Patent Description:
In rooms which are intended to be used for presentations and/or giving lectures etc, such as a class room or a conference/meeting room, it is desired to provide acoustics which are ideally suited for facilitating the transmission of sound, particularly speech, to the intended audience. The teachings herein pertain particularly to ordinary rooms as defined in ISO <NUM>-<NUM>. Acoustic quality for speech in an ordinary room encompasses not only speech intelligibility for the audience but also speaker comfort, i.e. the perceived comfort that a person speaking receives in the room. In: "<NPL>, is speaker comfort discussed and a parameter for quantification introduced. The parameter voice support is related to sound strength G. There is probably an optimum value but more investigations are needed.

Early reflections of the sound waves are generally considered favourable for the acoustic quality in a room for speech while late reflections are considered detrimental. A standardized measurement parameter of such early reflections is speech clarity C<NUM>, where the relationship between sound reflections before and after <NUM> are observed and where the former is considered early reflections and thus beneficial. Another parameter that is of importance is reverberation of different frequencies of sound, where excessive reverberation or reverberation time, T<NUM>, of certain sound frequencies can cause discomfort and/or reduce intelligibility of the speech. Moreover, as mentioned, the sound strength G is also of importance. All these factors/parameters are affected by the general design of the room as well as of if for instance a sound absorbent ceiling is provided in the room.

<CIT> discloses a multi-purpose arena comprising reflective panels as well as absorbent and reflective panels.

In view of that stated above, the object of the present invention is to provide an acoustic system that alleviates some of the problems with prior art solutions and improves speech intelligibility and speaker comfort in a room provided with a sound absorbent ceiling.

To achieve at least one of the above objects and also other objects that will be evident from the following description, an acoustic system having the features defined in claim <NUM> is provided according to the present disclosure. Preferred embodiments of the system will be evident from the dependent claims.

More specifically, there is provided an acoustic system for improving speech intelligibility, the acoustic system comprising a room having a first zone and a second zone. The system further comprising a ceiling of the room, the ceiling comprising a plurality of ceiling tiles. The ceiling tiles comprises a first group of ceiling tiles having sound absorbing properties and a second group of ceiling tiles having sound diffusing properties. The first group of ceiling tiles comprises ceiling tiles being arranged in the second zone and the second group of ceiling tiles comprises ceiling tiles being arranged in the first zone and being configured for reflecting sound to the first zone and to the second zone. The sound diffusing second group of ceiling tiles arranged in the first zone provides early reflections to both the first zone, which may be a presentation zone, which improves speaker comfort. Further still, the early reflections provided to the second zone, which may be an audience zone, improves the speech clarity and sound strength in the second zone which improves speech intelligibility. Moreover, reverberation time for octave frequency bands which are considered relevant for speech intelligibility are also reduced.

The ceiling may be a suspended ceiling, a direct fixed ceiling or a free hanging ceiling unit.

In one embodiment, the ceiling comprises a grid of profiles supporting the ceiling tiles.

The second group of ceiling tiles may further cover at least <NUM>% of a ceiling area of the ceiling. The second group of ceiling tiles may further still cover at the most <NUM>% of a ceiling area of the ceiling. The aforementioned ratios provide a desired balance where the overall sound absorbing functionality of the first group of ceiling tiles is maintained while the second group of ceiling tiles provides a significant improvement in speech intelligibility and improved speaker comfort.

The first group of ceiling tiles may comprise ceiling tiles mounted in the second zone.

The second group of ceiling tiles may further be hollow having a front surface provided with at least one opening facing the room. The volume of a hollow portion of the ceiling tile may be between <NUM>,<NUM><NUM> and <NUM>,<NUM><NUM>, preferably approximately <NUM>,<NUM><NUM>. The hollow shape of each second group ceiling tile and the at least one opening form a resonance chamber in each second group ceiling tile that allows it to absorb octave frequency bands which for instance the first group of ceiling tiles are less efficient at absorbing. The overall acoustic properties of the acoustic system are thus improved.

The at least one opening may further have an opening surface area of between <NUM><NUM> and <NUM><NUM>, preferably approximately <NUM><NUM>. The aforementioned surface area together with the structure and volume of the hollow portion of the second group ceiling tiles provides improved absorption of low sound frequencies, typically below <NUM>, more preferably approximately <NUM>.

