Low-frequency sound

Resonant Sound Absorbers. Two other types of sound-absorbing treatments, resonant panel absorbers and resonant cavity absorbers (Helmholtz resonators), are used in special appHcations, usually to absorb low frequency sounds in a narrow range of frequencies. Resonant panel absorbers consist of thin plywood or other membrane-like materials installed over a sealed airspace. These absorbers are tuned to specific frequencies, which are a function of the mass of the membrane and the depth of the airspace behind it. Resonant cavity absorbers consist of a volume of air with a restricted aperture to the sound field. They are tuned to specific frequencies, which are a function of the volume of the cavity and the size and geometry of the aperture. 

Low-frequency noise (in the range 3-50 Hz) may have other injurious effects on the body. Research has also indicated that a type of fatigue caused by low-frequency noise has a similar effect to that caused by alcohol. Infrasound (low-frequency sound) also has a synergistic effect with alcohol. Low-frequency noise is particularly important in the case of workers operating machinery (e.g. vehicles, cranes, etc.). It must also be remembered that very high power levels may be generated at low frequency and may not be readily detected by the ear. Attenuation of low-frequency noise is very difficult (see Section 42.7). 

Noise Vessel propulsion, sonar, seismic prospecting, low-frequency sound use in defense and research May disturb marine mammais and other organisms that use sound for communication. 

Short table length Short tables without interpolation result in distortion particularly with stored low frequency sounds... 

The units for the values in Table 5.11 are shown as dB A impulse for A, dB F impulse for flat, and dB L impulse for linear. One must pay attention when using a super low frequency sound meter to the linear reading. The linear range of its dynamic response is l-90Hz when the frequency component is over 90Hz, it becomes a low level frequency. 

The assistance of US to electroanalytical techniques during analysis is known as sonoelectroanalysis. This should also include the use of low-frequency sound (below 20 kHz), which has been found to significantly increase mass transport and the limiting current (and sensitivity as a result) [127-130]. 

Sounds produced by humans can also interfere with the ability of animals to communicate. Such interference can inhibit an animaPs ability to protect itself, to find food, and to live a normal life. For example, ships emit low-frequency sounds that interfere with whale communications. Other human noises can frighten whales away from their normal migration routes. In the desert, kangaroo rats Dipodomys spp.) exposed to the roar of a dune buggy lose their ability to hear snakes approaching. Japanese quail (Coturnix Coturnix Japonicd) have to call much louder than usual when they live in a noisy environment. Sooty terns (Sterna fuse at a) have been observed to abandon their nests when jets create sonic booms. Intense bursts of noise have also caused condors (Gymnogyps californianus) to abandon their nests. 

Infrasound stations use very sensitive microbarometers to detect low frequency sound waves from atmospheric explosions. These stations are arrays and are able to determine accurately the location and size of an atmospheric explosion. Altogether there are 60 stations in the network as shown in Table 13.8. 

Human loudness perception depends in a complex manner on both frequency and the overall loudness of sound. (For example, bass is more difficult to hear in music played at low volume than in the same music played at high volume.) To capture this behavior, two weighting scales have been developed for use in sound hazard analysis. The most common of these is the A weighting scale, which is commonly used to assess occupational and environmental noise. The A scale weights sounds in the 1000-6000 Hz range much more heavily than low-frequency sounds. The A-weighted intensities (dBA) of some common sounds are listed in Table 5. By contrast, the C weighting scale is used for very loud sounds and is a much flatter function of frequency. 

The other, less used correction scales are named, as may be expected B, C, and D. Referring to Figure 8.9 we can see that the C-scale is essentially flat over the range of interest and the B-scale lies somewhere between the A and C scales. With the understanding we have today of the influence of low-frequency sounds, we find that the B and C scales, although meant to be used with low-frequency sounds, do not apply adequate correction in... 

