The effects of vertical diffraction close to the HF source (on a typical speaker with tweeter mounted close to top of baffle), even on a low diffracting baffle design, are IMO one of the worst offenders to a vertical listening window. Floor and ceiling reflections also have a significant influence, but the delayed arrival times let the ear differentiate, unless the speaker is very close to a room boundary. Never mind the obvious vertical off axis lobing from driver phase difference in this equation. Any baffle placement scheme that has the tweeter close to the top baffle edge will suffer to some degree if tilted upwards. Alot of 2 ways have the HF acoustic center forward of the LF. Most of the time the main vertical lobe is tilted down, unless the crossover compensates for this, so the speaker may benefit a little from a slight upwards tilt (no further than being on axis with the woofer). 5 degrees vertical is alot of tilt and affects the perceived vertical stereo phantom image, mainly just due to poor vertical power response. Practically all passive xovers allow a certain amount of the lower level overlapping audio to combine unfavorably outside of immediate xover overlap region (one octave above and below the xover point). That junk sitting 20dB or lower outside of the main xover region is still very audible and causes some amount of combing and FR ripple that isnt readily visible in an FR plot, even off axis plots. This is especially the case if the xover is in the delicate 1 - 5k range where the ear is most sensitive. An interesting test of this theory would be to perform an HD sweep off axis. A well designed MTM arrangement may measure better in this regard.
Horizontal off axis listening isn't as critical thanks to some degree of driver placement symmetry on the baffle IOW the C to C driver distance doesn't appreciably change in the horizontal plane. Lobing and combing of the room reflections with the forward firing audio are the main contribution to perceived FR at the listening position. Most speakers have the same sided baffle edge profiles, so the diffracted components are the same L to R, in theory canceling the combing effect of both diffracting signatures out if the listener is perfectly on horizontal axis with the speaker. The main thing you hear with speaker toe-in or toe-out is combing, wall reflections and a combination of both, not so much the interaction of diffraction ripple with the two.
Horizontal off axis listening isn't as critical thanks to some degree of driver placement symmetry on the baffle IOW the C to C driver distance doesn't appreciably change in the horizontal plane. Lobing and combing of the room reflections with the forward firing audio are the main contribution to perceived FR at the listening position. Most speakers have the same sided baffle edge profiles, so the diffracted components are the same L to R, in theory canceling the combing effect of both diffracting signatures out if the listener is perfectly on horizontal axis with the speaker. The main thing you hear with speaker toe-in or toe-out is combing, wall reflections and a combination of both, not so much the interaction of diffraction ripple with the two.
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JanRSmith, Cool 
yeah there is already quite lot of stuff presented, long posts, might be hard to follow. They are mostly visualizing first reflections of typical multiway speaker and then exploring some ways how to make the responses play better with room, making vertical responses more alike and on todays posts even some horizontal responses seemed to improve with (sideways) tilt on the example case. By improve I mean close wall reflection got more alike to listening axis response and opposite sidewall reflection got worse which is supposed to be a good thing, less correlation to direct sound supposedly making positive stereo effect.
yeah there is already quite lot of stuff presented, long posts, might be hard to follow. They are mostly visualizing first reflections of typical multiway speaker and then exploring some ways how to make the responses play better with room, making vertical responses more alike and on todays posts even some horizontal responses seemed to improve with (sideways) tilt on the example case. By improve I mean close wall reflection got more alike to listening axis response and opposite sidewall reflection got worse which is supposed to be a good thing, less correlation to direct sound supposedly making positive stereo effect.
Yeah trying to explore the room boundary reflections here. I havent demonstrated what the diffraction ripple looks like or how it would affect, other than some of it happens to be visible in the graphs posted so far. Only consentrating similarity of the responses (of first reflections) and speculating how they might affect imaging and ways to improve them just by manipulating speaker position mainly. I'm not too familiar how the stuff is perceived by hearing system, going with intuition currently and with the quick listening tests posted earlier. First post explains it nicely, and on the few latest posts include some stuff on lateral reflections, IACC stuff touched a little bit.
