Measurement of sound insulation with a sound level meter

The present technique for measuring the airborne sound insulation of walls and floors, involving measurements in 16 one-third octave bands, is tedious and expensive. The method provides more information than is needed for most purposes, and is more suited to research.Several investigators have proposed the measurement of the overall A-weighted sound level difference using a sound level meter, with a broad band source of white or pink noise. Consistent results have been obtained but their relation to accepted rating methods such as STC is rather empirical.The reference curves used for airborne sound insulation, i.e. STC and HPGW are very similar to the A weighting curve, and if the latter were adopted as the reference curve, there would be a firm theoretical basis for measurement with a sound level meter. Measurement of the difference between the linear sound level of a source of white noise, and the A weighted received level, would in practice be a test of the conformity to the A weighting curve of the transmission loss curve of the partition. Adverse deviations would show as a higher received level. Favourable deviations would have little effect.A study of practical walls and floors, taken from National Building Studies Research Paper 33, showed that there was good correlation between the sound level difference calculated as if it had been measured directly with a sound level meter, and a proposed rating method similar to ISO R717, but using the A weighting curve as the reference curve. Ninety-six per cent of results were within ±1 dB.The practical difficulties of achieving a reasonably flat transmitted spectrum, and of correcting for room absorption will reduce this precision, but bearing in mind the practical success of other short tests, the proposed test should provide a rapid test which is adequate for approval purposes.     

Statistical analysis from a sound level meter

Increasingly, and particularly for motorway noise, sound level meters are being used to estimate $\text{L}{}_{\mathrm{<mtext>10</mtext>}}$, the noise level just exceeded for 10 per cent of the time, by noting the meter readings at regular intervals and manually analysing the array of data so obtained. In this paper we describe a simple attachment to a sound level meter, which is intended to ease the operator's task in making such measurements and to minimise operator bias. Comparisons are made between the results of sound level meter measurements of three types of noise and the results obtained using the more conventional technique which employs a level recorder and statistical analyser.It is concluded that, at least for motorway noise, the sound level meter technique gives values of $\text{L}{}_{\mathrm{<mtext>10</mtext>}}$ and of $\text{L}{}_{\mathrm{<mtext>90</mtext>}}$ within 1 dB(A) of the values obtained by the normal method. Furthermore, it is probable that the technique will be useful for the measurement of other types of noise in statistical terms, but further investigations of accuracy are required.     

Blast noise classification with common sound level meter metrics

A common set of signal features measurable by a basic sound level meter are analyzed, and the quality of information carried in subsets of these features are examined for their ability to discriminate military blast and non-blast sounds. The analysis is based on over 120?000 human classified signals compiled from seven different datasets. The study implements linear and Gaussian radial basis function (RBF) support vector machines (SVM) to classify blast sounds. Using the orthogonal centroid dimension reduction technique, intuition is developed about the distribution of blast and non-blast feature vectors in high dimensional space. Recursive feature elimination (SVM-RFE) is then used to eliminate features containing redundant information and rank features according to their ability to separate blasts from non-blasts. Finally, the accuracy of the linear and RBF SVM classifiers is listed for each of the experiments in the dataset, and the weights are given for the linear SVM classifier.     

A fast automatic calibration system for a sound level meter in an anechoic room

A fast automatic calibration system for a sound level meter in an anechoic environment has been developed. The precise and fast generation of the constant frequency-independent acoustic pressure field and reduction of digital voltmeter readout to sound pressure level were achieved by a newly designed software algorithm, assuming the system linearity. The performance test justified the assumed linearity, and showed that the searching speed was sufficiently fast within the small error limit.     

Use of a digital voltmeter to measure the output of a sound level meter

The use of a digital voltmeter and associated computer program to measure the varying output of a sound level meter is discussed. The computer program converts the voltmeter readings into sound levels and calculates quantities such as $\text{L}{}_{\mathrm{<mtext>10</mtext>}}$, $\text{L}{}_{\mathrm{eq}}$, etc. Using the dc output of a sound level meter, the dynamic range is about 25 dB. This increases to at least 45 dB on the ac output. In general, values found for $\text{L}{}_{\mathrm{<mtext>10</mtext>}}$, $\text{L}{}_{\mathrm{eq}}$, etc. are within 1 dB of results obtained by other methods.     

