Grandma Moon Speaks: Stereo Sound

Topics Covered:

  • Stereophonic Sound
  • Difference between Stereo Space with Headphones, and Surround Sound Space

My headphones are like my own personal ‘DO NOT DISTURB’ sign – Anonymous

Girl listening to headphones

Technically, stereophonic sound is every type of sound that is not monophonic. If there is more than one audio channel involved, it is stereophony. For our purposes though, since we have covered mono and surround earlier, we’ll use the word stereo to represent two speakers only.

The aim of using more than one audio speaker is to create the illusion of directionality and space. If a man walks past you in real life, his footsteps can be heard moving along with him. Television is usually placed in a fixed location, and two speakers or more allow for the illusion of sound to ‘follow’ the action, if required.

As we have seen in the last chapter, surround sound does an even better job of enveloping the listener in a 3D space. Its results are even more effective, so what’s so special about stereo?
The effect of stereo
First we’ll have to understand how having two ears at opposite ends affects our perception of sound. We have already seen that our perception of loudness depends on the sound pressure, and its direction and distance to the ear affects this property.

From the above image, it is clear that the same sound takes two different routes to each ear, and our brain has to somehow make sense of this conflicting information. The immediate reaction of the brain to any ‘important’ sound is to turn to face its direction. You can observe this property in practice by noticing how annoying it is to listen to music in only one ear, especially if there’s noise at the other!

It is a well known fact that to properly enjoy any stereophonic or surround sound, the ideal location is in the center of the space being created. If you and your friends are watching a movie, the person unfortunate enough to be sitting at the end will hear more through one ear, while the one lucky enough to be in the middle will hear equally through both. If you are standing outside the influence of the surround sound setup, you are missing out.
Stereo triangle
Stereo, too, has this problem, if the speakers are placed away from the body. The ideal location is to be at a distance in which you form an equilateral triangle between the speakers and yourself. Anybody outside this precise spot will not benefit as much as you will.

Where stereo solves the problem of space, is in its extraordinary application of headphones. When all other noise is eliminated, and sound is directly fed into your ears, a very special (I wouldn’t call it perfect) illusion of 3D space can be created, sound-wise.

If the effect of a superb surround sound system like the Dolby Atmos is to create a sense of community or realism, then stereo headphones create a sense of privacy and ‘personal-ism’. The connection between the sound and your ear is absolute.

The only care that needs to be taken is to keep the audio levels balanced, so the difference between the two speakers are 0dB.

Takeaways:

  • A system with more than one audio channel or speaker is called a stereophonic system. However, in common usage, it has come to mean two channels or speakers.
  • A dual-channel stereo system via headphones is capable of creating an almost ideal 3D space for music. This ‘personal’ space is different from the space created by a surround sound system – which tries to replicate nature.

Links for further study:

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