Research on reflections

[youngho]

FWIW, Beolab 90 in narrow mode is better controlled and behaved than in wide mode. It's still good in wide mode, but not like in narrow mode. In narrow mode the directivity is basically identical from all the way down to all the way up. In wide mode it's somewhat more "bloated", with wider directivity in the mids and the lows than in the treble, which means that the reflected sound gets a somewhat different timbral character from the direct sound. Plus some more areas where it's a tiny bit uneven. Wide mode is still good compared to most other loudspeakers, though, whereas omni mode is not good at all.

Showed the directivity graphs in this post from some time back: https://www.audiosciencereview.com/...ectional-loudspeakers.6552/page-3#post-466562

Can you please explain this to me? It seems like target candidates are basically straight horizontal lines when plotting directivity vs frequency. It seems to me that the wide beam comes closer to roughly approximating the target from 100 Hz to 4 kHz overall, while the narrow shows increasing directivity with frequency until 800-1000 Hz or so, then better approximation of the target until 7 kHz or so. This reminds me of the classic "smoothly changing" versus "relatively constant" directivity goals that Toole describes and that I outlined in my other post: https://www.audiosciencereview.com/...-on-readings-of-lokki-bech-toole-et-al.27540/

 

[youngho]

don't know how someone expects to have a good image if when what is supoused to come from the right is copied on the left and vice versa. the nearer wall reflction might be constructive, but the oposite wall reflection is terribly desctructive

It depends on the room and setup, so possibly late enough arrival times to not fuse perceptually but instead contribute to perception of spaciousness or envelopment, also level reduced due to distance...

 

[oivavoi]

Can you please explain this to me? It seems like target candidates are basically straight horizontal lines when plotting directivity vs frequency. It seems to me that the wide beam comes closer to roughly approximating the target from 100 Hz to 4 kHz overall, while the narrow shows increasing directivity with frequency until 800-1000 Hz or so, then better approximation of the target until 7 kHz or so. This reminds me of the classic "smoothly changing" versus "relatively constant" directivity goals that Toole describes and that I outlined in my other post: https://www.audiosciencereview.com/...-on-readings-of-lokki-bech-toole-et-al.27540/

Thanks for asking for clarifications! I am not sure I completely understood what you meant in the bolded sentences. You are right though, that whereas the narrow mode correponds to a "relatively constant" directivity, the wide mode corresponds to a "smoothly changing" directivity. So the point remains that comparing these two modes is not apples to apples, but rather apple to "somewhat orang-y apple", if that makes sense. Given that they have two different directivity profiles, in terms of constant vs smoothly changing.

The other thing I meant is that in narrow mode you can see that the relationship between the lines in the contour plot is basically the same from the bass to the treble. In wide mode the relationship between the lines in the contour plot is changing with frequency - the distance between the lines is larger some frequencies than at others.

I'm not sure if this makes sense at all... these are just how I as a layman make sense of these graphs. My basic contention is that the Beolab 90 is better-behaved in narrow mode than in wide mode, even though it's an excellent loudspeaker in wide mode as well. I could be mistaken about that, though!

 

[aarons915]

I see the reasoning for this, but it makes no sense.
- there is ambience in the recording. this totaly kills the idea of hearing an instrument like it is played in your room
- our rooms sound awfull

Not really because as Toole stated, a couple speakers in a room isn't enough to achieve the level of reflections present in live music, which is why he theorizes that wide dispersion speakers sound better to the majority of people. If you listened to music in a surround setup with the reflections located properly then I think further reflections would degrade the experience.

 

[youngho]

Thanks for asking for clarifications! I am not sure I completely understood what you meant in the bolded sentences. You are right though, that whereas the narrow mode correponds to a "relatively constant" directivity, the wide mode corresponds to a "smoothly changing" directivity. So the point remains that comparing these two modes is not apples to apples, but rather apple to "somewhat orang-y apple", if that makes sense. Given that they have two different directivity profiles, in terms of constant vs smoothly changing.

The other thing I meant is that in narrow mode you can see that the relationship between the lines in the contour plot is basically the same from the bass to the treble. In wide mode the relationship between the lines in the contour plot is changing with frequency - the distance between the lines is larger some frequencies than at others.

