Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R1/00—Details of transducers, loudspeakers or microphones
  • H04R1/10—Earpieces; Attachments therefor ; Earphones; Monophonic headphones
  • H04R1/1083—Reduction of ambient noise
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R1/00—Details of transducers, loudspeakers or microphones
  • H04R1/10—Earpieces; Attachments therefor ; Earphones; Monophonic headphones
  • H04R1/1016—Earpieces of the intra-aural type
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R25/00—Deaf-aid sets, i.e. electro-acoustic or electro-mechanical hearing aids; Electric tinnitus maskers providing an auditory perception
  • H04R25/40—Arrangements for obtaining a desired directivity characteristic
  • H04R25/405—Arrangements for obtaining a desired directivity characteristic by combining a plurality of transducers
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R25/00—Deaf-aid sets, i.e. electro-acoustic or electro-mechanical hearing aids; Electric tinnitus maskers providing an auditory perception
  • H04R25/55—Deaf-aid sets, i.e. electro-acoustic or electro-mechanical hearing aids; Electric tinnitus maskers providing an auditory perception using an external connection, either wireless or wired
  • H04R25/554—Deaf-aid sets, i.e. electro-acoustic or electro-mechanical hearing aids; Electric tinnitus maskers providing an auditory perception using an external connection, either wireless or wired using a wireless connection, e.g. between microphone and amplifier or using Tcoils
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R25/00—Deaf-aid sets, i.e. electro-acoustic or electro-mechanical hearing aids; Electric tinnitus maskers providing an auditory perception
  • H04R25/60—Mounting or interconnection of hearing aid parts, e.g. inside tips, housings or to ossicles
  • H04R25/604—Mounting or interconnection of hearing aid parts, e.g. inside tips, housings or to ossicles of acoustic or vibrational transducers
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R25/00—Deaf-aid sets, i.e. electro-acoustic or electro-mechanical hearing aids; Electric tinnitus maskers providing an auditory perception
  • H04R25/65—Housing parts, e.g. shells, tips or moulds, or their manufacture
  • H04R25/652—Ear tips; Ear moulds
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R25/00—Deaf-aid sets, i.e. electro-acoustic or electro-mechanical hearing aids; Electric tinnitus maskers providing an auditory perception
  • H04R25/65—Housing parts, e.g. shells, tips or moulds, or their manufacture
  • H04R25/658—Manufacture of housing parts

Definitions

• the invention concerns the physical design of an adaptive hearing protective earplug combined with an audio communications terminal.
• solutions for hearing protection and audio communication in noisy environments based on earplugs and ear-muffs with earphones (loudspeakers) , boom microphones, cheek-bone microphones, or throat microphones. All these solutions have one of more of the following undesirable properties: heavy and clumsy. uncomfortable . inferior quality of sound pick-up and restoration. poor noise attenuation. - attenuate both desired and unwanted sounds.
• the noise attenuation is automatically adapted to the noise conditions and communication modes.
• the present invention therefore simultaneously protects the hearing and provides improved communication abilities in different noise environments. It is intended for continuous use during the working day or other periods when hearing protection and/or voice communication is needed.
• the invention also concerns a device for utilising the speech sound produced in the ear of a person carrying hearing protective communications ear plugs according to the invention.
• the microphone is made with a characteristic emphasising the near field from the mouth. This type is sometimes referred to as "noise cancelling" .
• the protectors take the form either of sealing cups which enclose the ear, or ear plugs which block the ear canal.
• the latter type of protector is often preferred because of its small size and relatively good comfort.
• the cavity sealed off in the inner portion of the meatus by the ear plug is relatively free of external noise, this is the purpose of the ear plug in protecting the hearing.
• the sound field in the cavity generated by the persons own voice contains all the frequency components necessary to reconstruct the speech with good intelligibility.
• the solution according to invention takes advantage of these facts.
• a microphone to pick up the acoustic sound field in the inner portion of the meatus and processing the microphone signal according to the invention, a speech signal of high quality and low noise masking is produced.
