8.3 Early Reflections
Another situation that can reduce the subjective quality of reproduced sound is the presence of early reflections. By early reflections, we are referring to reflected sound waves that reach the listener within 10 to 20 milliseconds of the direct signal from the loudspeaker.
When a reflected sound reaches the listener more than 40 milliseconds later than the direct sound, the reflection is heard as a discrete echo. However, if the reflected sound arrives within around 20 milliseconds of the direct sound, the ear/brain system integrates the two sounds so that only one sound is heard. This integration is done in such a way that spatial information is preserved, providing an acoustical "picture" of the physical space that created the reflections.
However, the source recording also contains ambient information that portrays the original recording site. Early reflections in the listening room will tend to obscure the ambient information in the recording, leading to a loss of dimensionality or spaciousness. Secondary arrivals within the first 10 milliseconds are especially problematic, becoming less troublesome as the arrival time lengthens to 20 milliseconds or so.
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