Wanted: Proof of multiple subs and sub EQ

[amirm]

"Through PSI Audio’s patented technology, it will transform acoustic pressure into acoustic velocity and absorb it over a large range of frequencies."

I can try . When a sound wave hits the wall, by definition the velocity of the air molecules drops to zero. Inversely, pressure becomes maximum. This device sits by the wall so it is a "pressure bass absorber." This is in contrast to fiberglass type absorbers that are velocity absorbers and as such, don't work as well next the wall.

The part about conversion to velocity means that the woofer element moves in response to the pressure and hence pressure is converted to velocity. By putting an active signal in reverse on the woofer, the energy is absorbed.

 

[RayDunzl]

Thank you.

pressure becomes maximum

Hmm.

Oh...

http://hyperphysics.phy-astr.gsu.edu/hbase/sound/reflec.html

 

[mitchco]

Does the book have anything on crossover theory, or is it mostly how to employ active crossovers in Acourate?

The book is more about implementation and optimization details than crossover theory. The optimization, in my case, was moving one of the XO points from 500 Hz to 850 Hz because of a falling midrange response. I show before/after measurements and how I arrived at that design. The software has a wide-variety of standard crossover types, plus specialty types. Some examples are in this whitepaper on Thoughts About Crossovers

 

[Purité Audio]

Well at a solid boundary the velocity of the sound/pressure will be zero, that's why bass tends to accumulate against the walls , the PSI unit creates a low impedance around the device sucking the surrounding air into the internal membrane where it is dissipated, hence high pressure into velocity.
Keith.

 

[Cosmik]

...hence pressure is converted to velocity.

Wouldn't it be more correct for them to say that pressure is converted into acceleration not velocity? (If this thing works at all)

 

[h.g.]

From AVAA Website:

"Through PSI Audio’s patented technology, it will transform acoustic pressure into acoustic velocity and absorb it over a large range of frequencies."

Could someone translate the bold part for me?

As written it is nonsense: pressure cannot be converted to velocity and neither quantity is absorbed.

What appears to be being done is using the measured and stored acoustic impedance of the grille, Z, to determine the particle velocity, v, from the difference between the microphone acoustic pressure outside the grille, pm, and the acoustic pressure inside the grille in front of the cone, pc. That is, v = (pm - pc)/Z with the sign following from the adopted spatial coordinate system. The quantities have both phase and magnitude (i.e. complex) and the impedance will vary with frequency.

In general acoustic pressure and particle velocity are independent and need to be known but for the particular case of a single plane wave in air the particle velocity is the acoustic pressure divided by the acoustic impedance of the air (product of density and speed of sound) with the sign depending on the adopted coordinate system. So if the plane wave is to travel through the grille without being impeded this is the particle velocity the moving cone needs to create at the grille to match the measured acoustic pressure.

What about the unknown acoustic pressure inside the grille, pm? If the cone velocity exactly matches the particle velocity through the grille then although the amount of air between the grille and cone will be changing it will be changing by the precise amount that avoids compressing or expanding the air (i.e. it is moving to avoid any sucking or blowing). The air in front of the cone will be moving as an incompressible slug with the acoustic pressure remaining constant and we have an equation we can use. (Chunk of clarifying fluid mechanics concerning incompressible and compressible motion and the relationship between pressure and acoustic pressure as well as velocity and particle velocity?)

What gets absorbed is the energy contained in the sound wave. The rate of this is the product of the particle velocity and the acoustic pressure. Note that both quantities vary in time and so a cone moving in air can both add and subtract energy from sound.

 

[Cosmik]

As written it is nonsense: pressure cannot be converted to velocity and neither quantity is absorbed.

What appears to be being done is using the measured and stored acoustic impedance of the grille, Z, to determine the particle velocity, v, from the difference between the microphone acoustic pressure outside the grille, pm, and the acoustic pressure inside the grille in front of the cone, pc. That is, v = (pm - pc)/Z with the sign following from the adopted spatial coordinate system. The quantities have both phase and magnitude (i.e. complex) and the impedance will vary with frequency.

In general acoustic pressure and particle velocity are independent and need to be known but for the particular case of a single plane wave in air the particle velocity is the acoustic pressure divided by the acoustic impedance of the air (product of density and speed of sound) with the sign depending on the adopted coordinate system. So if the plane wave is to travel through the grille without being impeded this is the particle velocity the moving cone needs to create at the grille to match the measured acoustic pressure.

