Imaging and SoundStage

fas42

Addicted To Best
Jan 8, 2011
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Let me make sure I understand what some folks are saying here. Let's say the voice is mixed to dead center and you're sitting at the perfect sweet spot in a rolling chair. You roll to the left until you are nearly in front of the speaker...the voice image remains dead center, so it is not to your right, between the speakers? Do I have that right?

Tim
From my point of view that is correct, the image when you are almost in front of the left speaker will appear then to be just at the edge of the speaker. The last step is rolling a bit further, to the left of the speaker, the image should follow across and beyond the left speaker and still be directly in front of you as you stare directly forward.

Frank
 

DonH50

Member Sponsor & WBF Technical Expert
Jun 22, 2010
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Our definitions differ, Tim. In your example, if I roll my chair to the left, the voice will stay centered, and thus now sounds on my right as it should. IOW, it should be the same as if somebody was standing there talking. Does that mean I am no longer in the sweet spot? If I understand your definition, I am not. My definition would say if the the sound has not changed significantly, no funny artifacts or big changes in timbre, then I am still in the sweet spot. I realize that is very subjective; I tend to think of it as a "practical" definition. That "perfect" sweet spot you are defining, taken to extremes, would be a single point in space, yes? I would not argue with your definition, but compromise mine to allow for what I consider a more reasonable range of sweet spot. So what is my range, a few inches, couple of feet, wall-to-wall? I don't know, depends on the system and room, and probably my mood and phase of the moon. I can make all sorts of measurements and perhaps bound the problem, just haven't had the inclination. This is most decidedly defined by the listener IMO. It would be interesting to run controlled tests and define some standards...

Not sure I have made myself clear... - Don
 

Phelonious Ponk

New Member
Jun 30, 2010
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Our definitions differ, Tim. In your example, if I roll my chair to the left, the voice will stay centered, and thus now sounds on my right as it should. IOW, it should be the same as if somebody was standing there talking. Does that mean I am no longer in the sweet spot? If I understand your definition, I am not. My definition would say if the the sound has not changed significantly, no funny artifacts or big changes in timbre, then I am still in the sweet spot. I realize that is very subjective; I tend to think of it as a "practical" definition. That "perfect" sweet spot you are defining, taken to extremes, would be a single point in space, yes? I would not argue with your definition, but compromise mine to allow for what I consider a more reasonable range of sweet spot. So what is my range, a few inches, couple of feet, wall-to-wall? I don't know, depends on the system and room, and probably my mood and phase of the moon. I can make all sorts of measurements and perhaps bound the problem, just haven't had the inclination. This is most decidedly defined by the listener IMO. It would be interesting to run controlled tests and define some standards...

Not sure I have made myself clear... - Don

You expressed yourself just fine. I think perhaps my view of the "sweet spot" is heavily influenced by my near-field listening.

Tim
 

kach22i

WBF Founding Member
Apr 21, 2010
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First project. Get used to seeing the image.
In the past couple of weeks I've had the opportunity to listen to live outdoor amplified music, Ann Arbor is a great place for this in the summer.

There is no imaging in the stereophonic or mono playback sense.

Live music does not "pinpoint", not even with the clash of the drum kit's cymbals. You would have to be very near or stage with the band for even partial effect of that sort of localization to happen.

I'm not in an anti-imaging camp, but I do think its an artificial sweetener at times.

I have not read all five pages of this thread, but will attempt to do so.

Carry on.
 

Phelonious Ponk

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Jun 30, 2010
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In the past couple of weeks I've had the opportunity to listen to live outdoor amplified music, Ann Arbor is a great place for this in the summer.

There is no imaging in the stereophonic or mono playback sense.

Live music does not "pinpoint", not even with the clash of the drum kit's cymbals. You would have to be very near or stage with the band for even partial effect of that sort of localization to happen.

I'm not in an anti-imaging camp, but I do think its an artificial sweetener at times.

I have not read all five pages of this thread, but will attempt to do so.

