Noise caused by ACM8625 split vibration and Tone Tuner debugging

During the tuning process, some frequencies may produce abnormal sounds, which become a flaw in the perfect sound quality. For example, the noise caused by split vibration, the noise caused by a certain point in the piano music, the cavity itself, etc.

Split vibration may need a simple explanation. Take a real-life example. Drop a drop of water in the center of a large basin filled with clear water. You will find that the ripples aroused spread out in all directions. When the ripples touch the wall of the basin, they will be reflected back, and the reflected waves will interfere with the ripples that continue to spread. If you use a dropper to continuously and rhythmically drip water drops, it will arouse waves of ripples, and then generate waves of reflected waves. These waves interfere with each other, and the entire water surface has become active, and the ripples are no longer as clear as before.

This process is similar to the sound-generating process of a speaker. After the voice coil is energized, it becomes an electromagnet, which generates force with the permanent magnet, continuously driving the diaphragm to produce sound. However, this process cannot be regarded as a simple piston movement. The diaphragm is not a completely rigid body. When it moves, it will deform like the surface of water. The waveform propagates to the surroundings and the front end along the bonding point between the voice coil and the diaphragm. When it encounters the folded ring, the wave will be reflected back like a ripple, thereby interfering with other waveforms. The actual situation is more complicated than the ripples caused by water droplets splashing, because the driving frequency is much higher and changes much faster. When the frequency reaches a certain value, the diaphragm forms a regionalized vibration due to the mutual interference of the waves.

The above picture shows a 160mm diaphragm vibrating at different frequencies. It can be found that the diaphragm is invisibly divided into multiple areas at different frequencies, and the vibration phases of some adjacent areas are inverse to each other. This kind of local vibration in the region is called segmentation vibration. Through a simple understanding of segmentation distortion, we know that the diaphragm, as a propagation medium of vibration, its own physical properties will also affect the intensity of the segmentation vibration. The ideal material is a diaphragm with good rigidity and high internal damping. Good rigidity is not easy to deform, and high internal damping will quickly decay after vibration, but it seems that these two characteristics are opposite. The actual situation is that materials with good rigidity have low internal damping, such as metal diaphragms, and materials with poor rigidity have high internal damping, such as plastic diaphragms and paper-based diaphragms.

In addition to the change in materials, the module in the DSP of Zhisheng audio amplifier provides a Tone Tuner that can optimize the electrical signal for split vibration. The Tone Tuner module has been added to the 8625P/8625S products. The following is an explanation of several parameters of this module.

The frequency set by Center Frequency .

The rs hold threshold is set, for example -6dB.

Boost G ai n sets the gain, for example 8dB.

This example means that when the signal is less than -6dB, increase the Gain by 8dB, but it cannot exceed -6dB.

When the signal is greater than -6dB, it will be attenuated to -6dB, that is, it is always limited to -6dB.

Of course, the boost gain in this place can also be set to 0dB and only used as a limiting point for a narrow frequency.

In actual applications, what other narrow frequency problems can this tool be used for?