## Acoustics Module

### New App: Small Concert Hall Analyzer

This application analyzes the acoustics of a small concert hall using the *Ray Acoustics* interface. The app lets you define an omnidirectional sound source, wall absorption parameters, properties of diffusers, and the location of a microphone where the impulse response is measured. The results include a filtered energy impulse response for a given Fourier component. Conceptually, the app can be utilized to optimize a given concert hall for a certain type of use, for example, classical music performance, jazz music, or poetry reading. Upon running the app, you would then remove absorbing panels or change their material to obtain the desired acoustics.

*A screenshot of an app for a concert hall that simulates the impulse response for a given omnidirectional sound source and microphone location, wall absorption parameters, and the properties of the diffusers.*

A screenshot of an app for a concert hall that simulates the impulse response for a given omnidirectional sound source and microphone location, wall absorption parameters, and the properties of the diffusers.

### Impedance Boundary Condition in Pressure Acoustics, Frequency Domain

Several predefined impedance boundary conditions now exist in the *Pressure Acoustics, Frequency Domain* interface, each used to model a certain acoustic behavior at a boundary. Potential cases include modeling the losses associated with a porous layer; a simple mechanical system (approximated by a combination of loss, compliance, and mass); the behavior at the opening of a wave guide; or the acoustics of different parts of the human ear. More specifically, the ear impedance and skin impedance models provide a tool for engineers to add realistic acoustic loads when developing and simulating headphones, hearing aids, headsets, and other mobile devices.

The impedance boundary conditions are divided into several categories with different options: *User defined, RCL, Physiological, Waveguide-end impedance, Porous layer, *and* Characteristic-specific impedance*. Note that, depending on the studied frequency, impedance conditions are only approximations of the true behavior; their advantage is that they have very low computational cost and give a good first approximation to complex systems.

Depending on the space dimension, the options for the impedance model are:

*User defined:*Enter a user-defined expression of any kind.*RCL:*Contains options for all possible combinations of an RCL (equivalent acoustic resistance, compliance, and inertance) circuit.*Image (a)**Physiological:*Includes models for human skin and ear (ear drum, pinna, and full ear).*Image (b)**Waveguide-end impedance:*Flanged and unflanged pipe-end impedance models.*Image (c)**Porous layer*: Select a layer thickness and porous model (same options as for the Poroacoustics feature).*Characteristic-specific impedance:*For plane, spherical, and cylindrical waves.

In the example shown (d), the *RCL impedance* model is applied to enable the modeling of the mechanical properties of a microphone that is used for measurement purposes. Two variations of the *Waveguide-end impedance* conditions are used in the Open Pipe verification example found in the Application Library.

*In this tutorial example of a generic 711 coupler used in an occluded ear-canal simulator, the serial RCL impedance condition is used to model the mechanical properties (the impedance) of the microphone used for measurements.*

In this tutorial example of a generic 711 coupler used in an occluded ear-canal simulator, the serial RCL impedance condition is used to model the mechanical properties (the impedance) of the microphone used for measurements. (d)

View additional screenshot (a) »

### New Additional Poroacoustics Models

The list of poroacoustic fluid models has been extended to include two equivalent density fluid models for modeling sediments and fluids with inclusions; the *Wood* and *Williams EDFM* models. Several new sets of predefined parameters have also been implemented for the *Delany-Bazley-Miki* model.

*Wood: For modeling fluids with inclusions such as particles.**Williams EDFM: An effective density fluid model used for the propagation of acoustic waves in sediments.**Delany-Bazley-Miki: Several new predefined empirical coefficients, including the Modified Allard and Champoux coefficients.*

### Dipole Point Sources in Pressure Acoustics, Frequency Domain

Mathematically, a dipole is a source that corresponds to two monopoles that are close to each other and are completely out of phase. Dipoles appear when there are fluctuating forces in the medium, such as a small object that vibrates back and forth, for example. A complex acoustic source may be expanded and approximated by a collection of point sources (monopoles, dipoles, and quadrupoles).

### Quadrupole Point Sources in Pressure Acoustics, Frequency Domain

A quadrupole is, mathematically, a source that corresponds to two dipoles that are close to each other. A complex acoustic source may be expanded and approximated by a collection of point sources (monopoles, dipoles, and quadrupoles).

