Patent Application
20090175484
This invention relates to an audio system. In one aspect, this invention relates to the conversion of otherwise non audio systems such as office furniture, walls, ceilings and floors into distributed audio sources for active noise control solutions for acoustical privacy.
The office workspace has undergone significant changes in the last 30 years where work areas have become smaller with increasing emphasis on collaboration.
Sound control is a vital aspect of worker efficiency. Significant effort is expended in the design of the workspace in order to control the acoustics, reducing the environmental noise that interferes with a worker's concentration. In addition, public spaces are often plagued with environmental noise. It is desirable to reduce the perception and effect of environmental noise in public areas such as airports, subways, and trains.
Historically, sound control has been through the deployment of passive means such as large separation distances, acoustical ceiling tile, carpeting, partitions, and other absorptive materials to reduce the sound waves as they propagate from the source to a listener.
However, in the contemporary design standards, the distance between workstations is being substantially reduced. In addition, interior design is seeking to remove many of the absorption surfaces to create a cleaner environment. All of these elements are collaborating to create an acoustic environment where it is difficult to achieve optimal worker efficiency.
Office designers have noted that the noise level is not necessarily distracting. What has been determined is most distracting are those sounds that attract attention such as conversation between two or more people, fragments of telephone conversations, personal acoustic eruptions, etc. The attention attractor is the information content.
A further advance in office noise control is the addition of sound in the form of filtered white noise. The noise is shaped to decrease the signal to noise ratio of the distracting sound to the point where the sound is no longer intelligible and hence distracting. In this application, the speakers are typically mounted in the plenum between the acoustic ceiling and the overhead. The speakers are acoustic point sources where the projected sound has directionality that is frequency dependent. Effective coverage of masking sound is difficult in that the ideal application is one where the sound transmitting through the acoustic ceiling is uniform and of the correct spectral content. The basic sound characteristics of the sources make this a difficult task. Further complicating the matter is that the acoustic point sources typically need to operate at higher levels to overcome the acoustic absorption of the ceiling.
A more recent development in noise masking is the generation of acoustic babble. (US Patent Application Publication No. US/2005/0065778A1) In this process, a person's voice is processed by an electronic signal processor which randomly inverts, time delays and then feeds the processed signal to an audio speaker. The resulting acoustic signal substantially reduces the intelligibility of speech to where it is no longer a distraction to a worker within the original speaker's acoustic field.
U.S. Pat. No. 6,904,154 teaches that optimal performance of a distributed mode loudspeaker includes a member extending transversely and capable of sustaining bending waves over an area of the member. The member having a distribution of resonant modes of its natural bending wave vibration dependent on specific values of particular parameters, including geometrical configuration and directional bending stiffness(es). The values have been selected to predetermine the distribution of natural resonant modes consonant with required achievable acoustic action for operation of the device over a desired operative acoustic frequency range.
The distributed mode loudspeaker of the '154 patent is impractical in a built environment having structures and furnishings that rarely fall within the design parameters of the described distributed mode loudspeakers. In addition, the placement of the inertial type transducer is determined by factors related to optimal acoustic placement, but not relative to aesthetics, tampering, and convenience in installation and maintenance.
US Pat. Application No. US2006/0147051 A1 teaches inertial transducers of the magnetostrictive form using Giant Magnetostrictive Materials (GMM) as the active element. These types of inertial transducers have limited low frequency performance, excessive distortion and limited overall displacement. Mechanical engineering efforts to increase low frequency performance come at the expense of additional distortion. The limited displacement of the GMM based inertial transducer also restrict their application to panels or structures that are relatively stiff, thus not making them suitable for many other built environment surfaces. The '05 application teaches the use of a controller mixer for comparing ambient noise or other signal to control the acoustic output of the overall system or cause notification of other engagement with the system. The patent does not address configuring the signal for optimal acoustic response of the driven structure to improve audio fidelity to the input signal. Further, the application teaches that the invention can be used for anti-noise control but fails to address how a spatially incoherent acoustic source can create a coherent anti-phase signal for active noise cancellation.
