How to Choose a Loudspeaker -- What the Science Shows - Page 29 - AVS Forum | Home Theater Discussions And Reviews
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post #841 of 3756 Old 01-22-2019, 04:06 AM
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Originally Posted by spkr_diy View Post
Comparing X/Y and A/B techniques, one relies heavily on amplitude differences between the channels, while the other relies more heavily on phase (time of arrival at the mic capsules) differences. Do you get the impression there's any sort of consensus about which leads to a more accurate perception during reproduction?
I found ORTF (a near coincident technique) to give the most accurate soundstage representation. I did not worry about mono compatibility and found X/Y techniques to not sound as good. I experimented with angles between mic capsules (90 degrees and more) but felt having a bit of separation between them sounded better than having them coincident. ORTF (cardioid pattern with 110 degree angle and 17cm spacing) is similar to our head and the spacing between our ears. ORTF could only cover smaller ensembles though (solo piano, piano with voice, string quartets etc). For larger ensembles on bigger stages, I often used a Decca Tree or an ORTF pair center stage with flanking outriggers. Bob Fine (Mercury Living Presence) and Jack Renner (Telarc) used 3 omni mics across the front of orchestras, I did too. A/B technique (two spaced omnis) would often have the "hole in the middle" effect. Difficult to implement without a lot of experimentation on the spacing between the mics.

All of this is generalization, we often employed spot mics to enhance things that needed help.

I don't want to derail this thread with this sort of information, feel free to PM me if you have questions about recording techniques.

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post #842 of 3756 Old 01-22-2019, 05:30 AM
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This may not be the correct topic for the following question. But since it is related to science, and loudspeakers I figured I may as well ask it here since there is a wealth of knowledge in this thread already.

Last weekend I have moved to a new home, and will once again be using a spare room as a compact home theater which will also serve as a listening room. Since the room is compact and the loudspeaker will be close to the surrounding walls, achieving a sense of space will be a hurdle in two channel mode. Surround mixes can compensate for this to create a sense of envelopment, stereo however is 90% (if not more) of the source material for casual listening, and while upmixing can be satisfying, I would like to experiment a bit beyond that.

The blue surround lines represent an 'ideal' space in terms of space for a loudpeaker, added is a mirror image of the left loudspeaker which represents the first lateral reflection. The black surrounding line represents the actual room. Now, if we eliminate the first reflection using 4-5" of rockwool (or other material) visualed by the brown rectangle, and place a secondary left speaker at the 'ideal' reflection point of the virtual room (green rectangle), remix the left channel through a signal processor with the correct amount of delay (and perhaps add a negative high shelf filter as a representation of a normal reflected sound). My question regarding this is the following: what am I overlooking? Would this be a viable solution to create a 'wider' image, or will there be other effects, perhaps detrimental to the overall experience?

Thanks

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post #843 of 3756 Old 01-22-2019, 06:37 AM
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The research that I am aware of that relates to stereo imaging is in my book, especially Chapter 7.

If you hear something special in that respect it can only be that it is a fortuitous combination of the recording technique, your speakers, your room and your preferences. There are no standards for control room monitors and that is where the stereo soundstage is constructed by the recording engineer and musicians. The circle of confusion reigns supreme.

And, there is also the possibility that when the imaging is not special, for you, that someone back at the point of origin got what they wanted.

Think about it: control rooms tend to be on the acoustically "dead" side, and much monitoring is done using "near field" monitors three feet away. That means that the direct sound dominates what they hear and how they perceive what is going into the recording.

When we get to playback there are listeners who experience everything from dominant direct sound (directional speakers and/or dead acoustics) to reflection enriched sound fields generated by wide dispersion or even omni loudspeakers in reflective rooms. They all seem to have found some form of happiness. The first extreme yields a "tight" soundstage and pinpoint localizations, the second yields a more spacious soundstage and slightly fuzzy images. Humans are wonderfully adaptive - a very good thing!!!

I would like to think that whatever ones preferences with respect to soundstage and imaging, accurate, timbrally neutral, loudspeakers are a necessary starting point.

Phantom imaging is used extensively in 2-channel recordings to place sonic images between the loudspeakers. Some speaker pairs do a better job than others in replicating phantom images. What part of the spinorama, which is performed with just one speaker, elucidates a speaker pair's ability to accurately places those phantom images in space? Secondly, how do the trained listeners, when listening to a single speaker and a monophonic source, evaluate this phenomenon when making their preference evaluations?



