[Ethan Winer]

John,

> The first is the ceiling louvers, which of course are "broadband", but depending on construction would have the potential of disturbing/trapping bass wave travel. <

Wow, nice room! But I can't tell if the devices on the ceiling are absorbers or diffusors. Or maybe they're both?

> The second shows the half moon columns that too disturb low frequency flow (at least the look like they would) <

The curved deflector on the front wall will affect only higher frequencies. It would have to be much larger/deeper to do much at the low end. And the tube traps are of course absorbers. They do claim some deflection, but that too is at higher frequencies only.

--Ethan

[John Casler]

John,

> The first is the ceiling louvers, which of course are "broadband", but depending on construction would have the potential of disturbing/trapping bass wave travel. <

Wow, nice room! But I can't tell if the devices on the ceiling are absorbers or diffusors. Or maybe they're both?

> The second shows the half moon columns that too disturb low frequency flow (at least the look like they would) <

The curved deflector on the front wall will affect only higher frequencies. It would have to be much larger/deeper to do much at the low end. And the tube traps are of course absorbers. They do claim some deflection, but that too is at higher frequencies only.
 ...

Hi Ethan,

That is true.  That is why I suggested that maybe a device such as your traps might offer a benefit, if one is to be had.

I only posted those examples as "shape" ideas.

[John Casler]

 I don't know much about anything, which is why I included the disclaimer at the beginning of my post. I did look at the ceiling of that room. You can read about the construction of that room in the link that I included. What seems to take up a lot of space in that ceiling is the absorption...

Hi Young,

I guess my supposition was lost on you.  "dubious"???

Sorry, most likely it was my lack of explanation.  

Please know that I was more "asking" about the possiblity of things, from those more knowledgable than myself.  Glad you saw questions in my suppositions and added your input.

Also, I think you might have misinterpreted some of what I said, and it gives me an opportunty to clarify.

The picture of Lavigne's Louvers, as I stated in my post was only for illustration purposes.  I also mentioned that my supposition would be viable only "if" the louvers were constructed of a material rigid enough to to work on lower frequencies.

It appears my explanation failure was so gross that I don't know where to start.

First off, your references to the various nodes and antinodes is correct, but I'm not sure they affect my suppositions.

Since a "corner" is simply the "intersection" of two surfaces it actually has "no" surface area itself (unless the corner is rounded).

So in a normal corner, a "very small" (less than 1%) portion of the direct wave front that goes directly into that intersection actually encounters a surface area.   Almost "ALL" sonic energy is "directed" by the "boundaries" that form that intersection.

With the exception of nearfeild wave fronts, all sonic energy has the potential to be affected by room interaction.

Room interaction is the sonic reaction to direct and indirect sound energy.

Predicting sound energy relies on rather simple physics, which includes physical room measurments, speed of sound, and the more complex components of reflected, dispersed, absorbed, diffused and directed energy.  On top of this we have angles of incidence, and the resulting presurization of boundary specific areas.

It seems that you question my supposition that sound LF waves can be directed along these surfaces.

This is some of the most elemental of physics.  The energy traveling from a creation point will travel in a straight line until encounters something that will either reflect it, diffuse it, absorb it, or direct it.

The difference between reflection and direction is based soley on the angle of incidence.

My assertion that sound waves travel along boundaries is supported by many things (Megaphones, Horns, Symphony Orhestra shells, wave guides, etc) so this is a tenet of acoustics.

And before I explain further, I get the idea that you felt I am somehow championing the use of "foam" as a bass frequncy panacea and nothing could be further from the truth.  My mention of foam to what I called "interuptors" was simply to make them a bit more "broadband" in their application.

And I don't see where I said bass is "attracted to corners"  
 
Nothing I said could even be construed as such.  I said the the low frequency waves are "directed" by room boundaries since they cannot move them or move through them, they follow them until they reach a room intersection, where they then react to the intersection

Now if you can accept that sound has no option but to eventually encounter a boundary or disperse or dissipate, then it is likely that much of it will be "directed" and "collected" toward these intersections.

