Hi,
JK's preliminary measurements at 1m, which scales to 3m for the full size
version, indicate AFAICT that there is no significant assymetrical gain in
the bass range related to increasing the local frontal air velocity.
Which as some of us have being saying all along, has to be the case.
the AMT principle packs a far longer ribbon into a magnetic space,
and for a given diaphragm displacement creates more volume
displacement than a planar diaphragm does, that is how it works.
The resultant extra velocity is due to the extra volume displacement.
It is not a horn of any sort, just a driver arrangement that allows
easy force cancelling, and has its own foibles, related to slot depth.
rgds, sreten.
JK's preliminary measurements at 1m, which scales to 3m for the full size
version, indicate AFAICT that there is no significant assymetrical gain in
the bass range related to increasing the local frontal air velocity.
Which as some of us have being saying all along, has to be the case.
the AMT principle packs a far longer ribbon into a magnetic space,
and for a given diaphragm displacement creates more volume
displacement than a planar diaphragm does, that is how it works.
The resultant extra velocity is due to the extra volume displacement.
It is not a horn of any sort, just a driver arrangement that allows
easy force cancelling, and has its own foibles, related to slot depth.
rgds, sreten.
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perhaps this has been pointed out but........dose this sound the similar?
Atlantic Technology—Small Speaker But Big Bass | Stereophile.com
dose pass have a patent on this?
or is this different?
Atlantic Technology—Small Speaker But Big Bass | Stereophile.com
dose pass have a patent on this?
or is this different?
well that link isnt as in depth as this snip from the first page........
"Peter Tribeman, touting a prototype of his company's new loudspeaker, the AT-1. JA and I had just heard about the finer points of the AT-1's new bass-venting technology, the Hybrid-Pressure Acceleration System (H-PAS), which was supposed to combine all the benefits and qualities of a transmission-line enclosure, horn loading, and sealed and ported designs. At the time, I didn't care if it combined all of the qualities of Kim Kardashian, Sacagawea, Joan of Arc, and Marie Curie—I was just thrilled that the AT-1s were sounding so good in a partitioned ballroom."
"Peter Tribeman, touting a prototype of his company's new loudspeaker, the AT-1. JA and I had just heard about the finer points of the AT-1's new bass-venting technology, the Hybrid-Pressure Acceleration System (H-PAS), which was supposed to combine all the benefits and qualities of a transmission-line enclosure, horn loading, and sealed and ported designs. At the time, I didn't care if it combined all of the qualities of Kim Kardashian, Sacagawea, Joan of Arc, and Marie Curie—I was just thrilled that the AT-1s were sounding so good in a partitioned ballroom."
Atlantic Technology - H-PAS
a Karlson building friend said they were using K-techology - btw , in the early 1980's I had a pair of Phil Clements 2-way Phase Research speakers with custom 8" woofer and Audax ~1.5" dome - IIRC it had a similar claim to H-PAS. In practice they were 'so-so" - ran them with Nelson's Stasis II :^)
a Karlson building friend said they were using K-techology - btw , in the early 1980's I had a pair of Phil Clements 2-way Phase Research speakers with custom 8" woofer and Audax ~1.5" dome - IIRC it had a similar claim to H-PAS. In practice they were 'so-so" - ran them with Nelson's Stasis II :^)
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One of the things I should have posted which also would help understand the strength of the front and rear sources in the far field is the unequalized on axis (0 degrees) far field response. I will have to make some detailed analysis of that response to be sure, but from looking at that result it tells me that the gradient roll off is exactly what is expected from equal strength sources.
Simply increasing volume velocity can not increase efficiency. If it could then any driver would have an efficiency which increased with increased applied power. We know that a 6dB increase in amplifier power yields a 6 dB increase in SPL (and volume velocity), with no increase in efficiency. In creases in efficiency come from increasing radiation resistance. Horns have such a function as then act as transformers which what allow the small surface area of the driver to be transformed to the larger area of the horn mouth resulting in increased radiation resistance. In the slot loaded case, any increased efficiency on the front is are result of the cavity resonance. If you care to call that an increase in efficiency of the front side that is fine, but it has no effect on the low frequency response. The last figure on my page shows that the cavity resonance has negligible effect on SPL below 300 or 400 Hz.
