Sound science

[h.g.]

Much to the chagrin of a couple of the regulars here, on and off over the last few days I have been probing for knowledge about the basic science/physics of sound and finding it largely absent and what appears to be an absence of interest although the latter might have had a bit to do with defensiveness. I found this surprising given there was a clear and substantial interest in matters related to sound.

After a ponder I wondered if the root of the problem might be the maths (e.g. calculus) conventionally used to discuss the physics of sound leading to people not wanting to go there. So my first question is what proportion of a forum like this would be comfortable chatting about concepts involving differentiation and integration?

The electronic calculator enabled people to learn what division meant without needing to know how to perform long division. In a similar manner it is possible to use the numerical simulation of sound to present the basic science/physics without using any analytical calculus. This is almost never done because the physics of sound is almost always taught to engineers and scientists that have the maths. So the trickier second question is what might the level of interest be among people with an interest in home audio? I should stress that I am not talking about the results of simulations treating the software as a black box (e.g. room simulations) but using it to discuss the physics and what is inside that black box.

 

[tomelex]

I would like to think that each person brings something to the forum, and if you can relate it to audio, and it has science in it, then we would like to discuss. While I hate maths, integration and differentiation can be explained and then move on. In short my good man, begin your discussion. The other thing about maths, is one can then provide some verbal meaning of what the maths is saying so there can be some understanding.

We are few in numbers and limited in what we know, but here is the place for you to share and not be over-run with comments that don't contribute, and a reminder you are the moderator, you can delete what does not contribute to your thread. Press on and "learn" us what you want to share!

 

[amirm]

There is math and there is math. Pick a topic and explain it as you say so that we know what you are talking about.

So that I am calibrated on how far you can go, do you know what this equation is and a very simple and useful thing we can draw from it?

 

[iridium]

I hope h.g. has the correct answer.
BUT, if not, are you, Amir, going to educate us?

iridium.

 

[RayDunzl]

There is math and there is math.

The square of nabla times psi = , well, you get the idea.

Or, I could direct you to Włodzimierz Holsztyński , with whom I played ping-pong every afternoon at the Wiltel ATG ATM and Network Management Lab, at least until I devised a method to beat him, and he lost interest in playing with me, for a (probable) dose of mathematical humblement.

 

[NorthSky]

There is math and there is math. Pick a topic and explain it as you say so that we know what you are talking about.

So that I am calibrated on how far you can go, do you know what this equation is and a very simple and useful thing we can draw from it?

View attachment 951

Airflow deflection theory?

• http://www.integener.com/SABTSKManuscript/IE150918DeflectionTheoryPage1.htm

 

[amirm]

I hope h.g. has the correct answer.
BUT, if not, are you, Amir, going to educate us?

iridium.

Of course .

 

[NorthSky]

CFO - I like. ...Ryhme with UFO.

 

[AJ Soundfield]

 

[amirm]

"i" by the way in electronics is "real." It is only imaginary in math!

It is another way to express the phase of a signal.

 

[AJ Soundfield]

Ok fine, no "i"

 

[h.g.]

I would like to think that each person brings something to the forum, and if you can relate it to audio, and it has science in it, then we would like to discuss. While I hate maths, integration and differentiation can be explained and then move on. In short my good man, begin your discussion. The other thing about maths, is one can then provide some verbal meaning of what the maths is saying so there can be some understanding.

Calculus is typically learnt over a period of a couple of years at school followed by a few years use at university for it to stop being an exam exercise and become a useful tool for explaining and working out what is going on. How much of that is likely to be successfully included in a paragraph before moving on to use it to chat about the physics?

Rather inconsiderately the forum software here does not include numerical simulation software that would allow us to bypass the maths when expressing the physics. I am also not sure how well the results of simulations could be posted in a two stage process. For example, can we include some webgl to read and display a datafile from somewhere? Perhaps Amir can comment.

Science isn't going to be effectively introduced by chatting in a forum but by writing articles, chatting about that in a forum, going back to rework the article, chatting a bit more,... In other words something more like a wiki.

We are few in numbers and limited in what we know, but here is the place for you to share and not be over-run with comments that don't contribute,

If you look at the comments below how many are addressing the questions asked? Which I guess is answering the second question to a fair extent.

and a reminder you are the moderator, you can delete what does not contribute to your thread.

Why would I want to do that. If a discussion is edited by one side it is no longer a discussion but pushing the view of that side. Perhaps something to consider with comments in a blog but rather less so in a discussion forum.

 

[h.g.]

So that I am calibrated on how far you can go, do you know what this equation is and a very simple and useful thing we can draw from it?

An equation has how many equals signs? Is the notation consistent or mixed? The quantities involved are defined where? So we can indeed draw a few useful things.