Moreover, the second group of ceiling tiles may be configured to absorb sound having a sound frequency below <NUM>, preferably approximately <NUM>. Sound frequencies below <NUM>, especially around <NUM>, are typically difficult for a regular sound absorbent ceiling tile, such as those of the first group, to absorb. Furthermore, such low frequencies are not considered beneficial for speech intelligibility. The second group of ceiling tiles thus reduces such undesired low sound frequencies thus complementing the first group of ceiling tiles.

In one embodiment, the presentation zone covers a presentation position from which a speaker, i.e. a person, is intended to address an audience. Furthermore, ceiling tiles from the second group of ceiling tiles may be arranged directly above the presentation position. Having second group ceiling tiles arranged directly above the speaker provides a significant increase in the early reflections that the speaker can receive which improves speaker comfort.

Ceiling tiles from the second group of ceiling tiles may further be arranged covering an area of the suspended ceiling from the presentation position extending towards the second zone. Further still, ceiling tiles from the second group of ceiling tiles may be arranged in the audience zone. Extending the second group of ceiling tiles from the first zone towards and even into the second zone increases the early reflections and the sound strength that can be provided to the second zone.

Ceiling tiles from the first group of ceiling tiles may further be arranged in the first zone.

The second group of ceiling tiles may comprises ceiling tiles having a front surface facing the room having a shape selected from the group comprising: a single curved convex front surface, a double curved convex front surface, a multi-faceted convex front surface, an asymmetric at least partially inclined front surface, an asymmetrically curved convex front surface, an inclined concave front surface, an at least partially curved concave front surface and a multi-faceted concave front surface.

All references to "a/an/the [element, device, component, means, step, etc]" are to be interpreted openly as referring to at least one instance of said element, device, component, means, step, etc., unless explicitly stated otherwise.

<FIG> discloses an acoustic system <NUM> according to one embodiment herein. The acoustic system <NUM> comprises a room <NUM>. The room <NUM> may be a class room, a conference room or any other type of ordinary room as defined in ISO <NUM>-<NUM> in which it is desired to provide improved acoustic properties for speech intelligibility and speaker comfort.

The room <NUM> has a first zone A and a second zone B, the separation of which is indicated by the dashed line in the <FIG> and the following figures. The first zone A is preferably a presentation zone A, in which a presentation position <NUM> may be arranged. The speech is thus preferably emitted from the presentation zone A, either directly from a person/speaker and/or synthetically from a loudspeaker system.

The second zone B is the intended target of the sound emitted from the first zone A, and is thus preferably an audience zone B.

The system <NUM> further comprises a ceiling <NUM>, the ceiling <NUM> comprising a pluraliy of ceiling tiles <NUM>, <NUM>. The ceiling <NUM> may be a suspended ceiling <NUM> as is illustrated in <FIG>, in which the ceiling tiles <NUM>, <NUM> are attached to a grid of profiles <NUM> which is suspended from a structural ceiling <NUM> of the room <NUM>. The ceiling <NUM> may further be a direct fixed ceiling <NUM>, in which the ceiling tiles <NUM>, <NUM> are fixed to either directly to a structural ceiling or to a grid of profiles <NUM> attached closer/directly to the structural ceiling <NUM>. The ceiling may furhter be a free hanging ceiling unit <NUM> in which the ceiling tiles <NUM>, <NUM> are supported individually from the the structural ceiling <NUM>, for instance by means of wires, without any grid of profiles.

The ceiling tiles <NUM>, <NUM> further comprises a first group of ceiling tiles <NUM> having sound absorbing properties. The first group of ceiling tiles <NUM> may be conventional ceiling tiles <NUM> and may in one embodiment be manufactured from a mineral fibre material. Rooms provided with sound absorbing ceiling tiles presents certain difficulties for achieving a desired acoustic for achieving high speech intelligibility and speaker comfort. It has been realized that sound absorbing ceilings reduces the sound strength of higher octave frequency bands which are considered important for speech intelligibility, while such ceilings provides less sound absorption for lower sound frequencies that may be detrimental to speech intelligibility.

The ceiling tiles <NUM>, <NUM> further comprises a second group of ceiling tiles <NUM> having sound diffusing properties. The second group ceiling tiles <NUM> will be described in more detail in relation to <FIG>.

