The work described in this thesis comprises three parts: devising an original method capable of making absolute measurements of acoustic impedance (both modulus and phase) for brass instruments; developing formal subjective assessment procedures enabling the subjective dimensions of trombone quality to be quantified; discovering the extent to which the acoustic impedance of an instrument may be used to predict its subjective quality. The impedance measurement systems of various authors are reviewed, and the limitations imposed by such systems discussed. The computer controlled system devised by the author, which uses a hotwire anemometer to measure particle velocity, is then described in detail including transducer calibration and measurement accuracy. The factors governing the subjective quality of trombones, based on interviews with players, are introduced, and the techniques used to quantify subjective characteristics (Semantic Differential Scaling and Multidimensional Scaling) are presented together with a discussion of the advantages and disadvantages of each method. The results of a series of subjective experiments are given. Several hypotheses relating the subjective quality of an instrument to its impedance are discussed. For the trombone, the degree of harmonicity of the impedance maxima and the envelope of the impedance curve are shown to have an important effect on players' assessment.

This thesis describes a study into how sound interacts with activated carbon, a material that exhibits adsorbing and desorbing properties. Adsorption is where molecules from the surrounding gas are attracted to the material microstructure and held in place by a weak physical attraction force named after the scientist van der Waals\ desorption is the opposite process. Activated carbons include a complex porous structure, with a large internal surface area, and a considerable adsorption capacity caused by free electrons in the deformed graphene layers. The process of adsorption and desorption is usually associated with energy exchanges, caused by transfers of heat between the adsorbate molecules and the adsorbent surface. The study of acoustic interactions with granular activated carbons at normal conditions makes the subject of this doctoral thesis. Two main physical phenomena were seen to accompany sound propagation through the material: (i) an increase in volume compliance which is assumed to be caused by a change in the density of the interacting gas, and (ii) excess absorption at low frequencies thought to be due to the energy lost in the adsorption/desorption hysteresis. For the former, measurements on the impedance of low frequency Helmholtz resonators reveal significant shifts in resonance when activated carbon is used as a porous liner in the backing volume. At constant aperture dimensions, these shifts are attributed to a larger apparent volume of the resonator as compared to an empty backing volume. This phenomenon is in direct contravention of the physical theory associated with Helmholtz resonators as the resonant frequency of a device increases slightly when a porous solid is placed in the backing volume. An upper frequency limit of SOOHz is also determined where sorption effects in activated carbon are assumed to become almost negligible in relation to sound propagation. For the latter, the excess absorption at low frequency, a series of experiments to reveal the physical cause of the phenomenon have been undertaken. Hysteresis was observed during the sorption of humid air onto activated carbon at room temperature. At such conditions, the different rates of adsorption and desorption lead to a disturbance in the system equilibrium and cause a change in entropy. The return of the system to equilibrium is an exothermic process hence involves energy losses between activated carbon and the surrounding gas. This is suggested as a possible cause of the excess attenuation. However,the relaxation times are rather long for acoustic propagation, and further work is needed to examine this. An experimental apparatus to explore sound propagation through the material was devised. Results showed a violation of the equation of state for the relationship between volume and pressure: as the volume in a sealed chamber was reduced at constant temperature, the measured pressure change was found to be lower for a sample of activated carbon than when the chamber was empty; a phenomenon assumed due to the differences between adsorption and desorption rates. A new method for determining the porosity of a material exhibiting adsorption at acoustic pressures has been devised and found to be 81 ±7% for the granular sample examined. BET analysis and examination of electron microscope pictures allowed the pore size distribution to be found. Although the activated carbon sample has many very small pores (0.7nm in width), the BET isotherm showed that these will be saturated with water vapour in normal conditions. Consequently, the pores that affect sound propagation are those between the grains of the activated carbon, and the macropores (>50nm) on the surface of the grains. A theoretical model is developed and outlined based on the Langmuir isotherm. This was used to predict the sound propagation within the material and is compared to acoustic impedance measured in a large low frequency impedance tube, which was constructed especially for this project. The match between theory and measurement is rather poor, thought to be due to the lack of modelling the hysteresis effects in the adsorption- desorption cycle. Two applications of the material are examined, within a Helmholtz resonator and the cups of hearing defenders. In both cases, improved performance is seen. For instance, the use of the material in hearing defenders showed that activated carbon could be used to improve the attenuation at low frequencies in comparison to conventional foam liners.

