Benefits of Low Ambient Noise and Why It Can Be Detrimental
07/02/2024
MFAC
If you’re entering the field of acoustics, you’ve likely heard the term “ambient noise,” and today I’ll explain the numbers associated with ambient noise as per the title.
Firstly, concerning the definition of ambient noise, it’s often said to be the noise level at a measurement point when there is no noise from the targeted source. For instance, when you want to know the notification sound of a mobile phone, all other sounds except that notification sound are considered ambient noise. This is a somewhat specialized term used particularly in environments like anechoic chambers for measuring product sounds.
So why is the concept of ambient noise necessary? It’s to measure sounds more accurately. Even in the quietest places, air molecules colliding create sound. Therefore, when conducting measurements, it’s essential to account for all sounds besides the source noise to obtain precise figures. However, if the sound of the product is more than 10 dB higher than ambient noise, it’s generally acceptable to ignore the ambient noise, but within 10 dB, adjustments are necessary.
Now, is lower ambient noise always better? In conclusion, yes, but creating an anechoic chamber with lower ambient noise requires a significant increase in cost, so the ambient noise level generally depends on the product being measured. While ambient noise isn’t a standard criterion for judging anechoic chambers among various manufacturers, achieving lower ambient noise allows for broader compatibility with different products.
By the way, in recent projects, at the request of users, our relatively low ambient noise is about 3.7 dB(A). The ambient noise levels per frequency are as follows:
| Hz | AP | 63 | 125 | 250 | 500 | 1000 | 2000 | 4000 | 8000 |
|---|---|---|---|---|---|---|---|---|---|
| Anechoic Chamber Ambient Noise (All Stopped)(dB(A)) | 3.7 | -10.4 | -10.5 | -13.7 | -10 | -5.9 | -3.6 | -2.9 | -4.3 |
| Anechoic Chamber Ambient Noise (Air Conditioning Running)(dB(A)) | 3.9 | -10.9 | -8.2 | -10.4 | -9.3 | -6.1 | -3.7 | -2.9 | -4.2 |
| Anechoic Chamber Ambient Noise (Air Conditioning + Fan Running)(dB(A)) | 8.6 | -0.9 | -1.6 | -1.6 | -2.6 | -4.5 | -3.6 | -2.9 | -4.2 |
As you may have noticed, the sizes of these sounds are mostly negative. Sound is negative? What does that mean? To understand this, let me briefly explain how sound levels are calculated.
The level here refers to how many times greater the sound pressure (P) is compared to a reference sound pressure (P₀), which is the minimum audible value for humans, 2×10⁻⁵ Pa. This is expressed in logarithmic terms:
Lp = 20log(P/P₀)
When looking at this, if the sound pressure is less than the reference sound pressure, the result will be negative. To elaborate, logarithms typically express powers. For instance, the arrow part of the figure shows this.
And when expressing 0.1 in powers, it becomes 10⁻¹. This is where the negative comes into play. The larger the negative value, the smaller the number.
Therefore, when we talk about the negative of sound, it doesn’t mean true negative, but rather it signifies something very small and quiet.