, head gap, play head, record head, frequency response, frequency resolving
The following formula pertains:
Wg = V / 2F
wherein -
Wg = Playback head gap Width (in inches)
V = Tape Velocity (in Inches per Second or ips)
F = Frequency in Hz
-----------------------------------
For example, assume that we need a playback head for a professional tape deck that must record up to 20 KHz (20,000 Hz) and operate at a speed of 15 ips. The minimum gap size for the playback head would be:
15 / 2 x (20,000) = 0.000375 inches in width (or 0.375 mils)
-------------------------------
Note 1: These rules do not apply to the recording head of a tape deck; this is due to the AC bias signal imposed on the audio and the fringing that occurs at the edge of the tape recording head gap. Recording head gaps, as a rule, are wider than playback head gaps.
Note 2: The colloidal magnetic tape particle size, as a rule of thumb, should be about 1/10th the size of the playback head gap.
Note 3: A similar principle applies to the size of a stylus riding on a mechanical record, except that the Velocity term is "Tangential Velocity" not constant linear Velocity.
keywords: wavelength, head gap, play head, record head, frequency response, frequency resolving