It is therefore an objective of the present invention to provide a system and a method for improving the acoustic performance of a building interior such as but not limited to an open office plan, exhibition space or other public or living space. A further objective includes improving the overall worker efficiency within a workstation by utilization of otherwise non acoustic elements and surfaces of the built environment such as walls, ceilings, floors, windows, columns and finished case goods such as workstations, furniture, partitions, cabinets, whiteboards, tables and other commonly available furnishings within an interior environment to radiate sound by means of acoustically driving the aforementioned.
Another objective of the invention is to provide a means of optimizing the acoustic performance of the aforementioned traditionally non acoustic elements and surfaces of the built environment and other commonly available furnishings to result in audio reproduction that is optimally faithful to the input acoustic signal.
It is another objective of the invention to provide a means of actively adapting a masking signal to be configured for both general and localized environments thereby maximizing the effectiveness throughout the built environment.
According to the present invention, the transformation of otherwise non acoustic structures into acoustic soundboards is affected by the acoustic association of inertial type acoustic transducers which converts an electrical signal into a mechanical motion of said soundboard. The resulting mechanical motion in the attached soundboard structure then acoustically radiates into the surrounding environment.
Acoustic soundboard structure can be comprised of flat, single curve and multiple curved panels. These panels can be constructed of a nearly endless array of materials with a suitable range of mechanical properties. Examples of these materials are gypsum panels, glass, composite structures of a structural member with resin or metallic binders, wood, wood sheet goods, composite panels of structural skins and cores, consolidated organic and inorganic fibers, structural foams, metal, etc. A narrow subset of an acoustic source design having a distributed mode loudspeaker typically includes a regular geometric panel, preferred mechanical properties of said panel, and preferential acoustic exciter location relevant to the panel geometry to obtain a desired acoustic performance and frequency response. However, ill defined soundboards lacking the preferred mechanical properties and geometric regularity are far more plentiful and common. What is needed is a system that works around or with these properties.
It is common practice for an inertial type acoustic transducer to drive a soundboard structure that is ill defined both in geometry and mechanical properties. However, the acoustic performance using ill defined soundboards has heretofore been of low quality. Examples of ill defined soundboards are comprised of many different materials and applications such as panel type materials commonly used in building construction, outdoor leisure products, vehicles, furniture, etc. Some of the most widely available materials suitable for soundboard applications are the 1/32″ to 1′ thick sheet materials such as gypsum drywall, plywood, MDF, glass, consolidated fiber materials of natural and synthetic origin, composite fiber reinforced plastics, and metals. Panels may be configured from flat to compound curved structures that are capable of both pistonic and flexural bending motion.
The present invention describes a method and apparatus for optimizing the acoustic performance of the transducer coupled with a soundboard, even an ill defined soundboard. The method and apparatus is designed to compensate for the various physical properties and optimize the corresponding radiated sound.
The nearly universal use of these ill defined soundboards in building environments means it is nearly impossible to control the parameters that influence the acoustic radiation of the system. The radiated frequency response can vary significantly even with a single type of material such as gypsum panels used commonly in framed wall construction. These variabilities in acoustic radiation response are dependent upon such factors as the area of the wall, center spacing of the framing members, spacing distance and regularity of the mechanical fasteners attaching the gypsum panel to the framing, type of framing, and application of construction adhesive between frame and gypsum panel.
Although the acoustic parameters are unique from one application or installation to the next due to the variation in actual panel geometry, and in mechanical properties such as material thickness, modulus of elasticity and area density, these variations can be suitably compensated by means of parametric equalizers, graphic equalizers or other active and passive filter means.
Those skilled in the art of loudspeaker design will recognize the challenges of creating a sound reproduction system that is faithful to the original acoustic signal in light of these uncontrollable variables.
The present invention provides an inertial type acoustic transducer acoustically associated with a soundboard panel and driven by an electronic power amplifier. The acoustic signal to the power amplifier is modified by means of a signal conditioner to compensate for the non optimal response of the acoustic system. The preferred signal conditioner is a digital signal processor which employs algorithms for parametric equalization. Other common features that are implemented in the digital signal processor capabilities are graphic equalization, channel mixing, bass and treble tone control, high and low pass crossover frequency control, high and low pass digital filters for crossover network control and subwoofer integration, and independent channel gain.