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post #844 of 3756 Old 01-22-2019, 07:06 AM
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Originally Posted by craig john View Post
Phantom imaging is used extensively in 2-channel recordings to place sonic images between the loudspeakers. Some speaker pairs do a better job than others in replicating phantom images. What part of the spinorama, which is performed with just one speaker, elucidates a speaker pair's ability to accurately places those phantom images in space? Secondly, how do the trained listeners, when listening to a single speaker and a monophonic source, evaluate this phenomenon when making their preference evaluations?



Craig

Good question.


None of my other speakers (or any others I've ever heard) provides a sonic image as realistically spacious and 3 dimensional as the Omnidirectional speakers I own. But I'm wondering if this is an aspect I could pick up on an only mono test.
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post #845 of 3756 Old 01-22-2019, 07:21 AM
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Originally Posted by craig john View Post
Phantom imaging is used extensively in 2-channel recordings to place sonic images between the loudspeakers. Some speaker pairs do a better job than others in replicating phantom images. What part of the spinorama, which is performed with just one speaker, elucidates a speaker pair's ability to accurately places those phantom images in space? Secondly, how do the trained listeners, when listening to a single speaker and a monophonic source, evaluate this phenomenon when making their preference evaluations?



Craig
The first time I experienced a clear phantom image and a very vivid sound stage was with KEF LS50 (when positioned properly in a room). If I move the speaker positioning I reduce or lose this effect.

I also feel that LS50 usually disappear in the room. By that I mean, if you close your eyes, you can not locate their position in the room.

Are these two effects (phantom imaging and disappearing) related to each other?

Thanks



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post #846 of 3756 Old 01-22-2019, 07:37 AM
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Originally Posted by TimVG View Post
This may not be the correct topic for the following question. But since it is related to science, and loudspeakers I figured I may as well ask it here since there is a wealth of knowledge in this thread already.

Last weekend I have moved to a new home, and will once again be using a spare room as a compact home theater which will also serve as a listening room. Since the room is compact and the loudspeaker will be close to the surrounding walls, achieving a sense of space will be a hurdle in two channel mode. Surround mixes can compensate for this to create a sense of envelopment, stereo however is 90% (if not more) of the source material for casual listening, and while upmixing can be satisfying, I would like to experiment a bit beyond that.

The blue surround lines represent an 'ideal' space in terms of space for a loudpeaker, added is a mirror image of the left loudspeaker which represents the first lateral reflection. The black surrounding line represents the actual room. Now, if we eliminate the first reflection using 4-5" of rockwool (or other material) visualed by the brown rectangle, and place a secondary left speaker at the 'ideal' reflection point of the virtual room (green rectangle), remix the left channel through a signal processor with the correct amount of delay (and perhaps add a negative high shelf filter as a representation of a normal reflected sound). My question regarding this is the following: what am I overlooking? Would this be a viable solution to create a 'wider' image, or will there be other effects, perhaps detrimental to the overall experience?

Thanks

I was pondering about a similar setup with ambience channels but with centre (and subs so 5.1 stereo ) with some good upmixing processor


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post #847 of 3756 Old 01-22-2019, 07:46 AM
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I’d imagine the wallet effect would be detrimental. Lol

Posts like these make me glad I rent/purchase my living spaces with the intention of having an audio/media space/room. It cuts down on my options, but at the end of the day, as long as I have a decent media area and workout space in my place, I’m a happy cat...

I’m thinking the bass ranges would be quite difficult to work with if a speaker is that close to a wall. While it looks like the wall treatment would help with directional sound frequencies, I’d think the wave-like frequencies would be difficult to work with without heavy digital correction. You’d likely be maxing out some room modes.

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post #848 of 3756 Old 01-22-2019, 08:02 AM
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Originally Posted by craig john View Post
Phantom imaging is used extensively in 2-channel recordings to place sonic images between the loudspeakers. Some speaker pairs do a better job than others in replicating phantom images. What part of the spinorama, which is performed with just one speaker, elucidates a speaker pair's ability to accurately places those phantom images in space? Secondly, how do the trained listeners, when listening to a single speaker and a monophonic source, evaluate this phenomenon when making their preference evaluations?



