Although many car audio enthusiasts already understand how sound sounds, no technical guidance should start without affecting the basics of its subject matter. Writers sometimes mistakenly believe that the reader already knows a lot about the subject, and therefore they miss the basics. Because of this, it can be difficult for some to understand the reasons for installing the speakers in certain positions in a car, for example, or why a subwoofer works best in a certain size and type of body. Most people are embarrassed to admit that they do not understand what they believe everyone knows. The truth is that there may be several other people in the same group who would like to ask the same question.
Here I will describe the basics of the subject and briefly discuss how these basics apply to the world of automobile sound. This is not expected to be a sound guide, because we don’t want to send you to sleep! If you want to learn more about sound and how to play hi-fi sound, there are many good books on this subject.
So what sounds like?
The sound is caused by the movement of air. If a large wooden panel vibrates, the air next to it repels. If the vibration is slow, the air just goes out of the way, but as the vibration speed increases to several tens and several tens of thousands of excursions per second, the air cannot move fast enough and therefore shrinks when the panel pushes it away. Natural air elasticity comes into play. The air particles on the panel are pressed against the following particles, which click on the following, etc., creating a pressure wave. When the panel returns to its original position, the air becomes less dense as it fills the void in front of the panel.
The rate at which pressure waves are generated is called the frequency & # 39; and measured in * times cycles per second. Instead of cycles per second. we usually describe the frequency in terms of Hertz (1 cP = 1 Hz). Imagine a bath full of water. If you put your hand in the water and slowly move it back and forth, not so much - the water just slides on the sides of your hand. But if you move your hand very quickly, the water does not have time to get out of the way, and you create a wave in the bathroom. Soon the water flows along the edges of the tub and soaks the carpet. If you used something more than your hand to move water, such as a dinner plate, you could pour water without moving your hand as quickly as before. The air reacts in much the same way. Large objects and small objects can create pressure waves and, therefore, sound, but a small object must move faster so that the air in front of it (and behind it) is compressed.
You are probably one step ahead of me, but that is why we find tiny tweeters and very large woofers. All loudspeakers can reproduce sound, and the reasons why tweeters are small and loudspeakers are large have much in common with the size of the pressure wave they are trying to reproduce and the weight and characteristics of the moving panel; - which in the case of dynamics usually represents a cone, a dome or sometimes a flat diaphragm. To reproduce high frequencies, the cone or dome must move very quickly. The smaller and lighter, the easier it is for him to control this amplifier. We will come back to this later. First we need to understand a little more about the sound itself.
Pressure waves
The pressure waves of sound travel at a fixed speed of about 1,100 feet per second (in fact, the air temperature affects the exact speed, but we don’t need to worry too much about it). If we know the frequency (number of waves per second), we can calculate the distance between the corresponding points on successful paths - in other words, we can measure the wavelength or wavelength. The sound, which has a frequency of 1100 Hz, has a wavelength of one foot. A sound of 2200 Hz will have a wavelength of 6 inches, and a sound with a frequency of 550 Hz will have a wavelength of two feet.
Musical scale notes simply represent sounds at certain frequencies. Medium A on the piano, for example, is 440 Hz (wavelength is 2 feet 6 inches). In the case of a church tubular organ or an electronic synthesizer, it may be possible to play A, which is four octaves below average A. This is a very low basic or basic element, frequency (additional frequencies or harmonics will be added naturally, which gives each instrument its own individual tonal character) 27.5 Hz, the wavelength is about 40 feet! Literally at the other end of the A scale, playing on three octaves above the average A, has a frequency of about 3,500 Hz and a wavelength of just 3.75 inches.
The size of a musical instrument (and loudspeaker) tends to offer the size of the wavelength it is intended to produce. A piano lumen and large tubes of a church organ are capable of producing longer wavelengths, which means lower frequencies. Similarly, a 12-inch subwoofer is designed to create low bass. If we ignore the mechanical limitations for a moment, there is nothing to stop the good 6-inch mid-range speaker from reproducing very low frequencies. It can move with the required cycles per second, but its size means that it can displace a certain amount of air during each cycle. It can create very low frequencies, but only at very low output levels. This brings us back to the analogy of a hand and a dinner plate in a bath of water. The surface area of a 12-inch subwoofer looks like a dinner plate that can move enough air in one cycle to create a pressure wave that can bang windows in a house across the street!
Imaging and Phase ... creating the illusion of reality
When we install a hi-fi system at home or in a car, we try to reproduce a very complex picture of sound waves in an environment that is very different from the one in which the instruments and vocals were recorded. We try to recreate not only the sounds of various instruments and singers for sure, but also their positions at the stage of sound. This is often called "visualization." or an image of the scene. It can also be described as “staging,” but in automotive audio, this word is usually used to describe the position of the scene itself (regardless of whether it appears in front of or behind the audience), rather than the position of the performers on the stage.
