Time Correct Hearing In Space

Space and listening distance A sound document contains more or less distinct spatial information about the original acoustic environment. In the ideal case of perfect reproduction of a recorded sound event, there are no reflections through a listening room. In practice, this ideal case does not exist. A playback room adds its own, further room characteristics. The time window for the room-independent direct sound covers a very short time span of a few milliseconds (transients). So what is the sound-relevant information? Ultimately, it is the form of vibration that we as listeners receive at the listening position, at our auditory organs. We should measure this mode of vibration and look at the influence of the room on it. How does a reflection change the sound waves? When do room resonances have an influence, and in what form? How does a sheetrock wall affect the waveform when sound is reflected? What happens to a sound wave when it passes through a curtain and reflects off the wall behind it? What happens to the waveform when sound reflects off a cabinet wall? What is the sum of direct sound and reflection in terms of what we hear, namely the waveform? Depending on the room conditions, the proportion of "room-independent" sound (direct sound) will be more or less. We can only compensate for room acoustics to a limited extent. The listener's head is located at a certain place in the room. Only if we always place it at exactly the same point in the room will there be a modest chance of success. Sliding into a chair or changing seats while listening in a relaxed manner, however, turns all corrective measures on their head. And if several people want to listen at the same time? You could still tinker with the speaker - but for which of the myriad room acoustics? There are almost as many different rooms as there are homes. So what are commonalities in the living spaces of the group of people buying a particular loudspeaker? One thing all living spaces have in common is a floor. This is very close to the acoustic centres for floorstanding speakers and for compact speakers on a stand. In the user's home, the floor is an ever-present boundary surface with a significant effect on bass response. It follows: Loudspeakers should have a clear vertical focus. The second thing most living rooms have in common: There are several seating areas in the room. These are not arranged one above the other, but side by side. It follows: Loudspeakers should have a horizontal bundling that allows a practical, wide dispersion. In addition, the side walls, seen from the loudspeaker, should be rather averted and far enough away. And seating should also be a sufficient distance from reflective surfaces. A thick carpet in the area between the speakers and the seats is particularly beneficial. If there is a table in front of the seats, then its surface should be covered with a sound absorbing pad, table runners, etc., or numerous objects placed on it. This can also help. Since every listening room has its own reflection behaviour, there is no general validity for a somehow defined radiation behaviour of loudspeakers. The loudspeaker should emit a sound structure that is as exactly transformed as possible under the direct sound relevant radiation angles. The direct sound relevant radiation angles are in practice: horizontal approx. 0 to +/- 15°. vertical approx. 0 to +/- 5°. If you are building your own house, you can try to find an architect who designs rooms in such a way that they do not have parallel walls. Just a few degrees of slant to each other will do wonders. Not only when listening to loudspeakers, but any noise then builds up less. Myro a priori 10.02

Time1.step-response.jpg

The sound structures arriving at the listening position consist of the direct sound components, which are unaffected by the room (exception: low frequencies), and the indirect sound components, which are changed by the reflection. The low frequency range is the area where the first reflections are already superimposed on the transient response. Here there is virtually no unaffected direct sound component left. As an example, consider a 3-way transducer, the Myro Time 2. With the size of this loudspeaker and the necessary larger measuring distance you can see (left) very nicely the first room reflection and its superposition of the step response. We perceive the first milliseconds of direct sound, which reach our auditory organ unaffected by reflections, in the same way as those of a natural sound event. Impulses and transients, with the exception of the low-frequency range, reach the auditory organ directly. For the conversion and transmission of impulses and transients, it is logical to make a measurement at the location of the auditory organ. If the listening distance is small and the distance between the loudspeaker and reflecting surfaces is large, the direct sound component is large. With a large listening distance and a small distance between the loudspeakers and reflecting surfaces, the direct sound component is small. For near-field monitors, the transfer function is therefore usually particularly important in the direct sound, i.e. in the direct radiation direction. For far-field monitors, the transfer function is therefore usually also important outside the direct albedo direction.

The deformations of the sound waves during the reflection process are extraneous influences, as is the deformation due to incoherent sound transducers. But errors in the reproduction also propagate in the room acoustics:

• Room reflections of faithfully transduced sound structures sound like reflections of the original.
• Room reflections of sound structures that have not been faithfully converted do not sound like reflections of the original.

