IMPROVED LOW-FREQUENCY IMPACT INSULATION CLASS MEASUREMENTS BASED ON COMPARISON TECHNIQUES

In today’s world, noise pollution is growing as a major concern and it is becoming more and more difficult to find quiet places. But when the problem escalates to the extent that people are annoyed with loud noises even in their apartments, it becomes an alarming issue for engineers. Around the world, cities have defined some basic performance requirements for buildings, and isolation of residents from noise is one of the cardinal performance requirements. In the United States, building codes use the Impact Insulation Class (IIC) rating to characterize the performance of floor/ceiling assemblies. This method uses the response measured in one-third octave (OTO) bands from 100 Hz to 3150 Hz and compares it with a reference curve to obtain the rating. However, this standard suffers from some limitations. The standard assumes the receiving rooms in the testing labs to be modally dense for all frequency OTO bands under consideration but the labs usually have a non-modally dense acoustic environment for low-frequency bands. Due to this, different labs give different results for the same assembly, thereby making it difficult to get reproducible IIC measurements. With the method proposed in this report, the room contribution for these low-frequency OTO bands could be removed, paving a way to obtain more reproducible IIC measurements. This room contribution is removed by using a reference calibration assembly with a known sound power and employing the comparison technique. The comparison of measurements of the reference assembly in the test labs with the known sound power gives a calibration factor, defining how the room contribution affects the measurement data. These calibration factors are then used for the actual assemblies to get to the “true” sound power, unbiased by the effects of room contribution. This report uses a simply supported rectangular plate as a reference assembly and analytically calculates the mode shapes, mobility, and sound power radiation. These analytical predictions are compared with the experimentally obtained values. This reference assembly is then used in a reverberation room to characterize the room contribution in one-third octave bands. The reference assembly is then replaced by a new, unknown assembly, and the “true” sound power information is predicted using the proposed method

ALTERNATIVE METHOD FOR LOW FREQUENCY IMPACT SOUND MEASUREMENT FOR BUILDING FIELD TESTS

What do high heels, dog nails, and dragging furniture have in common? They are all frequent sources of noise pollution and annoyance in multi-story buildings. Building codes exist to control and mitigate such noise, but these codes are outdated and fail to protect the residents against noise annoyance. Footstep noise is still the number one cause of complaints among the residents. The impact performance of floor-ceiling assemblies is characterized using a single-number rating called the Impact Sound Rating (ISR). A standard tapping machine is used in pre-defined locations on the floor and the radiated Sound Pressure Level (SPL) is measured in the receiving room downstairs to calculate the ISR rating. This measurement method has a lot of variabilities that cause problems for the residents or the acoustical consultants. The force from the tapping machine depends on the floor compliance but it is not measured for the test. An FRF-like measurement is required to account for this force difference and compare the performance of different assemblies. Additionally, a non-diffuse sound field exists in rooms at low frequencies that cause high variation in the test results based on the microphone positions. In this work, a new measurement method is proposed that provides an FRF-like (without consideration of phase) performance using a ratio of autopower spectra (RPF) and shows an improved reproducibility in the low-frequency non-diffuse sound field region. A 1 – 1.5 dB measurement variability is expected as compared to 4 – 10 dB variability observed with the existing method. The guidelines to conduct the proposed test are detailed in this work

Does 3-Day Course of Oral Amoxycillin Benefit Children of Non-Severe Pneumonia with Wheeze: A Multicentric Randomised Controlled Trial

WHO-defined pneumonias, treated with antibiotics, are responsible for a significant proportion of childhood morbidity and mortality in the developing countries. Since substantial proportion pneumonias have a viral etiology, where children are more likely to present with wheeze, there is a concern that currently antibiotics are being over-prescribed for it. Hence the current trial was conducted with the objective to show the therapeutic equivalence of two treatments (placebo and amoxycillin) for children presenting with non-severe pneumonia with wheeze, who have persistent fast breathing after nebulisation with salbutamol, and have normal chest radiograph.This multi-centric, randomised placebo controlled double blind clinical trial intended to investigate equivalent efficacy of placebo and amoxicillin and was conducted in ambulatory care settings in eight government hospitals in India. Participants were children aged 2-59 months of age, who received either oral amoxycillin (31-54 mg/Kg/day, in three divided doses for three days) or placebo, and standard bronchodilator therapy. Primary outcome was clinical failure on or before day- 4.We randomized 836 cases in placebo and 835 in amoxycillin group. Clinical failures occurred in 201 (24.0%) on placebo and 166 (19.9%) on amoxycillin (risk difference 4.2% in favour of antibiotic, 95% CI: 0.2 to 8.1). Adherence for both placebo and amoxycillin was >96% and 98.9% subjects were followed up on day- 4. Clinical failure was associated with (i) placebo treatment (adjusted OR = 1.28, 95% CI: 1.01 to1.62), (ii) excess respiratory rate of >10 breaths per minute (adjusted OR = 1.51, 95% CI: 1.19, 1.92), (iii) vomiting at enrolment (adjusted OR = 1.49, 95% CI: 1.13, 1.96), (iv) history of use of broncho-dilators (adjusted OR = 1.71, 95% CI: 1.30, 2.24) and (v) non-adherence (adjusted OR = 8.06, 95% CI: 4.36, 14.92).Treating children with non-severe pneumonia and wheeze with a placebo is not equivalent to treatment with oral amoxycillin.ClinicalTrials.gov NCT00407394

