Norris Wilson said:
Hi all, I've been wrangling with Apple about getting them to kick out the replacement computer. Since I have a visit to the Physical Trainer on July 5th, what I don't want to happen is have the long-awaited replacement arrive when I'm at Kaiser Hospital - seeing a little note from FedEx attached to the front door would create a screech that BudP would hear in Seattle!
The diffraction thread has certainly picked up an astounding momentum. The use of sims instead of measurements speaks volumes - I'm looking forward to finally using both MLSSA and SoundEasy to answer this math-heavy guesswork with real data. Let's see, at last count, we have:
1) No diffraction on a fully symmetric dipole
2) Twice as much as a monopole
3) Lossy-mesh dissipation to spread out the time artifacts
4) Dimples as on a golf ball
5) Painted-on EnABL pattern
6) Fur! Furry cones!! Furry patented cones!!!
And that's just for starters. Sheesh.
I've been poking around the Meyer Sound Labs site. Most interesting. In addition to a good discussion that de-mystifies compression drivers, I found their MTS-4A system very interesting. It uses a cascade of 12, 15, and 18-inch drivers, all operating together at the lowest frequencies. Hmm, that seems familiar, guess John Meyer got there first.
I still have serious reservations about the idea I had a while back using a pair of 8-inch drivers combined with the new RAAL ribbon. It's one thing to tolerate beaming at the highest frequencies, it's quite another in the midband - and that's what stacked 8" drivers imply. All of my instincts (yes, ole woo-woo the wizard here) tell me to stay with a single 12" driver, and do my level best to get it to combine with horn+compression driver or the new RAAL ribbon.
The recent GedLee discussion has made me aware of just how serious horn coloration really is. I guess I'll just have to shell out the money and measure both CD/horn and RAAL ribbon drivers. None of this hokey 1/3 octave smoothing, though.
Now that I've been tipped off what to look for, I am going to very carefully examine the time vs off-axis angle, in small increments. I'm going to set MLSSA or another system on fast refresh, move the microphone slowly, and look for artifacts that move around in the time domain. That would be a direct consequence of a rough wavefront emerging from the horn mouth - and is usually concealed by conversion to freq domain and 1/3 octave smoothing. These artifacts are in the time domain, and that's the place to look for them.
I'm not looking for 60, 90, or 120 degree nominal beamwidth, but for fine-grained artifacts only a few degrees wide. I've seen this kind of stuff before, when a hard dustcap radiates pencil-beam artifacts that are very narrow, or when a cone is deep into the breakup region. I take narrow-beam artifacts very seriously - in a cone driver, it's a cause for rejecting it from consideration, no matter how steep the crossover filter is going to be.
Continuing the thread, the decision between the CD/horn and the RAAL ribbon will come down to personal-preference sonics and measurements. As mentioned earlier, I'm not looking for the usual Toole industry-standard criteria, but an absence of certain flaws - narrowband artifacts in the time and spatial domains. I don't like these things, since they are almost impossible to equalize, and I find them audible and difficult (for me) to ignore.
I am not in the steep-crossover-to-get-rid-of-it school; I tried that a long time ago, in my first speaker, and didn't much care for the results. Notch filtering is something I use with caution, for two reasons.
If the peak is minimum-phase, OK, then the notch filter corrects the time domain as well. This is easily checked with the impulse response. More significant, the peak may be directional. This is a big deal, since the compensated off-axis response is then grossly degraded, in both frequency and time domains. And if the peak is non-minimum phase, EQ is a bad idea anyway, since the driver is trying to tell you it's breaking up, and shouldn't be used in that frequency region (or at all).
Although the big 18 or 21-inch driver sitting close to the floor is appealing from the baffle-width and simplicity viewpoint, ragged response from 200 Hz on up is a huge downside. In the prosound world, they are almost always used with active 24 dB/octave filters, and that's something I'm trying to avoid. In my first speaker, the Audionics TLM-200, the KEF B139 had a huge 6 dB peak at 1.5 kHz. Even with a lowpass crossover at 200 Hz, it took a 3rd-order filter to shove that peak out of audibility - it was still audible as a subtle but annoying midrange coloration, even though the ripple on the overall response curve was almost invisible.
I don't like peaky drivers, basically. Minor slopes and ripples are one thing, easy to correct, but peaks are another, even if they're some distance out of the intended frequency range.
