The one that Oliver provided a link to. 😉
http://www.diyaudio.com/forums/mult...-pattern-stereo-speakers-235.html#post3763294
Again:
"The near-field setup lowers the time and intensity of modal effects relative to direct sound (Griesinger's approach), and it ALSO increases the effect of time and intensity between channels (or their difference). (..particularly for "impulsive" sounds.)"
Or said differently:
You'll get acoustic gain with proximity in the near-field for lower freq.s. The result then is an average intensity for direct sound is well above that of modal effects. The same is true for timing differences between direct and modal/ringing effects with respect to impulsive sounds.
^
Near field sub listening approaches free field conditions. Is this really what Griesinger is talking about?
Near field sub listening approaches free field conditions. Is this really what Griesinger is talking about?
Playback in headphone systems really need to be recorded on a head. The problem is each of our heads are different. I remember asking someone to do a recording using the same head mics I used, turned out the effects were not as dramatic to as listening to a recording made myself. The Linkwitz demo recordings were not as dramatic either. I am suspecting some recordings are just going to sound better to some individuals.
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Sorry Scott, but he is proposing to utilize the room in order to make a recording sound more pleasing.
"The question is: can we reproduce the experience of external, living bass in a small room? To do so, we must somehow cause the apparent direction of the reverberation to fluctuate chaotically around the listener, and to make the rate of change of direction mimic the reverberation in the original concert hall."
What specific concert hall is he talking about? Do I want every recording to "mimic the reverberation" of that specific concert hall?
I would partially disagree based on what I have heard first hand.
Also, this property akin to intelligibility, or lack of it, does not stop one from having enjoyable sound, it only limits how real an image can be replicated.
If you drive the R and L speakers with the same signal (mono), one will get something that spans anywhere from a detectable mono phantom image with an obvious Right and Left source, to the other extreme, a mono image floating in the middle and your unaware of the right and Left speakers as the source.
That might sound like boogity boogity audio talk but I am serious.
What governs this has to do with how the speaker radiates (as a complex or simple sources etc) and in room, how much reflected sound arrives at the LP relative to the direct sound. Neither of these things are sore thumb obvious features in measurements yet are plainly audible.
The issue is what I have been calling “spatial identity”.
When working on the old Unity horns in 1998, as they began to measure more like a single source in time etc, they also began to take on a weird effect that I had only heard on my old boss’s esl63’s and large panel ESS speakers (I used to make them in the way old days) and that was with a voice, the sound could “sound like” it was coming from behind the actually panel or speaker.
With the Unity horns it was getting harder to “hear” how far away it was if one had their eyes closed. It dawned on me that if I can hear where the source is (how far away), then the loudspeaker is / has to be radiating clues to it’s location in addition to the voice.
Those cues had to be differences between the right and left ear’s signals AND as the source acted more and more like a single radiation in time and space, the more equal the right and left ears signals were and so it had less and less spatial identity.
The less spatial identity, the more like the voice sounds like the recording distance depending on the reverb, hf attenuation and so on. The more it sounded and measured like one source, the less generation loss there was in the generation loss recordings. The less identity the speaker has AND the less it interacts with the room, the more (in stereo) it is able to create the window into another space effect (if in the recording).
Ideally (I think) the loudspeakers spatial identity should be as small as possible, in hifi maybe the simple easy route for a diy'r wanting to experiment in this area is a pair of good small full range drivers, eq’d, on flat baffles and up close relative to the room walls with subwoofer.
While limited in SPL and frequency extension, these radiate as a simple source over much of their range, the up close listening position makes the direct sound louder than even the loudest reflected sounds.
The cool part for our business in large scale sound is that the same interference patterns that can help give a speaker it’s spatial identity up close, give it an ever changing frequency response with changing distance and position and imposes a maximum usable working distance not limited by SPL but by sound quality. In the time domain, because of all the separate arrivals from source on each side, essentially prevents a mono phantom beyond wait “I think maybe i hear one”.
Here, if you can combine multiple drivers constructively driving a large horn, radiating like a simple single point with a very large difference between in pattern and out of pattern energy and an ideal mounting height and angle, one can illuminate an entire football stadium from the score board at one end. With pattern control and aiming, also have the seat to seat SPL vary no more than + -2dB SPL and have it sound hifi, “the same” in every seat and it floats in the air, no kidding.
While some don’t understand what they are hearing, at trade shows in the demo room we have often had people come up and listen to large synergy horns, even sticking their head into the horn mouth or walking into the Caleb’s 10 foot tall mouth to hear that no matter how much they move around up and down side to side, no matter how many drivers the box has, it always sounds like the voice or music is floating in the horn in front of you, like one driver somewhere ahead..
Best,
Tom
^
Tom, because the question came up earlier: what is your opinion on stereo in the free field versus acoustically small rooms?
Tom, because the question came up earlier: what is your opinion on stereo in the free field versus acoustically small rooms?