If we listened to and recorded the sound of one flute in our living room, for example, and then reproduced it using one full-range speaker located exactly in the same place as the flutist, there is a good chance (if the recording equipment and hi-fi systems have good enough quality) that it will sound more or less the same. The reverberation characteristics of the room will be the same, and since we only use one speaker instead of trying to artificially recreate the position of the phleutiste in the room using stereo instruments, the instrument should look exactly in the right place.
If we had a full orchestra in our living room, and we wanted to copy what we did with one flute, we would need to use a multi-channel recorder, several amplification channels and, although many speakers demanded, each of which was located correctly for each tool. Having witnessed this, made at the Paris exhibition in Paris several years ago, I can say that this may seem very realistic. The problem is that in most cases it is impossible to do in most homes, and, of course, not in the car, so we have ... yes, good old stereo.
Stereo aims to recreate the exact positions of various instruments using only one pair of loudspeakers, and this is achieved by increasing the level of a particular instrument in one of the channels relative to the other channel. Only the levels are different - the wavelengths from both the left and right channels will be the same differently. They are said to be in phase. This means that if you could somehow freeze the sound and see the wavelengths coming from two speakers, both wavelengths will be at the same point in their cycle.
When sound is recorded for stereo playback, it is assumed that the listener will be located at equal distance between the two loudspeakers. Of course, this rarely happens in the car, unless you are driving a McLaren F1. We compensate for the lack of seating on the center speakers by adjusting the balance on the CD player, which increases the volume level on one side relative to the other. This only corrects the stereo image to a point, because we are still physically closer to one speaker than to another, and the balance adjustment does not affect the phase and time of the signal that reaches our ears.
If we sit in front of the car, next to the left speaker, we will hear the sound from this speaker very little before the sound from the speaker on the right and from those speakers that are behind us. It is also likely that in the upper frequencies, where the wavelengths are very short, the sound that we hear through our left and right ears can be slightly damped. These temporal and phase distortions mix the brain and can destroy the stereo effect. When this happens, you hear most of the sound coming from the speaker closest to you, and not from an imaginary tread on the windshield — the stereo trick doesn't work.
Our previous water analogy can also help us understand what is meant by the sound that is in phase. and phase. Imagine you start a gentle wave at one end of the bath. If you use both hands to trigger two waves at exactly the same time, the wave peaks will occur at exactly the same point, and the waves can be called the “phase”. Now start a gentle wave from the other end of the bath. What happens when two waves meet? Both waves collide and effectively cancel each other. Now imagine the speakers on the front and rear of the vehicle, each of which produces sound pressure sounds. They mix and create very complex sound changes. As the pressure waves meet, the air can be amplified in the same direction in which it is already moving (so we get additions that can lead to peaks in the frequency response), or one pressure wave can compress against another, moving in opposite direction direction. In the latter case, if the two waves are identical in frequency and pressure and have exactly half the wavelength outside the phase, they completely cancel them, leaving silence.
Usually the two sound patterns are so complex that they will only be partially canceled, but the relatively clean tones of the long wavelength and high pressure are likely to be noticeably canceled. The lower the reproducible frequencies and the more loudspeakers reproduce this frequency range, the greater the likelihood of a phase occurring. If the loudspeakers are connected using the + and - buttons turned upside down, the loudspeakers are 180 degrees (half the wavelength). Theoretically, they should cancel themselves, but in practice, the bass region is experiencing the greatest return, and the sound reminder becomes confused, with a small or missing central image.
Speaker placement ... for those who don't have a McLaren F1
By installing a lot of speakers inside the car, we create a very complex combination of pressure waves that can cause problems with the overall sound. This does not necessarily mean that installing a large number of speakers is very difficult. We may want to break the frequency range into small portions — sub-bass, bass, mid-bass, mid-range, upper mid-range, high frequencies, and ultra high frequencies — so that each range has a pair of speakers designed for it. Due to the limitations of the loudspeakers, this can be a good idea if we are looking for absolute sound fidelity. Of course, the space in the vehicle is limited, and therefore we tend to install fewer speakers, usually covering sub bass, middle bass, mid-frequency and upper frequencies. This can give a good reproduction of the tonal qualities of various instruments and voices, but there are still problems with phase, “time alignment”, and & thetas; performance to consider.
We should try to avoid reproducing the same frequencies from speakers located at different distances from listeners. For example, if we have a pair of 6-inch speakers producing middle bass in the front of the car, we should avoid having another pair of speakers reproducing the exact same frequency range from the back shelf. Associated pressure waves will cause additions and subtractions in accordance with the phase of each wave at the point where they occur. The frequency peaks and valleys could be adjusted using the third octave equalizer, and the time of each speaker could be adjusted using the time-aligned and # 39; digital signal processor, but there is no practical way to compensate for phase distortion. It is much more reasonable to avoid problems from the very beginning as far as possible.
