Designing room acoustics is a difficult issue. It depends on many factors such as cubic capacity of the room, type of finishing materials. Acoustics strongly influences the comfort of use of rooms. Let's take a closer look at theory.
Longitudinal sound insulation (sound insulation), expressed by the Dnfw indicator, determines the sound reduction level between adjacent rooms. It depends on the thickness of partitions, constructional solutions applied and density of elements from which the partition is made. Denser materials and thicker partitions insulate much better. In addition to these properties, the sound transmission is also affected by the tightness of the connections and the quality of the installation elements. The value of this indicator is measured in laboratory conditions for a common ceiling over two separate partitions of rooms. The higher the value of the index, the better the insulation performance. This is extremely important for minimising outside noise and maintaining privacy.
Dnfw (weighted standardised longitudinal difference in levels) - weighted difference between the time and space averaged sound pressure level produced in two or more chambers by at least one sound source located in one of them, if the transmission only takes place along a specific lateral path. It is determined according to EN-ISO standards.
Sound reduction (sound insulation) - limiting the transmission of sound coming into a given interior from the space above the false ceiling. Expressed by the Rw indicator
Rw (weighted sound insulation index) - expressed by a single number, resulting from laboratory measurements, the index of sound pressure level reduction after passing through the partition. Determined according to EN-ISO standards.
Sound absorption (sound absorption) - a change in the energy of sound waves in heat (through friction) when passing through a medium or colliding with it as a result of introducing air into a resonance. Each sound produces sound waves of a specific energy. They diverge from the source, in all directions. Part of the energy is absorbed, the rest is reflected. If the room is small and each reflection absorbs a large amount of sound, a quieter environment with a shorter reverberation time will be achieved. If the room is spacious and the sound absorption is low, a noisier environment with a longer reverberation time is created. Sound absorption is the limitation of sound reflections inside a room using, for example, an absorbent suspended ceiling.
The sound absorption for a given material is expressed by the index αw.
αw (weighted sound absorption coefficient) - expressed as one numerical indicator describing the absorption of sound waves falling on the surface in an accidental manner, determined in accordance with PN-ISO standards. The calculations made shall be recorded in the form of a graph on which a calibration curve is plotted, which is gradually approximated to the measured curve until the 'best fit' is obtained. The value obtained will be in the range from 0 to 1 and will be a multiple of 0.05
Reverberation - sound resounding in a closed room after the primary source of sound is no longer emitted due to reflections of sound waves from different surfaces. Influences the sound quality and sound level in the room
Reverberation time - the time measured in seconds when a sound reflected in a closed room will weaken to one millionth of its original power after the sound emission has ceased. The reverberation time depends on the frequency of the sound waves emitted and is generally measured in a 1/3 or 1 octave wide band. For each room, depending on the area and purpose, the optimum range of reverberation times is achieved. For speech, the reverberation time should not exceed 0.8 seconds. Otherwise, sounds may start to merge. However, if the reverberation is too short (less than 0.4 seconds), the room will seem "dead" due to the lack of amplification from the space. This will also make conversation more difficult. In the case of music, a longer reverberation time is more advantageous - the notes merge and give the impression of fullness of sound. In a room without a proper reverberation, the music will seem "dry". The reverberation time should therefore be optimised for each room, regardless of its intended use. Too high or low sound absorption values for materials used in the room, if not intentional, are not acceptable.
Frequency - a number, expressed in Hertz (Hz), indicating how many times per second the cyclic changes in the sound wave generated by the sound source occur.
Herz (Hz) - unit of measurement of frequency. One cycle per second corresponds to one hertz.