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Simon - I agree as well, but with one caveat.
"Accurate" is not really a subjective term, but "realistic" can be. Far too often when people say that something sounds "realistic" they mean that it sounds pleasing to them. If "realistic" in audio were as quantifiable as "yellow" is in our TV then I would have no trouble with what you are saying. But to use "realism" instead of "accurate" when "realism" is whatever anyone defines it to be, then I have a problem and I believe that your video to audio analogy falls apart.
One thing that really impressed me when I was studying video for one of my books was how well quantified video was in a subjective sense. The engineers in that field do not do anything subjectively as is so common (ubiquitous?) in audio. The field is so well quantified that subjective assessment is not very useful. And yet few complain that they can tell that they are looking at a flat screen and not "the real thing."
Oh for the day that audio has such stability!
Free field bass has no envelopment. How can it be that Griesinger is trying to achieve that?
It's not boogity boogity to me Tom 🙂 I've heard the phantom mono image floating in space without a trace of localisation from either speaker before too, a lot of things have to come together to achieve it though, including: (but not limited to)
* Very close matching of high frequency response of left and right speakers (else you get tearing/blurring of the image as I described earlier)
* A reasonable amount of mid/high frequency directivity (wide dispersion need not apply)
* not too much sidewall reflection.
* Very minimal diffraction profile so the speaker acts as a true point source (or at least infinitely narrow vertically spaced point sources for a conventional multi way)
Tom I think you hit the nail on the head - I'm so pleased to see someone else describing this as this is exactly the conclusion I came to a while ago and in fact posted about it at length (perhaps even in this thread, I can't remember) although there wasn't really much comment from anyone else at the time.
I noticed from my own experiments on minimising diffraction from the tweeter on a relatively wide baffle speaker that when I had soft damping material around the tweeter (a small waveguide ribbon which already had a certain amount of directivity) that the apparent source of the sound in the depth axis moved back from being localised at the front plane of the speaker to well behind the speaker, exactly as you describe.
In fact on many recordings with a little bit of space/reverb the apparent location of the sound was actually well behind the living room wall that the speakers were sitting in front of - with no localisation to the speakers or anything in front of the wall at all!
Take the damping material away from around the tweeter (and tweak the EQ slightly to account for the difference in frequency response) and the localisation returned (albeit not strongly with these tweeters as they have a fair bit of directivity) to the front of the speaker.
I puzzled about this for a while and came to the same conclusion as you - our binaural hearing system is able to detect the width of the secondary radiation from the baffle edges - it hears a first arrival from the tweeter from a particular direction, then hears two delayed images from slightly different azimuths and is able to deduce the angular width of the sound source.
Our azimuth detection is acute enough to distinguish the difference in direction of the tweeter from the secondary radiation from the cabinet edges on all but the narrowest cabinets. Through experience the brain probably assumes that a sound object with a significant width must be close.
Eliminate the diffraction and the sound source acts as a true point source - the sound only comes from a single infinitely narrow azimuth with no physically displaced secondary radiation from baffle edges. The brain can no longer estimate the width of the sound source (infinitely narrow) so assumes it is far away.
Add the smallest amount of large room reverb in the recording and it strongly reinforces the brains impression that the sound source is far away. Diffraction presents a conflicting cue that spoils the illusion, absence of diffraction removes a conflicting cue.
Yep been there, done that 🙂 For all their flaws the point source nature of a full range driver is very instructive regarding imaging. A true point source is the ideal for imaging that's for sure, and a full range driver points to the potential even if it falls short in other ways.
The speakers that I was testing the diffraction reduction on were 2 ways with an 8" full range driver running up quite high (4Khz) crossed to the waveguide ribbon. The full range driver is fairly directional above about 1.5-2Khz so radiates very little along the baffle at high frequencies to diffract despite the basic shoebox cabinet. The ribbon tweeter has quite a bit of directivity of its own plus some soft absorption around it to mop up the little that was left - together the diffraction was very minimal so it was quite close to two vertically placed point sources.
My limited testing suggests that vertical displacement of the drivers (compared to a single point source) doesn't damage the "sound coming from behind the speakers" phenomenon noticeably, as long as the two drivers are both acting as point sources at high frequencies and are not radiating "width cues" from the baffle edges.
(Our ability to discern height is far more limited and inaccurate than width, almost all of the height cues come from around 8Khz which is entirely within the passband of the tweeter so effectively for height cues the speaker is a single point source at the location of the tweeter)
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My definition of realistic is quite simple - does it sound like the real thing with my eyes closed, or does it sound like speakers. I know that may sound trite and open to interpretation, but for me there is a difference between "sounds good to me" and "sounds real to me".