Although often linear (you need to define the quantities before we know) it has mathematical properties that make it far from simple to handle in general. This lead to the development of computational acoustics lagging other engineering areas like structural and fluid mechanics by decades with the acoustics community tending to stick with complex and limited analytical approaches.

In terms of physics it involves a range of simplifying assumptions about the motion, state of the fluid (assuming it is a fluid - you need to define the quantities before we will know), the forces involved,... For example, it can be used to discuss with Ethan the science of how subwoofers can both create and absorb sound (active absorbers) but the physics of his passive absorbers has been assumed away. Reducing the level of assumptions so the relevant physics is included in a general manner will introduce more equations and other types of waves like vorticity and entropy. However, in turn, we can make another set of assumptions to get back to your single equation but with sources on the right hand side. A more conventional way to write the equation is with the first or second term and the third on the LHS and the sources on the RHS using a defined and consistent notation.

My main question was not whether equations like the above are useful and informative to the bulk of the posters here, they obviously are not, but whether the physics about sound they represent is of interest. So far the answer has been no but perhaps one or two others will chip in with an interest if the discussion develops.

 

[amirm]

My main question was not whether equations like the above are useful and informative to the bulk of the posters here, they obviously are not, but whether the physics about sound they represent is of interest. So far the answer has been no but perhaps one or two others will chip in with an interest if the discussion develops.

As I mentioned, that equation is actually useful. I will explain later. Since you don't know what it is, we have established an upper bound on mathematics you meant to discuss. The math by the way, is college level.

Physics of sound is also useful if there is a) good teacher behind it and b) the person actually knows the physics of sound. I am waiting for you to demonstrate these skills. As I said, give an example of physics and explanation behind it.

As for forum software, for equations there are a number of online sites that let you write it and then output a picture you can post here. If the output already exist and you want a moving one like a simulation, get or build an animated gif. Here is a (relevant) example:

 

[h.g.]

As I mentioned, that equation is actually useful. I will explain later. Since you don't know what it is, we have established an upper bound on mathematics you meant to discuss.

I will look forward to it since you have clearly not understood my teasing. You also seem to have misunderstood the whole point of the exercise which is to explain the physics/science without using maths that few on the forum understand.

The math by the way, is college level.

That depends on how you go about solving it to produce the predictions required by science.

As for forum software, for equations there are a number of online sites that let you write it and then output a picture you can post here. If the output already exist and you want a moving one like a simulation, get or build an animated gif. Here is a (relevant) example:

My articles are not written like that. Several of the figures are animated 3d objects which the user can pan, rotate and zoom. For example, a figure for the mode shapes of a loudspeaker cabinet and drivers has a button to select the mode and the mouse controls the zoom, pan and rotate so the user can view the motion both inside and outside the cabinet. It is standard html5/css3/js using webgl and runs in the browser but how to best store and load the datafiles for each mode was the question. It is no problem when authoring a static website but I don't know about the restrictions on forums. If it is not ringing any bells with you then it is probably not worth pursuing further at this stage.

 

[amirm]

My articles are not written like that. Several of the figures are animated 3d objects which the user can pan, rotate and zoom. For example, a figure for the mode shapes of a loudspeaker cabinet and drivers has a button to select the mode and the mouse controls the zoom, pan and rotate so the user can view the motion both inside and outside the cabinet. It is standard html5/css3/js using webgl and runs in the browser but how to best store and load the datafiles for each mode was the question. It is no problem when authoring a static website but I don't know about the restrictions on forums. If it is not ringing any bells with you then it is probably not worth pursuing further at this stage.

Make a video out of it, upload it to youtube and then link it here. Here is that process in the computation fluid dynamics analysis that we used (by Keith Yates) to find optimal position for three subs as compared to a single one:

 

[h.g.]

Make a video out of it, upload it to youtube and then link it here.

Some things work better as a video but the efficiency of wrapping ones head around a set of mode shapes for a complex object by interactive viewing is preferred although the need to load the whole file before viewing can become intrusive it if takes more than a few seconds.

 

[DonH56]

There is math and there is math. Pick a topic and explain it as you say so that we know what you are talking about.

So that I am calibrated on how far you can go, do you know what this equation is and a very simple and useful thing we can draw from it?

View attachment 951

Appeared in chapter one or two of my first grad acoustics text back when I took the classes so long ago... Not sure I wanted the reminder, Amir.

 

[h.g.]

Appeared in chapter one or two of my first grad acoustics text back when I took the classes so long ago... Not sure I wanted the reminder

Does this mean you have not used the most common equation in acoustics to guide any of your reasoning about what is going on with sound? Was that because the physics is uninteresting, the form of maths is a bit of a barrier, or perhaps something else?

 

[amirm]

Appeared in chapter one or two of my first grad acoustics text back when I took the classes so long ago... Not sure I wanted the reminder, Amir.

At least you remember. I had forgotten it completely and had to learn it again a few years ago!