Octave Band Center Frequencies Research Articles

The reduction of the reverberation using the sound-absorbing metamaterial in the conference rooms

Sound-absorbing metamaterial, iwasemi consists of multiple perforated Fabry-Perot resonators which have different resonant frequencies reciprocally to achieve broadband sound absorption coefficient. We have installed acoustic panels that are optimized for the main band of human voices, 1/3 octave band center frequencies from 500 Hz to 1000 Hz, in some conference rooms and measured the reverberation time of the rooms before and after installation. The measurement result shows that the acoustic panels have decreased the reverberation time of the rooms dynamically in the target frequency band (e.g. a case of we measured, the reverberation time reduced from 1.11 seconds to 0.66 seconds at 500 Hz octave band center frequency). As shown above, it has been indicated that installing plastic acoustic panels using acoustic metamaterial improves the acoustic environment in the rooms.

Acoustic response of bi-directional functionally graded beam under axially varying load

This paper investigates the effects of bi-directional gradation, length-to-height ratio, and end conditions on the acoustic behaviour of bi-directionally varying functional graded beams. The acoustic responses, including sound-power level (dB), sound-pressure level (dB), and sound-radiation efficiency, are evaluated using Rayleigh’s integral and modal superposition method. The sound power levels are presented up to the selected bandwidth, as well as the octave band center frequency. In contrast, the sound pressure levels are presented as contour plots and in directivity pattern. The buckling load, calculated for quadratically decreasing axial load, is applied in increments from 0 to its highest value. The study reveals that the highest value in the gradation indexes in both directions significantly influences the sound power levels. It is also evident from the study that thin beams have higher sound power levels compared to thick beams. The directivity pattern reveals that bi-directional functionally graded beams predict higher sound pressure levels at the critical buckling load. From the current acoustic study, it is observed that both structural and end stiffness are influential factors in sound power levels (dB) and sound pressure levels (dB).

Estimation of impact sound reduction by wood flooring installation in a wooden building in Korea

Multi-family homes have been constructed traditionally using heavy materials like concrete/steel and bricks. Wooden structures are a promising substitute for typical heavyweight constructions. However, floor impact noise has been identified as the most annoying noise source in South Korea. Here, we have studied the effect of floorboard installation on impact sound changes before and after installing the floorboard on the floor of a wooden building. We used standard tapping and bang machines in this study to generate lightweight and heavyweight impact sounds. The changes in noise from lightweight and heavyweight impact sounds were estimated on the upper layer (UL) and lower layer (LL) floors before and after the installation of the plywood floorboard (PFB). The average of the octave band center frequencies at 125, 250, 500, 1000, and 2000 Hz from the lightweight impact before installation of PFB was 84.08 dB (UL) and 50.54 dB (LL), respectively, while 84.04 dB (UL) and 41.90 dB (LL) after the installation of the surface decorated PFB. Similarly, the heavyweight impact sound before installing PFB was 73.26 dB (UL) and 42.16 dB (LL), respectively, while after installation of PFB, impact sound appeared at 71.58 dB (UL) and 42.48 dB (LL). The results exhibited that lightweight impact sound could be reduced by about 8.6 dB on the LL. These results could entice the researcher or building engineer to design wooden floorboards for a comfortable building environment. This study is new because it compares the impact sound of the floor before and after it has been constructed.

Effect of ceiling and dry-type double floor on heavy-weight floor impact sound in concrete building and CLT building.

The air layer between the interior finishes and the structure is used as piping and wiring space. In many cases, ceilings and dry-type double floors are commonly constructed in Japan. However, the effect of the air layer of ceilings and dry-type double floors on the heavy-weight floor impact sound insulation performance has not yet quantitatively investigated. Therefore, in this study, the same floor and ceiling structures were constructed for concrete and CLT buildings, and the heavy-weight floor impact sound was investigated. As results, it was confirmed that the reduction amount of the heavy-weight floor impact sound by the ceiling tended to be smaller in CLT buildings than in concrete buildings. However, the trends were similar. Due to the dry-type double floor structure, the heavy-weight floor impact sound level was increased in concrete building and decreased in CLT building at 63 Hz in the octave band center frequency band. Therefore, it can be said that the dry-type double floor structure can be used to improve the heavy-weight floor impact sound performance in the CLT building.

