Understanding the basics of noise reduction

A well-balanced room with a perfect acoustic level is a key factor to the performance and well-being of workers all over the world.

If you would like to treat sound within a room, you should start by understanding the basic terminology of acoustics. And, like a lot of things, better acoustic performance begins with solid fundamentals.

What you’ll learn in this guide:

1. Definition of sound: Frequency, Decibels & Reverberation time
2. Building acoustics vs. Room acoustics
3. Principles for good acoustics: Absorption, Attenuation & Diffusion

1. Definition of sound

Sound consists of pressure waves running through the air. It can be described as energy, created by vibrations, transmitted through air or any other medium. The inner ear converts those vibrations into electric signals, which are sent to our brain, where they will be processed and perceived as the actual sound coming in.

These sound waves have two different characteristics:

• Frequency determines the tone of the sound
• Decibel determines the intensity of sound

— Frequency: how sound waves travel

The wavelength determines the sound frequency. It is measured as the number of repetitive vibrations per cycle per second and is expressed in Hertz.

The audible range of sound is between 20 to 20 000 Hz. The higher the frequency, the higher the tone. However, for space planning, the suggested frequency ranges from 100 Hz to 5000.

High tones

High frequency | Short wave | 2500 - 12000 Hz | e.g. ringtones, consonants

Mid tones

Speech frequency | Mid length wave | 250 - 2500 Hz | e.g. speech

Low tones

Low frequency | Long wave | 50 - 250 Hz | e.g. HVAC, vowels

— Decibel: the intensity of sound

Decibel is a logarithmic unit to express the ratio of sound intensity (volume) and is important as an indicator of the background noise level. Humans can hear sounds between 0 and 140 decibels. The value of decibels has no direct or indirect correlation with the sound frequency.

For example, the ticking of a clock and the buzzing of a vacuum cleaner may have the same frequency but a different volume.

Why it matters? In today’s open-plan workspaces, employees are exposed to noise pollution. The level of noise ranges from 60 to 80 decibels, whereas recommended background noise level in an office is around 45 dB.

Noisy offices above the suggested threshold may hamper:

• concentration & productivity
• Speech privacy
• Overall acoustic comfort & wellbeing

But there is always a way to avoid getting stressed by trying to keep focus at work. The solution could be several workplace microenvironments, designed with sound balance in mind for the activity and the people using these areas.

— Reverberation time: the time for a sound to drop dead

Reverberation time is the time needed for an original sound source to decay by 60 dB and is expressed in seconds. In order to generate excellent speech intelligibility and clarity, the reverberation time should be adjusted and balanced by means of absorptive material in function of the specific acoustical issues in a given space. The reverberation time will always be influenced by

• the volume of the room,
• room temperature, and
• existing absorptive materials in the room, e.g. materials, objects, and people.

Recommended reverberation time for different spaces (measured in seconds):

• Office: 0.7 – 0.9s
• Meeting room: 0.4 – 0.8s
• Cafeteria: 1.00s
• Gymnasium: 1.50s
• Auditorium: 1.50 to 2.00s

Try measuring the reverb time in your space with the BuzziSpace RT60 app. It allows you to simulate the improvement in room acoustics by adding sound-absorbing products. Download the app in the App Store, available for both iPhone and iPad.

Why it matters? In an office, high reverberation levels intensify noise levels and reduce speech clarity, as the sound reflects from walls and tables, among other hard surfaces.

The way to dampen reverberation is with absorption materials.

2. Building acoustics vs. Room acoustics

— Building acoustics

Building acoustics and room acoustics may sound like two sides of the same coin, but don’t be fooled. We have to make a clear distinction, as the solutions to treating problems associated with either of the two are very different. As the name implies, building acoustics has to do with the building and the transmission of sound from outdoor to indoor and between structural elements of a building, e.g. floors and walls.

This is the case when:

• Sound is transferred from outdoor to indoor, e.g. cars, trams, airplanes passing by
• Sound is transferred between floors, e.g. footsteps from the floors above
• Sound is transferred between adjacent rooms, e.g. an adjacent meeting room

Ideally, issues like these should be addressed by the architectural team through the insulation of windows, walls, ceilings, and floors. Another option is to remedy the transmission of sounds, so they will not escape the room, to begin with.

— Room acoustics

Room acoustics, pertain to noise and sounds within a room or any given space. Rather than focusing on insulation to remedying transmission of sounds, the key to room acoustics is absorption to prevent sound waves from bouncing back-and-forth in a room.

3. Principles for good acoustics

To create a better acoustical environment and reduce reverberation time in a room, BuzziSpace acoustic solutions are developed to perform on one or more of the following acoustic principles.