Müller BBM (Germany)

Cities sound. They can be loud, quiet, monotonous, or vibrant and exciting. How urban spaces sound in detail depends on the respective framework, which includes the urban planning and the different activities of the residents. The focus dealing with sounds of the cities in acoustic engineering lies mainly on the topic of noise. In fact, environmental noise has a negative impact on our health and reduces the quality of life. But the sound of cities is much more than just noise. Harmonious and appealing city sounds have a positive effect on well-being; it promotes orientation, and it can help to strengthen social and cultural bonds. Therefore, it is important to consider the sound of the city from the planning stage. This contribution sets out to show the possibilities of including planning tools within the concept of "Stadtklanggestaltung" (Urban Sound Design) into the field of administrative noise control and how the soundscape standardization sets a supporting framework to implement them in practice. Specific urban sound design and planning can make a significant contribution to developing high-quality urban places and to preventing possible conflicts in relation to controversial urban sound situations.

Driven by progress and requirements of the advancing machine age, Acoustics of the 20th century has run through a tremendous development. Starting from a profound understanding and formulation of its theoretical physical framework by Hermann von Helmholtz and Lord Rayleigh at the end of the 19th century, Acoustics and its many sub-disciplines developed to an important technical and engineering discipline which, at the beginning of the 21st century, had become a basic design tool for environmental compatibility and comfort features of most technical products and utilities. In Europe, this development has strongly been driven by urgent requirements of fast after-war reconstruction and growing needs of noise control which enforced particular interactive efforts of research institutes and companies to cope with the challenges of the time. Based on recent widespread contributions to the history of European Acoustics presented at Forum Acusticum 2023 in Torino, the relevance of noise control for the development of Acoustics in the last century will be highlighted and appreciated. With reference to some typical examples, it will be shown how the disciplines of engineering acoustics and noise control essentially contributed to renew and strengthen acoustics as an indispensable interdisciplinary field of science and technology.

The basic principles applied in gas compressor stations to manage noise and demonstrate compliance with statutory acoustic requirements are not different from those used with most other industrial activities.Well-known and proven standard procedures involve sound emission assessment, acoustic modeling, model verification, development of a noise control concept and its optimisation until compliance can be demonstrated.However, noise control for some of the typical equipment in gas compression is extremely demanding in terms of both acoustic and operational/safety aspects so that it requires special attention.Examples are the exhausts of the gas turbines driving the compressors and the extensive network of gas piping.Because of their high and strongly varying sound emissions the exhausts pose a significant challenge in designing effective silencers.In addition, flow-generated self-noise in the silencers is a risk that needs to be avoided.For the piping, sound attenuation by acoustic lagging is in conflict with corrosion and maintenance/accessibility problems and makes an optimised lagging concept an ambitious task.The present contribution illustrates typical problems encountered and possibilities to deal with them.It is based on data and experiences with gas compressor stations with very stringent acoustic requirements.

<div class="section abstract"><div class="htmlview paragraph">Vehicle Acoustic Prototyping in the low to mid frequency range commonly relies on the knowledge of the excitation forces generated by the vibration sources like tires and powertrain. It is current practice to measure the excitation as blocked forces either on a component test bench or using an inverse method on the vehicle itself. In both cases, the measurements are performed with (pre)selected bushings. Since the bushing stiffness results of a trade-off with other performances, like handling and durability, it is most likely that the final bushing stiffness will differ in a later or final design from those used during source excitation testing. As a result, estimating the impact of bushing stiffness changes on the vehicle’s acoustic performance becomes a major challenge in the NVH design process. It is the aim of the presented Stiffness Injection method to provide the sensitivity of the bushings stiffness to the responses at the driver’s ears. This is achieved by introducing extra (virtual) spring / damper elements between the connection points at both the active and passive side of the bushing using the Virtual Point Transformation and experimental Substructuring technique. Overall this results in a cost-effective way to optimize the bushings for NVH purposes. After an academic experimental validation, the limits of the approach are discussed from a theoretical and robust system design point of view. Finally, an industrial application will be presented.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Automotive OEMs have introduced a new development paradigm, modular architecture development, to improve diversity quality and production efficiency. It needs solid fundamentals of system-based performance evaluation and development for each system level and single component level. When it comes to NVH development, it is challenging to realize the modular concept because noise and vibration should be transferred through various transfer path consisting of many parts and systems, which interact with each other. It is challenging for a single system of interest to be evaluated independently of the adjacent parts and environments. In this study, a new system-based development process for a vehicle suspension was investigated by applying blocked force theory and FRF-based dynamic substructuring. The objective is to determine the better dynamic stiffness distribution of many bushes installed in a suspension system in the frequency range corresponding to road noise. The suspension force rig test methodology isolated the entire suspension system from the interaction with body structures. The blocked force outputs are measured directly on the suspension force rig. Dynamic substructuring is conducted to derive the transfer characteristics from tire wheel centers to multiple force outputs. Bush stiffness injection (BSI) method is developed through the dynamic substructuring of the system, by which suspension system-level blocked force differences by changes in multiple bush stiffnesses can be predicted without any actual bush-changing works. The BSI method enables a sensitivity analysis for each change in bush dynamic stiffness and an optimization study to determine the best combination of multiple bush dynamic stiffnesses.</div></div>

