Not trying to be argumentative but I thought it was low pressure/high velocity to high pressure/low velocity...
in particular I remember that larger radiation sources achieve higher pressure with lower velocity than smaller sources. I might be mixed up I think not.
Just to be sure 
, I checked Kolbrek's paper:
"...transform the high pressure, low velocity vibrations at the throat into low pressure, high velocity vibrations that can efficiently be radiated into the air."
Another quote from the same paper highlighting the importance of impedance:
"The loudspeaker, which is a generator of pressure, has an internal source impedance and drives an external load impedance. The air is the ultimate load, and the impedance of air is low, because of its low density. The source impedance of any loudspeaker, on the other hand, is high, so there will be a considerable mismatch between the source and the load. The result is that most of the energy put into a direct radiating loudspeaker will not reach the air, but will be converted to heat in the voice coil and mechanical resistances in the unit. The problem is worse at low frequencies, where the size of the source will be small compared to a wavelength and the source will merely push the medium away. At higher frequencies, the radiation from the source will be in the form of plane waves that do not spread out. The load, as seen from the driver, is at its highest, and the system is as efficient as it can be."
, I checked Kolbrek's paper:"...transform the high pressure, low velocity vibrations at the throat into low pressure, high velocity vibrations that can efficiently be radiated into the air."
Another quote from the same paper highlighting the importance of impedance:
"The loudspeaker, which is a generator of pressure, has an internal source impedance and drives an external load impedance. The air is the ultimate load, and the impedance of air is low, because of its low density. The source impedance of any loudspeaker, on the other hand, is high, so there will be a considerable mismatch between the source and the load. The result is that most of the energy put into a direct radiating loudspeaker will not reach the air, but will be converted to heat in the voice coil and mechanical resistances in the unit. The problem is worse at low frequencies, where the size of the source will be small compared to a wavelength and the source will merely push the medium away. At higher frequencies, the radiation from the source will be in the form of plane waves that do not spread out. The load, as seen from the driver, is at its highest, and the system is as efficient as it can be."
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I look at like this.
The acoustic impedance is a function of pressure and volume velocity (Za = P/Vv). The throat acoustic impedance is higher because of higher pressure (SPL) and lower volume velocity (it's cross section area is smaller like the small hose flow rate analogy). The mouth acoustic impedance is lower because its pressure is lower and its cross section area is larger so higher volume velocity. Acoustic impedance of free space air is low. Particle velocity should be proportional to volume velocity as well.
The acoustic impedance is a function of pressure and volume velocity (Za = P/Vv). The throat acoustic impedance is higher because of higher pressure (SPL) and lower volume velocity (it's cross section area is smaller like the small hose flow rate analogy). The mouth acoustic impedance is lower because its pressure is lower and its cross section area is larger so higher volume velocity. Acoustic impedance of free space air is low. Particle velocity should be proportional to volume velocity as well.
Energy, power, intensity and pressure
Sound Energy - Energy is defined as "the ability or capacity of an object to do work". If we think of a single speaker producing sound, as it moves it does work in the process of moving the air molecules around itself - the energy is transfered to the air molecules. Energy is usually denoted by a capital E and the unit of energy is the joule (J).
Sound Power - Power is simply the "rate of expenditure of energy" - that is how much energy is transfered in every second. For our speaker it describes how much energy is expended per second in moving the surrounding air molecules. Power is usually denoted by a capital P, and the unit of power is the watt (W).
Sound Intensity - As the speaker plays a sound, the energy travels out in all directions and as it does so it is spread out over a larger area. Sound intensity refers to the amount of sound energy that passes through a particular area in one second (i.e. power/area). Sound intensity is usually denoted by a capital I and the unit of intensity is W/m2 or Wm-2.
Sound Pressure - When the speaker isn't moving the surrounding air will be at atmospheric pressure (with a certain density of molecules). As the speaker moves outwards it applies a force to the air molecule pushing them together (compression), as it moves back it leaves a region of fewer molecules (rarefaction). The moving molecules then collide with adjacent ones and pass on the energy. The sound pressure is simply the amount of force that is applied by the moving molecule per unit area. Sound pressure is usually denotes by a small p, and the unit is the pascal (Pa) where 1Pa = 1 N/m2.
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That relationship of pressure to velocity at the mouth is also one reason that I think people like to stand close to a powerful bass horn. That ‘trouser flapping’ physicality could be attributed to the relatively high velocity at the mouth when compared to a sealed or ported enclosure.
