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Acoustics Academy’s Sound Made Simple guide clarifies complex acoustic terminology with insights to design with sound.

    • 1. AIRBORNE SOUND INSULATION: is the process of blocking the transfer of airborne sound from one space to another, i.e. from outside to inside via a window, or blocking via a construction element such as a wall, a door or window. Airborne sound is sound transmitted through the air, e.g. conversational speech, TV.

      Example: “the airborne sound insulation performance of my bedroom wall is poor as I can hear my neighbours talking from next door as well as their TV.”

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    • 2. IMPACT SOUND INSULATION: is the process of blocking the transfer of impact sound transmission through the structure of a building. Unlike airborne sound insulation, impact sound is sound transmitted into the structure, such as from footsteps on a hard floor or from dropping weights in a gym.

      Example: "The impact sound insulation of the floors in my building is not very good as I can hear my neighbour’s “clicking” shoes (impact sound) all the time! Thankfully I can’t hear them talking (airborne sound) though."

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    • 3. SOUND ABSORPTION: refers to a material’s ability to absorb the sound once it arrives to its surface, instead of reflecting it back into the room or towards the listener.

      Example: "a soft cushion has a higher absorption coefficient than a concrete wall."

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    • 4. SOUND DIFFUSION: refers to an object’s ability to scatter or distribute sound evenly after it reflects against it. Its main purpose is to spread/break down sound energy and to make listeners feel as if sound was coming from all directions.

      Example: "in a concert hall it is preferred that all seats have the same listening experience, therefore it is necessary to use room finishes that have sound diffusion performance in order to distribute the sound reflections evenly (i.e. very ornate Opera Halls are diffuse as they have many intricate decorative features that break up sound reflections, as opposed to a smooth concrete wall or curved ceiling).”

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    • 5. SOUND MASKING: this phenomenon occurs when one sound has enough energy to affect the audibility of another sound, also present in the environment. This generally means that the sound with more energy shadows the one with less, the latter becoming inaudible. This is due to the human hearing system only being able to perceive additional sounds no less than 10 dB lower than the dominant sound. 

      Example: “In a very quiet, empty living room you can hear a pin drop on the floor, but in a busy restaurant, the sound of the pin drop would be masked by the people talking.”

      Product example: “In open plan office buildings, sometimes a constant sound is purposely played in the open areas so that phone conversations are ‘masked’ by this sound, in order to reduce the likelihood of workers being distracted by nearby colleagues’ phone conversations. This product is called a ‘noise making system’.”

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    • 6. ACOUSTIC PRIVACY: is a measure of how audible and understandable a sound is between rooms. It is a function of the sound insulation of the dividing wall as well as the background sound in the room of the listener, such as any masking sound provided by ventilation systems.

      Example: "In my office building, I can hear people’s conversations in the meeting room next door, the acoustic privacy is so bad that I can hear every word they say! To improve this, we could either improve the sound insulation of the wall or raise the background sound level of the ventilation system to mask their voices."

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    • 7. VENTILATION SYSTEM NOISE: is the noise level produced by a piece of equipment, where the noisier units are considered the worst performing. Noise control equipment or products in this category can be measured by the Insertion Loss (IL), the ability for a product to reduce sound as it passes through it, i.e. a pipe or duct.

      Example: “an air-conditioning unit that is mounted outside of a building has a system noise level of NR45 at 10 meters distance, when operating at maximum. When a noise control enclosure is used to cover the unit, with an Insertion Loss (IL) of 15 dB, the resulting noise level is NR30 at 10 meters distance.”

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    • 8. VIBRATION ISOLATION: is the reduction of periodic shaking of a material or from one material to another. Vibration is distinct from sound in that it is felt, as opposed to being heard via our ears, an example is when we turn our phones to vibrate instead of playing a ringtone.

      Example: “vibration from a nearby trainline produces a shaking of the building, where the windows rattle and I can feel it in my feet. The only way to reduce this vibration is to isolate the structure of the building from the ground using special building mounts.”

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