• the user usually feels his own voice being distorted, a feature reducing the comfort of wearing hearing protectors .
• Ordinary hearing defenders changes the normal sound transmission path from the mouth to the eardrums .
• the auditory feedback f om the users own voice is affected resulting in an unintended change in the speech output.
• a normal response is to raise one's own voice level when using headsets or earplugs.
• the invention solves this problem by filtering and mixing in the user's own voice picked up by either the outer or the inner microphone at one ear and reproduce the signal at the loudspeaker in the other ear.
• An additional object of this invention is to provide a programmable personal noise exposure dose meter that measures the true exposure in the user's ear and calculates the hearing damage risk.
• Present day noise exposure dose meters also called dosimeters, usually consist of a microphone and a small electronics unit that may be attached to the body or worn in a pocket .
• the microphone may be mounted on the electronics unit or it may be fastened to the collar or on the shoulder.
• ANSI SI.25 specifies dosimeters.
• Dosimeters do not measure the noise that actually affects the hearing organ (e.g. when the user wears a hearing protector, helmet, etc.) . Even when the ear is not covered, measurements may be influenced by body shielding. - Dosimeters are susceptible to non-intentional or intentional errors, which may influence readings, such as wearers tapping or singing into dosimeter microphones or by wind-generated noise. Dosimeters are inaccurate if impulse or impact noise is present .
• the invention solves these problems by using a microphone that measures the sound at the eardrum and employs analysis procedures that take into account both stationary and impulsive sound.
• the dose meter is part of a communications terminal this includes external noises, incoming communication signal, as well as possible malfunctioning of the equipment. It is also an object of this invention to provide a device for verifying in situ that a hearing protector is properly used.
• Present day hearing protectors take the form either of sealing cups which enclose the ear, or ear plugs which blocks the ear canal. For both types, it is critically important to avoid leakage of the noise sound through or around the sealing and blocking parts of the hearing protectors .
• Irregular surfaces which the sealing material is not able to follow properly. Examples are spctacles used with ear cups, and ear plugs used by persons with irregularly formed ear canals.
• Ageing of the materials in the sealing may reduce the resilience of the sealing and thereby allow leakage around the sealing.
• the result of leakage is reduced damping of potentially harmful noise.
• the leakage should be detected and remedied prior to noise exposure.
• the leakage may not be clearly audible. Accordingly, noise situations may comprise of intermittent or impulsive components which may damage the hearing almost instantaneously if a hearing protector should be malfunctioning or imperfect without the user's knowledge.
• the invention solves these problems by an in situ acoustical measurement, which is analysed and reported to the user in audible form, or to external equipment by means of communication signals .
• the devices necessary or the measurement are an integral part of the hearing protector.
• Verification may be activated by the user at any time, or be continuously running when the application is critical.
• verification may be activated by other persons (or devices) than the user, e.g. to verify hearing protector function before admittance to a noisy area is allowed.
• Fig. 1 is a simplified vertical section along the central axis of the meatus of the outer ear of an erect human, with an inserted ear terminal according to one embodiment of the invention also shown in vertical section along the axis, locally coincident with the meatus axis.
• Fig. 2 is an electrical wiring diagram showing the functional components and connections between electronic components in a preferred embodiment according to the invention.
• Fig. 3 is an illustration of one method according to the invention, showing that spectral analysis of sound picked up in the ear is compared with spectral analysis of sound picked up by a microphone at a standard distance, e.g. of 1 metre, under otherwise quiet conditions.
• Fig. 1 is a simplified vertical section along the central axis of the meatus of the outer ear of an erect human, with an inserted ear terminal according to one embodiment of the invention also shown in vertical section along the axis, locally coincident with the meatus axis.
• Fig. 2 is an electrical wiring diagram showing the functional components and
• FIG. 4 is an illustration of speech sound analysis and following sound source classification with filtering conducted according to the sound source classification, according to one embodiment of the invention.
• Fig. 5 is an illustration of another method according to the invention, illustrating an analysis of sound ⁇ w t t ⁇ > ⁇ >
• the outer section 1 is formed to fit the concha around the outer portion of the meatus 3.
