Weak current College】 【audio and acoustics.

<br> <br> (1) acoustic history <br> <br> When the forest is a tree toppled, issued a bump the alarm sound, but no one in the original forest, so I did not hear the sound. This is .not a voice out? sound is definitely sent out, because when the tree trunks and branches in contact with the ground, they will produce some sound, but no one hears, but this sounds for humans or other animals hear is different, so this is .acoustic says Psychology (Psychoacoustics). <br> <br> I am here talking about acoustic principles, the most important thing is to make a transfer yinyuan to understand all aspects of acoustics, instead of an acoustic research, or master's degrees, doctoral thesis .of acoustics, so I speak in this book are acoustic theory actually can give in live operation sound one uses it. <br> <br> In 1915, a United States person named espridham a prevailing set of listeners with a clarion call to record .audio playback, and sound can be assigned to a group in the San Francisco City celebrate Christmas mass, electro-acoustics was born. When the first world war in the United States after President Harding (Harding) inauguration ceremony, the Bell telephone United States lap .to listen for connections at the time of the record player for clarion call, you can turn it on to watch the inaugural ceremony of a large group of people, thus resulting in a lot of professional audio and sound reinforcement project has been developed that subject. .Sound researcher not merely trying to improve the audio equipment, nor do all kinds of different experiments to understand human response to auditory. But the most advanced audio research and understand the whole audio learning is to study, to learn more about audio equipment every element, .and the human response to auditory Physiology, who in the past years until now have made a great contribution. As early as 1877, United Kingdom-Les Li Jazz (LordRaleigh) has already done research on the acoustical, he once said: "all whether .directly or indirectly related audio problems, be sure to use our ears to make a decision, because it is our auditory organ, and the ears of the decision should be regarded as final, it is not necessary to accept the appeal. But this is not .equal to all sound research are solely used for the ear. When we discovered the sound of the Foundation is a physical phenomenon, we detect the sound level is about to go to another domain, it is physics. Important for the fixed-rate is available .from the research in this area, and our sense of hearing induction also must accept these fixed rates. "We can see above a paragraph of text, even in the absence of electro-acoustic sound science, and veteran scientist were of the opinion that this .is the field of physics. <br> <br> Famous scientists United Kingdom Lord of Calvin often said: "when you measure things you mentioned, and can use numbers to show it to you on this thing has some knowledge. But if you can .'t use numbers to express it, so your knowledge remains humble and not complete; anything, this might be the only source of knowledge, but your ideas have not yet reached the scientific realm. "Calvin Lord (1824-1907) was a 19th .century one of the most outstanding scientists, later generations of scientists in order to commemorate this great man, the absolute temperature - 273.16 ° named 0 ° Calvin degrees. <br> <br> Davis and his wife (Don & CarolynDavis) is the sound system engineering .(SoundSystemEngineering) of the author of this book. This book is called the audio Bible, almost every foreign study audio people must read. I quote from his book in this paragraph: "a mathematical and physics knowledge is essentially about audio engineering. Both the .scientific understanding of the darker, more will make you leap from feeling on the ideas, but to achieve the scientific facts. Famous audio home covers Shi Mo-once said: 'in acoustics, in the face of it, obviously, are usually wrong' .. "<br> <br> I am in the above cited several scientists and the Institute of acoustics company, mainly because most people do sound, they of course is on sound and music very interested, but thought that depend on their hearing can identify .what is good or bad sound, do not understand that this is a profession of engineering knowledge, is not a good sound. As far back as the 19th century, Les pointed out that Sir Edward Lee is a scientific realm, modern sound engineering is also .the same as other scientific and scholarly efforts are being made to development, sound engineering is inseparable from the mathematics and physics. <br> <br> (2) effect of field codes and influence of the respective Studio tone <br> <br> .Here the explanation of on-site sound operation, it and recording technology there