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Effect of Loudspeaker Directivity Compared with In-room Measurements

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Kvalsvoll

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Rereading your comment, why would you say "focus is also lost in center position"? What should cause this "loss of focus"?
When the speakers are angled in so much that this time-intensity sort of works, there will be less direct sound and more reflected sound in the center position, because the speakers send more energy to other places than directly at the listening position in center. More reflected sound and less direct sound equals loss of focus.

But this is very easy to test for yourself. Toe-in your speakers around +30 degrees from pointing at center, that is 60 degrees from the front wall normal plane. Does this sound good? Is this a sound you can live with, in case you had a friend that might come over, some time? Or is it simply so, that this was a bad idea, because sound quality in center position is now compromised.
 
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"fall-off with distance" is the same for both stereo speakers so I'm not seeing why this is relevant to the discussion of time-intensity trading?
See my post #254 above.
 

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When the speakers are angled in so much that this time-intensity sort of works, there will be less direct sound and more reflected sound in the center position, because the speakers send more energy to other places than directly at the listening position in center. More reflected sound and less direct sound equals loss of focus.
Depends solely on boundary absorption and speaker directivity. The contralateral reflection is easily absorbed. You should ask Earl Geddes about this topic :)
But this is very easy to test for yourself. Toe-in your speakers around +30 degrees from pointing at center, that is 60 degrees from the front wall normal plane. Does this sound good? Is this a sound you can live with, in case you had a friend that might come over, some time? Or is it simply so, that this was a bad idea, because sound quality in center position is now compromised.
From the earlier discussion here it should be clear that toeing-in any arbitrary speaker doesn't work if you don't or if the speaker can't be equalized to anechoically flat within the listening window, which is now off-axis. You seem to be under the impression that I'm sort of new to these topics and that I wouldn't have tested things extensively. Rest assured this is not the case :)
And, I'm listening more often than not off-center as there's more situations where a friend comes over than not. It might be different for you.
 
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Floyd Toole

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I believe Toole recommends narrow directivity speakers for multichannel. He recommends wide directivity for two-channel, because his starting position is that two-channel should be turned into faux multichannel by bouncing reflections around the room, in search of so-called envelopment.
I don't recall ever saying explicitly that narrow directivity has ANY special virtue (except, obviously, in sound reinforcement and cinema systems). Practical cone/dome loudspeakers gravitate to wide dispersion because of their diaphragm sizes, wide-bandwidth horns are large, and workable arrays are expensive, so for mass market systems there is little choice. Fortunately, in many years of subjective testing, wider dispersion and the consequent lateral reflections have been approved of in stereo listening, mostly as a means of softening the image of hard panned left and right sounds (a section of an orchestra emerging from a single loudspeaker is unrealistic). As I point out in my books, "envelopment" is the result of strong lateral reflections arriving tens of milliseconds after the direct sound, something that small room reflections cannot accomplish. It is correlated with low interaural cross-correlation, something aided in performance spaces by higher reverberation times (more diffusion in the sound field). This can be approximated very well in multichannel systems, but not in stereo. The only "faux" multichannel that I have ever condoned is upmixing, and the success of that depends on the nature of the stereo mix and of the particular upmixer - there are several quite different options. None that I have experienced are gratifying for all recordings, but I now regularly use the Auto3D upmixer.
 

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As I point out in my books, "envelopment" is the result of strong lateral reflections arriving tens of milliseconds after the direct sound, something that small room reflections cannot accomplish. It is correlated with low interaural cross-correlation, something aided in performance spaces by higher reverberation times (more diffusion in the sound field). This can be approximated very well in multichannel systems, but not in stereo.