Given the fact that low bass is omnidirectional and all rooms have at least a few intersecting boundaries, I find it interesting that you would question that bass travels along them.  Now to be perfectly clear, this is not a statement about Bass energy "in total" since it is actually room filling, but when it encounters a boundary at small angle of incidence, it is channeled/directed/reflected (or whatever your term of choice is) along that boundary

For simplicity let us choose the "floor boundary" since many speakers have woofers close to the floor and it isn't to difficult to understand that the LF energy will travel along that boundary out into the room.

Let us examine the wave front that is traveling from the left woofer in a direct line to the exact rear right corner.  Now granted that woofer is "exciting" all the air around the speaker, but it is limited/contained and directed by the floor boundary (as long as the floor is rigid enough) to travel along that lower boundary.

Now you have to accept that it will travel until it reaches a wall or other object that will affect its journey.

My "interuptor" supposition was just such an object specifically desinged to "inerupt" that flow along that boundary.  I think you would agree that if we built a wall around the speaker, (a LF sonic dam if you will) that it would "interupt" the LF sonic energy, that would normally be traveling to the normal rooms corner.  The interuptor I surmised about, is a device somewhere in between a brick wall and "nothing".  The degree to which it would affect this wave front would be based on its efficiency to disrupt this flow to a positive end.

So the facts are, that "any" object that is in the path of a sonic wave front "will" have an effect, on that energy.  If it is a simple curtain, the effect will be small.  If it is a concrete wall, the effect will be greater.

While my explanation of the interuptor was probably not the greatest, the fact remains, if you place an object of sufficient rigidity in the path of a LF wave front, something will happen.  In fact, a bass trap is based on this exact same principle, except it is placed in a high efficiency area to maximize its result, with walls, floors, and ceilings being lesser areas.

What will happen?  As the wave front encounters the "interuptor" object it will lose some force, and look for a way to continue on.  This continuance will be in the form of the reflection/diffusion probably with some value lost to absorption as mentioned earlier.

The degree to which this affects the wave will be determined by the size, shape, and efficiency of the device.

So how does this relate to to "sonic collections" in the room corners?

Good Question, and that was also my own.

I have a tendency to think that it would have the potential to "reduce" pressure level to some degree simply because the encounter would reduce the efficient "direction" of that energy by that boundary.

When the energy first encounters the object it would find a pressure increase on the frontal edge, and a pressure decrease on the trailing edge.  I think this disruption could possibly prove to be "valuable" in controlling the inevitable "collection" at the various intersections.

Now remember this is looking at a "specifc" area of the sonic transmission and by no means is to represent anything but what is happening in that space at that time.  

And now let me address some specifics:

"Obstructive" devices, otherwise known as diffraction, have little to do with redirection of flow of "bass energy," and it's easy to imagine a room with concrete floors, walls, and ceilings treated with all sorts of foam and other fancy "obstructive" devices with little or no absorption at low frequencies. What will happen? The room will be very boomy.

I think you posted about "Anechoic" chambers?  Here is one:



Please not that I beleive this one is made out of concrete and the walls are covered with both an extreme amount and an extreme design of what I would call "sonic interuptors".

While I don't know this for a fact, they appear to be "rigid" and designed to address sonic energy flow along all boundary surfaces.

And an Anechoic chamber is not generally too "boomy".

I don't know much about anything, which is why I included the disclaimer at the beginning of my post. I did look at the ceiling of that room.

I am with you on this (my not knowing much part ) and my suppositions are based on some education, and some practical experience, mixed with a creative urge to tweak and question.

Again, I suggest constructing a room with concrete floor, walls, and ceiling. Cover all the surfaces of the room with that egg carton stuff. The room will still be boomy.  

I have no idea why you think I suggested "egg carton stuff" to disrupt bass energy.

I surely hope this additional information might offer additional insight into what I was questioning.

[ctviggen]

John,

I bet those are both reflective (diffusive) and absorptive.  I would think that diffusion is probably related to frequency/wavelength -- you need smaller diffusive elements for higher frequency/smaller wavelength.  Additionally, if you can diffuse high frequency signals, you can diffuse low frequency signals.  

By the way, is that anechoic chamber for sound or for radio frequency waves?