Craig
Imaging of all sorts, apart from the recording, depends on the loudspeakers' directivity (reflected sounds) and their relative position to the walls in the room, in relation to the listening spot. The directivity index will give you an idea of what can potentially happen in a room (in terms of how strong the reflected sounds will be), but the room and listening position are crucial.
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post #849 of 3756 Old 01-22-2019, 08:05 AM
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I’d imagine the wallet effect would be detrimental. Lol

Posts like these make me glad I rent/purchase my living spaces with the intention of having an audio/media space/room. It cuts down on my options, but at the end of the day, as long as I have a decent media area and workout space in my place, I’m a happy cat...

I’m thinking the bass ranges would be quite difficult to work with if a speaker is that close to a wall. While it looks like the wall treatment would help with directional sound frequencies, I’d think the wave-like frequencies would be difficult to work with without heavy digital correction. You’d likely be maxing out some room modes.
Speakers will be corrected below the transition frequency, and low bass will be re-routed to multiple subwoofers - I'm aware of how to deal with those problems, but thanks anyhow.
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post #850 of 3756 Old 01-22-2019, 08:07 AM
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Speakers will be corrected below the transition frequency, and low bass will be re-routed to multiple subwoofers - I'm aware of how to deal with those problems, but thanks anyhow.
You’re very welcome!
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post #851 of 3756 Old 01-22-2019, 08:10 AM
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I was pondering about a similar setup with ambience channels but with centre (and subs so 5.1 stereo ) with some good upmixing processor
Yes, I would also be emplying a full surround setup - this would be merely to enhance stereo listening in a non-ideal environment. I know some processors have built in support for what I'm hinting at above, but I wish to continue using my current 7.1 Anthem processor. I would be routing the L/R pre-outs to a seperate processor.

I'm still in the concept phase so I'm curious about what others think of this idea. If there's a valid, scientific, reason why I shouldn't be doing this, I'll of course save myself the trouble to buy two extra loudspeakers :-)
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post #852 of 3756 Old 01-22-2019, 08:10 AM
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Originally Posted by craig john View Post
Phantom imaging is used extensively in 2-channel recordings to place sonic images between the loudspeakers. Some speaker pairs do a better job than others in creating phantom images. What part of the spinorama, which is performed with just one speaker, elucidates a speaker pair's ability to accurately create those phantom images in space? Secondly, how do the trained listeners, when listening to a single speaker and a monophonic source, evaluate this phenomenon when making their preference evaluations? Craig
Phantom images are CREATED by using two loudspeakers when listening to STEREO material that was recorded with the intention of using two speakers to create phantom images. For the effect to work properly, you must setup your speakers and listening position correctly by creating an equilateral triangle and sitting at the apex.

Spinorama does not show any data related to stereo and how phantom images are created. The listeners in the tests in the MLL are not evaluating any aspect of stereo playback.
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post #853 of 3756 Old 01-22-2019, 08:46 AM
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Originally Posted by TimVG View Post
Imaging of all sorts, apart from the recording, depends on the loudspeakers' directivity (reflected sounds) and their relative position to the walls in the room, in relation to the listening spot. The directivity index will give you an idea of what can potentially happen in a room (in terms of how strong the reflected sounds will be), but the room and listening position are crucial.
I worked in treated and untreated recording control rooms. Phantom images will be created in a proper setup (listening at the apex of an equilateral triangle) for a listener by any pair of loudspeakers. You can be in a dead or live room, in the nearfield or far field and you will hear phantom imaging occur with stereo material. Phantom imaging is best demonstrated by recording with natural stereo recording techniques, a stereo pair of mics picking up an acoustic event in a room. Pop music recorded with just L/C/R panning will not have much imaging going on. Phantom center, hard left and right depending on what stereo "tricks" are used by the engineer. Recordings made using pan pots to place instruments elsewhere in the stereo panorama (anywhere but L/C/R) are more interesting IMO. When I mixed pop/rock material for recording or even live sound with stereo PA systems, I used pan pot placement to give instruments more space to live in the mix and make the sound field more interesting. Mixing in stereo for live sound is tricky because you have to keep audience coverage in mind, many live sound engineers work in mono for that reason. Hearing correct stereo in live sound only happens for seats centered on the stage and system. I tried to locate the mixing console in a good location (center) so I could enjoy a stereo mix and use of stereo effects.

How one hears those phantom images will be affected to some degree by the directivity of the loudspeaker and the room acoustics, but mostly it is related to sitting at the apex of the equilateral triangle. If you are center and too close to the speakers, the image will be exaggerated. If you are center and too far back, the accuracy of the image will be collapsed (degrees of LC and RC will be less noticeable). If you are off center, imaging is no longer accurate, you have to be centered between the speakers to hear a phantom center image centered between the speakers.