*The pressure field isosurface and sound pressure level surface plots around a quadrupole point source with the lateral configuration type for the power.*

The pressure field isosurface and sound pressure level surface plots around a quadrupole point source with the lateral configuration type for the power.

### Interior Velocity Boundary Condition in Thermoacoustics

This condition is used to specify a velocity on an interior boundary in thermoacoustics. The condition can be used to specify sources, such as the velocity of a diaphragm in a miniature transducer that is modeled using a lumped circuit model, for instance. The velocity components can be prescribed independently and there is an option to force continuity in pressure across the boundary. There are also options for the thermal conditions.

### New Data Sets that Simplify Evaluating and Plotting the Far Field Outside the Computational Mesh

The *Parameterized Curve* and *Parameterized Surface* data sets now support evaluation where there is no domain mesh by selecting the *Only evaluate globally defined expressions* checkbox. This way, the far-field variables can be evaluated outside the mesh on a predefined parameterized surface or curve. The new *Grid Data Sets* feature can be used to plot the far-field solution outside the computational domain, in volumes or surfaces. You can have access to the resolution for this grid through the *Grid 3D *settings window.

*The pressure field plotted outside the computational domain (outside the mesh) on the Piezoelectric Tonpilz Transducer example using the Grid 3D data set and the Far-Field Calculation feature. The postprocessing on the transducer is plotted on the model's mesh, while the postprocessing in the far-field is plotted on a simple and invisible rectangular grid in the space encompassing the transducer.*

The pressure field plotted outside the computational domain (outside the mesh) on the Piezoelectric Tonpilz Transducer example using the Grid 3D data set and the Far-Field Calculation feature. The postprocessing on the transducer is plotted on the model's mesh, while the postprocessing in the far-field is plotted on a simple and invisible rectangular grid in the space encompassing the transducer.

### New Array Data Sets

A new data set for creating arrays of data has been introduced that can readily be used to plot periodic solutions. These array data sets can, for example, be used to visualize solutions from models that utilize the *Floquet periodic* boundary condition.

### Ray Acoustics: Intensity Calculations in Graded Media

The intensity calculation is now supported for graded media, that is, media where the speed of sound is space dependent. One example is the case of ocean acoustics, where the speed of sound typically depends on depth, due to the fact that it is dependent on temperature and salinity. The intensity calculation is now based on a curvature tensor rather than the principal curvatures. Under the *Ray Properties* section in the settings window for the Ray acoustics node, you select the option *Using curvature tensor* under the* Intensity computation *section.

### Ray Acoustics: Fluid Models with Attenuation

The medium properties now have two fluid model options for modeling the attenuation of the acoustic waves due to bulk losses. Attenuation becomes important in air at high frequencies and in large spaces, like concert halls. It is also important in underwater acoustic applications. *The Linear elastic* with attenuation option allows a user-defined expression for the attenuation coefficient, while the *Thermally conducting* and viscous option sets up the classical attenuation expression due to viscosity and thermal conduction.

### Ray Acoustics: Improved Support for Ray Acoustics with Frequency-Dependent Material Properties

In ray acoustics models, it is now possible to specify directly in the *Material* settings window the material properties that are dependent on the ray frequency or another ray property, instead of in the *Medium Properties* settings window. To do so, all ray properties must be contained within the new noenv() operator, which allows quantities that exist only on rays to be included in expressions defined on domains.

### Ray Acoustics: Other Improvements

- Improved performance for the domain-level
*Accumulator*feature: The variable computed by the domain-level*Accumulator*feature is now up to and more than ten times faster and more accurate than in version 5.0. These models no longer require manual changes to the solver sequence. - New release type:
*Release from Data File*feature. You can now import initial positions and directions of rays from a text file. - New option for the
*Release from Grid*feature: You can now set the*Grid type*to*All combinations*or*Specified combinations*. This gives better control over the initial placement of rays.

### Documentation

New modeling chapters have been added to the Acoustics Module User's Guide. These chapters contain information about modeling, tips and tricks, and good practices pertaining to meshing, solvers, and more.

