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Sound

Department 1.6

Scientific News from the Department

Detection thresholds of infrasound complex tones

The growing number of infrasound sources (infrasound: frequencies below 20 Hz) in our environment is calling society's attention to infrasound exposure. Together with the Department of Experimental Audiology at the Otto von Guericke University Magdeburg, PTB has participated in the project titled "Infrasound and its relevance for audible sound". The project is funded by the Deutsche Forschungsgemeinschaft (DFG – German Research Foundation) and deals with the question as to how human 'hear' infrasound. Within the scope of this project, signals comprising several infrasound components (multi-frequency tone complexes) were used to investigate how the number of components influences the perceptibility of the signal (detection threshold). This allows conclusions as to the perception of complex signals to be drawn. Such signals are much more similar to those occurring in our real environment than single-frequency signals (pure tones). - more...

Use of Open Science in the development of an occupational safety measuring procedure

PTB is developing a measurement procedure to determine airborne ultrasound exposure at the workplace and is hereby pursuing an open-science strategy in order to make the research data and results freely available to the public. In this way, the development and testing of this procedure, which was designed for occupational safety and health, becomes transparent and comprehensible. Furthermore, it opens up new possibilities to create added value by re-using the datasets. - more...

Sound source system for investigating the perception of infrasound combined with audible sound

Within the scope of the EU joint project titled Ears II (EMPIR project No. 15HLT03), hearing tests were planned at PTB in order to investigate how humans perceive infrasound (frequencies f below 20 Hz) combined with sound in the "conventional" acoustic frequency range (i.e."audible sound" in the frequency range 20 Hz ≤ f ≤ 20 kHz). The first step consisted in developing a sound source system able to transmit infrasound and audible sound to the ear canal. One of the challenges of this first step was that extremely high sound pressure levels are required in the infrasonic range for humans to be able to perceive them, while at the same time, no audible distortions may occur. - more...

Directional response pattern of measurement microphones for high-frequency noise measurements

When carrying out noise measurements, it is usually assumed that the directional response pattern of the microphone used can be neglected. This is true when the microphone is clearly smaller than the wavelength of the investigated sound. This usually does not apply in the case of the ultrasound range. - more...

Reference data for a new audiometric headphon

For the recently developed circumaural audiometric RadioEar DD65v2 headphone, reference hearing thresholds were determined for pure-tone audiometry and free-field equalization data for use in speech audiometry. Reference hearing thresholds are specified in the ISO 389 series of standards "Acoustics – Reference zero for the calibration of audiometric equipment". For tone audiometry, the reference hearing thresholds of 25 otologically normal male and female test subjects between the ages of 18 and 25 were determined by means of sinusoidal signals of fixed frequencies between 125 Hz and 8 kHz. For this purpose, the individual hearing threshold of each of the test subjects was determined with an automated measuring arrangement by means of the so-called "bracketing method" according to ISO 8253-1. - more...

A measurement procedure to determine the exposure to airborne ultrasound at the workplace

A procedure to measure airborne ultrasound is being developed within the scope of Ears II, an EU research project. This procedure, which is designed for occupational safety, has been developed to reliably determine the exposure of staff to airborne ultrasound at the workplace. Important findings obtained during its development were provided by sound field scans with a high spatial resolution at a reference workstation at PTB. - more...

BISTI - Binaurale Erweiterung des Speech Transmission Index (STI)

Die Übertragungsqualität von Beschallungsanlagen wird häufig mit dem Speech-Transmission-Index (STI) bewertet, welcher ihre Modulationsübertragung erfasst. Für Notfall-Sprachdurchsagen fordern die Richtlinien einen Mindestwert des STI von 0,5. Die STI-Messung erfolgt üblicherweise mit einem einfachen Messmikrofon. Aus der Praxis ist bekannt, dass dabei die erzielte reale Sprachverständlichkeit in räumlich komplexen Situationen oftmals unterschätzt wird, da weder Kopfabschattung noch Zeitverarbeitung des binaural arbeitenden menschlichen Gehörs berücksichtigt werden. Zur Verbesserung der Einschätzung der mit Beschallungsanlagen in solchen Hörsituationen erreichbaren Sprachverständlichkeit wurde im Rahmen einer durch die AiF im Zentralen Innovationsprogramm Mittelstand geförderten Kooperationsprojektes mit TAC - Technische Akustik,  Grevenbroich, ein binauraler STI (BISTI) entwickelt. - more...

