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# Sound Insulation

## Definition

Sound level difference is defined as the difference between the sound pressure level Lpemitted in the room where the sound source is located (emission room or source room) and the sound pressure level in the receiving room Lpreceived:

Figure 2.2 Acoustic transmission paths between spaces.

Standardized sound insulation is defined as the sound level difference to which a weighting term taking into account the reverberation time T of the room, as compared to a reference reverberation time T0, is added. This usually is the quantity that is specified in requirements books and regulations.

## Computation

As compared to a laboratory situation where sound transmission solely occurs through the separating wall, sound transmission between two rooms of a building can be decomposed into:

• • Direct transmission.
• • Flanking transmissions through the various constructive elements linked to the separating wall. Such flanking uses coupling coefficients kj that are defined in the standards of the ISO 12354 series.
• • Leakage around some construction elements.
• • Secondary transmissions by means of duct layouts.

These are displayed in Figure 2.2.

The basic idea is for a computation model to take into account all of these contributions. Some commercial computer software offer the possibility to use a readily available library of components (complete with the kij values). Whenever a new material must be introduced by the user, it is wise to do so by modifying an as similar as possible material.

Most of the time, such software is able to produce graphic results (e.g., global sound insulation between the two rooms of interest, plus sound insulation through each main path). This helps identify which component needs urgent improvement.

## Which Insulation for Which Use?

Here are a few sound insulation ranges of sound insulation values that can normally be experienced:

• • Between offices with removable partitions: 25-35 dB. (Note: 30 dB is considered by several standards to be the minimum sound insulation value required to allow two of the same kind of activities to be carried out in two adjacent rooms. While a 25 dB sound insulation value can still be found, typically in front of wall elements, including doors, it is not recommended by standards.)
• • Between a doctor’s office and waiting room: 45-50 dB. (Note: 45 dB is considered by several standards to be the minimum sound insulation value required to allow privacy between two adjacent rooms.)
• • Between modern dwellings: 50-55 dB. (Note: This usually is the range required by most regulations.)
• • Between cinema theatres: 65-70 dB. (Note: This usually is the range required by the background noise levels targeted by the standards of the industry.)

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