Room acoustics
Room acoustics describes how sound behaves in an enclosed space. Sound of different frequencies behaves differently in a room. Reflections between walls, floor and ceiling create room modes at specific frequencies and locations. Reflections also produce reverberation. Frequency zones. The way that sound behaves in a room can be broken up into roughly four different frequency zones: Natural modes. The sound wave has reflections at the walls, floor and ceiling of the room. The incident wave then has interference with the reflected one. This action creates standing waves that generate nodes and high-pressure zones. A modal density  analysis method using concepts from psychoacoustics, the "Bonello criterion", analyzes the first 48 room modes and plots the number of modes in each one-third of an octave. The curve increases monotonically (each one-third of an octave must have more modes than the preceding one). Other systems to determine correct room ratios have more recently been developed. Reverberation of the room. After determining the best dimensions of the room, using the modal density criteria, the next step is to find the correct reverberation time. The most appropriate reverberation time depends on the use of the room. Times about 1.5  to 2 seconds are needed for opera theaters and concert halls. For broadcasting and recording studios and conference rooms, values under one second are frequently used. The recommended reverberation time is always a function of the volume of the room. Several authors give their recommendations A good approximation for broadcasting studios and conference rooms is: with V=volume of the room in m. Ideally, the RT60 should have about the same value at all frequencies from 30 to 12,000 Hz. To get the desired RT60, several acoustics materials can be used as described in several books. A valuable simplification  of the task was proposed by Oscar Bonello in 1979. It consists of using standard acoustic panels of 1 m hung from the walls of the room (only if the panels are parallel). These panels use a combination of three Helmholtz resonators and a wooden resonant panel. This system gives a large acoustic absorption at low frequencies (under 500 Hz) and reduces at high frequencies to compensate for the typical absorption by people, lateral surfaces, ceilings, etc.