Low-frequency Impact Research Articles

Impact sound insulation performance measurements on CLT floors – Effect of excitation source type: Tapping machine and rubber ball

Laboratory and field measurements of the impact sound acoustic performance of a CLT wood-based floors have been performed. French national regulation requires the use of the standardized tapping machine for impact sound performance measurements. Since the early 2000s, rubber ball impact source has been standardized in some Asian countries to measure and evaluate the low frequency impact sound performance of floors; this excitation source is now part of international standards concerning building acoustic measurement in laboratories and in-situ. Indeed, the impact sound level associated to this soft impact source is supposed to provide a better correlation with annoyance from jumping and/or running children in buildings. The paper reviews the measurements performed using the standard tapping machine and the rubber ball as impact source, on CLT based floors in a laboratory, as well as those on the CLT based experimental building. Impact sound improvements are presented and discussed. The necessity of measuring with both impact sources, rather than only with the tapping machine is examined.

Comparing low frequency impact insulation measured with the rubber ball versus the tapping machine

The heavy/soft impact source or rubber ball, defined in ISO 10140 and 16283, is used primarily in Japan and Korea to evaluate low-frequency impact insulation from sources such as walking without shoes and children jumping. ASTM test methods currently do not include the heavy/soft source, and low frequency impact noise insulation is currently measured with the tapping machine using ratings such as LIR and LIIC per ASTM E3207. ISO ratings using spectrum adaptation terms from 50 Hz or lower can also be used. The relationship between these ratings and those measured using the heavy/soft source has not been well characterized for assemblies that are common in North America. The authors present field and laboratory data of impact insulation with both sources. Analysis of the data describes the relationship between the sources, the information they provide to the designers of floor assemblies, and implications for classifications of low frequency impact insulation.

Developing guidelines for a reproducible method for low-frequency impact measurements in buildings

The impact noise performance in buildings is evaluated using the measured radiated sound pressure level when impacted by a standard tapping machine. Recent work has shown that there can be 4 - 5 dB variation in the sound pressure levels at different measurement locations in the room. This can lead to a high reproducibility error for field tests. In this work, the authors have developed a novel reciprocity-based measurement method that shows approximately 1 - 1 .25 dB standard deviation in low-frequencies. Additionally, this method provides output/input ratio-based measurements, which can be useful in design predictions. The method was developed using a simulation model and verified using testing in three structures.

Quantitative measurements of lightweight timber floors using low-frequency impact source; analysis of the accuracy of 1/3 octave band heavy-hard impact prediction modelling in lightweight structures

This paper analyses heavy weight drops on lightweight structures such as timber frame and mass timber, with particular emphasis on the accuracy of the 1/3 octave band heavy-hard impact prediction modelling. With the increasing popularity of lightweight structures such as mass timber, timber frame and steel frame, this research investigates the behaviour of lightweight slabs when free weights such us kettlebells are dropped on fitness flooring. A comparison of the spectral shapes of various base structures has been carried out, focusing on the low-frequency range and resonance of various base structure types. Third-party laboratory data is utilised to derive design recommendations when free weights or heavy hard impacts are proposed in lightweight structure developments. Previously, the author carried out a case study in the UK which demonstrates the accuracy of the 1/3 octave band prediction model for concrete developments using force pulse data collected at the in-house drop tower. While the prediction method shows good agreement for concrete buildings up to 200 Hz, there is interest in extending the range for use in lightweight structures.

Comparing impact insulation measured with the rubber ball versus the tapping machine

ASTM test methods for measuring impact noise insulation use a standard tapping machine, which generates impact noise by dropping steel hammers on the floor surface. An alternative source is the heavy/soft impact source or rubber ball, which is defined in ISO 10140. The heavy/soft source was developed in Japan to correlate with sources such as walking without shoes and children jumping. Compared to the tapping machine, it generates elevated noise levels at low frequencies and generally negligible noise above about 500 Hz. The relationship between low frequency impact noise insulation measured with the tapping machine, such as LIIC, and with the heavy/soft source has not been well characterized for assemblies that are common in North America. The authors present field and laboratory data of impact insulation with both sources, and analyze the data to describe the relationship between the sources and what information they provide to the designers of floor assemblies.

