Tapping Machine 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.

Sound insulation of access floors on CLT

The acoustic performance of access floors resting on concrete slabs has been long investigated. When such flooring solutions are used on lightweight construction systems, estimates of impact sound insulation improvements cannot be transferred without relevant loss of accuracy. To gain understanding on such behaviour, an experimental campaign has been carried out at the Building Envelope Lab of the Free University of Bozen-Bolzano on 16 access floors mounted on a 200 mm CLT slab. Three different panels (calcium silicate, encapsulated calcium silicate and encapsulated chipboard panels), two different pedestals (standard and resilient), and three flooring solutions (bare, carpet tiles, acoustic carpet tiles) were studied. Impact sound insulation measurements were carried out using both the tapping machine and the rubber ball as source. The results discuss in detail the outcomes of the measurement campaign as well as the relation between the two impact sources chosen.

Computational prediction of impact sound insulation of a timber floor excited by an ISO standard tapping machine

During the last decades, researchers have actively developed procedures to predict impact sound insulation of timber slabs and floors using the finite element method (FEM). Since the simulations have mainly been performed in the low frequencies, a full understanding of their suitability for research and development (R&D) purposes has not yet been created. The object of the study reported in this paper was to determine the applicability of a modern FEM simulation procedure for predicting the normalised impact sound pressure level Ln of a full timber floor, when information provided by material manufacturers is used as input data. Force excitation caused by the ISO standard tapping machine was determined utilizing explicit time integration and FEM. The modelling of sound radiation itself was performed in a frequency domain FEM analysis. The models of a timber floor in its construction stages were constructed before the laboratory measurements of impact sound insulation so that the set-up corresponded to a simulated R&D task. Based on the prediction results, the applied procedure was considered suitable for R&D purposes and needs for further studies were identified.

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.

Variability of low frequency laboratory measurements of acoustic isolation of floor/ceiling assemblies

It has long been recognized that building acoustics measurements performed in laboratories exhibit a high degree of variability between and within labs. Traditional metrics limited the use of data to above the 100Hz or 125Hz one-third octave bands. In recent years, focus has widened the range of frequencies of interest to the 50Hz one-third octave band or lower. Analyzing measurements of low frequencies in buildings is complicated by the physical reality of wavelengths that are similar in scale to common room dimensions resulting in modal behavior and the mathematical simplification of the wave equation in building acoustic calculations that assumes a diffuse field which discounts both phase and angle of incidence. Evaluation of common building isolation measurements of the same test floor/ceiling structure sample in the same lab and between labs across the frequency spectrum allows the comparison of the repeatability and reproducibility at low frequency ranges to those at high frequency ranges. Measurements and their associated metrics of various sources, including pink noise produced by loudspeakers, the standard tapping machine, and the impact ball are included in the analysis.

Impact noise calculations of CLT constructions using finite element

Cross-laminated timber (CLT) consists of multiple glued layers of wood, which have perpendicular orientation with respect to adjacent layers, and it has become an important building material due to its light weight, strength, and sustainability. One problem with CLT constructions is the impact noise, which for a bare CLT floor is poor. There thus is a need for calculation tools that can predict impact noise level of such floor constructions. For composed constructions, finite element is a flexible and usable tool. However, to simulate real measurement scenarios, the force produced by the ISO tapping machine then needs to be estimated. This paper revisits this estimation and performs calculations of the impact noise level of a CLT floor, and compares this with measured results.

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.

Acoustical performance of steel coil springs for vibration isolation

The acoustical performance of a set of commercially available steel coil springs was evaluated supporting a rigid structure above a slab on grade. The vibration isolation of this simple system is determined by exciting the on-grade slab with a tapping machine and measuring the resulting vibration transmitted into the isolated rigid structure above. Insertion loss of the system is determined by comparing the vibration level on the rigid structure with and without the vibration isolators under the same dynamic forces. The test results reveal the natural frequency, damping ratio, and insertion loss of the system as a function of the loading on the coil springs. The results also reveal the presence of surge frequencies (or wave resonances) that significantly degrade the system performance of at these specific frequencies, which are usually greater than 50 times the natural frequency of the loaded steel spring. Because of potential structure-borne noise transmission through steel coil springs into the supporting structure, designers should be cautioned when considering the use of steel springs to support equipment that can generate strong tonal vibrations in the surge frequency region of the springs.

