dlr,
Thanks Dave. This will take a bit to digest and understand what the implications are from a subjective point of view. I can see clearly that there would be summing nodes as you move off of the edge of the face of a baffle. What was not entirely clear was how far from the baffle these nodes extend laterally and what their off axis character might be, this from the paper by Andy Unruh.
One of the Vance Dickinson comments caught my eye, on first read through of Mr Unruh's paper. The beaming from a flat baffle. This definitely disappears, even when you are on axis for the driver, so long as both driver and baffle are EnABL'd.
There is not a noticeable aberration in frequency response as you move off axis or as you move past the baffle edge, as I think is being shown to happen in the plots that show an FR scaled to dB.
In a stereo mode there is a very slight positionally determined frequency response change, in the 1k to perhaps 6 k hz band. This is just barely enough to notice as you move across the space between two baffles, at a meter distance. By 2 meters this has fallen below a level that is audibly detectable.
In terms of localization, on axis or off, the apparent image location is always behind the box, and doesn't change it's perceived relative height, as you move from side to side or up and down, again at about 1 meter.
I am not sure if the faint lobe in midrange heard in stereo is from the baffle or from some other dissonant combinations of losses. Again, it is very slight and to date only from a multi driver system, as that is the only sort I have had baffles/boxes for.
All of the FR drivers, sitting nude on their pedestals, showed quite smooth roll off in FR off axis. The image also behaved as described above and there was no off axis lobe effect between stereo pairs with a centrally located music source, in either mono or stereo.
Again, this is after EnABL. For the F 120A drivers, most recently here, the before treatment character was a very abrupt beaming from off to on axis, with a centrally located high frequency peak. A stereo pair did not show any particular lobe artifacts and the perceived location in horizontal depth remained at speaker basket.
After EnABL the directionalityand off/on axis beaming disappeared, unless you got within a 10 degree, at a meter cone of the center aluminum dome. There, a slight tendency to localize high frequency sounds showed up. Outside of that cone, the image was stable and it's perceived location was behind the driver.
These location irregularities were from stringed instruments only and are likely an artifact of the metal used. I was able to eliminate this effect with a seperate tool, unrelated to driver treatment, at which point the perceived location for all frequencies remained stable and behind the driver baskets, regardless of lateral position, mono or stereo or just one channel playing.
As I indicated, it will take a while to understand how to use the spreadsheet and then how to build a baffle it predicts and measure a reliable EnABL'd driver and baffle against a plain set.
I have actually resuscitated the lap top that Laud is on. I will be able to do my usual crude measurements.
Bud
Thanks Dave. This will take a bit to digest and understand what the implications are from a subjective point of view. I can see clearly that there would be summing nodes as you move off of the edge of the face of a baffle. What was not entirely clear was how far from the baffle these nodes extend laterally and what their off axis character might be, this from the paper by Andy Unruh.
One of the Vance Dickinson comments caught my eye, on first read through of Mr Unruh's paper. The beaming from a flat baffle. This definitely disappears, even when you are on axis for the driver, so long as both driver and baffle are EnABL'd.
There is not a noticeable aberration in frequency response as you move off axis or as you move past the baffle edge, as I think is being shown to happen in the plots that show an FR scaled to dB.
In a stereo mode there is a very slight positionally determined frequency response change, in the 1k to perhaps 6 k hz band. This is just barely enough to notice as you move across the space between two baffles, at a meter distance. By 2 meters this has fallen below a level that is audibly detectable.
In terms of localization, on axis or off, the apparent image location is always behind the box, and doesn't change it's perceived relative height, as you move from side to side or up and down, again at about 1 meter.
I am not sure if the faint lobe in midrange heard in stereo is from the baffle or from some other dissonant combinations of losses. Again, it is very slight and to date only from a multi driver system, as that is the only sort I have had baffles/boxes for.
All of the FR drivers, sitting nude on their pedestals, showed quite smooth roll off in FR off axis. The image also behaved as described above and there was no off axis lobe effect between stereo pairs with a centrally located music source, in either mono or stereo.
Again, this is after EnABL. For the F 120A drivers, most recently here, the before treatment character was a very abrupt beaming from off to on axis, with a centrally located high frequency peak. A stereo pair did not show any particular lobe artifacts and the perceived location in horizontal depth remained at speaker basket.
After EnABL the directionalityand off/on axis beaming disappeared, unless you got within a 10 degree, at a meter cone of the center aluminum dome. There, a slight tendency to localize high frequency sounds showed up. Outside of that cone, the image was stable and it's perceived location was behind the driver.
These location irregularities were from stringed instruments only and are likely an artifact of the metal used. I was able to eliminate this effect with a seperate tool, unrelated to driver treatment, at which point the perceived location for all frequencies remained stable and behind the driver baskets, regardless of lateral position, mono or stereo or just one channel playing.
As I indicated, it will take a while to understand how to use the spreadsheet and then how to build a baffle it predicts and measure a reliable EnABL'd driver and baffle against a plain set.
I have actually resuscitated the lap top that Laud is on. I will be able to do my usual crude measurements.
Bud
BudP said:
Bud, as much as you may want to believe that there is any possible influence in diffraction with the EnABLE treatment, it is wrong. It will not affect the diffraction whatsoever.
The diffraction is related to the expansion of the sound wave from 2pi to 4pi space as it passes the edge of the baffle. Nothing that you do with any tiny material, EnABL or other, is going to stop that expansion. Your claims are without merit. I'm sorry, but those are the facts.
Stick to drivers, on those the mass and damping effects have some influence. There is none to be had on baffles.
Dave
dlr said:
I don't see why not?
As far as I can tell then anything placed at the edge of the baffle will alter the the propeties of the diffraction going on there.
dlr said:
No claims have been made about stopping anything as far as I'm aware.
Now please correct me if I'm wrong as I'm very much a newbie.
kaan said:
It has to be significant in relation to the wavelengths involved. Even when using a roundover, one of the best methods of diffraction control, the roundover has to have a significantly long radius in relation to the wavelength involved. This has to do with the acoustic impedance over the transition from 2pi to 4pi. It's a well-known phenomenon. Tiny bumps at or near the edge will do nothing to alter the abruptness of the transition of a square edge for the frequencies involved.
Yes, they have in fact. The claim is that "There is not a noticeable aberration in frequency response as you move off axis or as you move past the baffle edge". If it is not noticeable, then the listener is not able to hear differences guaranteed to exist that can be as much as 2-3 db and not of high Q, the latter normally making it easier to detect by ear. Having made literally hundreds of measurements with numerous materials over the years, nothing shown in the EnABL process is valid for diffraction.
The properties and use of felt alone dates back to the early 70's at least with the first usage of which I am aware being in the original LS3/5A designed by the BBC.
An externally hosted image should be here but it was not working when we last tested it.
That dates research by the best professionals back as far as 35-40 years. Many a manufacturer has addressed it. The methods of amelioration are well established.
Dave
Bud, I'm not going to bother getting in to the diffraction thing with you. That you have found a convenient rug to sweep all the dirt under is wonderful. You seem to have an ever more pervasive means of explaining what doesn’t make physical sense by evoking esoteric explanations of simple phenomena.
For those who migh be interested, let me point out that the BL generated by the passage of an acoustic wave over a surface is very, very, very....., very thin. For air is on the order of 0.085/Sqrt(F) inches thick. At 1k Hz that is 0.0027”. The ratio of wave length to acoustic BL thickness is 1.59x10^5/sqrt(f). At 1k Hz the wave length is more than 5000 time the acoustic BL thickness. At 20 k Hz the wave length is still over 1000 times the acoustic BL thickness. The point here is that the acoustic BL is so small that it play no role in the diffraction of wave in the audible range. Diffraction has to do with the turning of an acoustic wave. Thus, if we ignore the BL in the calculation of diffraction then when an acoustic wave is turned we will see the most extreme result. The acoustic BL could only reduce the effect and only is the aocustic BL were at least on the order of the wave lengths considered. If we were to consider enable patches to extend from the surface some finite distance then their affect on diffraction would be at a maximum when predicted by any theory that ignores BL effects. Under the best of circumstances consideration of the affect of an acoustic BL could only make the influence of an enable patch less.
Also, let’s distinguish between an acoustic BL and a typical hydrodynamics BL. We are addressing the BL created by the passage of an acoustic wave. We are not playing our speakers outside is a cross wind.
For those who migh be interested, let me point out that the BL generated by the passage of an acoustic wave over a surface is very, very, very....., very thin. For air is on the order of 0.085/Sqrt(F) inches thick. At 1k Hz that is 0.0027”. The ratio of wave length to acoustic BL thickness is 1.59x10^5/sqrt(f). At 1k Hz the wave length is more than 5000 time the acoustic BL thickness. At 20 k Hz the wave length is still over 1000 times the acoustic BL thickness. The point here is that the acoustic BL is so small that it play no role in the diffraction of wave in the audible range. Diffraction has to do with the turning of an acoustic wave. Thus, if we ignore the BL in the calculation of diffraction then when an acoustic wave is turned we will see the most extreme result. The acoustic BL could only reduce the effect and only is the aocustic BL were at least on the order of the wave lengths considered. If we were to consider enable patches to extend from the surface some finite distance then their affect on diffraction would be at a maximum when predicted by any theory that ignores BL effects. Under the best of circumstances consideration of the affect of an acoustic BL could only make the influence of an enable patch less.
Also, let’s distinguish between an acoustic BL and a typical hydrodynamics BL. We are addressing the BL created by the passage of an acoustic wave. We are not playing our speakers outside is a cross wind.
john k... said:
So ignoring that you think we need to deal with scales on the same order of the acoustic wavelength to have an audible effect, it is clear from these numbers that the EnABL spots are ~ an order of magnitude higher then the BL (at least at 1 kHz), so indeed the spots "look like the Andes to the BL event" so can certainly be effective at perturbing this BL. Then if this is the phenomenom that EnABL is addressing, then the question comes down to, "can this have an audible effect". Barring mass hysteria, the most sensitive (and the most confounding) test instrument we have says yes.
dave
John K,
May I ask a favor? I am attempting to look at your CSD plots with a typical windows magnifier, one that only tracks mouse pointer position. I cannot see more than a small slice of the graphs, as I roll the mouse pointer off and on.
Would it be a great undertaking, or even a small one, to make the comparison trigger either a mouse button selection, or a keyboard stroke? I realize you have many more important things to look into and that this won't have a high priority. Still, it would allow greater flexibility in viewing these excellent records and I think may provide some deeper understanding.
Thanks,
Bud
May I ask a favor? I am attempting to look at your CSD plots with a typical windows magnifier, one that only tracks mouse pointer position. I cannot see more than a small slice of the graphs, as I roll the mouse pointer off and on.
Would it be a great undertaking, or even a small one, to make the comparison trigger either a mouse button selection, or a keyboard stroke? I realize you have many more important things to look into and that this won't have a high priority. Still, it would allow greater flexibility in viewing these excellent records and I think may provide some deeper understanding.
Thanks,
Bud
planet10 said:
This is part of the problem, misunderstanding some of the phenomena involved. Baffle step is just part of diffraction. It's all a consequence of the same, continuous event. The term step is used to focus on one aspect of it because of the change in the front hemisphere response for a driver generating frequencies that fall into and below the "step" area, since in an anechoic environment those frequencies will eventually be 6db down from the nominal 2pi (front hemisphere) level.
Get the free software "The Edge" and/or the Baffle Diffraction Simulator. They show the entirety of one phenomenon, diffraction at a baffle edge.
You are correct with regard to any obtrusion on the surface such a screws. They have both reflection and diffraction, two separate phenomena (edit) as I've thought of it, but in essence probably only one, an alteration of the wave movement away from a straight line. I've measured it, but it is only significant when very close to a tweeter and only at the highest frequencies.
Reflections will show a positive-going impulse in relation to a positive impulse applied to a driver. Examples easily seen are floor reflections. Diffraction will show a negative-going impulse. This is because at the baffle edge, the acoustic impedance drops dramatically, allowing the energy to move towards the rear of the baffle. This essentially "sucks out" some of the energy, so-to-speak, directing it to the rear. It is 180 degrees out-of-phase with the front-side outward going positive impulse.
Of more significance than most obstructions such as screws is the diffraction of a driver on the same baffle as a tweeter, especially larger mid-woofers that my be very close to a tweeter.
Dave
john k... said:
I might be interested if I could understand your argument. So, tiny disruptions on a surface (Enable) will have a greater effect on measurements at a 1000x scale, than measurements capable of resolution at an equal scale? I'll remember to pull out a ruler next time I need to measure to 0.001".
http://www.openchannelsoftware.com/projects/RWGSCAT-CWGSCAT
http://www.openchannelsoftware.com/projects/FREDOM
http://www.openchannelsoftware.com/projects/PMARC_12
http://www.openchannelsoftware.com/projects/RIPPLE
http://www.openchannelsoftware.com/projects/STARS
http://www.openchannelsoftware.com/projects/VPI
http://www.openchannelsoftware.com/projects/FREDOM
http://www.openchannelsoftware.com/projects/PMARC_12
http://www.openchannelsoftware.com/projects/RIPPLE
http://www.openchannelsoftware.com/projects/STARS
http://www.openchannelsoftware.com/projects/VPI
Regardless of the posts the proof is in the pudding. A blind listening test using a stock driver vs an enabled one should determine if a sonic advantage favors a tweaked driver. Otherwise, i am done with looking at all the charts and listening to all the arguments. It does not matter if Moretite also changes the response of the driver - it may make it sound worse? A blob of clay on the dustcap will alter the response too... as would a great big X of silicone across the driver. The enable tweak is meant to improve the sound of the drivers it is applied to. It makes sense to listen to the drivers before passing judgment.
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