Acoustics

**Sound** is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.  
 * **Speed:** is the distance travelled during a unit of time (m/s) by a sound wave propagating through an elastic medium.


 * **Frequency:** is the number of complete cycles in one second, in other words, it is the number of waves that pass a point per second. It is measured in hertz (Hz)


 * **Wavelength:** is the distance between matching points on a wave. It is measured in meters.


 * **Longitudinal:** vibration parallel to the direction of travel of the wave. Sound waves are longitudinal
 * **Transverse:** vibration at right angles to the direction of travel of the wave. An example of this, are light and radio waves.

** Notes ** In the video they explain that the vibration of bodies produces different sources of sound as music. they also use a fork, which is an acoustic resonator, as an example. Because when it is hited it resonates at a specific constant pitch and emits a pure musical tone. **From sites: **  Room acoustics are about the way in which sound behaves in a room. Sound transmission, sound absorption, sound reflection and sound diffusion are all aspects that are important here. Room acoustics also include how we as humans perceive different acoustic phenomena.

 Different types of room will create such different sound fields that this in itself requires different descriptors. We can identify three different basic acoustic types:


 * Hard rooms: <span style="font-family: Verdana,Geneva,sans-serif; font-size: 130%;">Is a room with little sound absorption, in which the surfaces reflect most of the noise.
 * <span style="background-color: #ffffff; font-family: Verdana,Geneva,sans-serif; font-size: 130%;">Rooms with absorbent ceilings: <span style="font-family: Verdana,Geneva,sans-serif; font-size: 130%;">Is the most common type of room. This type requires several descriptors for an acoustic assessment. In these rooms, the reverberation time does not only depend on absorption
 * <span style="background-color: #ffffff; font-family: Verdana,Geneva,sans-serif; font-size: 130%;">Open-plan rooms: <span style="font-family: Verdana,Geneva,sans-serif; font-size: 130%;">This type is a room with extended forms such as open-plan areas and corridors. The reverberation time must be supplemented with descriptors that are adapted to the room’s geometrical shape and that can provide guidance for the acoustical design.

<span style="background-color: #ffffff; font-family: Verdana,Geneva,sans-serif; font-size: 130%;">A number of measurable room acoustic descriptors have been defined. These descriptors can be used to formulate room acoustic specifications and to check the effect of different procedures. We can find:
 * <span style="background-color: #ffffff; font-family: Verdana,Geneva,sans-serif; font-size: 130%;">Reverberance: linked to the speed at which sound energy disappears in a room.
 * <span style="background-color: #ffffff; font-family: Verdana,Geneva,sans-serif; font-size: 130%;">Speech clarity: concerns the quality of speech transfer to the listeners.
 * <span style="background-color: #ffffff; font-family: Verdana,Geneva,sans-serif; font-size: 130%;">Auditory strength: is the level at which we experience sound.
 * <span style="background-color: #ffffff; font-family: Verdana,Geneva,sans-serif; font-size: 130%;">Spacial decay: the sound level decreases as the distance from the sound source increases.