Simcenter Soundbrush – Everything you need to know
The Simcenter Soundbrush (formerly called LMS Soundbrush) is an easy-to-use acoustic tool that enables real-time, 3-dimensional visualization of a sound field. The Soundbrush measures sound intensity, which provides both the magnitude and direction of sound (see Figure 1). Mapping the sound intensity allows the user to locate the sources of noise, measure and visualize the sound propagation, as well as calculate objective quantities like sound power. Using an 3D tracking system, Soundbrush measurements are quick and easy to setup, and results are real-time – no further processing required.
This Simcenter Soundbrush article covers:
The Simcenter Soundbrush is a different kind of sound intensity probe. Traditionally, when making sound intensity measurements a prescribed measurement surface area is used (see Figure 2). The intensity probe must stay in this plane, and in a very specific orientation, typically normal to the measurement plane. Any variance in probe orientation or distance from the plane will distort the data being measured. Results apply only to this surface area, and no information is provided outside of it.
Soundbrush is different – it automatically tracks the location and orientation of the probe, and adjusts the data accordingly. Move the probe tip wherever intensity information is desired, and the Soundbrush does the rest. This allows the Soundbrush to map sound intensity not only at the boundary of an object, but also outward into the surrounding environment, giving insight into how the sound propagates away, and even reflects off walls and other objects.
In order to accomplish this, the Soundbrush utilizes a system of sensors, shown below in Figure 3.
These sensors include a tetrahedral intensity antenna (1), an illuminated sphere (2), onboard gyroscopes (3), and a tracking camera (4). The tetrahedral antenna allows Soundbrush to measure the X Y Z components of the sound intensity all at once, as opposed to one direction at a time, like a typical sound intensity probe (Figure 4).
The illuminated sphere and tracking camera work together to provide location of the Soundbrush in real time. During setup, the Soundbrush software automatically selects the best color of the sphere for the given lighting conditions, and locks in on its position. Movement in the lateral and vertical dimensions are handled optically by keeping a crosshair icon in the center of the sphere. As the Soundbrush moves closer to and further away from the tracking camera, the sphere size changes, and the software registers these changes. This process can be seen in Figure 5.
Finally, the onboard gyroscopes track all rotation of the probe, translating the known position of the sphere to the tetrahedral intensity antenna, where the measurements are being made. This translation allows for the Soundbrush probe to be held in any position during measurement, and the intensity vector will remain correctly oriented. Figure 6 below shows a comparison of a standard 12mm pressure-pressure sound intensity probe (in red) and the Soundbrush, held in 49 various orientations.
Putting all these systems together allows the user to wave the Soundbrush freely around the object under test. No longer must the operator worry about the orientation of the probe, or about keeping the probe tip in the measurement plane. Soundbrush tracks the location of the probe in real time, and corrects for all rotation during the measurement. The result is a fast, easy, stress-free test, providing real time sound intensity results in full 3D. (Figure 7)
Included & Optional Equipment
The Soundbrush comes complete with everything needed; all packaged in a rugged, water-proof Pelican case, complete with custom-fitted foam compartments and push-button locking closures (Figure 8).
Soundbrush Kit includes:
Setup of the Soundbrush requires only two USB connections to a PC: one for the Soundbrush, one for the tracking camera.
The Soundbrush offers two different antenna types – the tetrahedral sphere [3DINT] for measuring sound intensity, and the ½” microphone [MIC] antenna for measuring sound pressure (Figure 9). The Soundbrush kit can be ordered with either or both of these antennae, and both can be stored in the carrying case simultaneously. Soundbrush software automatically detects antenna type, and adjusts acquisition parameters to suit.
The spherical intensity antenna is capable of measuring 3D intensity from 100 Hz – 4,000 Hz. For higher frequency sources, the microphone antenna plots scalar sound pressure in 3D space from 3.15 Hz – 20,000 Hz (see Figure 10). This allows critical high-frequency sources to be located quickly and easily, when the intensity antenna is not appropriate.
Soundbrush Software Overview
The Soundbrush dedicated software leads the user step by step through the process- from creating a new project, setting up a geometry, to calibrating the sensors and acquiring data. There is no post-processing to be done, but more in-depth analysis can be performed, as well as automatic export of the project data to a Microsoft Excel spreadsheet (Figure 11).
Home – Create a new Soundbrush project or open an existing one. Import and export Soundbrush projects for easy sharing amongst colleagues or customers.
Setup 3D – Import a geometry from CAD or .STL. If no model exists one can be quickly created from scratch within the Soundbrush software. Import and paste pictures onto a generic volume. (Figure 12) For large CAD exports, Soundbrush even offers an optional STL model file size reducer which automatically simplifies complex models to exterior surfaces and a reduced number of triangles for fast import and lag-free rotation.
