The acoustics, or the science of sound, is important in order to understand the entire experience of sound in a room.

 
Absorbing surfaces take up the sound energy from the incoming wave. Thus, disturbing and undesired sound reflexes are efficiently muffled. At the same time, the total sound energy of the room is also reduced, which means that the direct sound gets less ”support” and can be experienced as softer. A much too muffled room is often experienced as oppressive and uncomfortable, so it is important that the amount of absorbents be balanced against the other surfaces. In for instance apartments, offices and classrooms, mostly square or rectangular rooms, it is almost impossible to ”angle off” all unwanted sound reflections. Here, the presence of absorbing surfaces in the room is necessary for a comfortable hearing experience.
 
Reflections from hard surfaces in the room represent a significant factor of vital importance to the acoustics of the room, in both negative and positive ways. The acoustics is completely depending on the angles of the surfaces and the distances to loudspeakers and listeners. When a sound wave hits a hard surface it is reflected, more or less as the light is reflected in a mirror. All incoming sound energy bounces on with undiminished power as a distinct reflection in a direction determined by the wave’s angle of incidence towards the surface. Reflections from hard surfaces, depending on when and from where they reach the listener, can either provide the direct sound with a good support or colour the sound and disturb the experience of the directional influence in the room.
 
Diffusion is a concept which, in connection with sound, often more or less means ”spreading”. A diffuser is a reflecting surface that does not provide any sharp reflex, but spreads the returning sound energy over time, so that the ring in the room increases without the occurrence of colouring and other side-effects. So as to prevent the development of frequency-colouring phase-outs between the different reflexes emerging from the different compartments of the diffuser, it is important the relation in time between the different reflexes is evenly balanced mathematically. Therefore, an optimal diffuser must be constructed starting from mathematical principles and avoid regular patterns in the surface structure. Diffusers are used in order to add ”depth” to the sound picture and improve the room experience. The room ”feels bigger” than it actually is.

Different frequencies – different acoustics
As the spreading speed of sound is the same at all frequencies, each frequency gets its own unique wavelength. Within the human range of audibility it varies from about 17 metres to 1.7 cm. Depending on the room’s measures there is in a room a limit frequency that divides the behaviour of the sound waves into two categories.  You talk about wave acoustics and geometrical acoustics. Wave acoustics is the part dealing with the behaviour of the sound waves at low frequencies (long wavelengths). Here, the rules on angles and reflection directions mentioned above do no longer apply, but the sound spreads with circular radiation from the sound source.

As a consequence, acoustic decorations for low frequency purposes become less depending on aspects such as reflection angles and distance to the listener. Instead, the placing is determined by the blast wave’s spreading properties in the room, e.g. condensations of the sound pressure mostly develop in the corners of the room, which is why it may be more efficient to place a bass absorbent in the corner. Furthermore, every room has its own resonance frequency which creates so called room nodes (amplifications and extinctions) on certain spots in the room. The total surface of e.g. absorbing material in the room is also of great significance.

Bass absorbents are necessary in small rooms in order to control the low frequencies. If there is no bass absorption, the room becomes ”bold” and the frequency passage in the bass register uneven. The extinction phenomenon occurs on different places in the room and no tone control or sub-bass loudspeaker in the world can change that. Low frequency absorbents are preferably designed as slit or hole panels with absorption material behind them. Then the slits in the slit panel, or the holes in the hole panel, will be acoustically tuned ”inverting organ pipes” which target-oriented absorb the sensitive frequencies of the room.
 
General information on all-day sound
Today, it is estimated that more than 17 % of Sweden’s population has tinnitus. Out of these, every fourth person is a teacher. A normal conversation has a sound level of about 65 dB, whereas the sound level in a classroom or in a pre-school may very well amount to 85 dB (or more), which is the risk limit for hearing damages.
 
The school and pre-school environments therefore represent an extremely important site to regulate acoustically, both in order to reduce the occurrence of hearing damages, and to give everyone a fair chance to follow the lectures. Bad acoustic properties have more negative effects on hearing-impaired persons compared to those who are not hearing-impaired. The reason is that our brain has difficulties sorting out undesired noise.


Absorption or ABSORPTION
Many materials dampen sound – but do they dampen at the right frequencies?
The problem with thin materials that only dampen high frequency sounds is that they muffle the most important letters of speech, the consonants. The low frequency noise (where the vowels are found) which still remains as a ”fog" erases the frequency of the consonants even more. Instead of supplying a good absorption and increased speech perception ability, the possibility to chat has been deteriorated. Consult us for the right products for your environment.

We are the main sponsor for HRF’s (National Federation of Hearing-impaired) campaign "Liberate Conversation".
If you are interested in reading more about all-day sounds and impaired hearing, visit:

www.befriasamtalet.se