Problem areas
In addition to creating reflections and diffusions, a room’s size, shape and construction all have the potential to cause some annoying problems. Top of the list are room modes. In the simplest terms, these occur when a frequency’s wavelength exactly matches the dimensions of a room, creating what’s called a standing wave. This ‘natural frequency’ becomes amplified. As an example, two parallel walls 12 feet apart will create a standing wave at roughly 94Hz.
In addition to room modes, you can also experience problems with boundary reflections, where a direct sound wave combines with a reflected one. This effect can happen perfectly in phase, perfectly out of phase or anywhere in between, and to human ears, it will make certain frequencies sound appreciably louder or quieter.
The good news is that both situations are only really problematic at lower frequencies (which have longer wavelengths). The bad news is that the problems can be quite marked, making particular bass notes far too loud, or alternatively, causing them to disappear completely.
To give you an idea of the frequencies that could be problematic in your room, there are a number of freeware mode calculators. A good starting point is RealTraps’ ModeCalc (PC only). RealTraps also have a useful application for pinpointing boundary reflections. See our main feature for more on bass modes and nodes (from p18)
realtraps.com