Stability Analysis of Planetary Rotor with Variable Speed Self Rotation and Uniform Eccentric Revolution in the Rubber Tapping Machinery

Natural rubber is a critical material that is essential to industry and transportation. In order to reduce the cost of rubber tapping and improve the efficiency and profitability of rubber production, the 4GXJ-2 portable electric rubber cutter and automatic rubber tapping robot have been developed. In their vibration tool holder, the planetary rotor with variable speed self rotation and uniform eccentric revolution is the most important transmission component, and its instability will cause irregular vibration of the tapping tool, thereby reducing the accuracy of vibration cutting and increasing noise. Base on the ANCF (Absolute Nodal Coordinate Formulation) 3D-beam element and 3D REF (3D Ring on Elastic Foundation), a novel eccentric 3D REF model of a planetary rotor is proposed. By introducing multiple coordinate systems, the coupled motion of uniform eccentric revolution, variable speed self rotation and flexible deformation is decomposed and the influences of these motions on the centrifugal force and Coriolis force are more clearly derived. The model is degraded and validated by comparing with other examples of a rotating circular ring model and uniformly eccentrically revolving annular plate. According to the Floquet theory and Runge−Kutta method, the unstable region of revolution speed of a planetary rotor in rubber tapping machinery is predicted as [817 rad/s, 909 rad/s], [1017 rad/s, 1095 rad/s] and [1263 rad/s,1312 rad/s]. Compared with the rubber-tapping experiment of rubber tapping machinery, the validity of the proposed model is further verified. This model provides important design references for the speed settings of those rubber tapping machines.

Computational prediction of impact sound insulation of a full-scale timber floor applying a FEM simulation procedure

During the recent decades, simulation procedures involving the finite element method (FEM) have been developed to enable prediction of impact sound insulation of timber slabs and floors. FEM simulations have previously been applied for timber floors mainly in low frequencies despite their evident ability to operate over a wide frequency range. Additionally, the validation processes have involved calibrations and experimental modal analyses which can seldom be performed in product development tasks concerning full structures. The purpose of this research was to study the applicability of a FEM simulation procedure to predict normalised impact sound pressure levels Ln of a full-scale timber floor if material data provided by the product manufacturers is used. The floor was studied at three construction stages where the FEM simulations were performed for the bare floor and the rib slab, and the floor covering was considered in the post-processing stage in case of the full floor. The impact force excitation generated by the ISO standard tapping machine was described with the recently published procedure involving explicit dynamics analysis. To serve the purposes of this study, the FEM models were fully constructed before the measurements were carried out. According to the results, the 1/3-octave Ln of the full floor and the floor without covering was predicted with a 0 to 9 dB accuracy depending on the frequency band and the single-number quantities with a 0 to 4 dB accuracy. The single-number quantities of the bare rib slab were underestimated with the simulations by 4 to 5 dB. Probable causes for the discrepancies between the simulation and measurement results pointed mainly to the uncertain material properties but possibilities for modelling inaccuracies could not be excluded.

Impact ball testing in a laboratory setting

Impact ball test data have been collected across multiple structures by a procedure similar to Annex A of ISO 10140-3:2021. The results are presented at a high level to examine where impact ball testing is useful and what design characteristics of different structural assemblies and floor finishes are highlighted by the impact ball as opposed to other impact sources including the standard tapping machine.

An Optimization Study on a Novel Mechanical Rubber Tree Tapping Mechanism and Technology

All-natural rubber is harvested from rubber trees (Hevea brasiliensis Muell. Arg.) by traditional tapping knives, so rubber tapping still heavily relies on labor. Therefore, this study explored a novel, hand-held mechanical rubber tapping machine for rubber tree harvesting. In this study, a mechanical tapping cutter with a vertical blade and adjustable guide was first described. The response surface method was applied to evaluate factors affecting the tapping effect. The experimental values were in close agreement with the predicted value. Machine-tapped latex was comparable in quality to hand-tapped latex. Based on the single-factor results, the response surface method (RSM) and the center combined rotation design (CCRD) optimization method were adopted to explore the influence of three factors influencing vertical blade height (A), cutting force (B), and spiral angle (C) on the tapping effect. Regarding the cutting rate of the old rubber line (Y1), cutting time (Y2), latex flow rate (Y3), and average cutting current (Y4) as evaluation indexes of the tapping effect, an optimization scheme was determined. The quadratic model fits for all the responses. The test results showed that the main factors affecting Y1, Y2, Y3, and Y4 were A and B, B, A and C, and B, respectively. Under optimal conditions, the influencing factors of A, B, and C were 10.24 mm, 51.67 N, and 24.77°, respectively, when the evaluation index values of Y1, Y2, Y3, and Y4 were 98%, 8.65 mL/5 min, 9.00 s, and 1.16 A. The range of the relative error between the experimental and predicted results was from −11.11% to 11.11%. According to the optimized treatment scheme, a comparison test was designed between mechanical and manual rubber tapping tools. To verify the availability and effect of the mechanical tapping method preliminarily, the important rubber tapping evaluation indexes included bark thickness, bark excision, latex flow time, cutting time, ash content, and cutting depth, which were selected to serve as a comparison test. There was no significant difference between hand and mechanical methods, except ash content (p < 0.05) and cutting time (p < 0.01). The mechanical tapping machine proposed in this study is meaningful to improve cutting efficiency, practicality, and operability. Furthermore, it provides crucial theoretical references for the development of intelligent tapping machines.

