Wavelength
The distance that a sound wave travels in one vibration cycle can be calculated by dividing the speed of the sound wave by its frequency. This gives the wavelength of the sound wave. The wavelength range is from 17 meters to 1.7 centimeters. In indoor acoustics, the calculation of the wavelength is of great significance for the analysis of the sound field. The role of the wavelength should be fully emphasized. For example, only when an obstacle has a size larger than one wavelength of the sound wave, will the sound wave reflect normally. Otherwise, phenomena such as diffraction and scattering will intensify, and the shadow area will become smaller, and the acoustic characteristics will be completely different. Another example is that a sound field larger than twice the wavelength is called the far field, and a sound field smaller than twice the wavelength is called the near field. The distribution and propagation laws of the sound field in the far field and near field are very different. Moreover, in smaller-sized rooms (compared to the wavelength), low-frequency sounds cannot be well reproduced because of their longer wavelengths. Therefore, in general households, if the volume of the listening room is not large enough, the low-frequency effect is difficult to reach the ideal state.
Many live sound engineers have not taken into account the relationship between audio and wavelength. In fact, this is very important: Audio and wavelength are directly related to the speed of sound. Under the pressure of the air at an altitude and at a temperature of 21 degrees Celsius, the speed of sound is 344 m/s, while the sound speed that I have come into contact with among domestic sound engineers is 340 m/s. This is the speed of sound at a temperature of 15 degrees Celsius, but most people mainly remember that the speed of sound changes with air temperature and air pressure. The lower the temperature, the higher the density of the molecules in the air, so the speed of sound will decrease. And if the live sound is done at a high altitude where the air pressure is reduced, the molecules in the air become more spread out, and the speed of sound will increase. The relationship between audio and wavelength and sound is: wavelength = speed of sound / frequency; λ = v / f. If we assume the speed of sound is 344 m/s, the wavelength of 100 Hz audio is 3.44 m, the wavelength of 1000 Hz (i.e., 1 kHz) is 34.4 cm, and the wavelength of a 20 kHz audio is 1.7 cm.
Dynamic range
The difference between the maximum and minimum sound pressure levels of audio equipment. The maximum sound pressure level of the equipment is limited by factors such as signal distortion, overheating or damage, so it is the maximum distortion-free sound that the system can produce. The lower limit of the sound pressure level depends on background conditions such as environmental noise, thermal noise, and electrical noise, so it is the smallest sound that can be heard. The larger the dynamic range, the less overload distortion will occur in strong sound signals, so it can ensure that strong sounds have sufficient impact, and can be more realistic when expressing sounds with large and intense changes such as thunder and lightning. At the same time, weak signal sounds will not be drowned out by various noises, and the delicate details will be expressed more vividly. Generally, the dynamic range of a high-fidelity audio system should be greater than 90 decibels. If it is too small, the reproduction of the musical force effect is poor, and the appeal is insufficient. In the adjustment process of professional audio systems, sound engineers should pay attention to the following two issues when adjusting the sound: First, the input gain of the mixer should not be set too low, otherwise weak sounds will be drowned out by the noise of the mixer equipment. Second, the threshold and compression ratio of the limiter should be adjusted with great caution. A too small threshold and a too large compression ratio will cause severe sound dynamic compression, so it should be reduced the dynamic loss of the sound as much as possible while ensuring the effect. In addition, there is also a dynamic range in amplification circuits and audio sources. At this time, the difference between the smallest distinguishable signal and the maximum distortion-free signal can be resolved.
Inversion
The situation where two identical sound signals have a phase difference of 180 degrees. When the same sound is initiated, the vibration directions of the speaker or microphone between them are opposite, which also belongs to inversion. There are four types of phase inversion in the audio system: left and right channel phase inversion, true phase inversion (i.e., the phase between the input signal and the output signal), microphone phase inversion, and phase inversion of some speakers in an array of multiple speakers. Phase inversion can cause phenomena such as sound short circuit (where the sounds cancel each other out and the volume decreases), loss of sound positioning, and muddy bass, which can cause damage to the reproduction of sound.
Decibel
A unit of measurement for electrical power gain and sound intensity, named after one-tenth of the unit bel. For every doubling of power, the gain is 3 decibels, and for every increase of 10 times, the gain is 10 decibels.
Hass Effect
An effect of a dual-source system. When the delay time of one of the two sound sources is within 5 to 35 milliseconds, the listener perceives the sound as coming from the first-arriving source, while the other source seems to not exist. If the delay is from 5 to 50 milliseconds, the sound gradually shifts towards the first-arriving speaker; if the delay is from 30 to 50 milliseconds, one can sense the existence of a lagging sound source. The Haier loudspeaker, named after Dr. Haier of the United States, is a speaker with a folded diaphragm. It was introduced in 1973 and has a special structure of an electric speaker, mainly used for high frequencies.
Lauras Effect
A pseudo (false) stereo effect. By delaying the signal and superimposing it in reverse on the direct sound signal, a clear spatial impression is immediately produced, and the sound seems to come from all directions. The listener has the feeling of being in the band.
Intermodulation Distortion
A type of signal distortion where a single audio signal with amplitudes in a certain ratio (usually 4:1) is mixed and through the playback equipment generates new frequency components. It is a nonlinear distortion and the new frequency components include the harmonics of the two single audio signals and various combinations of overtones and undertones.