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Extensions to the Mode Matching Method for Horn Loudspeaker Simulation

Kolbrek, Bjørn
Doctoral thesis
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http://hdl.handle.net/11250/2415853
Utgivelsesdato
2016
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  • Institutt for elektroniske systemer [2503]
Sammendrag
For loudspeaker horns, the throat acoustic impedance and the far

field directional characteristics are important measures of performance.

Both quantities depend greatly on the shape of the horn, and

the acoustical conditions at the mouth of the horn.

The Mode Matching Method (MMM) is a semianalytical method

for the simulation of sound propagation in ducts, and is the method

used as the fundamental building block in this work. In previous

work using this method, the horn has usually been assumed to be

mounted in an infinite baffle, a condition that is not realistic for most

real-world applications. Most horns are usually mounted in finite baffles

or cabinets, or placed close to reflecting surfaces or in rooms.

This work has therefore focused on extending the MMM to new cases

closer to real-world applications.

For horns without baffle, or with finite baffles or flanges, two methods

have been explored; one for axisymmetric horns based on the

solution for a semi-infinite unflanged duct, and one for general geometries

based on edge diffraction. For horns near infinite reflecting

surfaces, a method has been derived to compute the modal mutual radiation

impedance. For the final radiation condition, a horn mounted

in the wall of a room, two methods have been explored, where in

both cases analytical expressions for radiation impedance and radiated

pressure are found for shoebox shaped rooms. Experimental

verification of some of the cases mentioned above is provided.

The MMM is restricted to certain cross-sectional geometries; round

and rectangular geometries are treated in this work. In many practical

cases a rectangular horn is connected to a circular loudspeaker,

and in order to simulate this and similar configuration, a method has

been developed to interface the MMM with the Boundary Element

Method.

By modifying the MMM, it has also been possible to simulate radiation

from concave structures like loudspeaker diaphragms. Using

this approach it is also possible to simulate concave reflectors, as long

as the source is not outside of the cavity.

A final application of the MMM in this work, is the use of the

method to compute the transfer function and resonance frequencies

of non-shoebox shaped rooms. While the shape of the room is still

somewhat restricted compared to Finite Element Method simulations,

a wide range of rooms can be simulated.
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NTNU
Serie
Doctoral thesis at NTNU;2016:280

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