are many different places, many people thought the sound of the highest realm is recording technology, this is not comprehensive. In sound recording technology, basic is no feedback, because in .a recording room, all the external factors can be controlled, but the scene audio replay, we can avoid a lot of live audio, live sound and recording audio are two different types of learning. <br> <br> Live audio with Studio Audio .requirements are different, so there are a lot of equipment is different. For example, in the recording room sound mixer, their per-channel inputs are balanced with multiple parameters, so that recording can put each input of the sound source to do the most .sophisticated and fine tune, to achieve the best sound source. One used to do on-site sound mixer, usually in its every way input, equalization is relatively simple. Because very often, site tuner didn't have much time to each of the .sound source to do a careful fine-tuning, and on-site sound mixer volume control for each channel, putting them in addition to being able to do the volume attenuation, you can gain 10-14dB. If you do use a mixer, recording .studios that putting very often do not need to do gain, so this pusher is the English name of the fader, the mean is attenuator. Used in the field of high power amplifier sound, they will have fans as cooling purposesBecause the on-site audio .amplifier is often at maximum power output of the work, and there are a lot of time outdoors to do on-site sound, the surrounding temperature can be quite high. If in the recording room, usually will have air conditioning, temperature and of course .will not be too high, and the recording of indoor amplifier is used to push za, certainly do not need to output a lot of power, the power amplifier only need to use an ordinary radiator, can turn a small heat dispersion. If the amplifier .is equipped with a fan, fan sound instead of noise, in the recording room of power amplifier is essentially does not require a fan. <br> <br> Live audio of speakers, in order to put a lot of sound pressure spread painted in .the distance of the audience, so they need to be very efficient, but in the recording room za, is recording used to listen for the sound source or sound recording, the recording of the final result is sitting in the very near from the za to .listen, listen to speaker is a near the speaker sound field, does not require a high sensitivity, role with on-site audio speakers are completely different. <br> <br> (3) the relationship between audio and wavelength <br> < .br> Many site tuner without regard to the relationship between audio and wavelength, in fact, this is very important: audio and wavelength and the speed of sound is a direct relationship. At an altitude of air pressure, 21 Celsius when sound speed is 344m ./ s, and I contact domestic tuner, they commonly used sound speed is 34Om / s, this is at a temperature of 15 ° c is the speed of sound, but we remember the most important is the speed of the voice as the air temperature .and air pressure and changes in, the lower the temperature, the air of molecular density will increase, so the speed of the voice would fall, but if at high altitudes where you live sound, because the air pressure decreases, the air molecules become scarce ., the sound speed increases. Audio and the relationship between wavelength and sound is the sound of wavelength = speed / frequency; λ = v / f, if you assume that Sonic is 344m / s, 100Hz audio wavelength is 3.44m, 1000hz (ie .lkHz) wavelength is 34.4cm, and an audio wavelength for 20kHz 1.7cm. <br> (4) speakers of high, medium, and low frequency <br> <br> For example, we now have a time of 18 Cone Speaker unit ., the unit in a timber-built speakers and the speaker of the Panel area is l square, that is, the height and width of the Panel are l m. How we calculate this speaker of high, medium, and low frequency? first of .all we want to calculate the speaker panel diagonal length is 2-square = 1.414m, any frequency of l / 4 wavelength is over when this 1.414m sound box, it is the low frequency; if a frequency of l / 4 wavelength is 1.414 .m, wavelength is 4 × 1.414m = 5.656m, frequency = 344m / s ÷ 5.656m = 60.8 / s = 60.8Hz, so any audio below 60.8Hz, this speaker is its low frequency. When 60.8Hz or lower frequencies transmitted from .the speaker came out, their proliferation is spherical, equal to, if we put the speakers hung in a room in the Middle, the frequency of the volume of the speaker and the up and down the front, back, left out of the sound pressure .is the same, and drop out of the sound into a non-directional. When a frequency of l / 4 wavelength is less than the speaker panel diagonal length, but this wavelength is greater than the radius of the speakers, this frequency is the frequency .of sound box. For example, we have now is a time element, this 18-unit RADIUS is 9 inches, is the 22.86cm = 0.2286m 344m / s ÷ 02286m audio = 1505Hz, from 60.8Hz-1505HZ frequency is the frequency of .sound box. The speaker in frequency from the proliferation of shape is a hemisphere, that is, if we put this frequency from just hanging in a room center speaker released, the sound from the speaker panel for the diffusion of shape is a hemisphere. Behind .the speaker is not hear the sound of this frequency. 