The first group of ceiling tiles <NUM> comprises ceiling tiles being arranged in the second zone B and the second group of ceiling tiles <NUM> comprises ceiling tiles being arranged in the first zone A and is configured for reflecting sound to the first zone A and to the second zone B. In the embodiment shown in <FIG>, all of the second group of ceiling tiles <NUM> are arranged in the first zone A.

The second group of ceiling tiles <NUM> thus provides early sound reflections to the second zone B, in which the audience is positioned. The first group of ceiling tiles <NUM> absorbs sound particularly well in the medium to high speech sound frequency ranges, i.e. from <NUM> and above. The second group of ceiling tiles <NUM> particularly diffuses and improves reflection of sound having sound frequencies of <NUM> and above, thus compensating for the sound absorbtion of the first group of ceiling tiles.

The comfort for an eventual speaker in the presentation position <NUM> is improved by the early reflections indicated in <FIG> as the whole double arrowed lines.

In <FIG> is another embodiment of the acoustic system <NUM> shown, in which the second group of ceiling tiles <NUM> comprises ceiling tiles arranged in the second zone B. The ceiling tiles <NUM> from the second group arranged in second zone B provides additional reflections of sound, particularly to a far position <NUM> in the second zone B which improves speech intelligibility in the far position <NUM>.

<FIG> shows a comparison diagram of a measured speech clarity C<NUM> in a near position <NUM> (shown in <FIG>) in the second zone B. The acoustic system <NUM> according to the teachings herein, using ceiling tiles <NUM> from the second group in the first zone A and the remaining ceiling tiles <NUM> being sound absorbent ceiling tiles <NUM> from the first group, is compared to an acoustic system having only sound absorbent ceiling tiles <NUM> of the first group.

Speech clarity C<NUM> is, as mentioned above, the relationship between early and late reflections and is more specifically defined by the following formula, in which h= measured impulse response: <MAT>.

Table <NUM> below shows the corresponding measured C<NUM> values in dB that is plotted in the diagram of <FIG>.

The first graph <NUM> shows how the C<NUM> dB level varies with changing frequency when only absorbent ceiling tiles of the first group <NUM> are fitted, while the second graph <NUM> shows the corresponding C<NUM> dB levels when ceiling tiles <NUM> from the second group are arranged above the presentation position <NUM> in the first zone A. Combining sound absorbing ceiling tiles <NUM> from the first group with sound diffusing ceiling tiles <NUM> from the second group provides an increase in C<NUM> over the entire measured spectrum in the near position <NUM>, i.e. between <NUM> to <NUM>.

The octave frequency bands of <NUM> and <NUM> have shown to be particularly important for speech intelligibility and a significant dB increase between these sound frequencies is achieved in the near position <NUM> by the acoustic system <NUM> presented herein.

<FIG> shows a comparison diagram of a measured speech clarity C<NUM> in a far position <NUM> (shown in <FIG>) in the second zone B. The acoustic system <NUM> according to the teachings herein, using ceiling tiles <NUM> from the second group in the first zone A and the remaining ceiling tiles <NUM> being sound absorbent ceiling tiles <NUM> from the first group, is compared to an acoustic system having only sound absorbent ceiling tiles <NUM> of the first group.

The first graph <NUM> shows measured C<NUM> dB levels in the far position <NUM> when only sound absorbing ceiling tiles <NUM> from the first group is arranged in the ceiling <NUM>. The second graph <NUM> shows corresponding C<NUM> dB levels in the far position <NUM> when ceiling tiles <NUM> from the second group are fitted to the ceiling <NUM> in the first zone A above the presentation position <NUM>. For the far position <NUM>, an even more significant improvement is achieved in speech clarity between the octave frequency bands of <NUM> and <NUM>.

The second group of ceiling tiles <NUM> should preferably cover at least <NUM>% of a ceiling area of the ceiling <NUM> and at most <NUM>% of the ceiling area of the ceiling <NUM>. While also smaller or larger area portions of the ceiling <NUM> area may be covered by ceiling tiles <NUM> of the second group, the above limits provides desired functionality of the sound diffusing/reflecting properties of the second group of ceiling tiles <NUM> whilst avoiding an undesired reduction of the sound absorbing properties of the first group of ceiling tiles <NUM>.

