Low Frequency Calibration of Measurement Microphones

2009 ◽  
Vol 28 (3) ◽  
pp. 223-228 ◽  
Author(s):  
Gunnar Rasmussen ◽  
Kim M. Nielson
Keyword(s):  
Frequency Response ◽  
Sound Pressure ◽  
Low Frequency ◽  
Constant Force ◽  
Low Frequencies ◽  
Proportional Relation ◽  
Frequency Calibration ◽  
Large Piston

The calibration of measurement microphones below 100 Hz is not very well covered by the present IEC standards. The uncertainty increases rapidly and for very low frequencies it goes toward infinity. This paper approaches this issue and presents a unique way to verifying and calibrating the low-frequency response of measurement microphones. Using a small isolated calibration volume and applying a constant force to a large piston inside this volume, you obtain a direct proportional relation between force and sound pressure, allowing calibration of measurement microphones down to 0.01 Hz.

The Sound Environment of the Foetal Sheep

Behaviour ◽  
1982 ◽  
Vol 81 (2-4) ◽  
pp. 296-315 ◽  
Author(s):  
B.A. Baldwin ◽  
B.C.J. Moore ◽  
Sally E. Armitage ◽  
J. Toner ◽  
Margaret A. Vince
Keyword(s):  
Sound Pressure ◽  
Body Wall ◽  
Low Frequency ◽  
Sound Level ◽  
The Body ◽  
Human Foetus ◽  
Low Frequencies ◽  
Sound Environment ◽  
High Sound ◽  
Foetal Lamb

AbstractThe sound environment of the foetal lamb was recorded using a hydrophone implanted a few weeks before term in a small number of pregnant ewes. It was implanted inside the amniotic sac and sutured loosely to the foetal neck, to move with the foetus. Results differ from those reported earlier for the human foetus: sounds from the maternal cardiovascular system were picked up only rarely, at very low frequencies and at sound pressures around, or below, the human auditory threshold. Other sounds from within the mother occurred intermittently and rose to a high sound pressure only at frequencies above about 300 Hz. Sounds from outside the mother were picked up by the implanted hydrophone when the external sound level rose above 65-70 dB SPL, and the attenuation in sound pressure was rarely more than 30 dB and, especially at low frequencies, usually much less. However, attenuation due to the transmission of sound through the body wall and other tissues tended to change from time to time. It is concluded that the foetal lamb's sound environment consists of (1) intermittent low frequency sounds associated largely with the ewe's feeding and digestive processes and (2) sounds such as vocalisations from the flock, human voices and other sounds from outside the mother.

Reduction of the Sound Pressure Radiated by a Submarine by Isolation of the End Caps

2011 ◽  
Vol 133 (3) ◽  
Author(s):  
Mauro Caresta ◽  
Nicole J. Kessissoglou
Keyword(s):  
Sound Pressure ◽  
Low Frequency ◽  
Axial Direction ◽  
Radial Component ◽  
Axial Motion ◽  
Low Frequencies ◽  
End Caps ◽  
Passive Isolation ◽  
Radiated Sound ◽  
Finite Cylindrical Shell

A passive isolation approach to reduce the sound pressure radiated by a submarine is presented. The submerged vessel is modeled as a stiffened cylindrical hull partitioned by bulkheads and with two end caps of conical shape. Fluctuating forces from the propeller are transmitted to the hull through the shaft and a rigid foundation, resulting in axisymmetric excitation of the hull. The hull surface motion is mainly in the axial direction with a small radial component due to the coupling between the two orthogonal shell displacements. The sound pressure resulting from the axial motion is radiated from the end caps of the submarine. This work investigates reduction of the far field sound pressure by passive isolation of the end caps from the main hull. Isolation of the axial motion of the end caps from the cylindrical hull results in significant reduction of the radiated sound at low frequencies. The fluid loading approximation for a finite cylindrical shell in the low frequency range is also discussed.

scholarly journals Control the Frequency Response of a Loudspeaker by Changing Its Enclosure