I spent many hours sitting at mixing consoles recording and mixing music. I learned a lot by summing to mono and inverting polarity on the stereo mix to hear what "in phase and out of phase" sounds like. Recording a drum set with a lot of microphones requires checking to see how those mics combine to avoid phase cancellation.

I think we are getting off topic with this subject in this thread. Maybe time for a new thread if it is of interest?
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post #854 of 3756 Old 01-22-2019, 08:51 AM
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I worked in treated and untreated recording control rooms. Phantom images will be created in a proper setup (listening at the apex of an equilateral triangle) for a listener by any pair of loudspeakers. You can be in a dead or live room, in the nearfield or far field and you will hear phantom imaging occur with stereo material. Phantom imaging is best demonstrated by recording with natural stereo recording techniques, a stereo pair of mics picking up an acoustic event in a room. Pop music recorded with just L/C/R panning will not have much imaging going on. Phantom center, hard left and right depending on what stereo "tricks" are used by the engineer. Recordings made using pan pots to place instruments elsewhere in the stereo panorama (anywhere but L/C/R) are more interesting IMO. When I mixed pop/rock material for recording or even live sound with stereo PA systems, I used pan pot placement to give instruments more space to live in the mix and make the sound field more interesting. Mixing in stereo for live sound is tricky because you have to keep audience coverage in mind, many live sound engineers work in mono for that reason. Hearing correct stereo in live sound only happens for seats centered on the stage and system. I tried to locate the mixing console in a good location (center) so I could enjoy a stereo mix and use of stereo effects.

How one hears those phantom images will be affected to some degree by the directivity of the loudspeaker and the room acoustics, but mostly it is related to sitting at the apex of the equilateral triangle. If you are center and too close to the speakers, the image will be exaggerated. If you are center and too far back, the accuracy of the image will be collapsed (degrees of LC and RC will be less noticeable). If you are off center, imaging is no longer accurate, you have to be centered between the speakers to hear a phantom center image centered between the speakers.

I spent many hours sitting at mixing consoles recording and mixing music. I learned a lot by summing to mono and inverting polarity on the stereo mix to hear what "in phase and out of phase" sounds like. Recording a drum set with a lot of microphones requires checking to see how those mics combine to avoid phase cancellation.

I think we are getting off topic with this subject in this thread. Maybe time for a new thread if it is of interest?
I misread the original question and was talking about imaging/spaciousness in general - not specifically about phantom images. But thanks for the generous reply. I'd still like my above question discussed in here since it relates to choosing a loudspeaker and science :-)

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post #855 of 3756 Old 01-22-2019, 09:06 AM
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I misread the original question and was talking about imaging/spaciousness in general - not specifically about phantom images. But thanks for the generous reply. I'd still like my above question discussed in here since it relates to choosing a loudspeaker and science :-)

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THANK YOU !!! Rex's number 3 and 6 on his (corrected) list of a few months ago. It's by far the number one reason I choose what I choose.

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post #856 of 3756 Old 01-22-2019, 09:16 AM
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THANK YOU !!! Rex's number 3 and 6 on his (corrected) list of a few months ago. It's by far the number one reason I choose what I choose.
Well it's not magic in any case, an illusion indeed at best. Program material aside (Rex A. gave a very good overview on that). It's simply a matter of the sound that leaves a loudspeaker (in all directions) and reflects back through the room to our ears. My question above is related to the possibility of achieving this sense of spaciousness, which would be the result of reflections, through a secondary set of 'front wide' speakers, in non-ideal rooms.
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post #857 of 3756 Old 01-22-2019, 09:17 AM
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Originally Posted by craig john View Post
Phantom imaging is used extensively in 2-channel recordings to place sonic images between the loudspeakers. Some speaker pairs do a better job than others in replicating phantom images. What part of the spinorama, which is performed with just one speaker, elucidates a speaker pair's ability to accurately places those phantom images in space? Secondly, how do the trained listeners, when listening to a single speaker and a monophonic source, evaluate this phenomenon when making their preference evaluations?
As TimVG has said, the directivity index is a powerful clue as to the amount of indirect, reflected, sound there will be. The more there is the more "air" there is likely to be around images and the less focused will be the images themselves. Some people prefer one, some the other, and preference will always be influenced by program and how it was recorded. Rex Anderson has had things to say about this in this forum.