[John Casler]

John,

I bet those are both reflective (diffusive) and absorptive.  I would think that diffusion is probably related to frequency/wavelength -- you need smaller diffusive elements for higher frequency/smaller wavelength.  Additionally, if you can diffuse high frequency signals, you can diffuse low frequency signals.  

By the way, is that anechoic chamber for sound or for radio frequency waves?

Hi Bob, you may be right.  To me they look like plywood with wedge foam tips???

I don't know about "diffusing" LF   I would have to think about that.  We do know that LF can be reflected and directed so likely it could be reflected in multiple planes, angles, and timings for some type of diffusion.

I assume this chamber is for sound since it is from one of "Young's" links I followed.

[ctviggen]

Well,

Somebody fly us out there so we can find out!    It's an interesting design, although the WAF is low -- very low.  Heck, even Ethan's products are low on WAF.  That room might be in the negative territory!

[John Casler]

Well,

Somebody fly us out there so we can find out!    It's an interesting design, although the WAF is low -- very low.  Heck, even Ethan's products are low on WAF.  That room might be in the negative territory!

Plus except for extreme "nearfeild", it wouldn't please most who enjoy the sonic impartations (  hows that for a word?) of their listening rooms.

[youngho]

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?

You wrote: "Predicting sound energy relies on rather simple physics, which includes physical room measurments, speed of sound, and the more complex components of reflected, dispersed, absorbed, diffused and directed energy. On top of this we have angles of incidence, and the resulting presurization of boundary specific areas. It seems that you question my supposition that sound LF waves can be directed along these surfaces. This is some of the most elemental of physics. The energy traveling from a creation point will travel in a straight line until encounters something that will either reflect it, diffuse it, absorb it, or direct it. The difference between reflection and direction is based soley on the angle of incidence. My assertion that sound waves travel along boundaries is supported by many things (Megaphones, Horns, Symphony Orhestra shells, wave guides, etc) so this is a tenet of acoustics. "

I think that the sound waves reach the corners because there is nothing between the point source and the corner, not because they slide along the boundaries. You yourself quote Snell's law. I thought that megaphones and horns had to do changes in impedance between mouthpiece and outlet, that symphony orchestra shells had to do with reflections, and that  waveguides controlled dispersion. Perhaps you can point me to the name of the principle or law or tenet that governs how bass reaches a boundary and travel parallel to that surface. Are there particular frequencies above which this does not occur? Do frequencies above, say, 200 Hz also get "funneled" into corners? Is there, perhaps, some equation of frequency that predicts what portion is reflected at the angle of incidence and which portion is redirected to travel parallel along the boundary? As I wrote, I am not very knowledgeable about these matters, particularly because I only understand the most elementary physics. I would love to learn more. Thanks!

You wrote "The low frequency waves are "directed" by room boundaries since they cannot move them or move through them, they follow them until they reach a room intersection, where they then react to the intersection. Now if you can accept that sound has no option but to eventually encounter a boundary or disperse or dissipate, then it is likely that much of it will be "directed" and "collected" toward these intersections."

My understanding was that increased sound pressure levels at boundaries has to do with reflections and the creation of modes, not because sound is "directed" or "collected."

You wrote "The energy traveling along each wall for example is somewhat "funneled" into the corners." I misinterpreted this to mean that the bass was somehow attracted to the corners. I actually don't know how to interpret this at all. My apologies.

If you look at the web pages for the anechoic chambers, particularly the Meyer one, you'll note that the addressing of "sonic energy flow along all boundaries" does NOT seem to address low-frequency modes. The Meyer anechoic chamber is not used for tests below 80 Hz, despite the extensive use of "sonic interruptors." Does this support your suppositions?

The part about the egg carton stuff appeared in a paragraph that began with the word "Denverdoc" and a colon. The use of the word "Denverdoc" and the colon was meant to suggest that the remainder of the contents of that paragraph was intended as a response to a particular individual named "Denverdoc." I'm sorry if this wasn't clear. Is there another way that I could have made it so?

Thanks for your assistance,

Young-Ho

[woodsyi]

I have a perfect design for an Anechoic chamber.

Build a room of any size with 6" thick plexiglass.  Seal all seams and make the door airtight.  Drill a hole on the wall and attach a vent with huge fan/motor.  Place your audio gear in the room and crank it loud.  Then turn the fan on and Suck the air out of the chamber.  Hear the echo diminish.  Soon, there will be no echo.