Diffraction is inherent to any loudspeaker system and can be somewhat optimized by various means independently of the system overall response in respect to first reflections and direct sound, posititioning of the speaker. Bad diffraction might hide possible benefits here though, I suppose its always good to minimize diffraction ripple on the responses by good acoustic construct and using multiple ways (a multiway speaker) but this is another topic altogether. I'm glad you brought the subject out though, and gave some observations on it.
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The smaller the baffle, the higher the diffraction component reflected interferences are shifted up in frequency. That minimizes the audible effect and points to the benefit of a smaller baffle. Further, the combined effect off axis refraction and the main wavefront wrapping around the speaker is lessened by a rounded smaller baffle. The best case scenario for this is a spherical enclosure / baffle shape, but some people believe its the opposite of effect judging by the baffle step ripple down lower.
The combing caused by interaction of forward radiated HF and multiple edge diffractions does more audible damage to the perceived stereo image depth than any other reflected component. Many speakers that sound artificially huge stereo image wise tend to do so by means of many separate boundary reflections within the 0.25 - 1 ms time window. Later reflections add more width depending on the proportion of reflected energy vs direct radiated sound and the proportions of all reflected components to each other. Its a rather complicated issue to understand. The only reason I know this is from some research done by Lexicon I read a while back. I will post a link to this if I can find one.
A larger (or even infinite) baffle will push the diffraction artifacts farther away in arrival time to the main wavefront and as a result they will become considerably detached acoustic events processed in a different time domain by the ears. Some of that falls into the time domain of flutter echos, which on its own is the most destructive type of acoustic interference you can have in a listening space. By itself, the sound of diffracted energy combing with its like sources, has minimal audible consequences compared with any and all of the other boundary reflections. The only place it can dominate is in anechoic conditions, not in your typical listening space. If the room is acoustically very dead, the dominance of refracted energy components will make the speakers sound very flat in acoustic depth and height perception. All the finer spacial cues in the recording will be masked and no other reflections will be there to help recreat an acoustical space.
The combing caused by interaction of forward radiated HF and multiple edge diffractions does more audible damage to the perceived stereo image depth than any other reflected component. Many speakers that sound artificially huge stereo image wise tend to do so by means of many separate boundary reflections within the 0.25 - 1 ms time window. Later reflections add more width depending on the proportion of reflected energy vs direct radiated sound and the proportions of all reflected components to each other. Its a rather complicated issue to understand. The only reason I know this is from some research done by Lexicon I read a while back. I will post a link to this if I can find one.
A larger (or even infinite) baffle will push the diffraction artifacts farther away in arrival time to the main wavefront and as a result they will become considerably detached acoustic events processed in a different time domain by the ears. Some of that falls into the time domain of flutter echos, which on its own is the most destructive type of acoustic interference you can have in a listening space. By itself, the sound of diffracted energy combing with its like sources, has minimal audible consequences compared with any and all of the other boundary reflections. The only place it can dominate is in anechoic conditions, not in your typical listening space. If the room is acoustically very dead, the dominance of refracted energy components will make the speakers sound very flat in acoustic depth and height perception. All the finer spacial cues in the recording will be masked and no other reflections will be there to help recreat an acoustical space.
While diffraction is off topic there is something I'd like more info on
Baffle step ripple gets effectively weed out with spherical enclosure, what are you referring to with it being lower?
Sound diffracts all the way around enclosures but already after the baffle edge the part that diffracted was already attenuated so much hardly anything meaningfull comes fully around so this is a not problem.
For some reason I dont understand this, could you rephrase? Do you mean diffraction is meaningless in comparison to early reflections (of a room)? Certainly its effect is less in graphs, but I'm not sure about audibility due to much shorter delay than room reflections have. Geddes has beem talking about diffraction being highly audible especially when listening at loud volume. Besides, diffraction and room reflections are two separate things, both optimizable separately for any given speaker system. Its probably true that if either makes soubd very bad tge otger isnjust meaningless. For a hifi system one should address both, and all other "problems".
Where is refraction happening? Speed of sound stays the same outside enclosure and no refraction should happen, what are you referring to?