I am not in the steep-crossover-to-get-rid-of-it school; I tried that a long time ago, in my first speaker, and didn't much care for the results. Notch filtering is something I use with caution, for two reasons.
If the peak is minimum-phase, OK, then the notch filter corrects the time domain as well. This is easily checked with the impulse response. More significant, the peak may be directional. This is a big deal, since the compensated off-axis response is then grossly degraded, in both frequency and time domains. And if the peak is non-minimum phase, EQ is a bad idea anyway, since the driver is trying to tell you it's breaking up, and shouldn't be used in that frequency region (or at all).
Although the big 18 or 21-inch driver sitting close to the floor is appealing from the baffle-width and simplicity viewpoint, ragged response from 200 Hz on up is a huge downside. In the prosound world, they are almost always used with active 24 dB/octave filters, and that's something I'm trying to avoid. In my first speaker, the Audionics TLM-200, the KEF B139 had a huge 6 dB peak at 1.5 kHz. Even with a lowpass crossover at 200 Hz, it took a 3rd-order filter to shove that peak out of audibility - it was still audible as a subtle but annoying midrange coloration, even though the ripple on the overall response curve was almost invisible.
I don't like peaky drivers, basically. Minor slopes and ripples are one thing, easy to correct, but peaks are another, even if they're some distance out of the intended frequency range.
Lynn Olson said:
The best/most versatile display I've seen for "dialing down" time domain performance is this one:
http://www.dr-jordan-design.com/view3D.htm
http://www.dr-jordan-design.com/Winaudiomls.htm
(..of course its not cheap, its windows only, and you already have a real-time system.)
Continuing the design thread a little further, the least-aggravating path would be a smooth HF system (to be determined first) and a quartet of identical 12" drivers, in the delta pattern shown many posts ago.
A real time-waster in any speaker design is trying to make not-quite-good-enough drivers perform just a little bit better. This can take weeks or months of fruitless measuring, crossover twiddling, listening, over and over again. Better to select benign, well-behaved drivers in the first place. No serious peaks, no regions of high distortion, no directional breakups - in other words, sounds pretty decent without any EQ at all.
A real time-waster in any speaker design is trying to make not-quite-good-enough drivers perform just a little bit better. This can take weeks or months of fruitless measuring, crossover twiddling, listening, over and over again. Better to select benign, well-behaved drivers in the first place. No serious peaks, no regions of high distortion, no directional breakups - in other words, sounds pretty decent without any EQ at all.
ScottG said:
Already have a dual-core Athlon PC with M-Audio 192/24 soundcard in a compact and quiet HTPC enclosure bought for just this purpose. Even though I've been a Mac user since my first Mac Plus, I'm OK with using PCs for scientific purposes - they're much stronger in that area.
I just don't let them run around and play freely on the Internet, where they can get in bad neighborhoods - although I use Ad-Aware SE and Avast! just to be sure. By keeping most of the software clutter off WinXP SP2 and its Registry file, it runs pretty well, with no slowdown issues to contend with.
By using different machines for different purposes, maintenance issues are simplified. I've been measuring on PCs and transferring the pretty graphics over to Macs since my days at Tektronix in the late Eighties, where we did the same thing with Unix hosts and Macs for documentation. (I was usually the network guy that configured the TCP/IP software for the tech-writing group.)
Thanks for the links, will look into the software, which looks interesting.
Hi Lynn,
Indeed the fur did fly while you were fighting the good fight. In all of the driver posting I have looked at no one seems to have mentioned Gary Pimm's favorites, the Eminence Beta 8, so here is a link. Scroll down to the Acrobat file for specs.
http://www.partsexpress.com/pe/pshowdetl.cfm?&PartNumber=290-404
If any pro sound driver is going to match Raal's ribbons this looks like a good candidate.
Bud
Indeed the fur did fly while you were fighting the good fight. In all of the driver posting I have looked at no one seems to have mentioned Gary Pimm's favorites, the Eminence Beta 8, so here is a link. Scroll down to the Acrobat file for specs.
http://www.partsexpress.com/pe/pshowdetl.cfm?&PartNumber=290-404
If any pro sound driver is going to match Raal's ribbons this looks like a good candidate.