Sound Level Measurements in Berthing Areas of an Aircraft Carrier

Personnel assigned to aircraft carriers work and live in environments where hazardous noise areas and hearing recovery spaces such as sleeping areas are in close proximity to one another. Hazardous noise exposure occurring during on-duty time periods and elevated noise levels during off-duty periods in sleeping areas may be prohibiting adequate hearing recovery, thus potentially leading to hearing loss and may lead to adverse effects on sleep, leading to crew-member fatigue. This investigation characterizes Equivalent sound level (Leq) and standardized octave band center frequency noise levels according to berthing (sleeping) area location during flight operation and nonflight operation time periods on a US Navy aircraft carrier. In addition, the investigation compares noise measurements in sleeping areas to noise levels associated with auditory rest and poor sleep quality and quantity. Noise levels were measured in berthing areas aboard a US Navy Nimitz-class aircraft carrier during a routine at-sea period. Sixty noise measurements were taken in eight sleeping locations. Leq in decibels 'A' weighted (dBA) and noise levels from 16 to 16 000 Hz in (dB) were measured during flight operations [Leq (flt ops)] and nonflight operations [Leq (nonflt ops)]. Leq was also measured according to sleep area shipboard locations of forward (FWD) Leq (FWD), middle (MID) Leq (MID), and rear (AFT) Leq (AFT). These data were compared to the 70 dBA American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value (TLV) for effective quiet areas. In addition, these data were compared to noise levels associated with hearing loss and sleep parameters. Statistical analysis was conducted with R version 3.5.2 using an alpha level of 0.05. Leq (flt ops) in sleeping areas was a statistically significant (P < 0.05) 6.4 dBA higher than the Leq (nonflt ops). Leq (FWD) and Leq (MID) in sleeping areas was a statistically significant (P < 0.05) 15.2 and 15.0 dBA higher, respectively, than the Leq (AFT) noise levels. Mean noise levels at standardized center (1/1) octave bands were highest between 500 and 4000 Hz, ranging from 65.2 to 69.8 dB. A total of 72% of all area Leq measurements exceeded the 70 dBA ACGIH TLV classified as effective quiet to allow for temporary threshold shift recovery. All noise measurements exceeded the World Health Organization's noise threshold where adverse effects on sleep begin. Results suggest that sleeping area location in close proximity to relatively high noise sources and activities occurring on an aircraft carrier (i.e. flight operations) increase noise levels in sleeping areas. These findings raise serious concerns since high noise exposures both on duty and during off-duty/sleeping periods may inhibit auditory recovery from hazardous noise exposures. In addition, results suggest noise levels in sleeping areas are high enough to evoke negative sleep effects.

Calibration of a Digital Hydrophone Line Array at Low Frequency

The challenges of comparison calibrations of hydrophones in linear arrays at low frequencies are inherent in the length of the array, number of hydrophones, difficulty in achieving free-field conditions, and lack of a suitable low-frequency projector. These challenges were addressed by the development of complementary methods to simultaneously measure the complex sensitivity in the acoustic data channels of hydrophone line arrays with digital telemetry systems. The voltage sensitivities and RC time constants of the array data channels were then estimated by nonlinear regression of calibration data to a simplified model of the acoustic data channel. The methods are demonstrated by the simultaneous calibration of 200 data channels of a digital hydrophone line array at 1/3 octave band center frequencies ranging from 1.2 to 400 Hz. The 95% confidence interval of the voltage sensitivity estimates was not more than 1 dB.

Preliminary analysis of acoustic intensity in a military jet noise field

Acoustic intensity measurements of the F-22A Raptor are analyzed as part of ongoing efforts to characterize the noise radiation from military jet aircraft. Data were recorded from a rig of microphones and an attached tetrahedral intensity probe at various locations to the sideline and aft of the aircraft. Numerical analysis of the intensity at one-third octave band center frequencies along various measurement planes and at a 23 m radius arc reveals the magnitude and directionality of the vector acoustic intensity. Differences in the trends for low-frequency and high-frequency data are discussed and, via a simple ray tracing back toward the source, interpreted in terms of source location and extent. [Work supported by ONR.]

The relationship between noise frequency components and physical, physiological and psychological effects of industrial workers

A corollary to industrialization and urbanization is a significant increase in noise levels. In many industrial settings, the noise levels are such that they are potential health hazards. There are many studies which suggest that prolonged exposures to high noise levels have a negative impact on various aspects of human physiology. However, not much work has been conducted in studying the effects of various noise frequencies in the industrial environment. This paper has made an attempt to identify various noise frequency components to which the workers of six major industries in Mysore (Karnataka State, India) are being exposed, and their effects on the physical, physiological, and psychological systems of the working community with respect to their noisy industrial environment. The study results showed that the sampled industrial workers were repeatedly being exposed to noise of dominant low- and mid-octave band center frequencies. It is found that symptoms such as 'eye ball pressure,' 'awakening from sleep,' 'pains in neck,' 'frequent ear vibration,' 'chronic fatigue,' 'repeated headache,' 'backache,' and 'repeated ear pulsation' are observed to be highly associated with low- and mid-octave band center frequency noise exposure among the sampled workers. Furthermore, among the major psychological symptoms identified to be associated with octave band center frequencies, it is evident that 'irritability' is highly associated with low- and mid-octave band noise frequency characteristics.

