Noise control is an incredibly deep topic, combining physics, biology, engineering, law, and more—and that’s just scratching the surface.
To give you a better understanding of the kinds of considerations that go into designing noise control solutions for businesses, here are 10 noise control concepts you should know about:
10 Noise Control Concepts You Should Know
What’s the Difference Between Noise and Sound?
Sounds are vibrations in the air that we hear with our ears; sounds vary from whisper-quiet to deafeningly loud.
Noises are defined as unwanted or harmful sounds; these sounds are typically loud but may be unpleasant in other ways. All noises are sounds, but not all sounds are noises. The goal of noise reduction is not to eliminate sound, but to eliminate harmful and unpleasant sounds.
What Is the Difference Between dB and dBA?
Decibels (dB) are a unit of measurement for sound intensity. Each 10 dB increase means a tenfold increase in intensity; it’s a logarithmic scale.
What dB does not account for is human perception; it’s a raw interpretation of sound pressure levels. Humans, however, may notice some noises at 50 dB, but may not notice other noises at 50 dB. The Hertz (Hz) of a sound must be factored in; this is why the dBA scale was created.
dBA takes the sound spectrum into account when determining the subjective dB of a sound. The human ear is more sensitive to sounds from about 1000 to 4000 Hz; low-frequency noise and high-frequency noise outside of that range will seem less loud to us. A tone of 75 dB at 1000 Hz would be rated at 75 dBA. A tone of 85 dB at 20,000 Hz, on the other hand, would also be rated at around 75 dBA.
Is Hearing Loss Permanent?
While some hearing loss is temporary, most hearing loss caused by exposure to excessive noise levels will damage your hearing permanently. Your inner ear, known as the cochlea contains thousands of tiny hairs that are essential for hearing. Loud noises can cause wear and tear on these hairs, which leads to hearing loss. The human ear is a sensitive instrument; businesses should take all steps necessary to reduce noise levels.
What Is Tonal Noise?
Noise falls into various categories, including broadband and tonal. Broadband noise consists of a wide range of different frequencies, while tonal noise is concentrated in narrow bands of frequencies.
Tonal noise is typically more noticeable—and more irritating—than broadband noise. Fans, motors, and other machinery rotate or vibrate at a consistent speed, creating noise at a discrete frequency. Tones, at both a critical frequency based on the rotational speed and the related harmonics at higher frequencies, are much more noticeable than broadband noises.
What’s the Difference Between Sound Absorption and Sound Attenuation?
Sound absorption and sound attenuation are two different techniques used to control noise. In sound absorption, materials absorb sound, turning vibrations into heat and dissipating them. Acoustic panels that are used to absorb random incidence sound (sound waves coming from multiple directions rather than a specific source) are a good example of sound absorption.
Sound attenuation, conversely, attempts to dissipate sound energy from specific sources, like reducing duct-borne sounds from a source. Using a silencer baffle to attenuate the sounds generated by a fan in a duct is a good example of sound attenuation.
What Is Reverberation Time?
Reverberation time is the amount of time that must pass before a sound fades away in an enclosed space. More specifically, reverberation time is typically defined as the amount of time it takes for a sound’s volume to decay by 60 dB. If it takes a sound 5 seconds to reduce from 80 dB to 20 dB, then the reverberation time is 5 seconds.
In some circumstances, like concert halls, long reverberation times may be preferable but in industrial settings, short reverberation times are almost always preferred. Industrial settings tend to have a lot of acoustically reflective surfaces, and reverberation times can be quite high. Conversely, reverberation times are much lower in acoustically ‘soft’ spaces (e.g., library) or once a sound leaves the building. Varying reverberation times play an important role in noise reduction techniques and silencer selection.
What Are the Main Types of Noise Control?
There are four basic types of noise control: Sound insulation, sound absorption, vibration damping, and vibration isolation.
- Sound insulation aims to mitigate reverberation and isolate sound by blocking sound waves. Concrete and other dense materials are often used for these purposes.
- Sound absorption uses materials to turn sound waves into heat. Porous materials are typically the best choice for absorption.
- Vibration dampening aims to convert vibration into heat energy before that vibration can be transferred into other mediums, mitigating the noise that is created
- Vibration isolation isolates vibrating components from their surroundings, preventing those vibrations from reaching materials that can amplify them
What Are Silencers?
Silencers are designed to provide noise reduction close to a noise source, like a fan intake. The proximity of silencers to the noise source means careful design and engineering are particularly important. The goal is to reduce noise without creating unwanted aerodynamic issues, such as excessive pressure loss.
What Are Sound Enclosures?
Sound enclosures are structures designed to reduce the amount of noise pollution generated by equipment. They may feature sound-absorbing surfaces, solid walls for sound isolation, air vents equipped with silencers to ensure sufficient airflow while attenuating sound, and access points like doors and windows that are themselves insulated to prevent sound from escaping.
These enclosures are complex, combining many different noise reduction techniques. Sound radiated from a sound enclosure must typically be treated as an area source instead of a point source, changing the noise control techniques that will be used.
How Do Noise Control Concepts Apply to Residential Environments Compared to Industrial Settings?
In residential and institutional settings like hospitals and schools, noise control requirements are typically driven by noise ordinances; the goal is to stop noises that are emitted from these environments from creating disturbances in adjacent areas.
In industrial settings, noise control is typically driven by worker safety, though outdoor noise ordinances may also play an important role. Noise control in industrial settings tends to be installed directly onto the equipment; industrial silencers are a good example of this.
VAW Systems Noise Control Solutions
At VAW, we are passionate about designing, engineering, manufacturing and installing customized noise control solutions for facilities of any size and type. Noise control is a complex topic, and the concepts we have illustrated here are just the tip of the iceberg. By working with us, you will gain access to decades of knowledge and experience in noise control, giving you the tools you need to drastically reduce the presence of unwanted sounds in your business.