I think this is just a result of people(myself included) paraphrasing your book and using "envelopment" to refer to all general spatial impressions. And then people read those posts and criticize the paraphrasing instead of reading the book. :)

For those who haven't read it or forgot the specific contents(me): "Perceptions of space are substantially related to laterally reflected sounds. In small rooms, it is improbable for natural reflections to initiate impressions of envelopment; those cues must be in the recordings. However, sensations of ASW (apparent source width), image broadening and early spatial impression are very real and, it seems, desirable. Klippel chose as his objective measure of “feeling of space” (R) the difference between the sound levels of the multidirectional reflected sounds and the direct sound at the listening location." - Section 7.4.4, Sound Reproduction 3rd ed.

I don't recall ever saying explicitly that narrow directivity has ANY special virtue (except, obviously, in sound reinforcement and cinema systems). Practical cone/dome loudspeakers gravitate to wide dispersion because of their diaphragm sizes, wide-bandwidth horns are large, and workable arrays are expensive, so for mass market systems there is little choice.
What would you describe as narrow? I think there is some disconnect in terms of what people(on this forum) refer to as "narrow directivity" and what is in your book. The example "narrow" speaker in Section 7 is a Quad ESL 63 with roughly 8-15dB drop by 60-75° off-axis from 100hz-10khz. This is MUCH narrower than anything that has been reviewed on this site, people often refer to Genelec or Kef as having "narrow directivity" but I don't think they actually qualify in terms of your research.
 

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CBT is horizontally wide and vertically narrow. "fall-off with distance" is the same for both stereo speakers so I'm not seeing why this is relevant to the discussion of time-intensity trading?
No, so I wonder if it's possible that you haven't heard CBT speakers. Fall-off with distance within limits is linear, not squared. More importantly, due to the shading, intensity actually seems to go down as one approaches the proximal loudspeaker at a given height. Floyd Toole wrote: "It was distinctive in how little the sound level and timbre appeared to change with location in the room and how the loudspeaker did not get “loud” as one walked up to it....The row of “heads” across the width of this imagined room intersect with only one line; they are at a nearly constant sound level from 200 Hz to 8 kHz. And as one moves even closer to the loudspeaker, at the same height, the sound level goes down..."

Perhaps this isn't specifically relevant to time-intensity trading per se, but it certainly is in terms of widening the sweet spot for stereo, which I believe was the ultimate goal of the three papers you cited, even if you seem to subsequently dismiss, or at least seem to abstain from discussing, their models.

I have a pair of CBT24s but will not tire you with my non-scientific observations, except to say that the results exceeded any previous experiences with time-intensity trading with controlled-directivity loudspeakers, making them good speakers for a family room.
 

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We have some speakers, and they are different from other speakers.. Yes, not exactly descriptive.

Starting from the observation - sitting far off-center, those some-speakers tend to present a sort of soundstage, though diffuse and things have moved closer to the nearest speaker. Switching to other-speakers, the sound collapses into the nearest speaker.

So what is a some-speaker, and what is a other-speaker.

It is clear that it has to do with radiation pattern. A larger speaker with horn at least above 1-2K, can be an example of the first (some-speaker) type. A small speaker with dome tweeter can be the other-speaker type.

A pattern that manages to cover my far-off position from both L and R speaker with full frequency range coverage, is a good starting point. Then there is the shape of the wavefront - a horn with its larger radiating surface tend to maintain spl level better across a longer distance, thus keeping spl from the speaker far away from dropping.
Thanks, this is a little less vague. In general, from my personal perception, loudspeakers with narrow directivity patterns have been described by others to have a narrow sweet spot (extreme examples include planar dipolar speakers like Sanders and King Sound, also highly directive designs like JansZen), using descriptive terms like "vise-like" or "laser-thin" in terms of listening position. On the other hand, very widely directive speakers are often described as having a wide sweet spot, i.e. Roy Allison designs and innumerable others.

