Here is the piece I referenced above, sans graphs:
"5. Audible Effects of Wow and Flutter, Rumble, Tone Arm Resonances etc.
The Transient Distortion (section 4) was an example of how the high frequency domain influences the music domain by creating products that fall down into the audible range. This section will consider a similar effect from the low frequency domain that creates serious problems in the music domain by modulating the signals. In other words, the effect of subsonic signals folding up into the audible range (dare we call it BIM - Bass Intermodulation Distortion). Also here it is often heard that people say "I cannot hear 10 Hz, so I do not care". Again it is true that 10 Hz cannot be heard directly, but the effect of 10 Hz, however, is certainly audible. Some of these phenomena are illustrated in Fig.7.
The curve in the upper left hand corner of the figure shows a straightforward frequency analysis of the low frequency range 2 Hz - 60 Hz produced by an ordinary turntable with preamplifier. The most severe peak is produced by the mechanical resonance of the tone arm and the stylus, but motor rumble and hum is also clearly visible. Unfortunately, the tone arm resonance has a level typically only 10-20 dB lower than the signal produced simulatenously in the audible range.
This effect is indicated on the right hand side of Fig.7. Although the low frequency signals are not directly audible, they produce some clearly audible sidebands on the music signals. Also in this domain, the effect is typically 10% distortion. The most critical range of this is known from the wow and flutter weighting function which is most sensitive around 4 Hz. So really the closer the tone arm resonance is to 4 Hz, the worse the audible effect. A frequency analysis of the demodulated wow and flutter signal is also an interesting measurement of the phenomena. A typical result of this using the automatic B & K Wow and Flutter Meter 6203 is shown in the lower left hand corner of Fig.7.
The pronounced resonance at 0,61-1z is due to wrong centring of the record. It is a paradox that often we think we measure wow and flutter when in reality we are measuring the influence of the tone arm cartridge combination. It does not help to improve the turntable motor mechanism when it is the tone arm resonance that is creating the problem.
Unfortunately, the mechanical resonances in tone arms are excited all the time by the warps in the records. The effect seen in the time domain is a ringing that sometimes goes on for half a revolution of the record and also affects the tracking force so it changes from near nothing to twice the "steady state' tracking force.
An interesting test of this can be made simply by making a cut in the record and offsetting the two parts. Every time the stylus passes the
"step-function" a transient is produced. A recording on a storage scope or the B & K Narrow Band Analyzer 2031 will show the time function or the time and frequency functions respectively. A typical result of different time responses for different tone arms with the same cartridge is shown in Fig.8.
The phenomena of audible effects of mechanical resonances in turntables are described in further detail in the B & K Application Note 17-233 (Ref.7). The audible effect of the phenomena again is a "frequency smear" or a "confusion effect" of the sound picture."
"5. Audible Effects of Wow and Flutter, Rumble, Tone Arm Resonances etc.
The Transient Distortion (section 4) was an example of how the high frequency domain influences the music domain by creating products that fall down into the audible range. This section will consider a similar effect from the low frequency domain that creates serious problems in the music domain by modulating the signals. In other words, the effect of subsonic signals folding up into the audible range (dare we call it BIM - Bass Intermodulation Distortion). Also here it is often heard that people say "I cannot hear 10 Hz, so I do not care". Again it is true that 10 Hz cannot be heard directly, but the effect of 10 Hz, however, is certainly audible. Some of these phenomena are illustrated in Fig.7.
The curve in the upper left hand corner of the figure shows a straightforward frequency analysis of the low frequency range 2 Hz - 60 Hz produced by an ordinary turntable with preamplifier. The most severe peak is produced by the mechanical resonance of the tone arm and the stylus, but motor rumble and hum is also clearly visible. Unfortunately, the tone arm resonance has a level typically only 10-20 dB lower than the signal produced simulatenously in the audible range.
This effect is indicated on the right hand side of Fig.7. Although the low frequency signals are not directly audible, they produce some clearly audible sidebands on the music signals. Also in this domain, the effect is typically 10% distortion. The most critical range of this is known from the wow and flutter weighting function which is most sensitive around 4 Hz. So really the closer the tone arm resonance is to 4 Hz, the worse the audible effect. A frequency analysis of the demodulated wow and flutter signal is also an interesting measurement of the phenomena. A typical result of this using the automatic B & K Wow and Flutter Meter 6203 is shown in the lower left hand corner of Fig.7.
The pronounced resonance at 0,61-1z is due to wrong centring of the record. It is a paradox that often we think we measure wow and flutter when in reality we are measuring the influence of the tone arm cartridge combination. It does not help to improve the turntable motor mechanism when it is the tone arm resonance that is creating the problem.
Unfortunately, the mechanical resonances in tone arms are excited all the time by the warps in the records. The effect seen in the time domain is a ringing that sometimes goes on for half a revolution of the record and also affects the tracking force so it changes from near nothing to twice the "steady state' tracking force.
An interesting test of this can be made simply by making a cut in the record and offsetting the two parts. Every time the stylus passes the
"step-function" a transient is produced. A recording on a storage scope or the B & K Narrow Band Analyzer 2031 will show the time function or the time and frequency functions respectively. A typical result of different time responses for different tone arms with the same cartridge is shown in Fig.8.
The phenomena of audible effects of mechanical resonances in turntables are described in further detail in the B & K Application Note 17-233 (Ref.7). The audible effect of the phenomena again is a "frequency smear" or a "confusion effect" of the sound picture."