(1) Acoustic history
In 1915, an American named ESPridham put a telephony listener on a horn that played the record, and the sound was given to a group of people celebrating Christmas in San Francisco. Electroacoustics was born.
After the end of the First World War, at the inauguration of President Harding in the United States, Bell Company connected the phone's dynamic listening device to the horn of the record player at that time, and was able to pass the voice to the president. A large group of people at the ceremony, so many professional audio research and the development of sound reinforcement engineering.
The famous scientist Lord Calvin of the United Kingdom often said: "When you measure what you say and can express it with numbers, you have some knowledge of it. But if you can't express it with numbers, then your knowledge It is still rudimentary and imperfect; for anything, this may be the source of knowledge, but your mind has not yet reached the realm of science."
(2) The difference between recording studio sound and live sound
The requirements for live audio and studio audio are different, so there are many different devices.
For example, in the mixing console used in the recording studio, each input has a plurality of parameter equalization, so that the sound engineer can finely adjust the input source of each input as much as possible to achieve the best sound source effect. A mixer for live audio, usually in each of its inputs, the balance is relatively simple. Because many times, the live tuner does not have a lot of time to fine-tune the sound source of each channel. In addition, the volume control fader of each channel in the live sound mixer can not only attenuate the volume, but also Can gain 10-14 dB. If you are working on a mixing studio for the studio, this putter does not need to be used for a lot of time, so the English name of this putter is fader, which means the attenuator. For high-power amplifiers used in live audio, they all have fans for cooling purposes, because live audio amplifiers often work at maximum power output, and there are many times when you are doing live sound outdoors, the surrounding temperature may be quite high. If you are in the studio, there will usually be air conditioning, the temperature will of course not be too high, and the amplifier in the recording studio is mainly used to push the monitor speakers. Of course, there is no need to output a large amount of power, so the amplifier only needs to use ordinary The heat sink can dissipate very little heat. If the amplifier is equipped with a fan, the sound from the fan will cause noise, so the amplifier in the recording room basically does not need a fan.
The speakers used in live audio, in order to spread a large sound pressure to the audience at a long distance, so they need high efficiency sound reinforcement, but the monitor speakers used in the recording studio are used by the sound engineer to monitor the sound source. Or the final result of the recording, the sound engineer is sitting close to the monitor speaker to monitor, so the monitor speaker is a near-field speaker, which requires high sensitivity, which is completely different from the live sound speaker.
(3) The relationship between audio and wavelength
Many live tuners don't care about the relationship between audio and wavelength. In fact, this is very important: audio and wavelength are directly related to the speed of the sound. At an altitude of air pressure, the sound speed is 344m/s at 21 degrees Celsius, while the domestic tuner, their usual sound speed is 34Om/s, this is the speed of the sound at 15 degrees Celsius, but everyone is the most The main thing to remember is that the speed of the sound changes with the air temperature and air pressure. The lower the temperature, the higher the molecular density in the air, so the speed of the sound will decrease, and if the sound is made at a high altitude, As the air pressure is reduced, the molecules in the air become scarce and the sound speed increases. The relationship between audio and wavelength and sound is: wavelength = sound speed / frequency; λ = v / f, if the sound speed is assumed to be 344 m / s, the wavelength of 100Hz audio is 3.44 m, the wavelength of 1000hz (ie lkHz) is 34.4 Cm, while a 20 kHz audio wavelength is 1.7 cm.
(4) High, medium and low frequencies of the speaker
How do we calculate the high, medium and low frequencies of this speaker?
First, we need to calculate the diagonal length of the speaker panel, which is the square root of 2 = 1.414m. When the l/4 wavelength of any frequency is more than 1.414m, it is the low frequency for this speaker; if the frequency is l/4 When the wavelength is 1.414m, the wavelength is 4×1.414m=5.656m. This frequency=344m/s÷5.656m=60.8/s=60.8Hz, so any audio below 60.8Hz is its for this speaker. Low frequency. When the frequency of 60.8 Hz or lower is transmitted from this speaker, their diffusion image is spherical, which is equal to the volume of these frequencies when the speaker is hung in the middle of a room. The sound pressure coming out is almost the same, and the sound that is released becomes non-directional. When the l/4 wavelength of a certain frequency is smaller than the diagonal length of the speaker panel, but this wavelength is greater than the radius of the speaker, this frequency is the medium frequency of the speaker. For example, we now use an 18-inch unit with a radius of 9 inches, which is 22.86cm = 0.2286m. This audio is 344m/s ÷ 0.2286m=1505Hz. The frequency from 60.8Hz to 1505HZ is the medium frequency of this speaker. The shape in which the medium frequency is diffused from the speaker is hemispherical. That is, if we release this frequency from the speaker that was hung in the center of the room, the shape of the sound diffusing from the speaker panel is hemispherical. Behind the speaker is the sound that does not hear this frequency.
The frequency of 1505Hz and higher is its high frequency for this speaker. The shape of the sound that is diffused from the speaker at a high frequency is tapered, and the higher the frequency, the narrower the shape of the cone. Usually, if the frequency exceeds 4 times of the start of high audio, the shape of the sound will slowly become a straight line without spreading. If it is not sitting in the position of the alignment unit, these high frequencies will not be heard. Therefore, if many high-frequency units are paper cone type, the diameter of the paper cone is very small, and the high-frequency lower limit of the speaker is increased as much as possible, and it is desirable to increase the width of the high-frequency diffusion.
