Before you invest in your next sound system upgrade, it’s important to understand exactly how sound waves propagate in an enclosed space, and how the complex interrelationships of direct and reflected sounds are perceived by listeners in the context of music and speech program material. In order to wrap your head around that process, you first must master four fundamental terms that define how sound interacts with any architectural space.
Sound System Upgrade: 4 Must-Know Concepts
#1 – DIRECT SOUND
Defined – This one is relatively straightforward for a sound system upgrade. Direct sound refers to those acoustical waves that emanate directly from the sound source. The source could be a person speaking or singing, a musical instrument, or a loudspeaker. With pure direct sound, no reflected sound waves at all are reaching your ears.
However, it is rare that you will hear nothing but direct sound. Indoors, you’ll experience it only in an anechoic chamber — a room made for acoustical measurements that absorbs all sounds at all frequencies. Even outdoors it’s uncommon. You’d need to be away from any large objects since buildings, pavement, water, or even large tree trunks will reflect some sounds.
Benefits – Direct sound is always good, for two reasons.
First, direct sound is the foundation of both musical clarity and speech intelligibility. That’s because all of the sounds you hear, at all frequencies, are phase coherent when they reach your ear — at least relative to the immediate source. (If these direct sounds are from a loudspeaker, the phase relationships may be altered relative to the original source, but that’s another story.) Direct sounds will be free of any smearing of consonants in speech, so similar words are easily distinguished. Also, staccato music sounds with rapid transient changes are perceived individually with full clarity.
Direct sound is also important for localization and imaging. Direct sound tells our ears where the sound is coming from, and it allows us to distinguish the location of sounds in space with amazing accuracy. If you’ve ever sat in the front row of a symphony concert, you know that you can close your eyes and localize instruments in three-dimensional space from their direct sounds.
Downsides – There are no [downsides] to direct sounds unless they are distorted or too loud.
#2 – EARLY REFLECTIONS
Definition – Early reflections are sounds that arrive at your ear less than about 1/10 second after the direct sound. They are generated by acoustically reflective surfaces near the sound source and are perceived as an integral part of the direct sound.
Benefits – Even though we don’t perceive these reflections separately, we know when they are absent. Early reflections give an acoustical space a feeling of “life” and “air.” Without them, the space sounds “stuffy” or “dead.”