If we read through the diyaudio stereolith thread, we can refress our memory that the whole reason for the pillow direct sound blocker with The Cardboard was it's desired property of removal of listening distance dependency ! Back then, The Cardboard could not image without pillow at 2m distance, but could image at longer distances, say 5m.
Now, with x = 0.5, improvements have been achieved to this (for some reason hopefully appearing clearly to me some time soon) because the distance dependency appears to have diminished ! x = 0.5 images also at 2m, and at 5m too !
- Elias
I see - so the X0.5 circuit is there functionally instead of the sound blocker and sound-wise - as far as spatial presentation is concerned - the X0.5 and pillowed back-to-back are basically the same - have I understood You correctly?
They are not the same in perceptual sense, not even close ! The difference is big !
Now I understand something was lacking with The Cardboard and the pillow. It's the naturalness of the center panned image !
Because:
This is also true between x = 0.5 and The Cardboard and the pillow. Earlier center panned image was relying on fragile phantom imaging theorem, but now it appears as a real sound source. And because center panned image = mono, and because x = 0.5 generates a true mono source, it is much better !
This is most apparent with natural sounds, like human vocals singing which are usually panned at the center (appears as mono). Let's not forget perception of the human sound has been evoluted during millions of years, long before musical instruments took place, and perception of it has been perfected so any anomalies in reproduction of human sound is the easiest to detect.
- Elias
Let's not ignore possible issues without having any real measurements. In theory inverted phase will have the said high pass effect. We have to find out if it is significant or not.
Yes but the matrix introduces inverted phase. The higher x the more inverted phase components come into play.
I think it would be beneficial to have only positive vectors. This would have no negative effect on tonality. The (not so) simple question is what vectors are best? The original Stereolith radiates too much energy from the center.
That's the problem, omni at low frequencies and increasing directivity at higher frequencies.
We probably want to achieve some reasonable SPL too (FRS8 is a no-go here), so driver size becomes an issue - or could it even help?
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I see - so the center image sounds unnatural with pillow and not so with X0.5
but how can it be "because":
I can see it as important difference from three-speaker trinaural indeed but I can't see any analogy between three-box trinaural and one-box two-channel back-to-back
can You explain?
why fragile? in the absence of any conflicting cues characteristic for stereo, trinaural and so on?
in my experience all images projected by back-to-back are rather very robust, You can turn Your head and walk around the room and everything stays in place
so what kind of fragility do You mean?
but it is real only exactly for one case of the middle point of the stage
true in what sense? as opposed to what? is L+R not true mono in comparison? why?
anyway, we have been told already long time ago that any matrix derivations of center channel would be inevitably flawed because the center channel ideally has to carry only the information that is common to the L and R, not simple sum of L and R, even if it is divided by 2
can You comment on that point either?
The problem with center panned image with The Cardboard may have been exactly what was removed by the pillow, the direct sound is undefined as it's off axis sound (of the side elements), so at mid-high freqs it was relying solely on side wall reflections, which in turn makes it's performance comparaple with conventional two speaker stereo triangle in terms of phantom imaging. Thus it's fragile for a center panned image.
In SSS center panned image comes from a single location at all freqs ! This is a virtue.
- Elias
True, but for a conventional two speaker triangle center panned image is the worst scenario ! For SSS it is the best scenario !
As I said, for natural reproduction of the most important sounds, like vocals, true center source is an improvement because vocals are commonly mixed as mono in the center.
For me it appears counterproductive to spread the speakers far away, if the goal is to reproduce something in the center
- Elias
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For me it appears counterproductive to spread the speakers far away, if the goal is to reproduce something in the center
- Elias
I agree. Having a real center speaker is the most significant reason why I think about this single stereo speaker concept at all.
If a design of a small two way bookshelf loudspeaker were presented instead, the responses would hardly be of this kind
So what is the problem now ?
- Elias
yes I am confused - so was it removed or wasn't? does there remain a problem in spite of the pillow in comparison to "SSS" or not?For me it appears counterproductive to spread the speakers far away, if the goal is to reproduce something in the center
- Elias
well, in case of headphones sound sources are as much to the sides as it gets - typically at 90 degrees - have You any problems with center phantoms when You listen through headphones?
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The pillow remowed the direct sound from The Cardboard, yes.
And yes, there remain a problem with The Cardboard with the pillow, the center panned image may not be any better than in a conventional two speaker stereo triangle because it is still based on the unknown theory of phantom localisation which do not work for me at high freqs.
It cannot be compared because sound image will remain inside the head, which is not my goal
- Elias
I think you mean the example of the panning ? Yes, it could be different but in any case would depend on the arbitrary panning law.
I thought it's easier for me to deal with 0 and 1, even 0.5 it's quite hard
- Elias
Never took any pictures of the old console, but it definitely had side firing horns, and speakers facing forward, 90 degrees angle between, similar in effect to Elias box.
It may have been a local offering in Minneapolis, it did not much look like the Magnavox imperial.
The front facing speakers were basically full range, I did not even realize there were side firing horns until examining the unit in the 1980s.
may not be because of theory? but wasn't it in fact any better than conventional stereo?
It cannot be compared because sound image will remain inside the head, which is not my goal
- Elias
but was it in Your head when You listened to the original pillowed cardboard? was there anything wrong with it? if yes - what? Have You heard separate splitting phantoms instead of one then?
I think you mean the example of the panning ? Yes, it could be different but in any case would depend on the arbitrary panning law.
I thought it's easier for me to deal with 0 and 1, even 0.5 it's quite hard
- Elias
I did it in Excel. The file is attached. Just change the value for x.
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Before this can be solved, we need information about commonly used studio mixing practises ! For example side panning, what is the typical extreme case, is it L = 1, R = 0 ? Or, can it be L = 0.75, R = -0.25 ? In other words is the phase reversal between L and R commonly used ?
And, is it typical to do panning over full freq range, I think not but low freqs are allways mono ?!
What ever the case with mixing procedures, in practise this speaker will produce dipole loss only up to a specific frequency which depends on the box and element sizes. And because of this, the 'problem' could be solved by itself: At low freqs the speaker would have some dipole loss for stereo signal, but because the low freq signal is mono, their effects cancel !
- Elias