Don’t be Fooled by Advertised IIC Ratings

Snake Oil SalesmanThe Impact Insulation Class (IIC) rating system quantifies the impact insulation of a floor-ceiling system between two rooms. A tapping machine is placed on the finished floor, which is the top of the floor-ceiling assembly. Impact sound from the tapping machine is measured in the room below with a sound level meter.

IIC cannot be used to rate a particular material or product. The IIC values advertised by manufacturers are ratings for floor-ceiling assemblies that include their product. The advertised IIC rating is for the entire assembly.
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Acoustic Duct Silencer – Introduction

A Duct silencer is a piece of ductwork that is designed and manufactured to attenuate sound transmitted through the ductwork. The common duct silencer is a dissipative silencer. It uses changes in duct cross section and sound absorbing materials to attenuate sound.

Dissipative duct silencers are available in a number of configurations including straight, elbow, tee, and transition. They are also available as a rectangular or round duct section. The illustration below shows a typical straight rectangular configuration.
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Duct Branch Sound Power Division

When a sound wave traveling in a main duct encounters a branch, the sound power contained in the sound wave is divided between the main and branch ducts.  This acoustic phenomenon is referred to as branch sound power division.

The portion of sound energy that is transmitted into each branch is associated with the cross sectional area of the main and branch ducts.
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How to Mitigate Noise Transfer between Hotel Guestrooms

Sound GrilleQ  If you have an existing hotel with excessive room to room noise transfer through the ventilation shaft, what can you do to fix it?

A  You must add some form of sound attenuation in the path between the two rooms.  In this case, the path is the ventilation system. 

This is how I solved that problem in an existing five star hotel. 
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Outdoor Noise Barrier Basics

If you have a problem with noise propagation outdoors then an outdoor sound barrier may be the solution. Outdoor sound barriers attenuate sound between an outdoor sound source and receiver.

Outdoor sound barriers provide sound attenuation between a sound source and a receiver through multiple mechanisms. The illustration below shows what happens to sound when a barrier is placed between a source and receiver. The noise barrier interrupts the direct path from the source to the receiver.
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