Avoid First Reflections from Your Loudspeakers

When sound pressure comes out from your loudspeaker, it is typically aimed directly at your listening position. When it arrives at your listening position, it is referred to as "direct sound". Along the way towards that listening position, the sound pressure wave will hit the side walls, pieces of furniture, and so on, causing multiple reflections. The reflections are delayed slightly in their arrival to your listening position. These multiple delayed signals are referred to as reflections. Therefore, when the direct sound arrives at your listening position, it is quickly followed by the same sound, slightly delayed in time, causing a confusion to the music. If we were to play our speakers outside, this would not be a problem (unless it rained). Unfortunately, this is not the case, and we in fact listen inside. Therefore, we must deal with these reflections.

Since we cannot eliminate all reflections, we should concentrate our efforts on the biggest problems first. The biggest problems are known as "first reflections" because they are the first and most predominant reflections to arrive at our listening position. First reflections are almost always created when the sound coming from the loudspeaker hits the side wall (the walls closest to the left and right sides of the speakers). They are relatively easy to correct if you can identify where they occur. To minimize their effect on the sound of your system, you need to place either an object in their path to diffuse their energy (such as a piece of furniture), or an object in their path to absorb their energy (like a tapestry, curtain, or foam rubber).

Locating the point of first reflection is simple, but you will need the aid of a colleague and a small mirror. First, remove the grille cloth from your loudspeaker. Second, have your colleague hold the mirror against the approximate area of the first reflection on the side wall, holding the mirror at the same height as your tweeter is from the floor. Have the assistant move the mirror along the wall, while maintaining the correct height for the tweeter, until you can see the tweeter in the mirror. Mark that spot, and repeat the procedure on the opposite wall. The mirror has visually exposed the location of the first reflection.

If you are interested in learning more, check out our series on how to build a listening room by clicking on the link.

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