<FIG> shows a comparison diagram of a measured reverberation time T<NUM> in a near position <NUM> (shown in <FIG>) in the second zone B. The acoustic system <NUM> according to the teachings herein, using ceiling tiles <NUM> from the second group in the first zone A and the remaining ceiling tiles <NUM> being sound absorbent ceiling tiles <NUM> from the first group, is compared to an acoustic system having only sound absorbent ceiling tiles <NUM> of the first group. Reverberation time T<NUM> is desired to be kept as low as possible for achieving improved speech intelligibility and speaker comfort, especially for the octave frequency bands from approximately <NUM> to <NUM>. The first graph <NUM> shows T<NUM> for an acoustic system having only ceiling tiles <NUM> from the first group, while the second graph <NUM> shows T<NUM> for the acoustic system <NUM> according to the teachings herein. Table <NUM> below shows the corresponding T<NUM> values (s) that is plotted in the diagram of <FIG>.

It can be seen that the reverberation time T<NUM> is reduced for the important frequencies <NUM> and <NUM>. This is a non obvious effect of the provision of the ceiling tiles <NUM> of the second group to the acoustic system <NUM>. In most applications, adding diffusors to an acoustic system generally causes increase reverberation time. However, in the context of the teachings herein where diffusors are combined with absorbent ceiling tiles <NUM> from the first group, can improvements be achieved also in reverberation time T<NUM> for the most important octave frequency bands.

This extends also to <FIG>, which shows a corresponding comparison diagram for the far position <NUM>. , the diagram in <FIG> compares the acoustic system <NUM> according to the teachings herein, using ceiling tiles <NUM> from the second group in the first zone A and the remaining ceiling tiles <NUM> being sound absorbent ceiling tiles <NUM> from the first group with an acoustic system having only sound absorbent ceiling tiles <NUM> of the first group. The first graph <NUM> shows T<NUM> for an acoustic system having only ceiling tiles <NUM> from the first group, while the second graph <NUM> shows T<NUM> for the acoustic system <NUM> according to the teachings herein. Table <NUM> below shows the corresponding T<NUM> values (s) that is plotted in the diagram of <FIG>.

Also in the far position <NUM> can a decrease in the reverberation time T<NUM> be observed for the frequencies <NUM> and <NUM> compared to a prior art acoustic system where only sound absorbent ceiling tiles <NUM> of the first group are used.

<FIG> shows a comparison diagram of a measured sound strength G in a near position <NUM> (shown in <FIG>) in the second zone B. The acoustic system <NUM> according to the teachings herein, using ceiling tiles <NUM> from the second group in the first zone A and the remaining ceiling tiles <NUM> being sound absorbent ceiling tiles <NUM> from the first group, is compared to an acoustic system having only sound absorbent ceiling tiles <NUM> of the first group. It is desired to achieve a sound strength G which is appropriate for achieving improved speech intelligibility and speaker comfort, especially for the octave frequency bands from approximately <NUM> to <NUM>. The first graph <NUM> shows sound strength G for an acoustic system having only ceiling tiles <NUM> from the first group, while the second graph <NUM> shows sound strength for the acoustic system <NUM> according to the teachings herein. Table <NUM> below shows the corresponding sound strength G (dB) values that is plotted in the diagram of <FIG>.

As can be seen in <FIG>, and in the corresponding Table <NUM>, an increase in sound strength G is achieved particularly for the frequencies <NUM> and <NUM>.

<FIG> shows a corresponding comparison diagram for the far position <NUM>. , the diagram in <FIG> compares the acoustic system <NUM> according to the teachings herein, using ceiling tiles <NUM> from the second group in the first zone A and the remaining ceiling tiles <NUM> being sound absorbent ceiling tiles <NUM> from the first group with an acoustic system having only sound absorbent ceiling tiles <NUM> of the first group. The first graph <NUM> shows sound strength G for an acoustic system having only ceiling tiles <NUM> from the first group, while the second graph <NUM> shows sound strength G for the acoustic system <NUM> according to the teachings herein. Table <NUM> below shows the corresponding sound strength G values (dB) that is plotted in the diagram of <FIG>.

While the increase in sound strength G compared to the prior art system is not as significant in the far position <NUM> as it is in the near position <NUM>, a noticeable increase is still achieved for the desired frequencies of <NUM> and <NUM>.