Setup Reference – Calibrate the camera location using the included reference checkerboard. This process ensures all data will be correctly located around the 3D model by establishing a consistent origin and coordinate system between the software and the test object. Soundbrush automatically selects the optimal color for the illuminated sphere based on lighting conditions.
Acquisition – Real-time data display: populates intensity vectors during scanning, displays overall intensity level, live frequency spectra or octave displays.
Analysis – Rotate 3D data fields, add cutting planes, contour plots and calculate sound power (Figure 13).
Report – Automatically export intensity, pressure, particle velocity at each position and frequency to MS Excel spreadsheet.
Laptop with stereo speakers
To highlight the sound source localization capability of the Soundbrush, a laptop with stereo speakers was tested. The laptop played 500 & 1000 Hz tones out of the left (L) speaker, and a 2000 Hz tone out of the right (R) speaker simultaneously.
The Soundbrush is capable of showing the 3D intensity vector plots for various frequency ranges. When a band of frequencies is selected, the vectors will show the average intensity for the band, weighted by amplitude. For the laptop test, three different frequency bands were selected, with the corresponding vector plots shown in Figure 14 below.
When the full 100 Hz – 4000 Hz frequency band is selected (Figure 14 A) the vector plot shows two distinct sources of noise, the L & R speakers. The higher amplitudes of the 500 Hz & 1000 Hz peaks in the frequency spectrum also dominate the intensity field, resulting in a larger area of high amplitude red vectors for the L speaker than for the R speaker.
By narrowing the displayed frequency bands, it becomes possible to fully isolate each noise source (speaker). In Figure 14 B, the frequency band is restricted to frequencies between 500 – 1000 Hz. Sound in this frequency range is only being played through the left speaker, and the intensity vectors update accordingly, highlighting the source. To isolate the right speaker, the frequency band is changed to the 2000 Hz band (Figure 14 C), and the vector plot updates automatically.
The ability of Soundbrush to show sound intensity vectors in 3D on a frequency by frequency basis makes it a very powerful tool for sound source localization. Simply specify the frequency band of the noise problem, and Soundbrush shows where sound at that frequency is being generated, and how it is flowing around the structure.
One area where sound intensity measurements are often used is in noise barrier development. For example, an automotive dash mat needs to absorb or block noise coming from the powertrain, transmission and various accessories in the engine compartment from entering the passenger cabin. Sound intensity measurements allow engineers to see where sound is getting through the dash mat, and at what frequencies. Soundbrush excels in this application, because it also provides the 3D vector of the sound getting through (as opposed to only the normal component), which may help indicate the source of the noise, or where the weakness is in the barrier (Figure 15).
Another use of sound intensity in applications like the dash mat is calculating sound power. By calculating sound power for various sources of noise, it is possible to quantify how much each source adds to the overall noise. This makes it possible to address the largest contributors first, saving time and resources.
Figure 16 shows a cutting plane added to the 3D vector plot in the Soundbrush software, and the resulting contour plot. Moving the cutting plane through the 3D vector field displays a 2D contour plot of the sound intensity normal to the plane. For this test, the contour plot shows three main noise sources in the dash mat, which appear as bright red circles.
Calculating sound power for each of these source will allow them to be quantified and rank-ordered.
As sound intensity is defined as sound power per unit area (with units of watts per meter squared – W/m2), in order to get a calculated sound power in Soundbrush all that is needed is to specify an area. A calculation area can be added to the contour plot, and by simply sizing and locating the box over each of the sources, a sound power (decibel referenced to a picowatt) is shown in the upper left legend of the contour plot. The results for the three sources is shown below in Figure 17.
Thin plate in resonance
A thin metallic plate is driven by a modal shaker. The plate is excited at one of its resonant frequencies (176 Hz), producing a singular mode shape: the 5:1 mode shown in Figure 18 below.
Notice the vectors leaving, turning, and returning to the plate in Figure 19. This behavior shows that this mode of vibration is not an efficient acoustic radiator. There are similar levels of acoustic intensity flowing out of, and in to, the plate. By adding a cutting plane to the 3D plot, a mode reminiscent of the classic 5:1 mode shape appears in the 2D contour plot (Figure 20). The color and grey scale contours indicate sound intensity in opposite directions.
Disc noise propagation
A similar case, but one showing efficient acoustic radiation, is shown below. A shaker is attached to a metallic structure, in this case a circular metallic disc. The shaker excites the disc at a known resonant frequency, setting up a vibration pattern dominated by a single mode shape (Figure 21).
Figure 22 below shows two distinct intensity behaviors. Near the surface, some of the vectors point back into the plate, and some point away. Sound is traveling both into and away from the plate near the surface. However, as the intensity is measured further and further away from the surface, the intensity vectors all align, and show acoustic energy flowing away from the plate. This is acoustic radiation – sound traveling away from the surface and propagating away. This behavior is similar to that in a speaker, where almost all of the acoustic energy propagates away from the speaker’s driver surface.