Boundary effects

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Posted by Wayne Parham [ 70.234.143.3 ] on June 28, 2007 at 17:36:19:

In Reply to: Event 20/20 Passive Ported Monitor Questions posted by Chris on June 24, 2007 at 16:40:30:


Boundary reinforcement is an interesting phenomenon that's important to understand. When a speaker is placed in free space (up in the air away from boundaries), it acts much different than when used on the ground, near a wall or in a corner. As the radiaing angle is made smaller, the sound is more focused and is therefore louder.

Bass tends to sound louder when boundary loaded because high frequencies tend to be directional anyway, which focuses their energy even without a boundary. Think about treble volume in front of a speaker verses behind it, and also think about bass volume in front of a speaker and also behind it. When you place a speaker back against the wall, this prevents bass from radiating behind the speaker, rather, it is directed in the forward-facing direction. If it is also on the ground, then sound is constrained further and if in a corner, further still. Since bass tends to be omnidirectional, the boundary loading tends to have its greatest effect at those frequecies. So boundary effects modify SPL, and they also tend to act something like EQ.



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