2021 ◽  
Vol 4 (2) ◽  
Author(s):  
Pavlo Olehovych Riabokon
Keyword(s):  
Resonant Frequency ◽  
Resonance Frequency ◽  
Frequency Response ◽  
Rock Music ◽  
Low Frequency ◽  
Total Quality ◽  
Frequency Range ◽  
Low Frequencies ◽  
Frequency Components ◽  
Internal Volume

This article analyzes how to control frequency response of a loudspeaker by changing the volume of its closed-box enclosure. The calculation is performed by the method of  Thiele-Small on the basic of a pre-calculated loudspeaker, the parameters of which are given in third section. This became possible because of the simplification of the circuit on figure 1 to the form of circuit on figure 2. This allowed us to consider it as a second order filter (presence of two reactive elements). Obtained results are compared with corresponding characteristics of open-box enclosure of the same loudspeaker, that was pre-calculated by the author too. Results are presented graphically in figure 3 and 4. As can be seen from them, the resonant frequency of the loudspeaker in the closed-box enclosure is higher than the resonant frequency of the loudspeaker in the open box. The result in the form of a ratio  is listed in table 2. Analyzing the obtained data, it can be noticed that with the change of the internal volume of the closed box (and hence its total quality factor), it is possible to affect both the resonance frequency and the peak amplitude values in these frequencies by changing the FR. The result shown in figure 3 and 4 is achieved by taking into account effect of radiation only on the one side of the driver (in the case of open-box enclosure). Closed box was calculating by taking into account both sides radiation of the driver. Shifting the resonance frequency of the system towards higher frequencies and increasing the sound pressure on the resonance generally worsens the FR of the loudspeaker (reduces the reproduction of low-frequency components of sound and increases the unevenness of the frequency). However, certain variants of this group of frequency characteristics may be useful depending on the reproducible frequency range and need of emphasize the low-frequency components (for example, in rock music). If you need a smoothed low-frequency sound, it is appropriate to use systems with low overall quality and increased internal volume or open-box enclosure. Therefore, the volume of the closed-box enclosure significantly affects the resonant frequency and the shape of the frequency response of the loudspeaker. Reducing the volume of the enclosure of the loudspeaker leads to a decrease in its frequency range due to low frequencies and at the same time increase in the unevenness of the frequency response. The change in the resonant frequency of the system as the volume of the closed-box enclosure decreases, the less the volume of the closed-box.

scholarly journals Design and Analysis of a Novel Microspeaker with Enhanced Low-Frequency SPL and Size Reduction

2020 ◽  
Vol 10 (24) ◽  
pp. 8902
Author(s):  
Ki-Hong Park ◽  
Zhi-Xiong Jiang ◽  
Sang-Moon Hwang
Keyword(s):  
Sound Pressure ◽  
Low Frequency ◽  
Experimental Results ◽  
Multimedia Content ◽  
The Novel ◽  
Element Analysis ◽  
Low Frequencies ◽  
Acoustic Performance ◽  
Technological Developments ◽  
New Type

In the era of multimedia devices, smartphones have become the primary device for consuming multimedia content. As technological developments have facilitated a more immersive multimedia experience, enlarged displays and the use of several sensors have limited the allowable size of microspeakers. Although sound plays an important role when consuming multimedia content, the limited space for microspeakers in modern devices leads to poor acoustic performance, especially at low frequencies. To address this issue, this paper proposes a novel microspeaker structure that enhances the low-frequency sound pressure level (SPL), while also featuring reduced exterior dimensions. The structure was designed and analyzed using 3D finite element analysis. Through coupling analysis, the simulation results were verified on the basis of the experimental results. The novel microspeaker has one outer magnet surrounding the entire coil, unlike in prototype microspeakers, which have two outer magnets. The gap between the top plates and coil is reduced, and a new type of coil is introduced for the purpose of increasing electromagnetic force. The samples were manufactured, and their SPLs were tested in an anechoic chamber. The experimental results prove that the proposed microspeaker offers an improved SPL at low frequencies compared with prototype microspeakers.

scholarly journals Hearing in the African lungfish ( Protopterus annectens ): pre-adaptation to pressure hearing in tetrapods?

