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Modeling a time dependent signal in COMSOL ray acoustic physics

Posted 9 janv. 2018, 11:08 UTC−5 Acoustics & Vibrations, Modeling Tools & Definitions 5 Replies

Aishvarya kumar Jain
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Hello everyone,

I am relatively new to COMSOL. I would like to know weather it is possible to model a time dependent signal which is being emitted by a point source within COMSOL ray acoustic physics.

My simulation setup involves a simple room, where I have a point source somewhere on the floor and various recievers on the roof. Source will emit a chirp signal (a time dependent signal), where frequency is also a function of time.

I need to do a autocorrelation of the signal received at the receivers.

The problem that i am stuck with right now is, how to model this particular kind of signal in ray acoustics.

5 Replies Last Post 30 janv. 2018, 02:06 UTC−5
Mads Herring Jensen COMSOL Employee

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Posted: 7 years ago 16 janv. 2018, 09:40 UTC−5

Dear Aishvarya

Ray tracing is not a field simulation method so in general you cannot talk about sending in a time signal. The method is also a high freuqency method valid as long as the wavelength is smaller than typical geometric dimensions in the model.

Ray tracing is used to calculate the impulse response of a room for different source and receiver positions. This is possible in comsol 5.3a using the new impulse response post processing capabilities. Once you know the impulse response you can export it. In another signal processing software you can do a convolution with your full time signal to get the signal as experienced at a listening position.

I beleive that most infomration about tansmission etc can be extracted knowing the impulse response.

For an example see: https://www.comsol.com/model/small-concert-hall-acoustics-20145

Best regards Mads

Dear Aishvarya Ray tracing is not a field simulation method so in general you cannot talk about sending in a time signal. The method is also a high freuqency method valid as long as the wavelength is smaller than typical geometric dimensions in the model. Ray tracing is used to calculate the impulse response of a room for different source and receiver positions. This is possible in comsol 5.3a using the new impulse response post processing capabilities. Once you know the impulse response you can export it. In another signal processing software you can do a convolution with your full time signal to get the signal as experienced at a listening position. I beleive that most infomration about tansmission etc can be extracted knowing the impulse response. For an example see: https://www.comsol.com/model/small-concert-hall-acoustics-20145 Best regards Mads
Aishvarya kumar Jain
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Posted: 7 years ago 16 janv. 2018, 10:11 UTC−5

Hi Mads,

Thank you for the response.

Extracting the information from the impulse response is not what I desire. My main maotive is to determine the different sources and the time of flight of the signal of the respective sources. The detailed description of my problem is as follows:

I have more then one source in a room and each of them is characterised by a different chirp signal, which is being emitted in specific intervels. Through simulation I want to determine the time of flight of the signal from source to receiver. At receiver end, I want to do autocorrelation, to distinguish between the different chirp signals.

If this kind of simulation is not possible through ray acoustic module, what other options do I have. Frequencies that I am interested in ranges from 16kHz to 22kHz.

I am using COMSOL 5.3a.

Thank you.

Hi Mads, Thank you for the response. Extracting the information from the impulse response is not what I desire. My main maotive is to determine the different sources and the time of flight of the signal of the respective sources. The detailed description of my problem is as follows: I have more then one source in a room and each of them is characterised by a different chirp signal, which is being emitted in specific intervels. Through simulation I want to determine the time of flight of the signal from source to receiver. At receiver end, I want to do autocorrelation, to distinguish between the different chirp signals. If this kind of simulation is not possible through ray acoustic module, what other options do I have. Frequencies that I am interested in ranges from 16kHz to 22kHz. I am using COMSOL 5.3a. Thank you.
Mads Herring Jensen COMSOL Employee

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Posted: 7 years ago 23 janv. 2018, 08:41 UTC−5

Hi Aishvarya

If you are interested in the arrival time of differetn signals at receivers (microphones) you do not need to do any cross corelation. The approach would be to model one source at the time and then add multiple receiver data sets at the microphone positions. You can then add a global evaluation that uses the receiver data set as input. Here you can evaluate the special variable "re1first" for data set receiver 1, or "re2first" for recevier data set 2 etc. this variable gives you the exact arrival time of the first ray. We introduced this variable because we realized that the arrival time is important for loudpseaker alignment and otther applications.

Best regards Mads

Hi Aishvarya If you are interested in the arrival time of differetn signals at receivers (microphones) you do not need to do any cross corelation. The approach would be to model one source at the time and then add multiple receiver data sets at the microphone positions. You can then add a global evaluation that uses the receiver data set as input. Here you can evaluate the special variable "re1first" for data set receiver 1, or "re2first" for recevier data set 2 etc. this variable gives you the exact arrival time of the first ray. We introduced this variable because we realized that the arrival time is important for loudpseaker alignment and otther applications. Best regards Mads
Aishvarya kumar Jain
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Posted: 7 years ago 23 janv. 2018, 09:22 UTC−5

Hi Mads,

Thank you for this information. May I know what technique is being used to generate this value. Is it using a correlation method or just calculating the time of first disturbance.

I have checked it on a small model, but it doesnt seem to match with the timing of the first disturbance.

Thanks

Regards, Aishvarya

Hi Mads, Thank you for this information. May I know what technique is being used to generate this value. Is it using a correlation method or just calculating the time of first disturbance. I have checked it on a small model, but it doesnt seem to match with the timing of the first disturbance. Thanks Regards, Aishvarya
Mads Herring Jensen COMSOL Employee

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Posted: 7 years ago 30 janv. 2018, 02:06 UTC−5

Hi Aishvarya

It is simply based on the arrival time of the first ray. Notice that in small models with a small number of rays the default, built in expression for the receive size, may generate a "large" receiver (this is a virtual sphere). This may make the arrival time of the first ray deviate significantly from the idealized time of flight time. So increase the number of rays or manually set the size of the receiver to something small.

Best regards Mads

Hi Aishvarya It is simply based on the arrival time of the first ray. Notice that in small models with a small number of rays the default, built in expression for the receive size, may generate a "large" receiver (this is a virtual sphere). This may make the arrival time of the first ray deviate significantly from the idealized time of flight time. So increase the number of rays or manually set the size of the receiver to something small. Best regards Mads

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