AnalogMagik Tutorial No. 7:
How to measure Vibrations & Resonant Frequencies
ccurate signal retrieval during vinyl playback is highly dependent upon reducing vibrations which the turntable is subjected to. Vibration can come from many sources: foot stomping, motor rumbling, airborne sound waves, or improper turntable isolation, which will all translate into unwanted signals being picked up by the Cartridge. There are many ways to measure and quantify vibrations.
good way to quantify vibrations is to measure the Intermodulation Distortion Level (IMD) between two frequency signals. Intermodulation Distortions are essentially signals not recorded or present on the LP and are being picked up by the stylus, therefore it would be desirable to have the lowest IMD% number as possible. AnalogMagik have incorporated two low-frequency signals in this test. Note the test frequencies and algorithm in our formula employed in this test is different than the VTA IMD% analysis.
lay the "Vibration Measurement" track on the test LP and the Analog Magik software will display the amount of Intermodulation Distortion expressed in percentage on the computer screen. A good setup should yield a number lower than 2% to 3.0%. If the level of vibrations is too high, to begin with, it will mask the incremental changes which you are trying to measure on the different parameters and render them meaningless, therefore it is important to reduce vibrations to the minimal.
Repeat the measurement by making changes to your turntable, such as going from direct drive to belt drive, adjusting the tension of the suspension, changing the isolation platform, or changing the location of the turntable. A lower IMD% number would indicate an improvement has been made.
nalogMagik advise that the test we have incorporated is only one of many which can be used to measure vibrations. In our product development engineer's laboratory, they have ultra-precise vibration measurement devices which are 100x more accurate than what we have provided, but the device cost more than a car. While there are far more sophisticated tools and test equipment available, AnalogMagik have to balance between cost, effectiveness and market demand. They believe the one we have provided will provide a good starting point to help users quantify vibrations.
hen selecting cartridges, the total mass of the tonearm will interact with the compliance (elasticity) of the cartridge and produce a resonance frequency.
There are complex formulas which can be found online which will compute the theoretical resonance frequencies, however, we caution that such formulas are often overly generalised, and ignore factors such as temperature changes, barometric pressure, different resonant frequencies with different materials, etc. AnalogMagik have discovered that the computed numbers bear very little correlation to the actual measurement, so in reality, you really don't know what the numbers are unless if you actually measure it in a live setting.
It is generally agreed that the optimal resonance frequency should be between 8 to 12 Hz. A resonance frequency outside of this range will degrade playback performance.
The AnalogMagik Test LP has a test track which will work with the AnalogMagik software to determine the Vertical and Lateral resonance frequency of your cartridge and tonearm combination. Play the two test track in its entirety and the Resonant Frequency will be clearly displayed on the screen, under the 'Peak Frequency' window.
If the Resonance Frequency is not within the 8 to 12 Hz, you can attempt to change the frequency by changing the mass of the tonearm. Sometimes, the frequency is also affected by changing the tightness on the headshell screws or the counterweight. Temperature changes, as well as barometric pressure, will also affect the results so the numbers observed during hot and humid climate, may be different in cold and dry winters.