The present paper is a revised and shortened version of that presented to the Seventh International Congress on
Sound and Vibration held in Garmisch-Partenkirchen, Germany. It presents speculative and controversial ideas
on a possible fluid mechanics model for 'dark matter' in the Universe and the impact it would have on the established
theory of light propagation and its relation to sound propagation. Since 'dark matter' has escaped all observations
on Earth it must be assumed that should it be a particulate its particle mass and size will be almost infinitesimal
compared with all existing atomic and subatomic matter. Thus, its thermodynamic properties of mean
particle speed and wave propagation speed will approach that of light, and therefore provide the medium for the
propagation of electromagnetic radiation. The model satisfies the 'Principle of Relativity' and the classical theories
of fluid mechanics, gas dynamics, and thermodynamics, and reopens discussion on the hypotheses introduced
by Einstein concerning laws of nature, the propagation of wave motion in a void, and the absolute speed
of light. The presence of this form of 'dark matter' is shown to unify the theories of sound and light propagation
even though their speeds of wave propagation differ by an order of a million times. Hence both disciplines obey
the laws of space-time for they are solutions of the same homogeneous 'unique' wave equation, and the corresponding
convected wave equation for the case of moving sources. These equations satisfy covariant and coordinate
invariance and are therefore laws of nature for all speed ratios. When this model of 'dark matter' is applied
to cosmology, it provides a model for the expanding Universe. The results of electromagnetic and acoustic wave
motion generated by bodies and electric charges in motion, for the same speed ratio with respect to wave propagation
speed, are found, as expected, to be similar to the propagation of capillary waves in a ripple tank.

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Propagation of High Frequency Waves
in Slender Engineering Structures

Alexander K. Belyaev, Thurid Gloetzl, Franz Ziegler

A one-dimensional wave-guide based on a Cosserat-type primary structure with secondary substructures of
oscillator-type attached is developed. Propagating longitudinal waves are studied under simplifying assumptions:
e.g., straight axis, frictionally damped principal rod-structure with variable cross-section, unloaded mantle, i.e.,
excitation is solely concentrated at the foundation of the building model, etc. Using harmonic linearisation, the
resulting integral equation is solved by taking the logarithmic derivative and filtering out negligible contribu-
tions. The main results, crucial in tall building acoustics, are critical frequencies and the separation for spatially
increasing or decreasing amplitude frequency response functions, and the input-independent upper limit for the
strain amplitude. Two main counteracting effects on the propagating wave are identified: energy absorption (due
to friction in the primary structure and due to energy absorption in local resonance of the secondary systems)
and amplification by decreasing cross-sectional area.

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GSM TDMA Frame Rate
Internal Active Noise Cancellation

A common problem in the world's most widely-used cellular telephone system, the GSM system, is the interfer-
ing signal generated by the switching nature of TDMA cellular telephony in handheld and other terminals. Sig-
nals are sent as chunks of data, speech frames, equivalent to 160 samples of data corresponding to 20 ms at sam-
pling rate of 8 kHz. This paper describes a study of two different software solutions designed to suppress such
interference internally in the mobile handset. The methods are 1) notch filtering, which is multiplicative in fre-
quency, and 2) subtractive noise cancellation, which is an alternative method employing correlators. The latter
solution is a straigtforward, although somewhat unorthodox, application of ?in-wire? active noise control. Since
subtraction is performed directly in the time domain, and we have access to the state of the mobile, it is also pos-
sible to consider a recurring pause in the interference caused by the idle frame in the transmission, when the mo-
bile listens to other base stations communicating. More complex control algorithms, based on the state of the
communication between the handset and the base station, can be utilised.

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Sound Source Characterisation and Transfer Path
Analysis with Time Histories

The article describes a method to separate time histories of partial sound sources. The goal is to develop a noise
control engineering tool for use in sound quality improvement applications. Contributions from partial sound
sources are identified. The partial sound sources may be ranked for the purpose of creating a better mixture of
sound in selected listening positions. The strategy is to reproduce time histories of sources of importance. The
method described includes experimental and calculation parts. The experimental part consists of the recording of
sound pressure time signals, reciprocal measurement of frequency response functions, and source strength esti-
mation of partial sound sources. The calculation part comprises calculation of the cross-spectral matrix of source
strength, calculation of filters, and filtered sound pressure recording to obtain time signals of the individual
sources. Usually the contribution from partial sources is impossible to record directly. In this laboratory experi-
ment, such control was possible. The laboratory experiment shows that the method described makes it possible
to produce informative separation of time histories of partial sound sources. The effects of the errors in the cal-
culated time histories are audible but not pronounced.

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Acausality Alleviation via Nonlinear Future
Prediction in Feedforward Control of Vibrations

An augmented version of the LMS feedforward algorithm is used, in discrete time simulation, to control a twobeam
and one-spring system in an acausal configuration. For perfect control, the required control force is unbounded
due to acausality. Imperfect but good control is possible if about-to-act disturbances are known slightly
in advance. In the simulations, a broadband yet deterministic chaotic time series is used as the disturbance
(a brief characterisation of measured fan noise is presented for comparison). Signal determinism is exploited using
a neural network trained to predict some future values of the signal, and the prediction is included in the
feedforward loop of an augmented version of the filtered-X LMS algorithm. This controller significantly outperforms
the standard algorithm without future prediction. The present controller can be viewed as a neural network
based and disturbance-dependent approximation to an acausal controller; but also as a causal nonlinear controller
for a linear system in an acausal configuration.