T.R.T. Nightingale

Modeling vibrational energy transmission at bolted junctions between a plate and a stiffening rib

An analytical model is presented for structure-borne sound transmission at a bolted junction in a rib-stiffened plate structure. The model is based on the wave approach for junctions of semi-infinite plates and calculates coupling loss factors required by statistical energy analysis. The stiffening rib is modeled as a plate strip and the junction is represented by an elastic interlayer with a spatially dependent stiffness. Experimental verification is carried out on a series of Plexiglas plate structures with varying rib depth and bolt spacing. A well-defined connection length at the junction was created by inserting thin spacers between the plate and the rib at each bolt. Comparison between numerical and experimental data for this case showed good agreement. Measured results for the bolted junction without spacers suggested that structure-borne sound transmission could be modeled as a series of connections characterized by a finite connection length. This concept is explored further by determining an equivalent connection length which gives the best agreement between numerical and experimental data.

Prediction models in building acoustics : introduction to the special session at Forum Acusticum 1999 in Berlin

There is strong interest in being able to predict the apparent sound insulation in completed constructions so that the suitability of the construction details and materials may be assessed at the design stage. Methods do exist that provide estimates of the apparent sound insulation. An example of which is SEA. However, this method is likely too complex to be suitable for most practitioners and consultants as it relies heavily on the user to model the transmission mechanisms from first principles. Thus, from a practitioners point of view, a model that makes use of commonly available data for the acoustic performance of building products and elements – as measured by standardised laboratory measurement methods ISO 140 – and relates this to the acoustic performance in the completed buildings would be more useful. In response to this, CEN has started to create prediction models for several acoustic aspects in buildings beginning with separate models for the apparent airborne sound insulation and the apparent impact sound insulation. Practical models that allow the prediction of the sound reduction of the individual flanking paths in heavy monolithic constructions are now available (EN 12354–1 for the apparent airborne sound insulation and EN 12354–2 for the apparent impact sound insulation). A new quantity has been introduced in these models to characterise the structure-borne sound transmission at junctions of building elements. Work is now focusing on reliable input data to these models, describing measurement methods to determine the junction quantity, extending application to constructions that are not heavy and monolithic, and verifying the accuracy of the models. Further work is concentrating on models for other aspects such as facade sound transmission from outside to inside and vice-versa and the sound levels caused by mechanical equipment in buildings. This paper provides an overview of prediction models in building acoustics as an introduction to the special session at the Forum Acusticum 1999 in Berlin.

Vibration Response of Lightweight Wood Frame Building Elements

Direct and indirect measurements of the vibration response of several wood-framed walls and floors were made. The data indicate that these building elements do not behave like a homogeneous and isotropic system but rather exhibit a response typical of a periodic plate/beam structure. There is localization of energy near the excitation point and very strong attenuation with distance in the direction normal to the framing members. This region of high attenuation is followed by one of considerably reduced attenuation. A systematic study of a floor/ceiling assembly indicated that the onset of this second attenuation region was caused by the presence of a butt joint in the plate. It is speculated that the weak bending-to-bending coupling caused by the butt joint reduced the bending energy enough so that wave conversion from in-plane to bending at each plate/beam joint accounted for the presence (and in some cases near-constant level) of bending energy after the butt joint.

Structure-Borne Sound Transmission in Rib-stiffened Plate Structures Typical of Wood Frame Buildings.

Structure-borne sound transmission at a subfloor/joist connection typical of wood frame buildings is investigated experimentally and theoretically. The first part of this paper investigates the influence of the fastener spacing on the vibration attenuation across a joist. For this purpose, measurements were carried out on a small floor section for various coupling conditions of the joist. The experimental results suggested the existence of an effective coupling area characterizing the screwed joist/floor connection. In the second part of this study, a calculation model is developed based on Statistical Energy Analysis (SEA) and plate strip theory for the idealized case of a rigid line connection. The presented model is verified experimentally on a Plexiglas structure and a subfloor/joist connection. The experimental validation showed fair agreement between measured and calculated data, but revealed that more work is required to improve the prediction accuracy in realistic situations.

Effect of electrical outlet boxes on sound insulation of a cavity wall

The results of a systematic study investigating the effect on the sound insulation of wood stud walls having penetrations made by electrical outlet boxes are presented. The effect on sound insulation is shown to be almost negligible, regardless of box separation, if the boxes are themselves airtight and form an airtight seal with the gypsum board surfaces. However, if the boxes are not airtight, then the degradation to the sound insulation is strongly dependent on the separation between the boxes. Other significant factors include the presence of cavity absorption, and its method of installation. A series of retrofits for poorly installed boxes is examined and show that commonly available devices for reducing airflow (and sound insulation) through electrical boxes can be very effective but are highly dependent on installation.

