The basics of acoustics explained simply
What we perceive as sound begins with vibrations in the air. In this section, we explain the physical principles of noise, sound waves, and frequencies – and why they are so important for room design and acoustic planning.
Noise versus tone:
An acoustic classification
A noise is caused by irregular vibrations of the air and is perceived by the human ear as sound – unlike a tone, which has regular vibrations.
Noises accompany us daily: when speaking, walking, working or through environmental noises in indoor spaces.
Sound: from vibration
to perception
Sound is the propagation of pressure fluctuations in a medium, usually air. When something vibrates — for example a voice, a speaker or a piece of furniture — it sets the surrounding air molecules in motion.
These sound waves spread out concentric and eventually reach our ear.
The hearing converts these mechanical vibrations into electrical signals, which our brain interprets as noise, sound or tone.
Sound waves & frequency
Sound waves have two important properties:
- Frequency (Hertz, Hz): Indicates how often a vibration occurs per sec andond.
- Low tones = low frequency (e.g. 50 Hz)
- High tones = high frequency (e.g. 5,000 Hz)
- Amplitude (volume): The greater the displacement of the vibration, the louder the tone seems to us.
Physically, the amplitude is indirectly measured by the sound pressure .
Sound pressure and decibels explained simply
Sound pressure is the physical pressure caused by sound waves in the air.
If, for example, a voice or a speaker generates tones, the air molecules vibrate.
This results in a fluctuation between overpressure and underpressure – exactly what sound pressure is.
- Sound pressure is measured in the unit Pascal (Pa).
- Our ear perceives these pressure fluctuations as loudness.
- Evolutionarily, human hearing is most sensitive between 2,000 Hz and 5,000 Hz – a range that is crucial for speech intelligibility and many acoustic decisions (e.g., in room acoustics, speaker design, hearing aid adjustment).
What is decibel?
Decibel (dB) is a unit of sound pressure level that indicates how loud or quiet a sound is.
Since human hearing is sensitive, this logarithmic scale is used.
IMPORTANT TO KNOW
- An increase of 10 dB is subjectively perceived as a doubling of loudness.
- 0 dB is not the same as no sound, but the hearing threshold – the faintest tone that a person can just perceive.
Typical decibel levels in everyday life
| Noise source | Volume (dB) | Effect on us |
|---|---|---|
| Leaves rustling, breathing | 10–20 dB | Very Quiet |
| Whispering | 30 dB | Quiet |
| Normal conversation | 50–60 dB | Pleasant |
| Vacuum cleaner | 70–75 dB | Loud, slightly burdensome |
| Road traffic | 80–85 dB | Loud, harmful in the long run |
| Rock concert | 100–110 dB | Pain threshold approaching |
| Aircraft take-off nearby | 120–130 dB | Painful, possible hearing damage |
Already at 85 dB prolonged exposure can damage hearing – that is why soundproofing in workplaces, offices or gastronomy is so important.
IMPORTANT TO KNOW
- Decibels help measure loudness – but they do not say anything about the quality of the sound.
- A doubling of identical sound sources always results in +3 dB.
- An estimated doubling or halving of volume already occurs at around ±10 dB.
- Two noises with the same dB value can be perceived quite differently, depending on frequency, reverberation, and room acoustics.
The Audible Frequency Range
Humans generally hear within the range of approximately 20 Hz to 20,000 Hz (20 kHz). As age increases, the perception of high frequencies decreases.
Low Frequencies (< 250 Hz): e.g. humming of air conditioners
Mid-range Frequencies (250–2,000 Hz): Speech range – crucial for comprehensibility
High Frequencies (> 2,000 Hz): e.g. hissing, clinking, bird sounds
For good speech intelligibility, the mid-tone range is particularly important. A detailed frequency analysis is crucial for targeted room optimisation.
Echo & Room acoustics
When sound waves hit walls, ceilings or furniture, they are reflected – this causes echo.
- If the echo is too strong, a room sounds "echoey", speech becomes indistinct.
- Acoustic elements such as absorber or panels help to reduce this effect by absorbing sound or by deliberately diffusing.
Molto Coustic is your competent partner for targeted optimization of room acoustics.
Would you like to learn more about room acoustics?
Terms such as reverberation time, absorption or sound distribution are just a small part of the exciting world of room acoustics.
Discover more central topics and technical terms — explained concisely and prepared practically.
Your personal consultation:
MORITZ JUNGWIRTH
Business Development
+43 664 88846944
jungwirth@moltoluce.com