Basic Information about General Acoustics

How does sound work? How does sound travel?

Understanding the fundamental principles of sound is essential in building acoustics and environmental acoustics:

Sound Waves: Sound travels in waves and can be characterized by frequency (pitch), wavelength (inversely related to frequency), and amplitude (intensity). Imagine you’re in a room with a single speaker. When a song is played, the sound travels from the speaker in the form of waves. If you could see these waves, they would look similar to the ripples formed when you drop a stone into a pond. Each “crest” and “trough” of the sound wave represents variations in air pressure that our ears perceive as sound. If a wave has cycles with crests and troughs very close together, it indicates a short wavelength and a very high frequency. These data help us calculate the pressure amplitude of a wave at each point in the room.

What is frequency and how is it measured

Frequency: It is inversely proportional to wavelength. Frequency is the number of oscillations of air pressure that occur in one second. It is measured in Hertz (Hz) or cycles per second. It determines the pitch of the sound.
Sounds produced by an opera singer (soprano) tend to be low and correspond to low frequencies. Conversely, a child emits high-pitched sounds that correspond to high frequencies.

How does frequency affect the perception of sound?

The behavior of sound when interacting with objects varies depending on whether the frequency is low or high. Additionally, human perception of sound differs according to frequency, making it very important to take this magnitude into account to distinguish between different sounds.

What is the audible range for humans?

The audible range for humans is approximately between 20 Hz and 20,000 Hz. However, the sensitivity of the ear is not the same throughout this range. That’s why sonority curves, like the dBA, adjust sound levels based on human perception according to frequency.

What are infrasonic and ultrasonic waves? What device can measure both ranges?

Frequencies below the audible range are called infrasonic. Whales emit sounds up to 15 Hz at low frequencies. Frequencies above the audible range are called ultrasonic; for example, dogs can hear much higher frequencies than humans.
Devices like the Nor145, for example, can measure infrasonics from 0.5 Hz at low frequencies and ultrasonics up to 40 kHz, allowing records of sounds inaudible to our ears but that do affect our health and the environment around us.

What is a spectral representation of frequencies?

In the colour map shown as an example, frequencies represented in red are the bass sounds, for which the human ear is less sensitive. Frequencies in blue are the higher, treble sounds.
Additionally, we can see that the amplitude of the received sound varies at different frequencies depending on the sound source or the combination of sounds perceived at each moment.

What is wavelength and how is it measured?

Wavelength: The distance in meters traveled by a wave to complete one cycle. Usually, it’s taken as the distance between consecutive peaks of the sound wave.
In acoustics, knowing the wavelength is essential to understanding how sound interacts with objects in a room; for example, bass sounds with longer wavelengths can pass more easily through thin walls compared to high-frequency sounds with shorter wavelengths. In building acoustics, wavelengths play a crucial role in how sound reflects and absorbs, affecting the acoustic quality of spaces.

What is the amplitude of a sound?

Amplitude: The height of the sound wave, related to the sound pressure level (SPL), measured in decibels (dB).
Think of a radio where you can adjust the volume. When you turn up the volume, you increase the amplitude of the sound waves produced by the speaker, making the sound feel louder. If you keep increasing it, the amplitude becomes very high, which can be uncomfortable for the ears.

Managing amplitude is critical—for example, in an auditorium, where everyone needs to hear clearly without the sound becoming too overwhelming. A sound with an appropriate amplitude for outdoor listening might become excessive inside a room due to reflections and reverberations. Similarly, a sound that’s suitable in one room can be bothersome in adjacent spaces.

The concept of wave amplitude should be considered to measure the sound level within a space, accounting for how much is absorbed or reflected by materials. It’s also key to understanding how sound transmits to other areas, depending on material insulation and environmental factors.

Even, how far that sound can be heard in an open space also depends on its amplitude.

These practical examples are essential to understanding how acoustics is applied in building design. Architects and acoustic engineers must consider these properties when designing spaces, as the goal is to create an environment where sound is clear and comfortable for occupants, whether in a theater, a school, or an office.

From these concepts, others related can be explored, such as reverberation, insulation, acoustic conditioning, background noise, environmental noise, and many more.

We invite you to read and learn about these concepts below, and to join our free courses at Norsonic Academy, where you can gain all the necessary knowledge to carry out successful acoustic measurements.

In this video, you can see the parameters described above: