John,
It seems reasonable to me to ignore fluid (air) flow issues up to a certain point. Clearly, the assumption will break down beyond that point. If it doesn't seem like a reasonable assumption to you, that's fine, but it would take a much more detailed analysis to determine how reality deviates from the idealized model system. It also seems reasonable to me that for slot loading, resistive losses will be lower than for a ported box, even ignoring the acoustic stuffing usually put into the box.
Several people have proposed that in the far field there is no difference between the SPL from the slot and from the rear. I am open to being convinced on this point. However, my intuition says that energy is energy - i.e., in the far field 1W of acoustic power translates to the same SPL regardless of the size of the source; ignoring resistive losses and well below the frequency cutoff of the slot, the slot emits R^2 greater energy than the rear. I would welcome someone pointing out exactly where my idealized energy argument is incorrect.
Jeremy
But that can really not be the case that would be very strange that would mean that if you would make the total amount of energy you get out of the system bigger than the amount you put in. Look at the application of that effect for solving our energy crisis only by using narrower pipes before the steam hits the turbines or pistons that would really be a great invention if it were true.
Again, the acoustic loading increases due to the slot, as is evidenced by a lowering of the impedance. A x V increases as a result, so more energy enters the system. Thus far I think Nelson's reasoning is sound, like his argument that with the same volume displacement, higher air speed equals more momentum equals more energy.
My thing with this line of reasoning is that the effect is likely to be assymetrical, that is different between outwards and inwards cone movements. Air being pushed out maintains directionality, air sucked in comes from all directions. Theoretically, this should translate into even order distortion (which increases apparent loudness and therefore often sounds "rich").
vac
My thing with this line of reasoning is that the effect is likely to be assymetrical, that is different between outwards and inwards cone movements. Air being pushed out maintains directionality, air sucked in comes from all directions. Theoretically, this should translate into even order distortion (which increases apparent loudness and therefore often sounds "rich").
vac
Hi John
“Pretty much what I implied back in #84:”
I figured since there appeared to be some remaining skepticism so far as what it does and that a few people here do experiment, that I would expand on the assertion with some detail and suggest an experiment which will prove same.
Best,
Tom Danley
“Pretty much what I implied back in #84:”
I figured since there appeared to be some remaining skepticism so far as what it does and that a few people here do experiment, that I would expand on the assertion with some detail and suggest an experiment which will prove same.
Best,
Tom Danley
A couple of points.
First, there is no way you will get R^2 increase in energy with such an
arrangement. You do impart greater 1/2mv^2 energy to the air coming
out of the slot, but only part of that translates into spl at a distance, as
shown by the measurements.
Second, there have been several posts speculating about 2nd harmonic
distortion. I can assure you that while this is a real gas equation
phenomenon, it becomes substantial at a couple orders of magnitude higher
that we are talking about. It is a problem in horn throats at a Rolling Stones
concert, not in your living room.
First, there is no way you will get R^2 increase in energy with such an
arrangement. You do impart greater 1/2mv^2 energy to the air coming
out of the slot, but only part of that translates into spl at a distance, as
shown by the measurements.
Second, there have been several posts speculating about 2nd harmonic
distortion. I can assure you that while this is a real gas equation
phenomenon, it becomes substantial at a couple orders of magnitude higher
that we are talking about. It is a problem in horn throats at a Rolling Stones
concert, not in your living room.
Okay... incorrect other than a factor of 1/2 and being sloppy with using energy to mean kinetic energy.
Jeremy
A couple of points.
First, there is no way you will get R^2 increase in energy with such an
arrangement. You do impart greater 1/2mv^2 energy to the air coming
out of the slot, but only part of that translates into spl at a distance, as
shown by the measurements.
So (forgive me if i missed it) that's at say a typical listening distance of say 3 m, a net increase at say 50 Hz of +? dB?
There's plenty o' extra energy around at the input so that we are not creating perpetual motion machines. Only about 1% of the electrical energy is being converted into acoustic energy (give or take a factor of 10).
Jeremy
I have an idea for a symmetrical design that could put the front and back efficiency debate to rest. Because it is from two parts the distance between the cabinets can be experimented with and consequently the width of the slot can be adjusted.
View from the top. It is also very easy to build. The slot could also be arnged as a "V" so it could be wider in the back and slimmer in the front.
View from the top. It is also very easy to build. The slot could also be arnged as a "V" so it could be wider in the back and slimmer in the front.
im not sure what the disagreement is about.....
using the ½mv², then it follows simply that half the air moved twice as fast has each energy, ie ½(m/2)*2v² = ½mv² = KE
surely net energy is preserved? horn loading is the only way to improve efficiency on the one side, its just the transformation of energy that becomes more efficient
i think....
using the ½mv², then it follows simply that half the air moved twice as fast has each energy, ie ½(m/2)*2v² = ½mv² = KE
surely net energy is preserved? horn loading is the only way to improve efficiency on the one side, its just the transformation of energy that becomes more efficient
i think....
The arguments about energy and SPL are all related to the space the source is radiating in and how the wave expands. For example, take any driver. In one case mount it on the end of a pipe in the other mount it in an infinite baffle. Apply a signal so that the volume velocity is the same in both cases. In case 2 the far field SPL will be 6dB higher than in the 1st case and the intensity will be 4 times greater. That translates to a 3dB increase in efficiency of the driver just because it is radiating into 1/2 space as opposed to full space. But in both cases the velocity in the near field, very close to the source, is identical as is evidenced in the observation that a near field measurement fails to show the effect of the baffle step.
The reason is because pressure is dependent on volumetric displacement. On a volumetric basis, in full space the differential volumetric displacement into some arbitrary spherical volume enclosing the source is 1/2 that for case 2 where the same differential displacement is into a hemisphere. Yet the velocity imparted to the air in contact with the radiating surface of driver is the same in both cases because the cone motion is the same. I.E., mV^2 is the same.
The reason is because pressure is dependent on volumetric displacement. On a volumetric basis, in full space the differential volumetric displacement into some arbitrary spherical volume enclosing the source is 1/2 that for case 2 where the same differential displacement is into a hemisphere. Yet the velocity imparted to the air in contact with the radiating surface of driver is the same in both cases because the cone motion is the same. I.E., mV^2 is the same.
FUNKTION ONE does the main stage in Glastonbury and never went line source too. Although they do separate band horn sources. Slot loaded (possibly) smaller scale bass cabs on 2:04 in this video: FRANKFURT MUSIKMESSE Video 11, 2009. Funktion-one - YouTube
The biggies at start look like real bass horns. The ones later on at the base of the belt secured stack look like manifolds.
Earlier in the thread, responding to comments that there is no difference
at 2 meters, I performed the following experiment:
I measured the response on axis at 3 m. Then I turned the speaker around
so that the slot was facing the rear and re-measured, overlaying the curves.
The difference in the range between 30 and 100 Hz was about 2.5 dB.
No, not really. What I am looking at is modification of the u-frame form factor. I am investigating mounting the woofers on the sides of the u-frame rather than on the front so I can reduce the vertical height of the woofer enclosure. This is purely to allow me to modify the form factor and make the speaker esthetically more pleasing. I don't expect any unanticipated changes in performance.
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