NO AIR = NO SOUND

OOOPS, this is not just an anechoic chamber;  it would be an anaural and anemic chamber as well.   Have a good weekend y'all!

[John Casler]

I think that the sound waves reach the corners because there is nothing between the point source and the corner, not because they slide along the boundaries.

Hi Young,

I think it is very simple, but you have to grasp what is happening in the whole room.

I get the impression you're not seeing that a "corner" is a very small area.  It is very small.  In fact it is so small, as I mentioned in an earlier post it actually has little or no surface area at all.

So in fact for it to experience "a presurization" from LF sound waves, those waves must teavel along the boundaries until they meet in the corner.

How do you think that sound energy arrives and builds in that small "slice" if not by being directed by the boundaries that form it?

Sound waves don't "slide" along the walls, they are "directed and reflected along that path, much like a cue ball is "directed/reflected" towards a pocket on a pool table.

I think you might understand it more if you perform that simple "sink full of water" experiment (in a square sink) I suggested.

 I thought that megaphones and horns had to do changes in impedance between mouthpiece and outlet, that symphony orchestra shells had to do with reflections, and that waveguides controlled dispersion. Perhaps you can point me to the name of the principle or law or tenet that governs how bass reaches a boundary and travel parallel to that surface. Are there particular frequencies above which this does not occur? Do frequencies above, say, 200 Hz also get "funneled" into corners? Is there, perhaps, some equation of frequency that predicts what portion is reflected at the angle of incidence and which portion is redirected to travel parallel along the boundary? As I wrote, I am not very knowledgeable about these matters, particularly because I only understand the most elementary physics. I would love to learn more. Thanks!  ...

While there are some, more technically savy and articulate than I, who may be able to align the answers to those questions better, I can say that the physics of force containment and flow is very similar in a lot of areas.

My understanding was that increased sound pressure levels at boundaries has to do with reflections and the creation of modes, not because sound is "directed" or "collected."  

Sound waves are measured in frequency and pressure.  To have sound you must have frequency and pressure.

The bullies of the sound world are Low Frequencies.  The have the most energy/force.  That is why you can hear them over high frequencies if on the other side of the wall or in the next car.

It is also why you can actually physically "feel" them.  

Low frequencies in free space simply expand (disperse and dissipate) until they are fully dissipated, or hit an obect that will affect them in some way, such as the wall we are talking about.

 You wrote "The energy traveling along each wall for example is somewhat "funneled" into the corners." I misinterpreted this to mean that the bass was somehow attracted to the corners. I actually don't know how to interpret this at all. My apologies.  

No problem.  A funnel is a device that allows you to fill a small opening from a wider, larger one.  It would for example allow your to fill a "bottle" with a "bucket".

It takes a larger stream or load and "funnels" it to a more focused and smaller area.  It collects from a larger area and directs to a smaller.

I have no doubt with your apparant "technical" knowledge base, will soon align with your growing "practical" knowledge base (I wish mine would) and you will be much further ahead of the game.

[youngho]

John, I think you're seriously confusing waves and fluids.

You write: "Sound waves don't "slide" along the walls, they are "directed and reflected along that path, much like a cue ball is "directed/reflected" towards a pocket on a pool table."

What does this even mean? What is directed/reflected? I'd like to play pool with you. According to you, it would seem that bank shots are impossible and that even attempting to do so would result in scratching. For the rest of us, when you hit the cue ball so that it hits the bank, it does not get "directed/reflected" along the bank toward the pocket. It bounces back off the wall and generally tends to reflect at the angle of incidence, except that English and the deformability of the bank complicate things. What does pool have to do with sound? Not much.

Let's discuss your sink experiment. Your sink experiment uses water, which is a fluid. Can you make a standing wave by dipping your finger? No. Does this mean that standing waves do not exist because you can't create them with your sink experiment? No. Your sink experiment doesn't "prove" anything about sound. It's an analogy and a flawed one at that. Sound is not a fluid. A speaker cone does not move only once.

Let's conduct a thought experiment using your assumptions versus mine.

