[denverdoc]

Youngho,

Relative to the discussion here are figs 9, 10 and table 1.

My take on these was this: at ka values of four and less, the sound wave on hitting the wall at almost any angle of incidence, is "reradiated as it were virtually uniformly throughout 180 degrees. In other words, it doesn't rebound so much as spread out.  In fig 1, "2a" is the length of the room, in other words a=1/2 length.

Using the wave number, k = 2 pi/ c. So product ka is I believe what you would call a normalized quantity, as many wave phenomema are scaleable. By looking at table 1, you can get an idea of what the relationship between ka, frequency, and the room dimension is. Even ast intermediate values of ka, say equal to 4, the reflection is hemispherical, assuming I have understood all correctly. This roughly corresponds to the oft cited means of finding areas to treat the room with the use of mirrors. If you can see the speaker in a mirror located on the side wall or ceiling from the listening position, you will hear mid to high frequency reflections coming from that source. Note no one says this method has any validity for low freqwuencies and I think the last part of this paper illustrates why.

Hope this helps,
John S

[John Casler]

 John: I'm sorry if I was stating the obvious in stating the distinction between pressure and sound pressure levels, but you had written: "As this energy approaches the corners, it finds a reduced volume (air space) and actually increases in pressure (that's why the bass is so strong in the corners)." What is the relationship between volume and pressure, if not as defined by the ideal gas law? How do volume and sound pressure levels interact, if you meant "sound pressure levels" instead of volume in this sentence?  

Hi Young,

Sorry but I am not familiar with "the ideal gas law".

The relationship between volume and pressure, in this case, is that as bass energy follows the boundaries to a smaller and smaller volume (space) the "pressure" (sound pressure) increases.

You also wrote "Bass waves spread out in a room. They hit the wall and presurize against it." What did this last sentence mean?

Bass waves are energy.  As they encounter a surface, they have energy moving in the direction the wave is traveling.

This energy is based on the already excited air molecules exciting the molecules in front of them in the direction the wave is traveling.  This causes pressure to be exerted against the wall or any other boundary.  Loud low bass can actually move the boundaries, the furniture and cause them to reasonate

John: You had previously written "Bass runs to the walls, compresses/pressurizes, moves along them, collects, and then "slams" back out at you in a highly pressured "rebound."" This last sentence is a bit confusing, as it implies that the path of bass upon encountering a boundary ("runs to the walls") is parallel to it ("moves along them"). You compared the cue ball to sound waves, and cue balls certainly don't "run to the walls" and "move along them," at least in my experiences with cue balls and banks.  

Since I was thinking of an entirely different thing when I mentioned the cue ball, it really is a bad example.  

A better example would be thousands of miniture pool balls traveling into each other, and what the ones on the wall would do when they were hit by the balls beside them that had a wall on their other side.

 
John: What did you think of the fact that the Meyer folks, despite having an anechoic chamber, nonetheless test bass outside?  

Bass is much more difficult to control within fixed boundaries.

I assume the reason they tested bass outside is because it is a simple and cheap way to not have to control the bass.  They just let it dissipate.

All: Although I certainly would not argue that bass reflects in a purely specular fashion, the very existence of axial and tangential modes does suggest that the reflections are not purely diffuse, either. Rather than placing "sonic interruptors" or devices along the boundaries to disrupt "bass flow", I believe that you would be best served by placing bass absorption at the junctions of two (wall-wall, wall-ceiling, or wall-floor) or three boundaries (corners), due to the effects on standing waves.  

No doubt the most efficient method of controlling bass is at room boundary intersections, since that is where much of the bass energy collects and does the most damage.

My suggestion of "interuptors" (if you look back and review) was thrown out more as a question, than a statement of fact, that possibly disrupting/interupting that flow would offer some benefit.

I can state without a doubt that interuption by removing a section of the boundary will also do so.

That is, if we have a wall/floor/ceiling that has several breaks, slots, or openings, the opening allows the pressure wave containment to reduce.

My contention was that an interuptor might be designed to offer a similar result.

Again it was a question.  

 
Unfortunately, I don't appreciate being called "contentious," so this will be my last post in this thread. This seems like one of those asinine tricks like "Gee, you can't let anyone else get the last word, can you?"

Come on Young, chill out.  In some circles, being contentious is a very great compliment.  Ask any attorney   Did you notice that when I wrote it, I threw in a wink

Now using the word "asinine" does add an element that suggests, misinterpretation, but I have thin skin and "thinner hair"  

Let me show you what you originally posted:

Sorry, I'm a bit dubious of the explanations given in some of these posts. I only have a high school physics education, so I'm a bit uneducated, but some of this sounds a lot more like feng shui than acoustics.
 

If you challenge something someone says as "dubious" and then explain that you feel they are spewing "feng shui" acoustics, do expect that they might offer you sufficient explanation, to at least why they came to their conclusions.

[youngho]

*sigh*. Perhaps it doesn't really count as a new post if I'm reposting something that I'd already written before.

From the beginning of my last post on page 3 of this thread:

John:

I used the word "dubious" in the sense of "doubtful" or "uncertain," which is my understanding of one definition of the word. I wrote "I'm a bit dubious..." to suggest that I was uncertain or doubtful about some of the explanations. Am I using the English language incorrectly?

[denverdoc]

Ideal Gas Law

PV=nRT Lest we forget, this is the underpinning for all we are discussing here.  

Youngho, in fairness to all, I think you were a bit--well lets just say acrimonious, first pleading almost  total ignorance, and then slamming anything and everything that struck you as out of bounds. We are all trying to help each other better grasp a difficult subject at best, and a nearly chaotic one at worst; believe me when i say i share your scorn for high end BS as in cryogenic cables,  cable lifters, solid state microphonics, etc,etc, etc.
John S.

[John Casler]

Hey Guys, I think this thread has run it's course, and most likely "we" three are the only ones still reading it.

The problem with internet posting, is it can somtimes convey "tone" that isn't intended, or sometimes its intended and dosn't get conveyed.

I am always up for "spirited" discussion, "IF" it is a sharing that can offer some benefit.  Even if something stated is "incorrect" it offers stimulation to understanding or at least the quest.

I never mind being questioned, and often times should be for some of the stuff I come up with.

There are obviously several paths to audio enlightenment and each can be supported with facts and opinion.

I find it very interesting to not only share, but actually "be" challenged (in a gentlemanly manner) since challenges cause you to search further to either support or modify your awareness.

And that gentlemen (to me) is were its at

[Rob Babcock]

Things have become a little snippy.  I let everyone have their say, and now I think it's best to lock this up.