1505Hz and higher frequencies, this speaker is its high frequency. High frequency from speaker diffusion sound shape is cone-shaped, the higher the frequency, the more narrow conical shape. Usually if a frequency .exceeding start 4 times higher audio, sound diffusion out of shape will gradually turn into a line and non-proliferation, if not sitting on the unit's location, you cannot hear the high frequency. So many high-frequency cell if it is a cone- .shaped, this cone diameter is small, the speaker of the lower frequency as possible, hoping to make the width of the high frequency dispersion. We often see home audio speakers in the treble range, typically used when the l-2 cone cells, or .half-spherical cell, the reason is for this reason. And professional on-site sound treble unit, which makes a lot of high frequency sound pressure, so that must be handled with horns. <br> <br> (5) the various .types of sound field <br> <br> When a paper cone speakers accepted from amplifier the signal passes, the cone is made before and after the shake, move forward when Cone, cone impact to it in front of the air molecules in the air .in front of the cone will increase pressure, these elements will continue to move forward, crash them in front of the air molecules, resulting in slightly higher air pressure. When the cone to Cone back, on the front of the air molecules will result in .a slight vacuum, then these molecules will follow Cone back, causing the air pressure decreases slightly. But we must not forget that the air is a stretch, but in the air in front of the cone is just being shaken pelvic movement paper, cannot achieve .the air itself of elastic when we have to look at this frequency wavelength, the sound is to leave the paper-basin until the distance 2.5 times the wavelength, the air is the result of the elastic voice. For example a 100Hz frequency, its wavelength .is 3.44 meters, so the sound you want to leave the paper trough 2.5 × 3.44 m = 8.6 m, is the real voice of the 100Hz. If you use 10OHz, leave the cone distance haven't 8.6 meters for the phonetic lOOHzField, rather .than 8.6 m is 100Hz far sound field. Why do we have to understand how sound field? very often in a band in the hands of the electric bass, he often do not understand the last sound field effect, but in his electric bass speakers, .a balancing knob is write a bass (Bass), is the title of the musicians. Electric bass hand usually stand on the left the electric bass speakers do not far away, if he stood near the sound field, sometimes feel the bass, will turn .this Bass equalization knobs to be adjusted, but the audience in their position will hear very strong bass, very often lead to undesirable results. These strong bass also ran into the singer's microphone, if the tuner because that singer's voice is not enough, all the .way to the singer's voice to improve this, but at the same time the electric bass, low-volume also improves, tuning will encounter difficulties. Electric bass is the lowest E chord, but because the pickups 41Hz is placed in the last paragraph of the .chord, so 41hz first homophonic 82Hz is the main electric bass frequencies, 82Hz wavelength is 4.2 m (344m / s divided by 82 / s = 4.195m), so I almost want to leave the electric bass speaker 10 meters is the distant sound field ., 82Hz but because electric bass hand does not stand to leave his speakers so far distance, he heard the voice just near the sound field, rather than the audience heard voices. So when it comes to speakers of sound field, most notably note frequency and .wavelength, rather than merely to see how far away from the speaker is equal to the distance or near most major sound field, is to remember us when you listen to music, is far from the location of the sound field, instead of near the location .of the sound field. <br> <br> (6) direct sound field, reflection sound field, not direct sound field <br> <br> When the speakers in a room sound, listeners can hear directly from the speaker passes on sound ., this is the direct sound field (indirectfield), but can also be heard from the wall, ceiling and floor are reflection of sound, this is called reflection sound field (reverberantfield). The audience heard more direct sound field of sound, sound