What about the unknown acoustic pressure inside the grille, pm? If the cone velocity exactly matches the particle velocity through the grille then although the amount of air between the grille and cone will be changing it will be changing by the precise amount that avoids compressing or expanding the air (i.e. it is moving to avoid any sucking or blowing). The air in front of the cone will be moving as an incompressible slug with the acoustic pressure remaining constant and we have an equation we can use. (Chunk of clarifying fluid mechanics concerning incompressible and compressible motion and the relationship between pressure and acoustic pressure as well as velocity and particle velocity?)

What gets absorbed is the energy contained in the sound wave. The rate of this is the product of the particle velocity and the acoustic pressure. Note that both quantities vary in time and so a cone moving in air can both add and subtract energy from sound.

Is this, effectively, a loudspeaker working in anti-phase to a signal picked up by a microphone, give or take?

 

[h.g.]

Is this, effectively, a loudspeaker working in anti-phase to a signal picked up by a microphone, give or take?

Not really. It is more in-phase rather than anti-phase. In order to remove the sound wave we don't want to cancel the pressure measured by the microphone but to leave it alone and get the cone to exactly follow the undisturbed particle velocity of the air. By doing this nothing is done to the air to create a reflection. Of course the other side of the moving cone then creates sound which needs to be absorbed inside the cabinet.

 

[Cosmik]

Not really. It is more in-phase rather than anti-phase. In order to remove the sound wave we don't want to cancel the pressure measured by the microphone but to leave it alone and get the cone to exactly follow the undisturbed particle velocity of the air. By doing this nothing is done to the air to create a reflection. Of course the other side of the moving cone then creates sound which needs to be absorbed inside the cabinet.

It depends from which direction you regard it as "anti" I suppose. For a positive pressure picked up by the microphone is it effectively creating an equal negative pressure at the right moment?

 

[h.g.]

It depends from which direction you regard it as "anti" I suppose. For a positive pressure picked up by the microphone is it effectively creating an equal negative pressure at the right moment?

Not really. The idea of generating something equal and opposite is not really what is going on although one probably could come up with something convoluted along those lines with a bit of effort. The energy in a plane sound wave travels through the air at the speed of sound by each lump of air pushing on the lump of air in front of it which then follows the same motion but slightly delayed in time. What the cone is seeking to do is to move in exactly the same way as air would have done if that were present instead of the cone. If this can be done then all the energy in the sound that would have been passed to the next lump of air will be passed to the cone with nothing being reflected back (the same impedance in engineering speak). All the energy that was in the sound wave in the air is transferred to energy in the cone. The cone in turn then transfers that energy to the air inside the cabinet as sound to be dissipate as heat.

The key idea is the cone moving with the sound wave without disturbing it to allow the energy in the sound to be transferred to the cone without disturbance.

 

[Ethan Winer]

The key idea is the cone moving with the sound wave without disturbing it to allow the energy in the sound to be transferred to the cone without disturbance.

Yes, exactly. In order to absorb sound the cone has to function as a shock absorber, so to speak. If the cone "butted heads" with the wave and opposed its direction, it would reflect twice as much as a plain boundary! (With two such devices at opposite sides of the room you'd get runaway feedback. ) So the cone has to move in the same direction as the wave, but slow it down, sort of like a baseball mitt catching a fly ball.

--Ethan

 

[Cosmik]

Yes, exactly. In order to absorb sound the cone has to function as a shock absorber, so to speak. If the cone "butted heads" with the wave and opposed its direction, it would reflect twice as much as a plain boundary! (With two such devices at opposite sides of the room you'd get runaway feedback. ) So the cone has to move in the same direction as the wave, but slow it down, sort of like a baseball mitt catching a fly ball.

I think there is some confusion over inward and outward movement of cones, and positive/negative pressure. To generate an equal and opposite pressure, the 'absorber's' diaphragm has to move in the same direction as the wave - not "butting heads" with the wave. That is, if a speaker cone accelerates outwards at one side of the room, generating a positive pressure, a diaphragm at the other side must accelerate in the same direction at the appropriate moment in order to generate an opposing negative pressure to null the wave.

If the two waves meet half way across the room you can think of positive and negative meeting and cancelling each other out. If the two waves meet 0.1mm off the absorber diaphragm, you can think of a baseball mitt catching a ball...

 

[h.g.]

That is, if a speaker cone accelerates outwards at one side of the room, generating a positive pressure, a diaphragm at the other side must accelerate in the same direction at the appropriate moment in order to generate an opposing negative pressure to null the wave.

If the two waves meet half way across the room you can think of positive and negative meeting and cancelling each other out. If the two waves meet 0.1mm off the absorber diaphragm, you can think of a baseball mitt catching a ball...