The precision of the images depends on the sounds from both loudspeakers being identical. Mismatched loudspeakers will obviously do poorly, and asymmetry in positioning with respect to adjacent boundaries will add problems; more with widely dispersing loudspeakers than with those delivering more dominant direct sound.

Chapter 7 in my book includes much discussion about these factors.

In mono double-blind tests it is found that the best loudspeakers seem to "disappear" behind the screen. They do not draw attention to themselves, meaning that both real (hard panned L & R) and phantom images have a better chance of being persuasive. This "disappearance" is primarily the result of loudspeakers not adding resonances of their own to the collections of resonances that comprise voices and musical instruments that entertain us - in a word: neutrality. Neutrality is predictable from spinorama data.
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post #858 of 3756 Old 01-22-2019, 09:26 AM
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Well it's not magic in any case, an illusion indeed at best. Program material aside (Rex A. gave a very good overview on that). It's simply a matter of the sound that leaves a loudspeaker (in all directions) and reflects back through the room to our ears. My question above is related to the possibility of achieving this sense of spaciousness, which would be the result of reflections, through a secondary set of 'front wide' speakers, in non-ideal rooms.
"Well it's not magic in any case, an illusion indeed at best"

Not magic perse, but an illusion as all of it is an illusion of the 'real' event. And yes, of course it's in the recording to a varying degree, but the speaker's ability to re-produce it varies. Some brands/designs better than others.

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"Well it's not magic in any case, an illusion indeed at best"



Not magic perse, but an illusion as all of it is an illusion of the 'real' event. And yes, of course it's in the recording to a varying degree, but the speaker's ability to reproduce it varies. Some brands/designs better than others.
And that is the point. How to choose speakers based on Spinorama data that will exhibut this property?

Someone said directionality. How much? Is there an optimum amount or is it more the better?

Lack of speaker resonance makes sense.

What other properties contribute to phantom image stability and "disappearing" (other than what has already been mentioned)?

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post #860 of 3756 Old 01-22-2019, 09:40 AM
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And that is the point. How to choose speakers based on Spinorama data that will exhibut this property?

Someone said directionality. How much? Is there an optimum amount or is it more the better?

Lack of speaker resonance makes sense.

What other properties contribute to phantom image stability and "disappearing" (other than what has already been mentioned)?

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Just to be clear, as is the case with Tim, I'm not talking about the 'phantom image' as in phantom center image. I'm talking about all of the 'three dimensional' voodoo, handwaving stuff I'm always talking about.

Is it controlling dispersion to reduce, but not eliminate, crosstalk? Some notice that the 'illusion' seems to work better with the equipment rack in the middle to reduce crosstalk.

And is it the physical center of the room or the acoustic center?

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@SouthernCA

You may simply want to read a copy of Floyd Toole's book which answers many of these questions. It's a summary of many years of research in easy-to-follow language. It's not that expensive.. You can't expect the man to keep answering things literally explained in detail in his book for sake of convenience. The answer is that it depends. There is preference, application and space to consider. It's easier to focus on finding a neutral loudspeaker to start, than to worry about absolute directivity as a primary factor.
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Originally Posted by Scotth3886 View Post
Just to be clear, as is the case with Tim, I'm not talking about the 'phantom image' as in phantom center image. I'm talking about all of the 'three dimensional' voodoo, handwaving stuff I'm always talking about.

Is it controlling dispersion to reduce, but not eliminate, crosstalk? Some notice that the 'illusion' seems to work better with the equipment rack in the middle to reduce crosstalk.

And is it the physical center of the room or the acoustic center?
Crosstalk is a different subject. It's good to reflect on the original situation that the source material was conceived in. For stereo recordings, there is a good chance that some form of compensation is already present in the recording.

It's also the reason that content mixed using a dedicated center channel translates ever so poorly when played back on only two loudspeakers.
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post #863 of 3756 Old 01-22-2019, 09:51 AM
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Originally Posted by TimVG View Post
This may not be the correct topic for the following question. But since it is related to science, and loudspeakers I figured I may as well ask it here since there is a wealth of knowledge in this thread already.

Last weekend I have moved to a new home, and will once again be using a spare room as a compact home theater which will also serve as a listening room. Since the room is compact and the loudspeaker will be close to the surrounding walls, achieving a sense of space will be a hurdle in two channel mode. Surround mixes can compensate for this to create a sense of envelopment, stereo however is 90% (if not more) of the source material for casual listening, and while upmixing can be satisfying, I would like to experiment a bit beyond that.