The Signature of Sporadic E of an Equatorial Ionosphere of the Low Latitude Region

Sporadic E is usually referred to as the large unpredictable formation of regions of very high electron density in the E region as one of the anomalies that is present in the equatorial region. This work studies the variability of sporadic E in the region with respect to the propagation of low frequency communication and impact on the equatorial region during the occurrence of this anomaly. Hourly data for the year 2010, a year of low solar activity obtained in-situ from a Digisonde Portable Sounder (DPS-4) from the African sector, Ilorin, Nigeria (8.5oN, 4.5oE, -2.96 dip) and the Southern American sector online at Jicamarca, Peru (12 oS, 76.8 oW, 0.74 dip) and Fortaleza, Brazil (3 oS, 38 oW, -7.03dip) were used for this study. The result obtained shows that sporadic E is usually observed at the region during the daytime and early evening (0600- 1700 local time) and is more prevalent during solstice months. Two types of sporadic E were observed in the region: blanket and transparent sporadic E. 12% of the transparent sporadic E was observed during the March equinox while 9% of blanket sporadic E was observed during this period; September equinox shows 15% of transparent and 7% blanket sporadic E respectively, while June solstice has 21% transparent and 7% blanket sporadic E. During the December solstices, 14% transparent and 7% blanket sporadic E was observed. During the March equinox, the blanket sporadic E was observed around 0200 hour local time, and that of the transparent sporadic E at about 1000 hour local time. Observation during the September equinox shows that it occurs around 1100 hour and 0200 hour respectively. It was observed that there is no correlation between sporadic E and geomagnetic storm. Sporadic E has been observed to be one of the anomalies that are responsible for the scintillation and scattering of the lower frequency signal in the said region when present.

Numerical modelling of impact seismic sources using the stress glut theory

SUMMARY Meteorite impacts have proved to be a significant source of seismic signal on the Moon, and have now been recorded on Mars by InSight seismometers. Understanding how impacts produce seismic signal is key to the interpretation of this unique data, and to improve their identification in continuous seismic records. Here, we use the seismic Representation Theorem, and particularly the stress glut theory, to model the seismic motion resulting from impact cratering. The source is described by equivalent forces, some resulting from the impactor momentum transfer, and others from the stress glut, which represents the mechanical effect of plasticity and non linear processes in the source region. We condense these equivalent forces into a point-source with a time-varying single force and nine-component moment tensor. This analytical representation bridges the gap between the complex dynamics of crater formation, and the linear point-source representation classically used in seismology. Using the multiphysics modelling software HOSS, we develop a method to compute the stress glut of an impact, and the associated point-source from hypervelocity impact simulations. For a vertical and an oblique impact at 1000 m s−1, we show that the moment tensor presents a significant deviatoric component. Hence, the source is not an ideal isotropic explosion contrary to previous assumptions, and draws closer to a double couple for the oblique impact. The contribution of the point force to the seismic signal appears negligible. We verify this model by comparing two signals: (1) HOSS is coupled to SPECFEM3D to propagate the near-source signal elastically to remote seismic stations; (2) the point-source model derived from the stress-glut theory is used to generate displacements at the same distance. The comparison shows that the point-source model is accurately simulating the low-frequency impact seismic waveform, and its seismic moment is in trend with Lunar and Martian impact data. High-frequencies discrepancies exist, which are partly related to finite-source effects, but might be further explained by the difference in mathematical framework between classical seismology and HOSS’ numerical modelling.

Rotating Sonotrode Design for Ultrasonic-Assisted Arc Welding of Metal Materials.

In the process of the ultrasonic-assisted arc welding of metal materials, traditional ultrasonic application methods, such as the low-frequency impact of ultrasonic horns on a base material, can easily cause the non-fusion defect. In order to solve this problem, a rotating sonotrode with a groove and double thin ends was designed in this study. The ultrasonic vibration is transmitted into the weld pool by the rolling of the sonotrode on both sides of the weld. The resonant frequency was set at 50 kHz. Firstly, based on the Mindlin theory, a rotating sonotrode without a groove was designed by solving the frequency equation and by conducting a finite element simulation. Secondly, the effects of the groove, perforation, and transition mode on the resonant frequency, stress distribution, and amplification factor were investigated by finite element simulation. Finally, the optimum rotating sonotrode with a groove was obtained. The results show that the size of a rotating sonotrode that has a small frequency error can be obtained by using the discrete interval solver method combined with finite element simulation. The groove can significantly reduce the resonant frequency. The stress concentration can be effectively reduced by using the elliptical transition mode. The resonant frequency and amplification factor of a rotating sonotrode with a groove could be effectively adjusted by a method of double-position joint perforation. The final resonant frequency was 49.721 kHz and the amplification factor was 3.02. This study provides an effective design method for a sonotrode with double thin ends and a groove structure.