There is no opposing negative pressure created to null the wave. If you place a microphone just in front of the cone doing the absorbing you will measure all of the incoming sound wave pressure variation and nothing else. The pressure is not zero in front of the cone.

If you did want to create zero pressure in front of the cone then that would be achieved by doubling the cone motion: half to absorb the incoming sound wave and half to create an outgoing sound wave that is the inverse of the incoming sound wave. This will create zero pressure in front of the cone and double the velocity. Note a stationary cone/hard wall creates double the pressure and zero velocity. The problem is that the emitted outgoing wave will create a pattern of nodes and antinodes just like the case for a wall although the pattern will be different.

The constant acoustic pressure in front of the cone in the PSI absorber is due to the presence of the grille. There is a pressure drop across the grille. Between the grille and the cone the air is moving as an incompressible slug without being compressed and so without creating sound. However that slug has kinetic energy due to its motion and so the energy in the incoming sound wave is still being transported to the cone.

The cone of the speaker is moving but it is not creating the sound it would if there was no incoming sound wave. This is because the incoming wave is moving the air to lead the motion of the cone by just the right amount to remove the compression/expansion of the air in the incoming wave but not by any more or less which would compress/expand the air and create an outgoing wave.

 

[Ethan Winer]

After all the talk about how ugly acoustic treatment is, I think this photo of a Dolby Atmos setup is relevant. But hey, there's none of those fugly bass traps!

 

[Fitzcaraldo215]

After all the talk about how ugly acoustic treatment is, I think this photo of a Dolby Atmos setup is relevant. But hey, there's none of those fugly bass traps!

Well, audiophiles, actually in this case a videophile, gotta do what they gotta do.

 

[NorthSky]

It was only to review an immersive sound system, in Mark's room...from AVSForum where Mark is one of the top contributors.

Here: http://www.avsforum.com/forum/89-sp...yle-atmos-system-experience.html#post37725865

And no way Mark is keeping his living room permanently like that...lol

If I wanted a nice looking room and professionally treated acoustically, I would choose one like the one Ethan has. But would add couple more subs, couple more floor speakers, and four overhead speakers, plus a new pre/pro (latest Yamaha one), thirteen channels of separate amplification, two Dirac Live black boxes (for sixteen channels of prime EQ), a 4k BR player, 4K true front projector, and 4K ultra high speed HDMI cables with active power signal for the cable's length. So roughly $36,000 of new investment to keep up with today's latest hipsters.
The room would still look nice, but the movie experience would lead to a totally new and improved dimension level...auditory and visually. Yes, for a room like his...four subwoofers.

And, I would invite Mark Seaton for a filet mignon with French dry red wine bottles, and Italian dessert with Remy Martin Courvoisier cognac, quadruple XXXX, and a Cuban cigar for digestive. ...Then ask Mark for some feedback advice.

 

[amirm]

After all the talk about how ugly acoustic treatment is, I think this photo of a Dolby Atmos setup is relevant. But hey, there's none of those fugly bass traps!

Guaranteed the person is single. That is one ugly setup.

 

[amirm]

It was only to review an immersive sound system, in Mark's room...from AVSForum where Mark is one of the top contributors.

Here: http://www.avsforum.com/forum/89-sp...yle-atmos-system-experience.html#post37725865

Ah that explains it:

"GoldenEar's CEDIA demo was strikingly immersive, so I immediately asked for a system to review. Founder and chief designer Sandy Gross agreed to provide it, but there was one sizeable obstacle to overcome: I rent, so I can't cut four big holes in my ceiling, especially since there's no wiring up there to begin with. I knew I needed to hang speaker enclosures from the ceiling, but I was not enthused by the prospect of building the boxes that the HTR-7000s would require.

Sandy's solution to the enclosure problem was simple enough; he suggested I borrow the same sealed boxes used in the 2014 CEDIA demo. The enclosures are designed to take the place of tiles in a standard drop ceiling, but if I could figure out how to hang them, I was welcome to borrow the boxes—which I did. Soon enough, I had a fully functional 5.1.4 Atmos system."

Seems like I was right with him being single though.

 

[NorthSky]

How can I make myself invisible*?
Thank you .

* From my profile privacy settings; I did unclick it to be incognito but the green sign on the top left corner of my avatar still shows of.

 

[Thomas savage]

After all the talk about how ugly acoustic treatment is, I think this photo of a Dolby Atmos setup is relevant. But hey, there's none of those fugly bass traps!

A commendable level of commitment!

Amir is right though, this is a perfect example of what the world would be without the feminine.

Still, I see much of my own crazed mind in the picture a considerable level of uncomfortable recognition in fact

I applaud him!