The interference phenomenon occurs when the sound waves emitted by two sound sources with the same frequency, the same vibration direction, and the same pace are superimposed on each other. If they are in the same phase, the sound pressures of the two sound waves are strengthened after they are superposed. On the contrary, if they are in the opposite phase, the two sound waves will weaken each other and even completely cancel each other. Due to the interference of sound waves, the sound field in space often appears a fixed distribution, forming antinodes and wave nodes, that is, what we usually call standing waves.
The conditions that cause sound wave interference are often encountered. Let’s take the case of two speakers playing the same frequency sound as an example to illustrate:
(1) When two loudspeakers vibrate and sound in the same phase, due to the equidistant relationship, the sound wave is always in the same phase state when reaching the points on the central axis between the two loudspeakers, so the sound waves from the two loudspeakers are the office reinforces each other.
(2) When the two speakers vibrate and sound in opposite phase, the situation is just the opposite. When the sound wave arrives at each point on the central axis between the two speakers, it is always in the anti-phase state, so the sound waves from two speakers where they cancel each other out, the two speakers are not as strange as one speaker.
This tells us that when connecting speakers and power amplifiers, they must maintain the same polarity of their positive and negative polarity; otherwise the second case above will occur.
Of course, such results for stereo systems often result in inaccurate positioning of the sound image, that is, a feeling of “floating” sound sources.
In the hall, interference due to sound waves may also occur due to wall reflections. For example, direct waves emitted from sound sources and reflected waves from walls or flat tops interfere with each other at various points in space. If they are sig signals, this interference phenomenon will inevitably cause great differences in the sound fields at various points in space. In some places, the sound waves will be strengthened, and in some places the sound waves will be weakened or even completely cancelled out as a “dead point”. Fortunately, language and music are compound sounds composed of many frequencies, which can have the effect of “recommending” and “filling in and filling up” to make the interference effect less obvious. However, since the interference effects produced by different frequency signals are different, that is, the signals of some frequencies are mutually reinforcing, while the signals of other frequencies are mutually weakened, they often lead to non-uniform transmission characteristics of the room.
The size of large and medium-sized karaoke’s is generally much larger than the wavelength of low-frequency sounds, the shape is often irregular, and there are many irregularly shaped objects such as doors and windows in the hall. These will cause “interference” and “destruction” to cause interference conditions, and thus the interference phenomenon is not so serious.
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