![]() The compressions (bunched up areas) keep moving along, eventually dying out due to the friction of the air, or ending up on someone's ear drum. Molecules moving in a forward direction will get bunched up, or compressed, and then more spaced apart, or rarefacted, as they bounce backward away from each other. Each air molecule stays in one place, bouncing back and forth, slamming into the molecule ahead of it, and then slamming into the molecule in back of it. The wave along the slinky is like a sound wave as it travels through air. (Now you want a slinky, don't you? Go buy one and play with it!) It will look like a wave, traveling along the length of the slinky, over and over, as long as you continue to move the one end. But you'll see the bands as they bunch up, and the location of the bunched up section will continue to move to the other end of the slinky. This will be repeated along the whole length of the slinky. Each band of the slinky will run into the next band, and then move backward away from it. ![]() If you hold one end still, and move the other in and out in a regular rhythm, each band of the slinky stays pretty much in place, just moving back and forth as much as you originally moved the end of the slinky back and forth. The journey from the eardrum into the brain is very cool. Sound Wave - A sound wave is a disturbance of air molecules, propagated through air.įor our discussion, assume the disturbance of air molecules will eventually disturb the tympanic membrane (ear drum) causing a vibration to go into the brain, where it is interpreted as sound. Phase differences are very important in voice though, because different portions of the vocal folds may vibrate out of phase with each other, resulting in very complex vibration. In the complex sounds we hear, we don't perceive the phase differences as a separate entity. If we could hear two simultaneous sine waves with the same frequency and amplitude but were out of phase with one another, we might only hear a slight buzziness to the sound. In sound, phase doesn't have a perceptual correlate in the way frequency and amplitude do. If one vibration starts it's excursion in one direction at exactly the same time another starts its excursion in the opposite direction, they are said to be 180 degrees out of phase. Phase is measured in degrees away from midline, just like degrees of a circle. Rather, it's a property of vibration that exists at any moment in time. Phase doesn't actually measure any property of vibration. Usually, this is in comparison to when other vibrations begin their first excursion away from midline. Phase refers to the moment in time the vibration starts its first excursion away from midline. Read on, and we'll discuss this topic more, but some of the discussion is beyond the scope of this website. In the case of the voice, the amplitude of the vibration of vocal folds may determine the intensity of the sound wave, but many other factors influence our perception of the voice's loudness. ![]() Those are all measured differently, and don't correspond to each other in a one-to-one fashion. Acoustic scientists distinguish between the amplitude of vibration, the intensity (or sound pressure level - we won't go into detail on this property in this section), of the sound wave, and the loudness of the sound perceived. So we say that the perceptual correlate of amplitude is loudness.īUT, there's not a direct correlation between amplitude and loudness the way there is for frequency and pitch. The greater the amplitude, the louder the sound we perceive. In sound, amplitude of vibration gives us the loudness of the sound. Amplitude is measured in decibels (the abbreviation is dB, you can say decibels or dB, but not dB's - the abbreviation is already plural). Amplitude measures the strength of vibration. (Yes, vocal folds can vibrate faster than 1000 Hz, or 1000 vibrations per second!)Īmplitude is how far the pendulum swings away from its midline, in either direction. Click here to see the equivalences of pitch and frequency. So, we say that the perceptual correlate of frequency is pitch. The faster the vibration, the higher the pitch that we perceive. In sound, frequency of vibration gives us the pitch of the sound. Frequency is measured in Hertz (the abbreviation is Hz, but we always say "hertz"). Frequency measures the speed of vibration. There are only three properties that can be manipulated with a swinging pendulum, and these factors help illustrate the properties of vibration.įrequency is how many times per second the pendulum crosses its midline.
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