• External sounds are attenuated by a combination of passive and active noise control.
• the passive attenuation is obtained by means of an earplug 1,2 with a sealing system 2 inserted in the outer part of the ear canal or meatus 3.
• the active noise control is achieved by using one or two microphones Ml, M2 and a loudspeaker SG together with electronic circuits in an electronics unit 11 mounted in the earplug system.
• the algoritmes for noise control are per se known and will not be described in any detail here, but may include active noise cancelling by. feedback of acoustic signals converted by at least one of said microphones (M1,M2) throught the sound generator (SG) .
• Ear terminal comprising a sound generator (SG) arranged for being directed toward the meatus and being coupled to said electronics unit (11) , wherein the electronics unit (11) comprises filtering means for active sound transmission e.g. by amplification of chosen frequencies converted by said outer microphone (Ml) and generating a corresponding acoustic signal through said sound generator (SG) .
• Pick-up of the user's voice is performed by a microphone M2 with access to the closed space in the meatus 3.
• This signal is processed by means of analogue or digital electronics in the electronics unit 11 to make it highly natural and intelligible, either for the user himself or his communication partners or both parts.
• This signal is of high quality and well suited for voice control and speech recognition.
• Online control and verification of the hearing protector performance is obtained by injecting an acoustic measurement signal, preferrably by the sound generator or loudspeaker SG in the meatus, and analysing the signal picked up by the microphone M2 that has access to the acoustic signal in the meatus 3.
• T3,T4 or a valve that equalises static pressure differences, while retaining strong low frequency sound attenuation.
• a safety valve V to take care of rapid decompression may be incorporated in the pressure equalisation system T3,T4.
• Fig. 1 illustrates an embodiment according to the invention.
• the earplug comprises a main section 1 containing two microphones Ml and M2 and a sound generator SG.
• the main section is designed in a way that provides comfortable and secure placement in the concha (the bowl-shaped cavity at the entrance of the ear canal) . This may be obtained by using individually moulded ear-pieces that are held in position by the outer ear or by using a flexible surrounding pressing against the structure of the outer ear.
• a sealing section 2 is attached to the main section.
• the sealing section may be an integral part of the earplug, or it may be interchangeable .
• the sound inlet of microphone Ml is connected to the outside of the earplug, picking up the external sounds.
• the microphone M2 is connected to the inner portion of the meatus 3 by means of an acoustic transmission channel TI.
• the acoustic transmission channel may contain optional additional acoustic filtering elements.
• An outlet S SG of sound generator SG is open into the inner portion of the meatus 3 by means of an acoustic transmission channel T2 between the sound generator SG and the inward facing portion of the sealing section 2.
• the acoustic transmission channel T2 may contain optional additional acoustic filtering elements.
• the two microphones and the sound generator are connected to an electronics unit 11, which may be connected to other equipment by a connection interface 13 that may transmit digital or analogue signals, or both, and optionally power.
• Electronics and a power supply 12 e.g. a battery may be included in main section 1 or in a separate section.
• the microphones M1,M2 may in a preferred embodiment be standard miniature electret microphones like the ones used in hearing aids. Recently developed silicon microphones may also be used.
• the sound generator SG may in a preferred embodiment be based on the electromagnetic or electrodynamic principle, like sound generators applied in hearing aids.
• a safety valve V is incorporated in the ventilation duct comprising the channels T3 and T4.
• the valve V is arranged to open if the static pressure in the inner part of the meatus 3 exceeds the outside pressure by a predetermined amount, allowing for pressure equalisation during rapid decompression. Such decompression may occur for military or civilian air personnel experiencing rapid loss of external air pressure. Such a decompression may also occur for parachuters, divers, and the like. Pressure equalisation for slowly varying pressure changes is obtained by using a narrow vent T4 which may bypass the valve V.
• the main section of the earplug may be made of standard polymer materials that are used for ordinary hearing aids.
