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Sound Reflection

May 10th, 2012
contra, sound  [html]
The thing that makes sound hardest to work with is that it bounces off things. If you set up a speaker in a dance hall and stand out in the hall listening to it, only some of the sound you hear is coming directly from the speaker. The rest of it is reflected off the walls, ceiling, etc. Because all of these different paths are different lengths, it takes the sound many different amounts of times to reach your ear. Our ears are remarkably good at correcting for this, but it makes it much harder to figure out what the original sound was.

How can you change the amount of sound that goes directly to people's ears instead of first bouncing off other surfaces? Replacing all the surfaces with something that was very good at absorbing sound would be ideal, but not usually practical. Hanging quilts and fabric does work, but you need to do it in a way that's not a fire hazard, which makes it expensive. Much easier to control is the placement of speakers. If you put speakers on high stands almost to the ceiling, pointing straight horizontally out over people's heads, a lot of what they hear is going to be bouncing off the ceiling. Not so good. If you put them on low stands, just a foot or two over their heads, you'll fix the muddiness but at the expense of making it loud at the front of the hall and quiet in the back. The ideal place to put a speakers for a hall is in the top corner pointed down at an angle. This generally requires hanging them, though, so if you don't own the hall you are stuck with stands.

The most practical situation for most halls is to tilt the speaker forward. Some have built in tilters, like my K10s, and most can use external ones. This lets you put the speaker on a high stand but angle it down. [1]

Another case where this comes up is with band monitors. Ideally the monitors are pointed right at the heads of the musicians, but if you don't place them carefully it's easy to end up with them pointed at their knees when they're standing or over their heads when sitting. This means they'll get plenty of non-directional low-frequency sound but high-frequency sound mostly gets to them after bouncing off something else first. They might complain that it sounds 'muddy' or 'not very clear'. They might ask for the monitors to be louder when they already sound very loud to you. Or they might just accept it. Which is sad, because it's usually such an easy fix and high frequency sound is so important to hearing whether you're playing in tune and with the other musicians.

[1] Low frequencies are much less directional than high ones so you could build a speaker where only the horn (for high frequency sound) was angled down. This has the advantage over tilters of making it easier to keep the center of gravity of your big heavy speaker stay right over the stand instead of forward, as most external tilters will shift it.

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