A retrospective
Microphone with vibrato effect
We can hear beautiful music from the record, and the source of this beautiful music is collected through the microphone. A microphone is an electronic device that converts sound into mechanical vibrations, which in turn convert them into electrical signals. In professional recording studios, the most commonly used type of microphone is the condenser microphone, which produces two electrode plates that are close to each other to form a capacitor. One of the electrode plates is a very light, very thin metal film (or gold-plated film) that is used to convert sound into mechanical vibrations. When the film vibrates, the distance between the two electrode plates will change, and the capacitance will also change, so that the voltage at both ends of the capacitor will also change, resulting in an electrical signal.
However, the electronic components in the circuit can also generate unnecessary electrical signals due to mechanical vibrations. The chatter effect describes the phenomenon in which certain components in an electronic device convert mechanical vibrations into electrical signals that we don't need, also known as "noise." The tremor effect is also known as the "microphone effect" because microphones work by converting vibrations into electrical signals.
If you're a fan of tube amps, you've heard the term "microphone effect." Because the tube is the electronic component that is most affected by the microphone effect. In the tube, it usually contains a cathode, a gate, and an anode. There is an equivalent capacitance between the electrodes. These electrodes also vibrate under the influence of external forces, and the distance between the electrodes is constantly changing, resulting in an electrical signal. These electrical signals are not what we need, but they are amplified by the amplification circuit and finally transmitted to the speaker.
In 1962, the British company Mullard published an investigation report on the effect of electron tube microphones. They designed three accelerometers for the tubes, using a 50mW speaker (note that the unit is "milliwatts") to emit sound at different frequencies to simulate the vibrations of the tubes under the influence of sound waves, and then to observe the accelerometer readings on the tubes. They found that the vibration of the tube varies with the frequency of the sound, and the acceleration reaches a maximum of 0.1 g at a specific frequency. Taking EF86 as an example, they found that 90% of the tubes will produce a gate voltage below 320uV at 50mg acceleration due to the microphone effect, and even 600uV at 0.1g acceleration.
In further research, Mullard placed the electron tube on the shaker, which generated vibrations of different specific frequencies, and then observed the vibration of each component inside the tube through a high-magnification magnifying glass, in order to improve the parts of the tube and reduce the microphone effect. Mullard's main approach was to increase the rigidity of these components and to change the internal structure to reduce the microphone effect.
The advent of transistors has greatly reduced the chatter effect
But does that mean that the chatter effect no longer exists?
In the era when the valve was the mainstream component, engineers would do shock absorption treatment for the tube. Among them, due to the large use of electron tubes in tube computers, it is necessary to absorb the electron tubes or circuit boards equipped with electron tubes to reduce the microphone effect, otherwise it will cause various problems. The most common solution is to put a "damper" on the tube housing, or to have a shock absorption treatment between the circuit board and the chassis, both of which are also common in the audio amplifier section. These "dampers" are a soft rubber ring, but heavier brass tubular rings are also used. As for the circuit board and the casing, rubber pads are used to isolate the circuit board, and even the circuit board of some amplifiers is isolated by a spring casing. It is usually used on preamps and phono amplifiers, because of the high magnification of these amplifiers.
Until the advent of transistors, transistors were widely used in the electronic field because of their advantages in size and efficiency, and the problem of noise effect was also greatly reduced. But does this mean that the vibrato effect on the circuit does not exist anymore? Some audiophiles tap the PCB circuit board with a small stick when DIY the amplifier, and find that they hear the same sound from the speaker as they knock on the PCB circuit board, which is the sound caused by the vibrato effect. Because other parts on the circuit board, such as the capacitors, the PCB circuit board itself, and even the audio cables, are also sources of the noise effect.
For capacitors, some ceramic capacitors are also a source of the noise effect, and they are also often used in audio equipment. During operation, the ceramic medium will be deformed under the influence of external force, so that the distance between the electrodes will continue to change, resulting in voltage changes. At the same time, some vibrations (the process by which electrical energy is converted into mechanical energy) are generated under the action of an electric field in the medium, resulting in noise. As a result, electronic component manufacturers are also looking for ways to improve to suppress the noise generated by the components during operation. For example, KEMET Electronics Corporation has proposed a solution to reduce the noise generated by capacitors during operation. For PCB circuit boards, the wiring of PCB circuit boards will also have the problem of distributed capacitance, as long as the small vibration under the influence of external force will also produce a fluttering effect. The same is true for wires, where there is a distributed capacitance between the wire and the shield that transmits the signal, which can also produce a chatter effect even under small vibrations.
The chatter effect is acceptable (unavoidable)
After the above brief introduction, do you feel that there is an alarmist feeling in an instant? In a sound system, there are so many electronic components, plus external vibrations, or vibrations produced by itself, is the vibrato effect inevitable? Indeed, the vibrato effect is inevitable in electronic equipment, and from another angle it is acceptable or must be accepted. The problem is not to eliminate, but to reduce the impact of vibration on electronic components through technical means (component selection, shock absorption, etc.), to reduce noise to the extent that the human ear cannot be heard, and to reduce the impact on the performance of electronic circuits, which is the ultimate goal.
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To be continued