Bud
Driver QC
Good news ... Apple has sent the replacement 2.66GHz quad-core machine, the tracking code says it's in Denver already, so it should be here Monday morning. After that I attach the Firewire cable and use Migration Assistant to selectively move parts of the G5 machine to its new Intel environment. At least the file structure is the same, and Rosetta is supposed to emulate the G5 for the older software. Much of the power of the quad Core Duos will disappear into Rosetta, at least until I shell out the bucks for the latest versions of Photoshop and various other applications.
------------
I'm going to be writing a short series on the steps I'm going to be doing as the design gets under way, probably later this summer. The most probable configurations are 1x8" + 3x12", and 4x12". I'll be measuring and auditioning the 18Sound 12NDA520 and 8NMB420 on a large flat baffle, like a door.
After measuring each at different angles, I'll be auditioning a stereo pair and comparing them to the Ariels, which have a smooth response curve that fits into a 5 dB window. Similar low-coloration candidates would be the Celestion SL600's, Quads, BBC monitors, or other speakers with smooth curves. I don't think comparing the drivers to speakers with rougher responses - such as many audiophile speakers or vintage prosound - would reveal very much, except to compare one set of colorations against another.
The full-range auditions will use pink-noise, comparing the 12NDA520 against the Ariel, the 8NMB420 against the Ariel, and the 12NDA520 running in parallel with the 8NMB420 against the Ariel. This should give a general idea where the dominant colorations of the drivers are, and how well they combine with each other. Only after assessing the general character of these drivers will I move on to musical assessment, and even then I'll be using my Denon HT receiver just to see how they sound on average-quality electronics. I don't see any point to using fancy amps when making go-nogo decisions about drivers - the basic character of drivers are pretty audible with nearly any amplifier.
Good news ... Apple has sent the replacement 2.66GHz quad-core machine, the tracking code says it's in Denver already, so it should be here Monday morning. After that I attach the Firewire cable and use Migration Assistant to selectively move parts of the G5 machine to its new Intel environment. At least the file structure is the same, and Rosetta is supposed to emulate the G5 for the older software. Much of the power of the quad Core Duos will disappear into Rosetta, at least until I shell out the bucks for the latest versions of Photoshop and various other applications.
------------
I'm going to be writing a short series on the steps I'm going to be doing as the design gets under way, probably later this summer. The most probable configurations are 1x8" + 3x12", and 4x12". I'll be measuring and auditioning the 18Sound 12NDA520 and 8NMB420 on a large flat baffle, like a door.
After measuring each at different angles, I'll be auditioning a stereo pair and comparing them to the Ariels, which have a smooth response curve that fits into a 5 dB window. Similar low-coloration candidates would be the Celestion SL600's, Quads, BBC monitors, or other speakers with smooth curves. I don't think comparing the drivers to speakers with rougher responses - such as many audiophile speakers or vintage prosound - would reveal very much, except to compare one set of colorations against another.
The full-range auditions will use pink-noise, comparing the 12NDA520 against the Ariel, the 8NMB420 against the Ariel, and the 12NDA520 running in parallel with the 8NMB420 against the Ariel. This should give a general idea where the dominant colorations of the drivers are, and how well they combine with each other. Only after assessing the general character of these drivers will I move on to musical assessment, and even then I'll be using my Denon HT receiver just to see how they sound on average-quality electronics. I don't see any point to using fancy amps when making go-nogo decisions about drivers - the basic character of drivers are pretty audible with nearly any amplifier.
Lynn Olson said:
Nice link, thanks Lynn. Interesting that they say "Not many people make high drivers at this quality level - there's only really TAD and JBL ." Leaving out one of their suppliers- Yamaha! There are a lot of other CD out there, wonder why Meyer didn't like them?
It must be the 4" JBL that sounds so good in the Meyer CQ-1 boxes. Very nice. But not in the CQ-2. Same driver, different horn, different crossover. Sounds rough. Have not yet heard the new Meyer CDs - AFAIK.
OK, back to my fur lined speakers.
The link also lists the conflicting requirements that they need to address which aren't necessarily the same as ours . They do a LOT for durability. Perhaps not quite as important for we HiFi'ers if it happened to compromise the sound. Then again, at the price they would probably ask you would want it to stay together! Anyway, out of curiousity, are they available to individuals? or only in a cabinet?
