Direct sound

Sound in rooms: direct sound , early reflections and reverberation

In acoustics, direct sound D (also referred to as sound in the direct field or sound in the free field ) is the sound in an enclosed space that first arrives at the listening or measurement location without having experienced sound reflections in the meantime . In contrast to this is the room sound R, which is also referred to as sound in the room field or diffuse sound in the diffuse field .

The incidence of the first wave front as direct sound is decisive for determining the direction, i.e. for the localization of a sound source by the hearing with our ears ( precedence effect ). In contrast, the room sound makes a decisive contribution to the overall audibility of a room; For example, if there is a transit time difference Δ t> 30 ms between the direct sound and the arrival of the first reflection, the impression of a large room is created . A nearby sound source is characterized by the fact that the room sound component is low.

The “fixed” individual value for the predelay in reverberation devices is not to be equated with the acoustic start time gap , which is composed of many different reflection values.

The sound terms direct field or free field and diffuse field are not always clearly distinguished from the terms near field and far field : D irect field (free field) and diffuse field are determined by the room acoustic properties of the surrounding area; on the other hand, the acoustic terms near field and far field only describe the distance of the sound sources, the spatial effect is not considered here - a low-reflection room is assumed.

When describing the sound-technical room for sound recordings , one speaks of the sound- determining D / R or R / D ratio between the sound levels D and R of direct and room sound:

	${\ displaystyle {\ frac {D} {R}}}$	${\ displaystyle {\ frac {R} {D}}}$
D> R	${\ displaystyle> 1}$	${\ displaystyle <1}$	Direct field
D = R	${\ displaystyle = 1}$	${\ displaystyle = 1}$	you are at a theoretical point in space with the reverberation radius r _H
D <R	${\ displaystyle <1}$	${\ displaystyle> 1}$	Room sound field

The logarithmic ratio of direct sound to room sound is described by the reverberation measure .

Web links

Initial gap and the impression of closeness (PDF file; 72 kB)
Start time gap and pre-delay (PDF file; 147 kB)
What does the important initial gap mean (PDF file; 46 kB)