The blue surround lines represent an 'ideal' space in terms of space for a loudpeaker, added is a mirror image of the left loudspeaker which represents the first lateral reflection. The black surrounding line represents the actual room. Now, if we eliminate the first reflection using 4-5" of rockwool (or other material) visualed by the brown rectangle, and place a secondary left speaker at the 'ideal' reflection point of the virtual room (green rectangle), remix the left channel through a signal processor with the correct amount of delay (and perhaps add a negative high shelf filter as a representation of a normal reflected sound). My question regarding this is the following: what am I overlooking? Would this be a viable solution to create a 'wider' image, or will there be other effects, perhaps detrimental to the overall experience?

Thanks

IMHO you can't get there from here. You are on your way to a surround sound system, so why not finish the job. The spaciousness you seek ultimately cannot be created by in-room reflections, certainly not in such a small room. My solution for classical music, at one time in my life, is shown in Figure 7.19 in my book. It was great - almost omni speakers in a very large well diffused room. But your small space needs perceptual enlargement that I think is possible only with multichannel upmixing. You might be surprised at how good it can sound. . It is adjustable and can be turned off. Auro3D can be pleasant.
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post #864 of 3756 Old 01-22-2019, 09:51 AM
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Quote:
Originally Posted by TimVG View Post
Crosstalk is a different subject. It's good to reflect on the original situation that the source material was conceived in. For stereo recordings, there is a good chance that some form of compensation is already present in the recording.

It's also the reason that content mixed using a dedicated center channel translates ever so poorly when played back on only two loudspeakers.
We disagree, but that's not going to be a shock.

"Crosstalk is a different subject"

Different subject, yes, but may be very germane to reproducing soundstage as I want it presented to me in-room.
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post #865 of 3756 Old 01-22-2019, 09:58 AM
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Originally Posted by torii View Post
if people dont like a 2k+ bookshelve its cause they picky/have a sound they after...I havent heard a poor bookshelf yet at 2 grand
Zu Audio might be able to help you out. I haven't heard them, but looking at the measurements in several reviews and odd design choices, I really to care to even give them a try.
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post #866 of 3756 Old 01-22-2019, 10:02 AM
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Just curious : What would be downside of using Salons wherever M2s are used ? (Except maybe very large rooms)

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post #867 of 3756 Old 01-22-2019, 10:11 AM
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Dutch and Dutch 8C active speakers seem to be interesting solution to individual room response, albeit at a fairly hefty price.
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post #868 of 3756 Old 01-22-2019, 10:27 AM
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Originally Posted by Floyd Toole View Post
I don't think there is a debate to be had with respect to sealed vs. vented designs. Nowadays it is all predictable from computer modeling programs. The amount of time-domain misbehavior between them is below the threshold of detectability, BUT, the differences in amplitude response is not. Even my original research published in 1985-86 showed that bass extension, by itself, was correlated with overall sound quality ratings. The lower roll-off rate of closed boxes is an advantage.

A will assume that you have not read my book, because your concerns/interests are very likely addressed there - Chapters 8 and 9. Given the powerful modes in small rooms the real challenge is allowing the subwoofer to communicate to the listener (preferably more than one) without both amplitude and time-domain corruptions that far exceed those in subwoofers themselves - reflex or sealed, passive, active or servo.

I suspect the only place where one could conduct meaningful comparisons of the factors you list is outdoors - avoiding the corrupting listening room. The main purpose of servo woofers is to reduce non-linear distortions at high sound levels. The "impulse response" of subs is determined by their frequency responses (they are minimum phase devices) and that can be changed with equalization whether external to the sub or internal. As I said in an earlier post (#832), when the air flow in reflex ports becomes turbulent, the design is corrupted. Closed box subs do not have this problem, but producing the same quantity of bass requires greater diaphragm excursions - risking non-linear distortion - which was the motivation for servos many years ago - as I recall. Nowadays, much improved subwoofer motor and suspension designs are adequate for most needs. Non-linear distortions at low frequencies are difficult to hear because of simultaneous masking.

FYI, significant recent research has shown that humans are remarkably tolerant of low-frequency ringing. The dominant factor is steady-state frequency response at the listening location - See Section 8.3 "Do we hear the spectral bump, the temporal ringing, or both?"