Noise exposed of the operators of combine harvesters with and without a cab

A considerable number of the combine harvesters in Turkey are rather old and used without cabs resulting in unhealthy working conditions for their operators. Noise is one of the detrimental factors. This study deals with determining and comparing the noise exposed on the operators of the combines with and without a cab used for wheat harvesting in Turkey. The sound pressure levels (dB) at octave band center frequencies (31.5–8000 Hz) and the sound levels (dBA) at the ear level of the operators were measured on 37 different combine harvesters with four different makes and different years from 1976 to 2001. Fifteen of the combines were without a cab, another 15 had original cabs while remaining seven combines had cabs mounted on them after manufacturing. The sound pressure levels were in a decreasing trend from the lower frequencies to higher frequencies. This trend was more noticeable for the combines with original cab and with the cab mounted after manufacturing compared to the ones without cab. The use of a cab was more effective in the insulation of the noise at the medium and higher frequencies, which have more bothersome effect compared to the lower frequencies. The sound pressure levels were 75–102 dB and 46–89 dB at low (31.5–500 Hz) and high (500–8000 Hz) frequencies for all combines, respectively. The sound pressure levels at the frequency of 4000 Hz at which the human ear is most sensitive were 6–17 dB lower for the combines with the cabs mounted after manufacturing and 9–28 dB lower for the ones with the original cabs compared to the combines without cab. The sound levels were 85–90, 81–83, and 76–81 dBA for the combines without cab, with cab mounted after manufacturing, and with original cab, respectively. The study showed that the use of a cab was useful in the insulation of the noise, particularly at higher frequencies. In addition, it protects the operator from the factors having detrimental effects on the working efficiency such as high temperature and dusty environment. The authors strongly recommend mounting of a cab on to the combines currently being used without a cab in rental system in Turkey to provide healthy working conditions for their operators.

Sound attenuation of dual-wall, fiberglass-lined, circular ducts with and without airflow

A major test program for measuring the sound attenuation characteristics of dual-wall, fiberglass-lined, circular ducts from six different duct manufacturers was completed. Octave band dynamic insertion loss values for octave band center frequencies from 63 to 8000 Hz were measured. The inside diameter of the ducts that were tested ranged from 12 to 48 in. Sound tests were conducted with and without airflow. Six airflow velocities from 1000 to 6000 fpm were examined. Regression analyses were conducted on the measured insertion loss values. Regression equations for the dynamic insertion loss values were developed that can be used to estimate the dynamic insertion loss of dual-wall, fiberglass-lined, circular ducts for zero flow and for duct airflow velocity from 1000 to 6000 fpm. The equations are valid for duct diameters from 12 to 72 in.

Relative contributions of passband and filter skirts to intelligibility of bandpass speech: Some effects of amplitude and context

Recently, Warren and Bashford [J. Acoust. Soc. Am. 106, L47–L52 (1999)] reported over 90% intelligibility for everyday sentences reduced to a 1/3-octave band (center frequency 1500 Hz, slopes 100 dB/octave, peak levels 75 dB). Surprisingly, when the bandpass sentences were partitioned using 2000-order FIR filtering, the rectangular 1/3-octave passbands had only 24% intelligibility, while the filter skirts separated by a 1/3-octave notch had an intelligibility of 83%, despite their severe spectral tilts. The present study found that when monosyllabic word lists were substituted for the sentences, the whole-band intelligibility was 26%, the passband 4%, and the filter skirts 16%. Intelligibility also was measured for 1/3-octave sentences with peak levels ranging from 85 down to 35 dB: The whole band intelligibilities ranged from 90% to 68%, and the filter skirt pairs each had three to four times the passbands’ intelligibility. These findings demonstrate the ability to compensate for extreme distortions of the spectral profile of speech. Hence, it is necessary to consider the contribution of frequencies outside the nominal passband as defined by the 3 dB downpoints along the filter slopes when dealing with filtered speech. [Work supported by NIH.]

