The entirety of the listening conditions and the quality that can be achieved are formed by
- the geometric and acoustic properties of the listening room,
- the properties and arrangement of the loudspeakers in the listening room,
- the listening location or listening zone (sweetspot) for optimally selected listening positions,
with which the resulting sound field properties are generated at the reference location.
The listening conditions in loudspeaker stereophony can largely be assessed through measurements. The following most important electroacoustic quality parameters can be used to define technically ideal listening conditions, which are achieved when all transmission errors are below the human perception threshold. In practice, transmission errors are permitted within a tolerance range, provided that they do not strongly falsify the sound event being heard .
The considerations about distortion refer to loudspeaker reproduction in rooms of any kind, i.e. mono, stereo and multi-channel or 5.1 or surround sound. The spatial requirements are not critical for mono playback.
Distortions of the output signal that are linear to a certain influencing variable are called linear distortions. In the case of loudspeakers, these are essentially changes in level due to frequency (discoloration of the amplitude response) and changes in phase due to frequency (distortion of the phase response).
In the case of playback via loudspeakers, it would be desirable if the aforementioned distortions were below the human perception thresholds. In relation to the amplitude frequency response, this would mean that all frequencies of the human hearing range (20 to 20,000 Hz) can be reproduced with a level deviation of no more than 0.5 dB, or better still 0.25 dB. This can be achieved today with complex digital equalization processes. In practice, however, the relevant recommendations and standards specify larger tolerances of up to ± 1.5 dB, whereby broadband discolorations should not be included - broadband discolorations are more audible and disturbing than narrowband ones.
The distortion of the phase response is aurally uncritical in wide frequency ranges, since the hearing is quite insensitive to internal phase rotations. In the psychoacoustic literature one speaks of distortions of the group delay in the range of 1 to 2 ms for the perceptibility in the directional localization . In the bass range, however, due to the large period lengths (because of the low frequencies), audible delay time distortions can occur, which is why the limit should ideally be set at 10 ms. In practice, this can be achieved with digital time correction or suitable loudspeaker designs (closed bass cabinet), but this parameter is often not optimized (bass reflex cabinet).
Distortions that are not linearly related to the input variables are referred to as such. In acoustics , harmonic non-linear distortions are known , which are known as distortion factor . For distortion ( THD ), there are numerous perception thresholds secured in psychoacoustics , which an ideal loudspeaker must under all listening conditions (levels). In the bass range (20 to 200 Hz) the hearing is relatively insensitive to distortion, up to 5% can remain inaudible. In the presence / brilliance range (1000 to 4000 Hz), where the hearing is most sensitive, the distortion factor can sometimes be recognized at values below 0.5%.
Non-harmonic non-linear distortions are unpleasantly more noticeable for the auditory impression. However, it is hardly possible to specify sensible limit values because non-linear distortions depend too heavily on the nature of the source signal, so that there are no standardized measurement methods. In psychoacoustics, however, it is assumed that non-harmonic non-linear distortions are largely related to harmonic distortions.
Spatiality and illustration
Ideally, the additional indirect sound generated by the loudspeakers in the listening room should not overlay the sound recording or change the hearing impression. This is difficult to achieve in practice, which is why this parameter is often insufficiently optimized.
- Reverb radius
- the reverberation radius characterizes the distance to a sound source at which direct and indirect sound have the same level. With loudspeaker stereophony , the main microphone should always be positioned within the reverberation radius. The listening distance and directional characteristics of the loudspeakers must be adapted to one another accordingly.
- Indirect sound does not discolour
- Compared to direct sound, indirect sound should not contain any audible, frequency-dependent increases or decreases in level that could distort the impression of space. This requires a loudspeaker with a frequency-neutral directional characteristic and a listening room with a frequency-neutral reverberation time .
Discrete reflections , which could disturb the localization and the impression of space, should be attenuated by 10 dB, better by 20 dB compared to the direct sound . This can be achieved by choosing a large distance from the loudspeaker to the wall, by optimizing the directional characteristics of the loudspeakers and by taking room acoustics measures, such as e.g. B. by introducing damping or diffusivity generating elements.
The placement of the speakers for stereo playback should correspond to the stereo triangle , i.e. H. the two loudspeakers form an equilateral triangle with the listener. This triangle has three equal 60 ° angles; So, seen from the listener located on the center line, the loudspeakers are at an angle of ± 30 °, which results in an audio event direction of 100%.
When playing music over 5.1 (home cinema), the loudspeaker placement should correspond to or approximate to the ITU group, which, however, is of no importance for movie playback.
- Wolfgang Josef Tenbusch: Basics of the loudspeakers. Michael E. Brieden Verlag, Lüdenscheid, 1989, ISBN 3-9801851-0-9 ( Sound and Sound Edition 1).
- Michael Dickreiter, Volker Dittel, Wolfgang Hoeg, Martin Wöhr (eds.): Handbuch der Tonstudiotechnik , 8th, revised and expanded edition, 2 volumes, publisher: Walter de Gruyter, Berlin / Boston, 2014, ISBN 978-3-11- 028978-7 or e- ISBN 978-3-11-031650-6
- Speaker base | Stereophony | Monophony (electroacoustics) | Quadraphony
- Distance law | Intensity stereophony | Runtime stereophony | Equivalence stereophony | Stick stereophony
- Interchannel | Pressure microphone | Pressure gradient microphone
- Listening conditions and playback arrangements for multi-channel stereophony (PDF file; 287 kB)