(5) various sound fields
When a cone speaker receives the signal from the amplifier, the cone will rock forward and backward. When the cone advances, the cone hits the air molecules in front of it, and the air in front of the cone will As the pressure increases, these molecules continue to move forward, colliding with the air molecules in front of them, causing a slight high pressure. When the cone is retreating, the air molecules in front of the cone create a slight vacuum, and then the molecules follow the cone back, causing a slight pressure drop in the air.
But the air in front of the cone is just shaken by the action of the cone, and it can't reach the elasticity of the air itself. At this time, we have to look at the wavelength of this frequency. The sound is to be 2.5 times the distance from the cone. The air exerts the elasticity that causes the sound. For example, a 100Hz frequency, its wavelength is 3.44 meters, so the sound is about 2.5 × 3.44 meters = 8.6 meters away from the paper cone, is the true 100Hz sound. If you use 100Hz, the distance from the paper cone is not more than 8.6 meters, it is 100Hz near sound field, and more than 8.6 meters is 100Hz far sound field. When it comes to the far and near sound field of the speaker, the most important thing is to notice the frequency and its wavelength, instead of simply looking at how far away from the speaker is equal to the far or near sound field, the most important thing is to remember that when we listen to music, we are going to The position of the far sound field, not the position of the near sound field.
(6) Direct sound field, reflected sound field, and no direct sound field
When the speaker makes a sound in a room, the listener can hear the sound directly from the speaker. This is the direct sound field, but you can also hear the sound reflected from the wall, ceiling and floor. This is called the reflected sound field. . The more the direct sound field is heard by the audience, the smaller the sound of the reflected sound field is, the better the sound is, because the sound of the direct sound field is controllable, but the sound of the reflected sound field is uncontrollable, only The sound from the direct sound field will be rendered and the clarity of the original sound will be reduced. Therefore, the listener who is closer to the speaker will feel a better sound, and the audience sitting behind is likely to be The sound field they hear is louder than the sound of the direct sound field, and the sound effect will be poorer and the clarity will be reduced.
(7) Interface interference
When we choose where to place the speakers, it is important to note that the sound from the speakers is disturbed by the interface next to it. For example, the main speakers placed on both sides of the table, their bass cones off the ground and the wall next to it, if it is about 1 meter, a 4 meter wavelength audio will be interfered by these two interfaces. A frequency of 4 meters is 86Hz (344m / s ÷ 4m = 86Hz), when the sound of 86HZ is released from the speaker, the large air pressure just hits the ground and the wall within 1/4 weeks, and then l/4 The week is reflected back in front of the cone of the speaker, but this time the cone is retreating. The large air pressure reflected from the ground and the wall will be offset by the backlash of the cone, causing the loss of important bass. If this happens, you should move the speaker back to the table 0.5-1 meters, so that the sound from the speaker can not directly hit the ground, and if you can move the speaker to the wall near the two sides, you can use the reflection of the wall. Make a bigger volume. The frequency of 80-100Hz is very important. It is the resonance point of our lung space and the resonance frequency of the bass drum. If it is because the interface is not understood, the position where the speaker is placed is wrong. It is really not worth it. .
(8) high and low sound effects
It is difficult to specify a certain frequency above the treble or below a certain frequency. We often say that human hearing is from 20Hh-20KHz, but the frequency of 20kHz is rarely heard by people, usually only young people under 20 years old. They can only be heard if their ears are not damaged. If you do an auditory test, the highest listening frequency is only 8 kHz. When the sound is transmitted, the high frequency is much faster than the low frequency attenuation. If the comparison is made with 1 kHz and 10 kHz, when the sound ran 100 meters, the frequency of 10 kHz will attenuate by 30-35 dB compared to the volume of I kHz. High frequency sounds are more directional than low frequencies. After the high-frequency sound comes out of the unit, if it is blocked by the object, the high-pitched sound can no longer be transmitted. This is very different from the low frequency, because the high-frequency wavelength is relatively short, and it will not be blocked by the object. Turning, but the low-frequency wavelength is relatively long, so many times even if an object is blocked in the front, the low frequency can also turn. For example, some professional speakers are designed to put a high horn in front of its woofer, but for the low frequency emitted by this woofer, it simply can't see what is blocking the sound in front, so low frequency It can be passed on as usual.
From our auditory point of view, we need to hear high-frequency sounds to distinguish different types of sounds, but if we simply talk about people's conversations, we only need to hear the frequency of 4kHz and below, we can immediately identify What is the person talking. For example, the voice transmission of the phone, the high frequency only reaches 4 kHz, so sometimes when a person who has not talked with you for a long time, when he calls you, just say: [Hey], you can immediately identify him as you. The voice of a friend who has not spoken for a long time. We listen to high frequencies and have directionality, that is, we can identify the direction of high frequency sound sources. Because the high-frequency sound has passed to our two ears, there is already a very small time difference, so when they come to the ear, there are different phase changes, and we can identify the phase of the sound by changing the phase.
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