Acoustic insulation absorbs, transmits, or redirects sound waves – vibrations in the air that pass-through objects and result in audible sound. Noise, or unwanted sound, is measured in decibels (dB) and has a specific frequency distribution that’s measured in Hertz (Hz).
Unlike some noise control products, custom acoustic insulation can be “tuned” to address specific frequencies. Examples include the low-frequency rumble of a big diesel engine and high-frequency sounds like squeaking and squealing.
Acoustic insulation can strengthen product designs, but engineers need to know which questions to ask and what types of solutions are available. In this introductory article, you’ll learn about the basic elements of noise control. You’ll also learn about the basic types of acoustical materials and how they’re fabricated.
Three Elements of Noise Control
There are three elements to noise control: source, path, and receiver.
- Source is the origin of the noise to control. For example, is the source of the sound a bell, a whistle, or a loudspeaker? Maybe you’re trying to silence traffic noises or industrial machinery instead. Low-frequency sounds, especially those that cause vibrations, are especially challenging. Yet failing to quiet them can result in damage to human hearing or mechanical failure.
- Path describes how the sound is transmitted. In the case of a bell, whistle, or loudspeaker, the sound may travel through a factory’s interior wall and disturb the occupants of an adjacent room such as a front office. With mobile equipment such as logging trucks and military vehicles, engine sounds travel from under the hood to inside of the cab.
- Receiver considers the listener’s requirements, expectations, or preferences. On a factory floor, some noise is expected as long as it doesn’t exceed regulatory limits. Passengers on a train, bus, or airplane want to be able to hear themselves talk. The owner of a sports car wants to hear the engine’s sounds, but without excessive amounts of road noise.
Four Types of Acoustic Insulation Materials
There are four types of acoustical materials: absorbers, barriers, dampers, and facings.
Sound Absorbers are used at the source and the receiver. They’re made of acoustical foams and absorb sounds instead of blocking or damping them.
Sound Blockers are used at the source and sometimes at the receiver. Often, they are made of mass loaded vinyl (MLV). As their name suggests, sound blockers are designed to block rather than absorb or dampen sound.
Sound Dampeners are used at the source and the receiver. Unlike barriers, they reduce sound energy instead of blocking it. They can also help with vibration control.
Facings are like control knobs that allow custom acoustic insulation to tune-out specific frequencies. They can also address environmental or aesthetic concerns.
How Acoustic Insulation is Fabricated
The materials for custom acoustic insulation are supplied as sheets or rolls in various lengths, widths, and thicknesses. Using water jet cutting, a fabricator can cut materials to size without knives or dies – tooling that adds costs to projects. First, however, the fabricator can laminate different materials together to create an insulation “sandwich” with particular properties.
For example, a fabricator can laminate a facing to an absorber. Then, on the other side of the sound-absorbing foam, the fabricator may apply an adhesive with a removable liner for peel-and-stick installation. The resulting product looks like an insulation “sandwich” with the facing on top, the liner on the bottom, and the foam in the middle.
Stop the Noise with a Closer Look
The article you’ve been reading is the first in a series about stopping noise with acoustic insulation. Future articles will take a closer look at absorbers, barriers, dampers, and facings. In the meantime, please contact Elasto Proxy with your questions about custom acoustic insulation.