• the sealing part may be made of a resilient, slowly re- expanding shape retaining polymer foam like PVC, PUR or other materials suitable for earplugs.
• the earplug may be moulded in one piece 1,2 combining the main section 1 and the sealing section 2.
• the material for this design may be a typical material used for passive earplugs (Elacin, acryl) .
• the earplug in one piece comprising the main section 1 and the sealing section 2, all made of a polymer foam mentioned above, but then the channels T1,T2,T3,T4 have to be made of a wall material preventing the channels T1,T2,T3,T4 to collapse when the sealing section 2 is inserted in the meatus 3.
• the microphone Ml picks up the ambient sound.
• a signal from the microphone Ml is amplified in El and sampled and digitised in an analogue to digital converter E2 and fed to a processing unit E3 that may be a digital signal processor (DSP) , a microprocessor ( ⁇ P) or a combination of both.
• DSP digital signal processor
• ⁇ P microprocessor
• a signal 51 from microphone M2, which picks up the sound in the meatus 3 between the isolating section 2 and the tympanum 4 is amplified in the amplifier E4 and sampled and digitised in the analogue to digital converter E5 and fed to the processing unit E3.
• a desired digital signal DS is generated in the processing unit E3.
• This signal DS is converted to analogue form in the digital to analogue converter E7 and fed to the analogue output amplifier E6 that drives the loudspeaker SG.
• the sound signal produced by the loudspeaker SG is fed to the tympanum 4 via the channel T2 into the meatus 3 as w LO t to ⁇ > ⁇ >
• a connection to another equipment e.g. a communication radio .
• One embodiment of the invention concerns the use of the ear terminal as an "in-the-ear voice pick-up" .
• the sound of a person's own voice as heard in the meatus is not identical to the sound of the same person's voice as heard by an external listener.
• the present embodiment of the invention remedies this problem.
• the microphone M2 illustrated in Fig. 3 picks up the sound in the inner portion of the meatus 3 sealed off by a sealing section 2 in an ear protecting communications device of the earplug type.
• the signal is amplified by the amplifier E4 illustrated in Fig. 2, A/D converted by the A/D converter E5, and processed in the digital signal processing (DSP) or microcomputer unit E3.
• DSP digital signal processing
• the processing may be viewed as a signal dependent filtering taking into account the speech signal properties as well as computed estimates of the location of sound generation for the different speech sounds. Thereby the speech intelligibility and naturalness may be improved.
• Figs. 1 and 3 show examples of embodiments of the invention, with the microphone M2 being integrated in a hearing protective communications earplug.
• the acoustic transmission channel TI connects microphone M2 to the inner portion of the meatus 3.
• Microphone M2 picks up the sound field produced by the person's own voice.
• the signal may be amplified in amplifier E4, A/D converted in A/D converter E5 and processed in the digital signal processing (DSP) or microcomputer unit E3.
• DSP digital signal processing
• a processed signal from E3 may be transmitted in digital form through a digital interface E12 to other electrical units.
• the processed signal from E3 may be D/A converted and transmitted in analogue form to other electrical units.
• Fig. 4 illustrates one possible signal processing arrangement according to the invention. It illustrates an example of the type of signal dependent filtering which may LO ⁇ to to ⁇ > ⁇ > in o L ⁇ o L ⁇ o L ⁇ ro O ⁇ ! ⁇ - TJ TJ ⁇ - 0 ⁇ ⁇ 0 ⁇ fl rr 01 Hi tr ⁇ 01 01 tr ro rr ⁇ TJ ft ⁇ T rr 3 ⁇ 0 3 tr o tr
• the analyses may be short time spectral estimates, e.g. 1/9 octave spectra in the frequency range 100 Hz to 14000 Hz.
• the test sequences which the subject utters may comprise speech sounds held constant for approximately 1 second. For voiced sounds, the subject person may make the pitch vary during the analysis period.
• the transfer functions of the filters described in connection with Fig. 4 may be based on diagrams of H(f), the spectral density levels of the free field microphone M3 subtracted from the corresponding levels of the in-the-ear microphone M2.