Frequency and Transducer Relationship
The present invention also proposes a means for using multiple channels of amplification to acoustically drive the associated transducer over its optimal frequency bandwidth. The preferred implementation of limiting the frequency bandwidth to the respective transducer is through digital means. However, this invention is not limited to using digital cross-over networks.
Other possible implementations of inertial type transducers acoustically associated with a soundboard are the use of a plurality of acoustic transducers that are optimized to operate over a limited frequency range. Those skilled in the art will know that electrodynamic transducers have increasing electrical impedance with increasing frequency. This is related to the mutual inductive coupling between the voice coil and the magnetic structure. This increasing impedance will typically act as a first or second order low pass filter. The present invention improves the high frequency performance by using means of decreasing the mutual inductance through a shorting ring that promotes formation of blocking eddy currents in the magnetic circuit. Alternatively, different transducers may be configured for high frequency operation. An example of this is the use of different transducers for low and high frequency operation. Limiting the audio signal frequency bandwidth to the respective transducer can be done through an electronic crossover network in the digital signal processor or through passive crossover networks that are well known to those familiar to the art of loudspeaker design.
a. Room Resonance and Feedback Loop Avoidance
Sound radiation from a soundboard is different from a traditional speaker. The radiation from a soundboard results from bending waves being introduced into a panel. The propagation of the bending wave speed is frequency dependent, thus as broadband energy is input to the panel, the panel motion becomes random. The non linear propagation speed generates broadband wave number spectra in which some radiate to the far field. The near field acoustic energy has evanescent decay properties and does not radiate to the far field.
The modal dispersion of the bending wave energy in the panel causes the soundboard to have a unique acoustic center of radiation at each instant in time. Over time, this acoustic center point averages to a location at or near the point of acoustic stimulation. This phenomenon of instantaneous center of acoustic radiation means that at a fixed reference point, the distance between the acoustic source and the reference point is different for each time reference. As a result, the soundboard will not necessarily stimulate normal room resonant modes or in the case of a microphone pickup, cause feedback loop gain. This advantage is a result of the spatially incoherent nature of the acoustic radiation. This phenomenon has been exploited in the present invention to suppress room mode resonance or in the case of amplification of a microphone signal, suppress feedback amplification gain, decreasing the need for notch filters for feedback elimination.
b. Radiation Area and Attenuation as a Basis for Lower Sound Pressure
Observationally, the radiation area of a conventional diaphragm speaker is on the order of 0.005-1.227 square feet corresponding to speaker cones nominally 1-15 inches in diameter. A general rule of thumb is that the far field radiation characteristics are observed at 7 to 8 diameters away. This is in contrast to the acoustic radiation area of a soundboard which in most practical applications is on the order of 1s-100s of square feet. As a result, for most practical applications within a built environment, the listener will be within the near field acoustic radiation of the source. With a conventional speaker where the surface of the cone is substantially coherent (the cone surface is moving in phase relative to each other), the acoustic near field could be problematic in that frequency dependent nulls may be experienced. However, with a soundboard, the surface is spatially incoherent, and the instantaneous center of acoustic pressure is different at each differential time. No near field nulls are experienced.
As a further bonus, the propagation characteristics of sound do not attenuate at the same rate. Practical experience shows that the propagation attenuation is on the order of 1/R, where R is the distance from the source to observation point. For each doubling of distance between source and observation point, the sound level is ½. Conventional speaker attenuation with distance is characteristic of far field radiation and is on the order of 1/R2. Thus for each doubling of distance between the acoustic source and observation point, the sound level is reduced by ¼.
