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Old 11th April 2013, 09:36 PM   #31
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I suggest trying this simulator:
Ripple Tank Simulation
It's a Java based simulator of the old school physics "ripple tank". It has a number of built-in examples to try.
Read all the notes before trying. Check out the "3D mode" which clearly illustrates the positive and negative pressures and how cancellation works.

Note: Due to the current Java based Internet exploits, you probably have (and should have) Java disabled in your browser. If so, you won't see the simulation when you go to the page. In that case, either enable Java for that page or download and run the app locally.
- Download the ZIP file.
- Create a folder and unZIP the files into it.
- You will have a local copy of the Web pages plus the Ripple.jar file. If you have Java installed, double-clicking on the .jar file will run the application.

Last edited by Don Hills; 11th April 2013 at 09:40 PM.
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Old 11th April 2013, 10:00 PM   #32
xrk971 is offline xrk971  United States
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Bvbellomo,
If you don't see how a quarter wave or half-wave resonator does anything, look at any woodwind/brass instrument and you will see how sound wave amplification works by taking the tiny vibrations caused by air flowing across an edge to oscillate and drive the air column inside the instrument to make a big sound. How loud is the sound of pursed lips blowing in plain air versus blowing in a tuba, trombone, french horn? If you play with the simulation tools, there are 10 to +15 dB gains to be had in the bass region with a back loaded horn or transmission line. Sure, a plain straight pipe TL will have terrible peaks and dips, but the point of good design is to mitigate all those things. Look at the predicted response curves of the many excellent designs that folks on this forum have produced and you will see that the peaks and valleys are for the most part, minimal. Look at the response curve for the TABAQ MLTL - it is flat as a board. I wouldn't dismiss the TL's or BLH's based on your experiments with simple straight tubes. And they are not bulky or large either so I am not sure why you say they take too much floor space. The Cornu BLH is a wall mount flat speaker and takes zero floor space.
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Old 12th April 2013, 05:53 PM   #33
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Quote:
If you don't see how a quarter wave or half-wave resonator does anything, look at any woodwind/brass instrument and you will see how sound wave amplification works by taking the tiny vibrations caused by air flowing across an edge to oscillate and drive the air column inside the instrument to make a big sound.
I am not saying it doesn't work, just that I don't understand how. Some of the best physicists today say they don't understand gravity, yet none are in fear of floating away into the sky.

I played around with the app, and will some more, but don't see how to edit the model numerically. Just drawing walls with my mouse and adjusting a slider for frequencies is of very limited use.

Wall-mounted anything may be out do to WAF.
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Old 12th April 2013, 10:07 PM   #34
xrk971 is offline xrk971  United States
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Google some tutorials on how to use HornResp - very helpful in getting started. You should not be using mouse with slider to start. The design should be manually entered as a series of areas, lengths, type of expansion based on an initial design that you come up with in sketch using rules of thumb or a starting known design from someone else.

How it works is the based on acoustic wave propagation theory, which is based on fluid mechanics, which is based on the Navier-Stokes equations, which is nothing more than an implementation of Newton's second law: F=ma, plus the conservation of mass equation. So we do indeed understand it all the way down to the governing equations. You may say we do not understand why F=ma works (like F_gravity=c x m1 x m2 / r^2. Those are phenomenological relations and cannot yet be proven, hence they are called "Laws". But that is irrelevant and should not stop one from using the relationship which for the most part works very well at describing the universe and has been used for successfully designing and making things like airplanes, rockets, cars, bridges, satellites, speakers, etc. Get to quantum levels and we use different equations...
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