• a simplest embodiment of the invention may reduce the system in Fig. 4 to one single time invariant filter.
• the analysis and selection processing may then be omitted.
• the transfer function of the single filter is still based on diagrams of the spectral density levels of the free field microphone subtracted from the corresponding levels of the in-the-ear microphone, described in connection with Fig. 3.
• the transfer function may be a combination of the results for the various speech sounds, weighted in accordance with their importance for the intelligibility and naturalness of the processed speech.
• Another embodiment of the invention is best understood under the term "Natural Own Voice", indicating that a person wearing an ear terminal shall perceive his own voice as being natural while having the meatus blocked by an earplug.
• the inner microphone M2 or the outer microphone Ml, or a combination of both picks up the sound signal representing the users voice signal.
• the signal is amplified, A/D converted, and analysed in the digital signal processor E3. Based on previously measured transfer functions from the user's speech to the microphone M2 (and/or Ml) , the microphone signal may be filtered to regain the naturalness of the user's speech.
• the signal is then D/A-converted, amplified and reproduced at an internal loudspeaker SG.
• the internal loudspeaker SG may be arranged in a similar ear terminal 1,2 in the wearer's other ear to prevent local feedback in the earplug.
• the loudspeaker SG arranged in the same meatus 3 as the inner pickup microphone M2 is situated, may be used, thus demanding feedback cancellation.
• the desired signal to the loudspeaker SG in the other ear may be transmitted. via electric conductors outside of the wearer's head, or via radio signals.
• Fig. 6 shows one preferred embodiment of the invention with the natural own voice feature being integrated in two active hearing protective communications earplugs.
• Each earplug may comprise a main section 1 containing two microphones, an outer microphone Ml and an inner microphone M2, and a sound generator SG.
• the right and left earplugs are generally symmetrical, otherwise identical for both ears.
• Section 2 is the acoustic sealing of the hearing protector.
• An acoustic transmission channel TI connects microphone M2 to the inner portion of meatus 3.
• Microphone M2 picks up the sound from the meatus 3. When the user is speaking and the ear canal is sealed, this signal is mainly the user's own voice signal. This signal is filtered and reproduced at the loudspeaker SG at the other ear.
• An acoustic transmission channel T2 connects sound generator SG to the inner portion of meatus 3.
• a block diagram of the electronic system is shown in Fig. 2.
• Fig. 4 shows an example of the type of signal dependent filtering which may be applied to the microphone signal in order to obtain a good reconstruction of the voice.
• the microphone M2 signal is analysed in the DSP/uP processing unit E3.
• the analysis represented by block 21 in Fig. 4 may ⁇ LO to to ⁇ > ⁇ »
• record of the analysis may according to a preferred embodiment be stored in a memory, e.g. in the RAM E8 for later read-out and processing.
• Fig. 1 shows a preferred embodiment of the invention with the personal noise exposure dose meter integrated in an active hearing protective communications earplug, comprising a main section 1 containing two microphones, an outer microphone Ml and an inner microphone M2, and a sound generator SG. Since this embodiment is part of a hearing- protecting earplug, a sealing section 2 is attached to the main section.
• An acoustic transmission channel TI connects microphone M2 to the inner portion of the meatus 3. Microphone M2 therefore picks up the sound present in the meatus 3, just outside the eardrum (tympanum) 4.
• An acoustic transmission channel T2 connects sound generator SG to the inner portion of the meatus 3.
• the sound generator SG may provide audible information to the user, in form of warning signals or synthetic speech.
• FIG. 2 A block diagram of one possible implementation of this embodiment is shown in Fig. 2.
• the sound is picked up by the microphone M2, amplified, and AD-converted before it is fed to the processing unit E3 with DSP or uP (or both) as central processing units.
• the memory units E8 with RAM, E9 with ROM, and E10 with EEPROM may store programs, configuration data, and analysis results.
• Information to the user is generated in the central processing unit E3, DA- converted, amplified, and may be presented as audible information via the loudspeaker SG.