Methods to control low frequency impact noise in wood‐frame construction

The control of low frequency impact noise is of great importance in Japan and Korea. For impact noise rating, both countries use standardised heavy and soft impactors that inject high levels of low frequency power into a wood‐frame floor due to the high force applied and “good” impedance match between the source and the floor. This paper reports on a parametric study designed to confirm the important parameters for controlling low frequency impact noise and how these parameters are affected by changes to construction details. The paper shows that increasing the drive point impedance floor surface while minimising the structural coupling between the gypsum board ceiling and the structural framing (joists) are important elements. Additionally, a well‐designed floor topping can be very effective when applied to a suitable floor. The paper presents data to show the relative importance of direct and flanking transmission paths. Furthermore, it is shown that repeated impacts by the Bang Machine physically chang...

Subjective evaluation of low‐frequency impact sounds on floor‐ceiling assemblies.

To investigate meaningful ratings and criteria for the acoustical performance of building partitions, it is necessary to understand the subjective judgments of listeners when hearing transmitted or radiated sounds. Impact sounds on floors caused by footstep noise (walking, running, etc.) are particularly bothersome and are not well characterized. A series of recordings of the sound radiated into the room below a floor‐ceiling test assembly when an impact occurs on the topside of the assembly (floor surface) is ongoing. The primary impact sources considered are real adult walkers, and a heavy rubber ball, standardized in JIS A 1418‐2. The binaural recordings are presented to listening test participants, who rate subjective attributes of the sounds such as annoyance. In this way the floor‐ceiling test assembly is rated (and can be ranked) subjectively, and metrics derived from purely physical measurements can be assessed and interpreted. Preliminary results from measurements on a range of lightweight wood f...

Room requirements for laboratory measurement of transmission loss and impact sound insulation.

Laboratory measurement of transmission loss (ASTM E90) and impact sound insulation (ASTM E492) have one thing in common: measurement of the sound power radiated into the receive room by the specimen under test. In E90 the reported quantity, transmission loss (TL), is the difference between the incident and transmitted sound power, whereas for E492 the reported quantity, normalized impact sound pressure level (NISPL), is a direct measure of the radiated sound power of the floor. A derivation of the TL and NISPL equations using a statistical energy analysis (SEA) framework shows that the ASTM equations are based on the assumption of power balance and statistical sampling of the sound field. This SEA framework is used to define the acoustical conditions of the receive room (number of modes in each frequency band, the average loss factor in each band, and hence the modal overlap factor), which are then related to the physical properties such as room shape, volume, absorption, etc. The conditions necessary for...

Transmission of impact sound in wood‐framed construction

Ongoing studies in the flanking transmission facilities at NRC‐IRC have developed a framework for predicting the overall sound transmission, including flanking, in wood‐framed multifamily buildings. Power flow via each flanking path is affected by five factors that determine a path transfer function specific to the type of excitation (airborne or impact) and the construction details. This paper examines how common construction details affect transmission of impact sound between adjacent rooms, which are either side‐by‐side or one above the other. Since the source room floor is an element common to all impact flanking paths, a series of toppings were evaluated as treatment options. Additional layers of gypsum board and improvement due to resilient mounting were evaluated for the walls in the receiving room. Estimates of the resulting impact SPL were obtained by summing the energy transmitted by the direct path through the floor assembly separating the pair of rooms (if applicable) and all the flanking paths involving the relevant wall‐floor junctions. These estimates provide the basis for a design guide to predict sound isolation in typical wood‐framed row housing or apartment buildings.

Flanking impact sound transmission in wood‐framed multifamily construction

This paper reports findings from a recently completed study of flanking sound transmission involving the wall/floor junction in wood‐framed multifamily buildings. Flanking transmission exists in all buildings, but it can be controlled through good design. The paper examines how common construction details affect flanking paths between horizontally, vertically, and diagonally separated rooms. Variables considered include mounting conditions and orientation of the floor joists, framing of the wall assembly and any associated fire blocking, and mounting and number of layers of gypsum board. Estimates of the apparent sound insulation were obtained by summing the energy transmitted by the direct path through the wall or floor assembly separating the pair of rooms, and all the flanking paths involving the relevant wall‐floor junctions. Results indicate that if there is no floor topping (i.e., the subfloor is bare) the apparent sound insulation for both airborne and impact sources is typically limited by flanking transmission involving the floor. Since, the source room floor is an element common to all impact flanking paths, three different toppings were evaluated as treatment options, and additional layers of gypsum board and resilient mounting were considered as options for the walls. The effectiveness of each option is discussed