The physical implication of this radiation characteristic of the soundboard is that the acoustic source level at the panel can be significantly lower to have the same room filling affect as a conventional speaker playing at a higher sound pressure level.
c. Placement and Orientation not Critical to Frequency Coverage
Those skilled in the art will appreciate the challenges in designing a speaker to have appropriate frequency response in both the main response axis of the speaker as well as the off axis. At high frequencies, the sound tends to focus in a narrow beam and becomes less focused at lower frequencies. In addition, the edges of the speaker baffle can create di-pole radiation affects that will color the off axis response of the speaker system.
In contrast, when using a soundboard, the radiation characteristics are largely omni-directional, meaning that there is no or limited focusing of the acoustic radiation relative to the soundboard. Thus the placement and orientation of soundboard structures needs no special placement or orientation to properly cover the frequency band for masking and/or other audio functionalities.
d. Damping Means to Limit Reflection of Bending Waves
Some materials with low internal damping return a significant portion of the incident bending wave energy back into the panel at the panel terminus. The substantial change in panel impedance at the edge of the panel causes the incident bending wave to be reflected back toward the acoustic transducer which can induce back Electro Magnetic Field (EMF) into the driving power amplifier. The back EMF into the power amplifier can increase output signal distortion, thus reducing the overall fidelity of the soundboard output. The present invention addresses the use of visco-elastic or constrained layer and other damping means to limit the reflection of bending waves from the edge of the panel.
a. Amplification and Fidelity Control
The nearly infinite variety in soundboard construction, geometry, and edge boundary conditions all have an affect on the bending wave properties, and hence the ultimate acoustic radiation from said panel. In conventional speaker design, development and production, the speaker engineer carefully selects all aspects of the speaker to arrive at a desired acoustic response. The present invention as described above includes non ideal placement of the inertial type acoustic transducer on non ideal soundboard and will result in acoustic radiation that does not maintain sufficient fidelity to the input audio signal unless that fidelity is otherwise addressed.
In the present invention, the soundboard, inertial acoustic transducer and the power electronics work as a system. The soundboard and acoustic transducer properties are largely predetermined. Thus it is necessary to affect the overall acoustic output of the system to result in a reduction of magnitude distortion. This affect is accomplished by causing preferential adaptation in the power electronics where its amplified signal is inversely distorted to improve the acoustic fidelity of the overall system.
b. Psychoacoustic Processing
Another aspect of the present invention is the utilization of psycho acoustic processing techniques where enhancement of the low and high frequency response may be realized. Psycho-acoustic bass enhancement results in perception of a sound at a low frequency when in fact a component at that frequency is not present. The enhancement provides the added advantage that the bass response of the system is enhanced while reducing the overall physical displacement of the soundboard system. This can be particularly attractive where the physical displacement of the soundboard may have detrimental affects to worker comfort or induces secondary buzzing and rattles.
c. Masking and Separate Zone Control
The digital signal processor of the present invention has integrated computer interfacing means whereby an external controller may communicate with the amplifier to control its operating parameters. These operating parameters are ideally assessable through a graphical user interface. Interfacing and communicating with other computers or controllers is by means of wired and/or wireless networks and may be addressable as a node on a network. This enables the direct distribution and streaming of audio content from centralized network servers. The network may supply a common audio signal to all or a portion of the acoustic zones to create background, foreground music, voice paging or emergency signaling. The audio signal source can be, but is not limited to, line level analog mono/stereo, Sony/Philips Digital Interface Format (S/PDIF), direct digital stream or Ethernet packet.
Multiple distributed acoustic sources may be used throughout the built environment. Each separate acoustic source can be considered a node on a network that is individually addressable for specific audio signal input. The ability to address each acoustic source as an individual node enables further optimization in the active acoustic noise control system where specific masking is applied locally near the point of disturbance. In applications where filtered random noise is utilized, sampling of the background noise near each node can be used to shape the noise spectrum so as to be more effective in masking the acoustic disturbance.
Other masking technologies such as Babble® as supplied by Sonare®, 444 N. Wells, Suite 305, Chicago, Ill. 60610 use pre-recorded speech of a talker. The recorded speech is processed so that when played back in conjunction with actual speech of the talker, the intelligibility of the talker is highly disrupted. The present invention when utilized with Babble can monitor the nodes of the network and when a known talker is detected, the surrounding immediate zones can be activated with the corresponding Babble processed signal, thus rendering a zone of privacy for the talker. Masking and or Babble processing my also be employed to create zones of privacy for open area or closed meeting spaces.