• the digital interface is used for programming, control, and readout of results.
• the signal processing for the computation of noise exposure is shown in the flow diagram in Fig. 7.
• the signal from microphone M2 is amplified, converted to digital form and analysed by algorithms in processing unit E3.
• sample-by-sample equalization represented by block 41 is applied to compensate for irregularities in the microphone response, the transmission channel TI and the missing ear canal response due to the blocking of the canal by the earplug.
• the processed samples may according to the invention be evaluated in at least two ways.
• an A-weighting represented by block 42 is applied to obtain the stationary or semistationary noise dose. Standards for this A- weighting exists: IEC 179, and the samples values are squared and accumulated in blocks 43 and 44 respectively.
• a C- weighting represented by block 45 is applied according to internationally accepted standards, also IEC 179, and the peak value (regardless of sign) is saved in block 46.
• the noise dose and peak values are finally compared to predetermined limits in a decision algorithm represented by block 47 so that a warning may be given.
• the audible information to the user may be provided in form of warning signals or synthetic speech.
• the warning signal may also be transmitted to other parties, e.g. industrial health care monitoring devices.
• the time record of the two may also be stored in the memory of the processing unit E3 for later readout and further evaluation.
• this embodiment of the invention may be used as ear protection when the terminal is used as a headphone coupled to CD players for similar, monitoring the noise dose submitted from the headphones to the ear over time, or in peaks .
• a small electro-acoustic transducer (sound source) SG and a microphone M2 are arranged in a sealing section 2 arranged for attenuating sounds entering the meatus cavity 3.
• a digital signal processing (DSP) or microcomputer unit E3 in the main section 1 or in the sealing section 2 is used to generate a predetermined signal which is D/A converted by the D/A converter E7, amplified by amplifier E6 and applied to the sound source SG, which generates a sound field in the closed part of the meatus 3.
• the microphone M2 picks up the sound in the meatus cavity 3.
• This signal is amplified by amplifier E4, A/D converted by A/D converter E5, and analysed in the digital signal processor or microprocessor E3. The result of the analysis is compared to stored results from previous measurements, of the same type in a situation with good sealing conditions.
• the user may get audible or other messaged confirmation if the leakage is acceptably low, or a warning signal if leakage is unacceptably high.
• a signal may be transmitted to other instances, e.g. an external industrial health monitoring unit, with information about the leakage.
• an ear terminal according to the invention is used for checking for leakage in the hearing protection while the wearer is at a gate controlling admittance to a noise exposed area. If leakage occurs, a signal may be transmitted from the ear terminal to a corresponding signal receiver at the gate, having means to block the gate for entrance until the leakage condition is remedied and verified.
• Fig. 1 illustrates an embodiment of the invention where the verification device is integrated in a hearing protective earplug.
• This embodiment comprises an outer section 1 containing a microphone M2 and a sound generator SG.
• An inner sealing section 2 is attached to the outer section, but may be made in one integrated outer section/sealing section 1,2.
• An acoustic transmission channel T2 connects sound generator SG to the inner portion of the meatus 3.
• the sound generator SG produces a predetermined acoustic signal, which generates a sound field in the meatus 3.
• An acoustic transmission channel Tl connects microphone M2 to the inner portion of the meatus 3.
• Microphone M2 picks up the sound field being set up by the sound generator SG.
• the signal generation and analysis is carried out in a digital signal processing (DSP) or microcomputer unit E3 with appropriate amplifiers and converters as described in the previous paragraphs. All the electronics 11 as well as the power supply 12 are provided in the outer section 1.
• DSP digital signal processing
• Fig. 8 illustrates a signal processing arrangement according to a preferred embodiment of the invention.
• This embodiment utilises a signal which produces reliable characterisation of the sound field in the cavity, preferably while not being annoying to the user.
• the signal may comprise one or more sinusoidal components presented simultaneously, or in sequence. Alternatively, a pseudorandom sequence may be employed. In both cases, prefersably both the in-phase and the out-of-phase portions of the sound field are analysed and used in the verification algorithm.
