“In-Phase, Out-of-Phase and Phase Shift” – What do they mean?

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Today, we’d like to introduce “In-phase”, “Out-of-phase” and “Phase shift”, some interesting and curious phenomena in sound.

Those words may sound like difficult terms for you, so we try to explain by giving familiar examples to make you understand easily hereunder.

Sound is a “Wave”

First of all, sound is a phenomenon in which air vibration propagates as a wave. The sound wave can be expressed in a shape repeating peaks and troughs. How these curves are figured along the timeline, that information is called “phase”.

As one of the examples, consider two sounds that have waves figured exactly in the same shape. In case both two peaks and troughs fit coincidently, it’s called “in-phase” or “positive phase.”

What does “out-of-phase” mean?

On the other hand, when each of two waves figure in an opposite way, in other words when one wave is at peak, while the other is at trough, that correlation is called “out-of-phase” or “reverse phase.” Then upon combining one out-of-phase wave with the other, they cancel each other out and the sound disappears finally.

One of the familiar examples making use of this phenomenon is “noise cancelling earphones.” These pick up ambient noise with a microphone and cancel it out by outputting the sound to be transformed to out-of-phase. This process enables us to realize a quiet environment.

Speakers’ arrangement and Phase

Next, let’s see the speakers’ case: when speakers are making the sound as in-phase, it sounds rich and powerful. However, when those are in out-of-phase, the sound cancels each other out, resulting in a flimsy sound or almost no sound.

In order to avoid such a phenomenon, it is important to always check that speakers are all “in-phase” when connecting and positioning them.

What is “Phase-shift”?

Then, what does “Phase-shift” mean? It refers to a condition in which two waves are neither perfectly synchronized nor out-of-phase. For example, one wave figures a peak, while the other also figures a peak but a bit behind the first one.

If this shift is small, the sound may only change slightly. However, if it’s large, only the low and middle frequencies may be lost, making the sound murky and causing degradation of sound quality.

So, one of the most important things is how to minimize the phase shift in designing the acoustic equipment.

Let’s listen and compare “In-phase”, “Out-of-phase” and “Phase shift”!

It should be easier for you to experience the in-phase, out-of-phase and phase shift by listening to the actual sound.
We have made a video, so please check it out at the link below.

How to use “sound phases” in an anechoic chamber

Now, let’s move on to Sonora’s expertise: anechoic chamber.

An anechoic chamber is a unique room in which sound is hardly reflected. In this environment, sound waves travel straight ahead without reflecting, so the “phase” of sound can be accurately observed. For this reason, it’s utilized to evaluate the performance of speakers and earphones, and to research noise control solutions as well.

For example, when testing speakers in an anechoic chamber, it becomes easier to spot design errors, such as the sound emitted by the speaker being out-of-phase. This kind of precise verification helps upgrade product quality.

Summary

“In-phase”, “Out-of-phase” and “Phase shift” are some of the curious properties of sound, but they are also closely related to our daily lives. Thanks to these technologies, we can enjoy such high sound quality in noise-canceling earphones and speakers.

And Sonora’s anechoic chamber should be one of the best solutions to support your research and product development on sound phase.

If you are interested in our technology, be sure to check out Sonora’s anechoic chamber!