Low-Frequency, Open, Sound-Insulation Barrier by Two Oppositely Oriented Helmholtz Resonators

In this work, a low-frequency, open, sound-insulation barrier, composed of a single layer of periodic subwavelength units (with a thickness of λ/28), is demonstrated both numerically and experimentally. Each unit was constructed using two identical, oppositely oriented Helmholtz resonators, which were composed of a central square cavity surrounded by a coiled channel. In the design of the open barrier, the distance between two adjacent units was twice the width of the unit, showing high-performance ventilation, and low-frequency sound insulation. A minimum transmittance of 0.06 could be observed around 121.5 Hz, which arose from both sound reflections and absorptions, created by the coupling of symmetric and asymmetric eigenmodes of the unit, and the absorbed sound energy propagating into the central cavity was greatly reduced by the viscous loss in the channel. Additionally, by introducing a multilayer open barrier, a broadband sound insulation was obtained, and the fractional bandwidth could reach approximately 0.19 with four layers. Finally, the application of the multilayer open barrier in designing a ventilated room was further discussed, and the results presented an omnidirectional, broadband, sound-insulation effect. The proposed open, sound-insulation barrier with the advantages of ultrathin thickness; omnidirectional, low-frequency sound insulation; broad bandwidth; and high-performance ventilation has great potential in architectural acoustics and noise control.

Assessing Wind Impact on Noise Level Measurements for Application in Architectural Acoustics: A Preliminary Study

In this study, we have used wind data obtained from an earlier work covering several locations in Nigeria to estimate the possible impact of wind on sound pressure levels. Estimated Weibull parameters were used to compute the most probable wind speed, the average wind speed and the duration for which wind speed exceeds or equal the most probable speed. Adopting the proposed criteria that wind is able to strengthen or weaken sound pressure levels by 3dB depending on wind direction, the effect of wind on sound pressure level was determined. Results showed that wind effect seemed more predominant for the sub-sahelian stations such as Sokoto, Kano, and Maiduguri where the impact was found to be +/- 3dB obviously due to the characteristic high wind speeds recorded at those stations. The situation is almost the same for the midland region except that moderate impacts were found in some of the stations like Yola, Yelwa and Bauchi. However, moderate wind impacts generally characterize the Guinea Savannah and the coastal regions with the exception of Enugu with an impact of +/- 3dB. The result for Warri was found to be insignificant. It was concluded that most locations within the Nigerian environment may attain the wind conditions that would necessitate an adjustment in noise level measurements for application in architectural acoustics. In order to further validate the results of this preliminary study, it was recommended that detailed field survey where all relevant parameters such as wind speeds, wind directions and noise levels are simultaneously measured be conducted.

Introduction

The book is arbitrarily structured around the parameters of melody, rhythm, harmony, texture, and pre-compositional approaches. All chapters start with a brief note on terminology and general recommendations for the instructor and the student. The first five chapters offer a variety of exercises that range from analysis and style imitation, to the use of probabilities. The chapter about pre-compositional approaches offers original techniques that a student composer can implement in order to start a new work. This last section of the book fosters creative connections with other disciplines such as math, visual arts, and architectural acoustics. Each of the 100 exercises contained in the book proposes a unique set of guidelines and constraints intended to place the student in a specific compositional framework. Through those compositional boundaries the student is encouraged to produce creative work within a given structure. Using the methodologies in this book, students will be able to create their own outlines for their compositions, making intelligent and educated compositional choices that balance reasoning with intuition.

A design framework for absorption and diffusion panels with sustainable materials

Architectural acoustics has not traditionally had unified design methods that specify acoustical performance, visual appearance, and sustainable material selection, leading to underperforming products that contribute to a waste stream of petro-chemical foam and fiberglass materials. The evolution of design, materials, and manufacturing techniques in recent years has created new opportunities to reimagine acoustic diffusers and absorbers. Previous work by the authors have demonstrated a unifying framework for design and collaboration in architectural acoustics. The framework uses visually-driven computational design method inspired by shape grammars that generate a wide range of acoustic phase grating diffuser arrays that display unique visual and performative qualities. Simulation and evaluation metrics to assess the complexity of each design are rated in terms of their diffusion and absorption coefficients and a visual aesthetic coefficient. This paper extends the framework to include digital fabrication protocols and sustainable material specifications - including the use of fungi-based materials. Built prototypes demonstrate an expanded acoustic design space that gives acousticians the potential to create custom diffuser shapes with precise acoustical response. The innovative combination of computational design methods and sustainable fabrication protocols will be discussed, and the acoustic properties of arrays will be evaluated and compared to simulations of corresponding designs.