A single subwoofer has a big job cut out for itself - room modes can only be attenuated by optimized parametric equalization, and that only works for a single mic location. Automated EQ schemes may or may not provide optimum solutions. The most practical solutions, from the research I know of employ multiple subwoofers, usually two or four. Because of the physics of small rooms at low frequencies, there is a substantial overall efficiency gain with multiple subs, meaning that smaller subs can be used; an advantage not everyone is aware of. After proper installation of a multiple sub scheme, many of the room modes cease to be audible problems, simple EQ is adequate, and multiple listeners get to hear similar and similarly good bass. It is eerie to walk around a room and the bass is constant, tight and deep.

As for a single setting of bass level being desirable, it is, but that can only happen in an ideal world where professionals and consumers subscribe to the same definitive performance standards. I call it the circle of confusion; it's in the book, and I cannot see it going away. Pity.
Dr. Toole, I found this post very informative. However, I don't think I understand everything. Would you mind elaborating on a few of these points you made?

You mentioned that the difference in amplitude response between sealed and ported designs is detectable. Could you elaborate what this means? I don't think I understand.

You also mentioned the the lower roll off rate of sealed designs is an advantage. Can you explain why?

If a ported sub is tuned below 20hz (the threshold of audibility) would the lower roll off rate of a sealed design still be an advantage?
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post #869 of 3756 Old 01-22-2019, 11:51 AM
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Originally Posted by buckchester View Post
Dr. Toole, I found this post very informative. However, I don't think I understand everything. Would you mind elaborating on a few of these points you made?

You mentioned that the difference in amplitude response between sealed and ported designs is detectable. Could you elaborate what this means? I don't think I understand.

You also mentioned the the lower roll off rate of sealed designs is an advantage. Can you explain why?

If a ported sub is tuned below 20hz (the threshold of audibility) would the lower roll off rate of a sealed design still be an advantage?
There are very likely other internet sites and forums that focus on this topic. There are certainly large sections of books that do - but not mine . If you look at the comparative frequency responses of the designs, and the variations possible by playing with the driver and box parameters it is easy to see potentially audible differences. However, as I have said before, room modes swamp a lot of this if they are not "handled". Chapter 8.

Reflex designs have a range of performance options with respect to resonance and rolloff frequency, and Q (damping). The attenuation in rolloff is 12 dB/oct. You suggest that so long as the rolloff happens below 20 Hz all should be well. But 20 Hz is not the limit of hearing, it is around the lowest frequency we hear as being tonal, having pitch. Below that bass exists as a pressure, whole body, experience - a compression wave in an explosion for example. If it is there you know it, and it is nice. Movie bass in cinemas is almost always "booms", loud to be sure, but in my experience often with pitch. Through a system that extends persuasively to and below 20 Hz explosions and gunshots are a different more credible experience - no pitch. This can be achieved with reflex systems tuned very low, or in small closed box systems with large amps. In multi-sub installations that offer efficiency gains those are logical choices. But, it is a choice.

My early research showed a correlation between low-frequency cutoff and sound quality ratings. There was no trend based on - 3dB frequencies, a little trend based on -5 dB , and a persuasive trend based on the - 10 dB level - obviously adjacent boundary room gain was involved. See Figure 5.3 in my book. Olive's subsequent work showed that bass extension and smoothness accounted for about 30% of the factor weighting in overall sound quality judgments - See Section 5.7 in my book. Sealed boxes that roll off at - 6 dB/oct. have an advantage, especially if size is a consideration.
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post #870 of 3756 Old 01-22-2019, 01:01 PM
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Originally Posted by Floyd Toole View Post
IMHO you can't get there from here. You are on your way to a surround sound system, so why not finish the job. The spaciousness you seek ultimately cannot be created by in-room reflections, certainly not in such a small room. My solution for classical music, at one time in my life, is shown in Figure 7.19 in my book. It was great - almost omni speakers in a very large well diffused room. But your small space needs perceptual enlargement that I think is possible only with multichannel upmixing. You might be surprised at how good it can sound. . It is adjustable and can be turned off. Auro3D can be pleasant.
Auro3D is what I had in mind as the end goal actually - I found it to be very nice for music and movies alike, from the demos I experienced at their headquarters, only a couple of hours drive from here. The idea above was a concept I had in mind for DIY upmixing as a new processor (which auro 3D would require) that is qualitatively as good as my Anthrm is going to set me back a good amount of money
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