(1) acoustic history
A tree fell in the forest with a loud noise, but there was no one in this virgin forest, so there was no sound. Is this a sound? The sound is definitely coming, because when the trunk and branches touch the ground, they will produce some sounds, but no one will hear them, but this sound is different for humans or other animals, so this is what acoustics calls psychology.
The principle of acoustics I'm talking about here is mainly to enable a Andhadhun to understand all aspects of acoustics, instead of conducting acoustic research or master's or doctoral thesis on acoustics, so the acoustic theory I'm talking about in this book can actually be used by people who operate acoustics on the spot.
19 15, an American named E.S. Pridham put a telephone receiver on a speaker that could play a recording. When this sound could be heard by a group of people celebrating Christmas in San Francisco, electroacoustic was born. After the First World War, at the inauguration ceremony of President Harding in the United States, Bell Company of the United States connected the handset to the speaker of the record player at that time, which was able to transmit the sound to a large group of people watching the inauguration ceremony of the President. Therefore, many professional sound research and sound reinforcement projects have been developed. Audio researchers not only try to improve audio equipment, but also do various experiments to understand human responses to hearing. But the most advanced audio researchers know that acoustics should be studied as a whole, and we should understand every link of audio equipment and people's physiological response to hearing. They have made great contributions in the past few years. As early as 1877, LordRaleigh of Britain had done research on acoustics. He once said: "All problems related to acoustics, whether direct or indirect, must be decided by our ears, because the ears are our hearing organs, and the decisions of the ears should be regarded as final and there is no need to accept complaints. But this does not mean that all acoustic research is carried out by ears alone. When we find that the basis of sound is a physical phenomenon, and detect this sound realm, we will turn to another field, that is physics. Important rates can come from research, and our auditory induction must accept these rates. " From the above paragraph, we can see that even when there was no electroacoustic acoustics, the older generation of scientists thought it was a field of physics.
Lord Calvin, a famous British scientist, often said, "When you measure what you say and can express it in numbers, you already know something about it. But if you can't express it in numbers, then your knowledge is still rough and incomplete; For anything, this may be the origin of knowledge, but your mind has not yet reached the realm of science. " Lord Calvin (1824- 1907) is one of the most outstanding scientists in19th century. To commemorate this great man, later scientists named the absolute temperature -273.438+06 degrees Celsius as 0 degrees Calvin.
Don & Caroline Davis is the author of Sound System Engineering. This book, called the Bible of Sound, is a must-read for almost everyone who studies sound abroad. I quote this passage from his book: "Knowledge of mathematics and physics is a necessary condition for a substantive understanding of sound engineering. The deeper you know about these two kinds of sciences, the more you can transcend the ideas you get from your senses and cite facts with science. The famous audiologist James Moya once said:' In acoustics, anything that seems obvious on the surface is usually wrong'. "
I quoted the warnings of several scientists and audiologists above, mainly because most people who do acoustics are of course interested in acoustics and music, but they think that acoustics can be distinguished only by hearing, but they don't understand that this is a professional engineering knowledge, and they can't do acoustics well. As early as the19th century, Sir Riley pointed out that this is a scientific field, and modern sound engineering is developing as hard as other scientific disciplines, so sound engineering cannot be separated from mathematics and physics.
(2) The difference between live sound and studio sound.
There are many differences between the live audio operation explained here and the recording technology. Many people think that the highest level of audio is recording technology, which is not comprehensive. In recording technology, there is basically no feedback, because all peripheral factors can be controlled when operating in the recording studio, but when playing back live audio, we can't avoid many problems of live audio, so live audio and recorded audio are two different kinds of knowledge.
The requirements of live sound and studio sound are different, so there are many different devices. For example, in a sound mixer used in a recording studio, each input has multiple parameter balances, so that the sound engineer can make the most accurate fine adjustment for each input sound source, thus achieving the best sound source effect. Mixers for live sound are usually simple for each input. Because most of the time, Andhadhun doesn't have much time to fine-tune the sound source of each channel, but in the live audio mixer, the volume of each channel is controlled by the push rod, which can not only attenuate the volume, but also gain 10- 14 dB. If you make a mixer for a recording studio, this putter often does not need gain, so its English name is fader, which means attenuator. High-power power amplifiers for live audio will have fans to dissipate heat, because the power amplifiers for live audio often work at the maximum power output, and in many cases, when doing live audio outdoors, the ambient temperature may be quite high. If there is air conditioning in the recording studio, the temperature will certainly not be too high, and the power amplifier in the recording studio is mainly used to push the monitor speaker, of course, it does not need to output a lot of power, so the power amplifier only needs an ordinary radiator to dissipate a little heat. If the power amplifier is equipped with a fan, the sound emitted by the fan will cause noise instead, so the power amplifier in the recording studio basically does not need a fan.