Hydrophone calibration with an extended frequency range

A new kind of measurement setup enables the simultaneous calibration of amplitude and phase in a frequency range up to 100 MHz

Hydrophones are used to characterize the acoustical pressure of ultrasonic signals in water. They are commonly used by medical equipment manufacturers to characterize the acoustical fields of diagnostic and therapeutic medical equipment. Especially for measurements that are mandatory by law – e.g. the Medizinproduktegesetz for the protection of the patient – or defined in international standards, calibrated hydrophones must be used. The use of those hydrophones provides traceability of the measurement to the SI system. For this task PTB, operates a primary standard and performs hydrophone calibrations for international customers – manufacturers of medical products and measurement systems, laboratories, regulators and research institutes. - more...

New testing procedures for software in sound  level meters in legal metrology

Sound level meters serve the purpose of measuring sound levels and, thereby, in particular, to measure and check the observance of legally prescribed maximum or reference values (for example, in accordance with the "Technical Instructions on Noise Abatement" ["TA Lärm"]). Sound level meters can be found in private life (e.g. in home building), in environmental protection, and at work (in the form of worker protection). In order to ensure a correct and verifiable measuring process, all equipment used in official transactions must undergo a type examination that is carried out according to the Measures and Verification Act. Now, also a software test must be included in this type examination.  - more...

Ultrasound level meter for practical use in occupational health and safety

A measuring system for airborne ultrasound is being developed within the scope of a technology transfer program. This system is specially dedicated to the practical application of measuring noise for occupational health and safety purposes. It will allow the determination and assessment of risks represented by widespread ultrasonic machines which can cause very high sound pressure levels. - more...

Erweiterung des Frequenzbereiches des PTB-Schallnormals bis herunter zu 2 Hz für die Rückführung akustischer Messungen im Infraschallbereich

Die Primärkalibrierung in der Druckkammer liefert das zurzeit präziseste Verfahren zur Darstellung der Schalldruckeinheit. Um diese mit höchstmöglicher Genauigkeit zu realisieren, bedient man sich des Reziprozitätsverfahrens zur Kalibrierung von hochstabilen genormten Kondensator-Mikrofonen, den sogenannten Laboratoriums-Normalmikrofonen. Sie zeichnen sich dadurch aus, dass sie einen großen... - more...

Robust membrane hydrophone for the measurement of high-intensity therapeutic ultrasonic fields

Exceptionally robust piezoelectric membrane hydrophones for measurement of extreme acoustic pressure waveforms were developed until ready for marketing in Working Group 1.62 Ultrasonics of PTB in cooperation with the Gesellschaft für Angewandte Medizinische Physik und Technik (GAMPT) mbH, Merseburg. - more...

PTB-Kalibrierservice für Luftultraschall

Bisher gab es für Messungen von Schall mit Frequenzen über 20 kHz noch keine metrologische Rückführung für die Schalldruckeinheit Pascal. An der PTB wurde nun ein Verfahren zur Kalibrierung von Mikrofonen im Ultraschallbereich bis zu 100 kHz entwickelt. Damit können Bezugs- und Gebrauchsnormale für Labore aus Industrie und Forschung hergestellt werden, um eine Rückführung für Luftultraschall zu... - more...

Neue Bezugshörschwellen zur Anwendung mit einem Ohrsimulator für Neugeborene

Da Neugeborene und Kleinkinder erst bei ziemlich lauten Schallereignissen eine Reaktion zeigen, die eine Hörempfindung beweist, werden bei Ihnen zur Gehörprüfung objektive Audiometrieverfahren, wie z. B. die Messung der durch akustische Stimuli ausgelösten Hirnströme, eingesetzt. Die Schallreize (Stimuli) werden dabei über Einsteckhörer wiedergegeben. Die dafür erforderlichen... - more...