I'm not sure if this makes sense at all... these are just how I as a layman make sense of these graphs. My basic contention is that the Beolab 90 is better-behaved in narrow mode than in wide mode, even though it's an excellent loudspeaker in wide mode as well. I could be mistaken about that, though!

Oh, I thought it was the opposite. With constant directivity, it should be a horizontal line for directivity relative to frequency. That's what Geoff Martin shows as possible candidate targets. The Wide mode comes closer to approximating the horizontal line for a much wider range of the frequency response, so I consider it as "relatively constant" (i.e. it's a messier but wider horizontal line). The Narrow mode is much more slanted until 1 kHz, then horizontal until 7 kHz (so much neater but only half as wide for the horizontal part), contour lines are nice and parallel, much less jagged, "smoothly changing" but less constant in terms of directivity due to increasingly wide radiation at frequencies below 1 kHz.

In my own conceptual model, right or wrong, I would expect the Narrow mode to be perceived as providing much better imaging but the Wide mode to be perceived with more width and envelopment, as well as possibly perception of more realistic timbre of instruments and reproduction of symphonic music.

 

[oivavoi]

Oh, I thought it was the opposite. With constant directivity, it should be a horizontal line for directivity relative to frequency. That's what Geoff Martin shows as possible candidate targets. The Wide mode comes closer to approximating the horizontal line for a much wider range of the frequency response, so I consider it as "relatively constant" (i.e. it's a messier but wider horizontal line). The Narrow mode is much more slanted until 1 kHz, then horizontal until 7 kHz (so much neater but only half as wide for the horizontal part), contour lines are nice and parallel, much less jagged, "smoothly changing" but less constant in terms of directivity due to increasingly wide radiation at frequencies below 1 kHz.

In my own conceptual model, right or wrong, I would expect the Narrow mode to be perceived as providing much better imaging but the Wide mode to be perceived with more width and envelopment, as well as possibly perception of more realistic timbre of instruments and reproduction of symphonic music.

Ok, I understand what you mean now. In wide mode it does indeed have more correspondence in dispersion from 100 hz to about 2000 hz, whereas the narrow mode gets much wider than the rest below 200 hz. So it's the bass that "sticks out" in narrow. In wide mode it's the treble which differs from the rest, as it gets narrower from around 4000 hz. My unspoken assumption was just that the widening in the bass doesn't matter, as the room takes over in the bass in any case, whereas the narrowing in the treble does matter for perception. Hence I called narrow "constant" and wide "smoothly changing". But I see why you can construe it the other way.

Your conceptual model fits very well with my own listening impression of these speakers, in the B&O shops where I have heard them. But if these speakers were placed away from room boundaries, and the wide mode had constant directivity as well (=same dispersion in the treble as in the mids and bass), I'm not sure if I would have perceived it the same way.

 

[bo_knows]

I've been wanting to compile some of the current research on reflections into one thread for awhile as a reference and of course some debate as I know there are differing opinions on some of this and I admit some of this going to be my own editorializing based on personal experience with various speaker designs. Much of this is dealing with music listening in stereo, I realize in a home theater or studio, fewer reflections is seen as beneficial by many people. It's also important to note that there isn't really an agreed upon standard for what exactly is "wide" or "narrow" dispersion but these globe plots of the BMR and LS50 Wireless 2 clearly show the extremes:

View attachment 160987

Current Research


There is countless evidence that the majority of people prefer reflections when listening to music as it gives a sense of space and sounds more like live music. Dr. Toole also speculates that since Stereo can't possibly replicate a live performances 3d sound field that reflections may help to fill in the gaps and simulate it a bit better. Further research by Toole and Sean Olive have shown that listeners not only prefer reflections but that "Early Reflections" have a higher importance than later arriving reflections and that they also need to closely match the direct sound for the highest preference in listening tests. This research is the basis for the early reflections curve in the CTA-2034 measurement spec. I would go a step further and say the while the average of all the early reflections is important, I like to see that all of the early reflections are close to that average. Dr. Toole also considers sidewall reflections to be more important than vertical reflections but there isn't much research on that and I'll show some research later that shows that we probably can't neglect vertical reflections.

