Noise Control of a Domestic Refrigerator Using a Natural Material Based Composite

This paper studies the acoustics of a frost free three door domestic refrigerator. Then, as a case study, the radiated noise reduction in the refrigerator using a natural material base composite is presented. Composites manufactured out of Jute, which is a plant fiber abundantly and cheaply available in India and Bangladesh are used in the noise reduction in the refrigerator. Mostly in this work, composites made out of felts of jute were used as barriers for noise control of the refrigerator. Measured acoustical, thermal and physical properties of various jute composites are reported. Noise sources in the refrigerator were characterized using sound intensity method and sound pressure level measurements. It is found that the compressor and the evaporator fan are the predominant noise sources. The jute composite treatment done to the refrigerator shell around the evaporator fan reduced the refrigerator noise level by 5 dB and improved its measured sound quality metrics without affecting the cooling performance of the refrigerator.     

MP3 player listening sound pressure levels among 10 to 17 year old students

Using a manikin, equivalent free-field sound pressure level measurements were made from the portable digital audio players of 219 subjects, aged 10 to 17 years (93 males) at their typical and "worst-case" volume levels. Measurements were made in different classrooms with background sound pressure levels between 40 and 52 dBA. After correction for the transfer function of the ear, the median equivalent free field sound pressure levels and interquartile ranges (IQR) at typical and worst-case volume settings were 68 dBA (IQR?=?15) and 76 dBA (IQR?=?19), respectively. Self-reported mean daily use ranged from 0.014 to 12 h. When typical sound pressure levels were considered in combination with the average daily duration of use, the median noise exposure level, Lex, was 56 dBA (IQR?=?18) and 3.2% of subjects were estimated to exceed the most protective occupational noise exposure level limit in Canada, i.e., 85 dBA Lex. Under worst-case listening conditions, 77.6% of the sample was estimated to listen to their device at combinations of sound pressure levels and average daily durations for which there is no known risk of permanent noise-induced hearing loss, i.e.,?≤ 75 dBA Lex. Sources and magnitudes of measurement uncertainties are also discussed.     

Assessment of Traffic Noise Pollution in Burla Town,India; An Inclusive Annoyance Study

Noise pollution is one of the major public health problems in urban areas throughout the world. Noise is unwanted sound which produces undesirable problems in day to day life of human being (e.g., physiological and psychological problems). Rapid increase of the industrialization, urbanization, infrastructure, volume of motor vehicles, and increase in the road networks brought noise pollution to the highest level of disaster in a current situation. In urban areas, road traffic noise plays commanding role among all noise sources and affects the exposed inhabitants. The present work is done to evaluate and assess the traffic noise and its effects in Burla town. Burla, Vidyanagari of Odisha, is an emerging town in India, as it hosts national level of teaching and research institutions like IIM Sambalpur, a medical college- cum-hospital (VIMSAR), a technical university (VSSUT) and Sambalpur University. In last two decade, the road traffic volume has been increased and is facing severe noise pollution to its inhabitants. Noise pollution assessment was made at different locations of the town. This study unveiled the dismal state of noise pollution in the town. Noise contour maps were drawn to visualize the noise level at the traffic and its surroundings. The numbers of hearing impaired patients in different hospitals of the locality are increasing. That shows grim picture of the situation. Regression equations were established taking noise levels with percentage of highly annoyed people during study indicates strong correlation.     

城市历史街区声景观及视听感知实验研究*

城市历史街区声景观是空间环境的重要内容,直接影响人们的感知体验。论文以济南老城泉水街区为例研究城市历史街区的声景观并进行视听感知实验。结果表明,现场声元素喜好度显著高于实验室单听评价。鸟鸣、鹅叫声在现场和实验室评分都较高,大流速流量水景声在现场评分高而实验室评分低,小流速流量水景声在实验室和安静环境中评分较高,在吵闹环境中评分较低;声环境满意度与视觉景观优美度、声源组成喜好度、安静度之间存在显著正相关关系,与环境声压级存在显著负相关关系,但当较高的环境声压级主要由水声贡献时,声环境满意度明显提高;应从提高景观优美度、优化声源组成、降低环境声压级等方面进行声景观设计。论文为声元素喜好度和声环境满意度研究提供参考。     