Interesting that they ended up with aluminum diaphram, plastic suspension, Just like most of the other top rated drivers such as Radian. Circular slots in the phase plug also seems to be the way to go in the high end.... For smaller drivers, all plastic seems to work well too.
Interesting that they ended up with aluminum diaphram, plastic suspension, Just like most of the other top rated drivers such as Radian. Circular slots in the phase plug also seems to be the way to go in the high end.... For smaller drivers, all plastic seems to work well too.
Variac said:
You know what they say about Meyer Sound. "You can buy better speakers, but you can't pay more for them!"
BTW, I'm a big Meyer fan.
Good question about buying the drivers. Have not ever had to do it, not even diaphrams or cones. Never killed one. You can be sure that if you can buy them, they won't be cheap.
I'll ask around just for fun.
Hi
Especially the chapter about " Low Distortion " and what Beranek says at
http://www.meyersound.com/support/papers/REM/index.htm
"http://www.meyersound.com/support/papers/REM/index.htm"
I found very revealing.
I guess it can be seen as kind of scientific explanation to the nonlinear behaviour of air which was mentioned earlier in this thread.
Need more input !
BTW thanks everybody for "the fly of the fur". It made my perception even more precise about inherent side effects of OB's AND I learned a very useful new idiom = "fly of the fur" !
Greetings
Michael
Especially the chapter about " Low Distortion " and what Beranek says at
http://www.meyersound.com/support/papers/REM/index.htm
"http://www.meyersound.com/support/papers/REM/index.htm"
I found very revealing.
I guess it can be seen as kind of scientific explanation to the nonlinear behaviour of air which was mentioned earlier in this thread.
Need more input !
BTW thanks everybody for "the fly of the fur". It made my perception even more precise about inherent side effects of OB's AND I learned a very useful new idiom = "fly of the fur" !
Greetings
Michael
Yes, I found the Beranek description of distortion increasing as the sound travelled down a straight pipe most interesting. It should be kept in mind that Beranek is describing extremely high sound pressures where air itself is distorting (rarefactions approaching zero), thus the longer the pipe, the further the air has to travel in a self-distorting condition. I think these are levels equivalent to 180~190 dB SPL, found in explosions and the nozzle of a working rocket motor.
Maybe in a high-powered concert system with extremely small dimensions inside the phasing plug assembly the air itself goes nonlinear. I also sometimes wonder about the "bug screens" used in outdoor prosound equipment - I've heard the before-and-after, and no question, the mesh of the bug screen audibly coarsens and roughens the sound, adding a quite noticeable "grainy" quality. I'm sure that is some kind of velocity effect due to turbulence in and around the mesh.
I do get suspicious of any type of intentional diffraction or sharp bends in the acoustic path - there's a price to be paid that doesn't always show up in measurements. Something as "simple" as the kind of polishing and porting that is standard practice in high-performance cars would probably benefit the internal pathways of compression drivers as well.
Good news on the computer front - the applications and data survived their transition from the G5 to the Mac Pro, and it seems to be working pretty well, with near-silent operation. (My ears and mind are appreciative.) Speeds better on some things (intel binaries for OS X and Safari), maybe a little slower on other things (Rosetta emulation). If I pay the Gates Tax, I can get another copy of XP Pro and run it with either Boot Camp or Parallels, since the Mac Pro is basically a high-performance PC with EFI replacing the usual BIOS. That would facilitate the kind of cut-n-pasting I do between PC and Mac software environments.
Maybe in a high-powered concert system with extremely small dimensions inside the phasing plug assembly the air itself goes nonlinear. I also sometimes wonder about the "bug screens" used in outdoor prosound equipment - I've heard the before-and-after, and no question, the mesh of the bug screen audibly coarsens and roughens the sound, adding a quite noticeable "grainy" quality. I'm sure that is some kind of velocity effect due to turbulence in and around the mesh.
I do get suspicious of any type of intentional diffraction or sharp bends in the acoustic path - there's a price to be paid that doesn't always show up in measurements. Something as "simple" as the kind of polishing and porting that is standard practice in high-performance cars would probably benefit the internal pathways of compression drivers as well.