<FIG> shows an acoustic system <NUM> according to one embodiment. The ceiling <NUM> comprises sound absorbing ceiling tiles <NUM> of the first group and sound diffusing/reflecting ceiling tiles <NUM> of the second group, the latter are arranged in a rectangular pattern in the first zone A, i.e. in the presentation zone A. No ceiling tiles <NUM> of the second group are arranged in the second zone B. Such an arrangement of the second group of ceiling tiles <NUM> may be suitable for a room <NUM> in which the second zone B has a short extension such that the distance between the presentation position <NUM> and the far position <NUM> is relatively short. While three lateral/transverse rows of ceiling tiles <NUM> of the second group are shown, it is to be realized that fewer or more rows of ceiling tiles <NUM> could be provided in the first zone A.

<FIG> shows yet another embodiment of the acoustic system <NUM> in which the ceiling <NUM> is longer and in which the distance from the presentation zone <NUM> to the far position <NUM> is longer than in the embodiment of <FIG>. The arrangement of the second group of ceiling tiles <NUM> is thus adapted such that ceiling tiles <NUM> from the second group are also arranged in the second zone B, i.e. in the audience zone B. The ceiling tiles <NUM> will thus provide increased early reflections to the far position <NUM>, compensating for the longer distance and improving sound strength and speech clarity thereto.

<FIG> shows yet another embodiment of the acoustic system <NUM>, in which the second group of ceiling tiles <NUM> are arranged in longitudinal rows extending from the first zone A into the second zone B. It is to be realized that the rows do not have to extend into the second zone B, for instance if the distance between the presentation position <NUM> and the far position <NUM> is sufficiently short such that this is not required. This could for instance be determined by measuring speech clarity, reverberation time and/or sound strength in the far position <NUM> while changing the extension of the rows until a desired level is found.

By arranging the second group ceiling tiles <NUM> in individual longitudinal rows, the ceiling tiles <NUM> can be allowed to be spread out over a larger area of the ceiling <NUM> and thus provide sound diffusion/reflection over a larger area without exceeding the preferred area limits defined above. The rows may further extend longer into the second zone B while keeping within the preferred area limits.

<FIG> shows one embodiment of the acoustic system <NUM> in which the second group ceiling tiles <NUM> are arranged in a chess-pattern. The chess-pattern arrangement of the second group ceiling tiles <NUM> provides a more even distribution of the second group ceiling tiles <NUM> over the ceiling <NUM> and facilitates even diffusion/reflection. As for the embodiment shown in <FIG>, arranging the second group ceiling tiles <NUM> in a chess pattern allows spreading the ceiling tiles <NUM> over a larger area while keeping within the area ratio limits specified above.

Turning now to <FIG> in which one embodiment of a second group ceiling tile <NUM> is shown in a side view. The ceiling tile <NUM> is shown attached to/supported by a grid of profiles <NUM>. The ceiling tile <NUM> may for this purpose comprise a base <NUM>, the base <NUM> may be formed integrally with the ceiling tile <NUM> or as a separate part that is connected to the rest of the ceiling tile <NUM>. The second group ceiling tile <NUM> is provided with a front surface <NUM>, the front surface <NUM> being configured to face the room <NUM>. The second group ceiling tile <NUM> base <NUM> may be manufactured from a wooden material or a wood based material. The front surface <NUM> may be formed by a sheet material such as hard board material. Other materials could however also be used for manufacturing the second type ceiling tile <NUM>, e.g. metallic materials such as steel sheet metal or polymeric or composite materials or any other material that provides satisfactory sound reflecting properties.

To achieve a desired diffusion/reflection of sound waves, the front surface <NUM> shown in <FIG> is provided with a single curved convex shape. In the present disclosure, convex is defined as a shape which protrudes outside/below the overall surface of the ceiling <NUM> while a concave shape is the opposite, i.e. a shape that is recessed inside/above the overall surface of the ceiling <NUM>.

The curved front surface <NUM> of the ceiling tile <NUM> in <FIG> is preferably arranged as illustrated in <FIG>, i.e. such that the curvature is in the longitudinal direction of the room <NUM> to facilitate diffusion/reflection of sound both back towards zone A and towards zone B. In other words, a near end 114a of the ceiling tile <NUM> front surface <NUM> should be arranged facing the first zone A or the presentation position or away from the second zone B, while a far end 114b should be arranged facing the second zone B or away from the first zone A.