Effects of Periodic Materials on Distance Attenuation in Wall–Slab Structures: An Experiment

This research examines the application of periodic materials in wall–slab structures to mitigate impact noise and vibration propagation, a prevalent issue in multifamily housing. Traditional methods, such as floating floors, have proven insufficient in addressing low-frequency impact noises and in facilitating the identification of noise origins, leading to increased resident annoyance. Periodic materials, known for their effectiveness in controlling plane waves in civil engineering, were applied to the intermediate slab of a wall–slab experimental setup. The research involved assessing the attenuation of noise and vibration over distance before and after the application of periodic materials by measuring indoor sound pressure levels and the natural vibration amplitude of the structure’s members upon impact. The results showed that periodic materials not only facilitated distance attenuation but also significantly diminished noise and vibration throughout the structure, without the side effects of vibration amplification seen in prior civil engineering applications. This indicates a practical advancement in using these materials, offering a novel approach to sound insulation and enabling more precise impact source localization. Ultimately, this study contributes to improving urban living by suggesting a method to enhance acoustic comfort in multifamily housing, underlining the importance of further exploration in architectural applications of periodic materials.

Evaluating the uncertainty of laboratory measurements of low-frequency impact noise

Impact noise at low frequencies, specifically the third-octave bands below 100 Hz, is important to occupant reaction and are, therefore, routinely measured in field impact testing. For laboratory impact testing, the situation is less clear. Because the measured levels depend strongly on the specifics of the test chamber, it is expected that the reproducibility of low-frequency impact noise between laboratories to be poor and the translation to field measurements to be difficult. Despite these difficulties, the authors will demonstrate that it is possible to extract useful low frequency information from laboratory testing. The utility of laboratory testing for design of low-frequency impact noise is discussed.

On the vibroacoustics of cross-laminated timber embedded with acoustic black holes

The adoption of cross-laminated timber (CLT) in building construction is challenged by low-frequency impact noise. Conventional treatments typically involve increasing the mass of the floor assembly or employing structural decoupling techniques, both of which result in increased floor thickness. This study explores an alternative solution by examining the feasibility of embedding acoustic black holes (ABHs) into CLT floors. The ABH acts as a passive waveguide, concentrating vibrational energy in specific regions where it is transferred to damping layers and reduced. Using the finite element method, we investigated the vibroacoustic behavior of CLT plates within the 50–600 Hz frequency range. Our primary focus was on the influence of the ABH’s outer radius and the number of ABH inclusions within a CLT plate. The findings indicate that increasing the outer diameter of the ABH lowers the cut-on frequency and enhances the effective damping of the CLT plate. The increase in damping extends the effectiveness of the ABH to a broader frequency range, with the most noticeable effect above the cut-on frequency. The number of ABH inclusions impacts the structural modes below the cut-on frequency, and the optimal number of inclusions depends on the frequency of interest.

Subzero temperatures and low-frequency impact on MFC piezoelectric transducers for wireless sensor applications

This research paper is a continuation of a prior study [12] that focused on the positive temperature range. The current work investigates the behavior of a laminated Macro Fiber Composite (MFC) piezoelectric transducer when exposed to negative temperatures. The study aims to understand the sensitivity of the transducer under varying ambient temperatures and frequencies, particularly for applications in wireless sensor networks. The integrated Macro Fiber Composite piezoelectric transducer is both theoretically modeled and empirically verified. Experimental tests involve subjecting the laminated MFC piezoelectric transducer to sinusoidal forces generated by an electro-pulse waveform generator, while a thermal chamber is used for temperature control. Controlled displacement is applied to the transducer at low-frequency (5 to 25 Hz) ranges and different moderate temperatures (0 to -40 degrees Celsius). The results highlight the significant influence of temperature and excitation frequency on the generated voltage by the MFC transducer.