Carry on.

You've got it exactly right, George. There is no pinpoint imaging in a live concert, particularly an amplified one. It is a part of the recording, not a live event. I find it a useful substitute for visual cues that are not there when listening to recorded music, but mostly I just find it fun to listen to, and as I've said here before, I'm making no attempt to reproduce a live event that does not exist, I'm trying to reproduce the recording.

Tim
 

kach22i

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Apr 21, 2010
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Of course, if the soundboard operator did mix the instruments inputs and distribute them among the speakers like they do in a studio, you would get "some" of that imaging effect...i

So part of the issue with these outdoor live amplified Rock music events is that the instrument feeds are getting all mixed together and come out the same PA speakers?

That would explain a lot.

At the one event I purchase their CD, by Laith Al-Saadi. It's been two weeks and I have not even opened it. Guess I'm in for a treat if it stands a chance of sounding better than live.:cool:
 

Rutgar

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Apr 20, 2010
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There is no imaging in the stereophonic or mono playback sense.

Live music does not "pinpoint", not even with the clash of the drum kit's cymbals. You would have to be very near or stage with the band for even partial effect of that sort of localization to happen.

I'm not in an anti-imaging camp, but I do think its an artificial sweetener at times.


Carry on.

And a pro-audio system being mixed by an engineer isn't artificial?

If you didn't hear any imaging, then I'd have to say that good imaging is just 'one' reason why high-end audio equipment is better that 'pro-audio' equipment for music playback. Whether the source is live musicians being mic'd, or recorded music playback.
 

Phelonious Ponk

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Jun 30, 2010
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And a pro-audio system being mixed by an engineer isn't artificial?

If you didn't hear any imaging, then I'd have to say that good imaging is just 'one' reason why high-end audio equipment is better that 'pro-audio' equipment for music playback. Whether the source is live musicians being mic'd, or recorded music playback.

I'll take good studio monitoring equipment over "high-end" for precise imaging every time. Pro audio for live concerts? A different animal altogether. But Katch is right. Pinpoint imaging comes from recording. It rarely exists in live venues and seldom exists on playback systems in big rooms. It's not natural. But it sure is fun.

Tim
 

Art Noxon

WBF Technical Expert (Room Acoustics)
Mar 29, 2011
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Eugene, OR
www.acousticsciences.com
Yes, we hit a dead zone again....overwhelmed, engulfed by the endless, tedious and un interesting yet demanding needs of business. I am sorry to have disappeared. Going to Cal Audio Show in SF this weekend, giving a talk each of the 3 days between 10 and 11 am. I’ll cover the elements of setting a room up, as outlined in the article I wrote for Harry Pearson’s new edition of his book. No notes, no powerpoint, just winging it, my favorite topic... The following was written in response to posts at the end of June. I wanted to fix it up, maybe expand here ant there a little and here we are 2 weeks later and nothing to show. I needed to check out panning details and never got back on track.

============================================

Hello,

Here we are visiting and wandering through stereoland.

I’m glad the gentle movement of the head feels like it might hold some validity. I’d like to hear about other people experiences with rigid fixed staring vs grooving in the dark and listening.
Image panning

Yes, amplitude panning is more common, it’s what normal engineers and normal mixing boards pan pots use. Time delay panning (precedence effect) can be used, but there are no time delay pan pots. Delay panning means a mono signal is time delayed to one speaker compared to the other. The first signal to reach the ears will be the direct, not the tome delayed signal. The ear thinks that the image is located away from the time delayed speaker and towards the not time delayed speaker. Lots of psychoacoustic testing has been done with the combination of delay and amplitude panning. See Google: Precedence Effect Acoustics

Sometimes people refer to phase and delay panning as one and the same. Let’s get our vocabulary adjusted here so we don’t get into trouble. Phase and delay at some particular frequency are truly two version of one idea. However in music, we have a complexity of tones changing all the time. A fixed time delay will result in a wild shifting of phase, depending on the frequency. Generally it is best to depend on the idea that phase and time delay are very separate things. For example:

A 2ms delay will be a 33 degree phase shift for a tone whose period is 10ms (100 Hz) ms and a 16 degree phase shift for a tone whose period is 20ms (50 Hz) . A fixed time delay has got phase moving all over the place. A 10 ms delay for a 5ms period (200 Hz) is a 760 degree phase shift. Enough of this...

Speaking of phase. We also know there is such a thing as phase reversal. You start with a mono signal set to image dead center. You reverse polarity of the two channels and you have the experience of listening to reversed phase LR signals. It’s strange. Not so strange is to leave say 80% of the mono mix in phase and take 20% of it and reverse the phase and add everything back together. Now you get a central image with a tinge of eeriness, a sense of lateral presence has been added to the direct signal. This is something like what recording engineers do once in a while. I invite our studio people in Seattle or other studio people to share some experiences with their techniques for mixing to get image positions, stage width and lateral presence.

A little of something is interesting, but too much..... is too much. Here’s some questions you can only answer if you’ve actually been there.

1) How do you FEEL when you walk in to a room where the speakers are setup accidentally reversed polarity, but you don’t know it yet?

2) Once you know it, what do you hear? There is a difference between what you feel and what you hear.

3) What do you hear if some bozo at the factory reversed polarity of the woofer but the mids and tweets are in phase?

OK, we have amplitude panning, delay panning and we also can add a tincture of reversed phase to get spaciousness, ambience, lateral presence as well as side localization of images.

Some discussion has occurred, starting with image stability or movement while moving sideways into a deep excursion into concert sound system imaging.

The sonic stage follows the listener as they move their head to the right or left. It might not move as much as the person moves but it does move. Moving the listening position sideways, until it is straight out from one speaker does not mean the stage collapses onto that speaker. It’s a blend of both L and R signals at any position, and each position experiences its own unique amplitude and delay panning effect. Delay panning simply corresponds to the path difference between the listener and each speaker. However, the directivity of the speaker means the amplitude changes with the angle we have to the speaker. Stage and imaging is about treble information. That means the beam directivity of the mid driver and tweeters as well as the shaping of the front baffle matters with respect to lateral image stability. It is because the loudness changes with angle, resulting in an amplitude panning effect being added to the geometric delay pan effect.

I just have to say....what the heck is all this wisdom floating through the air about the subject of ...the house mix at a concert, for the live audience...sounding better or worse than ... the album mix done in the sound truck, for the concert CD? My experience, though limited, is that these two sonic imaging and sound stage experiences have little to nothing do with each other. This conversation is about dealing with the audiophile soundstage and the images within it.

And after all this we still are not talking about imaging and sound stage very much. Lets get back to trying to map out your soundstage. We are also curious about stage depth and layering. How to make a great audio party effect, the sonic zoom lens, which is an audio parlor trick that I won’t tell about until we get past our homework on stage width, depth, illumination mapping and imaging detail such as size, brightness, position, variation with frequency and things like that.


By the way...
I’m not following, and excuse me for my ignorance...but what is the “left ten” and the “right ten”. Sounds like one of the speaker wires? I want to track your fixed center image experience. Please explain.

As to how is it that an electronically fixed image position changes, from day to day. The odds are that it’s the human that changed from day to day, not the electronic balance. We have a -10 dB inducing muscle in our inner ear. It normally is stimulated by sudden loud noise and protects hearing from damage. However is it also a muscle and as such it can just operate when ever it wants to, just like other muscles involuntarily flex every once in a while. I’m positive that our ears experience perceived sound level shifts due to this muscle action even though there is no sonic shock to stimulate it into action.

Limited bandwidth image shift. Image positioning is a treble range issue. Yes, choose a limited bandwidth and do amplitude shifting with it. My hunch is that we are less sensitive in bass to image shift but more sensitive as the frequency is raised. I don’t imagine easily that high frequency image shift doesn’t work, 2k and above. Seems to me that higher frequency image shifts work better.