It increasingly seems to me that that this discussion, which has shifted from the original "directivity affects listener perception and other measurements beyond on-axis frequency response," may have broken down in multiple ways:

1. What should discussion of directivity mean when it comes to "controlled" or "constant," i.e. continuously changing or relatively flat DI, and if so, over what bandwidths? I had tried to introduce some discussion under point C here: https://www.audiosciencereview.com/...-on-readings-of-lokki-bech-toole-et-al.27540/
2. For off-center "sweet spot" discussions, what are the parameters used? I believe that Allison was focussed primarily on timbre. In the first paper cited by @markus , they seemed to have focussed on "wide-band signal" and image fusion. The second paper cited by @markus appeared to conflate multiple factors: "Some of the parameters considered for comparison were: sound localization, apparent source width ~ASW!, coloration, and loudness." In my opinion, "sweet spot" discussions may increasingly vary between "realistic timbre" vs "realistic imaging" at increasingly off-center positions, perhaps related to directivity, but research may help define this further. @markus seems to have declined to comment further on the papers that he himself cited. @markus , please refrain from citing papers if you do not discuss them further.
3. For central "sweet spot" discussions, again, what are the parameters used, and how might directivity affect that? See again here: https://www.tonmeister.ca/wordpress/2015/06/30/bo-tech-what-is-beam-width-control/. I believe that Geoff Martin's perceptions are compatible with those derived from Tapio Lokki's papers that I very crudely attempted to summarize and conflate above (#1).
 
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No, so I wonder if it's possible that you haven't heard CBT speakers. Fall-off with distance within limits is linear, not squared. More importantly, due to the shading, intensity actually seems to go down as one approaches the proximal loudspeaker at a given height. Floyd Toole wrote: "It was distinctive in how little the sound level and timbre appeared to change with location in the room and how the loudspeaker did not get “loud” as one walked up to it....The row of “heads” across the width of this imagined room intersect with only one line; they are at a nearly constant sound level from 200 Hz to 8 kHz. And as one moves even closer to the loudspeaker, at the same height, the sound level goes down..."

Perhaps this isn't specifically relevant to time-intensity trading per se, but it certainly is in terms of widening the sweet spot for stereo, which I believe was the ultimate goal of the three papers you cited, even if you seem to subsequently dismiss, or at least seem to abstain from discussing, their models.

I have a pair of CBT24s but will not tire you with my non-scientific observations, except to say that the results exceeded any previous experiences with time-intensity trading with controlled-directivity loudspeakers, making them good speakers for a family room.
Excellent example - a speaker that is not "cardioid", not horn, but still works very well for the purpose of filling a room with sound.

Other designs that can have similar properties are line source dipoles, such as the magnestat panels with long, tall true ribbon tweeter. When you move up close, it does not get louder.

By placing what we can call the focal point behind the speaker, it creates a pattern that has already develop into something closer to a plane wave, even before the sound escapes the speaker. This gives the very beneficial property that the spl does not fall off as distance is increased in a similar way as it does for a point source. A point source drops 6dB for each doubling of distance, a cylindrical pattern has only 3dB drop, and a plane wave is equally loud for all practical distances inside a small room.

And this is one important property which explains why I can move around across the room, and still experience a soundstage that does not collapse into the nearest speaker. The speakers are designed to have a radiation pattern that is different from the typical point source, and this pattern gives the benefit of less attenuation per unit distance.

This can be achieved with a horn, in my speakers in combination with other solutions, for practical reasons to keep the size of the speaker reasonable.
 
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Thanks, this is a little less vague. In general, from my personal perception, loudspeakers with narrow directivity patterns have been described by others to have a narrow sweet spot (extreme examples include planar dipolar speakers like Sanders and King Sound, also highly directive designs like JansZen), using descriptive terms like "vise-like" or "laser-thin" in terms of listening position. On the other hand, very widely directive speakers are often described as having a wide sweet spot, i.e. Roy Allison designs and innumerable others.
My speakers have a large sweet spot. And they would typically be described as very narrow. But that is not quite true, because they have rather wide coverage with uniform frequency response, and drops off steep outside this area.
 