I’ve definitely noticed this feeling with well-designed tapped horns, as well as classic front-loaded horns with a sealed rear chamber. Standing near a TH412 at full chat is a very moving experience! There’s a lot of Whole Body Vibration, to use the proper term.
You do get some of the same effect from modern, large ports on powerful dual-18 subs when driven with lots of voltage swing, but there’s something that’s just violently fun about a bass horn with a large enough mouth radius to be effectively loading at 30Hz.
It is also quite damaging to your hearing, of course, but very few of the pleasures in life come without risk
I’ve definitely noticed this feeling with well-designed tapped horns, as well as classic front-loaded horns with a sealed rear chamber. Standing near a TH412 at full chat is a very moving experience! There’s a lot of Whole Body Vibration, to use the proper term.
You do get some of the same effect from modern, large ports on powerful dual-18 subs when driven with lots of voltage swing, but there’s something that’s just violently fun about a bass horn with a large enough mouth radius to be effectively loading at 30Hz.
It is also quite damaging to your hearing, of course, but very few of the pleasures in life come without risk
what I am trying to do is point to the particular aspects that make the most difference between a large and a small sound source at the same distance same SPL, while in the omni parts of the spectrum for both....
Intensity is one, that caught my attention in early conversation. Is it intensity that increases with large radiation mass within a certain listening distance
Another thought... where the air couples with the diaphragm on a horn. Cannot this be seen as a sort of "new" diaphragm face and size? Without coupling from the horn the "face" remains at the true face, the diaphragm...
if the above is true or true-ish, then a woofer situation like the Jubilee might go like this.... the BR port is the only coupled item at LF, and the front horn raises path length increasing Delay, and loses some efficiency along the way.....
The BR section of the Jubilee vs the same BR section on a flat, equivalently wide/tall baffle
Yup, like this:That relationship of pressure to velocity at the mouth is also one reason that I think people like to stand close to a powerful bass horn. That ‘trouser flapping’ physicality could be attributed to the relatively high velocity at the mouth when compared to a sealed or ported enclosure.
....but there’s something that’s just violently fun about a bass horn with a large enough mouth radius to be effectively loading at 30Hz.
It is also quite damaging to your hearing, of course, but very few of the pleasures in life come without risk
Somehow I tend to prefer FLHs over THs, at least from experience with PA.
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A lot of my question concerning the outcome of the front horn of the Jubilee can be answered in HornResp...I'll try to look inot that today.
My list of things that separate Small from Large Radiation source, that stick;
Radiation Mass/Impedance
Intensity
....thats the whole list lol..... The part that I would nit pick is the intensity at the omni directional spectrum for a large and small source....I think that intensity is still higher with the larger source.
As far as TH vs TL vs FLH with the same CSA at the mouth.....is the difference really that significant? I wouldn't think so.
My list of things that separate Small from Large Radiation source, that stick;
Radiation Mass/Impedance
Intensity
....thats the whole list lol..... The part that I would nit pick is the intensity at the omni directional spectrum for a large and small source....I think that intensity is still higher with the larger source.
As far as TH vs TL vs FLH with the same CSA at the mouth.....is the difference really that significant? I wouldn't think so.
According to hornresp....we go from high velocity to low velocity....Which makes sense to me on the surface. I also recognize the complexity of the discussion and that the devil is in the details. Anyone have those details>?
HornResp is showing High Pressure and velocity going to Low at the mouth. The pressure side of it makes sense to me, thinking about putting the microphone down the throat, increasing SPL.... The velocity side of it makes seems to me also....I think lol.....A larger radiation source needs less Velocity to create pressure. The same reason a Large woofer has to travel less distance to create the same SPL as a little driver traveling much father. The coupling of the Air turns the airmass that is couple to the driver into a "diaphragm" thats the size of the CSA where it couples to.
Is Akabak the only program I can have access to, that simulates Radiation Mass>?
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Driver + horn are a single electro-acoustic system, but you seem to refer to acoustic origin.
Particle velocity vs Volume Velocity....Volume velocity almost sounds like another word for intensity. Thanks for the input @DonVK
This picture below might help me explain what I think is going on at different notes of a horns output.....The Chartreus areas represent coupled air masses.....The coupled air masses move in unison (to some degree?) with the diaphragm. like a dynamically changing air piston whos size depends on frequency. So at the lower notes, just above cutoff, the air mass is largest (this heavy mass causes GD).....as we move up in frequency the corresponding CSA/Axial length of the couple air mass, moves deeper into the horn.....