Testing the accuracy of smartphones and sound level meter applications for measuring environmental noise

This paper reports on experimental tests undertaken to assess the capability of noise monitoring applications to be utilized as an alternative low cost solution to traditional noise monitoring using a sound level meter. The methodology consisted of testing 100 smartphones in a reverberation room. Broadband white noise was utilized to test the ability of smartphones to measure noise at background, 50, 70 and 90 dB(A) and these measurements were compared with true noise levels acquired via a calibrated sound level meter. Tests were conducted on phones using the Android and iOS platforms. For each smartphone, tests were completed separately for leading noise monitoring apps culminating in 1472 tests. The results suggest that apps written for the iOS platform are superior to those running on the Android platform. They show that one of the apps tested – SLA Lite – is within ±1 dB of true noise levels across four different reference conditions. The results also show that there is a significant relationship between phone age and its ability to measure noise accurately. The research has implications for the future use of smartphones as low cost monitoring and assessment devices for environmental noise.     

A note on the limitations in the use of the impulse precision sound level meter

The limitations in the use of the Impulse Precision Sound Level Meter for the assessment of the sound energy of recurrent impact noise have been investigated. For repetition rates above 30 impacts per second the meter reading and level predicted by an energy law agree to within ±2 dB. Below 30 impacts per second, for pulses with decay times in the range 2 to 28 msec, a simple empirical correction applied to the meter reading will produce results that follow the energy law. For decay times in excess of 28 msec simple corrections are not adequate and therefore the Impulse Sound Level Meter cannot be used in practice.     

A theoretical model for the evaluation of measurement uncertainty of a sound level meter calibration by comparison method in an anechoic room

A theoretical model for the evaluation of measurement uncertainty of a sound level meter (hereafter as `SLM') calibration by comparison method in an anechoic room was developed. Through this model, the uncertainties in the semi-automatic calibration and that in the full-automatic calibration were estimated for the recently developed SLM calibration system. In order to estimate the standard uncertainty against the SLM positioning, which is a significant uncertainty component, the sound field curve-fitting formulae were adopted. The validity of the curve-fitting method was proven by the similarity of the spatial distributions of radiation sound field produced by the plane circular piston source and that by the cone shape source. A linear equation was used to fit the measurements of the sound field distribution along the radiation axis. A quadratic equation was used to fit the measurements along the radial axis normal to the radiation axis. The fitting parameters gave us the sensitivity coefficients of the propagation of the uncertainty. In addition, one of the quadratic fitting parameters was found to be a positional uncertainty itself. Using this model, the expanded uncertainties were evaluated for the semi-automatic and full-automatic calibration of SLM.     

Long-life batteries for sound level meters

The use of rechargeable, nickel-cadmium batteries instead of the throw-away type is suggested for sound level meters. The advantages are saving of money, and greater convenience in the use of sound level meters on site visits. A simple method for recharging the batteries is discussed, which should be of interest to engineers and public health inspectors, as well as acoustic specialists.     

一种数字水准仪编解码技术的研究

鉴于数字水准测量时,线阵CCD采集信号使视场和分辨率受视距大范围变化的制约,水准仪编解码困难,提出一套新的编解码方案,采用混合编码,基于面阵CCD接收器,利用二维信号的优越性,解决视距太小不能满足条码样本数与视距太大图像分辨率低的矛盾,研究水准测量的技术核心问题,并通过算法优化,达到实时在线测量的要求。测试结果表明,测量范围为2m～10m时,测量绝对误差在-1mm～1mm之间,证明了所提出的编解码方法的正确性与可行性。     

Road traffic sound level distributions

A microprocessor-controlled instrument has been used to form a traffic noise level histogram with a resolution better than 0·1 dB per channel. The instrument calculates the mean, standard deviation, skewness and kurtosis of the distribution, along with L_N and L_eq values. The results of over 200 measurements, of 400 s duration, are shown to be in disagreement with predictions based on the commonly assumed Gaussian distribution. Skewness values ranging from +1 to ?1 have been observed, while kurtosis can exceed 4. Measurements taken near freely flowing, pulsed and banked traffic have been used to describe the “typical” distribution shape, it being observed that banked traffic noise has markedly different characteristics from other types of traffic. Simultaneous measurements taken on each side of the road have been related to the position of the traffic on the road and these data have led to a simple model for estimating the distribution shape and statistical parameters.     

智能型电位差计的设计与研究

介绍了采用先进的电子技术设计出新型高精度的电位差计,该食品电子线路用高稳定性可调电源取代传统电位差计的干电池和标准电池,用高灵敏度的电子检流计取代机械检流计,配上单片机,通过对可调电源的测量,转换成对被测物理量的测量,即可精确的测量出待测电动势值。     

浆氮电容式密度计及液位计的实验研究

采用电容式密度计及液位计来测量浆氮密度及液位的变化,使用整体屏蔽法对测量系统进行保护以减小寄生电容并提高其抗干扰能力。从理论上分析整体屏蔽法在提高测量系统性能上的作用,并通过实验加以验证。在实验中对密度计和液位计进行标定以提高其测量的精度,并使用密度计测量制备过程中浆氮密度的变化情况。     