基于声舒适度的地下餐饮空间声级阈研究

为了确定地下餐饮空间内使用者主观声舒适度可接受时的声压级阈值范围,本文选取典型的封闭式地下餐饮空间作为研究对象,采用实地问卷与实测相结合的方法进行调研。结果表明:地下餐饮空间内整体环境舒适度主观评价偏低,声舒适度评价与整体环境舒适度评价具有强相关性,因此声环境是影响地下餐饮空间内整体环境舒适度的因素。在影响主观声舒适度评价的客观指标中,混响时间可不作为主要影响因素考虑;而背景噪声声压级是影响地下餐饮空间内声舒适度主观评价的重要指标。使用者声舒适度为可接受时,地下餐饮空间内背景噪声声压级阈值为70-75 dB(A)。     

Nuclear level densities in <Superscript>47</Superscript>V, <Superscript>48</Superscript>V, <Superscript>49</Superscript>V, <Superscript>53</Superscript>Mn,and <Superscript>54</Superscript>Mn from neutron evaporation spectra

The spectra of neutrons from the (p, n) reactions on ⁴⁷Ti, ⁴⁸Ti, ⁴⁹Ti, ⁵³Cr, and ⁵⁴Cr nuclei were measured in the proton-energy range 7–11 MeV. The measurements were performed with the aid of a fast-neutron spectrometer by the time-of-flight method over the base of the EGP-15 tandem accelerator of the Institute for Physics and Power Engineering (IPPE, Obninsk). Owing to a high resolution and a high stability of the time-of-flight spectrometer used, low-lying discrete levels could be identified reliably along with a continuum section of neutron spectra. An analysis of measured data was performed within the statistical equilibrium and preequilibrium models of nuclear reactions. The relevant calculations were performed by using the exact formalism of Hauser-Feshbach statistical theory supplemented with the generalized model of a superfluid nucleus, the back-shifted Fermi gas model, and the Gilbert-Cameron composite formula for the nuclear level density. The nuclear level densities for ⁴⁷V, ⁴⁸V, ⁴⁹V, ⁵³Mn, and ⁵⁴Mn were determined along with their energy dependences and model parameters. The results are discussed together with available experimental data and recommendations of model systematics.     

基于大能量火花放电的枪声模拟系统设计*

为准确模拟某型枪械实弹射击枪声,设计了一种基于大能量火花放电的枪声模拟系统,理论分析和仿真验证了系统工作原理,并对所模拟枪声的声级以及时域和频域特性进行了试验测试。仿真和测试结果表明:点火电容放电所辐射的电场击穿高能电极空气间隙,可有效控制储能电容组火花放电模拟枪声;模拟与真实枪声的声级误差约为-2.1~5.8 d B(A),标准差为1.974 dB(A),模拟与真实枪声的时域信号随时间增加均以指数形式迅速减小且频谱分布规律一致;模拟与真实枪声信号在时域进行相关运算后存在着明显的相关峰,二者有较好的相似性。     

Characterisation of valves as sound sources: Fluid-borne sound

The sound pressure level in receiving rooms, caused by taps at the ends of pipe systems, is considered. The structure-borne sound power, from the pipes to the supporting wall, was obtained from intensity measurement of the fluid-borne sound power of the tap. The fluid-borne sound power is combined with a ratio of structure-borne sound power to fluid-borne sound power, obtained from laboratory measurements of similar pipe assemblies. Alternatively, a reception plate method is proposed, which avoids the necessity for intensity measurements. The structure-borne power into walls, to which the pipe work is attached, provides input to the standard building propagation model, which yields the predicted sound pressure level in the adjacent room.     