The larger CSA of the airmass, in the lower notes increases Volume Velocity dramatically.....And is also the responsible for increasing the Radiation Mass
below cutoff, we lose coupling....the radiation mass shrinks to the size of the diaphragm.
This picture below might help me explain what I think is going on at different notes of a horns output.....The Chartreus areas represent coupled air masses.....The coupled air masses move in unison (to some degree?) with the diaphragm. like a dynamically changing air piston whos size depends on frequency. So at the lower notes, just above cutoff, the air mass is largest (this heavy mass causes GD).....as we move up in frequency the corresponding CSA/Axial length of the couple air mass, moves deeper into the horn.....
The larger CSA of the airmass, in the lower notes increases Volume Velocity dramatically.....And is also the responsible for increasing the Radiation Mass
below cutoff, we lose coupling....the radiation mass shrinks to the size of the diaphragm.
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Thx Ro
That helps explain some of the parent source location difference i've been hearing in my syns, between the same primary conical horn with and without secondary flares.
Btw, for about 10 years i kept a block of 4 of Tom D's Labhorn subs out on the deck....your pict earlier on this page reminded me of them.
My adjacent neighbor behind the sub deployment was wonderful....he made sure that his home owners policy would cover his widows being knocked out !
Said he loved the loud music, but the house was really rattling....
Radiation mass is not exactly what I mean above, but @Ro808 the front of the coupled mass, is what I was trying to convey earlier....I wonder if it even has a title? When the coupling is gone, the "front" is at the diagprahm face. Some type of front, it seems it me be called.
I think that there is a proximity effect depending on how large this couple mass is. placing the front at different points in the axial length. The lower notes having the mass reach to the mouth....its like the source is a little bit closer in those notes...but it won't be exactly evident in the timing.
It is likely past this Front or point, or soon there after you start to loose velocity
"1. Radiation mass Transition between piston velocity field (normal piston velocity) and sound field in free space."
What happens when you put a Line in front of source producing bass....when that line is not large enough to waveguide bass, and not long enough to couple an airmass within the line?
Just playing with Horn resp...Seems that not much is happening if I create an expanding line from the BR section of the model I made. I tried a final CSA of 6000cm2 or so with line length of 30 some odd inches.
Adding line length pushes Fb lower but since the line is expanding, its potency of effect, is not there. Barely a change at 85cm....Lowering csa from 6000 at said length drives Fb lower... Neither option creates more sensitivity/efficiency, actually losing, the longer the line.....midrange sensitivity/efficiency seems to increase though..... you can see the knee of that filter, move lower as the Horns cutoff moves lower with increasing horn size....below this front horns cutoff, the BR section loses output that would be there without the added line length.... Interesting...
Adding line length pushes Fb lower but since the line is expanding, its potency of effect, is not there. Barely a change at 85cm....Lowering csa from 6000 at said length drives Fb lower... Neither option creates more sensitivity/efficiency, actually losing, the longer the line.....midrange sensitivity/efficiency seems to increase though..... you can see the knee of that filter, move lower as the Horns cutoff moves lower with increasing horn size....below this front horns cutoff, the BR section loses output that would be there without the added line length.... Interesting...
Loudspeaker units often feature a thin diaphragm, and as a consequence, the fluid load on the structure must be included; this is known as a two-way-coupling or strong coupling.
At the interface between the mechanical structure and the acoustic domain, the boundary conditions are defined such that the structure acts as an acoustic source, and the backinduced pressure from the air is acting on the surface of the structure. The boundary condition on Γas for the mechanical domain is relating the incident pressure to the stresses in the structure (the outer boundary of the acoustic domain is denoted ΓA).
The boundary condition on Γas for the acoustic domain is using the relation between the acoustic field velocity and the acoustic pressure evaluated on the boundary. Here it assumed that the structural velocity and the acoustic velocity is equal in the interface between the two computational domains.
These boundary conditions can be described with a coupling matrix. n is the normal vector of the interface between the acoustic and structural boundary pointing outwards from the acoustic boundary.
Combining the mechanical, acoustic and coupling matrices yields the entire system of equations used for solving vibro-acoustic problems.
(Equations omitted
)
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The radiation mass from a larger woofer or larger horn under load, has more volume velocity and intensity to the listening position and obviously around the source
Are not, these, the building blocks, of the direct field or direct energy?
Good god - 4! I built two for a friends HT. They are near field behind the sofa and are scary, I waived all responsibility for the integrity of his ceiling....