Acoustic knowledge

Sound

Sound refers to pressure fluctuations that propagate through an elastic medium. The medium can be either gaseous, such as airborne sound like in the case of air, or liquid, as in the case of underwater sound, or solid, which is referred to as structure-borne sound. The motion of the sound waves is transmitted by the collision of particles within the medium. This results in compressions and rarefactions of matter, through which sound is propagated. In a vacuum, where no matter is present, there is no propagation of sound or no acoustics.

Room acoustics vs. building acoustics

Room acoustics and building acoustics are two related but distinct disciplines that deal with sound in different environments.

Room acoustics primarily focuses on designing and optimizing the sound within a specific space. It considers the interaction between sound sources, sound propagation, and the reflections, absorptions, and diffusions of sound on the walls, ceilings, and floors of a room. The goal of room acoustics is to achieve optimal sound quality, whether in concert halls, recording studios, theaters, or other spaces where sound plays a crucial role. Measures are taken to control reverberation times, minimize reflections, and ensure even distribution of sound within the room.

Building acoustics, on the other hand, deals with sound insulation and transmission between different rooms or buildings. Its main focus is to reduce unwanted sound from a source to a receiver. This can include traffic noise, noise from neighboring apartments, or sound from technical equipment. Building acoustics employ sound insulation measures such as soundproof windows, sound-insulating doors, sound-absorbing materials, sound insulation of walls and ceilings, as well as special construction techniques to minimize sound transmission. Building acoustics play a significant role in residential buildings, offices, hospitals, schools, and other areas where privacy, peace, and noise protection are essential.

Although room acoustics and building acoustics have different focuses, they are closely interconnected. The acoustic design of a room influences both sound quality and sound insulation. For example, a well-designed concert hall must not only provide excellent sound but also ensure effective sound insulation against external disturbances. Therefore, room acoustics and building acoustics need to be considered in a holistic approach to create optimal acoustic conditions in various environments.

In today's world, where we are increasingly surrounded by noise, room acoustics and building acoustics are becoming increasingly important. Careful planning and implementation of these concepts can help us feel comfortable in our spaces, whether it's listening to music, working, studying, or relaxing.

Overall, room acoustics and building acoustics are crucial disciplines that deal with sound in various environments. They contribute to our enjoyment of sound while simultaneously reducing unwanted noise. By striking the right balance between room acoustics and building acoustics, we can create a pleasant and harmonious acoustic environment.

The reverberation time

The frequency refers to the rate of air pressure changes in airborne sound and is measured in Hz (Hertz). One Hertz corresponds to one vibration per second. The frequency of sound reproduction is perceived by humans as pitch. In acoustics, doubling the frequency corresponds to an octave interval. Thirds (1/3 octaves) are used as smaller intervals. The human ear can perceive frequencies between 16 Hz and 20 kHz. However, there are significant individual differences, and with increasing age, the upper limit decreases significantly.

Alpha

Alpha s

Alpha-s ist a precise indicator of sound absorption, as it is specified for a specific frequency range. An Alpha-s value of 0 represents no absorption, while a value of 1 signifies complete absorption. Multiplying the Alpha-s value by 100 gives the absorption value in percentage. For example, Alpha-s(250Hz) = 0.88 indicates a sound absorption of 88% in the frequency range of 250Hz. A carefully measured absorber (from 100Hz to 5000Hz) has a total of 18 different Alpha-s values (100Hz, 125Hz, 160Hz, 200Hz, 250Hz, 315Hz, 400Hz, 500Hz, 630Hz, 800Hz, 1000Hz, 1250Hz, 1600Hz, 2000Hz, 2500Hz, 3150Hz, 4000Hz, and 5000Hz).

Alpha-p (Practical Sound Absorption Grade)

To determine this indicator, Alpha-s (as) values are determined and converted into Alpha-p values. Three Alpha-s values are rounded to one Alpha-p value. Thus, an absorber measured in the range of 100 Hz to 5000 Hz will have six different Alpha-p values (125 Hz, 250 Hz, 500 Hz, 1000 Hz, 2000 Hz, and 4000 Hz).

Equivalent Absorption Area

The "Equivalent Absorption Area" is a term used in room acoustics, particularly for panel absorbers. Panel absorbers are used to absorb sound in a room, thus reducing reverberation. The Equivalent Absorption Area indicates the surface area that an ideal point absorber would need to have in order to achieve the same sound absorption as the panel absorber.
When calculating the Equivalent Absorption Area, various factors are taken into account, such as the absorption coefficient of the material, the size and shape of the absorber, and the angle at which the sound hits the absorber. These calculations help determine the Equivalent Absorption Area.
The Equivalent Absorption Area is a useful concept for comparing the sound absorption efficiency of panel absorbers. It allows for the evaluation of different absorbers in terms of their effectiveness in reducing reverberation and helps in making decisions to improve room acoustics.
Panel absorbers are commonly used in room acoustics to enhance sound quality and speech intelligibility. They are employed in concert halls, recording studios, theaters, cinemas, offices, and many other environments where good acoustic conditions are essential.

The sound absorption coefficient

The sound absorption coefficient indicates the ratio between absorbed and reflected sound energy. An absorption coefficient of 1 corresponds to 100% sound absorption, while a value of 0 corresponds to 0% absorption (100% reflection). It is important to note that the sound absorption coefficient is frequency-dependent.