• An example of the signal processing is shown in the flow diagram in Fig. 8. In the example, two pure tones of different frequencies f x and f 2 are generated by algorithms in the processing unit E3. The generators are represented by blocks 81 and 82 respectively.
• the generators generate both the in-phase (sin) and out-of-phase (cos) components.
• the in-phase components are added together in block 83, converted to analogue form, amplified and applied to the sound generator SG.
• the resulting sound field is picked up by the microphone M2, amplified, converted to digital form and analysed by algorithms in the processing unit E3 for a series of detectors represented by blocks 84, 85, 86 and 87.
• the in-phase and out-of-phase components of the microphone M2 signal are analysed for each of the two frequencies.
• the detector algorithm performs a sample-by-sample multiplication of the two input signals and smoothes the result with a low-pass filter.
• the four detector outputs are applied to a decision algorithm represented by block 88 where they are compared to stored values.
• the decision result may be a digital "go" / "no go” real time signal indicating acceptable noise protection attenuation or unacceptable protection conditions.
• the result of the analysis is compared to stored results from previous measurements of the same type in a situation with good sealing conditions.
• the stored values for the decision algorithm may according to a preferred embodiment be based on previous laboratory experiments, but values for the decision algorithm may also be determined, e.g. making an average and setting a lower acceptance limit for a general-purpose embodiment of the invention.
• the number and values of frequencies and the smoothing characteristics of the detectors are chosen as a compromise between audibility and response time. If a continuously running verification should be necessary, low frequencies, e.g. in the range of 10-20 Hz, of sufficiently low levels may be utilised in order to avoid annoyance. The pure tones may then be partially or fully aurally masked by the residual noise transmitted by the hearing protector.
• the acoustic phenomenon on which the embodiment of the invention is based is illustrated by the electric analogy diagram in Fig. 9.
• the sound generator SG is modelled by its acoustic Thevenin equivalent represented by blocks 91 and 92.
• the sound pressure pi is generated by the Thevenin generator 91, resulting in a volume velocity through the Thevenin impedance Zl(f) 92.
• the microphone M2 is modelled by its acoustic impedance Z3 (f) represented by block 93.
• the sound pressure p2 at the microphone entrance is converted to an electric signal by the microphone.
• acoustic impedance Z2 (f) represented by block 95.
• a leakage in the hearing protector may be modelled by a change in the variable acoustic impedance Z2(f) .
• the change will usually affect both the frequency dependent modulus and the frequency dependent phase of Z2 (f) . This change leads to a change in the relationship between the sound pressures p2 and pi, which is analysed as described in connection with Fig. 8.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Acoustics & Sound (AREA)
• Signal Processing (AREA)
• Soundproofing, Sound Blocking, And Sound Damping (AREA)
• Headphones And Earphones (AREA)
• Noise Elimination (AREA)
• Measuring Pulse, Heart Rate, Blood Pressure Or Blood Flow (AREA)

Applications Claiming Priority (3)

Publications (2)

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ID=19911520

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• 2000
  • 2000-09-01 NO NO20004370A patent/NO313400B1/no not_active IP Right Cessation
• 2001
  • 2001-08-31 DK DK01963616T patent/DK1322268T3/da active
  • 2001-08-31 ES ES01963616T patent/ES2319734T3/es not_active Expired - Lifetime
  • 2001-08-31 CA CA002418031A patent/CA2418031C/fr not_active Expired - Fee Related
  • 2001-08-31 EP EP01963616A patent/EP1322268B1/fr not_active Expired - Lifetime
  • 2001-08-31 AT AT01963616T patent/ATE419819T1/de not_active IP Right Cessation
  • 2001-08-31 WO PCT/NO2001/000361 patent/WO2002017839A1/fr active Application Filing
  • 2001-08-31 AU AU2001284548A patent/AU2001284548A1/en not_active Abandoned
  • 2001-08-31 DE DE60137349T patent/DE60137349D1/de not_active Expired - Lifetime

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