In order to reduce the sound radiation or the transmission of sound, plate-shaped components are often coated with damping materials.In the case of bending waves, the descriptive dynamic-mechanical properties are the bending loss factor and the bending stiffness.The most frequently used method is the resonance curve method (also called Oberst method), in which the dynamic-mechanical properties are determined in the one-dimensional bending eigenmodes of a rectangular bar.However, this very robust method has two serious disadvantages for many applications.Firstly, the loss factor can only be reliably determined up to a value of η ≤ 0.1, as the neighbouring modes overlap too much for higher values of the loss factor.Secondly, the properties can usually only be determined at two to three resonance frequencies.Based on the measurement setup of the resonance curve method, a new test method was developed that overcomes the above-mentioned disadvantages of the resonance curve method.The bending loss factor and the bending stiffness can be measured as a continuous spectrum and the upper measurement limit for the bending loss factor is not limited due to the system.This new bending wave method is based on the theory of the so-called rigid Bernoulli beam.

Perceptually convincing auralization of joint musical performances requires an accurate representation of individual source signals. Recording instruments in anechoic environments typically lack the natural and intrinsic characteristics of joint performances due to limited room acoustic and inter-musician feedback. An alternative is to use close miking techniques to capture individual instruments in a joint performance, but minimizing microphone cross-talk and room acoustic feedback is a challenge here. This study investigates the perceptual quality of close-mic recordings in auralization of an ensemble in comparison to the binaural recordings. Binaural and close-mic recordings of a string ensemble performance with different number of violins were collected from Detmold concert house, and its auralization was performed using the Binaural Room Impulse Responses (BRIRs) obtained from in-situ measurements and room acoustic simulation. The recorded and auralized samples were perceptually evaluated by expert listeners in terms of their naturalness and similarity. Although the binaural recordings were not always rated to be highly natural, the clip-on microphone signals auralized using BRIR measurements show a similar distribution of naturalness to them which demonstrates their applicability for auralization-related applications. However, less natural and dissimilar ratings of simulated samples indicate the need for improvement of auralization using geometry-based room acoustic simulations.

Abstract Due to the increasing bypass ratios of modern engines, the fan stage is increasingly becoming the dominant source of engine noise. Accordingly, it is becoming more and more important to develop not only efficient but also quiet fan stages. In this paper the noise emission of a fan for an aero-engine with bypass ratio of 19 is reduced within a multidisciplinary design optimization (MDO) by means of a hybrid noise prediction method while at the same time optimizing the aerodynamic efficiency. The aerodynamic performance of each configuration in the optimization is evaluated by stationary Reynolds-Averaged Navier- Stokes (RANS) simulations. These stationary flow simulations are also used to extract the aerodynamic excitation sources for the analytical fan noise prediction. The resulting large database of the optimization provides new insights into which extent an MDO can contribute to the design of both quiet and efficient fan stages. In addition to that the hybrid approach of numerical flow solutions and analytical description of the noise sources enables to understand the noise reduction mechanisms. In particular, the influence of rotor blade loading on the aerodynamic efficiency and the noise sources as well as the potential of configurations with a comparatively low number of outlet guide vanes (OGV) is explored.

This is a summary report of the most important aspects discussed during the YSI 2300 Analyzer Replacement Meeting. The aim is to provide the interested reader with an overview of the complex topic and propose solutions for the current issue. This solution should not only be adequate for the United States or Europe markets but also for all other countries. The meeting addendum presents three outcomes of the meeting.