How to Examine a Turntable Tonearm? What Can Be Tested at All?

Benny Audio writes: “I was interested in vibrations, so I measured the vibration levels in the vertical axis using a sensor placed at the cartridge point. What was I looking for? I was searching for the frequencies at which the largest vibrations or resonances occur.

Why? I was looking into this to improve the tonearm design, aiming to minimize resonances and vibrations during vinyl playback. This, in turn, would reduce the tonearm’s influence on the cartridge’s performance.

Before conducting any measurements, I defined the methodology for the study. Methodology refers to a clearly defined, consistent, and reliable system of rules and procedures.

Since the resonance testing of the tonearm would be carried out multiple times, the research methodology needed to be unambiguous and fair for each variant.

First Element of the Test Station – The Record

Tonearm vibrations occur at specific frequencies of the audio being played. Therefore, I needed a record with a track covering ideally from 20 Hz to 20 kHz. By playing such an isolated signal and measuring the tonearm’s vibrations at that moment, I obtained information about the relationship between frequency and vibrations.

I did not examine the audio signal but only the level of vibrations. The fundamental reason is that a vinyl record is an imperfect source of sound, so any distortions in the audio may not necessarily be related to vibrations.

For the tests, I used the Ortofon Test Record, where on both sides, the first four tracks are signals from 800 Hz to 20 kHz in the left and right channels. This signal lacks the range of 20–800 Hz, which I checked using another record, the HiFi News Analogue Test LP Cartridge.

From this point, things became more challenging. How to measure vibrations? They needed to be measured somehow, data collected, related to the played frequency, and then interpreted on a graph. A subject fit for at least an engineering thesis (or maybe I’m misjudging the level of difficulty 😊).

Second Element of the Test Station – The Vibration Sensor

There are various sensors available. The popular ones used in toys and phones analyze changes in three axes simultaneously. Unfortunately, they are cheap, common, and… useless for precise measurements.

I needed a professional sensor with high resolution, a relatively small operating range, low mass, and a considerable range of detectable vibration frequencies.

I found one weighing 1 gram. I’ll keep the specifications to myself. 🙂

Third Element of the Test Station – The Microphone

Why a microphone? I wanted to simultaneously read two pieces of information: the level of vibrations (acceleration) and the frequency of the played signal.

I was not examining sound quality, only sampling the played frequency, so the microphone did not have to be exceptional. Anything with a working range from 20 Hz to 20 kHz was sufficient.

Both the microphone and the sensor have analog outputs, so they needed to be appropriately interpreted.

This was handled by the fourth element of the test station – The Microcontroller.

The microcontroller was supposed to collect data from the sensor and microphone (in fact, both elements are sensors) and display them on a graph.

It’s that simple—unfortunately, only in theory.

Fifth and Final Element – The Microcontroller Software
I wrote the program to:

● Sample (128 times) the signal after 12-bit conversion from the microphone.
● Then convert the signal from the accelerometer to 12 bits.
● Gather the highest values from 10 cycles of the above readings and display them on a graph.
● Normalize the values and display them on the X-axis (which represents time), while the Y-axis shows both the sound frequency and the acceleration level of the accelerometer in g, where 1g = 100 kHz.
The readings were at a maximum level of 0.4g.

And Now the Result. Example

I examined the signal from 800 Hz to 15 kHz , analyzing vertical and lateral vibrations—once attaching the sensor on top of the headshell and once on the side.

The test was conducted on the current version of the Immersion tonearm and turntable, using a Denon DL 103R cartridge.

● Blue Line – Frequency: You can see how the curve slowly climbs to about 15 kHz.
● Yellow Line – Level of Lateral Vibrations: At around 10 kHz, the value reaches about 0.12g (10,000 Hz = 0.1g, meaning g is multiplied by 100,000 to achieve the same scale).
● Green Line – Vertical Vibrations (inverted): Shown in negative for easier viewing.
You can see that lateral and vertical vibrations occur at the same moments, so in further analyses, I focused only on the vertical ones.

The first significant vibrations appear at around 8–9 kHz, then a moment of calm, followed by a larger amplitude (max 0.37 g) at 12–13 kHz.

Thus began the journey of examining tonearm resonances. This method allowed for the construction of an ideal tonearm without going through the process of listening to successive prototypes. Only the final version was listened to, and it left no doubt.