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Speech Therapy

Precision hearing

Equipment for hearing tests gains a more efficient calibration system

eduardo cesarTo remain still in a soundproof room listening to the sounds emitted by loudspeakers or headphones is routine for those who go through a hearing test, which measures a person’s hearing capacity and are solicited by doctors and speech therapists. The sounds, in various levels of volume and intensity, are generated by a piece of equipment called an audiometer that needs to be calibrated every year to standard measurements. For this procedure the apparatus has just gained a new methodology, which is more precise and works by way of mini cameras. The company responsible for this innovation is the company Inter-Metro, which had FAPESP’s support through the Small Business Innovation Research (PIPE) program. Specializing in industrial acoustic measurements, the company developed a new system after verifying the occurrence of deviations in the calibration of the audiometers in clinics, hospitals and consulting rooms.

The problem was detected starting from an analysis of the methods of calibration realized under the guide lines of the National Institute of Metrology, Normalization and Industrial Quality (Inmetro), the federal organ responsible for attesting to the quality of this type of equipment based on international standards. In the results amassed, the director of Inter-Metro, the physicist Oswaldo Rossi Júnior, encountered a wide offering of audiometry services on the market, but of questionable quality, including some companies making calibrations using inadequate equipment or even in an erroneous manner. “What we are trying to carry out the calibration in accordance with the norms established by Inmetro, with equipment of a high standard and an innovation in the logistics which is to take the micro camera for tests to the client’s premises, and not the contrary, as it happens now”, says Rossi Júnior.

In order to remedy the deficiencies of the calibration of the audiometers that emit frequencies between 125 Hertz and 8,000 Hertz, the company made use of some technological procedures for the creation of an environment without echoes and other external interferences. Thus the Semi-Anecoica Mini Camera measuring 70 centimeters in height, 80 centimeters in breadth and length was assembled. Smaller than conventional cameras, the mini camera is built with wood and its interior is finished with layers of various materials including a special varnish, aluminum, sponge material of medium and high density, lead pellicles and a special absorbing sponge, with a specific curvature for absorbing sound, which impedes its propagation, as well as eliminating external noises.

Within the mini camera are installed either an artificial ear, an apparatus that simulates  The human tympanum (fine membrane located at the entrance to the ear that conducts the sound via the air), or an artificial mastoid, simulating the bone conductor located in the part behind the ear (receives acoustic signals via the bone and transmits them to the auditory nerve). In the case of the artificial ear, an internal microphone reproduces the auditive capacity of the human ear. Thus, any frequency of sound emitted by the audiometer within the mini camera is captured by the microphone of the artificial ear that remains connected to a sound spectrum analyzer, examining the level of sound, in each frequency,  and electronically demonstrating everything that is emitted by the device. The same thing occurs when the artificial mastoid is in use, imitating the vibration via the bone.

According to physicist Rossi Junior, as well being a precision technique, the system, which only exists in Denmark, also demonstrates an advance in the calibration of audiometers, because all of the elements that make it up are portable. “We developed a system composed of a sonorous noise meter and a spectral analyzer that can be transported to distant regions, where the possibility of calibration are smaller”, says  Rossi Junior. With the possibility of being sent to the localities where the practice of calibration is deficient, the Inter-Metro system also avoids the audiometers being damaged during transport or by inadequate handling. “This improves all of the apparatus involved, because the grouping together of various audiometers to be calibrated in a determined locality justifies taking the system to more distant regions”, suggests the director.

Less time – In order to achieve good calibration results, director Rossi Junior carried out tests and measurements in the company’s laboratory. The results were considered satisfactory, as they were within the standards determined by Inmetro. The physicist also verified that the complete calibration time for audiometers using the mini camera decreased, on average, by two hours, a lot less than the three hours of the traditional process. Starting from the prototype developed by Inter-Metro, director Rossi Junior intends to build another six mini cameras by the end of 2005 to be sent, initially, to various towns and cities in the interior of São Paulo. For this to happen, direct partnerships with clinics and consulting rooms that will receive the equipment, will be established. The results will be sent to the Inter-Metro laboratory in São Paulo, where they will be analyzed.

The company began operating in 1997 with the help of the Brazilian Association of Non-Destructive Tests (Abende). During 1999 it started its commercial operation in the area of equipment calibration. Currently, the company carries out around sixty types of metrology tests, among them the calibration of decibel meters (for example, measuring the intensity of industrial sound) and sonorous dosimeters (which measure the sound intensity that a person receives during a day, for example). The project that culminated in the new system consumed around two years of research time. In accordance with a norm from Inmetro, the system is approved only for measurements during calibration, any  adjustment to the apparatus being vetoed. In the case where an adjustment is necessary, it must be made in another local and afterwards returned for calibration, when its efficiency will be attested to.

The Project
Establishing a metrological standard for an audiometric system with parametrization of the respective functions of calibration and trustworthiness (nº 00/13113-8); Modality Small Business Innovation Research (PIPE) program; Coordinator Oswaldo Rossi Júnior – Inter-Metro; Investment R$ 82,980.00 (FAPESP)