field ., the more hours of sound, the sound is better, because the voice of the direct sound field can be controlled, but the reflection of sound is the sound field control, you'll only make direct-field sound plus politicize the clarity of the .original sound, so sit bottom cut away from the speakers near the audience will feel better sound effects, and sitting at the back of the audience is most likely they heard the sound of reflection sound field than direct sound field sound, sound effects will be relatively .poor and clarity. Sometimes a team of the band performing on stage, because they have no za, and both sides of the main speakers are placed near the station of the location, the band and singer hear sounds totally free from direct sound field and drop .them, they stand location is called not direct sound field, sound effects, of course, not be good, this also affects the performance of the band, the audience heard is not very good performance. <br> (7) interface interference <br .> <br> When we select where to place the speaker's position, it is important to note that the speaker's sound is affected by the impact of interface next to it and cause interference. For example, on a single port on both sides of the main .speaker, their bass cone next to leave the ground and the wall if it is about 1 m, a 4 metre wavelength audio will be affected by the interference of two interfaces. A 4 metre wavelength frequencies is 86Hz (344m / s ÷ 4m = 86Hz .), when the sound from the speaker 86HZ put out large air pressure is 1 / 4 weeks just hit the floor and walls, l / 4 week reflecting back to the speaker's cone before, but this time it happens that cone to back, the original .reflection from the surface and walls of big air pressure is cone back off a lot of action, resulting in the loss of vital Basso. If you encounter this situation, you should put the speakers to the back 0.5-1 m, Jean speakers that sound .cannot be directed to the ground, but if you can put the speaker to move to near the sides of the wall, the more you can use the walls of the reflection system to make greater volume. 80-100Hz this frequency is very important, it .is our lungs space resonance point is the bass drum resonance frequency, if this is due to not understanding the interface of interference pendulum wrong speaker positioned, is really not worth it. <br> <br> (8) high, bass <br> .<br> It is difficult to specify a frequency above the treble or bass of a certain frequency following is, we often say that human hearing is from 20Hh-20KHz, but 20kHz frequency is very little one can hear, usually only a 20-year .-old young people, their ears have not been any damage can be heard. If you do hearing test, greatest test frequency just 8kHz. When the sound went out, high-frequency attenuation than low frequency is much faster, if compared with 10kHz 1kHz ., when voice ran 100 m, 10kHz 'frequency compared to the volume will decay IkHz 30-35dB. (See figure ①) compared to the low frequency and high frequency sound is more directional. High frequency sound came out from the unit, if the .subject-object of barrier, treble will no longer be transmitted in the past, this was followed by low-frequency are very different, because the high frequency of wavelength is relatively short, the object will not be blocked after the turn, but low frequency .wavelength is quite long, so a lot of time even if there are objects in front of the barrier, low frequency can also be turned over. For example, some professional loudspeaker design is a high-pitched horn on its bass unit front, but on .the bass units out of the low frequency, it did not see the front is something irresistible voice, so you can still upload low frequencies. <br> <br> From our sense of hearing, we need to hear high frequency sounds to distinguish the .various types of sound, but if you simply tell the people of conversation, we only need to hear 4kHz and following of the frequency, you can immediately tell what people are saying. For example telephone voice transmission, high frequency only 4kHz, so sometimes when .aA very long time no talk with you, so when he phoned you, as long as the said: "Hello!", you will be able to identify as soon as he is with you for a long time no talk of a friend's voice. .We hear the high frequency also has a directional, which means we can identify the direction of high frequency sound sources. Because high frequency voice to our two ears, already has a very subtle difference, so they came to the ears of a different phase change ., we will use this changes the identification phase can. <br> <br> According to the design of the audio system and design calculations, has clearly saw the system expected in the acoustic characteristics of sound reinforcement systems. <br>.