Non-destructive testing of concrete layer adhesion by means of vibration measurement

A common practice in the construction of the garage floors of residential and office buildings is the construction of the concrete slab in two steps: one thick layer at the beginning of the work, a second thin layer at the end of it. This procedure saves time but also brings in the problem of a cold joint between the two layers which, eventually, may get loose or even split. However it is difficult to control the status of the concrete layers until they are completely split unless one make use of destructive tests such as the extraction of test samples.In this paper we demonstrate the use of vibrational data to assess and control the status of the joint between the two layers. To that end we have carried out two series of experiments.The first one is an experimental procedure in the laboratory with the goal to see if vibrational data are able to distinguish among different levels of fixation between the two layers. We use a concrete slab as the thick layer and a MDF board as the thin layer, bonded by means of gypsum plaster. Different amounts of the surface covered by the gypsum plaster give different levels of fixation between the layers. For each configuration we produced vibration with a standard tapping machine and measured it with the aid of a vibrometer. Our results are positive; with a simple test vibrational data can distinguish whether two layers are fixed by 25% or less, by 50% or by 100% of their surface. With the laboratory results we have designed a non-destructive test to be carried on in-situ measurements so as to ascertain the level of fixation of two layers of a concrete slab. The test is based on the installations described in Annex A of ISO 16251-1, so that it does not require large investments or facilities. It is able to cope with different kind of data and is independent of the characteristics of the slab thanks to the statistics tools applied to the data.The second one is the application of the test to data measured in an actual building with the aforementioned problem in its garage floor. We measured vibration induced by a different source, a car passing by, and in several locations, both with loose and well fixed layers. The vibration was recorded by the same vibrometer as above. Notwithstanding the differences in the data source, the test can be applied to the data and the results are compatible with the known status of the slab: we obtain a 77.0% of sensitivity and 54.5% of specificity, while only a 1.0% of false positives and none false negatives. The only drawback of the test is its high number of undecidable cases, which amounts to 24.1%.

Comparison of different methods to determine the sound reduction index R of walls

The laboratory method (ISO 10140-2:2021) is probably the most accurate method to determine the sound reduction index R of walls. Flanking noise (ISO 10848-1 and 4:2017) is almost fully eliminated in the laboratory setup whereas this is not the case for in situ measurements (ISO 10052:2021). The measurements are even more difficult for measurements in open air or in factory halls with mock-up setups. Manufactures of building elements, such as prefabricated walls, are interested in quick measurements of the sound reduction index R of their products. This paper compares the traditional laboratory measurements, the intensity method and the Sopranoise road barrier method (EN 1793-6) with the vibration velocity / sound pressure method (ISO 140-4:1998). Different setups were measured using different methods in laboratory and in open air. Most of the experiments were done with loudspeakers used as an excitation source, but some were also done with shakers and a tapping machine. The importance of the use of sound shielded accelerometers will be elucidated.

Assessing the low-frequency measurement procedure for the measurement of impact sound insulation using the rubber ball

ISO 16283-2 includes a procedure for measuring field impact sound insulation at low frequencies using a tapping machine to improve the repeatability, reproducibility, and relevance of results in the 50, 63, and 80 Hz one-third octave bands in small receiving rooms (volumes less than 25 m3). However, the low-frequency measurement procedure with excitation from a standardized rubber ball was not included because the link between measurements of Li,Fmax from the central region and corners had not been established at the time of writing. This paper assesses the use of the low-frequency measurement procedure with a rubber ball source through measurements of Li,Fmax in a vertical transmission suite at the Building Research Institute (Japan). It also provides analysis of the modal sound field in the receiving room due to rubber ball excitation of the concrete slab. The results indicated that the low-frequency measurement procedure was beneficial in this 60 m3 room to estimate the room average sound pressure level below 80 Hz. Future work could therefore evaluate the low-frequency procedure in the field with different room volumes and floor constructions.