When you decide where to place the speakers, especially mid-range and tweeters, try setting them so that the left and right speakers of each matched pair are equidistant from the listeners. It is very difficult to achieve, but do your best. Legroom positions often work well for midrange speakers, and sometimes for tweeters. If you decide to set the tweeters higher, try, if possible, to set them to a position equal to half the distance from the middle range loudspeaker - there is some evidence that placing medium and tweeters exactly 180 degrees can improve the stereo image.
Large loudspeakers are often installed in doors without much influence on the image if you make sure that the crossover point is set so that their output does not overlap the frequency range of the mid-range loudspeakers. A subwoofer or subwoofers are usually installed in the back of a car because of their size. Be careful when choosing the slope and setting the crossover point on the channel (s) serving these speakers. From 6 dB per octave bottom pass # 39; the filter (a filter that only tracks frequencies below a certain crossover point) is set to 100 Hz, the output at 200 Hz will only be 6 dB lower, and since the subwoofers tend to be loud, pressure waves generated in the center frequency range are likely It will be strong enough to interact with the speakers in front of the car. It is usually wise to choose a slope of 12 dB or 18 dB for subwoofers.
Installing full-range loudspeakers on the rear shelf or in the rear doors is often confused by the stereo image in front of the car, because the same sounds come from more than one source, and this is unnatural. If you need to install speakers here to provide a “rear atmosphere” or dual front stage because you often carry passengers in the rear seats, adjust the front / rear fader controls on the CD player so that the front speakers are louder than the rear speakers, with listening from the driver's seat.
You may still find that the stereo image in the front of the car is confused. If this is the case, it’s worth experimenting with paying attention to +/- connections to all the full-range speakers on the rear panel, putting them 180 degrees out of phase. with those in front. It may seem crazy, but sometimes it works well. Always make sure that you cancel connections on both loudspeakers in a pair.
In an ideal situation, all sound at all frequencies should start from the same place. A loudspeaker system that attempts to provide this is often described as a single point source & because different drive devices are physically aligned, so that, theoretically, at least the sound will be “out of phase”; and & times in the entire frequency spectrum. However, what usually happens in a car, the speakers are located at some distance from each other and at different angles relative to the driver and passengers. A speaker that is aimed directly at the listener is called “on the axis,” while a speaker mounted on the bottom of the door next to the driver is described as “off-axis”; The output characteristics of the speaker change when it is tapped with an axis. Phase changes also affect its frequency response. It is important to know this and experiment, where possible, by changing the angle of the speaker for best results.
Встряхните, погрейтесь и ... Почему материалы резонируют
Одна вещь, которую мы хотим избежать в автомобильной аудиосистеме, - это любые панели (такие как металлические панели самого автомобиля), которые резонируют, то есть вибрируют из-за движения воздуха в замкнутом пространстве автомобиля. Это плохо, потому что эти панели будут создавать собственный звук или, в случае стен басового корпуса, если они не будут серьезными, то мы потеряем часть мощности и определение с низких частот.
Музыкальные инструменты, которые производят звук естественным образом (не в электронном виде), делают это, заставляя что-то резонировать - например, гитарные и фортепианные струны или шкуры и металлические поверхности набора ударных и т. Д. - Египет, непосредственно перемещая воздух, как в случае духовые и медные инструменты. Каждый материал имеет конкретную резонансную частоту. - это частота, с которой материал будет вибрировать или резонировать наиболее свободно - и это, вместе с размером резонирующего объекта и многими другими факторами, способствует звуку, который объект будет производить, если он достаточно возбужден.
Конечно, что-то очень строгое и жесткое, как кирпич, вряд ли будет резонировать, чем гитарная струна или тонкая кусок дерева. Кирпич - гораздо менее эффективный резонатор, чем дерево. Иногда это может быть полезно, особенно при построении басового корпуса, где нам нужно, чтобы стороны были очень жесткими и акустически «мертвыми». так что это не резонирует, так как это добавит некоторый собственный звуковой характер (или цвет) к басовому звуку, который мы пытаемся воспроизвести.
К сожалению, кирпичные басовые шкафы в машинах на самом деле не слышали, и нужно было разработать более практичные альтернативы для того, чтобы сделать деревянные корпуса и металлические части автомобиля менее резонансными. Хорошая качественная древесностружечная плита (MDF) особенно чувствительна и обеспечивает хорошую отправную точку, и при необходимости ее можно обработать звукоизоляционным листом или обработкой распылением. В случае звукоизоляционного листа эти связи акустически "мертвы" материал к более легковозбужденной панели, такой как внутренняя боковая панель автомобиля, дверная панель или внутренняя ботинок (багажник). Лист помогает поглощать панельный резонанс, потому что его собственная резонансная частота очень низкая, поэтому резонанс происходит на гораздо более низкой частоте и становится менее заметным. В случае NoiseKiller, обработкой аэрозолей, разработанной шведской компанией Audiform, резонанс, поглощаемый материалом, не просто сдвигается по частоте. Вместо этого он превращается в небольшое количество тепла. Производитель утверждает, что материал не производит абсолютно никакого звука - другими словами, панельный резонанс полностью устраняется.
