john k... said:
I did take a lot of nonlinear acoustics theory in school because it is of paramount importance underwater. And yes a wavefront does steepen as it propagates, but not at an excessively high rate in air (unlike underwater - water being 1000 times less linear than air). And you are right that the Beranek work is old enough so as to be misleading if not downright incorrect. The distortion does not increase linearly with frequency, but then again, the statement is somewhat ambiguous so I am not sure what is really meant.
The facts of nonlinearity in air are these. In a waveguide that falres rapidly - as the OS does - the distortion is generated in only the first inch or so - not much time for these nonlinearities to grow. But the important point is that the nonlinearity is very low order, which, acording to our results and anyone else who has studied the problem, are virtually inaudible. My bet is on there not being any audible nonlinear distortion in a well designed waveguide well up into the sound levels at which the driver will fail. There are serious problems with diffraction in waveguides and these do grow with SPL level so that waveguides are not without their problems, but this is NOT due to the nonlinearity of the air. I believe that Alex Voishvillo (JBL Pro) is now also of this same opinion.
Hi, a lot of theorie´s in all this post´s! And it take a lot of time to read, the most of it...
I add a little more!
I wouldn´t use speaker that are bigger than 8" All this "pro" stuff has high efficient, but the cones are to heavy and to slow for high quality listen!
Also, you can built a fullrange OB without crossover and without filter! You have much more directly information and you are nearer to the original.
My OB is standing in a small room, 2 meter from the back wall and 2 meter to hear position. By this long way; the reflexion from the back wall isn´t so much importend!!!
I show my OB here in the fullrange forum: http://www.diyaudio.com/forums/showthread.php?threadid=103043
Have a nice time and good luck to your OB-Projekt, Hatti
I add a little more!
I wouldn´t use speaker that are bigger than 8" All this "pro" stuff has high efficient, but the cones are to heavy and to slow for high quality listen!
Also, you can built a fullrange OB without crossover and without filter! You have much more directly information and you are nearer to the original.
My OB is standing in a small room, 2 meter from the back wall and 2 meter to hear position. By this long way; the reflexion from the back wall isn´t so much importend!!!
I show my OB here in the fullrange forum: http://www.diyaudio.com/forums/showthread.php?threadid=103043
Have a nice time and good luck to your OB-Projekt, Hatti
gedlee said:
Dr. Geddes, since you're the only one in this forum that's studied nonlinear acoustics in air and water, I have a question for you: just how bad is that "first inch or so" in a waveguide or horn?
At a SPL of 110 dB at one meter in the frequency range of 1 to 5 kHz, what is the magnitude of the purely acoustic distortion? Is it -40 dB relative to the undistorted component, -60 dB, -100 dB or what? Curious about the magnitudes involved, and their spectral appearance.
Is the distortion all even-order harmonics (2nd, 4th, 6th, etc.) or is the harmonic structure more complicated than that? Is is a noiselike modulation, or is it just harmonic components?
Lynn Olson said:
The nonlinearity in air is purely 2nd order (x^2), so it will only generate a second order harmonic (2x). It is purely harmonic distortion, no random modulation, but like all nonlinearities, it will have modulation effects between two sign waves of different frequencies. Unlike the nonlinearity of an amp stage, this nonlinearity acts continuously as the wave propagates. This means that the 2X that was generated early on will have another 2X generated to create a 4X, then an 8X, etc. So the longer the wave propagates at intense SPLs the greater the effective "order" will be. For a short propagtion of a resonably intense wave, there will only be a second harmonic of any magnitude.
The levels of these harmonics is highly dependent on specifics, but an intense sound wave generating about 100 dB at say six meters, in a OS waveguide, which has a fairly rapid flare, will have a 2nd harmonic about 20 dB down. At about 90 dB it will fall dramatically to about 40 dB down. The higher harmonics will fall faster than the lower ones.
In essence this kind of distortion is a sort of brick wall limitation. It will become very objectionable very quickly when the sound becomes very intense, but its effect will be negligable below that point. I'd say that to my ear, in a Summa, this point is reached at about 110 dB SPL in my room. Above that level and I can't take the sound anymore. Now this could be caused by many many things however, but at about 110 dB SPL, the system crashes. Unlike many systems, which gradualy start sounding worse, the Summas seem to hold up very well until they crash, and all of a sudden the sound is bad. This is not a typical effect in my experience.
If you want more than 110 dB SPL, then you need to get a pair
(And in a few years some hearing aids!!)
Dr. Geddes, the answer is much appreciated. This gives me a good idea what to look for when I start measuring.
Hmm ... looking forward to getting SoundEasy running on my PC, and examining the spectral characteristics of a compression driver on a waveguide. The information about an abrupt "brick wall" is especially interesting - it's at a very high level, but it's there. I would guess on a generic PA-grade phasing plug the onset of the "brick wall" could easily be at a lower level.
I'm beginning to wonder if there really is some kind of modulation noise with compression drivers - a measuring system with a 100~120 dB dynamic range should reveal if it's hiding in the shadows. This kind of program modulated "noise" is troublesome in digital systems where the jitter gets into the DAC convertor chip, which typically has little resistance to this kind of error, and translates the time distortion into amplitude distortion. (When sample widths at the encoding and decoding ends are different, even by very small amounts, amplitude distortion results, and can measured on high-dynamic range measuring system. The spectral artifacts frequently exhibit close-in 100 or 120 Hz sidebands from PS-induced jitter.)
At the Physical Training clinic today, I used a cane for the first time, and got about 100 feet before the onset of fatigue. Also some stair-training on low stairs, getting me ready for going up and down stairs without going on my butt and using my arms to lift myself up and down. Maybe by late summer I can finally get some gear downstairs in the basement and start making some measurements on the PC with the ACO Pacific 1/2" microphone. These are things I want to see for myself.
Gary Pimm and John Atwood have shown me how to make close-in spectral measurements with 100~120 dB on-screen dynamic range, reach into the clutter, and look for spectral components lurking in the noise. Fairly standard stuff for amplifier design, where 100/120 Hz IM sidebands can appear in all kinds of places.
Hmm ... looking forward to getting SoundEasy running on my PC, and examining the spectral characteristics of a compression driver on a waveguide. The information about an abrupt "brick wall" is especially interesting - it's at a very high level, but it's there. I would guess on a generic PA-grade phasing plug the onset of the "brick wall" could easily be at a lower level.
I'm beginning to wonder if there really is some kind of modulation noise with compression drivers - a measuring system with a 100~120 dB dynamic range should reveal if it's hiding in the shadows. This kind of program modulated "noise" is troublesome in digital systems where the jitter gets into the DAC convertor chip, which typically has little resistance to this kind of error, and translates the time distortion into amplitude distortion. (When sample widths at the encoding and decoding ends are different, even by very small amounts, amplitude distortion results, and can measured on high-dynamic range measuring system. The spectral artifacts frequently exhibit close-in 100 or 120 Hz sidebands from PS-induced jitter.)
At the Physical Training clinic today, I used a cane for the first time, and got about 100 feet before the onset of fatigue. Also some stair-training on low stairs, getting me ready for going up and down stairs without going on my butt and using my arms to lift myself up and down. Maybe by late summer I can finally get some gear downstairs in the basement and start making some measurements on the PC with the ACO Pacific 1/2" microphone. These are things I want to see for myself.
Gary Pimm and John Atwood have shown me how to make close-in spectral measurements with 100~120 dB on-screen dynamic range, reach into the clutter, and look for spectral components lurking in the noise. Fairly standard stuff for amplifier design, where 100/120 Hz IM sidebands can appear in all kinds of places.
Lynn Olson said:
This effect was hypothesized when I was working with B&C. We set up a subjective test to scale its importance - the results were published in JAES about 18 months ago.
We found that in about 30 blind listeners no one could detect nonlinear "distortions" in a compression driver at any level up to the thermal limit of the devices. We tested across three manufacturers. In essence nonlinear distortions were not a factor in audiblity, however there were statistically significant audible frequency response differences.
At that time, I had a patent application on a way to reduce turbulence in a compression driver thus reducing random flow modulation effects. After the results of this study I abandoned this application - what would be the point of a patent solving a non-problem?
Hi
Earl, what you describe here is quite an unique behaviour I wasn't aware of as yet. Thanks for pointing out so clearly.
Interesting that in that blind listening tests no one was able to discover. It would mean that mankind DIDN't evolve kind of crosscorrelation detector for that to gain additional information about the surrounding where the sound was originating from.
Not that bad, just another weird theory to bury
110dB ( A-weighted LEQ ) at 6m is quite common at even small pop concerts not necessarily driven by huge multiple driver line arrays but rather by a single (or double) driver stack.
Considering that OS wave guides are MUCH more shallow than the usually used horns, I would expect MUCH more 2nd HD than the 10% you measured on OS's and subsequently also considerable amounts of higher order HD, am I right in this?
Greetings
Michael
Earl, what you describe here is quite an unique behaviour I wasn't aware of as yet. Thanks for pointing out so clearly.
Interesting that in that blind listening tests no one was able to discover. It would mean that mankind DIDN't evolve kind of crosscorrelation detector for that to gain additional information about the surrounding where the sound was originating from.
Not that bad, just another weird theory to bury
In essence this kind of distortion is a sort of brick wall limitation....... If you want more than 110 dB SPL, then you need to get a pair
110dB ( A-weighted LEQ ) at 6m is quite common at even small pop concerts not necessarily driven by huge multiple driver line arrays but rather by a single (or double) driver stack.
Considering that OS wave guides are MUCH more shallow than the usually used horns, I would expect MUCH more 2nd HD than the 10% you measured on OS's and subsequently also considerable amounts of higher order HD, am I right in this?
Greetings
Michael
mige0 said:
The reason that we can't hear low orders of distortion is that the ear masks these things. In nature there is no transmission path that would generate these nonlinear effects and so our hearing would have no need to accomodate them.
110 dB is not too common in a small room such as we are talking about here.
Actually the OS situation is the opposite of wht you are saying. OS waveguides flare rather rapidly minimizing the sound level and the nonlinearity very quickly. Virtually all of the nonlinearity is in the compression driver as these flare very slowly. But we showed that this distortion was not significant, so the distortion added by the OS waveguide would not be significant either.
Nonlinear distortion in these devices (drivers and waveguides) is simply not a factor at any but the very highest SPLs. Far more important are the diffractions in the waveguides (and drivers), but certainly in typical horns with intentional diffraction for directivity control. The diffraction effects are also level dependent and more than likely dominate the sound perception in 90% of the devices out there today - maybe even 100%, even at very high SPLs.
Hi
Earl, ok, I reread your posting and saw that I got confused. You already did that listening tests with HORNS.
This listening tests didn't focus on even order HD but rather on IM ( so I don't have to bury my theory ) ?
I agree 100%
But Lynn is going to redefine the range of "common listening levels in small rooms"!
But seriously – I was actually asking about your findings here in the context of increased SPL's found at concerts.
My "visualisation" of diffraction in horns ( and wave guides ) is that there is continuous diffraction as long as the wave front follows the horn curve ( = low "reflection" due to the creation of low level second sources along the boundary ) and kind of abrupt diffraction at the mouth.
I would expect the mouth to behave like lets say the "water surface" when seen from underneath at diving = lots of reflection.
Could you give a understandable pin point description about the HOM issue please ?
Greetings
Michael
Earl, ok, I reread your posting and saw that I got confused. You already did that listening tests with HORNS.
This listening tests didn't focus on even order HD but rather on IM ( so I don't have to bury my theory ) ?
I agree 100%
But Lynn is going to redefine the range of "common listening levels in small rooms"!
But seriously – I was actually asking about your findings here in the context of increased SPL's found at concerts.
My "visualisation" of diffraction in horns ( and wave guides ) is that there is continuous diffraction as long as the wave front follows the horn curve ( = low "reflection" due to the creation of low level second sources along the boundary ) and kind of abrupt diffraction at the mouth.
I would expect the mouth to behave like lets say the "water surface" when seen from underneath at diving = lots of reflection.
Could you give a understandable pin point description about the HOM issue please ?
Greetings
Michael
Earl,
as an attempt to summarize, to my understanding:
There are two mechanisms leading to distortion perception:
a- nonlinearity of compressed air at very high SPL's. Usually not dominant in audibility;
b- internal WG or horn reflections, including HOMs, which are not minimum phase and are perceived as though they were nonlinear distortions. Usually significant audibility in conventional WG / horn designs.
Ad a, this also applies to the internal compression chamber of a compression driver, but the distances are usually too short to generate significant nonlinearities.
Ad b, these effects are hard to measure, though they might be viewable on a CSD to some extent. The generation process might include the compression chamber, but is usually confined to the proximate throat area of a WG. Mouth reflections may occur in addition to that, but are of a so far not well determined significance. Minimization of all these effects through OS profile, rapid flare rate, and foam.
Just trying to get a handle on the issues.
as an attempt to summarize, to my understanding:
There are two mechanisms leading to distortion perception:
a- nonlinearity of compressed air at very high SPL's. Usually not dominant in audibility;
b- internal WG or horn reflections, including HOMs, which are not minimum phase and are perceived as though they were nonlinear distortions. Usually significant audibility in conventional WG / horn designs.
Ad a, this also applies to the internal compression chamber of a compression driver, but the distances are usually too short to generate significant nonlinearities.
Ad b, these effects are hard to measure, though they might be viewable on a CSD to some extent. The generation process might include the compression chamber, but is usually confined to the proximate throat area of a WG. Mouth reflections may occur in addition to that, but are of a so far not well determined significance. Minimization of all these effects through OS profile, rapid flare rate, and foam.
Just trying to get a handle on the issues.
mige0 said:
But Lynn is going to redefine the range of "common listening levels in small rooms"!
Greetings
Michael
Oh, I think the multiway active-crossover all-horn enthusiasts are already there - Magnetar, Romy the Cat, Bruce Edgar, many of the posters on the Audio Asylum High-Efficiency forum, Klipschorn and Altec fans, etc. etc. These guys are king of the high-SPL hill.
The hard part is approaching this kind of peak SPL while retaining a clean time signature with good decay characteristics - getting away from high-diffraction PA and constant-directivity technology, and moving forward towards modern approaches to driver and waveguide design. That's not off-the-shelf technology.
Dr. Geddes is one of the first - in many decades - to take time/decay response of waveguides seriously. In time, more will follow in Earl's footsteps, although I expect religious fistfights to break out between the Altec/JBL/WE anachronophiles and proponents of the new-method approaches.
I'm just sitting on the sidelines of this - I'm not in any position to design waveguides or commission OEM-special compression drivers.
mige0 said:
In a device with a smooth wall your "vision" is correct, the diffraction is created continuously as the wave travels. If there is an abrupt change in the wall slope then there will be a larger diffraction at that point. The contour which generates the least diffraction as the wave travels - i.e. has the most gradual change from flat to curved wavefront is the OS. Thats why it works so well - it is the surface of minimum slope change.
The HOM are the diffracted waves, which must now reflect off of the walls. They must travel a longer distance than the main wave, thus they are spread out in time. This, as it turns out, is highly audible effect which grows substantially with SPL level. Hence, a waveguide might sound fine at lower levels, but become objectionable at higher levels. The more HOM the sooner this happens.
MBK said:
Pretty much right on for a simple explanation. Two things happen at the mouth however, reflection and diffraction. The reflection part causes a frequency response aberation that causes coloration, the diffraction is ore like distortion, being SPL dependent. Neither is a good things and handling the mouth properly is something seldom done right in the marketplace.
Hi Lynn, Earl, all
Sorry for popping in so late in the thread but I would offer a few comments as well.
For one, little (good) has been said here about the conical horn, yet, its walls have the least change (none) one can have, it is a segment of spherical radiation space bounded by a physical boundaries and if driven at an acoustically small point, radiates a section of spherical wave front, with the effectively the same arc, regardless of frequency, down to where its mouth size losses control.
The nonlinear (shocking up) distortion in air is also less in a conical horn as its initial expansion is very rapid. This problem is sort of a “wavelengths traveled times the SPL” issue so a Hyperbolic would be worse than exponential of the same mouth and low cutoff etc.
Not all compression drivers are created equal or create the same problems.
For example, in subjective listening, on two identical 50 degree conical horns, both made “flat”, both having similar responses and acoustic phase, still sounded very different.
Of two of the best modern compression drivers available, The B&C DE250 sounded very much like a horn compared next to the BMS 4550 which sounded very “open” and airy.
The possibly interesting part was the BMS driver has a different internal approach, which so far as the horn is concerned, starts as an acoustically small conical horn inside the driver. There are no phase plug summation slots, (which by path length, generally would appear to produce a converging, not diverging wave front one would want in a source that was large enough to already exhibiting some directivity at the throat).
As a result, with an acoustically small origin and small acoustic size where the break point in angles was, there was much less “origin” garbage from the BMS style phase plug arrangement which produces a diverging wave front from inside the driver.
Yes, mouth diffraction is an issue with horns, not popular but for any given shape, the larger you make it, the less of a problem it is because the SPL is always falling as you move from the origin.
One practical down side of conical or other constant directivity devices is that they reveal the drivers true power response which makes hifi folks uneasy, a truth they don’t want to see or have to deal with as “things are suppose to be flat”.
A related down side is that the conical horn (for a given size) exhibits somewhat less low frequency loading on the driver due to its rapid initial expansion also.
There are solutions to most things, practical or not is another issue.
I have been working with a company on a new phase plug geometry for dome compression drivers, so far, that seems to work too.
Anyway, some thoughts on a Saturday morning.
Best,
Tom Danley
Sorry for popping in so late in the thread but I would offer a few comments as well.
For one, little (good) has been said here about the conical horn, yet, its walls have the least change (none) one can have, it is a segment of spherical radiation space bounded by a physical boundaries and if driven at an acoustically small point, radiates a section of spherical wave front, with the effectively the same arc, regardless of frequency, down to where its mouth size losses control.
The nonlinear (shocking up) distortion in air is also less in a conical horn as its initial expansion is very rapid. This problem is sort of a “wavelengths traveled times the SPL” issue so a Hyperbolic would be worse than exponential of the same mouth and low cutoff etc.
Not all compression drivers are created equal or create the same problems.
For example, in subjective listening, on two identical 50 degree conical horns, both made “flat”, both having similar responses and acoustic phase, still sounded very different.
Of two of the best modern compression drivers available, The B&C DE250 sounded very much like a horn compared next to the BMS 4550 which sounded very “open” and airy.
The possibly interesting part was the BMS driver has a different internal approach, which so far as the horn is concerned, starts as an acoustically small conical horn inside the driver. There are no phase plug summation slots, (which by path length, generally would appear to produce a converging, not diverging wave front one would want in a source that was large enough to already exhibiting some directivity at the throat).
As a result, with an acoustically small origin and small acoustic size where the break point in angles was, there was much less “origin” garbage from the BMS style phase plug arrangement which produces a diverging wave front from inside the driver.
Yes, mouth diffraction is an issue with horns, not popular but for any given shape, the larger you make it, the less of a problem it is because the SPL is always falling as you move from the origin.
One practical down side of conical or other constant directivity devices is that they reveal the drivers true power response which makes hifi folks uneasy, a truth they don’t want to see or have to deal with as “things are suppose to be flat”.
A related down side is that the conical horn (for a given size) exhibits somewhat less low frequency loading on the driver due to its rapid initial expansion also.
There are solutions to most things, practical or not is another issue.
I have been working with a company on a new phase plug geometry for dome compression drivers, so far, that seems to work too.
Anyway, some thoughts on a Saturday morning.
Best,
Tom Danley
Tom Danley said:
Hi Tom
I posted some comments on conical horns before, but perhaps you did not see them. I do not recommend conical horn usage because it requires a wavefront at the throat which is pretty much impossible to obtain. The mismatch of wavefront required and wavefront submitted will cause a great deal of HOM in the conical horn.
If by "if driven at an acoustically small point" you mean at frequencies below where the throat is 1/2 wavelength, then I might agree with you (if the horn is long) - in this case the HOM generated by the throat will not propagate. But I use waveguides well beyond this frequency and the shape of the wavefront at the throat is critical to the wavefront propagation in the device. No source that I know of can create a well defined spherical wave across a flat aperature. But a well designed compression driver CAN create a flat wavefront in an circular aperature, which is ideal for use on a OS waveguide.
As to your listening tests, the driver and horn make a combination. The DE250 works very well on my waveguides. It may not work very well on some other horn however.
Hi Earl
Sorry I did not see your earlier reply, I don’t have a lot of time to cruise lately.
This seems to me to be an issue of “acoustic size”, with the Unity and Synergy horns, I had found that one could drive the conical horn at a point smaller than 1 / 4 wavelength across, without provoking the more complex radiation issues.
The issue would then seem to be one of “how high can you drive a given conical horn or other horn with a stock driver?”
Even a one inch exit driver, is so large acoustically at 20KHz, that its aperture dimension without a horn can confine the radiation angle.
Internally drivers aren’t all the same, most use annular slots to combine the various regions on the dome, to concentric rings at the beginning of the exit horn.
If you assume the speed of sound is fixed and you trace the path lengths, it seems to me that most drivers would tend to produce a converging wave front at the summation point, not a plane wave.
Both of these would seem non-optimal for a diverging horn.
I guess I figured that since the compression driver internal geometry was already a governing factor in its radiation pattern “up high” and most all horns end with a diverging wavefront that it made sense to re-arrange the phase plug paths to make it produce a diverging wavefront since the horn begins well within the driver itself.
The BMS driver is a different geometry entirely; it is a ring radiator and only has one (not several different) acoustic path from the radiator to the summation point and that is a smaller dimension than on the dome drivers. From that small summation point, there is a conical horn which expands out to the one inch exit.
Here, if one drew a picture of the horn and driver air path, one could see that the conical shape extends internally to a small point at the apex.
I didn’t say the DE250 wasn’t good, not at all, it was the best sounding hf driver I had found and in a previous audition, its ancestor the DE-25 was the best available then.
Not only that but they are also very rugged unlike some of the old style “Kleenex in the rain” toughness of some hf drivers.
It’s just that when we did it side by side, the difference was clear.
Yes, that listening test only applies to “that” horn but I believe the BMS geometry is partly “why” as it has no mechanism or structure to produce anything but a diverging wave front when its dimensions are acoustically large enough to have control over its radiation angle.
Best,
Tom
Are you back in the states now?
Sorry I did not see your earlier reply, I don’t have a lot of time to cruise lately.
This seems to me to be an issue of “acoustic size”, with the Unity and Synergy horns, I had found that one could drive the conical horn at a point smaller than 1 / 4 wavelength across, without provoking the more complex radiation issues.
The issue would then seem to be one of “how high can you drive a given conical horn or other horn with a stock driver?”
Even a one inch exit driver, is so large acoustically at 20KHz, that its aperture dimension without a horn can confine the radiation angle.
Internally drivers aren’t all the same, most use annular slots to combine the various regions on the dome, to concentric rings at the beginning of the exit horn.
If you assume the speed of sound is fixed and you trace the path lengths, it seems to me that most drivers would tend to produce a converging wave front at the summation point, not a plane wave.
Both of these would seem non-optimal for a diverging horn.
I guess I figured that since the compression driver internal geometry was already a governing factor in its radiation pattern “up high” and most all horns end with a diverging wavefront that it made sense to re-arrange the phase plug paths to make it produce a diverging wavefront since the horn begins well within the driver itself.
The BMS driver is a different geometry entirely; it is a ring radiator and only has one (not several different) acoustic path from the radiator to the summation point and that is a smaller dimension than on the dome drivers. From that small summation point, there is a conical horn which expands out to the one inch exit.
Here, if one drew a picture of the horn and driver air path, one could see that the conical shape extends internally to a small point at the apex.
I didn’t say the DE250 wasn’t good, not at all, it was the best sounding hf driver I had found and in a previous audition, its ancestor the DE-25 was the best available then.
Not only that but they are also very rugged unlike some of the old style “Kleenex in the rain” toughness of some hf drivers.
It’s just that when we did it side by side, the difference was clear.
Yes, that listening test only applies to “that” horn but I believe the BMS geometry is partly “why” as it has no mechanism or structure to produce anything but a diverging wave front when its dimensions are acoustically large enough to have control over its radiation angle.
Best,
Tom
Are you back in the states now?
Hi Tom, welcome to the on-going discussion! I've been absent partly because of transitioning to my new computer, which is mostly done now. Also have been making progress on walking, I can walk across the living room unaided (but need to rest after doing that) and can go about 100 feet using a cane.
The trick with the cane is getting started, slowing down, and finding a rest-point when fatigue and wobbly-balance approach. I've discovered strength and balance are inseparable - when balance suddenly gets wobbly, that's actually a signal that strength is fading, and to find a rest-point ASAP. Still, making progress, and staying closely attuned to physical limits on a moment-by-moment basis. Nothing like this experience to make you keenly aware of how suddenly your life can change, and the day-by-day, moment-by-moment awareness of physicality - location in space, possible resting places, planning the dynamics of rising from a chair and navigating to another point, etc. Like learning new dance steps but not as much fun. Then again, being able to move more freely is pretty wonderful when you've been denied it for six months.
Tom, the reason I've kind of shied away from conical horns is the "megaphone coloration" - maybe I'm missing something, but what is the distinction between a conical horn and a hand-held megaphone? To my untrained eye, they look the same - but at the same time I've heard lots of horns with many different profiles that had lots of "megaphone coloration", so I guess things are not as they appear.
Still, I'm curious about how diffraction at the edge of the horn mouth is addressed. Diffraction is troublesome enough at the edge of a conventional direct-radiation cabinet - I've had to use fairly large radii to get it to acceptable levels - and it would seem to be worse when the exiting wavefront sees a much sharper boundary at the edge of the horn mouth. What techniques do you use to alleviate this coloration?
The trick with the cane is getting started, slowing down, and finding a rest-point when fatigue and wobbly-balance approach. I've discovered strength and balance are inseparable - when balance suddenly gets wobbly, that's actually a signal that strength is fading, and to find a rest-point ASAP. Still, making progress, and staying closely attuned to physical limits on a moment-by-moment basis. Nothing like this experience to make you keenly aware of how suddenly your life can change, and the day-by-day, moment-by-moment awareness of physicality - location in space, possible resting places, planning the dynamics of rising from a chair and navigating to another point, etc. Like learning new dance steps but not as much fun. Then again, being able to move more freely is pretty wonderful when you've been denied it for six months.
Tom, the reason I've kind of shied away from conical horns is the "megaphone coloration" - maybe I'm missing something, but what is the distinction between a conical horn and a hand-held megaphone? To my untrained eye, they look the same - but at the same time I've heard lots of horns with many different profiles that had lots of "megaphone coloration", so I guess things are not as they appear.
Still, I'm curious about how diffraction at the edge of the horn mouth is addressed. Diffraction is troublesome enough at the edge of a conventional direct-radiation cabinet - I've had to use fairly large radii to get it to acceptable levels - and it would seem to be worse when the exiting wavefront sees a much sharper boundary at the edge of the horn mouth. What techniques do you use to alleviate this coloration?
Lynn,
Glad to hear your recovery is well underway. These things take time, be sure to drink alot of water, and Ca supplementation is always a good thing for >50. Look into Grapeseed extract, as well. From a clinical standpoint, almost too good to be true, but is is true. Been on it for 13 years, and if I run out, my body is telling me to get more, after about five days... good luck...
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I really want to try the Tone Tubby Alnico 12's as the wideband driver in OB, here, Alnico, hempcone, to me, what can be better? I would like to know what quickie treble element you personally would order ~first, to try with that driver. I do notice the Fostex T90a alnico tweeter horn, at least according to published spex would easily be capped in @5KHz, this is the one I have my eye on. Suggestions for quickie implementation are appreciated. I have a pair of Eminence Delta 15LF left over from the DarkStar thang, and will eventually try those as bass drivers. Thanks for your collective opinions here. HempTone Alnico 12's, here we come....
Glad to hear your recovery is well underway. These things take time, be sure to drink alot of water, and Ca supplementation is always a good thing for >50. Look into Grapeseed extract, as well. From a clinical standpoint, almost too good to be true, but is is true. Been on it for 13 years, and if I run out, my body is telling me to get more, after about five days... good luck...
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I really want to try the Tone Tubby Alnico 12's as the wideband driver in OB, here, Alnico, hempcone, to me, what can be better? I would like to know what quickie treble element you personally would order ~first, to try with that driver. I do notice the Fostex T90a alnico tweeter horn, at least according to published spex would easily be capped in @5KHz, this is the one I have my eye on. Suggestions for quickie implementation are appreciated. I have a pair of Eminence Delta 15LF left over from the DarkStar thang, and will eventually try those as bass drivers. Thanks for your collective opinions here. HempTone Alnico 12's, here we come....