SummaryStandards for measuring room acoustic parameters, such as ISO 3382, in manyc ases do not, or only partially, specify the requirements that ameasured impulse response should meet to allowcalculation of acertain parameter.A mong other things, it is often left to the user of the standard to findapractical interpretation of the time infinity that appears in the theoretical formulas defining the parameters. Hence, the parameter value may depend on the decay range and measurement time. Under the most adverse conditions this may lead to variations in the calculated parameter values larger than the Just Noticeable Difference (JND).U sing the suggested ISO 3382 'infinite' integration time limits for some parameters and otherwise the crosspoint of decay line and noise level as the 'infinite' integration time limit for the other parameters, the influence of the decay range on the calculated parameter values is investigated. This is done for all ISO 3382-1 parameters:

The most widely recognized objective stage acoustic parameters are the Early Support (ST early ) and Late Support (ST late ). In these parameters the early and late reflected sound energy is measured within a certain time interval. Different time interval limits have been proposed for the stage acoustic parameters but there is no agreement on the preferable limits. There is a growing interest to measure stage acoustic parameters at various source to receiver distances. In this paper the influence of perceptual and architectural parameters, synchronicity, source to receiver relationship and the measurement system on stage acoustic parameters is discussed. Based on existing and new insights an optimization and extension of the ST parameters is proposed such that they can be measured at any distance between source and receiver using the most appropriate time interval limits. Theoretical assumptions were checked and confirmed based on systematic analyses of measured results for different concert hall stages with various conditions and various source to receiver distances. SummaryThe most widely recognized objective stage acoustic parameters are the Early Support (ST early )and Late Support (ST late ). In these parameters the early and late reflected sound energy is measured within acertain time interval. Different time interval limits have been proposed for the stage acoustic parameters butthere is no agreement on the preferable limits. There is agrowing interest to measure stage acoustic parameters at various source to receiver distances. In this paper the influence of perceptual and architectural parameters, synchronicity,source to receiver relationship and the measurement system on stage acoustic parameters is discussed. Based on existing and new insights an optimization and extension of the ST parameters is proposed such that theycan be measured at any distance between source and receiveru sing the most appropriate time interval limits. Theoretical assumptions were checked and confirmed based on systematic analyses of measured results for different concert hall stages with various conditions and various source to receiverdistances. PACS no. 43.20.El, 43.55.Br,43.58.Gn 776 ©S.Hirzel Verlag · EAA Wenmaekers et al.:M easurements of stage acoustic parameters ACTA ACUSTICA UNITED WITH ACUSTICA Vol. 98 (2012)

Stage acoustic parameters aim to quantify the amount of sound energy reflected by the stage and hall boundaries and the energy decay over time. In this research, the effect of orchestra presence on parameter values is investigated. The orchestra is simulated by dressed mannequins, which have been compared with humans with respect to acoustic properties. Impulse response measurements were performed in a concert hall, a theatre, a rehearsal room, and in two orchestra pits. Conditions were empty stage floors, stage floors with music stands and chairs only, and floors occupied by the mannequin orchestra. Results show that the direct and reflected sound levels and the energy decay are significantly affected by the orchestra compared to an empty stage or a stage with chairs and stands only. Both the direct sound and early reflected sound levels are reduced by the orchestra with the distance. The late reflected sound level is reduced considerably more than can be expected based on Barron's revised theory. It can be concluded that measurements on a stage without the orchestra being present results in significant differences. A practical method is presented to perform a "musician friendly" stage acoustic measurement with a real orchestra.

Microwave cavity resonance spectroscopy is introduced and demonstrated as a new approach to investigate the generation of acoustic waves by a pulsed radio-frequency driven atmospheric-pressure plasma jet. Thanks to recent advancements in the diagnostic method, the lower detection limit for pressure changes in air is ∼0.3 Pa. Good agreement with conventional pressure transducer measurements with respect to the temporal evolution, the pressure amplitude and the spectral response is found. Fourier analysis revealed that the acoustic waves induced by the plasma can most likely be attributed to standing waves in the discharge geometry. Additionally, the plasma-induced acoustic waves of a few (tens of) Pa are proposed as an active mechanism in plasma medicine.

