Another propagation of sound is cross-media propagation. That is, from one medium, through the critical contact surface of two kinds of media into another medium, at this time, the transmission of acoustic energy is essentially the transmission of vibration amplitude. When propagating across media, the greater the density difference between the two media, the greater the loss of acoustic energy. In practice, the air is the normal space for human activity, so the greater the difference from the air density of the material is generally high density of materials (the material is much lower than the air density, in addition to vacuum, there is really not much), can be regarded as sound insulation materials. The higher the density, the better the soundproofing effect.
Such materials are made of plates, called soundproof panels. Soundproof panels not all frequencies of the sound can be blocked, the object has an inherent resonant frequency, close to the object resonant frequency of the sound, soundproofing board soundproofing effect significantly reduced.
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