Ultra Wide Dispersion Speakers

I personally think the research that shows people generally like wide dispersion has been taken too far in some cases and some speakers have prioritized "wide dispersion" at the expense of other qualities in a speaker. The most extreme examples of course are speakers showcasing the RAAL 64-10 ribbon tweeter which have the widest dispersion of any speaker on the market but are also limited vertically due to their geometry. Now I admit I have limited experience with this tweeter because I auditioned them in a smaller room where wide dispersion maybe didn't matter as much but my big takeaways were that they sounded pretty normal regarding spaciousness except it was very obvious they were lacking vertically when switching back to my LS50. The LS50 sounded "bigger" because of it which was pretty surprising considering the 64-10 is known for wide dispersion and the spaciousness that comes with it. This comparison was the 1st moment that I realized that maybe vertical dispersion is more important than conventional wisdom gives it credit for.

Dr. Toole's study that was the basis for comparing speakers in mono actually also shows something interesting about dispersion and whether ultra wide dispersion is a goal worth pursuing. Aside from showing that listening to the speaker in mono makes it easier to discern differences in sound quality, another argument can be made that when listening to just 2 speakers in stereo, these spatial differences largely disappear. This is more along the line of what I hear in my own room listening to the "narrow dispersion" LS50s in 2 and 3 channel stereo for music, they don't seem to be lacking in spaciousness at all to my ears.


View attachment 160988



Ideal Dispersion

Based mostly on my thoughts between the RAAL 64-10 and the KEF LS50 I have been wondering if there is maybe an "ideal" dispersion considering both the horizontal and vertical planes. I've heard people debate that the widest dispersion is the best or even that we should be matching the dispersion pattern to the room dimensions. Neither approach has ever made sense to me, it seems like we should be trying to simulate the dispersion patterns of real vocals and instruments as best we can to get closest to the ideal speaker directivity, assuming of course that your goal is to get closer to a live acoustic performance in your room. I've never noticed that live music in smaller venues sounds bad in one room compared to another, they all sound natural to my ears. Musical instruments are obviously complex and no speaker is going to simulate all instruments but generally the sound is radiated fairly evenly from wherever the sound originates since they will be complex patterns from multiple point sources. The human voice also has a fairly even polar pattern and most notably isn't extremely wide horizontally or vertically.

View attachment 160989



Vertical Reflections

Another interesting debate is about the importance of vertical reflections where there is surprisingly very little research done on. Dr. Toole briefly mentions a study where he states "...intuition is rewarded in that the dominant audible effect of the lateral reflection was spaciousness (the result of interaural differences) and that of the vertical reflection was timbre change (the result of spectral differences)" but it isn't clear if the reflection was a perfect timbral copy of the direct sound or if it was distorted to match what would be the typical ceiling reflection from a speaker with vertically arranged drivers.

I've only found 2 other studies that give some information on vertical reflections. The first one is:
"The Effect of a Vertical Reflection on the Relationship between Preference and Perceived Change in Timbral and Spatial Attributes" where I'll quote the abstract:

This study aims to investigate a vertical reflection’s beneficial or detrimental contribution to subjective
preference, compared with perceived change in timbral and spatial attributes. A vertical reflection was
electro-acoustically simulated and evaluated through subjective tests using musical stimuli in the
context of listening for entertainment. Results indicate that the majority of subjects preferred audio
reproduction with the addition of a reflection. Furthermore, there is a potential relationship between
positive preference and the perceived level of both timbral and spatial differences, although this
relationship is dependent on the stimuli presented. Subjects also described perceived differences where
the reflection was present. These descriptors provide evidence suggesting a link between timbral
descriptions and preference. However, this link was not observed between preference and spatial
descriptions.

