Handbook of Noise Control Materials
6Pages

ection I. A. Basic Concepts of Blocking and Absorbing Sound B. Variables Affecting Performance Section II. Vibration Damping Treatment Section IV. Practical Considerations Section V. Noise Treatment Inside Cabin

A. BASIC CONCEPTS OF BLOCKING AND ABSORBING SOUND Acoustic insulation materials work by two processes: absorption of sound energy, which dissipates sound as heat ener- gy and reflection, which reflects noise away from a location where quieting is desired. A single composite insulation mate- rial will be effective as both an absorber and a reflector. Considering the example of an engine in a boat, if it is sitting open with no enclosure around it, it will create a very loud noise throughout the boat, perhaps as much as 105 dBA . If we install an engine box around the motor using 5/8" thick...

The most significant variables for noise control materials are weight of the reflecting barrier layer and thickness of the absorption and decoupling lay- ers. Secondary factors are the protective surface fac- ing materials and materials for the mass layer. The particular type of acoustic foam or fiberglass is of lesser importance among the legitimate and effective acoustic materials available. The universal problem in attenuating noise of marine engines, generators, and propellers is reduc- tion of mid and bass frequency rumbles. High fre- quency sounds of turbo chargers, gearboxes, engine...

BASIC DISCUSSION OF VIBRATION DAMPING TREATMENTS Damping materials absorb vibrational energy from resonating panels in a direct analogy to sound absorbing materials interacting with noise in the air. By absorbing energy, damping reduces the structure- borne noise radiated from the panel to which it is applied. Damping also reduces the structureborne noise traversing the treated panel and traveling to more remote parts of the boat (structure). Methods of vibration damping include "extensional" and "constrained layer" treatments. Extensional damping materials are applied as a single layer...

B. Mass Layers - Mass layers must be non-porous and limp for maximum effectiveness. Plywood and other stiff lightweight materials do not block sound as well because their stiffness properties allow them to trans- mit noise through sympathetic vibrations, i.e. the panel becomes a sounding board. Plastic sheets loaded with mineral compounds are the most common type of mass layer. These plastics have their best application in places where the mass layer must withstand high phys- ical abuse. Because of its high density and low stiffness, vinyl is one of the best noise barrier materi- als and is...

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