Take, for example, a 10x26x17 (HxWxD)room. Place a floorstanding subwoofer in one corner playing pink noise with bandwidth containing frequencies from 20 to 120 Hz. Lie down in the opposite corner. What do you hear? At certain frequencies is the bass boomy, and if so, what?

Take your premise that "bass energy" is "directed" or "funneled" or "collected" into the corner, or that bass somehow is "directed/reflected" along the boundaries to the corner. Can you make any predictions about which frequencies will be boomy? Bass at ALL frequencies should be collect in corners, but this is simply not the case. Corners sound boomy because certain frequencies are louder than others. If all frequencies were louder, then the bass would be smooth but louder. Which frequencies, based on your premise? Impossible to predict, as far as I can tell.

Take my premise that sound reaches the corner because it has an uninterrupted path or because it's reflected. Sound pressure levels are increased at boundaries due to axial mode formation. I predict that you'll hear peaks at axial modes corresponding to height, width, and depth. For height, these are 56.5 and 113 Hz. For width, these are roughly 21.7, 43.5, 65.1, 87, and 108.6 Hz. For length, these are 33, 66, and 99 Hz.

Go to the center of the room. What happens?

According to you, bass should be evenly reproduced at all frequencies because it's not "collected" or "funneled" into the center, right?

According to me, you're standing in the node for odd-order axial modes, so you'll hear a relative null at 21.7, 33, 56.5, 99, and 108.6. Although 65.1 is the third mode for width, it's the second mode for length. The center of the room is also the antinode for even-order axial modes, so you'll hear peaks at 43.5, 87, 113 Hz.

You write "The physics of force containment and flow is very similar in a lot of areas," but sound does not flow, really. Sound is not a liquid that comes out of the speaker, hits the wall, and is directed toward the corner. I have no idea what force containment is. What does "force containment" (try Googling it and see what you get) have to do with sound?

You write "My assertion that sound waves travel along boundaries is supported by many things (Megaphones, Horns, Symphony Orhestra shells, wave guides, etc) so this is a tenet of acoustics," yet you are unable to "align the answers" to my questions about these particular things. Why is that?

You write "A funnel is a device that allows you to fill a small opening from a wider, larger one. It would for example allow your to fill a "bottle" with a "bucket". It takes a larger stream or load and "funnels" it to a more focused and smaller area. It collects from a larger area and directs to a smaller." A funnel works on FLUIDS. What does a funnel have to do with sound? A megaphone and a horn place the sound source at the smaller aperture. What do you think happens if you have a reverse horn, which would resemble a funnel?

Am I the only person here with some fundamental misunderstanding of basic physics and acoustics? If so, I'll have to go to my parents' house and dig up my old copies of Hans Ohanian's "Physics" textbook and F Alton Everest's "Master Handbook of Acoustics" to see if my memory is so askew.

Young-Ho

[John Casler]

John, I think you're seriously confusing waves and fluids.

 ...

Air is a fluid.   Sound is to air, as waves are to water.  With their own specific set of physical properties of course.

Let's discuss your sink experiment. Your sink experiment uses water, which is a fluid. Can you make a standing wave by dipping your finger? No. Does this mean that standing waves do not exist because you can't create them with your sink experiment? No. Your sink experiment doesn't "prove" anything about sound. It's an analogy and a flawed one at that. Sound is not a fluid. A speaker cone does not move only once.

I would imagine that if you placed different frequency vibrations into a square or rectangualar sink, you would certainly get standing waves.

My experiment was not to show exactly what happens during all sound, but to offer a visual representation of how the energy moves from the source, along a boundary, and into a corner.

Again it is obvious you haven't tried this simple experiment or you would have seen what happens. (I assume )

And the experiment was not an analogy, it is an experiment, and sound is the energy within the air which "IS" a fluid.  Ask your physics prof about that.

Take, for example, a 10x26x17 (HxWxD)room. Place a floorstanding subwoofer in one corner playing pink noise with bandwidth containing frequencies from 20 to 120 Hz. Lie down in the opposite corner. What do you hear? At certain frequencies is the bass boomy, and if so, what?

