GYPROC SOLUTIONS - Acoustics

Acoustics solutions in an internal environment are about two things – communication and concentration. Communication is basically about hearing and being heard. Good speech intelligibility is fundamental, be it informal conversations at your office desk, or formal meetings with several people in a conference room, or in a class room. Good speech intelligibility can be achieved by having optimum sound absorption in the room and the key to achieving that is by having a short reverberation time.

Concentration requires a minimum of disturbing noise. The attention level required by the task in hand must not be interrupted by conversations on the other side of the room or in a room next door. Key is to achieve a low noise level and short sound propagation within the area in which the conversation is taking place, as well as short absorption time.

Saint-Gobain Gyproc India through its wide range of products and
systems provides excellent acoustic solutions both from the point of
absorption and insulation.

Key terms used in acoustics.

Sound level

A sound wave is an expression of a change in air pressure, where the source of sound is the deciding factor for how big the pressure changes are. A split of the audible area cannot be done as per rule. A small increase in pressure change by a little volume of sound results in a significant audible difference. In contrast, a small increase in a pressure change by a lot of volume of sound does not result in the same audible impression. The reason for this is that the ear only registers a change in relation to the original strength. Therefore, a scale of strength with intervals which grow proportionately with the strength is used. This is known as the decibel scale (dB). A decibel is a proportional measurement of energy or force and it is organised logarithmically. The choice of a logarithmic scale overcomes several problems and is roughly equivalent to the sound level that is characteristic for the ear. As an example, the doubling of a perceived sound level is the equivalent to a 10dB change.

Frequency

Frequency (f) has an influence on all aspects of acoustics. A clear tone has a single related frequency. All musical instruments, however, produce complex sounds made by different frequencies, while the lowest of these normally determines the pitch, the name of the perceived frequency. Frequency is referred to in Hertz (Hz). The ear can register frequencies between 20 Hz and 20,000 Hz, but the top limit decreases with age. The ear can also grasp the frequency logarithmically; but no new logarithmic measuring system is used. The fundamental musical interval is the octave, which is the equivalent of doubling of the frequency. Acoustic measuring methods are also traditionally based on the octave intervals with the centre frequency at 125, 250, 500, 1000 Hz.

Reverberation

In an enclosed space, when a sound source stops emitting energy, it takes some time for the sound to become inaudible. This prolongation of the sound in the room caused by continued multiple reflections is called reverberation. Reverberation time plays a crucial role in the quality of music and the ability to understand speech in a given space. When room surfaces are highly reflective, sound continues to reflect or reverberate. The effect of this condition is described as a live space with a long reverberation time. A high reverberation time will cause a build-up of the noise level in a space. The effects of reverberation time on a given space are crucial to musical conditions and understanding speech. It is difficult to choose an optimum reverberation time in a multi-function space, as different uses require different reverberation times. A reverberation time that is optimum for a music program could be disastrous to the intelligibility of the spoken word. Conversely, a reverberation time that is excellent for speech can cause music to sound dry and flat.

Reflection of sound

When a sound wave hits a surface, it is reflected, absorbed or spread or even a combination of this. Reflected sound strikes a surface or several surfaces before reaching the receiver. The strength of an individual reflection is determined by the acoustic properties of the surface, from which it is reflected, as well as the distance it has covered.
When a sound wave hits a completely even surface it is reflected as a mirror image. All irregularities in the reflecting surface will influence the reflection. If a reflecting surface has absorbing properties some of the energy will be absorbed but the pattern of reverberation will also be affected by the angle the sound wave comes from. This especially applies to reverberations from a thin board which begins to vibrate because of a sound wave so that the reverberation angle fluctuates.
Surfaces which are not even spread the energy of the sound wave. A diffuse surface can be regular for e.g. curved or irregular. For e.g. A diffuse surface used in studios. Reflective corners or peaked ceilings can create a "megaphone" effect, potentially causing annoying reflections and loud spaces. Reflective parallel surfaces lend themselves to a unique acoustical problem called standing waves, creating a "fluttering" of sound between the two surfaces.
Reflections can be attributed to the shape of the space as well as the material on the surfaces. Domes and concave surfaces cause reflections to be focused rather than dispersed which can cause annoying sound reflections. Absorptive surface treatments can help eliminate both reverberation and reflection problems.

Sound absorption (NRC)

When a wave hits a surface, part of the energy is absorbed by the surface. Put simply, one can say that all the materials have an absorption factor and are thereby absorbent. The absorption factor for different materials denotes how much energy remains in the material. It is better if you have a numeric value that expresses their level of performance in acoustic applications. This helps you to specify and install a particular product. Noise Reduction Coefficient (NRC) Rating helps you determine it. The Noise Reduction Coefficient (NRC) is a single-number index for rating how absorptive a particular material is. NRC value is simply the average of the mid-frequency sound absorption coefficients (250, 500, 1000 and 2000 Hertz rounded to the nearest 5%). This industry standard ranges from zero (perfectly reflective) to 1* (perfectly absorptive). It is always expressed as a decimal rounded to the nearest .05. *(Based on the testing methodology, and depending upon the material's shape or surface area, some products can test at an NRC above 1.)
The NRC rating is only measured at 250, 500, 1000 and 2000 Hz. This is perfectly acceptable for speech, but can be inadequate for music (and other low-frequency sounds). Because this rating is an average, two materials with the same rating might not perform the same. The absorption properties of a material depend on both the degree of perforation and the size of the cavity or more precisely on the cavity's impedance. All of the building parts/materials have a more or less absorbing effect and are thereby a decisive factor in the room's total absorption. Some building parts/materials provide an absorbing contribution to the low medium and high frequencies. Therefore, in many cases it would be an advantage to use an absorbing product which has broad absorption that is reasonably spread throughout the frequency range from 125 – 4000 Hz.

Ceiling attenuation class (CAC)

Ceiling attenuation class (CAC) is the measure for rating the performance of a ceiling system as a barrier to airborne sound transmission through a common plenum between adjacent closed spaces. CAC thus indicates how well the ceiling acts as a barrier to sound transmission when the wall between adjacent offices goes only to the ceiling, and stops short of the underside of the floor above.
It is a special and significant measure in providing acoustic privacy between adjacent work areas.
A ceiling system with a CAC < 25 is considered to be low performance, whereas one with CAC > 30 is high performance. 30 is a typical CAC fit for offices.

Background noise

The best known reason for poor reception is bad signals due to noise conditions, that too exceptionally loud background noise.
Even though it is only proven for serious cases of noise existence it is logical that this has a direct influence on speech reception even in the case of low levels of background noise.
A speaker's normal speech level is approx. 60 dB, measured at a distance of one metre, even though literature in some cases suggests that teachers talk with raised voices at approx. 70 dB.
It is obvious that to achieve reasonable noise conditions, even in small classrooms, background noise must be low.

Products associated with acoustics are:
AcouStud | Ecophon | Gyptone