OK, I have to start packing for the Cal Audio Show, long drive tomorrow and I’ll be back after the show, hopefully with stories about setting up demo rooms.

Again, sorry to disappear. I just get buried sometimes, thanks for being patient.
Art Noxon
 

terryj

New Member
Jul 4, 2010
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By the way...
I’m not following, and excuse me for my ignorance...but what is the “left ten” and the “right ten”. Sounds like one of the speaker wires? I want to track your fixed center image experience. Please explain.


Art Noxon

Oh hi art, was just (once again) enjoying an captivating and interesting post from you, was not till I got to this point that I realised some of it (at least) was directed towards an earlier post of mine.

Sorry, I meant my left ten inch driver and my right ten inch driver. Somewhere along the line (and still do not know when I did this, don't recall touching that amp at all) I hooked the left ten input to the right driver, and vice versa.

So, when I was confused about the imaging I switched to mono from the cdp, naturally (as they were both getting identical signals) the image was dead centre and stable, similarly with PN thru the system, yet when I switched back to stereo, the imaging became confused once again, as the left ten was playing from the right channel and the right from the left.

Twas a simple solution once I worked backwards!:rolleyes:

Can you define what you consider the 'treble' to start from? I am not so convinced as you about that (depending perhaps on what you define treble as). I can (and often do for personal reality) play just the tweeter (say 3k and up)..gee there is not much there tbh!! It is very hard (when playing in mono or using PN) to even get a definite defined centre image, just a bunch of 'nothingness'. Hmm, maybe my ears are shot haha.

Upper and lower mids? Different story, very distinct centre image, easily heard if in the right place etc etc.

Anyway, as always, enjoy your posts. Thanks
 

Art Noxon

WBF Technical Expert (Room Acoustics)
Mar 29, 2011
38
1
0
Eugene, OR
www.acousticsciences.com
Hello crew,

Back from Dagogo’s Cal Audio Shows and was it fun to hear all those different systems. And beautiful too. I got to meet Steve, our founder and also our forum moderator. Glad to know we have one. That was such a pleasant surprise. He came to one of my 4 lectures.

By the way, I have typed up my lecture and can email it to anyone who wants to read it. The lecture title changed every day, even though the lecture content was pretty much the same. No script, but still I stayed on track. I talked about the 20 year evolution of my understanding about what TubeTraps do right when they get loaded into listening rooms. And I ended up at where I am today. It is a funny lecture, story actually, because it tracked the sequence of partial answers, each of which were true enough but each of which ultimately could not account for the whole effect, and therefore were not really the right answer.

I knew that whatever the answer was, it had to account for what the Golden Ear crowd said the TubeTraps did, and I’m glad I lived long enough to be able to discover what finally seems to be the end of that saga/story. My “search for the holey grail” ended happily……but then, the story is full of such happy …but short lived …false endings. So I muse, how do I know I am really at the end of this road? I’ve thought s many times before I was at the end. Just because I can finally account for what the Golden Ear crowd tells me, it probably is presumptuous of me to think that the adventure is over. At best, it’s resting place, a plateau in the learning curve. But in truth the comedy adventure goes on. It reminds me of a song my kids used to torture me with….It’s the song that never ends…..round and round it goes, never stopping…

Treble is musical treble, anything above 262 Hz, middle C. The wavelength is just over 4’ and the ¼ wavelength is 1 foot. The head is just large enough to cast a shadow over one ear compared to the other. The concept of Left and Right signal paths are just beginning to be physiologically sensible.

One of the things we are missing, when it comes to communication, is context. We need to compare apples to apples. A listening setup that is nearfield in an acoustically dark room does not image like a large setup in a fairly bright room. Maybe you guys know each other’s systems well enough that you don’t need reminders, but I know I don’t.