Measuring the force due to standard tapping machine and floor impedance for ASTM standards

The standard tapping machine used for the ASTM test standards on impact noise insulation does not have any provision to measure input force. A modified tapping machine with a force transducer was used for eight different residential floors, revealing that the force injected into the structure varies by approximately 37 dB. This variation is due to the combination of the tapping machine and the floor compliance. On one of the floors for the same test, the force injected due to the tapping machine varies by 2.6 dB for a single hammer. The floor impedance was also measured using accelerometers and the lightweight floor impedance is about 40 dB lower than heavyweight floors. The impedance varies by 20 - 30 dB throughout the frequency spectra for the four light-weight joist-framed floors. The authors propose that this injected force be measured, and an injected-to-radiated energy ratio be used to compare various floor-ceiling assemblies

Predicting sound power response from a simply supported rectangular panel for impact insulation class (IIC) test

Impact Insulation Class (IIC) test defined by ASTM is widely used to characterize the response and performance of floor/ceiling assemblies. However, this method suffers from some limitations at low-frequencies. Because of the non-modally dense behavior of the receiving room in the lowest third-octave band, 100 Hz, the room correction lacks repeatability across different laboratories. This results in poor reproducibility of IIC results from lab-to-lab. In this method, we are proposing to use a test panel of known sound power to calibrate the receiving room, foregoing the requirement of a diffuse field. The known sound power of the test panel comes from analytical calculations for simply supported rectangular plates and the prediction is compared with the experimental response measured using an intensity probe

Improved low-frequency sound measurements for impact insulation class (IIC) rating using a comparison technique

In multistory buildings, the isolation of sound from floor to ceiling is a major concern. The building codes use an impact insulation class (IIC) rating defined by ASTM to characterize the acoustical performance of floorâ–“ceiling assemblies due to impacts. The measurement process defined in this standard has repeatability and reproducibility limitations due to low-frequency, non-diffuse sound fields in receiving rooms. A comparison method is proposed in this article that uses a reference sample with known sound power to calculate the room or path contribution to the measured sound pressure level, which is then used to calculate the sound power of the floorâ–“ceiling assembly. The proposed method is tested for a small-scale hardboard plate, and the test results are within 1 to 2 dB of baseline sound power values. A simply supported plate used as the reference plate showed MAC values higher than 0.9 for analytical and experimental mode shapes. The analytical natural frequencies are within 1% to 2% of experimental frequencies and analytical sound power values are within 1-2 dB of experimental data. This study showed that for a small-scale assembly, the new methodwas able to characterize the room contribution within 1 to 2 dB

Modeling a representative room to explore standard sound measurement methods for ASTM Impact Sound Rating testing

ASTM ISR (Impact Sound Rating) test method suffers from non-reproducibility problems, especially in lower frequency bands in smaller rooms where the sound field is non-diffuse. The problem arises from the fact that Sound Pressure Level is measured in these rooms, which is dependent on the room dimensions if the sound field is non-diffuse due to low modal density. Currently, this non-diffusivity is ignored leading to non-reproducibility issues. In this work, we explore the ASTM standard discrete method, ISO discrete method, and the ISO corner method for sound measurement. We also explore the sound power computation using intensity measurements and the diagonal microphone measurement method. This initial work will be followed by exploring more simulation methods and real world testing on practical structures

Guidelines to measure low-frequency floor impact performance with high reproducibility

The impact performance of a floor-ceiling assembly is calculated as a single number rating using the ASTM standard but this method suffers from high measurement variability due to a non-diffuse sound field, especially in low-frequencies. The same assembly tested by different engineers can get different results. This work is part of a large project undertaken by the authors to develop a new measurement method for floor-ceiling impact noise performance with an improved reproducibility in low frequencies. A simulation model was used to guide a new measurement method based on the reciprocity principle. Different types and shapes of assemblies were simulated and the learnings were used to develop measurement guidelines with a standard deviation of 1 - 1.5 dB, a significant improvement from the existing variation of 4 - 10 dB. In the future, the proposed guidelines would be tested in real structures

Exploring Reciprocity method to measure radiated sound during a standard impact test

The existing standard measurement method to obtain the performance of a floor-ceiling assemblies for footstep noise suffers from several problems, especially the non-reproducibility due to room modes at low-frequency one-third octave bands, and the lost information on the input force. This makes it difficult to evaluate and compare one floor-ceiling assembly with another. In this work, we are exploring an alternate approach to obtain a frequency response function based measurement of a floor ceiling assembly by using a speaker as an input source and acceleration as a measured response. For a simulation model and for a concrete structure tested for this work, this reciprocity method showed great success when compared to a force input and a microphone response frequency response function