Automated reverberation time experiments employing artificially generated noise

Using an IBM compatible PC, an inexpensive and simple method was developed to conduct acoustic absorption measurements in a reverberant chamber. The technique provided random noise distributed around 1/3 octave band center frequencies from 200 to 1000 Hz, through a D/A converter, to speakers within the chamber. Turbo-Pascal software was written to create a random noise file for each of the 1/3 octave bands. As a consequence, while a random noise signal was sent by the computer, that signal was identical for each experiment, for a specific 1/3 octave band. The noise signal, of 3-s duration, was programmed to increase to maximum intensity, and decrease to zero over a period of 25 μs, eliminating a steplike transient to the dynamic system at termination. The decaying noise was sampled 1000 times per second using an A/D converter, and the decay rate calculated. This technique was initiated with a keystroke and produced a sound-pressure level versus time plot file, allowing determination of the reverberation time and absorption coefficient of the chamber.

Correlation between excess attenuation and geometric or meteorological parameters

Extensive experimental measurements of sound propagation and vertical sound‐speed profiles over level agricultural terrain are presented. A high‐power speaker generating pure tones at approximately one‐third octave band center frequencies from 160–4000 Hz was used as the noise source. Sound levels were measured and recorded at ranges of 2, 125, 250, and 500 m from the source during various time periods of interest from 3–7 July 1990. Simultaneously, meteorological conditions were measured using a variety of tower mounted anemometers and temperature sensors. A total of 50 sets of 10‐min averaged data at each of 12 frequencies and 4 ranges was obtained. Temperature and velocity profiles were reconstructed using Monin‐Obukhov scaling theory. A statistical regression analysis to determine the correlation between excess attenuation and measurable geometric and meteorological parameters was completed. Sample measurements are presented and comparisons are made to the Daigle model [J. Acoust. Soc. Am. 65, 45–49 (1979)].

Gap detection in normal and hearing-impaired listeners.

Temporal resolution, estimated by measuring the minimum detectable gap (delta t ms) separating two successive signals, was assessed in five normal-hearing and five cochlear-impaired listeners. The signals were octave-band noises (400-800 Hz, 800-1600 Hz, and 2000-4000 Hz) presented in a background of continuous, broadband notched noise that was applied to eliminate unwanted spectral cues. Temporal resolution in all listeners showed systematic improvement with an increase in octave-band center frequency. Resolution in the hearing-impaired subjects was significantly poorer than normal regardless of whether the comparisons were made at equal sound pressure level or at equal sensation level.

The acoustic pressure field alongside KEMAR's head with a view towards in situ hearing aid tests

To simulate actual usage conditions, it is expected that the frequency response of heating aids will be measured on the head of the KEMAR manikin over the frequency range of 0.2 to 8 kHz. The acoustic pressure around the head can vary rapidly with both the frequency and the location. In order to compare and interpret the hearing aid response at various frequencies and locations on the head, it is necessary to precisely know the pressure variations. The amplitude and phase of the acoustic pressure were measured in increments ranging from 2 to 5 mm alongside KEMAR's head with frontal sound incidence. The acoustic driver was located in front of EMAR at a distance of 1.0 and ∼ 3.5 m from the ear canal axis. The test frequencies were the octave band center frequencies from 0.5 to 4.0 kHz and the third octave band center frequencies from 4.0 to 8.0 kHz. It will also be shown that pink noise of 6% and 29% at 6.3 and 8.0 kHz has a smoothing effect on the acoustic pressure variation with location.

Acoustic pressure field alongside a manikin's head with a view towards in situ hearing-aid tests.

The frequency responses of hearing aids measured in a free field differ from those measured on the head of a person or a manikin due to the scattering of the sound by the head and the torso. In order to compare and interpret the response of hearing aids located on the head at various frequencies it is necessary to know precisely the spatial pressure distribution. The amplitude and phase of the acoustic pressure were measured alongside a manikin’s head in increments ranging from 2 to 5 mm with frontal sound incidence . The acoustic driver was located in front of the manikin at distances of 1.0 and 3.5 m from the ear-canal axis. The test frequencies were the octave band center frequencies from 0.5 to 4.0 kHz and the third-octave band center frequencies from 4.0 to 8.0 kHz. The sound pressure level varies smoothly, as a function of position, alongside the head for frequencies equal to or less than 2.0 kHz. At frequencies equal to or greater than 4.0 kHz the pressure level changes rapidly with position. Particulary severe pressure minima were found to exist around the pinna at 6.3 and 8.0 kHz. The smoothing effect of test signals using pink noise of 6% and 29% bandwidth on the acoustic pressure variation alongside the head and behind the pinna is also shown.