Simply increasing volume velocity can not increase efficiency. If it could then any driver would have an efficiency which increased with increased applied power. We know that a 6dB increase in amplifier power yields a 6 dB increase in SPL (and volume velocity), with no increase in efficiency. In creases in efficiency come from increasing radiation resistance. Horns have such a function as then act as transformers which what allow the small surface area of the driver to be transformed to the larger area of the horn mouth resulting in increased radiation resistance. In the slot loaded case, any increased efficiency on the front is are result of the cavity resonance. If you care to call that an increase in efficiency of the front side that is fine, but it has no effect on the low frequency response. The last figure on my page shows that the cavity resonance has negligible effect on SPL below 300 or 400 Hz.
ok so its not the same thing. to my mind the way it was decribed sounded like this desighn
Apparently you don't consider 40% gain significant.
Hi, the model measurements don't have 40% gain in the bass region, rgds, sreten.
I'm not a loudspeaker designer, but spent lots of time in applications of measuring acoustics, for Bruel and Kjaer and HP. One thing is pretty clear - talking about sound pressure, especially in an undefined acoustic space (i.e. not an anechoic chamber) is pretty uncertain. Especially talking about far field response.
If you talk about sound power, that's different - it's independent of the space, but much harder to measure.
If you direct acoustic pressure from being half sphere or full sphere to being even somewhat directional, you will increase pressure in a "favored" direction, without increasing acoustic power (i.e. true efficiency). It may only occur in the "near field" or "free field", but the effect should not be denied based on only what eventually works out in the far field, usually also called the reverberant field where direct and indirect pressures are equal.
So it's possible to increase (by restricting direction) apparent measured pressure on the favored axis, and hence, if all you go by is pressure, what most loudspeaker people call "on axis efficiency".
Another input - In room acoustic treatments, especially ones that absorb below 200 Hz that are placed behind a dipole radiator, can also make these measurements variable in a relatively small enclosed space. They will absorb the back wave, and for a dipole, increase the bass effect due to less cancellation.
Just getting my toes wet again
Bob
Hi Bob,
Thank you for your comments. The point of my experiment using a scaled down model is to allow anechoic (or so called quasi-anechoic) measurements to be obtained at frequencies low enough to allow the physics of such a woofer configuration to be explored. Room related effect are thus eliminated or minimized. Also, based on the wave lengths considered the near field/far field transition is taken as the point where the radiation of the source takes on the characteristic of a spherical wave. For small values of the wave number (low frequency) this takes place at about 3 times some characteristic dimension of the source. For my model, with an 11" baffle width, 1M distance should be sufficient. Thus, my measurements should provid a good representation of what the far field behavior of such a configuration should be without significant contamination for room effects. In that light we can then make use of specific characteristics of the measured response in comparison to known theoretical behavior to look for deviations or similarities which would provide a path for further thought and experimentation.
I should also point out that the limitations of looking only at the axial response is exactly why I took the time to perform a full set of polar response measurements. Never the less, there are specific characteristics of the axial response which reveal information about the relative strength of the front and rear sources.
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Perhaps you are not familiar with the mathematics of decibels.
10 dB is a factor of 10. 10^0 = 1. 10^1 = 10.
1.5 dB (John's upper estimate for the bass region) equals 10^0.15 = 1.41,
which is 41% greater energy
2.5 dB (The number I got on the full size version) equals 10^0.25 = 1.78,
which is 78% greater.
'Acoustical gain' is a good thing, but as always there's no free lunch. This is not a horn anyway, so it's not a shame at all the gain (if any) is (far) less than a real horn.
--- and, how about the 'negative gain' of all the beloved OB speakers ?
As a sub, for me, it's major strong points are packaging flexibility and lowered fs.
Slot type opening can be arranged in various configurations to fit the main speaker, which is an excellent feature. It's more so for a penal type speaker user like me.
Lowering fs without penalty in efficiency (within such package) is already a gain itself. The fs of my woofer in free air is 27~29Hz (WT3 measurements and the number in datasheet are pretty in sync), in slot loaded OB, it drops below 15Hz. (with some other cheap tricks, actually it's now 13.5Hz)
I guess most of you don't remember (or know) this: http://www.diyaudio.com/forums/multi-way/123512-ultimate-ob-gallery-3.html#post1517866
That was one of my works 3 years ago. As you may see there're 3 18" on the 'tightly' fit baffle. (simple math, so there're 6 in both channel) That creature didn't deliver the 'sense' of the room being pressurized as this slot loaded one can. I think it's the extended response contributed by lowered fs.