### New Tutorial: Helmholtz Resonator Analyzed with Different Frequency Domain Solvers

This tutorial model simulates a frequency sweep of a generic Helmholtz resonator – a classic acoustics resonating circuit with a known theoretical solution – to illustrate how to use different solvers in the frequency domain. In addition to the *Stationary* solver, the model uses the *Asymptotic waveform evaluation* solver and the *Stationary, Frequency domain-modal* solvers, which both reconstruct the result based on expansions around a few exact solutions in the sweep range.

*In this tutorial example, the average pressure in the volume of a Helmholtz resonator is plotted as function of frequency. The response has been solved using the default Frequency Domain solver, the Frequency Domain solver with Asymptotic Waveform Evaluation (AWE), and the Frequency-Domain Modal solver.*

In this tutorial example, the average pressure in the volume of a Helmholtz resonator is plotted as function of frequency. The response has been solved using the default Frequency Domain solver, the Frequency Domain solver with Asymptotic Waveform Evaluation (AWE), and the Frequency-Domain Modal solver.

### New Tutorial: Piezoelectric Tonpilz Transducer with a Prestressed Bolt

This tutorial model shows how to model prestressed acoustic-structure interaction models using the perturbation solver. A tonpilz transducer is simulated at relatively low-frequency, but high-power sound emission conditions, which is a popular working configuration for transducers used in SONAR applications. The transducer is made up of piezoceramic rings stacked between a head mass and a tail mass that are connected by a central bolt.

The tutorial demonstrates how to incorporate the effect of pretension in the bolt. The frequency response of the transducer is studied to determine the structural and acoustic responses of the device, such as deformation, stresses, radiated power, sound pressure level, the transmitting voltage response (TVR) curve, and the directivity index (DI) of the sound beam. The tutorial model requires the Acoustics Module, Structural Mechanics Module, and AC/DC Module.

*The tonpilz piezoelectric transducer is a transducer for relatively low-frequency, high-power sound emission. The transducer is made up of piezoceramic rings that are stacked between massive ends and prestressed by a central bolt. The resonance frequency of the device is lowered by the tail and head mass. In this tutorial model, the transducer's frequency response is studied when the bolt is prestressed. The image shows the deformation of the tonpilz transducer at 40 kHz. The tutorial requires the Acoustics, Structural Mechanics, and AC/DC Modules.*

The tonpilz piezoelectric transducer is a transducer for relatively low-frequency, high-power sound emission. The transducer is made up of piezoceramic rings that are stacked between massive ends and prestressed by a central bolt. The resonance frequency of the device is lowered by the tail and head mass. In this tutorial model, the transducer's frequency response is studied when the bolt is prestressed. The image shows the deformation of the tonpilz transducer at 40 kHz. The tutorial requires the Acoustics, Structural Mechanics, and AC/DC Modules.

### Updated Tutorials

Several tutorials in the Acoustics Module's Application Library have been updated to showcase new features. Among these are the following:

*Open Pipe*: Uses the new*Waveguide-end impedance*boundary conditions for a flanged and unflanged circular pipe.*Generic 711 Coupler - An Occluded Ear-Canal Simulator*and*Lumped Receiver Connected to Test Set-Up with a 0.4cc Coupler*: Both tutorials use the new*RCL impedance*boundary condition.*Porous Absorber*and*Reflections off a Water-Sediment Interface*: Both use the new*Periodic data set*feature to represent the solution in postprocessing.*Bessel Panel*: Now solved with an iterative solver.*Jet Pipe*: The model is now solved using several study steps and the results are displayed by including the circumferential dependency.*Brüel & Kjær 4134 Condenser Microphone*,*Loudspeaker Driver*,*Generic 711 Coupler-An Occluded Ear-Canal Simulator*, and*Reflections off a Water-Sediment Interface*: All four tutorial examples now feature and use predefined multiphysics couplings.

*In the updated Jet Pipe model, the circumferential behavior of the pressure field is now included in postprocessing using a Revolution 2D data set. The model showcases the aeroacoustic behavior of noise emitted from a turbofan.*

In the updated Jet Pipe model, the circumferential behavior of the pressure field is now included in postprocessing using a Revolution 2D data set. The model showcases the aeroacoustic behavior of noise emitted from a turbofan.