The ceiling tile <NUM> shown in <FIG> could further have a double curved front surface <NUM>, such that front surface <NUM> is semi-spherical. Such a front surface <NUM> will provide sound diffusion not only in the longitudinal direction of the room but also in lateral/transverse directions.

The second group ceiling tile <NUM> may be hollow and having a volume of a hollow portion <NUM> of the ceiling tile <NUM> of between <NUM>,<NUM><NUM> and <NUM>,<NUM><NUM>, preferably approximately <NUM>,<NUM><NUM>. The weight of the ceiling tile <NUM> can thus be reduced. The hollow portion <NUM> is further especially beneficial if the second group ceiling tile <NUM> is provided with an opening <NUM> in the front surface <NUM>, as is illustrated in <FIG>.

The opening <NUM> should be arranged such that it faces the room <NUM> and have an opening surface area of between <NUM><NUM> and <NUM><NUM>, preferably approximately <NUM>-<NUM><NUM>. The opening <NUM> will allow the second group ceiling tile <NUM> to function as a resonating absorbent and with the volume of the hollow portion <NUM> specified above together with the opening <NUM> surface area will especially low sound frequencies be absorbed. Particularly sound frequencies below <NUM>, more preferred between <NUM> and <NUM>, even more preferred approximately <NUM>.

This is especially beneficial when considering the second group of ceiling tiles <NUM> in combination with the absorbing ceiling tiles <NUM> from the first group, as the first group of ceiling tiles <NUM>, which are preferably conventional sound absorbing ceiling tiles <NUM>, are particularly efficient at absorbing sound in octave frequency bands with higher frequencies while generally less effective for sound with a lower frequency. Such low octave frequency bands as between <NUM> and <NUM> are further not desirable for improving speech clarity/intelligibility, the second group of ceiling tiles <NUM> will thus complement the first group of ceiling tiles <NUM> in absorbing these frequency bands and thus providing an improved total acoustic property of the acoustic system <NUM>. <FIG> shows yet another embodiment of a second group ceiling tile <NUM> in a side view. The embodiments shown in <FIG> shares most features with the embodiment shown in <FIG>, emphasis below will thus be made on the unique features for each embodiment. The description of features in relation to <FIG> in the aforementioned, and of features of embodiments in <FIG> in the following, is thus unless stated otherwise applicable to each embodiment of the second group ceiling tile <NUM> disclosed herein.

The ceiling tile <NUM> shown in <FIG> has a triangularly shaped convex front surface <NUM>. The ceiling tile <NUM> comprises a near end 114a of the ceiling tile <NUM> front surface <NUM> that is configured to be arranged facing the first zone A or the presentation position or away from the second zone B, while a far end 114b of the front surface <NUM> should be arranged facing the second zone B or away from the first zone A. The embodiment shown in <FIG> provides a more directed sound reflection, i.e. less sound diffusion/scattering than the embodiment shown in <FIG> for instance, given that they are provided with similar surface structure/finish. The triangularly shaped ceiling tile <NUM> could thus be beneficial for instance when an improvement of speech intelligibility of a certain area of the room <NUM> is desired.

<FIG> shows a side view of a second group ceiling tile <NUM> having a front surface <NUM> with an irregular shape. Such a ceiling tile <NUM> could be formed to achieve a tailored sound diffusion/reflection to each area of the room <NUM>.

<FIG> shows a side view of another embodiment of the second group ceiling tile <NUM> in which the front surface <NUM> is convex and multi-faceted. The size and shape of each facet of the multi-faceted front surface <NUM> can be varied which determines the overall sound diffusion/scattering by the ceiling tile <NUM>. For instance, having fewer facets will reduce the diffusive properties of the ceiling tile <NUM> as the facets will be larger and be oriented at a larger angular separation from each other in comparison to a similar ceiling tile <NUM> having more facets. The multi-faceted front surface <NUM> thus facilitates providing a desired sound diffusion property to the ceiling tile <NUM>, and to control where the sound is reflected to.