2010 ◽  
Vol 7 (1) ◽  
pp. 139-141 ◽  
Author(s):  
Jakob Christensen-Dalsgaard ◽  
Christian Brandt ◽  
Maria Wilson ◽  
Magnus Wahlberg ◽  
Peter T. Madsen
Keyword(s):  
Sound Pressure ◽  
Low Frequency ◽  
West African ◽  
Low Frequencies ◽  
Frequency Responses ◽  
Protopterus Annectens ◽  
Vibration Detection ◽  
Low Frequency Vibration ◽  
African Lungfish ◽  
Early Tetrapods

Lungfishes are the closest living relatives of the tetrapods, and the ear of recent lungfishes resembles the tetrapod ear more than the ear of ray-finned fishes and is therefore of interest for understanding the evolution of hearing in the early tetrapods. The water-to-land transition resulted in major changes in the tetrapod ear associated with the detection of air-borne sound pressure, as evidenced by the late and independent origins of tympanic ears in all of the major tetrapod groups. To investigate lungfish pressure and vibration detection, we measured the sensitivity and frequency responses of five West African lungfish ( Protopterus annectens ) using brainstem potentials evoked by calibrated sound and vibration stimuli in air and water. We find that the lungfish ear has good low-frequency vibration sensitivity, like recent amphibians, but poor sensitivity to air-borne sound. The skull shows measurable vibrations above 100 Hz when stimulated by air-borne sound, but the ear is apparently insensitive at these frequencies, suggesting that the lungfish ear is neither adapted nor pre-adapted for aerial hearing. Thus, if the lungfish ear is a model of the ear of early tetrapods, their auditory sensitivity was limited to very low frequencies on land, mostly mediated by substrate-borne vibrations.

Adaptive gain control of vestibuloocular reflex by the cerebellum

1976 ◽  
Vol 39 (5) ◽  
pp. 954-969 ◽  
Author(s):  
D. A. Robinson
Keyword(s):  
Frequency Response ◽  
Time Constant ◽  
Low Frequency ◽  
Gain Control ◽  
Head Movements ◽  
Image Motion ◽  
Slow Phase ◽  
Vestibuloocular Reflex ◽  
Low Frequencies ◽  
Plastic Changes

1. The gain of the vestibuloocular reflex (slow-phase eye velocity/head velocity) was measured in 17 adult cats. 2. The gain of the reflex, in the dark, was 0.90 (+/-0.15 SD) over the frequency range 0.03-1.2 Hz. 3. In the range 0.01-0.15 Hz, the phase behaved as though the overall reflex time constant were 12 s or greater. The cupula time constant is 4 s. Therefore, the central part of the reflex must manipulate the canal signal to improve its low-frequency response by a factor of at least three. 4. When the cats wore left-right reversing prisms chronically and were also rotated for 2 h every day, the reflex underwent large, plastic changes. The gain, tested in the dark, decreased by 93% at 0.05 Hz and 55% at 1.2 Hz. In effect, the low-frequency response was abolished. The process took about 8 days. 5. In the light, with reversed vision, the gain decreased further and, at low frequencies, the eye movements did reverse in direction. 6. When the vestibulocerebellum was removed, the gain, in the dark, rose to about 1.17 and the plastic changes caused by reversing prisms were completely abolished. 7. Reversing prisms create vestibuloocular dysmetria. The change in gain they produce is considered to be an adaptive response designed to reduce image motion on the retina during head movements. The vestibulocerebellum is necessary for this adaptive process. It is proposed that detecting and repairing dysmetria (of natural origin) is an important cerebellar function.

High-Intensity Acoustic Test Facility Using Hydraulics

1999 ◽  
Vol 42 (1) ◽  
pp. 46-50
Author(s):  
Paul Lieberman
Keyword(s):  
Sound Pressure Level ◽  
Sound Pressure ◽  
Low Frequency ◽  
Fatigue Tests ◽  
Pressure Level ◽  
Test Facility ◽  
Hydraulic Control ◽  
Hydraulic Facility ◽  
Low Frequencies ◽  
Hydraulic Simulator

The hour-long duration acoustic fatigue tests at levels above 190 dB overall sound pressure level (OASPL) can be achieved with the required sound pressure level (SPL) spectrum using available test facilities with a hydraulic simulator, which operates at only 3 to 10 psi. Furthermore, the hydraulic control at the low frequencies is available, whereas there is a 50-Hz frequency cutoff for acoustic test facilities. Many structures have destructive low-frequency resonant modes which would be properly excited in the hydraulic facility and not in the acoustic facility.

