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Program to show room mode nodes and anti nodes
http://www.johnlsayers.com/phpBB2/viewtopic.php?f=3&t=6210
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Author:  lex [ Tue May 16, 2006 6:36 am ]
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Brilliant animation! That's exactly what I was looking for. It really helps to visualize this. I see they have a whole teaching section too, linked at the home page.

http://www.isvr.soton.ac.uk/SPCG/

I'm busy reading the print outs now from several sites and the ones you mentioned. I'll be back with a better understanding or maybe new questions. Thanks again.

Author:  knightfly [ Tue May 16, 2006 11:35 am ]
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So much good stuff in here (thanks David, Andre, and Lex for asking :=) I've made it a "sticky" so it won't get buried... Steve

Author:  lex [ Wed May 17, 2006 4:01 am ]
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Good idea Steve. I agree, this has turned into a great learning thread.

http://www.isvr.soton.ac.uk/SPCG/Tutori ... quency.htm

I looked at the bottom animation and was confused for a while. I was wondering about how that was possible without changing the pitch. But then pitch is dependent on the frequency. Then I thought how the velocity could only change if the medium changed or the conditions of the air changed. If this happened, then all waves would adjust and would still have the same frequency. I think I understand it now.

So the bottom animation is really an example of the same frequency moving through two different mediums.

Author:  lex [ Thu May 18, 2006 11:14 am ]
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Quote:
The correctable frequency range for both “peak” and “dip” correction spans from 20 Hz -250 Hz. The upper limit of 250 Hz was picked because of its wavelength. (The wavelengths at 20 Hz and 250 Hz are 56.5 feet and 4.5 feet respectively.) According to Jim Muller, above 250 Hz the wavelengths become so short that room resonance modes merge together to be indistinguishable. The short wavelength would also require a different correction from seat to seat. If you were to correct for frequencies that are in the 5 kHz - 10 kHz region, the wavelength is so short (on the order of inches) that even head movement in a given seat would yield response fluctuations! Frequencies above 250 Hz are best dealt with through the use of acoustic absorption materials like foam or fiberglass. V4 wisely leaves this range untouched.


Found this quote here:
http://www.hometheaterhifi.com/volume_1 ... -2004.html

Author:  lex [ Sun May 21, 2006 3:06 am ]
Post subject:  Question for a Physicist

This one is definitely a theory question for the physicist acoustician if you would be kind to enlighten me :idea: or give me directions. :)

After reading and observing about sound basics (frequency, velocity, wavelength, compressions, rarefactions, rays, waves, amplitude, intensity), and its behavior in different circumstances (diffraction, diffusion, reflection, refraction, interference), I am left with some fundamental questions.

Quote:
In distant rooms the bass notes are more prominent because their longer wavelengths are readily diffracted around corners and obstacles.
(pg 245 Master Handbook of Acoustics)

Ok, we are all familiar with this type of phrase but I'm wondering, why? I know after reading this excellent book that sound at different frequencies behaves differently depending on which range it falls. (pg 324 of the Master Handbook of Acoustics is excellent)

Here are a couple of paragraphs from Everest on these differences:

(pg 236 Master Handbook of Acoustics)
Quote:
Below 300-400 Hz, sound is best considered as waves (chapter 15 expounds on this). Sound above 300-400 Hz is best considered as traveling in rays. A ray of sound may undergo many reflections as it bounces around a room. The energy lost at each reflection results in the eventual demise of that ray. Even the ray concept is an oversimplification: Each ray should really be considered as a "pencil" of diverging sound with a spherical wavefront to which the inverse square law applies.

The mid/high audible frequencies have been called the specular frequencies because sound in this range acts like light rays on a mirror. Sound follows the same rule as light. The angle of incidence is equal to the angle of reflection, as in Fig. 10-2.


Why do the high frequencies act as rays and why do the low frequencies act as waves? The frequency only determines the amount of wavefronts or compressions per unit of time but the wavefronts are the same(originate at a source and spread out in spherical fashion) for any sound. So why is it the wavefronts of low sounds can go around objects while the wavefronts of high sounds are reflected? Is this a difference of energy that it comes down to? The wavelengths are afterall the distance between the compressions or rarefactions and not a measurement of the wideness of a wave. The wavefront is not linear and finite, it is curved and infinite. So why is the wavelength which strikes perpendicular to the object the determinant of why a wave can go around an object?

Can someone help me understand this or tell me where I can find this information because I have been reading and not finding anything except general explanations? Thanks.

Author:  Eric_Desart [ Sun May 21, 2006 9:35 pm ]
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For info to others.

You also entered the same here, where some responses followed:
http://forum.studiotips.com/viewtopic.php?t=2301

Author:  Eric_Desart [ Mon May 22, 2006 6:26 am ]
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This one is good in 3D

http://web.archive.org/web/200108092000 ... terOne.asp

:twisted: I always loose this link. Since it's a sticky I at least know where to find it back. Bob Golds originally found this one.

Author:  knightfly [ Mon May 22, 2006 7:45 am ]
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Thanks for posting that, as well as the studiotips thread Eric; now we BOTH can find 'em 8) Steve

Author:  lex [ Wed May 24, 2006 6:41 am ]
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Thanks Eric, I was going to do that but you beat me to it. :wink:

Author:  ts-12 [ Sat Sep 27, 2008 11:55 am ]
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David French wrote:
This is the closest thing I've seen.

http://www.hunecke.de/english/calculato ... modes.html

quick question: in that calculator: the "Distribution of Frequencies" graph, the blue bars represnt: the frequncies that will be 'dead' or 'too loud' in the room?

and the 'room box': what do black or white colors represent?

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