Assessment of airborne ultrasound noise

Noise by airborne ultrasound is increasingly polluting our daily environment and can be a risk to our health. There is a growing need for an understanding of the perception and the influence of ultrasound and for establishing consistent regulations. The EARS project has brought researchers of several disciplines together and combined neuroimaging and audiological measurements to create a basis for the assessment of ultrasound noise... - more...

Significance of the results from the EARS project on wind turbines

In our environment and at the workplace, technical sources produce low frequency sound, which is normally considered inaudible. Installations for the production of green energy are among those sources, namely wind turbines producing infrasound. - more...

Thermochromic foils as a simple and magnetic resonance imaging (MRI) compatible way of recording ultrasound-induced heating

Ultrasound is used in medicine for several therapeutic purposes - besides other applications, ultrasound can be used to selectively and locally heat tissue, for example in order to destroy tumors by overheating them. The two most common methods for determining this increase in temperature are either not traceable and provide a poor temporal and spatial resolution (measurements with magnetic...  - more...

Are infrasound and ultrasound audible?

Noise is one of the fundamental environmental factors impairing health and well-being. Whereas in the hearing frequency range, the handling of noise is well grounded and regulated, in the infrasound and ultrasound range, not only the understanding of perception is missing but also fundamental requirements for measuring instruments as well as applicable, practice-related measurement instructions.  - more...

Better accessibility for the hearing-impaired in public transport areas by optimizing public address announcements

The transmission quality of public address systems is evaluated by means of the Speech Transmission Index (STI) that essentially describes the goodness of modulation transfer (DIN EN 60628-16). An STI value of 0 corresponds to a total loss of signal modulation, whereas an STI value of 1 represents ideal signal transmission. For emergency warning systems an STI value ≥ 0.5 is required, which... - more...

Sound source for the objective investigation of the auditory perception of infrasound by means of magnetoencephalography (MEG) and magnetic resonance imaging (MRI)

Contrary to general opinion, the hearing of infrasound (f < 16 Hz) is possible and leads to distress which differs from person to person. However, the mechanisms of this auditory perception by human beings are still largely unexplained. Within the scope of the European research project "EARS", these mechanisms are to be investigated in detail by means of objective procedures of medical... - more...

Directivity pattern of airborne ultrasonic sources

Airborne ultrasound can be emitted with a very strong directivity by sound sources such as ultrasonic cleaning baths or welding equipment. Due to this focusing, very high and hearing-damaging sound pressure levels may occur locally. A new measuring arrangement now allows the emissivity of various sound sources to be determined with high resolution and with level accuracy. - more...

Causes of cell damage in connection with cataract surgery

After cataract surgery, damage to endothelial cells located on the internal side of the cornea is observed in the majority of patients. The causes of this cell damage have not yet been fully clarified; this can affect the corneal dehydration for which these cells are responsible. The – in this case – reduced performance of the endothelial cells leads to a temporary swelling of the cornea in the... - more...

Small sources, loud noise

Ultrasonic equipment, such as, e.g., ultrasonic cleaning baths, can cause very loud noise. High-frequency airborne ultrasound was measured up to 100 kHz on a solid metrological basis for the first time, and different assessment quantities were determined quantitatively. - more...

A sensor to determine the effectivity of ultrasonic cleaning devices

Ultrasonic baths have long been widely used in industry and trade. Despite this, no uniform procedure has existed so far to compare the cleaning results obtained by different devices or the cleaning effectivity of a device in various operating modes. PTB has developed a procedure which allows the abrasion of particles from a surface – hence a cleaning process – to be measured directly. - more...

New procedure for the testing of exponential sweep signals with the aid of Hilbert transform

Acoustic signals are analyzed with the aid of sound level meters, using so-called filter banks. These must be investigated with respect to their real-time capability. For this purpose, test signals are used which must in turn fulfill specific conditions. A new procedure for the testing of test signals for the real-time testing of filters can help to avoid incorrect test results. - more...

Improved damping of acoustic room modes by tunable Helmholtz resonators

In certain frequency ranges, disturbing sound waves cannot be damped with conventional absorbers. An optimization procedure and the use of finely tuned resonators, which are correspondingly dimensioned and positioned in the room, allow different damping effects to be achieved. - more...