Take your premise that "bass energy" is "directed" or "funneled" or "collected" into the corner, or that bass somehow is "directed/reflected" along the boundaries to the corner. Can you make any predictions about which frequencies will be boomy? Bass at ALL frequencies should be collect in corners, but this is simply not the case. Corners sound boomy because certain frequencies are louder than others. If all frequencies were louder, then the bass would be smooth but louder. Which frequencies, based on your premise? Impossible to predict, as far as I can tell.

If I'm not mistaken the reason "certain" frequencies are "cancelled" has to do with the RTA (?) of that wave length in relationship to specific room measurments.  Meaning that the wave length is reflected from the opposite boundaries and arrives to cancel itself with its opposing energy.  This does not affect my assertion, and happens in both cases.

All formulas and prediction of acoustic interaction would be the same.

Go to the center of the room. What happens?

According to you, bass should be evenly reproduced at all frequencies because it's not "collected" or "funneled" into the center, right?

I have not posted anything that states that.  All the air within the room is subject to both the direct waves, and reactive artifacts from the room.  This will produce energies encountering counter energies at the same predicted locations.  All LF acoustical predictions of room nodes, anti-nodes and cancellations have not and do not change.

Not sure how you have been drawing conclusions here.

You write "The physics of force containment and flow is very similar in a lot of areas," but sound does not flow, really. Sound is not a liquid that comes out of the speaker, hits the wall, and is directed toward the corner. I have no idea what force containment is. What does "force containment" (try Googling it and see what you get) have to do with sound?

You are correct "sound is not a liquid". it is vibrational or reasonant energy travling in a fluid..that fluid is AIR.

Just try to get sound in a vacumn.  It requires a medium in which to travel.  That medium must be either liquid, gas, or solid.

Sound is an energy/force, which draws its properties from fluid dynamics.

Force containment (in this case) is the observance that the sound energy travels through the "fluid" (air) and encounters a "containment" which are the boundaries of the room.

You write "My assertion that sound waves travel along boundaries is supported by many things (Megaphones, Horns, Symphony Orhestra shells, wave guides, etc) so this is a tenet of acoustics," yet you are unable to "align the answers" to my questions about these particular things. Why is that?

Because I am not a Physics teacher and I wouldn't want to give you information that I don't know is 100% complete.  I'm very surpirsed that the lightbulb hasn't gone off yet

You write "A funnel is a device that allows you to fill a small opening from a wider, larger one. It would for example allow your to fill a "bottle" with a "bucket". It takes a larger stream or load and "funnels" it to a more focused and smaller area. It collects from a larger area and directs to a smaller." A funnel works on FLUIDS. What does a funnel have to do with sound? A megaphone and a horn place the sound source at the smaller aperture. What do you think happens if you have a reverse horn, which would resemble a funnel?

I am not going to give you any more simple examples    

It doesn't work

Am I the only person here with some fundamental misunderstanding of basic physics and acoustics? If so, I'll have to go to my parents' house and dig up my old copies of Hans Ohanian's "Physics" textbook and F Alton Everest's "Master Handbook of Acoustics" to see if my memory is so askew.

Young, I don't think you have a memory problem (well maybe you didn't remember that air is a fluid   ), but it is probably the way I state things is so unscientifically foreign (no formulas just simple experiments) that it just doesn't "compute" to you yet.

I don't know if the animation posted below will help you at all, but look at how the sound is "contained" by, and follows the boundaries.  It looks a lot like my "sink" experiment.

Too bad it doesn't continue to the corners

[youngho]

You write: "Air is a fluid. Sound is to air, as waves are to water."

Air is a gas. Water is a liquid. Sound travels through air as longitudinal waves. Waves in water are transverse waves.

You write: "And the experiment was not an analogy, it is an experiment, and sound is the energy within the air which "IS" a fluid. Ask your physics prof about that."

The wave front will reach the corner and that the circular (or semicircular, once it reaches the boundary) shape of the initial wave front will remain unchanged all the way until the corner because there is no obstruction. The graphic you show supports this.

You write: "If I'm not mistaken the reason "certain" frequencies are "cancelled" has to do with the RTA (?) of that wave length in relationship to specific room measurments."

What does RTA stand for? Real Time Analysis? Can you provide some explanation for how RTA affects standing wave formation?