For the decay of instruments or for continuous tones, the interaction of the listening room with the sound emitted by the loudspeaker plays the decisive role in addition to the direct sound component, because especially in the steady state, the interaction of loudspeaker and room determines what happens. To achieve this, a loudspeaker should of course have a sound structure that is as consistent as possible under different dispersion angles. The organ is the best example of an instrument with a high level in the steady state, and it is precisely here that the interaction of loudspeaker and room takes effect.

Myro Grand Concert II Design Study

Ultimately, what counts is the sound structure that arrives / takes effect at the auditory organ. The direct sound component, although proportionally smaller than the indirect sound, has a greater importance in rooms, because only in it room-independent information about the original is contained. The recognition and localization of sound events within the original (recording), i.e. also the recognition of the original room sound, is only clearly possible in direct sound. The next most important are the early, briefly following, energetic, first reflections. Everything that reaches our hearing organ after multiple reflections and attenuation tends to get lost in the general chaos of reflections and is of secondary importance. For the larger radiation angles relevant to indirect sound, the quality of the sound structure radiated by the loudspeaker is also decisive for the impression of "authenticity". The listening experience with signal / time accurate loudspeakers is: Due to the excellent intelligibility and the detachment of the sound from the loudspeaker, the perception of the original information gains dominance over the perception of the listening room. The direct sound is of clearly superior importance for the perception of the original sound. Quantitatively, this experience cannot be justified, because the direct sound amounts to only about one fifth of the total sound. For locating and recognizing a sound structure stored in a recording, the following order of priority therefore applies: 1. direct sound (transients) 30-fold (!) increased nerve firing rate from the auditory organ to the brain, thus maximum attention maximum dynamics / amplitude values the only sound component with the chance to transmit original structures 2. first early reflections the shortest time sequence to direct sound high energy content can superimpose and alienate direct sound 3. multiple reflected sound components (reverberation) long time sequence on the direct sound decreased energy content strong structural deformations due to the reflection processes (non-linear absorption) 4. quasi steady states (space modes) long time sequence to the direct sound high energy content no longer contain original sound structures And there are the aspects of the transformed sound components excited self-resonances of the room-boundaries excited self-resonances of all objects in space which act as frequency-filters and transform certain sound-parts into mechanical vibrations and heat. The mechanical vibrations in turn act as sound sources and are not insignificantly involved in the sound of the room. In all considerations, the only thing that counts is the quality of the sound structure. First early reflections, which superimpose the transient processes, are next to the strong dynamic compression in some recordings at the top of the list of factors that can relativize the advantage of the signal / time accurate conversion. For playback with loudspeakers, the following therefore applies: optimisation of room acoustic parameters, speaker placement, seating position, etc. perfect reproduction of the direct sound component. Here, too, the transient response is of particular importance. as little loudspeaker sound as possible in the direction of nearby room surfaces. an as evenly as possible directed radiation behaviour of the loudspeaker.

For the reproduction with loudspeakers applies:

• optimization of room acoustic parameters, speaker placement, seating position, etc.
• a reproduction of the direct sound component as perfect as possible. Here, too, the transient response is of particular importance.
• as little loudspeaker sound as possible in the direction of nearby room surfaces
• as evenly directed radiation behaviour of the loudspeaker as possible

Can room correction help?
The sense of hearing is capable of differentiating the incoming pressure fluctuations of the air (sound waves). It does not simply form the sum of the amplitude values, like a measuring procedure, but perceives the individual information contained therein. Without this ability, all the many amazing hearing properties could not be explained.
An electronic room correction, which, if it is committed to the ideal of the original input signal, is an over-all correction, would have to be capable of a differentiated correction of the direct sound and the reflected sound components arriving at the listening position from different directions, with different transit times, with their individual structure. However, this is not possible due to the principle. In this respect the following recommendations result:

1. Use loudspeakers with a linear frequency band
2. The loudspeakers should have a regular directivity (over the whole frequency response an even decrease of the level off axis)
3. a favourable positioning of the loudspeakers and the listening place with regard to excitation and effect of the modes
4. even reverberation times of the room
5. only then, if there are still problems with modes, narrowband reduction of the frequencies of the disturbing modes

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