As to the distortions by the extra load, or other measurable aspects, I leave those debates to you. I've tested and heard the distortion of my woofer on OB, I know what it's like. I don't bother to do the test again because now in slot-loaded, it doesn't sound like that and pretty good to my ears and body. I know it's not convincing at all, but fine with me.
So, up to now, is there still only me (except Nelson) using this stuff for playing music after 26 pages? Is this DIY forum or what?
--- and, how about the 'negative gain' of all the beloved OB speakers ?
As a sub, for me, it's major strong points are packaging flexibility and lowered fs.
Slot type opening can be arranged in various configurations to fit the main speaker, which is an excellent feature. It's more so for a penal type speaker user like me.
Lowering fs without penalty in efficiency (within such package) is already a gain itself. The fs of my woofer in free air is 27~29Hz (WT3 measurements and the number in datasheet are pretty in sync), in slot loaded OB, it drops below 15Hz. (with some other cheap tricks, actually it's now 13.5Hz)
I guess most of you don't remember (or know) this: http://www.diyaudio.com/forums/multi-way/123512-ultimate-ob-gallery-3.html#post1517866
That was one of my works 3 years ago. As you may see there're 3 18" on the 'tightly' fit baffle. (simple math, so there're 6 in both channel) That creature didn't deliver the 'sense' of the room being pressurized as this slot loaded one can. I think it's the extended response contributed by lowered fs.
As to the distortions by the extra load, or other measurable aspects, I leave those debates to you. I've tested and heard the distortion of my woofer on OB, I know what it's like. I don't bother to do the test again because now in slot-loaded, it doesn't sound like that and pretty good to my ears and body. I know it's not convincing at all, but fine with me.
So, up to now, is there still only me (except Nelson) using this stuff for playing music after 26 pages? Is this DIY forum or what?
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Perhaps you are not familiar with the mathematics of decibels.
10 dB is a factor of 10. 10^0 = 1. 10^1 = 10.
1.5 dB (John's upper estimate for the bass region) equals 10^0.15 = 1.41,
which is 41% greater energy
2.5 dB (The number I got on the full size version) equals 10^0.25 = 1.78,
which is 78% greater.
Hi,
Of course I'm familiar with decibels and your clutching at straws.
Any number of issues could give the ~ 25% discrepancy (~ 1dB),
for bass, including the most obvious one, a residual nearfield effect.
Faced with measurements your making unreasonable claims.
The evidence points to equal level sources in the farfield,
as does the physics. There is nothing unusual going on.
rgds, sreten.
As Jk states, the depths of the 90 degree nulls are too
deep for there to be a real 1dB difference front to rear.
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First, my apologies for confusing near field and far field definitions in my post above, it has been awhile. The far field, in architectural acoustics consists of the free field and reverberant field. The free field is defined for a point source where one observes a 6dB reduction in pressure for a doubling of distance from the source.
The reverberant field is where there is no longer a reduction in SPL with distance, as the random reflections from other surfaces create a somewhat constant steady pressure. This transition from free to reverberant field can be different for different frequencies, as it's based on absorption/reflection properties of the room, also frequency dependent.
To really understand this assumed anechoic measurement in an enclosed room, I would recommend taking SPL measurements on axis from the near field outward, and look at the difference between front and rear axis, (where you start with a roughly 10dB SPL front rear / difference.
All the modeled 1M measurements, if I understand them, need to be divided by 3 in frequency, and x3 for distance. This means you are modelling what happens almost 10ft away in the full size model. In a real world listening situation, with dipoles well out from the back walls, some people may care what happens at a lesser distance, say between 5-10ft. on axis from the front of the speakers. What do the plots look like as you move in slowly towards the near field?
Last - in the polar plots, I can see significant unequal front rear effects at 200Hz model, /3 = 66 Hz. Is not 66Hz important for bass anymore ?
Bob
Back from vacation and I made some measurements of the isolated slot and rear radiation with the baffle mounted on a box. The results have been added to the bottom of my web page.. No real surprises. No low frequency efficiency gain form the slot compared to the rear.
Hi,
So the ~ 1dB difference (before the slot resonance starts to affect things)
is due to the assymetry of the front and rear baffle step responses ?
The front starts rising before the rear ? That is not obvious .....
So the front "sees" a larger baffle than the rear ? go figure .....
So that implies ~ 1dB of the reported ~ 2.5dB effect is due to the above,
and therefore the other ~ 1.5dB must be due to residual nearfield effects.
rgds, sreten.
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