Sound above 400Hz is considered to be directional. In fact, the higher the frequency, the more directional the sound waves tend to be. In a home theatre or 2-channel listening room, these waves bounce off the nearby walls and produce very noticeable second order reflections which compete with the direct sound from the loudspeakers.
You can easily control these reflections by strategically placing acoustic panels along the side walls to absorb them. As a rule, you should mount them at ear and/or speaker height and position them along the wall to capture the early reflections from the loudspeakers.
The Mirror Trick
For optimal placement, the easiest and most effective way to position the panels is to use the mirror trick. To do this, you will need an assistant!
- Sit in the listening position
- Have your assistant move a mirror across the wall surface in between you and the speakers
- Using a pencil, mark the beginning and end points where the speakers are visible in the mirror
- Note that you will want to view the left and right speakers (and centre if used) in the mirror
- This will define the area that would be ideally treated
- Repeat for the second side
You can then mount your Primacoustic panels to the wall using Impalers. Note that you do not have to cover the full area; covering most of the surface will provide plenty of control. (If you are unsure how much treatment you need, check out this article.)
After treating the side walls, you can further improve control by absorbing the rear reflections on the wall behind the sitting position. For this, you would turn around while remaining in the listening position and then follow the same approach by marking the wall where you can see the speakers in the mirror. Primacoustic Scatter Blocks™ are a good option in this instance since they offer general area absorption without completely deadening the room. Too much absorption will remove the energy and excitement.
As a final measure, for those that want maximum definition, placing a couple of 3″ thick acoustic panels behind the loudspeakers on the front wall will help eliminate comb-filtering caused by omnidirectional low frequencies emanating from the loudspeaker.