Another aspect of the invention is the ability of a local node to introduce a unique audio signal from sources such as but not limited to MP3 players, radios, CD, portable music players, and computers. The local audio signal will be reproduced at the local zone for personalization of that space and mixed in with the other masking signals for that specific zone. It is also conceivable that a locally input audio signal can be shared with other distributed nodes.
In summary, a major feature of the present invention is the ability of the amplifier to adjust its parameters to address each unique application. The signal conditioned amplifier will power inertial type transducers. The inducers will be mounted on a wide variety of structures such as but not limited to: hot tubs, whirlpool baths, in-ground pools, gypsum paneled walls and ceilings, composite panels such as in marine applications, train carriages, buses and aircraft, wood and wood sheet goods and glass and acrylic panels as employed in architectural and furniture applications.
Other objects, features, and advantages of the present invention will be readily appreciated from the following description. The description makes reference to the accompanying drawings, which are provided for illustration of the preferred embodiment. However, such embodiment does not represent the full scope of the invention. The subject matter which the inventor does regard as his invention is particularly pointed out and distinctly claimed in the claims at the conclusion of this specification.
In the drawings, which illustrate exemplary embodiments of the invention:
Referring first to
In the present invention, the soundboard 120, inertial acoustic transducer 100 and the power electronics (110-130) work as a system. The soundboard 120 and acoustic transducer 100 properties are largely predetermined. Thus it is necessary to affect the overall acoustic output of the system 10 to result in a reduction of magnitude distortion. This affect is accomplished by causing preferential adaptation in the power electronics where its amplified signal is inversely distorted to improve the acoustic fidelity of the overall system.
The proposed amplifier architecture in this invention may be configured such that the digital signal processor 130 will initialize an equalization algorithm when a microphone or other means for detecting sound is associated with said means for processing sound signal 130. Means for detecting sound 162 causes mans to process a sound signal 130 to initialize a series of test signals that can be, for example, white noise, filtered noise, MLS, swept sine or other stimulation signals. A frequency response analyzer is then utilized to compute the resulting acoustic frequency response of the system. Means to equalize 145 can equalize using conventional algorithms such as parametric, graphical or inverse Fourier Transform (F−1) filters.
An inverse Fourier Transform filter may be used by the present invention. It results in the calculation of the compensation filter F−1 by inversing the overall frequency response F of the system. The measured, smoothed, overall magnitude response F is divided into a defined target response to provide an inverse spectral description of the overall system compensating filter response. The compensation filter estimate F−1 is derived from the complex spectrum defined by the inverse magnitude and the inverse phase response of the overall frequency response F. The coefficients of the compensation FIR filter can now be calculated by deriving corresponding filter coefficients by merely applying an inverse Fourier transform to the inversed transfer function, directly deriving the impulse response (e.g. the coefficients) of the filter.
In many applications where the acoustic system (soundboard 120, transducer 100 and electronics 110, 130) will be embedded in serial production structures, or structures with similar overall properties e.g. furniture panel surfaces, a pre-defined equalization curve is determined and then stored in an addressable non volatile memory 150. By selecting the appropriate memory address, the amplifier can be configured to the optimal setting without any other interfacing requirement.