生态水体景观视觉影响下道路交通声评价的实验研究

采用里克特5级量表(1:非常不舒适;5:非常舒适)实验研究了不同声级的道路交通声评价在生态水体景观视觉影响下的规律。分析发现:与单听觉测试条件相比,生态水体景观将道路交通声级与声评价的相关系数由-0.91降低至-0.81~-0.57,其中30 dBA的道路交通声评价值下降0.13~0.68,而70 dBA的道路交通声评价值升高0.10~0.22。在一定声级范围内景观要素对道路交通声评价的影响不同:人工要素比自然要素影响下的道路交通声评价值高0.33/10 dBA;自然水体远景比近景影响下的道路交通声评价值高0.33/10 dBA;人的活动要素比动物活动要素影响下的道路交通声评价值高0.28/10 dBA,      

Noise generation by vacuum cleaner suction units. Part III. Contribution of structure-borne noise to total sound pressure level

Noise emitted by a vacuum cleaner suction unit consists of airborne and structure-borne noise. The airborne noise is generated mainly by the turbo blower and the structure-borne noise is generated mainly by the driving electric motor. The structure-borne noise depends on the suction unit design and on operating conditions, and is especially distinct at partial flow rates when rotating stall and surge appear. Among geometrical parameters, the stator of the blower and the electric motor, or metal shield if any, have the greatest effect on the structure-borne noise. Therefore, in this part of the paper, the effects of vibrations of the electric motor structure on the noise characteristics have been measured and analysed at the design and off-design operation. The contribution of structure-borne sound to the total sound pressure level becomes relatively less important at higher flow rates and with a vaned diffuser built-in the blower.     

上下并联轴流风机室外机气动声学预测模型

本文基于CFD模拟方法,分析了空调器室外机上下并联轴流风机系统噪声源分布,建立了室外机气动声学预测方法.研究发现,上下并联轴流风机系统由宽频和离散频率噪声组成,宽频噪声是影响室外机噪声总声压级的重要因素.涡声分析表明,涡脱落噪声是宽频噪声的主要影响因素.基于CFD的叶片尾缘涡脱落噪声预测方法计算得到宽频声压误差为2 dB,考虑离散频率影响时,室外机A计权总声压级预测误差小于2 dBA.基于CFD的点源时域预测模型,捕捉到了上下并联轴流风机系统的离散频率噪声峰值,且在上下叶轮前二阶谐波处预测值与实验值吻合较好.     

Acceptable range of speech level for both young and aged listeners in reverberant and quiet sound fields

The speech level of verbal information in public spaces should be determined to make it acceptable to as many listeners as possible, while simultaneously maintaining maximum intelligibility and considering the variation in the hearing levels of listeners. In the present study, the universally acceptable range of speech level in reverberant and quiet sound fields for both young listeners with normal hearing and aged listeners with hearing loss due to aging was investigated. Word intelligibility scores and listening difficulty ratings as a function of speech level were obtained by listening tests. The results of the listening tests clarified that (1) the universally acceptable ranges of speech level are from 60 to 70 dBA, from 56 to 61 dBA, from 52 to 67 dBA and from 58 to 63 dBA for the test sound fields with the reverberation times of 0.0, 0.5, 1.0 and 2.0 s, respectively, and (2) there is a speech level that falls within all of the universally acceptable ranges of speech level obtained in the present study; that speech level is around 60 dBA.     

基于薄膜编码超表面的宽频超薄声散射体

该文提出了一种基于薄膜编码超表面的宽频超薄声散射体。利用附加质量块的薄膜和空气腔组成的薄膜结构构建了反射声波相位差接近180°的两种共振单元。将两种共振单元按照一定的顺序进行排列,可以组成深亚波长尺寸下的声学超表面。所构建的声学超表面可以产生宽频有效的散射声场。通过有限元仿真软件对多个频率的近场散射声场分布、远场声指向性和扩散系数进行了仿真计算,仿真结果显示,该散射体可以高效地散射入射声波,并且散射效果在一定的频率范围内是宽频有效的。     

Chinese speech intelligibility at different speech sound pressure levels and signal-to-noise ratios in simulated classrooms

The speech intelligibility in classroom can be influenced by background-noise levels, speech sound pressure level (SSPL), reverberation time and signal-to-noise ratio (SNR). The relationship between SSPL and subjective Chinese Mandarin speech intelligibility and the effect of different SNRs on Chinese Mandarin speech intelligibility in the simulated classroom were investigated through room acoustical simulation, auralisation technique and subjective evaluation. Chinese speech intelligibility test signals recorded in anechoic chamber were convolved with the simulated binaural room impulse responses, and then reproduced through the headphone by different SSPLs and SNRs. The results show that Chinese Mandarin speech intelligibility scores increase with increasing of SSPLs and SNRs within a certain range in simulated classrooms. Chinese Mandarin speech intelligibility scores have no significant difference with SNRs of no less than 15 dBA under the same reverberation time condition.     