The interesting thing to me was even with a large dip in the vertical reflection, a little over half of the participants still preferred the tracks with the reflection, also 59 out of 78 of the total ratings were positive. This is the measurement of the reflection:

View attachment 160990
The other study is called: "Influence of first reflections in listening room on subjective listener impression of reproduced sound" This study compared the effects of absorbing various first reflections and comparing the results. Basically, the fewer reflections you absorb the wider the soundstage and envelopment but you lose clarity. Absorbing reflections is similar to them being absent so it's interesting that removing the ceiling reflections lessens image width and envelopment just slightly less than removing sidewall reflections. Here are a few of the key graphs: (Rs is absorption of sidewall, Rf= ceiling)

View attachment 160991

Conclusion

I don't think definitive conclusions can really be drawn yet until we get some more research on these issues but it is food for thought. I'd like to see the effect of vertical reflections when the reflection isn't distorted as it was in one of the studies I showed. I'd also like to see how listeners perceive overall spaciousness when listening to speakers with differing horizontal and vertical dispersion.

My personal experience with multiple listening tests (sighted and blind, all level-matched and instantly A/Bing) is that my ears agree with most of the research I have posted. I have found that once at least 2 speakers are playing, I don't notice much difference in spaciousness but I do notice a difference when vertical response is very limited. This tells me that all early reflections need to be considered when going for that live spacious sound, not just the sidewall reflection. I also believe that since early reflections seem to be mostly what matters regarding spaciousness, the large difference shown in the globe plots between a wide and narrow dispersion speaker may not perceptively sound that different when the 1st reflections are within a decibel or so in amplitude. More in the preference realm but I also find listening to music in 3 channel stereo with the center about 3-5db lower than the fronts is a great way to get even more spaciousness while also reducing the stereo imaging effect which makes music sound more like music and less like headphones.

I would think accurately reproducing what is on the media vs "assuming of course that your goal is to get closer to a live acoustic performance in your room" are in my mind two different goals. One needs to define the goal in order to attempt to achieve it. That being said, IMHO, without some kind of standard this is not achievable.
What I'm trying to say, if the goal is to hear what the mastering engineer has heard in the studio, we will have to recreate the same environment in our homes (is stereo reproduction adequate enough to capture the live sound is a different topic). Most of the music being sold/offered today is still in stereo. So, if there's a template for example that shows, mastering studio dimensions are x,y,z, following room treatments were used and placed here, and the mastering engineer was sitting this far from the monitors. He or she was using Kii Audio three speakers (used them just as an example, which I assume need fewer room treatments and it could reduce the size and cost of the mastering studio). Now, if we can build our listening room using a template like this, we have a good chance to hear what the mastering engineer heard. In this case, to achieve this goal, I see things in black and white. In my mind, this would be the scientistic way of approaching this goal since it will be repeatable over and over again. Anyway, sorry for the rant but this is how I feel about what the mastering engineer intended for us to hear but in our homes. I do understand that with good monitors and good room, one can accurately reproduce what is on the media but it may not be the same sound that the mastering engineer heard hence the need for the "template".

This is the ultimate audiophile goal? Right? To hear what mastering engineer intended, no more no less.
Utopian view, huh.

 

[aarons915]

I would think accurately reproducing what is on the media vs "assuming of course that your goal is to get closer to a live acoustic performance in your room" are in my mind two different goals. One needs to define the goal in order to attempt to achieve it. That being said, IMHO, without some kind of standard this is not achievable.
What I'm trying to say, if the goal is to hear what the mastering engineer has heard in the studio, we will have to recreate the same environment in our homes (is stereo reproduction adequate enough to capture the live sound is a different topic). Most of the music being sold/offered today is still in stereo. So, if there's a template for example that shows, mastering studio dimensions are x,y,z, following room treatments were used and placed here, and the mastering engineer was sitting this far from the monitors. He or she was using Kii Audio three speakers (used them just as an example, which I assume need fewer room treatments and it could reduce the size and cost of the mastering studio). Now, if we can build our listening room using a template like this, we have a good chance to hear why mastering engineers heard. In this case, to achieve this goal, I see things in black and white. In my mind, this would be the scientistic way of approaching this goal since it will be repeatable over and over again. Anyway, sorry for the rant but this is how I feel about hearing what the mastering engineer intended for us to hear but in our homes. I do understand that with good monitors and good room, one can accurately reproduce what is on the media but it may not be the same sound that the mastering engineer heard hence the need for the "template".