Improved prediction of extreme ENSO events using an artificial neural network with weighted loss functions

The El Niño–Southern Oscillation (ENSO) causes a wide array of abnormal climates and extreme events, including severe droughts and floods, which have a major impact on humanity. With the development of artificial neural network techniques, various attempts are being made to predict ENSO more accurately. However, there are still limitations in accurately predicting ENSO beyond 6 months, especially for abnormal years with less frequent but greater impact, such as strong El Niño or La Niña, mainly due to insufficient and imbalanced training data. Here, we propose a new weighted loss function to improve ENSO prediction for abnormal years, in which the original (vanilla) loss function is multiplied by the weight function that relatively reduces the weight of high-frequency normal events. The new method applied to recurrent neural networks shows significant improvement in ENSO predictions for all lead times from 1 month to 12 months compared to using the vanilla loss function; in particular, the longer the prediction lead time, the greater the prediction improvement. This method can be applied to a variety of other extreme weather and climate events of low frequency but high impact.

Vibration and impact sound properties of hybrid steel-timber floor structures

Lightweight floor structures, such as timber or hybrid timber floors, face challenges associated with excessive vibrations and elevated levels of low-frequency impact sound. Especially here, accurate prediction of a floor’s vibration and acoustic behavior is essential. However, typical laboratory testing of building elements is costly and time-consuming. To reduce costs, in this study, adapted simulations are carried out on two types of hybrid steel-timber floor structures to evaluate vibrations and impact sound. The hybrid elements are made of laminated veneer lumber as the top and bottom layers and a trapezoidal steel component as the web. Vibration measurements are used in combination with Bayesian optimization to efficiently calibrate Finite Element models, which are subsequently utilized to quantify and validate the floor structures regarding vibrations and impact sound. The two types of cross-sections, i.e., closed and open, are investigated and compared. The impact sound pressure level computations reveal promising results in predicting the behavior of the hybrid structures. However, further countermeasures are required to fulfill vibration serviceability requirements.

Performances of low frequency impact sound in wooden buildings

Since 1999 Sweden has required an extended frequency range for sound insulation in residential buildings, using 50 Hz as the lower limit. This regulation update has driven the design and development of multi storey residential building systems with wooden structures in a positive direction. Already in the mid 1980'ies there existed scientific proof that it the perceived impact sound will improve if the frequency range was extended below the lower standard limit 100 Hz at that time. Lately, researchers have indicated that the perceived impact sound can be even further improved if the frequency range is extended below current lower standardized limit of 50 Hz. Assume that the frequency range for impact sound requirement will be further extended to include frequencies from 25 Hz, what would that mean for modern wooden apartment buildings? Acouwood and Kuster & Partner AG are collecting data from 20 Hz, no matter if the standard measurement procedure cannot be applied below 50 Hz. It gives a good overview of potential annoyance risk but also of acoustic performances of modern sustainable multifamily buildings and how they can be improved. This paper summarizes measurement results of impact sound from 20 Hz in several wooden buildings.

Novel frameshift variants expand the map of the genetic defects in IRF2BP2.

At present, the knowledge about disease-causing mutations in IRF2BP2 is very limited because only a few patients affected by this condition have been reported. As previous studies have described, the haploinsufficiency of this interferon transcriptional corepressors leads to the development of CVID. Very recently, a more accurate phenotype produced by truncating variants in this gene has been defined, manifesting CVID with gastrointestinal inflammatory symptoms and autoimmune manifestations. We analyzed 5 index cases with suspected primary immunodeficiency by high throughput sequencing. They were submitted for a genetic test with a panel of genes associated with immune system diseases, including IRF2BP2. The screening of SNVs, indels and CNVs fulfilling the criteria with very low allelic frequency and high protein impact, revealed five novel variants in IRF2BP2. In addition, we isolated both wild-type and mutated allele of the cDNA from one of the families. In this study, we report five novel loss-of-function (LoF) mutations in IRF2BP2 that likely cause primary immunodeficiency, with CVID as more frequent phenotype, variable expression of inflammatory gastrointestinal features, and one patient with predisposition of viral infection. All identified variants were frameshift changes, and one of them was a large deletion located on chromosome 1q42, which includes the whole sequence of IRF2BP2, among other genes. Both de novo and dominant modes of inheritance were observed in the families here presented, as well as incomplete penetrance. We describe novel variants in a delimited low-complex region, which may be considered a hotspot in IRF2BP2. Moreover, this is the first time that a large CNV in IRF2BP2 has been reported to cause CVID. The distinct mechanisms than LoF in IRF2BP2 could cause different phenotype compared with the mainly described. Further investigations are necessary to comprehend the regulatory mechanisms of IRF2BP2, which could be under variable expression of the disease.