A detailed study of the Rayleigh-Brillouin spectrum of liquid argon recently made by Fleury and Boon (1969) showed that the normalized spectrum, 5(q, cu)/5(q), is described by Eq. (10.4.30) to within experimental error. In their experiment q 2.1 x 105 cm-1, T = 85 °K and P = 592.5 mmHg. From Eq. (10.4.41), the sound speed is cs = 850 4 m/sec this compares very well with the low-frequency sound speed measured acoustically, cs = 853 m/sec. A typical spectrum is shown in Fig. (10.4.1). 

As whistles burn, the output of these high frequencies is roughly constant. However, there is an ever increasing output of low frequency sound. 

Very low frequency sounds also have a psychological effect. Tigers produce an 18 cps component in their roar that induces a feeling of terror in humans and paralyzes prey for up to 10 s (Ross, 2004). 

When seeking materials suitable for low frequency sound absorption, compliant or elastomeric materials become a natural con-... 

Garland, C.W. and Williams, R.D. Low-frequency sound velocity near the critical point of Xenon. Phys. Rev. A 10 (1974), 1328-1332. 

Infrasound stations (60) detect the very low frequency sound that can be detected in the atmosphere using microbarometers (acoustic pressure sensors). 

Poor sound absorbers. Brick surfaces, painted concrete blocks, hardwood floors, gypsum board, or smooth nonporous plaster (lime or gypsum) are all poor absorbers. With solid structural backing these finishes seldom afford as much as 10 percent absorption at any wavelength from 125 hz to 4,000 hz. Ordinary window areas may absorb up to 25 percent of the low-frequency sounds (125 to 250 hz) but much less at the higher frequencies. 

Sound is measured by its frequency and intensity. Frequency is the pitch (high or low) of a sound. High-frequency sound can be more damaging to your hearing than low-frequency sound. Intensity is the loudness of a sound. Loudness is measured in decibels (dB). 

Claudication is a clinical, easy to make diagnosis. Claudication of the upper extremities, although much less frequent than that of the lower extremities, is also a clinical diagnosis. The extremities should be examined carefully. Examination of the peripheral arterial system should include an evaluation of the volume and character of the arterial pulses of the carotids and of the arteries of the upper extremities the subclavian, the brachial, the radial, and the ulnar. Physical examination should definitely encompass the abdominal aorta for abnormal pulsations, ectasias and/or bruits, and the arteries of the lower extremities femoral, popliteal, dorsalis pedis, and posterior tibialis. The pulse volume can be graded on a scale of 0 to 4. In addition to palpation, physical examination of the peripheral arterial system should include auscultation over the carotids, auscultation over the subclavian arteries above, and below the mid-clavicular area. A bruit over the subclavian artery and disappearance of the radial pulse with compression of the subclavian artery is evidence for subclavian syndrome. On occasion, a bruit may be heard by auscultation deep in the axilla. The bruit, a composite of low frequency sounds, is better appreciated when the examiner is using the bell of the stethoscope. 

Komarov SV, Kuwabara M, Sano M (1990) Mechtmism of acoustic defoaming by applying low frequency sound. CAMP ISIJ 12 721... 

Acoustic (low frequency sound pulses) o Sub-bottom profiler... 

Gmucova, K Thurzo, L Orhcky, J. Pavlasek, J. (2002). Sensitivity Enhancement in Double-Step Voltcoulometiy as a Consequence of the Changes in Redox Kinetics on the Microelectrode Exposed to Low Frequency Sound. Electroanalysis, Vol.l4, No.l3, Quly 2002), pp. 943-948, ISSN 1521-4109 Gmucova, K. Orhcky, J. Pavlasek, J. (2004). Non-Cottrell Behaviour of the Dopamine Redox Reaction Observed on the Carbon Fibre Microelectrode by the Double-Step Voltcoulometiy. Collect Czech. Chem. Commim., Vol.69, No.2, (February 2004), pp. 419-425, ISSN 0010-0765... 

Mikkelsen, 0. Schroder, K.H. (2000). Low Frequency Sound for Effective Sensitivity Enhancement in Staircase Voltammetiy. Anal. Lett, Vol.33, No.7, (April 2000), pp. 1309-1326, ISSN 0003-2719... 

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