Institut Teknologi Bandung

Anugrah stated that the fundamental idea in designing an acoustic room is the people. They are the users who conduct activities inside. Aside from the acoustic factors, room designation also focuses on both thermal and visual viewpoints.

Soundscape is one of the methods in evaluating the relationship between people and their surrounding sounds that are taken, experienced, and understood depending on the context. In association, acoustic circumstances are defined as sounds from environmentally modified sources.

The association of humans with their environment is influenced by four aspects. First is the context of the room designation and activities that are done inside. Next is the environmental perception, which relates to the thoughts and emotions wished to be conveyed through the layout.

The source of the sound is the third aspect that describes the ease of hearing. A negative source is referred to as noise; it can be either high-leveled exceeding 80 dB or lower-leveled yet annoying ones like the buzz of a mosquito. The final aspect is the environment itself.

“There are two things to consider the context of acoustic rooms. The first is noise control and the latter is the interaction between the source and environment to create a certain perception on said context,” Anugrah informed.

Four parameters are applied to illustrate these interactions: the noise, volume, levelness, and the impulse responses of the sound in a room.

Noise of Sound

Noise measurement inside a room can be determined using the dBA scale and NC (noise criteria). The scale is used because human ears’ responsiveness towards sounds is nonlinear- they are more receptive to frequencies around 4000 Hz. “In this scale, ‘A’ is expressed as the highest correlation in the lowest frequency. It also gives an increase in correction to higher frequencies,” Anugrah specified.

NC is a measuring parameter for various frequencies. To determine it, the value that is the closest to the top and almost in tangent with the resulting curve is chosen. As a designer, it is easier to state the noise of a room in NC than to describe the entire data of intensity in differing frequencies.

Volume of Sound

This parameter comprises the sound source’s pressure levels. There are several conditions to be aware of. First, the main sound must be higher than the background noise- both are different by a minimum of 10-15 dB. This sound has to be below 80 dBA for the safety of listeners. Lastly is the fact that every person has their own hearing preferences. For instance, different music genres can have varying loudness levels.
The fourth condition is the sound system of the room. “Good acoustic conditions do not often mean the lack of using a sound system. We only use those if it is needed. In this context, sound systems can elevate the sound quality,” Anugrah added.

Levelness of Sound

Levelness is necessary for a few places like classrooms and worship sites. In contrast to public offices, healthcare centers, and libraries, the noise level of these places is scaled down. “Imagine a scenario where noise levels are reduced in hospitals. Conversations between nurses can be heard by patients. That scenario is what we are trying to avoid,” Anugrah depicted.

A few years ago, Anugrah assessed the sound levelness of a church. The site is built so that the room used for walking produces sounds with deviations of no more than 5-6 dB, whereas rooms where people seldom move around can generate up to 10 dB. In lower areas, the dB values can be higher than the noise background for these rooms.

Impulse Responses of Sound

Impulse responses measure the reverberation time and the sound’s clarity. Reverberation time is the room's level of sound pressure to decay by 60dB. It is also the time spent by the sound to become inaudible when the source is turned off. Its value is influenced by two factors: average absorption coefficient and surface area of the room.

The greater the room's volume, the higher the recommendation for the reverberation time. “From the SNI, these values can fluctuate. A 10 000m3 studio, for instance, has the reverberation time of 0.7 seconds, but worship sites are allowed to accommodate values up to 2.1 seconds.” Anugrah continued.

The clarity of a sound is measured via the D50 parameter. Its calculation is derived from the reverberation time and uses the ratio between the value measured 50 milliseconds in the beginning to the total energy. Another parameter, C50, represents the energy ratio between the same value obtained 50 milliseconds earlier and its remainder.

Reporter: Amalia Wahyu Utami (Teknik Fisika 2020)
Translator: Ruth Nathania (Teknik Lingkungan, 2019)