Baffle step ripple gets effectively weed out with spherical enclosure, what are you referring to with it being lower?
Sound diffracts all the way around enclosures but already after the baffle edge the part that diffracted was already attenuated so much hardly anything meaningfull comes fully around so this is a not problem.
Possibly, if big enough enclosure the delayed sound could have delays like first boundary reflections, many milliseconds. Its impossible to get them further out though, without making room bigger. For this reason if there is any they would happen sooner than later and just show effects lower in frequency than with some smaller sized box with its diffraction. Comb filtering like boundary reflections make except at least magnitude lower, diffraction ripple is usually few db, main diffraction hump could be several but boundary interference can make serious +10db dips. All this means the diffraction related "back wave", the part that makes the interference with direct sound appear in frequency response is much attenuated, more than 10db, whereas boundary reflections can be almost as loud as direct sound, perhaps attenuated only few db.
For some reason I dont understand this, could you rephrase? Do you mean diffraction is meaningless in comparison to early reflections (of a room)? Certainly its effect is less in graphs, but I'm not sure about audibility due to much shorter delay than room reflections have. Geddes has beem talking about diffraction being highly audible especially when listening at loud volume. Besides, diffraction and room reflections are two separate things, both optimizable separately for any given speaker system. Its probably true that if either makes soubd very bad tge otger isnjust meaningless. For a hifi system one should address both, and all other "problems".
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Sorry, I misspelled defraction to refraction.
A major contributor to what I believe you are hearing in the vertical axis is defraction related interference with the main tweeter wavefront and the combing it does with the defraction. Geddes is correcr regarding the impact defraction has at higher spls. Its definitely going to surpass the room reflections in negative impact of overall sound quality.
The finer details of perceived depth and height (not width) of stereo image however is impacted mostly by anything that dwells in the shorter time domain of well under 1 ms. Pushing the diffraction induced artifacts further out in time away from the main wavefront arrival helps our ears pay less attention to it, but doesn't decrease it in severity. IOW its processed by the brain as a separate event ie room reflection, so its not interfering much in the ears detecting spacial cues.
The net effect of diffraction induced distortions (diffracted artifacts combing with each other as well as with main wave front) is low in amplitude, but high in non linearity, so a little goes a long way in ruining what gets to our ears and smears spacial cues. As I tried to explain before, the room reflections are mainly a reproduction of original audio in a filtered fashion, delayed in time based on what portion of audio is filtered and reflected. When you modulate two very short time domain non linear acoustic events, it turns into more severe non linear "noise", which by nature doesn't blend well, sort of like a click or pop in vinyl, so it sticks out even in very small amplitudes.
A major contributor to what I believe you are hearing in the vertical axis is defraction related interference with the main tweeter wavefront and the combing it does with the defraction. Geddes is correcr regarding the impact defraction has at higher spls. Its definitely going to surpass the room reflections in negative impact of overall sound quality.
The finer details of perceived depth and height (not width) of stereo image however is impacted mostly by anything that dwells in the shorter time domain of well under 1 ms. Pushing the diffraction induced artifacts further out in time away from the main wavefront arrival helps our ears pay less attention to it, but doesn't decrease it in severity. IOW its processed by the brain as a separate event ie room reflection, so its not interfering much in the ears detecting spacial cues.
The net effect of diffraction induced distortions (diffracted artifacts combing with each other as well as with main wave front) is low in amplitude, but high in non linearity, so a little goes a long way in ruining what gets to our ears and smears spacial cues. As I tried to explain before, the room reflections are mainly a reproduction of original audio in a filtered fashion, delayed in time based on what portion of audio is filtered and reflected. When you modulate two very short time domain non linear acoustic events, it turns into more severe non linear "noise", which by nature doesn't blend well, sort of like a click or pop in vinyl, so it sticks out even in very small amplitudes.
Sorry diffraction is linear distortion. Yes, diffraction is bad and I have relatively low diffraction system which doesn't mean diffraction wouldn't still be audible on the tests in this thread but its about as good as it gets, last wee bit of wiggle goes away with new waveguide some day. Its freestanding waveguide (whose mouth termination makes some) and minimal enclosure woofer, not bigger than the driver (cardioidish).