Speakers used in a live sound system need to be very efficient in order to spread sound pressure to distant audiences. The monitor used in the recording studio is the final result of the sound source or recording used by the sound engineer. The sound engineer sits near the monitor, so the monitor is a kind of speaker close to sound stage, which does not need high sensitivity, and its function is completely different from that of the live sound speaker.
(3) the relationship between audio and wavelength
Many Andhadhun didn't notice the relationship between audio and wavelength. In fact, this is very important: audio and wavelength are directly related to the speed of sound. At high air pressure, the speed of sound at 2 1℃ is 344 m/s, but when I come into contact with Andhadhun in China, their common speed of sound is 34 om/s, that is, the speed of sound at 15℃, but what we remember most is that the speed of sound will change with the change of temperature and air pressure. The lower the temperature, the higher the molecular density in the air, and so does sound. The relationship between audio and wavelength and sound is: wavelength = speed of sound/frequency; λ = v/f, assuming that the speed of sound is 344 m/s, the wavelength of 100Hz audio is 3.44 m, the wavelength of 1000hz (i.e. 1 khz) is 34.4 cm, and the wavelength of a 20kHz audio is1.7cm..
(4) High, medium and low frequencies of the loudspeaker
For example, we now have a 18 cone speaker unit, which is installed in a wooden speaker. The panel area of this speaker is L square meters, that is, the height and width of this panel are L meters. 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, that is, the square root of 2 = 1.4 14m. When the L/4 wavelength of any frequency exceeds 1.4 14m, it is low frequency for this speaker. If the L/4 wavelength of a frequency is 1.4 14m, the wavelength is 4× 1.4 14m = 5.656m, and the frequency is 344m/s ÷ 5.656m = 60.8/s = When the frequencies of 60.8Hz or lower diffuse from the loudspeaker, their diffusion images are spherical, which means that if we hang the loudspeaker in the middle of a room, the sound pressure emitted by the volume of these frequencies is almost the same in the front, back, left and right and up and down of the loudspeaker, and the released sound becomes directionless. When the L/4 wavelength of a certain frequency is less than the diagonal length of the speaker panel, but this wavelength is greater than the radius of the speaker, this frequency is the intermediate frequency of the speaker. For example, we are using 18 hour unit with a radius of 9 inches, that is, 22.86cm=0.2286m, and the audio frequency is 344m/s÷02286m= 1505Hz. The frequency from 60.8 Hz to 1505Hz is the intermediate frequency of this speaker. The shape of the intermediate frequency diffused from this speaker is hemispherical, that is, if we release this frequency from the speaker hanging in the middle of the room, the shape of the sound diffused from the speaker panel is hemispherical. You can't hear the sound at this frequency behind the speaker. 1505Hz and above is the high frequency of this speaker. The shape of the sound diffused from the sound box at high frequency is conical, and the higher the frequency, the narrower the shape of the cone. Usually, if the frequency exceeds 4 times of the original high-frequency audio, the shape of the sound will gradually become a straight line and will not spread. If you are not sitting in the position of the calibration device, you will not hear these high frequencies. Therefore, if many high-frequency units are paper pots, and the diameter of the paper pots is very small, it is necessary to raise the lower limit of the high frequency of the speaker as much as possible, hoping to increase the width of high-frequency diffusion. We often see high-pitched units in home audio speakers, usually using L-2 paper basin units or hemispherical units. That's the reason. The high-pitched unit of professional live audio must be treated with a loudspeaker because it emits a lot of high-frequency sound pressure.
(5) Different kinds of sound stage.
When the paper cone speaker receives the signal of the power amplifier, the paper cone will shake back and forth. When the paper cone moves forward, it will touch the air molecules in front of it, and the air in front of the paper cone will increase the pressure. These molecules will continue to move forward and collide with the air molecules in front, resulting in a slight high pressure. When the paper basin retreats, the air molecules in front of the paper basin will produce a slight vacuum, and then these molecules will retreat with the paper basin, resulting in a slight pressure drop in the air here. But let's not forget that the air is elastic, but the air in front of the paper basin has just been shaken by the role of the paper basin, and it can't reach the elasticity of the air itself. At this time, we will look at the wavelength of this frequency. Sound will not be elastic until the distance from the paper basin reaches 2.5 times the wavelength. For example, a frequency of 100Hz has a wavelength of 3.44m, so the sound should leave the paper basin by 2.5x3.44m = 8.6m, which is the real sound of 100Hz. If calculated by 100Hz, the distance from the paper basin is a near sound field of 000Hz before it reaches 8.6m, and a far sound field of 100hz when it exceeds 8.6 m.. Why do we need to understand the sound field? Many times, the electric bass player in a band often doesn't understand the effect of being close to sound stage. On his electric bass speaker, there is a balance knob that says bass, which is the title of this musician. Electric bass usually plays near the electric bass speaker. If he stands near sound stage, sometimes he feels that the bass is not enough, so he will turn up the balance knob of the bass as much as possible, but the audience will hear a strong bass in their own position, which will often have a bad influence. These strong bass will also run into the singer's microphone. If Andhadhun thinks the singer's voice is not enough, he will turn up the singer's voice all the way, but at the same time, he will turn up the low volume of the electric bass, which will make the tuning more difficult. The lowest e-string of electric bass is 4 1hz, but the first harmonic of 4 1Hz is the main low frequency of electric bass, and the wavelength of 82Hz is 4.2m (344 m/s divided by 82/s = 4. 195 m), so it almost leaves the electric bass speaker. Therefore, when we talk about the distance between the loudspeaker and sound stage, the most important thing is to pay attention to the frequency and its wavelength, instead of simply looking at how far away from the loudspeaker equals how far or how close to sound stage. The most important thing is to remember that when we enjoy music, we should be far away from sound stage, not near sound stage.