Impact sound insulation prediction and uncertainty quantification using a detailed source model in the modal Transfer Matrix Method

The main goal of this work is to provide an efficient and accurate prediction of the impact sound insulation of layered structures for the entire building acoustics frequency range (50-5000 Hz). To this end, the modal Transfer Matrix Method (mTMM) has been developed to predict the impact sound radiation from layered floors resulting from tapping machine impacts, while accounting for simply supported boundary conditions. A detailed source model is presented which accounts for both the impact locations of the individual hammers and the discrete 2 Hz force spectrum. It is also discussed how this detailed source model can be implemented into the mTMM. Monte Carlo simulations provide insight into the uncertainty of the radiated sound power and the impact sound insulation improvement for bare and layered floors, resulting from the impact force location. Numerical validation is provided by comparison to finite element models of various floors. Narrow-band sound pressure level measurements on a layered floor have been performed to validate the detailed source model and its use in the mTMM. A comparison of measured and predicted results indicates the importance of a detailed source approach, especially at low frequencies

Cylindrical-cam modulation instantaneous angular speed sensor for reciprocating-rotary machine

This paper presents the theory and implementation of a novel sensor system for measuring the instantaneous angular speed (IAS) of a shaft with reciprocating rotary motion. The system comprises a laser displacement sensor and an S-shaped cylindrical cam sleeve fixed to the shaft. As the shaft rotates with reciprocating rotary motion, the cylindrical cam modulates the IAS signal of the machine to achieve a change in profile radius. The signal is then demodulated to obtain the IAS of the reciprocating rotary motion. The sensor system is experimentally validated using a vibration-assisted tapping machine. Results show that the IAS readings are consistent with the machine’s set parameters. Furthermore, the novel sensor produces considerably smooth and stable traces of the IAS, demonstrating its high accuracy and reliability in obtaining the IAS of reciprocating rotary motion transients. The frequency error rate of the system is less than 3%, and the highest resolution of the angular amplitude is 4.788″. Finally, a cutting experiment confirmed the feasibility and validity of the proposed sensor system in optimizing the parameters of the vibration-assisted tapping machine.

A study on the evaluation of impact sound reduction performance of floor mats for reducing floor impact sound in apartment buildings

This is a study on the performance evaluation of floor mats used to reduce floor impact sound in apartment houses in South of Korea. A total of 8 types of floor mats and 5 or more test rooms with different floor structures were used to measure and evaluate impact sound reduction performance. The impact source is a Bang machine (heavy-weight impact sound 1), a rubber ball (drop of height 100 cmHeavy-weight impact sound 2) tapping machine (light-weight impact sound), and a rubber ball drop height of 40cm that simulates the actual impact force. As a result of the test, the impact sound reduction performance for the light-weight impact sound was evaluated as excellent. It was evaluated at the level of ambient background noise. Also, the reduction performance of the bang machine was somewhat different depending on the floor structure. In addition, there are cases where it is rather amplified in the low frequency band (63 Hz). In the case of rubber ball (drop of height 100 cm), the reduction performance was different depending on the floor structure. However, the impact sound reduction performance was evaluated to be sufficiently reduced. The impact noise reduction performance at the rubber ball drop height of 40 cm was found to be slightly higher than that at the drop height of 100 cm.

Suitability of standardized single-number ratings of impact sound insulation for wooden floors – Psychoacoustic experiment

Wooden floors usually have worse impact sound insulation (ISI) at low frequencies than concrete floors having the same rating level. Rating level is usually expressed by single-number quantities (SNQs), such as weighted normalized impact sound pressure level Ln,w. Psychoacoustic research among wooden floors is very limited although a controlled laboratory experiment is the strongest method to point out the most adequate SNQs to be declared for the floors. The purpose of our study was to determine how four standardized SNQs of ISO 717-2, Ln,w, Ln,w + CI, Ln,w + CI,50, and LiA,Fmax,V,T, and a recently proposed SNQ, Ln,w + CI,25, are associated with the annoyance of natural impact sounds transmitted through wooden floors. Fifteen floors were built in the laboratory based either on cross-laminated timber (heavy) or open box wood (light) slabs. Different coverings and suspended ceilings were applied on these slabs. The ISI was tested within 25–3150 Hz using both tapping machine and rubber ball. Thereafter, five natural impact sounds were recorded for each floor: rubber ball drops, steel ball drops, walking, jumping, and chair pushing. Fifty-two people rated the annoyance of these 75 recorded natural impact sounds in psychophysics laboratory. Annoyance was best associated with Ln,w for all the five impact sound types. That is, measurement of ISI within 100–3150 Hz is sufficient from subjective point of view. All four SNQs based on tapping machine explained annoyance better than the SNQ based on rubber ball. Our results can significantly guide the future research, development, and regulations of wooden floors.