For one thing, we could specify the setback distance, the distance between the listener and the speaker. Another thing we can specify is bright or dark, in terms of the room reflectivity.
=========================================

Let’s stop talking about imaging for a while.

=========================================

Choose a good orchestral recording, one that uses nothing but two mics, a crossed pair of omni mics, the minimalist “Blumlien pair” setup. Many orchestral recordings are done this way.
Once we have the recording, we want to play it on our system. An orchestra in general is putting out the same sound power towards the microphones from all different locations on the stage.
This is the classic signal source for stereo auditioning of the size, shape and brightness of your sound stage. The stereo pair of mics, when listened to, see a wide uniformly thick, uniformly “bright” shaped sound stage, from left to right. In this case, brightness means loudness. Here bright does not mean lots of top end.
Imagine being in a special seat during a legitimate orchestral concert. You are suspended about 15’ above the stage floor and up and out over the seated audience about 15 to 20 feet back from the edge of the stage. That’s where the Blumlein pair happens to be located. You can imagine the huge sound stage that is sonically visible, nearly full left to right and everything is uniformly loud, uniformly present. At this point, we have no soloists, just full on orchestra. You are not too close or too far from anything. That is what the sound stage should look like upon playback in your room.
Now, what you do next is to “map” your sound stage, the one you hear. Yes it’s subjective. When I say map I mean a profile. A line that goes up and down as it moves left to right. What you do is search the loudness or presence of the orchestra, on average, using your mind to sweep the sound stage left to right or the other way. It’s as if you have a parabolic dish and you sweep it across the orchestra, noting how the volume of sound changes as you sweep from 9 o’clock left to 3 o’clock right. Well maybe it’s 9:30 to 2:30. But something like that.
You set up a paper with a line drawn horizontally, which is your axis. Then above that line, say 2 to 3” above it you draw another line, parallel. That is 100%. Then you mark angles using a protractor, every 15 degrees starting in the middle of the axis line and place the angle marks on the 100% line. What you then draw is the relative loudness, presence of sound vs angle as some % above and below 100%.
This is an effort to quantify or measure the average loudness or strength of sonic presence of the sound stage at different angles as you mentally sweep across the sound stage. The ear brain has the ability to echolocate, which means we can sonically look in certain directions, even without changing head position. The relative strength of sonic presence should not change if we do move our heads. It doesn’t matter if we move or not, we’ll still get the same answer, as long as we move pretty much the same when we compare the strength to other angles as well.
If somebody has hearing aids or a hearing impairment the process of echolocation ranges between difficult to impossible. Still, try, it is good to practice, as in practice makes perfect. Remember, draw where the sound seems to come from. Don’t let your eyes trick you into thinking they know where the sound comes from. Look with your ears.
To practice this, you can prepare your chart and then just sit in a room and map out the strength of sonic presence as it varies across the front side of you. You might hear noise from an air diffuser to the right, and your hard drive louder and to your left and community noise in through a window to your far left. You can make a double line chart and map 360 degrees.
OK, that’s the assignment. We are developing one technical skill in “critical listening”. Check in as you begin doing this.
Art Noxon
 

Ron Party

WBF Founding Member
Apr 30, 2010
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Oakland, CA
Back from Dagogo’s Cal Audio Shows and was it fun to hear all those different systems. And beautiful too. I got to meet Steve, our founder and also our forum moderator. Glad to know we have one. That was such a pleasant surprise. He came to one of my 4 lectures.
Hi Art. It was a pleasure attending your seminar. Hope you had a chance to hand out a few of our fliers.
 

LInks

New Member
Jun 28, 2011
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Vancouver BC
www.allmusic.com
Choose a good orchestral recording, one that uses nothing but two mics, a crossed pair of omni mics, the minimalist “Blumlien pair” setup. Many orchestral recordings are done this way.
I believe you meant crossed figure of 8 or bi-directional. 2 coincident omnis would give you mono.
 

Wasatch

New Member
Feb 17, 2012
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Layton, UT
Awesome thread, thanks Art for sharing.
 

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