SPECTRAL ANALYSIS OF RUMBLE VERSUS MOTOR ISOLATION GROMMETS
All measurements were made using a test record with a 5
cm/sec, 1 kHz reference tone and an unmodulated test groove. A Rek-O-Kut
Magnet Preamp was fed directly from the Rek-O-Kut K-33 turntable, and its output fed to an Audio Precision audio analyzer.
Below is a graph showing the spectrum of noise generated
by a Rek-O-Kut K-33 turntable which was in original condition. After 45
years, its motor grommets
were in very good condition and still quite pliable.
Looking at the 120 Hz region (very audible), we see that
the noise level is only 38 dB below the maximum recorded level. This noise
level was quite obnoxious and
rendered it unusable for serious music listening.
The following graph shows the spectrum of noise produced with new Rek-O-Kut improved motor isolation grommets.
Looking at the same area, we see a signal to noise ratio of 53 dB. This is an improvement of 15 dB, rendering noise inaudible.