This is the ultimate audiophile goal? Right? To hear what mastering engineer intended, no more no less.
Utopian view, huh.

Good points and this brings us back to Toole's "Circle of Confusion" in that there may be different goals from the live performance, to recording that performance and then what the engineer wants it to sound like to what the end consumer prefers. I might be in the minority for my preference of trying to recreate an acoustic performance in a small venue in my living room, I know some people love their stereo imaging for example but I have heard many people agree that they want to recreate a band in their space as close as possible(probably not as loud of course). With all of our preferences in mind, it might not be a bad thing for engineers to master the way they're doing it now, just get a good pure recording, make sure the direct sound is intact and let the consumer choose and set up their speakers for their preferred reflections in room.

 

[Chromatischism]

Not really because as Toole stated, a couple speakers in a room isn't enough to achieve the level of reflections present in live music, which is why he theorizes that wide dispersion speakers sound better to the majority of people. If you listened to music in a surround setup with the reflections located properly then I think further reflections would degrade the experience.

I can understand this. My speakers are fairly wide at +/- 60 degrees and are a controlled directivity design. When I switch off upmixing, the sound collapses to the front of the room. I gain clarity and imaging but I lose envelopment, relatively to having the surrounds on. I only use such modes with certain types of music, testing Memoirs of a Geisha by John Williams last night which is a good candidate for it. I don't prefer it for rock or pop type music, at this point, however it seems to work if the recording was a live performance.

 

[abdo123]

I have one question, in what world the LS50 is considered narrow directivity?

 

[oivavoi]

I would think accurately reproducing what is on the media vs "assuming of course that your goal is to get closer to a live acoustic performance in your room" are in my mind two different goals. One needs to define the goal in order to attempt to achieve it. That being said, IMHO, without some kind of standard this is not achievable.
What I'm trying to say, if the goal is to hear what the mastering engineer has heard in the studio, we will have to recreate the same environment in our homes (is stereo reproduction adequate enough to capture the live sound is a different topic). Most of the music being sold/offered today is still in stereo. So, if there's a template for example that shows, mastering studio dimensions are x,y,z, following room treatments were used and placed here, and the mastering engineer was sitting this far from the monitors. He or she was using Kii Audio three speakers (used them just as an example, which I assume need fewer room treatments and it could reduce the size and cost of the mastering studio). Now, if we can build our listening room using a template like this, we have a good chance to hear what the mastering engineer heard. In this case, to achieve this goal, I see things in black and white. In my mind, this would be the scientistic way of approaching this goal since it will be repeatable over and over again. Anyway, sorry for the rant but this is how I feel about what the mastering engineer intended for us to hear but in our homes. I do understand that with good monitors and good room, one can accurately reproduce what is on the media but it may not be the same sound that the mastering engineer heard hence the need for the "template".

This is the ultimate audiophile goal? Right? To hear what mastering engineer intended, no more no less.
Utopian view, huh.

Good points. But mastering of popular music (broadly conceived) these days is usually done with the aim that tracks should sound good on radios, in cars, and on lifestyle speakers. Hence the loudness wars etc. For me, at least, I'm not terribly concerned with recreating what the mastering engineer heard - I would in any case have perceived things differently sitting in the same chair, given that our hearing and head related transfer function are different. I simply want my music to sound good and realistic/convincing to me in my own room with my own loudspeakers!

 

[aac]

The only way to solve this "circle of confusion" thing is to master for non-environmental room design. This will try to remove the room from the equation.
Then any audiophile can build such a room for himself to get as close as possible.

But thats not gonna happen, obviously.

 

[Chromatischism]

I can understand this. My speakers are fairly wide at +/- 60 degrees and are a controlled directivity design. When I switch off upmixing, the sound collapses to the front of the room. I gain clarity and imaging but I lose envelopment, relatively to having the surrounds on. I only use such modes with certain types of music, testing Memoirs of a Geisha by John Williams last night which is a good candidate for it. I don't prefer it for rock or pop type music, at this point, however it seems to work if the recording was a live performance.