Yes I think if one listens to speaker with diffraction then elevation and tilt and what not might make it diffraction more audible. Trying to inspect effect of room boundaries here on this thread through simulation examples, some listening tests in single speaker mono but not sure if that translates to stereo system at all. Diffraction you raised here on discussion is good info for people who might test this stuff this in stereo. It might be hard to discern what makes what sound (with tilt) as many things change. Also for me, but currently I think its not problem on my system. Rights reserved to change my view on this of course.
The latest trick explained earlier today to help with those first room reflections is to tilt speaker sideways, not up. This should also ease out diffraction, if it makes any difference at all, as baffle edges would now be diagonal to vertical and horizontal (listening) planes, not parallel. There was other benefits as well, explained earlier today.
Have you tried tilting speaker sideways, not up?
Yes I think if one listens to speaker with diffraction then elevation and tilt and what not might make it diffraction more audible. Trying to inspect effect of room boundaries here on this thread through simulation examples, some listening tests in single speaker mono but not sure if that translates to stereo system at all. Diffraction you raised here on discussion is good info for people who might test this stuff this in stereo. It might be hard to discern what makes what sound (with tilt) as many things change. Also for me, but currently I think its not problem on my system. Rights reserved to change my view on this of course.
The latest trick explained earlier today to help with those first room reflections is to tilt speaker sideways, not up. This should also ease out diffraction, if it makes any difference at all, as baffle edges would now be diagonal to vertical and horizontal (listening) planes, not parallel. There was other benefits as well, explained earlier today.
Have you tried tilting speaker sideways, not up?
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This is interesting aspect of it, effect to localization. How much room reflections effect, how much diffraction effects. Do you have links to papers on the subject? I believe we should make sure, as speaker designers, that the speaker disappears and only nice stereo sound is perceived.
Not sure how much this affects when woofers are lowpassed before issues and tweeter is in waveguide making hardly any diffraction, on aminimal baffle the edge is about at same location as the transducer itself, altgough there is an edge. Not sure if its still meaningful, perhaps it is, although for example Linkwitz website reads something along the lines that "dipole systems make very good stereo, and diffraction is hardly audible." from which I've made conclusion that good stereo stuff is reached almost regardless of diffraction by making sure speaker play nicely with the room, just minimize diffraction to be sure it doesn't affect performance.
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Also I remember Patric Bateman and mark100 say about synergy horns / MEH that they disappear very well, especially depth perceptio disappears. Danleys and most MEHs seen in the forums have hardly any mouth termination so "severe" diffraction happens, reflection back to the horn, and also the taps would diffract some, but somehow at least the disappearing trick and overall good sound seem to be there regardless of some diffraction happening. Perhaps its just that it is a point source, true one in many sense including diffraction, there is only one "diffraction signature" for all ways, no separate ways with their own diffraction fingerprints. Also all room reflections are as similar as direct sound as good the waveguide is. Typically they have quite narrow coverage angle and relatively well controlled so I assume most of the sound is due to how it works with the room and rooms attribution is rather minimal (beong narrow coverage angle point source). Well just speculating, probably many reasons, there is deep mystery to diffraction in this sense.
Perhaps after clearly identifying what the sound and effect is then it would be somewhat easier to identify audible diffraction. Currently I find it hard to separate it from all other audible "issues", like first reflections.
For this reason I'll assume position changes in my system have most audible effect due to rooms contribution changing.
Perhaps after clearly identifying what the sound and effect is then it would be somewhat easier to identify audible diffraction. Currently I find it hard to separate it from all other audible "issues", like first reflections.
For this reason I'll assume position changes in my system have most audible effect due to rooms contribution changing.
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Anyone already tested the side tilt? gotta dig out small two way monitors tomorrow and try out. Point source per first reflections + extra benefits speculated, I have high hopes
ps.