Kurtosis corrected sound pressure level as a noise metric for risk assessment of occupational noises

Current noise guidelines use an energy-based noise metric to predict the risk of hearing loss, and thus ignore the effect of temporal characteristics of the noise. The practice is widely considered to underestimate the risk of a complex noise environment, where impulsive noises are embedded in a steady-state noise. A basic form for noise metrics is designed by combining the equivalent sound pressure level (SPL) and a temporal correction term defined as a function of kurtosis of the noise. Several noise metrics are developed by varying this basic form and evaluated utilizing existing chinchilla noise exposure data. It is shown that the kurtosis correction term significantly improves the correlation of the noise metric with the measured hearing losses in chinchillas. The average SPL of the frequency components of the noise that define the hearing loss with a kurtosis correction term is identified as the best noise metric among tested. One of the investigated metrics, the kurtosis-corrected A-weighted SPL, is applied to a human exposure study data as a preview of applying the metrics to human guidelines. The possibility of applying the noise metrics to human guidelines is discussed.     

Experimental investigation on the sound pressure level for a high thermal capacity burner during a running cycle

In many research or technical expertise studies the maximum noise level of a boiler is associated with the maximum thermal load of the burner. However, this type of air injected burners presents a complex running cycle with different functioning periods, where different parts (engine, fan, flame) of the burner are running separately or in the same time. In this study we are focused on the analysis, by experimental measurements, of the entire functioning cycle of a boiler by pointing out the noise differences and their importance when doing an experimental acoustical investigation. The entire 1/3 octave spectrum of the sound pressure level (SPL) was recorded during a complete running cycle by means of logging software associated to the sound meter. The sound equivalent level was calculated for each period of the running cycle and compared to the norms and with two theoretical prediction models that take into account the heating power and the boiler room volume. It was found that the most accurate data are obtained when the measurements are done in one-third octave. The maximum noise level was established to be not for the maximum thermal load period, but for the ventilation period of the boiler (before gas injection) with 82.1 dB at 125 Hz. A shut down delay was detected at the end of the cycle with 13 s for higher frequencies, due to the vibration of the boiler parts. Two 3D graphical representations point out the most important frequencies characterizing each running state of the burner. Compared to the noise curve (NC85) the minimum differences between the admissible values and the ones produced by the burner were found to be around 5.5 dB and therefore no acoustical treatment was needed. The results of the SPL prediction models matched the experimental data only for some of the boiler cycle periods and for only some of the frequencies. This type of detailed experiment investigation of the burner noise highlights the periods of the running cycle and the frequencies where the noise level requires acoustical treatment.     

Minimal input models for sound level prediction in fitted enclosed spaces

Highly advanced computer models for the prediction of sound fields in rooms are now available. However, these tools are complex and require a skilled acoustician to use effectively and hence there is a need for more simpler models. A simple model needs to be accurate and quick to use, but most importantly should require a minimum amount of input data to construct the model. This is only achievable if the scope of the model is reduced to one or two acoustic parameters. Three simple models were investigated two empirical based formulae and a geometric acoustic model. The models were validated in six configurations of an experimental room simulating a textile workshop and two real engineering workrooms. It was found that all the models executed near instantaneously, but the obtainable prediction accuracy and consistency was proportional to the amount of input data. The models are now available on the Web, running directly inside Netscape or Internet Explorer.     

Estimation of the long term average sound level from hourly average sound levels

It is shown how to estimate the long-term average sound level, L_AeqLT (for free flowing road traffic) from measurements of the hourly A-weighted equivalent sound level, L_Aeq1h. To estimate the parameters of the model which describe noise emission and attenuation, concurrent measurements of L_Aeq1h at two distances from the considered road are needed. A semi-empirical formula is derived for L_AeqLT approximation. Also the uncertainty of this approximation is given as a function the distance from the road and receiver height.     

Accuracy in the measurement of sound levels in situ with sound level meters

Differences among readings on different sound level meters when measuring the same signal have been studied with the object of specifying the measuring accuracy in in situ measurements. Three sound level meters of different origins have been used, and five kinds of noises have been measured in five places of different acoustical characteristics. The measurements were performed by three experienced operators. Results of the standard deviation of the measurements made by different operators using different SLM are supplied.     

Estimation of annoyance due to low level sound

The concept of sound character is introduced as a physical attribute responsible for any systematic differences in annoyance due to different sounds at the same A-weighted equivalent sound level. It is thought that this sound character is more important at low sound levels than at high ones. A pilot experiment with refrigerator sounds indicated a clear effect of sound character. In particular, sharp onsets were shown to worsen the character of such sounds.