Abstract
The active control of sound can be used to control the acoustics of
interior spaces, to reduce the sound radiation of machines and equipment, to
decrease and even to refine noise in a more comfortable form in, e.g., ducts
and vehicles.The JMC method, developed by Jessel, Mangiante and Canévet, is a
systematic tool in the active control of sound.It is applied mostly by using
scalar weighting, in which all the first-order field quantities and primary
source strengths are weighted similarly.In this thesis, a modified JMC method
is developed, in which the primary sources remain unchanged in all cases, the
situation being more similar to a practical one.On the basis of the modified
JMC method, the vector and dyadic weightings are defined, the former weighting
the sound pressure and particle velocity independently, and the latter also
changing the direction of the particle velocity.These new weightings increase
the possibilities in field reshaping.In the JMC method, three types of
secondary sources are needed: monopoles, dipoles and quadripoles.It is found
that in multi-source configurations, the last ones are automatically generated
by the dependence of the dipole distribution on the lateral coordinates.Four
three-unit approximations of the JMC element (i.e., detector-actuator
combination according to the JMC method) are developed, in which one of either
the primary field quantities or the secondary source quantities is
approximated by the help of a field impedance function.For waveguides (e.g.,
ducts), ideal unidirectional three-element and two-element JMC source
configurations and their approximations are discovered.The inter-channel delay
in the control structure of the two-element actuators may be optimized
downstream or upstream, or omitted altogether.Especially the last case turns
out to be advantageous in the practical implementation of digital control
systems.The adaptive JMC structures for the new ideal two-element solutions
are presented.The results of this thesis enlarge the possibilities in the
active control of sound and facilitate more useful applications to be realized
in ducts and three-dimensional spaces.
Original language | English |
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Qualification | Doctor Degree |
Awarding Institution |
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Supervisors/Advisors |
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Award date | 28 May 1999 |
Place of Publication | Espoo |
Publisher | |
Print ISBNs | 951-38-5377-2 |
Electronic ISBNs | 951-38-5378-0 |
Publication status | Published - 1999 |
MoE publication type | G5 Doctoral dissertation (article) |
Keywords
- ducts
- JMC method
- JMC element
- active noise control
- waveguide
- unidirectional actuators