Meanwhile got an idea I need also try, use figure 8 microphone null aimed to speaker and front back to ceiling and floor. This should magnify attribution of direct sound and lateral reflections. Hold it at hand and rotate, monitor with headphones or record to be monitored later. Same method could be used to gauge lateral reflections, reduce vertical reflections and direct sound. Perhaps could cancel out floor reflection or ceiling reflection as well, just by aiming the side null. Anyone ever tried? edit. Uh, but the problem is that mic hears differently than hearing system.. well, could be fun experiment nevertheless
gotta dig out small two way monitors tomorrow and try out. Point source per first reflections + extra benefits speculated, I have high hopes ps.
Meanwhile got an idea I need also try, use figure 8 microphone null aimed to speaker and front back to ceiling and floor. This should magnify attribution of direct sound and lateral reflections. Hold it at hand and rotate, monitor with headphones or record to be monitored later. Same method could be used to gauge lateral reflections, reduce vertical reflections and direct sound. Perhaps could cancel out floor reflection or ceiling reflection as well, just by aiming the side null. Anyone ever tried? edit. Uh, but the problem is that mic hears differently than hearing system.. well, could be fun experiment nevertheless
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lol you guys crack me up. I can sort of understand the MEH thing in how they tend to disappear. That tends to be due to point source behavior from some experimentation I did with some fostex FX120 fullrange drivers. The enclosures I used were made from small plywood with 1/4 " round edges. I also used 24" x 24" flat baffles with the same enclosures behind them. These drivers melted into the room and vanished with both the baffle and enclosure only. The main difference was the more immediate sound in the lower midrange from the large baffle, but the imaging was just as good both ways.
If you can take THD measurements with those vertical tests, it would be interesting to see how it affects things.
I'm looking for links to the theory i was referring to. I wish it was easier to find all this stuff in a sea of page ranking...
If you can take THD measurements with those vertical tests, it would be interesting to see how it affects things.
I'm looking for links to the theory i was referring to. I wish it was easier to find all this stuff in a sea of page ranking...
Looking forward to that link. I am currently focusing on controlling diffraction.
It is an unfortunate acronym, because "meh" is a texty-jargon way of expressing low enthusiasm....
"Did you like my pineapple mustard lasagna?"
"Meh, I like normal lasagna better"
I try never to use the term "meh" on these forums because Multiple Entry Horn (MEH) is an important concept.
"Did you like my pineapple mustard lasagna?"
"Meh, I like normal lasagna better"
I try never to use the term "meh" on these forums because Multiple Entry Horn (MEH) is an important concept.
I assumed it was not that "meh"😎🙃, but searching meh in combination with audio did it.
Danley Synergys have sort of termination, wedges. Jericho series and some diyers leave the wedge off in large horns that go low. In SH50 it obviously is crucially important, like in Danley Hyperion
I have looked through your thread and l’m not sure l accept your simulations.
The underlying fact is that all rooms have a reverberation time which can vary across the audio spectrum. RT60 is the known reference for measurement of reverberation time.
All indirect sound reaching the listener position is time domains related as a dominant factor. The incidence or sound reflections points is determined by the power response of the loudspeaker and the primary first reflection points in the room. Above the Schroder frequency this sound is like rays of light. Below the Schroder frequency the sounds is represented as modal frequencies that either peak or null.
With your simulations or measurements if taken in a snapshot in time you will only see the direct sound at that time slice. All the first reflections arrive latter. That is the reverberant sound of the room. These reflections can only be removed with absorption. Diffusion can be used to scatter reflections.
Critical listening rooms must employ absorption on adjacent surfaces. Typically the ceiling has a cloud to counter the reverberation time as the floor is impractical. These treatments can be useful for modal frequencies with correct design.
The room size has a significant impact on the above. You can measure the above with REW and collect data on a particular room without resorting to simulations which at best are made on assumptions which can lead in incorrect hypothesis and conclusions
In my own experience using Dirac room measurements and correction the visible correction is always below the Schroder frequency. An untreated room will always impact on the reverberation related issues regardless of the loudspeaker or crossover design. Those factors primarily address the on axis direct sound by design. If the power response is uniform it’s a bonus in terms of uniform absorption of the reverberant sound.