Acoustics refers to how sound behaves in a room. It is about the way sound waves are scattered, reflected and absorbed. A key concept here is reverberation time, or RT (Reverberation Time). RT is the time it takes for a sound to diminish by 60 dB after the sound source has stopped. Long reverberation times can lead to unwanted reverberation, making conversations difficult to understand and reducing concentration.
Controlling noise within an environment
Controlling noise is most effective when done close to the source or cause of noise pollution. In offices, the ceiling is often the best place to control noise as it provides the largest open space for acoustic solutions.
An optimal noise level in an office is between 35 and 40 dB. Sound cannot always be controlled at the source, as with conversations or a slamming door, so it is crucial to optimise the entire space. Sound moves rectilinearly, but is affected by obstacles that can reflect, deflect or absorb it.
Installing acoustic panels on the ceiling can help reduce reverberation and create a comfortable acoustic environment. This way, we improve both speech intelligibility and the overall working experience.
The following are some common effects of sound that we can influence and optimise.
Controlling noise within an environment
Sound is everywhere and represents a considerable nuisance in our daily lives. It is measured on a scale of 0 to 130 and its unit is the Decibel. It is known as sound level. The discomfort that our clients encounter is often linked to an excessive sound level.
Absorption
Absorption occurs when sound waves are trapped in a soft porous material. Depending on the thickness of the material, the absorption value is determined.
Diffusion
Diffusion occurs when a sound wave hits an object and is diffused and scattered by the hard and distorted structure of the material.
Diffraction
Diffraction occurs when sound bends itself around an object, or conversely, when it escapes through a small opening and then spreads out. Diffraction is tried to counteract as much as possible. There is talk of a ‘leak’ when diffraction occurs in an unintended environment.
Insulation
Insulation occurs when the entire sound wave is stopped by a material. If the material is almost completely insulated but still allows a small amount of sound to pass through, this is called transmission.
Reverberation or echo and how to avoid it?
Reverberation occurs when sound reflects repeatedly in a room and mixes with the original sound. This differs from echo, where the delayed sound is clearly heard after the original sound.
Both effects are often undesirable and can be distracting. Fortunately, reverberation can be effectively reduced by capturing indirect sound. The ceiling plays an important role here, as sound often reflects via this route.
It is therefore crucial to place acoustic products strategically, paying attention to absorption value and design.
Sound absorption
PET Felt has an acoustic value of 0.45, meaning it absorbs 45% of the sound energy!
All materials have acoustic properties: they can absorb sound, reflect it or both. Their effectiveness depends on the frequency and type of material. Absorption coefficients indicate how well a material absorbs or reflects sound, expressed as an acoustic value (aw).
Softer, more porous materials usually have a higher acoustic value and absorb more sound, while hard materials reflect sound more
and have a lower value.
Calculating the right acoustic space
Reverberation time, or RT60, is the time it takes for a sound to diminish by 60 dB in a room. A long RT60, above 2 seconds, creates an echo effect, while a short RT60 below 0.3 seconds produces “dead” acoustics where sound is barely reflected. Ideally, the RT60 should be between 0.5 and 1.5 seconds for good acoustic balance.
To calculate the reverberation time, we use the following formula:
T=0.16×(O/V)
in which:
T is the reverberation time in seconds,
V is the volume of the space,
O is the area of acoustic material in the room (including sofas, carpet, acoustic ceilings, lighting, and so on).
An accurate measurement of RT60 requires specialised equipment, but this formula allows you to make an initial estimate of the acoustic properties of a room.