The reaction of a captive herring school to playbacks of a noise-reduced and a conventional research vessel

2015 ◽  
Vol 72 (4) ◽  
pp. 491-499 ◽  
Author(s):  
Nils Olav Handegard ◽  
Alex De Robertis ◽  
Guillaume Rieucau ◽  
Kevin Boswell ◽  
Gavin J. Macaulay
Keyword(s):  
Sound Pressure ◽  
Low Frequency ◽  
Clupea Harengus ◽  
Research Vessel ◽  
Frequency Noise ◽  
Atlantic Herring ◽  
Low Frequencies ◽  
Vessel Noise ◽  
Fish Avoidance

Fish avoidance of vessels can bias fisheries-independent surveys. To understand these biases, recordings of underwater radiated vessel noise from a noise-reduced and a conventional research vessel were played back at the same sound pressure levels (SPL) as experienced in situ to Atlantic herring (Clupea harengus) in a net pen at two different densities. The noise-reduced vessel recording was also scaled to the same SPL as the conventional vessel to test if characteristics other than SPL affected the reactions. Overall, only weak reactions were observed, but reactions were stronger in the low-density school, in the middle of the pen, and for the scaled silent vessel compared with the conventional vessel. These observations may be attributable to the lack of low frequencies (<50 Hz) in the playbacks, differential motivation for reaction driven by fish density, higher low-frequency noise in the middle of the pen (but lower overall SPL), and characteristics other than SPL. These results call into question the use of SPL as a proxy for fish reaction to vessels as used in standards for construction of research vessels.

scholarly journals Calculation of sound pressure level of marine propeller in low frequency

2018 ◽  
Vol 37 (1) ◽  
pp. 60-73 ◽  
Author(s):  
Mohsen Gorji ◽  
Hassan Ghassemi ◽  
Jalal Mohamadi
Keyword(s):  
Sound Pressure Level ◽  
Sound Pressure ◽  
Low Frequency ◽  
Hydrodynamic Pressure ◽  
Pressure Level ◽  
Navier Stokes ◽  
Marine Propeller ◽  
Low Frequencies ◽  
Directivity Patterns ◽  
Good Agreement

The research performed in this paper is carried out to calculate the sound pressure level of the marine propeller by Reynolds-Averaged Navier–Stokes solver in low frequencies band. Noise is generated by the induced trailing vortex wake and induced pressure pulses. The two-step Fflowcs Williams and Hawkings equations are used to calculate hydrodynamic pressure and its performance as well as sound pressure level at various points around the propeller. The directivity patterns of this propeller and accurate explanation of component propeller noise are discussed. Comparison of the numerical results shows good agreement with the experimental data.

Predicted and Measured Low Frequency Response of Small Rooms

1997 ◽  
Vol 4 (2) ◽  
pp. 73-86 ◽  
Author(s):  
Sophie Maluski ◽  
Hocine Bougdah
Keyword(s):  
Frequency Response ◽  
Low Frequency ◽  
Sound Transmission ◽  
Sound Level ◽  
Low Frequencies ◽  
Acceptable Error ◽  
Modal Characteristics ◽  
Sound Fields ◽  
Mesh Model ◽  
Room Model

The sound level difference of party walls at low frequencies [25–200 Hz] has been shown to be strongly dependent on the modal characteristics of the sound fields of the separated rooms. The modal characteristics can be modelled by numerical methods and a Finite Element Method has been selected to model sound transmission between adjacent rooms separated by a party wall. The numerical eigenfrequencies were compared with the theoretical eigenfrequencies to select a mesh model for which the eigenfrequencies are processed within an acceptable error range. As a prelude to the study of sound transmission between dwellings, the simulation of one single room, modelled with the selected mesh model, was validated by predicting the frequency response and comparing values with measured frequency response of a 1:4 scale room model. Results show promising agreement and establish the reliability of the work.

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