Acoustics

What is sound? Sound is caused by vibrations and is a form of kinetic energy. How do these vibrations travel through the air to our ears? The air is pushed together at the higher pressure (compression) and pulled apart at lower pressure (rarefaction) by the vibrating ruler. These changes in pressure are passed through the air in the form of sound waves. Speed: Distance travelled in unit time (m/s) Frequency: Number of complete waves in one second (Hz). It is the number of waves that pass a point per second. To determinate frequency is used the formula: f= Cycles/time Wavelength: Distance between matching points on the wave. This is sometimes called Lambda and it is measured in meters. Longitudinal: Vibration parallel to direction of travel Transverse: Vibration at right angle to direction of travel Waves carry energy from one place to another. Sound, light and radio signals all travel in the form of waves. Two types of waves are: Transverse and longitudinal. Transverse waves vibrate at right angles to the direction of travel of the wave. Longitudinal waves vibrate parallel to the direction of travel of the wave. Sound waves are longitudinal. Different waves travel at different speed. Sound travels 330 meters every second (330m/s), radio waves travel at the speed of light, an amazing 300.000 kilometers per second)    Sound is only caused by objects vibrating. Large objects make big waves, or in scientific terms, they create waves of large wavelength and this means they create waves which are low in pitch or low in frequency. Small objects, on the other hand, creates small wavelength and that creates high pitch or high frequency notes. Bugles work vibrating, they push air, causing compression and then they move them apart causing low pressure or rarefaction, and it is the variation in pressure that gives you the sound wave. This pressure is actually very small, it can only really move light things such as bubbles. Sound energy can be compared with a balloon: when we are blowing it, it gets bigger and more transparent, that’s because the rubble of the balloon spreads in a bigger area; the same thing happens with sound energy. When we clap our hands, we can actually see the hands vibrate quite a lot, this is really the source of noise, and it is call acceleration noise. When we play our hands together, the air is compressed, which creates an acoustic wave and that is what we hear, when we clap our hands in different ways we can get different noises. When we fill a balloon with flower, we can see the shock wave, the air inside of the balloon is at high pressure and when it burst, this pressure goes away which forms the familiar bang we hear. So, what causes a whip to crack? Well that is a sonic boom. Sonic booms are often associated with supersonic aircraft and whit a space shuttle. Coming down a river you can see wave coming out the back, and the same thing happens with the aircraft, before it slows down to the speed of sound, this waves can out of the way, but if it doesn’t, then these waves bunch together and eventually forms the shock wave which is the sonic boom you hear, and that speed is the speed of sound. The tip of the whip is accelerated at 2 o 3 times the speed of sound When designing for room acoustic comfort, have the person, the room and the activity in mind. If you design buildings find out what they should be thinking about, and what the possibilities are, get some inspiration. __ Interview about noise and sound  __ Prof. Murray Hodgson with Vancouver by Design What is the sound in a space? First, it is the noise or bad sound (we can hear the music and all the other people talking, etcetera), then it is the signal, in other words, the useful sound that is the opposite to the noise, and the reverberation, which is the echo of the sound in a room, all of those are part of the acoustic of the architectural space. The professor Hodgson picked a cafe for the interview for sonic reasons: the noise in the eating establishment around. A noise place like this can be a bad place (in terms of noise) but that depends on the opinion, because in some surveys, people said that they like to have some sound like music around them, but in a moderate level, but he thinks restaurants make some noise for giving to the place a young and exciting feel. Other issue is if the noise covers up the conversations, that gives you a little more privacy, but the real problem comes when you can´t hear your own conversation. Signal, for the professor, is a wanted or useful sound, noise is simply unwanted sound, so sitting in a public place, the person who you are talking to, thinks your voice is signal, in other words wanted, but the people around, if you are talking to loud, may think it is just noise and unwanted. But if we turn off that noise, we may feel like everybody can hear us and we can hear them, so the music or sound behind us may be classified as signal or noise. Is an acoustic designer an artist or a scientist? It is more like a scientist. A building is a physical system, and it gives sound reflection in some places, on the other hand the people that are going to use it are not only physical systems, so the requirement for what you need is practically physical, you don’t want to damage people hearing in a industrial building, it is in part emotional and it is also artistic because you should create a mood. Also, when you are creating a concert hall you want to preserve the quality of music but also give people a good experience (emotional) so it is a complicated issue. When you are in a concert hall you don´t want to feel totally isolated, but certainly you want to hear what is happening in the stage, the other thing is that the stage has to be able to hear itself and they may want to hear you because they want to know you are there, it is complicated. What impact sound has in our wellbeing? Extremely noise in the work space can turn you deaf. Noise can also cause stress, fatigue, it can make you feel uncomfortable, it can reduce your quality of life and this is something than can also happen in your neighborhood, if is too much noise outside it can get into your house. The acoustic of a space can be design by getting the right architectural form, materials and equipment. There is more than the artistic side of the building, and usually that is forgotten.
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