ABSTRACT
There are several methods to capture and visualize the
acoustic properties in the vicinity of an object. This article
considers scanning PU probe based sound intensity and
particle velocity measurements which capture both sound
pressure and acoustic particle velocity.
The properties of the sound field are determined and
visualized using the following routine: while the probe is
moved slowly over the surface, the pressure and velocity are
recorded and a video image is captured at the same time.
Next, the data is processed. At each time interval, the video
image is used to determine the location of the sensor. Then a
color plot is generated. This method is called the Scan and
Paint method.
Since only one probe is used to measure the sound field the
spatial phase information is lost. It is also impossible to find
out if sources are correlated or not. This information is
necessary to determine the sound pressure some distance
from the source, at the driver's ear for example.
In this paper, the method of Scan and Paint is enhanced in
such way that it is possible to handle partial correlated
sources. The key of the novel method is having a pressure
microphone at the listener position which is used as a
reference sensor. With all this data, it is possible to derive the
spatial phase of the sources measured relative to the listening
position.
INTRODUCTION
Novel scanning methods have been recently introduced to
accurately map stationary sound fields in an efficient way [ 1,
2, 3, 4]. In the previous literature, sound pressure, particle
velocity, intensity, sound absorption or acoustic impedance
have been measured with a new scanning method developed
by Microflown Technologies called “Scan & Paint” [ 2, 3].
The properties of the sound field are determined and
visualized via the following routine: while the probe is
moved slowly over the surface, pressure and velocity are
recorded and, at the same time, a video image is captured.
Next, all data is processed. At each time interval, the video
image is used to determine the location of the sensor. Then, a
color plot is generated.
Nonetheless, phase information has not been taken into
account so far, only magnitudes of each measurable quantity
have been characterized. Measuring this quantity implies a
huge improvement for transfer path analysis problems, where
the contribution of multiple correlated sources to a given
position strongly depends on the phase characteristics of each
one of them.
This paper introduces the measurement procedure and the
implemented calculations so as to preserve the phase
information of the sound field. Lab results are presented to
validate the method experimentally. In addition, the method
demonstrated in a car interior, giving accurate results.
THEORY
Current scanning methods have two main disadvantages: they
are only able to characterise time stationary sound fields; and,
they do not usually preserve phase information. The first
disadvantage is an implicit feature of any scanning method
due to the fact that different areas of a virtual plane scanned
are not measured simultaneously. Nonetheless, relative phase
of the sound field can be measured by using a microphone
reference [ 4]. This information is necessary for transfer path
problems. Hence, not only the theoretical considerations of
A Scanning Method for Source Visualization and
Transfer Path Analysis Using a Single Probe
2011-01-1664
Published
05/17/2011
Daniel Fernández Comesaña, Jelmer Wind and Hans-Elias de Bree
Microflown Technologies BV
Copyright © 2011 SAE International
doi: 10.4271/2011-01-1664