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1. What should discussion of directivity mean when it comes to "controlled" or "constant," i.e. continuously changing or relatively flat DI, and if so, over what bandwidths? I had tried to introduce some discussion under point C here: https://www.audiosciencereview.com/...-on-readings-of-lokki-bech-toole-et-al.27540/
I use the term "controlled directivity" in the meaning that the pattern is designed to match a specific requirement.

Constant-directivity has been used for devices (horns..) that manages to have a constant radiation pattern/angle across some part of the frequency range. Typically, a speaker with a horn for higher frequencies and direct radiator for lower mid and bass. This will of course result in a speaker that can have this constant-directivity only at higher frequencies, lower frequencies will be a result of the size of the driver and the baffle, and goes toward omni at low frequencies.
 

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2. For off-center "sweet spot" discussions, what are the parameters used? I believe that Allison was focussed primarily on timbre. In the first paper cited by @markus , they seemed to have focussed on "wide-band signal" and image fusion. The second paper cited by @markus appeared to conflate multiple factors: "Some of the parameters considered for comparison were: sound localization, apparent source width ~ASW!, coloration, and loudness." In my opinion, "sweet spot" discussions may increasingly vary between "realistic timbre" vs "realistic imaging" at increasingly off-center positions, perhaps related to directivity, but research may help define this further. @markus seems to have declined to comment further on the papers that he himself cited. @markus , please refrain from citing papers if you do not discuss them further.
Huh? What is it I "need" to discuss? And what is the "second paper"? Sorry I've linked quite a few resources along the way. Can't remember in which order. Especially because it was last year :) Happy new year by the way.

Edit: Found it. You're talking about the Rodenas paper. Not sure why you say it would "conflate multiple factors". Best case time-intensity trading should widen the sweet spot without compromising the central listening position. So any perceptual quality that can be had from a central listening location should be retained when moving to the left or the right, not just phantom image location. The central listening position itself should not be negatively affected.

All of this is hard to test as the room has a significant influence. Regarding how the room response might influence stereo image perception I found this bit interesting while rereading "Sound reproduction":

“In the era during which it was fashionable for the loudspeaker end of a control room (zones 1 and 2 in Figure 7.5) to be acoustically “dead,” and the opposite end (zone 3) to be “live,” I toured an elaborate recording complex that was nearing completion. I had not experienced one of these new rooms, and was given a demonstration. I bellied up to the center of the console and listened; something was wrong, the center image was strangely unclear at times. Looking around, I saw that the entire back wall (zone 3) was covered with beautiful and expensive wooden diffusers, vertically arranged to spread the sound horizontally. I asked for monophonic pink noise to be played, and from the stereo seat there was simply no center image—the sound spread across much of the space between the loudspeakers. Everybody could hear it; it was not subtle. This was obviously not a good thing. The movers were still on the premises, so we found some moving blankets and hung a couple of them in front of the diffusers. The center image snapped into place where it belonged. The problem: too much uncorrelated sound arriving from behind the listener, scrambling the information in the direct sound from the loudspeakers. Lesson: there can be too much of a good thing. The ETC probably looked just fine, though. Somebody measured but did not listen.”

Excerpt From
Sound Reproduction
Floyd E. Toole
 
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youngho

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Edit: Found it. You're talking about the Rodenas paper. Not sure why you say it would "conflate multiple factors". Best case time-intensity trading should widen the sweet spot without compromising the central listening position. So any perceptual quality that can be had from a central listening location should be retained when moving to the left or the right, not just phantom image location. The central listening position itself should not be negatively affected.
ASW, localization, and loudness do not seem to correlate together in the work of Lokki et al, also the 2013 PhD thesis by William Evans. In the latter, there was an interesting preliminary investigation 4.2.7 Stage 3: Small-Scale Free-Roaming Evaluation: "Contrary to results from the formal listening tests in Denmark, Loudspeaker 3 (the Array), was unanimously perceived to be the most liked system when listeners were allowed to listen at any position in the room. Most feedback commented that the system exhibited a ‘consistency at all positions in the room’.
All of this is hard to test as the room has a significant influence. Regarding how the room response might influence stereo image perception I found this bit interesting while rereading "Sound reproduction":