<FIG> shows a side view of yet another embodiment of the second group ceiling tile <NUM>. The front surface <NUM> of the ceiling tile <NUM> in <FIG> has an asymmetrically curved convex shape. The curvature increases (i.e. the radius of the curvature decreases) towards the near end 114a of the ceiling tile <NUM>, while it decreases (the radius increases) towards the far end 114b. This provides more sound diffusion in the direction of the first zone A, while the diffusion is less for sound reflecting towards the second zone B. This could be beneficial in certain applications where it is for instance determined that the presentation zone <NUM> receives too high sound strength while the far position <NUM> recieves a too low sound strength. Having less sound diffusion for the sound reflecting towards the second zone B will allow improvements in the sound strength in the second zone B, while sound strength can be reduced in the first zone A by the increased diffusion in that direction.

<FIG> shows a side view of yet another embodiment of the second group ceiling tile <NUM>. The ceiling tile <NUM> shown in <FIG> comprises an convex asymmetric and at least partially inclined front surface <NUM>, which is further provided with a flat surface at the near end 114a thereof. The flat surface may for instance be arranged directly above the presentation position <NUM> to provide early reflections to improve speaker comfort. The inclined portion is arranged at the far end 114b of the ceiling tile <NUM> and faces the second zone B such that sound is reflected thereto. The front surface <NUM> shape illustrated in <FIG> provides less sound diffusion that a continuously curved front surface <NUM> as shown in e.g. <FIG>, but this could be desired to achieve a sufficient sound strength in a particular area of the room <NUM>.

<FIG> shows a side view of one embodiment of the second group ceiling tile <NUM> in which the front surface <NUM> is an inclined concave surface <NUM>. The inclined concave front surface <NUM> may be provided with a surface structure/finish that facilitates sound diffusion even though the surface <NUM> is evenly/uniformly inclined. The concave shape facilitates mounting of the ceiling tile <NUM> in for instance rooms <NUM> where ceiling height is limited and/or for other reasons ceiling tiles <NUM> that protrude from the surrounding ceiling <NUM> are undesired. The front surface <NUM> is inclined such that it faces towards the second zone B, whereby sound is reflected from the first zone A towards the second zone B. The ceiling tile <NUM> could further be arranged behind the presentation position <NUM> whereby returning sound reflections also to the first zone A can be achieved.

<FIG> shows a side view of one embodiment of the second group ceiling tile <NUM> in which the front surface <NUM> is a multi-faceted concave front surface <NUM>. The front surface <NUM> of the ceiling tile <NUM> is comprises an increasing incline towards the near end 114a thereof. While the front surface <NUM> is shown having facets, it is to be realized that the increasing incline towards the near end 114a could be achieved with a continuous curvature as well. The front surface <NUM> furhter comprises a flat portion at the far end 114b of the ceiling tile <NUM>, which reduces sound diffusion to the far position <NUM> of the room <NUM> and thus improves sound strength at this position which is desirable in certain applications.

<FIG> shows a side view of one embodiment of the second group ceiling tile <NUM> in which the ceiling tile <NUM> further comprises a second hollow portion <NUM>, the second hollow portion <NUM> is preferably in communication with the hollow portion <NUM>. The second hollow portion <NUM> extends above the overall surface of the ceiling <NUM> and may be beneficial if the desired interior volume as mentioned above cannot be achieved without having a detrimental effect on the shape (and thus the sound diffusive properties) of the second group ceiling tile <NUM>. The interior volume of the ceiling tile <NUM> can thus be increased without affecting the shape of the front surface <NUM> of the ceiling tile <NUM>.

The lateral and longitudinal extension of the ceiling tile <NUM> is generally limited, especially when the ceiling tile <NUM> is supported by grid of profiles <NUM>. Typically, the ceiling tiles <NUM>, <NUM> have the following modular dimensions: <NUM> x <NUM> or <NUM> x <NUM>, in order to fit in existing grid of profiles <NUM>. Achieving both a desired interior volume and a desired shape of the front surface <NUM> can thus be problematic whilst also having to consider the standardized modular dimensions of the grid of profiles <NUM>. Providing a second hollow portion <NUM> removes some of the limitations that the above relationships could otherwise present in shaping the second group ceiling tile <NUM>. The second hollow portion <NUM> is applicable to all embodiments of the second group ceiling tile <NUM> disclosed herein.

<FIG> shows perspective views of embodiments of the second group ceiling tile <NUM> in which at least one opening <NUM> is provided in the front surface <NUM>. The opening <NUM> may as shown in <FIG> be arranged centrally on the front surface <NUM>, be arranged towards the near end 114a of the ceiling tile <NUM> as shown in <FIG> and towards the far end 114b of the ceiling tile <NUM> (not shown). The opening <NUM> may further be arranged along the perimeter of the base <NUM> of the ceiling tile <NUM> (not shown).