This thesis has investigated objective measurements that relate to the perceived spatial attributes of reproduced sound. Research has been conducted into extant measurements that aim to quantify the perceived spatial attributes of concert hall acoustics, and those that are most likely to be successful for measuring the properties of reproduced sound have been identified. A relatively new measurement technique that may relate to the spatial perception of reproduced sound has also been analysed. This measurement is based on the quantification of the magnitude of fluctuations in interaural time and level difference. This has been investigated in detail, and the subjective effect that this measurement relates to has been elicited in a number of subjective experiments. The experiments used various types of noise stimuli that contained a range of fluctuations in interaural time difference. It was found that when the fluctuations are contained within a part of the signal that is perceived to be a sound source, a variation in the magnitude of the fluctuations alters the perceived width of that source. When the fluctuations are contained within a part of the signal that is perceived to be reverberation, a variation in the magnitude of the fluctuations alters the perceived width of the acoustical environment. This research has been applied to the development of novel objective measurement techniques, and to the specification of the subjective attributes that relate to these techniques. A final evaluation experiment has found that listeners can relate to the attribute descriptors that have been elicited, and that the novel objective measurement techniques that have been developed match the subjective data at least as well as the extant measurement techniques.

The bore profile and input impedance of a musical wind instrument provide valuable information about its acoustical properties. The time domain technique of acoustic pulse reflectometry can be used to measure the input impulse response of a tubular object, such as a wind instrument, from which both its bore profile and input impedance can be calculated. In this thesis, after a discussion of the theory of acoustic pulse reflectometry, the operation of a practical reflectometer is described and measurements of input impulse response, bore profile and input impedance are investigated. In general, the experimentally measured input impulse response of a tubular object contains a DC offset which must be removed for accurate bore reconstruction. A new, faster method of determining the DC offset is introduced which doesn’t require prior knowledge of the object’s dimensions. The bore profile of a test object, calculated by applying a lossy reconstruction algorithm to its input impulse response (after removal of the DC offset), is found to agree with directly measured radii to within 0.05mm. Various brass instrument reconstructions of similar accuracy are presented. An input impedance curve, calculated from the input impulse response of the test object, is found to have peak frequencies which agree with those of a theoretical curve to within 0.7% (a considerably better agreement than when a standard frequency domain measurement technique is used). Impedance curves of various brass instruments are presented. Bore reconstructions are used to confirm the presence, and in certain cases, the positions of leaks in instruments. For the special case of a leaking cylinder, the impedance curve is successfully used to calculate the size of the leak. Finally, a method is investigated which allows the practical reflectometer to measure longer objects than previously possible.

Security threats to important infrastructure cause problems to not only those who live nearby but also in a much wider sense. It is therefore desirable to consider the use of automated systems capable of detection and identification of potential threats. This thesis describes an investigation into acoustic and seismic methods for achieving such a system specifically for commercial road vehicles. Accurate algorithms have been developed for recognition of moving vehicles using fusion of acoustic and seismic signals. It has been found that seismic signals are less susceptible to interfering signals, making them optimal for detection of vehicles. Their much narrower bandwidth also increases processing efficiency and speed. Thus, the algorithm developed utilises firstly only seismic signals to detect vehicle presence, and then employs both acoustic and seismic signals for classifying type of the vehicle. The detection algorithm is purely time domain and uses seismic Log Energy together with a modification of Time Domain Signal Coding. The best detection accuracy obtained was 97.71 % with Support Vector Machine and 99.02 % with Learning Vector Quantisation Neural Networks. The classification algorithm to distinguish between trucks and cars utilises three relatively simple time domain methods: Zero-Crossing Rate, Log Energy and Autocorrelation of seismic signals; combined with LPC coefficients collected from acoustic signals. Classification with either SVM or LVQ reached 93.30 % or 80.80 % respectively. This study therefore has demonstrated it is possible to detect an approaching vehicle and classify its type by using acoustic and seismic signal processing.

The title of the practical research, 'The Transit Of Sound And The Perception Of Sonic Phenomena', is an inquiry into the fundamental nature of our physical environment and how sound behaves as it passes through that environment. Art works have been produced as practical research for the study and attended by visitors who could experience vibration as the manifestation of the transit of sound through different materials: air, water and solid matter. I chose familiar settings for five of the artworks, such as sitting in a car, lying in the bath, or being in a house. I developed different ways that the visitors could engage with the works and aimed to build on the visitors’ experiences of these places; heightening their perception by revealing or suggesting previously unnoticed physical evidence of the transit of sound through materials other than air. The experience of this body of works has revealed that the central element throughout is the visitors’ own imagination. In the study I increasingly chose locations to explore that required the visitors’ imaginations: connecting locations that included both our expanded environment; the planet and outside the earth’s atmosphere, and our own internal environment of the body. The study provided experiences for the visitors in each of the different artworks where vibration, as the manifestation of the transit of sound through different material, informed them of the planet's physical properties as articulated through sound. The final artwork, 'You Are Here', uniquely placed the experiences in an environment whereby the visitors could go home and relate their experiences directly to the rooms of their own homes, bringing their thoughts and reflections of the planet and their relation to it ‘closer to home’.

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