“In the era during which it was fashionable for the loudspeaker end of a control room (zones 1 and 2 in Figure 7.5) to be acoustically “dead,” and the opposite end (zone 3) to be “live,” I toured an elaborate recording complex that was nearing completion. I had not experienced one of these new rooms, and was given a demonstration. I bellied up to the center of the console and listened; something was wrong, the center image was strangely unclear at times. Looking around, I saw that the entire back wall (zone 3) was covered with beautiful and expensive wooden diffusers, vertically arranged to spread the sound horizontally. I asked for monophonic pink noise to be played, and from the stereo seat there was simply no center image—the sound spread across much of the space between the loudspeakers. Everybody could hear it; it was not subtle. This was obviously not a good thing. The movers were still on the premises, so we found some moving blankets and hung a couple of them in front of the diffusers. The center image snapped into place where it belonged. The problem: too much uncorrelated sound arriving from behind the listener, scrambling the information in the direct sound from the loudspeakers. Lesson: there can be too much of a good thing. The ETC probably looked just fine, though. Somebody measured but did not listen.”

Excerpt From
Sound Reproduction
Floyd E. Toole
He had also discussed this years before with some graphical representations (see page 23): http://www.wghwoodworking.com/audio/LoudspeakersandRoomsPt2.pdf
 

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ASW, localization, and loudness do not seem to correlate together in the work of Lokki et al, also the 2013 PhD thesis by William Evans. In the latter, there was an interesting preliminary investigation 4.2.7 Stage 3: Small-Scale Free-Roaming Evaluation: "Contrary to results from the formal listening tests in Denmark, Loudspeaker 3 (the Array), was unanimously perceived to be the most liked system when listeners were allowed to listen at any position in the room. Most feedback commented that the system exhibited a ‘consistency at all positions in the room’.
Sorry, I don't follow. "Correlate together"? Correlate to what? Are we still talking about time-intensity trading?
 
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Thanks, this is a little less vague. In general, from my personal perception, loudspeakers with narrow directivity patterns have been described by others to have a narrow sweet spot (extreme examples include planar dipolar speakers like Sanders and King Sound, also highly directive designs like JansZen), using descriptive terms like "vise-like" or "laser-thin" in terms of listening position. On the other hand, very widely directive speakers are often described as having a wide sweet spot, i.e. Roy Allison designs and innumerable others.

It increasingly seems to me that that this discussion, which has shifted from the original "directivity affects listener perception and other measurements beyond on-axis frequency response," may have broken down in multiple ways:

1. What should discussion of directivity mean when it comes to "controlled" or "constant," i.e. continuously changing or relatively flat DI, and if so, over what bandwidths? I had tried to introduce some discussion under point C here: https://www.audiosciencereview.com/...-on-readings-of-lokki-bech-toole-et-al.27540/
2. For off-center "sweet spot" discussions, what are the parameters used? I believe that Allison was focussed primarily on timbre. In the first paper cited by @markus , they seemed to have focussed on "wide-band signal" and image fusion. The second paper cited by @markus appeared to conflate multiple factors: "Some of the parameters considered for comparison were: sound localization, apparent source width ~ASW!, coloration, and loudness." In my opinion, "sweet spot" discussions may increasingly vary between "realistic timbre" vs "realistic imaging" at increasingly off-center positions, perhaps related to directivity, but research may help define this further. @markus seems to have declined to comment further on the papers that he himself cited. @markus , please refrain from citing papers if you do not discuss them further.
3. For central "sweet spot" discussions, again, what are the parameters used, and how might directivity affect that? See again here: https://www.tonmeister.ca/wordpress/2015/06/30/bo-tech-what-is-beam-width-control/. I believe that Geoff Martin's perceptions are compatible with those derived from Tapio Lokki's papers that I very crudely attempted to summarize and conflate above (#1).
For 2. and 3., there will always be a problem with evaluation based on listening, it will always be subjective, and for each property, there is a problem getting comparable data out of it.