To achieve a preferable sound field in traditionally shoebox-shaped sports halls, the sound absorbing material is often applied in the upper part of the hall. The applicability of predicting the acoustics of sports halls by three different acoustic calculation methods is investigated: a diffuse field method, a geometrical acoustics method and a full wave-based method. The predicted reverberation time and sound pressure level are compared to measured data for two sports halls in the low frequency range up to the 630 Hz 1 3 octave band. From the three methods, results from the wave-based method agree best with the measured results. Results indicate the importance of the chosen material properties in the prediction methods used. Sound pressure levels resulting from the diffuse field method are comparable with results from the other prediction methods, but the reverberation time prediction is not reliable using this method.

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A substantial amount of research has been devoted to producing a calculation model for air absorption for pure tones. However, most statistical and geometrical room acoustic prediction models calculate the reverberation time in full octave bands in accordance with ISO 3382-1 (International Organization for Standardization, 2009). So far, the available methods that allow calculation of air absorption in octave bands have not been investigated for room acoustic applications. In this paper, the effect of air absorption on octave band reverberation time calculations is investigated based on calculations. It is found that the approximation method, as described in the standard ANSI S1.26 (American National Standards Institute, 1995), fails to estimate accurate decay curves for full octave bands. In this paper, a method is used to calculate the energy decay curve in rooms based on a summation of pure tones within the band. From this decay curve, which is found to be slightly concave upwards, T 20 and T 30 can be determined. For different conditions, an effective intensity attenuation coefficient m B;eff for the full octave bands has been calculated. This m B;eff can be used for reverberation time calculations, if results are to be compared with T 20 or T 30 measurements. Also, guidelines are given for the air absorption correction of decay curves, measured in a scale model.

Some room acoustic parameters require the sound power of the sound source. The Sound Strength G uses the free field sound pressure levelat10meters distance as areference value. Speech intelligibility parameters likethe Aweighted Speech Level, L p,A,S,4m ,and the Speech Transmission Index, STI, can require an absolute source level defined at 1mdistance from the sound source. The Early and Late Support parameters use the sound levelat1m distance as areference level. In this paper,all proposed methods to obtain the sound power levelfor room acoustic applications are investigated, using various omnidirectional sound sources with adodecahedron shape containing 12 loudspeakers. It is shown that, for octave bands 250 to 8,000 Hz, the sound power can be determined with 0.8 dB uncertainty when using precision methods (diffuse field, intensity or free field). Alternative laboratory calibration methods, that only measure in as ingle plane of the sound source, showd eviations up to 2dBp er octave band. Different stepwise rotational averages, used in such as ingle plane free field method, have been investigated. It can be concluded, that the uncertainty is significantly reduced only when using 12.5 degree steps (ISO 3382-1)a nd when using equal-angular rotations with 5o r7s teps. Furthermore, the uncertainty of insitu calibration has been investigated. Acomparison of results from different researchers shows that acorrection factor should be applied to correct the in-situ calibration for its deviation from the laboratory calibration. Foreach calibration method the uncertainty is presented. Results showthat some methods might be sufficiently accurate to be able to measure single number ratings for G, ST, L p,A,S,4m and STI with an uncertainty in the order of magnitude of 1JND, provided that no other measurement errors are introduced in the measurement chain. PACS no. 43.55.Br,43.55.Mc, 43.58.Vb, 43.58.Fm Received07July 2014, accepted 05 August 2015.sured in the free field at ac ertain distance. Also, when determining speech intelligibility parameters, like STI,the signal to noise ratio is determined based on aratio of absolute sound pressures (following ISO 16268-16 [2], only if background noise is taken into account, and following ISO 3382-3 [3], for all measurements in open plan offices). Following ISO 3382, all of these room acoustic parameters should be determined using an omnidirectional sound source. Ac ertain deviation from omnidirectionality is allowed and the deviation limits are giveninthe standard.Lundeby et al.[4] asked 8different teams to determine room acoustic parameters for 10 source-receiverc ombinations in a1,800 m 3 auditorium. He found astandard deviation for the levelp arameter Sound Strength G of only 0.2 to 0.3 dB for the octave bands 125, 1,000 and 4,000 Hz. These results would suggest that G can be measured with very high accuracy, even when using av ariety of loudspeaker types (a single loudspeaker in abox, acube with six loudspeakers and ad odecahedron with twelvel oudspeakers). Unfortunately,intheir...