Good news on the computer front - the applications and data survived their transition from the G5 to the Mac Pro, and it seems to be working pretty well, with near-silent operation. (My ears and mind are appreciative.) Speeds better on some things (intel binaries for OS X and Safari), maybe a little slower on other things (Rosetta emulation). If I pay the Gates Tax, I can get another copy of XP Pro and run it with either Boot Camp or Parallels, since the Mac Pro is basically a high-performance PC with EFI replacing the usual BIOS. That would facilitate the kind of cut-n-pasting I do between PC and Mac software environments.
I think it is interesting that Meyer cuts the quote from Beranek off where they do since Beranek continued to develop the relationship for 2nd order distortion in an exponential horn. Also, the equation presented is good for any SPL level. I also find it interesting that the reference the 1996 edition. The information is contained in the original 1954 text. That is, it's nothing new. Marketing, you got to love it!
Also of interest is some information in Kinsler and Frey, (1950) where they show that the phase velocity (speed of sound) in an exponential horn is not constant with frequency. The ramifications being that exponential horns must introduce transient wave form distortion.
I’m not particularly interested in horn systems and haven’t spent much time looking at them. I just bring this up because I find it interesting that this basic analysis of horn system was performed over 50 years ago. Perhaps someone with more experience could comment on how significant these effects are. If they were discussed previously in the thread I apologize as I didn’t pay too much attention to anything on horns. It was the 1996 reference that I found amusing.
Oh, I also want to point out that the nonlinearity of air is ever persent. It also accounts for distortion in sealed box woofer systems as the air compliance can be quite nonlinear at the pressure levels inside a woofer enclosure.
Also of interest is some information in Kinsler and Frey, (1950) where they show that the phase velocity (speed of sound) in an exponential horn is not constant with frequency. The ramifications being that exponential horns must introduce transient wave form distortion.
I’m not particularly interested in horn systems and haven’t spent much time looking at them. I just bring this up because I find it interesting that this basic analysis of horn system was performed over 50 years ago. Perhaps someone with more experience could comment on how significant these effects are. If they were discussed previously in the thread I apologize as I didn’t pay too much attention to anything on horns. It was the 1996 reference that I found amusing.
Oh, I also want to point out that the nonlinearity of air is ever persent. It also accounts for distortion in sealed box woofer systems as the air compliance can be quite nonlinear at the pressure levels inside a woofer enclosure.
Hi
Lynn, digging deeper into the topic of HSS I mentioned at post 850, you will find out that you don't necessarily need to install rocket motors to your favourite listening seat.
An array of piezos is all it takes to get astonishing results.
Basically a "HF sound carrier" at reasonable SPL outside our listening ability is amplitude modulated and due to the nonlinearity of air we can hear its envelope.
What was referred to the limitations there at VERY high SPL's I guess was that the equations given by Beranek don't apply correctly as there may enter some secondary thermodynamic effects or something else.
I am not familiar enough with wave guide and horn theory to solve the contradiction between the statement that there is increased (2nd) distortion in horns and wave guides - especially with the longer ones - and the common knowledge that horns perform best when it comes to high SPL reproduction.
Nevertheless the nonlinearity of air is a gradual effect that is not limited to extreme SPL's !
Interesting that there is a term in that distortion equation that represents the distance the sound wave travels at increased SPL.
This would suggest that ANY path length travelled through by the sound wave unless reaching 4PI space would affect our perception (also U-frame subs to give an example in this thread's context).
I assume here that humans developed a cross-correlation to at what SPL a sound arrives and at what extend that specific SPL dependent distortion is perceived. If so, a "new" coloration of sound would be introduced with ANY non direct radiating device.
If I go one step further, the same would also apply the other way around to any damping material in the path between the source and our ears as this would also be detected by the cross correlation I assume we are capable of.
Sure for now its just deductive speculation and the audible effects may be rather sublime and nothing to worry about in real DIY life but it would be interesting to know if there is any proof or research on that ?
Greetings
Michael
Lynn, digging deeper into the topic of HSS I mentioned at post 850, you will find out that you don't necessarily need to install rocket motors to your favourite listening seat.
An array of piezos is all it takes to get astonishing results.
Basically a "HF sound carrier" at reasonable SPL outside our listening ability is amplitude modulated and due to the nonlinearity of air we can hear its envelope.
What was referred to the limitations there at VERY high SPL's I guess was that the equations given by Beranek don't apply correctly as there may enter some secondary thermodynamic effects or something else.