The room is the easy part, acoustic properties of a room can be sufficiently described in a measurement, and different rooms can be compared. It is possible to find metrics that can tell how good a room is.

If a loudspeaker can be described in a similar way, so that a manageable set of measurements and data can describe how it sounds, then it would be possible to predict how one specific loudspeaker-room combination will sound. Then loudspeakers can be compared, from data and specifications alone.

Getting there must start by finding how measurable properties of the speaker relate to the sound we hear and experience. Some of this is already known. Building on what is known, and then doing experiments to find more of the missing parts, is the way forward.

How to quantify subjective impressions like clarity, holography, image rendering, soundstage depth. Not so easy. It is very difficult to establish a common reference point for such parameters. One day you hear something that surely must be a 10 for clarity, and then the next day you hear something that surprisingly is so much better, now the scale must be extended, this is a 12. And how do you describe how a 10 sounds like, so that a person that never heard your 10-system can use this same scale, to evaluate other systems and speakers.
 
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Added some analysis of sound field properties for direct and reflected sound:

Again, theory correlates well with observations. We see the direction of the sound field starts with direct sound dominating in the on-axis direction, and then the velocity drops off quickly, and reflections have no distinct direction.
 
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Also started the description of the 2-speakers in 2-rooms experiment:

Still believe a simple frequency response measurement can describe differences in sound between 2 speakers? Look at this frequency response:
fr 1_1smooth.png


Green lines form media room, red lines from Room2. Here we see room-placement makes for larger differences than between the 2 speakers. So they should sound the same. But they do not.

Also observe that there is no tilt, no "harman curve". Though the media room does have a slight increase downwards in frequency. This is because both those speakers have controlled directivity from around 100hz and up.

1/12 smoothing, because some of you will say the smoothing masks all differences:

fr 1_12smooth.png


Ok, one speaker actually has a smaller rise in level above 10K. Differences below 100Hz is caused by differences in calibration of the bass-system in the media room.
 
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"How to read measurements: 2 speakers in 2 rooms" has been moved to a separate thread.

The intention is to show how measurements can be interpreted to give information on sound quality of a system. It is possible, on a larger scale, to be able to see whether the room-speaker combination can be significantly improved, by doing changes, such as better room acoustic treatment.

Some general conclusions:
  • Better directivity reduces negative effects of room acoustics
  • Proper acoustic treatment is required to achieve the best result regardless of speaker
  • Speakers will still sound different in a good room
  • Measurements can show if there is potential for improvement with better room acoustic treatment
  • It is difficult to predict exactly how a system sounds from measurements
Loudspeaker directivity has a huge effect on sound presentation, and proper room acoustic treatment is mandatory for any speaker system to achieve top level performance.
 
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Continuing with 2 speakers in 2 rooms:

Radiation pattern can be shaped to improve early reflection attenuation and at the same time increase late reverb from the room.

Measurements show an interesting difference between the speakers:
  • Speaker A has better early decay attenuation, but increased late decay energy, compared to speaker B.
Speaker A left/first, in Media room, speaker B right/last, in media room:

decay2020 f205 moderatht.png
decay2020 f105 moderatht.png


We see the lines for speaker A is a little more spaced out early in time, and then compress later in time, compared to speaker B.

Spectrogram with 60dB scale and 200ms range, in Room2, show how speaker A has similar late energy compared to speaker B, and early decay is better for speaker A.

Spectrogram, 60dB scale, 200ms time range, Room2, speaker A left/first, speaker B right/last:
spect60db f205 room2.png
spect60db f105 room2.png


Trying to make this as simple and short as possible, and focus on one aspect only - how radiation pattern can affect early-to-late reflected energy.

One way to look at it, is that speaker A creates a sound similar to a larger room.
 
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