Acoustics+Vocabulary

- Sound – where does it come from? A sound is created when the particles in a medium (usually air in our world) are set moving and forced out of a state of rest. This happens, for example, when we speak. Our vocal chords produce audible pressure variations (high and low pressure) in the air. Sound travels in air at a speed of approximately 340 metres per second. It spreads like a wave and is a mechanical vibration.

- Sound pressure and decibels Sound pressure, or sound pressure level, is the result of the pressure variations in the air achieved by the sound waves. The lowest sound pressure which can be heard by humans is called the hearing threshold, the highest which can be endured is known as the pain threshold. A compressed, logarithmic scale is used based on the decibel unit (dB). If two equally strong sound sources are added together, the combined sound pressure level does not double but increases by three decibels.

- Generating and understanding speech Speech occurs by air being forced past the vocal chords, which then begin to vibrate. The more air forced past the vocal chords per time interval, the stronger the sound. The vowels create the sound volume of speech, while the consonants are the bearers of information. - Normal hearing The energy of the vowels primarily lies in the range 250 – 2,000 Hz and that of voiced consonants (b, d, m etc.) in the range 250 – 4,000 Hz. Unvoiced consonants (f, s, t etc.) vary considerably in strength and lie in the frequency range 2,000 – 8,000 Hz. To be able to understand speech clearly, it is therefore important to have good hearing across the entire range of frequencies from 125 – 8,000 Hz.

- Impaired hearing When hearing is impaired, it is common to lose the ability to understand consonants which often contain little sound energy and lie in the frequency range 2,000 – 8,000 Hz.

- What are acoustics? is the term for the study of sound and how sound is experienced. The field of acoustics is divided into several specialist areas. The word acoustics comes from the Greek akoustikos (“to do with hearing”) and akouo (“to hear”).

- What are room acoustics? Room acoustics are about how sound behaves in a room. To understand this, it is necessary to look at phenomena such as sound absorption, sound reflection, sound diffusion and sound propagation. Room acoustics are also about how we, as people, perceive different acoustic phenomena. Building acoustics also involve sound insulation and consideration of how sound moves from one room to another.