You write: "Because I am not a Physics teacher and I wouldn't want to give you information that I don't know is 100% complete."

But you already have.

You write: "I don't know if the animation posted below will help you at all, but look at how the sound is "contained" by, and follows the boundaries. It looks a lot like my "sink" experiment. Too bad it doesn't continue to the corners."

But it does. The upper left and lower left corners.

Young-Ho

[youngho]

I should add a few notes:

1. You're right. Air and water are fluids. However, air is a gas, and water is a liquid. When I mentioned waves in water above, I meant waves on the surface of the water, as per your "experiment." However, sound really is a longitudinal wave (molecules go back and forth in the direction of wave propagation), and dipping your finger into water really does produce a transverse wave (molecules go up and down perpendicular to the direction of wave propagation).

2. Sound pressure levels are a measure of the intensity of periodic pressure fluctuations. The periodicity depends on the frequency of sound. Sound therefore depends on alternating high and low pressure regions travelling through the medium under discussion (here, air). You wrote that 'Sound waves are measured in frequency and pressure. To have sound you must have frequency and pressure." This is not quite correct. Sound is measured in frequency and SPLs. To have sound, you must have periodic fluctuations in pressure at a certain frequency.

3. The energy of a wave can be measured in terms of power, or energy transferred per unit time. This is a function of the speed, frequency, and amplitude of the wave, as well as physical properties of the medium under consideration. You wrote that "The bullies of the sound world are Low Frequencies. The have the most energy/force." This isn't quite correct. If speed and amplitude are equal, then high frequency sound actually has more energy than low frequency sound.

Young-Ho

[youngho]

Well, unfortunately, I may not have much opportunity to post for the rest of the weekend. If other folks believe that bass is "funneled" into corners, than cue balls are "directed/reflected" towards pockets instead of following basic laws of physics, and sound waves travel parallel to a boundary when they encounter it, then there's not much I can say. I'm sure you'll enjoy the acoustics in your room.

I would appreciate knowing that "force containment" is, though. Thanks!

Cheers, and happy listening!

Young-Ho

[John Casler]

I should add a few notes:

1. You're right. Air and water are fluids. However, air is a gas, and water is a liquid.

Hi Young,

It will all "align" very soon, since your search for knowledge is great.

2. Sound pressure levels are a measure of the intensity of periodic pressure fluctuations. The periodicity depends on the frequency of sound. Sound therefore depends on alternating high and low pressure regions travelling through the medium under discussion (here, air). You wrote that 'Sound waves are measured in frequency and pressure. To have sound you must have frequency and pressure." This is not quite correct. Sound is measured in frequency and SPLs. To have sound, you must have periodic fluctuations in pressure at a certain frequency.  

Not sure why you are challenging my general statement with a slightly more specific (Pressure vs Sound Pressure Level, and Frequency vs Peiodic Fluctuations) since all understand it as it stands.

3. The energy of a wave can be measured in terms of power, or energy transferred per unit time. This is a function of the speed, frequency, and amplitude of the wave, as well as physical properties of the medium under consideration. You wrote that "The bullies of the sound world are Low Frequencies. The have the most energy/force." This isn't quite correct. If speed and amplitude are equal, then high frequency sound actually has more energy than low frequency sound.

You certainly are contentious

While we can argue this point all day long (I'm not interested) my point is the same.

Bass Energy/Power can actually "move" large heavy objects such as walls and floors, their pressure is so great at a given SPL.  On the opposite end of the spectrum, High Frequencies can be stopped in their tracks by a folded blanket

 Well, unfortunately, I may not have much opportunity to post for the rest of the weekend. If other folks believe that bass is "funneled" into corners, than cue balls are "directed/reflected" towards pockets instead of following basic laws of physics, and sound waves travel parallel to a boundary when they encounter it, then there's not much I can say. I'm sure you'll enjoy the acoustics in your room.

Please don't get hung up on the word "funneled".  I actually used the term "directed" initially.  I also specified that much is determined by the angular incidence of the energy, this my cue ball example. The cue ball simply illustrates that "angular incidence" will play a role in determining the path of reflection, refraction, and direction.  

I guess I have to make clear it is not a "fully demonstrative" model of what happens to a sound wave.