High-g Shocking Testing of the <i>Martlet</i> Wireless Sensing System

This article reports the latest development of a wireless sensing system, named Martlet, on high-g shock acceleration measurement. The Martlet sensing node design is based on a Texas Instruments Piccolo microcontroller, with clock frequency programmable up to 90 MHz. The high clock frequency of the microcontroller enables Martlet to support high-frequency data acquisition and high-speed onboard computation. In addition, the extensible design of the Martlet node conveniently allows incorporation of multiple sensor boards. In this study, a high-g accelerometer interface board is developed to allow Martlet to work with the selected microelectromechanical system (MEMS) high-g accelerometers. Besides low-pass and high-pass filters, amplification gains are also implemented on the high-g accelerometer interface board. Laboratory impact experiments are conducted to validate the performance of the Martlet wireless sensing system with the high-g accelerometer board. The results of this study show that the performance of the wireless sensing system is comparable to the cabled system.     

Investigation of Chinese word recognition scores of children in primary school classroom with different speech sound pressure levels

Chinese word recognition (CWR) test was conducted by grades 3 and 5 children under the different conditions of reverberation time (RT), background noise level (BNL) and speech sound pressure level (SSPL) in three primary-school classrooms. The CWR scores and signal to noise ratios (SNRs) have been obtained at listening positions. Results show that the CWR score for grades 3 and 5 children increases with increase of SSPL, decrease of RT or increase of age, but it decreases with increase of BNL under the same conditions. For a mixed noise of 56 dBA (speech-spectrum-like noise and ambient noise), the CWR scores in the classroom for grades 3 and 5 children reach a peak at SNR of 15–20 dBA under the same RT and age of children condition. For the natural ambient noise, the CWR score for grades 3 and 5 children gradually increases with increase of the SNR. The high SSPL could not guarantee good CWR for children in classroom, which also depends on RT and BNL in classroom. When the classroom has long RT or high BNL, the increase of SSPL would not be necessarily to achieve better CWR. The novelty of the present study is to further evaluate and confirm the results under environments of real classrooms (not simulated room in laboratory).     

Sound level variation findings for pianissimo and fortissimo phonations in repeated measurements

Ten vocally untrained female university students vocalized /a:/ at five given pitches within the average female speaking range (196, 220, 262, 330, and 396 Hz) as softly as possible (pianissimo) and as loudly as musically acceptable (fortissimo). To study the repeatability of voice range profile (sound level) measurement, the procedure was repeated 10 times in each of the five sample sessions during the day, in connection with vocal loading that included five oral readings (45 min each), 15-min pauses, and a lunch break (45 min). A sound level meter specially designed for voice range profile measurement was used. The effect of the loading was seen on the mean sound level changes and intraindividual variation on SDs. The difference between the first phonation and best performance indicates significance of the repetition of the measurement. The sound level averaged across the pitches rose significantly during loading. The intraindividual SD varied between 3 and 4 dBA according to pitch and loudness, and the sound level difference between the first phonation and best performance was 5 dBA in pianissimo and 7 dBA in fortissimo     

Potential solutions to improved sound performance of volume based lightweight multi-storey timber buildings

Lightweight building systems in general suffer from poor sound insulation, especially in the low frequency region. Since no reliable mathematical models that can predict the impact sound pressure level exists, the lightweight building design is to a high extent based upon previous experience and upon measurements. A special difficulty is related to experimental measurements since the variation among identical units must not be neglected. A modern volume based lightweight wooden building concept has here been tested by numerous well controlled measurements, in laboratory as well as in more field like conditions. The volume construction technique offers new possibilities and challenges to improve sound insulation in light weight timber construction. The main purpose was to investigate how different constructional solutions in the floor, like plaster board, mineral wool, elastic glue, dividing board, floating floor etc., affect the sound insulation. Many of the tested modifications resulted in only marginally changed impact sound pressure level but parameters that substantially can improve the sound insulation were found in using elastic glue to mount the floor boards, to install extra board layers and to use floating floors.