The invention can include said means to equalize 145. Specifically, the digital signal processor 130 may apply, but is not limited to, the following plurality of parameters 140: parametric equalization or graphic equalization. Said plurality of parameters is preferably stored in a nonvolatile memory 150. In the preferred embodiment of the power amplifier 110, the digital signal processor 130 will also include N×M matrix mixing where N is the number of input channels and M is the number of amplification channels, digital crossover with Linkwitz-Riley, Butterworth and Bessel filters, frequency and gain selectable bass and treble tone control, time delay, independent and master gain control, compression limiting, loudness and psycho-acoustic bass extension. The plurality of parameters 140 may be pre-programmed in the non-volatile memory 150 where upon selection of the appropriate memory registrar 152, the plurality of parameters or one of said parameters 140 will be recalled to optimize the various processing functions for a particular acoustic soundboard 120 and transducer 160 combination. Also, integrated with the digital signal processor 130 is a phantom power supply 160 to power means for detecting sound 162. In the preferred embodiment, means for detecting sound comprise a microphone 162 or an accelerometer where the overall system response of
The induced mechanical motion to the acoustic transducer 100 can cause it to operate in a non-linear manner thus introducing other sources of distortion. One means of controlling the reflected bending wave energy employed by the present invention is to dissipate the incident bending wave as it approaches a perimeter 505 of the panel or soundboard 120. Those skilled in the art will recognize that visco-elastic and/or constrained layer type damping are very effective at transforming bending wave energy into heat. A recent development in damping treatment is the sprayable visco-elastic polymer materials such as QuietCoat® 118, 119 and 207 supplied by Quiet Solutions®, 1250 Elko Drive, Sunnyvale, Calif. 94089 which, as applied, creates a visco elastic damper 520. Another means employed in the present invention for controlling reflected bending wave energy is to apply a damping material such as polyurethane foam around the perimeter 505 of the panel 120 which is sandwiched between the panel 120 and a supporting structure (a constrained layer damper) which suspends the panel in its place.
In some applications of the present invention, it will be necessary to mechanically suspend a soundboard panel 120 within a larger structure. It may also be desired to have the soundboard 120 vibrationally isolated from the supporting structure. Those skilled in the art can appreciate the various means of mechanical isolation through visco-elastic mounts, compliant or other type means.
More particularly,
The invention is well suited to commercial sound applications where voice paging, noise masking, foreground, background and other distributed sound may be required. The use of the acoustic transducer 100, amplifier 110 and networking allows for zone specific control. The digital signal processor 130 has integrated computer interfacing means whereby an external controller may communicate with the amplifier 110 to control its operating parameters 140. These operating parameters are ideally assessable through a graphical user interface. Interfacing and communicating with other computers or controllers is by means through wired and/or wireless networks and may be addressable as a node on a network. This enables the direct distribution and streaming of audio content from centralized network servers. The network may supply a common audio signal to all or a portion of acoustic zones to create background, foreground music, voice paging or emergency signaling. The audio signal source can be, but is not limited to, line level analog mono/stereo, Sony/Philips Digital Interface Format (S/PDIF), direct digital stream or Ethernet packet.
Multiple distributed acoustic sources may be used throughout the built environment. Each separate acoustic source can be considered a node on a network that is individually addressable for specific audio signal input. The ability to address each acoustic source as an individual node enables further optimization in the active acoustic noise control system where specific masking is applied locally near the point of disturbance. In applications where filtered random noise is utilized, sampling of the background noise near each node can be used to shape the noise spectrum so as to be more effective in masking the acoustic disturbance.
Other masking technologies such as Babble® as supplied by Sonare®, 444 N. Wells, Suite 305, Chicago, Ill. 60610 use pre-recorded speech of a talker. The recorded speech is processed so that when played back in conjunction with actual speech of the talker, the intelligibility of the talker is highly disrupted. The present invention when utilized with Babble can monitor the nodes of the network and when a known talker is detected, the surrounding immediate zones can be activated with the corresponding Babble processed signal, thus rendering a zone of privacy for the talker. Masking and or Babble processing my also be employed to create zones of privacy for open area or closed meeting spaces.
Another aspect of the invention is the ability of a local node to introduce a unique audio signal from sources such as but not limited to MP3 players, radios, CD, portable music players, and computers. The local audio signal will be reproduced at the local zone for personalization of that space and mixed in with the other masking signals for that specific zone. It is also conceivable that a locally input audio signal can be shared with other distributed nodes.
Thus, the present invention has been described in an illustrative manner. It is to be understood that the terminology that has been used is intended to be in the nature of words of description rather than of limitation.
Many modifications and variations of the present invention are possible in light of the above teachings. For example, the components of the system may be integrated together. Therefore, within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described.