I am not familiar enough with wave guide and horn theory to solve the contradiction between the statement that there is increased (2nd) distortion in horns and wave guides - especially with the longer ones - and the common knowledge that horns perform best when it comes to high SPL reproduction.
Nevertheless the nonlinearity of air is a gradual effect that is not limited to extreme SPL's !
Interesting that there is a term in that distortion equation that represents the distance the sound wave travels at increased SPL.
This would suggest that ANY path length travelled through by the sound wave unless reaching 4PI space would affect our perception (also U-frame subs to give an example in this thread's context).
I assume here that humans developed a cross-correlation to at what SPL a sound arrives and at what extend that specific SPL dependent distortion is perceived. If so, a "new" coloration of sound would be introduced with ANY non direct radiating device.
If I go one step further, the same would also apply the other way around to any damping material in the path between the source and our ears as this would also be detected by the cross correlation I assume we are capable of.
Sure for now its just deductive speculation and the audible effects may be rather sublime and nothing to worry about in real DIY life but it would be interesting to know if there is any proof or research on that ?
Greetings
Michael
mige0 said:
Yes, I didn't see the exponential part of the Meyer page. That second quote from Beranek is the lead in sentence to Beranek’s development of the equation for the increase in distortion as a wave travels through an exponential horn. While I haven't worked it through, it would seem obvious that how the distortion increases would depend on the duct (horn. pipe, etc) geometry. One thing is for sure, it isn't going down. Any way, probably why they don't show the result is because it shows that most of the distortion is generated in the initial part of the horn. For example, if an infinitely long exponential horn increases the distortion by a factor of X, then a horn with mL/2 = 1, where m is the flare constant, will increase distortion by a factor of 0.63X. If mL/2 = 2, 0.86X, mL/2 = 4, 0.98X. Anything longer that mL/2 =4 doesn't contribute much to distortion, according the Beranek's result. Beranek's result also indicates that distortion goes up linearly as frequency goes up. I would imagine more modern horn theory would alter the magnitude of these results somewhat. Don’t hold me to this as I’m just quoting from Beranek’s 50+ year old text.
Fundamentally I would suspect that all of this is a result of the fact that while acoustics is based on linear theory, the assumption of linearity is just an approximation. It's a good approximation at normal SP levels, but the nonlinearity is ever present. The thermodynamics of wave propagation says that compression waves travel faster than expansion waves. In a lossless system, compression waves build upon themselves where as expansion wave disperse. So there is a tendency for sin waves to move towards something like saw tooth waves as it travels down a duct. Certainly that would represent a lot of distortion. However, at normal acoustic pressures the distance required is probably quite great and over that distance other nonlinearities most likely need to be considered, like dissipation.
diffraction
I'd like to understand better....so I'll ask here.
As background I note through "EDGE" that a larger radiused edge produces fewer ripples in the response and less magnitude in those ripples.
I'm interested in links, references and discussion to help me understand:
Does diffraction result in harmonic (re) radiation? If so, does the abruptness of the edge affect the distribution of harmonics and their magnitude as I assume from EDGE?
Does the proposed use of a "lossy mesh" let the wind out of the signal? (My apologies for the analogy.) Would this then reduce the magnitude of diffraction at the edge? Would the backwave losses through the "lossy mesh" offset those of the front wave?
I could go on...better not...
I'd like to understand better....so I'll ask here.
As background I note through "EDGE" that a larger radiused edge produces fewer ripples in the response and less magnitude in those ripples.
I'm interested in links, references and discussion to help me understand:
Does diffraction result in harmonic (re) radiation? If so, does the abruptness of the edge affect the distribution of harmonics and their magnitude as I assume from EDGE?
Does the proposed use of a "lossy mesh" let the wind out of the signal? (My apologies for the analogy.) Would this then reduce the magnitude of diffraction at the edge? Would the backwave losses through the "lossy mesh" offset those of the front wave?
I could go on...better not...
If we consider the finite element level of flow over any type of surface, there is always a relative velocity in reference to the surface as the wave propagates, the boundary layer become thicker until it finally will separate. With a horn or openly radiateing wave, this effect is reduced because the pressure decreates as the wave propagates. If everyone remembers the EnABL pattern mentioned before, it basically creates a turbulent boundary layer rather than the normal laminar boundary layer, and the effect on the propagating wave would be like adding roller skates instead of sliding an object along a surface. Thus resulting in less distortion in the wave.