Published on September 11, 2014
The Recording Environment firstname.lastname@example.org www.stuartjones.org
Agenda Sound Waves Room Acoustics Sound Wave Reflections Absorption Coefficients The Sabine Equation Reverb Calculation Example Estimating the Reverberation Time Reverb Calculation Example 2 Correcting the Reverberation Time Absorbers Reverberation
Sound Waves Sound Propagation The Recording Environment View slide
What is Sound? Sound is produced when an object (the source) vibrates and causes the air around it to move. The Recording Environment View slide
Sound Propagation • Sound travels in air as a lengthwise or longitudinal wave. This sort of density wave is the way in which sound is transmitted through air, gases and liquids. • In solids we also find transverse waves. The Recording Environment
Sound Propagation Longitudinal Wave The Recording Environment Snell's Illustration of Sound Waves http://www.youtube.com/watch?v=OQPI5Ng-3vI&list=PL689066FDE3D631CE
Sound Propagation Transverse Wave Disturbance takes place perpendicular to the direction which it is moving The Recording Environment
Sound Propagation Transverse Wave Machine The Recording Environment http://www.youtube.com/watch?v=tihcRFWeZlQ&list=PL689066FDE3D631CE
Clip taken from - Sound Waves and their Sources (1933) The Recording Environment
The Recording Environment
Sound Waves Sound Wave Properties The Recording Environment
Sound Waves: Fundamental Mathematical Relationships The Recording Environment
Time Amplitude + 0 - t The rate at which the source oscillates is the frequency of the sound wave it produces, and is quoted in hertz (Hz) or cycles per second (cps). 1000 hertz is termed 1 kilohertz (1kHz) The Recording Environment
In air, the speed of sound is approximately 340 meters per second The frequency and wavelength of a sound wave are related very simply if the speed of the wave (usually denoted by the letter c) is known. c = fλ (speed of the wave = frequency x wavelength) or λ = c/f (wavelength = speed of the wave x frequency) (λ = The Greek letter lambda is often used to represent wavelength) The Recording Environment
time (ms) 2 4 6 8 10 12 14 16 18 20 22 24 ms 0.7 1.4 2.0 2.7 3.4 4.1 4.8 5.4 6.1 6.8 7.5 8.2 m distance (m) Relationship between elapsed time and traversed distance for the propagation of a sound wave in air The Recording Environment
Room Acoustics The Recording Environment
Influence of Acoustical Space on the Sound Event The Recording Environment
In enclosed performance spaces, a new phenomenon appears: reverberation, which is caused by sounds being repeatedly reflected from all surfaces and objects in the room. The Recording Environment
Room influences may be described in two ways: 1. Objectively through measurement of the sound events and their variation with time (room acoustics. 2. Subjectively through verbal description of the audible experience (aural acoustics) Both methods are necessary depending on the question at hand; either the objective or subjective one may assume the greater importance. The Recording Environment
The Recording Environment
Fundamentals of Aural Acoustics The Recording Environment
Fundamentals of Aural Acoustics 1. The Listenability of a Room - Generally describes its suitability for certain sound events.e.g Good listenability of a room for speech means that we hear speech well at every seat in the house without the need for reenforcement. 2. The Transparency of a Room - The ability to differentiate between simultaneously played instruments or instrument groups in spite of superimposed room reverberation. Transparency is a basic requirement when we hear complex musical structures. The Recording Environment
Fundamentals of Room Acoustics The Recording Environment
Sound propagation in an enclosed room (the rays show the propagation direction and intensity) The Recording Environment
Direct Sound First Reflections Reverberation Sound Level Time Direct Sound and diffuse sound (reverb build-up, early reflections and decay) in an enclosed space The Recording Environment
RT60 The term RT60 refers to the time it takes the reverb to decay by 60dB. RT is measured at the point at which the reverb decays to -60dB of its peak level. The Recording Environment
The Recording Environment
• Direct sound arrival is followed by reflections from room surfaces. • Overlapping reflections are heard as reverberation. • Direct-to-Reverberant ratio gives cues to size of room, type of room surfaces, and distance from source. The Recording Environment
Significance of Room Tone for Microphone Placement and the Listening Experience The Recording Environment
Significance of Room Tone for Microphone Placement and the Listening Experience • The microphone generally picks up both direct and diffuse sound. • While the direct sound is influenced little by the nature of the room, the diffuse room tone transmits information about the room size and the nature of the wall treatment. • The acoustical attributes of the room tone provide information about the cultural and social environment into which a musical performance has been placed. The Recording Environment
Significance of Room Tone for Microphone Placement and the Listening Experience • Thus church music requires the acoustics of a large church for which it generally is written; symphonic music is written for concert halls, chamber music for the small, private room in a castle or home. • Folk music needs the intimate atmosphere of a pub. • In pop music and other similar musical forms, we see the creation, through the use of artificial reverberation of new acoustical surroundings which really do not exist in real life. The Recording Environment
Sound Wave Reflections The Recording Environment
Sound Wave Reflections Creation of Sound Reflections The Recording Environment
Sound Wave Reflections Creation of Sound Reflections 1. Sound reflections within a room occur when sound reaches a boundary surface without too much absorption. 2. Dimensions and nature of the surface determine how the diffused sound is scattered. The Recording Environment
Sound Wave Reflections The Haas Effect The Recording Environment The Haas effect can be summarised as follows: • The ear will attend to the direction of the sound that arrives first and will not attend to the reflections providing they arrive within 30 ms of the first sound. • The reflections arriving before 30ms are fused into the perception of the first arrival. However, if they arrive after 30ms they will be perceived as echoes. Angus, J & Howard, D (2009) Acoustics and Psychoacoustics. UK, Elsevier.
Comb Filtering The Recording Environment
direct path Diagram showing an example of a comb filter created by the combining of two signals with the same amplitude, but with a time delay between them of just 1 ms. Comb Filtering A.C.M.E Mixing Desk The Recording Environment speaker
Mic Reflected Sound Sound Source Direct Sound Surface Resulting Frequency Response dB An affected waveform shows lots of sharp peaks and troughs that look not unlike the teeth of a comb The Recording Environment
Splayed Ceiling Design Ceiling reflections cause acoustic interference at the listeners position The Recording Environment
Splayed ceiling reduces unwanted reflections The Recording Environment
Pressure Max Min Max Min Max Min Max. Boundary Maximum Minimum Pressure Reflection The formation of a standing wave by reflection at a boundary
Room Resonances, Natural Frequencies & Modes The Recording Environment
Image showing room resonances, natural frequencies & modes
Boundary Boundary F 2F 3F 11.3 Feet 100Hz 200Hz 300Hz Image showing room resonances, natural frequencies & modes 100Hz The Recording Environment The same effect will occur at frequencies that are multiples of 100Hz (200Hz, 300Hz, etc)
Node Anti Node The Recording Environment
The Recording Environment email@example.com k www.stuartjones.org
The Recording Environment part 1. Introduction to Room Acoustics
This page (in the DigiFreq Articles area) contains detailed information about the following topic: Creating the Right Recording Environment (Part 1).
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