(6) Direct sound field, reflected sound field and indirect sound field.
When the loudspeaker makes sound in a room, the audience can hear the sound indirectly coming from the loudspeaker, which is called direct sound field, but they can also hear the sound reflected from the wall, ceiling and floor, which is called reflected sound field. The more the audience hears the sound of direct sound stage, the less the sound of direct sound stage is reflected, the better, because the sound of direct sound stage can be controlled, while the sound of direct sound stage cannot be controlled. It will only add noise to the sound from the direct nursery and reduce the clarity of the original sound, so the audience sitting near the speaker will feel better acoustic effect, while the audience sitting at the back is likely to hear the reflected sound stage sound louder than the direct sound stage sound. Sometimes the band performs on the stage, because they don't monitor the speakers, and the main speakers on both sides are placed near the podium. The sound heard by the band and singer is not played from direct sound stage at all, so the position where they stand is called indirect sound stage, and the sound effect will definitely not be good, which will also affect the band's performance level and let the audience hear poor performance.
(7) Interface interference
When we choose the location of the speaker, it is very important to note that the sound emitted by the speaker will be affected by the side interface and cause interference. For example, the main speakers placed on both sides of the platform, if their bass paper pots are about 1 m away from the ground and the wall next to them, an audio with a wavelength of 4 meters will be disturbed by these two interfaces. The frequency of 4m wavelength is 86HZ (344m/s ÷ 4m = 86Hz). The speaker emits 86Hz sound, and the atmospheric pressure hits the ground and the wall within 1/4 weeks, and then it is reflected back to the paper basin of the speaker within L/4 weeks, but just then the paper basin will retreat, and the atmospheric pressure originally reflected from the ground and the wall, if this happens, you should move the speaker back to the platform for 0.5- 1 m, so that the sound emitted by the speaker cannot directly hit the ground. If you can move the speakers to the walls on both sides, you can use the reflection of the walls to make the sound louder. The frequency of 80- 100Hz is very important, which is the * * * ringing point of our lung space and the * * * ringing frequency of the bass drum. If you put the speaker in the wrong position because you don't know the interface interference, it's really not worth it.
(8) High and low effects
It is difficult for us to designate a certain frequency as treble or a certain frequency as bass. We often say that people's hearing is 20 HH to 20kHz, but the frequency of 20 KHz is rarely heard. Usually only young people under the age of 20 can hear it if their ears are not damaged. If you do a listening test, the highest listening frequency is only 8kHz. When the sound comes out, the high frequency decays much faster than the low frequency. If we compare 1kHz with 10kHz, when the sound runs 100 meters, the' frequency' of 10kHz will be 30-35 dB lower than the volume of 1 khz. (Please refer to Figure ①) Compared with low frequency, high frequency sound is more directional. After the high-frequency sound runs out of the unit, if it is blocked by an object, the high-frequency sound cannot pass through. This is very different from low-frequency sound, because the wavelength of high-frequency sound is short and will not turn after being blocked by objects, while the wavelength of low-frequency sound is long, so many times even if there is an object in front, low-frequency sound can turn. For example, some professional speakers are designed to put a tweeter in front of their bass unit, but for the low frequency emitted by this bass unit, it can't see anything that blocks the sound at all, so the low frequency can be transmitted as usual.
From our sense of hearing, we need to hear high-frequency sounds to distinguish different kinds of sounds, but if we only talk about human voices, we only need to hear frequencies of 4kHz and below, and we can immediately tell who is speaking. For example, the high frequency of telephone voice transmission only reaches 4kHz, so sometimes people who haven't talked to you for a long time just say "hello!" when they call you. You can immediately recognize the voice of a friend who hasn't spoken for a long time. We are also directional when listening to high frequency, that is, we can identify the source direction of high frequency sound. Because the time difference of high-frequency sounds reaching our ears is very small, they have different phase changes when they reach our ears, and we can identify them by this changed phase.