It's one of those things that you can't describe but you know it when you hear it. For me it sometimes makes the hair on my neck stand up. 🙂
One thing I've learnt is that some of the traditional measurements like frequency response don't predict whether the illusion of reality will occur or not (and it is an illusion, there is no doubt about that) and that it can happen on a speaker with a less than optimal frequency response, but that if you take that system that produces the illusion convincingly and then make improvements to its frequency response "accuracy", the illusion of reality doesn't go away - so it seems to be independent of (or orthogonal to) moderate frequency response errors.
(Obviously gross frequency response errors will spoil it but I've seen errors of several dB not spoil it or even make it sound noticeably less real, provided the errors are identical in left and right speakers)
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I have heard that frequently with dipoles (both planar and quasi point source) in front of a diffusive front wall in my listening room (which also has little in the way of early side wall reflection), and heard the same from the LX-521 at Burning Amp a couple years ago in an otherwise terrible room.
Sure, you would expect to hear that with a dipole, especially a planar one, but I think hearing it from a forward firing monopole is less common.
With most studio recordings there is no "real" anyway, so the best we can say is "could have been real (in some imagined venue)". At orchestral performances there can be a substantial difference between "front of house" and "balcony", and I get stereo "imaging" that falls within that "audience box" range-of-variation rather often as well. If it sounds like "balcony" and what one wanted was "front row orchestra" that does not make the stereo presentation "not real" . . . it's still in the range of what one might have heard at performance. The bottom line for me is that I hear a plausible spatial presentation from quite a lot of the recordings that I have, as good as "real" (and sometimes better). The "art" works . . .
All very good points.
Perhaps the key to the illusion of it being real is simply acoustic "plausibility". Unless you were there at the live event you don't know precisely what it sounded like anyway, and a lot of studio work as you say is manufactured.
If what you hear falls within certain plausible parameters it passes your brains subconscious plausibility checks and is accepted as real. If it fails any of the plausibility checks the gig is up and the sound is unmasked as a reproduction.
If only we knew objectively what those plausibility parameters were... 😉
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It seems like most of what you post is "at length"🙂 I don't know how you have the time.
Most of what you post is "at length" 🙂 I don't know how you have the time.
It's not trite, its my first order criteria. If I close my eyes and I can find the speakers then something is wrong. I seek speakers that "disappear". When Duke LeJeune once commented that my speakers disappear better than any others he had heard I was quite pleased. This was exactly what I as trying to achieve. It's not at all common by the way. Is this "the real thing", I don't know, but it is clear that the speakers are not influencing the sound.
You are both confusing reproduction with "acoustics". 😉
Earl,
He doesn't want free-field production of actual sources, rather REPRODUCTION of the signal that contains envelopment cues reproduced IN a free-field condition at lower freq.s.. (or at least a condition that, like a free field condition, allows for better detection of time and intensity differences - when compared to a small room condition.)
Markus,
Lets put some more emphasis on the quote you've selected:
""The question is: can we reproduce the experience of external, living bass in a small room? To do so, we must somehow cause the apparent direction of the reverberation to fluctuate chaotically around the listener, and to make the rate of change of direction mimic the reverberation in the original concert hall."
..getting that "reverberation to fluctuate chaotically around the listener" and trying to "mimic" the rate of change of direction of the original concert hall
-is all about reproducing the signal in a manner that allows the listener to better detect these conditions.
From Griesingers very first simplistic example (starting on the bottom of page 4) he ends it with this (bottom of page 6):
excerpt chosen for emphasis (with type-face alterations):
"If the loudspeakers move in phase, this mode is not excited..
Thus if the signal driving the loudspeakers fluctuates randomly in phase, the apparent direction of the sound at the listener position will also fluctuate randomly! We will have achieved our goal of reproducing the original envelopment, at least at this *frequency."
*.."frequency" in the context is specifically referencing the freq. of the mode (..that would have otherwise been excited).
..and if that's not clear enough, then I don't think that anything will be. 😉
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Even if you were . . .
I have often listened to (snippets of) a performance from a slightly-cracked-open back door of a hall, or from the wing behind the violas. The sound in both cases is undeniably "real". I can almost always replicate the former from a recording (some degradation of the system required 🙄) for a simulated "real" sonic experience. Certainly not the best "sound" . . . but worlds better than no sound at all, and I can still quip "that's just what it sounds like in the lobby" 😛
And as I've said several times before . . . it doesn't bother me that I cannot "localize" bass in my listening room, because with rare exception I can't localize (low) bass in the concert hall either (sometimes to the point of not being able to tell which side of the stage they're standing on without looking, and if they're in the pit simply never). It's not a significant part of the "musical experience".
I pretty much agree with Earl's comment . . . if I can say "the bass is coming from the right speaker" there is something seriously wrong with the system. It's just not like that in the real world.
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I completely agree, but since it is not practical to design a speaker for each room, you need tone control. Mainly on the < 150 Hz end, plus some above 2K. Best on the speaker itself, like on the old Philips MFB.
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