Inverse Square Law: What is it?

Conference rooms bring their fair share of challenges, from poor acoustics to bad connections. While there are many ways to improve your conference experience, one approach that often gets overlooked is microphone placement. To better understand the importance of distance to and between microphones, the inverse square law can be a useful concept to know. In this guide, we discuss the basics of the inverse square law and how it applies to acoustics.
 

What is the Inverse Square Law?


If you run into a physicist and ask them to define the inverse square law, they might say something along the lines of “the intensity of a force changes in inverse proportion to the square of the distance from that force.” This definition might be a little confusing, but this law of physics is not as complicated as it sounds.  

In simple terms, the inverse square law states that any energy or force will have a drastic dropoff in strength as it travels further away from the point source. Any source which spreads out in all directions without getting lost obeys the inverse square law. This “source” can be applied to the following energies and forces:
 
  • Sound
  • Gravitation
  • Electrostatics
  • Light
  • Radiation

Let’s use light as an example. Say you’re driving down a dark highway, and your headlights are on. The light rays from the headlights disperse as they travel. So, the further away the light rays get from the headlights, the more spread out they are. Therefore, the strength of the light rays weaken and shallow out. 
 

How Does the Inverse Square Law Apply to Acoustics?

Sound is a form of energy that adheres to the inverse square law. When you’re optimizing a conference room for your business, it’s helpful to have a general understanding of how sound travels and reverberates.

In the realm of acoustics, the inverse square law states that the intensity of sound decreases by approximately 6 dB for each doubling of distance from the sound source. On the other hand, the opposite is true when you move closer to the source.
Let’s say you have a YVC-1000. You connect a microphone to it that’s 1 foot away from your mouth. When you move 2 feet away from the microphone, the sound will decrease by 6 dB. If you double that distance to 4 feet, the sound will drop another 6 dB, resulting in a 12 dB loss from the original level. The diagram to the left should give you a better visualization of how the inverse square law works with acoustics. 

Microphone placement is one of the most vital aspects to consider when setting up your ideal conference room. If you’re sitting too far away from the microphone, it’ll pick up more room reverb, making your voice sound muddy and intelligible. For best audio capture, it’s recommended to have a dedicated microphone for each person in your meeting. In this case, the microphones can capture each voice clearly and directly, providing a much better conferencing experience.
 

Inverse Square Law Formula

As mentioned earlier, the inverse square law specifies that the intensity of sound weakens by 6 dB for each doubling of distance from the sound source. However, this explanation is under the context that you’re in a free field – a place where there are no reflective surfaces. Unfortunately, this isn’t the case with most conference rooms, so 6 dB should be viewed more like an approximation.

inverse-square-law.PNGSound intensity is defined as power over area. If you want to calculate the sound intensity at any distance from the source, there’s a formula you can use:

Here’s what each symbol represents:
  • I = Intensity of sound
  • P = Power of the source
  • r = Distance between the source and the point of interest

The diagram to the left illustrates how sound spreads out and weakens the further away it gets from the source:

Overall, if you take anything away from the inverse square law regarding acoustics, remember that greater distance = lower sound level.



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