Surface removal of ductile metal using cyclic low-frequency impact of a discrete particle-less waterjet

The discrete waterjet (DWJ) offers advantages in material removal because of the cyclic impact loading, but the specific removal characteristics and corresponding mechanisms have not been yet fully understood. Therefore, the flow field and material removal characteristics of the DWJ were studied through numerical and experimental methods, including the velocity and impact pressure distribution, surface morphology, quantitative statistics of erosion crater, and fractography under different jet pressures and exposure times. The results indicate that mechanical interruption has a positive impact on increasing the maximum velocity (53.0% at 30 MPa) of the waterjet head and altering the impact pressure distribution, resulting in an asymmetric erosion crater with a tapering groove along the edge. Meanwhile, the DWJ has superior working efficiency (higher erosion area, depth and volume) and energy utilization (lower specific energy) than the continuous waterjet (CWJ), while avoiding the unfavorable high crater lips. A large amount of material removal does not necessarily occur in the initial stage of waterjet impact, and it is related to material properties, waterjet parameters and specific evaluation indexes. The increase of waterjet pressure accelerates the material removal process and improves the energy consumption efficiency. The materials removing process is divided into four stages: surface deformation due to the cyclic impact pressures, surface break-ups localized near the surface unevenness, independent fragment forming mainly by water wedge pressure, and larger removal of materials due to these cyclic processes.

Unlock the myth of low-frequency footstep thumping noise in lightweight wood floors

Major occupants' complaints received in lightweight wood floors of Impact Insulation Class (IIC) above 55, are low-frequency footstep thumping noise. Lack of understanding of fundamentals and solutions motived this study. A series experiments were conducted to answer the following questions: 1) what are the frequency range of the low-frequency footstep thumping noises heard by the occupants in mass timber slab floor and in light frame wood joisted floor when the floors are impacted by the ISO tapping machine, footsteps of a person walking with shoes, and with bare foot? 2) how look like the impact sound spectrums below 50 Hz (ISO) or below 100 Hz (ASTM)? 3) Can the tapping machine excite the low-frequency noise down to the range of wood floor natural frequency around 15 Hz? 3) Can the current measurement system measure the sound signals at such low frequency range reliably? 4) can the measured spectrums of impact sound signals reveal the low-frequency impact noise issues? 5) what are the special construction details of the wood floors contributing to the low-frequency impact noise problem? 6) what are the solutions for the problem? Our experiments answered the questions. The findings and solutions will be shared in the full-length paper.

New ASTM ratings for impact noise insulation

New ratings to evaluate impact noise insulation have recently been published as ASTM standards, which are commonly used to evaluate building acoustics measurements in North America. ASTM E3207 defines new ratings for low-frequency impact insulation, defined by the 50-80 Hz third-octave bands. ASTM E3222 defines new ratings for high-frequency impact insulation, defined by the 400-3150 Hz bands. These ratings are based on the two-rating method of evaluating impact noise isolation proposed by the authors [LoVerde and Dong, J. Acoust. Soc. Am. 141 (2017)]. By evaluating the low and high-frequency components of impact noise independently, the proposed ratings perform better than existing ratings in terms of correlating with subjective reaction, designing assemblies, and evaluating products and mitigation measures. Motivations, development, and examples illustrating the use of the new ratings are presented, and suggested classification schemes are discussed.

Theoretical substantiation of low-frequency shock-contact impact as a way to increase the efficiency of ultrasonic drilling of extraterrestrial soil

A physical and mathematical model of ultrasonic destruction and deformation of solid soil has been developed, taking into account the presence of additional influences (low-frequency impact, rotational). The numerical implementation of the model is carried out in the form of a computer program for calculating the process of deformation and destruction of the soil. The presented results of calculations proved the possibility of additionally increasing the efficiency of ultrasonic drilling by more than 2.5 times due to the imposition of low-frequency shock-contact action.