In one embodiment, as shown in <FIG>, two openings <NUM> are provided with one being arranged at the near end 114a and the other at the far end 114b of the ceiling tile <NUM>. It is to be realized that more than two openings <NUM> could also be provided. The total surface area of the opening(s) <NUM> is between <NUM><NUM> and <NUM><NUM>, preferably approximately <NUM><NUM>.

The opening(s) <NUM> allows sound waves to transfer to the inside of the hollow portion <NUM> (and optionally the second hollow portion <NUM>) whereby frequencies below <NUM>, preferably approximately <NUM>, can be absorbed, as mentioned above. The volume of the hollow portion <NUM> together with the thickness of the ceiling tile material that constitutes the front surface <NUM> and the area of the opening(s) <NUM> defines the resonance frequency of the ceiling tile <NUM> according to the following formula: <MAT> fr=resonance frequency, S=area of opening <NUM>, L=length of the channel formed by the opening <NUM> from outside to inside of front surface <NUM>, V=volume of hollow portion <NUM> or hollow portion and second hollow portion <NUM> combined.

The volume of the hollow portion <NUM>, or of the hollow portion <NUM> and the second hollow portion <NUM> combined, is preferably between <NUM>,<NUM><NUM> and <NUM>,<NUM><NUM>, preferably approximately <NUM>,<NUM><NUM>. The thickness of the material in the ceiling tile <NUM> that forms the front surface <NUM> is between <NUM> and <NUM>, preferably approximately <NUM>, which defines the length channel formed by the opening <NUM>. The opening <NUM> total surface area is, as mentioned, between <NUM><NUM> and <NUM><NUM>, preferably approximately <NUM><NUM>.

The second group of ceiling tiles <NUM> will thus complement the first group of ceiling tiles <NUM> in absorbing the undesired low frequency bands of below <NUM> thus forming an improved acoustic system. The second group of ceiling tiles <NUM> further facilitates diffusion of sound and provides increased early reflections to both the first zone A and to the second zone B, which increases speech clarity C<NUM>, increases sound strength G and reduces undesired reverberation time T<NUM> particularly for the desired octave frequency bands of between <NUM> and <NUM>.

What is further shown in <FIG> is that the second group ceiling tile <NUM> having a multi-faceted front surface <NUM> may have facets that are curved such that they are flat or such that they are individually shaped in a parametric manner. This allows a high degree of adaptation of the sound diffusing properties over the front surface <NUM> of the second group ceiling tile <NUM>.

An improved acoustic system <NUM> that improves speech intelligibility and speaker comfort by enhancing desired octave frequency bands and absorbing undesired octave frequency bands is thus provided.

It is to be realized that while each embodiment of the second group ceiling tile <NUM> is described separately above, the ceiling <NUM> could be provided with any combination of the different embodiments of the second group ceiling tiles <NUM>. For instance, ceiling tiles <NUM> as shown in <FIG> could be provided centrally in the first zone A above the presentation zone while ceiling tiles <NUM> as shown in <FIG> could be arranged surrounding the aforementioned ceiling tiles <NUM> to only mention one example.

Claim 1:
An acoustic system (<NUM>) for improving the acoustic quality in a room (<NUM>) for speech, the acoustic system (<NUM>) comprising a room (<NUM>) having a first zone (A) and a second zone (B), the first zone (A) comprising a first end of the room (<NUM>) and the second zone (B) comprising a second end of the room (<NUM>) opposite the first end of the room (<NUM>), the system further comprising a ceiling (<NUM>) of the room (<NUM>), the ceiling (<NUM>) comprising a plurality of ceiling tiles (<NUM>, <NUM>), wherein the ceiling tiles comprises a first group of ceiling tiles (<NUM>) having sound absorbing properties and a second group of ceiling tiles (<NUM>) having sound diffusing properties, wherein the first group of ceiling tiles (<NUM>) comprises ceiling tiles being arranged in the second zone (B) and the second group of ceiling tiles (<NUM>) comprises ceiling tiles being arranged in the first zone (A), and wherein the ceiling tiles (<NUM>) arranged in the first zone (A) are arranged such that sound directed thereto is reflected to the first zone (A) and to the second zone (B).