Homeowners will spend thousands of dollars on a state of the art sound system in search of audio nirvana, without considering the most important component: the room in which the sound system will play. Although many people today are much better educated about the intricacies of audio technology than in the past, there still exists a large gap in knowledge about room acoustics. The fundamentals presented below will shed some light on the subject, but there is no more effective way to achieve audio nirvana than hiring an acoustician.

Basic Acoustics

The acoustical properties of enclosed spaces have a profound effect on the performance of sound systems. The "three R's" of room acoustics are Reverberation, early Reflections, and room Resonances.

Early reflections (up to about 60 milliseconds after the arrival of the direct sound) provide a sense of texture and source width. The ear/brain auditory system will combine the early reflections with the initial direct sound, whereas later reflections become identified as a property of the enclosed space. The early reflections, therefore, can be used by the brain as a part of the decoding process, and most studies have shown they actually improve sound quality.

Reverberation will enhance music, but it tends to mask speech intelligibility. The reverberant sound field consists of sounds from multiple reflections off surfaces, but because each reflection is attenuated by absorption, the sound field will fade out within about a second or so. Many large rooms have too much reverberation (more than 2 seconds), while most small rooms have too little (less than 1/2 second). Bathrooms, with little absorption, are the exception. On the other hand, the direct sound field is independant of the room but is proportional to the directivity index of the sound source. For instance, a horn speaker will focus the sound and therefore have a higher directivity index than a dome speaker, and will tend to improve speech intelligibility. Music always sounds better with some reverberation, but the exact right amount is frequently debated.

Room resonances can be calculated and mapped using the formula: speed of sound (1130 feet per second) divided by wavelength equals frequency. Where the wavelength of the first resonance is 2 times the room length (or width), and subsequent resonances are integral multiples of that. Measure a room dimension (in feet), multiply times 2, and divide it into 1130: that will be the first room resonance. The first resonance for each of the room dimensions (usually 3) will cause large peaks and valleys in loudness at those frequencies across the room at various locations. Contrary to popular opinion, splaying walls will not eliminate standing wave resonances, but instead will broaden the resonant frequency and lessen the intensity of the peak.