You still have not demonstrated just what "basic laws of physics" are not being observed.

Physics has not been changed by anything I have proposed.  In fact, aside from my assumed inability to communicate this well to you, it is all based on simple physics.

[denverdoc]

You all might find this to be of some relevance to the above discussion:

www.acousticshut.fi/asf/bnam04/webprosari/papers/o25.pdf

(Youngho, I think you misunderstood me, I was suggesting obstructions would only break up axial modes if the dimensions were some appreciable fraction of the wavelength. Jumped into the thread w/o looking at all the links).



If I am understanding the above reference, when it comes to low frequencies, and interactions with walls, the wall tends to behave as a diffuser. "Bank shot" physics are most evident with high wave numbers.
Cheers,
John

[John Casler]

You all might find this to be of some relevance to the above discussion:

www.acousticshut.fi/asf/bnam04/webprosari/papers/o25.pdf

(Youngho, I think you misunderstood me, I was suggesting obstructions would only break up axial modes if the dimensions were some appreciable fraction of the wavelength. Jumped into the thread w/o looking at all the links).



If I am understanding the above reference, when it comes to low frequencies, and interactions with walls, the wall tends to behave as a diffuser. "Bank shot" physics are most evident with high wave numbers.
Cheers,
John

Hi John,

Although the link didn't work, so I didn't read the text, you bring up an interesting point, and that is that low and high frequencies have some different behavoirs.

My pool table example was more to say that the reflective/refractive/directive behavoir was dependant on the "angle of incidence". (and I should have added, the behavoiral qualities of the frequency)

Possibly the most difficult thing for many to "wrap around" is the transition from the "omnidirectional" energizing properties of LF to the more "directional" qualities of HF.

[denverdoc]

Sorry, should have tested the link before posting. Dropped a period, try this:

www.acoustics.hut.fi/asf/bnam04/webprosari/papers/o25.pdf

John

[youngho]

Denverdoc: If you could explain that paper in simple terms, I would appreciate it. As far as I can tell, this is an attempt to model the reflections of an octave band, with directivity dependent on the relative size of the reflecting surface relative to the wavelengths involved. The penultimate sentence "At high frequencies and large surfaces the directivity is very sharp in the direction of the specular reflection, but at low frequencies and small surfaces the directivity tends to be uniform" doesn't tell me what "high," "large," "low," and "small" actually mean. Would you be able to extract some meaning for these terms for me, please? Would one perhaps be able to predict what kinds of reflections occur when an 80 (or 40 or 20) Hz tone reflects off the side wall in a 10x17x24 room (HxWxD)? This paper was way over my head, so thanks!

Denverdoc: I agree with you that having nonparallel surfaces disrupts the predictable formation of standing waves. However, this does not mean that standing waves won't form...just not in a predictable manner...

John: "Sound is to air, as waves are to water." This is an analogy. Your sink "experiment" is your attempt to model how sound waves interact with room boundaries, although it is not consistent with how sound actually interacts with room boundaries (where are the standing waves from dipping a finger into water?). An analogy can be defined as "A form of logical inference or an instance of it, based on the assumption that if two things are known to be alike in some respects, then they must be alike in other respects." The sink "experiment" shows transverse waves travelling in water, not longitudinal waves travelling through the air. This is why I called it an analogy.

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

John: You wrote "Sound waves don't "slide" along the walls, they are "directed and reflected along that path, much like a cue ball is "directed/reflected" towards a pocket on a pool table." I had understood the pronoun "that" in the phrase "along that path" to refer to "along the walls" and thus to the corner, as I had originally used the word "slide" in a previous post in the sentence "The sound waves reach the corners because there is nothing between the point source and the corner, not because they slide along the boundaries." I had conseuqently understood your intent to mean "Sound waves are directed and reflected along the walls into the corners, much like a cue ball is "directed/reflected" towards a pocket on a pool table." This meaning is consistent with a previous statement that you had made and which follows. I must have been mistaken in my interpretation of the original, slightly ambiguous sentence.

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.

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

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.

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?"

I would appreciate answers to my questions above, nonetheless, and I yield the last word to you. Cheers, and happy listening,

Young-Ho