There was similar discussion of this content-dependent preference here.

 

[fineMen]

Thanks for having me,

<edit, language barrier>:

why not going for two distinctive speaker systems working in unison
1) something that would give directional clues for stereo sensation, namely high directivity left/right
2) additionally something that would support (1) by adding as much reveberation as is needed for a well balanced timbre. Could be a mono speaker, technically realized as e/g a DML with wide, de-correlated directivity

Why would one expect from a pair alone to fulfill the combined requirements for directivity and tonal balance in all directions?

Tried with a narrow professional speaker pair and a larger DML capable of high output. It worked out fine.

Benefit: cheaper, actually; more power; and foremost adjustability to preference every other minute

 

[aarons915]

I have one question, in what world the LS50 is considered narrow directivity?

I've argued the point myself but I think it depends on your definition as I mentioned in the main post. If response out to 90 degrees is important then you can clearly see in the globe plots that something like the BMR has a much wider response than the LS50. In my experience the early reflections seem most responsible for spaciousness and if that's true then most speakers on the market today should sound close in that regard but I don't think you can ignore the vertical reflections.

 

[fineMen]

... but I don't think you can ignore the vertical reflections.

Agreed, it is only so, that the vertical is hard to get right. So people find excuses to neglect it. It's a cumbersome topic since the multi-way speaker was invented. KEF, when ist started business tried to address the issue even with traditional designs like the Calinda. It was a strong concern, even back in that days. So they went on to coaxials, which is now a trademark of theirs.

I don't think the Blümlein stereo is a solution. It only became handy once. It is time to overcome ;-)

 

[richard12511]

Can you please explain this to me? It seems like target candidates are basically straight horizontal lines when plotting directivity vs frequency. It seems to me that the wide beam comes closer to roughly approximating the target from 100 Hz to 4 kHz overall, while the narrow shows increasing directivity with frequency until 800-1000 Hz or so, then better approximation of the target until 7 kHz or so. This reminds me of the classic "smoothly changing" versus "relatively constant" directivity goals that Toole describes and that I outlined in my other post: https://www.audiosciencereview.com/...-on-readings-of-lokki-bech-toole-et-al.27540/

I see it the same way as you. To me the wide mode has better "constant directivity"(like JBL M2), whereas the narrow mode has more traditionally "smoothly narrowing directivity"(like Genelec/KEF). Which is better? I'm honestly not sure; I don't even know which I actually prefer. I'd have a tough time picking either wide or narrow as measuring "better", particularly if constant directivity is a goal.

 

[test1223]

The only way to solve this "circle of confusion" thing is to master for non-environmental room design. This will try to remove the room from the equation.
Then any audiophile can build such a room for himself to get as close as possible.

But thats not gonna happen, obviously.

Even with a room you only defined one half of the equation since speakers contribute the other half.

There are some standards for listening rooms e.g. itu-r or ebu. Some older ones are very specific. There are some practical conclusions how to build a listening room which also would help consumers to build a great sounding room.

A room with very strong diffuse later reflections is very expensive to build but should provides the best sense of envelopment without major downsides. It divers to much to a normal room that almost no one would build such a thing.

 

[abdo123]

In my experience the early reflections seem most responsible for spaciousness

That’s a really controversial opinion as for me delaying the early reflections and reducing their amplitudes increase spaciousness.

 

[theyellowspecial]

Speakers about 1.5' from sidewalls I can make almost any speaker work by crossing them in-front of the listening position. Only speaker I couldn't get to work was DBR62 with 160* spread. Just too much reflective energy for a true high-fidelity listening experience. Aria 906 also has 160* spread, but it's doable because the wide spread is only in the treble so the midrange doesn't get washed out. The best speakers in my room with this placement are the 120* speakers. My favorite so far is the A130. Go figure it's also the cheapest. Still need to try something narrow like the Klipsch RP-600m @ 80* spread. I'm definitely more a high-fidelity guy than a "spaciousness" guy, especially going back and forth between different speakers/placements. Of course, this is mostly a limitation of the room being imposed on the speakers.