Imaging, placement and orientation
This is my recipe for best spectral balance and imaging:
I've been recommending this configuration since the 1970's, and it works every time. Seems to be gaining in popularity in recent years too.
This is my recipe for best spectral balance and imaging:
I've been recommending this configuration since the 1970's, and it works every time. Seems to be gaining in popularity in recent years too.
MtBiker said:
Creating a believeable soundstage is elementary, when you think about it. The only thing that is required to create a stereo image is that the levels of the left and the right speaker are consistent, and the timing is correct.
That's it. That's all there is to it.
So why do few speakers image well? This is simple also. The sound which emanates from the cone of the loudspeaker is reflected by the cabinet, by the floor, by the walls nearby, and by objects in front of the speaker. That's why speakers don't image well.
So if you want a convincing image, all you have to do is address these issues. Treat the floor. Move the speakers away from the walls. The most difficult challenge is the cabinet of the speaker itself. When the sound from the speaker hits the edge of the cabinet, it diffracts if there is a sharp edge there. This diffraction creates a phantom image, delayed in time. This phantom image, generated by diffraction, is the primary reason that large speakers typically image worse than small ones. While small speakers suffer from diffraction, they do not suffer from diffraction to the same degree as large speakers in a conventional cabinet, and the delay is greater with a large speaker. The only solution to cabinet diffraction is a cabinet with NO SHARP EDGES. ANYWHERE. The speakers which I am listening to as we speak practically look like a bar of soap, and they use a waveguide. This attention to detail is the reason they image so well.
The timing problem is more difficult, and the only real solution there is to use a minimum of drivers, and to locate them in a way that they're timing differences are minimized. The timing issue is most prevalent in the midrange and in the upper midbass. At low frequencies and at high frequencies the timing issue is not as critical.
tinitus said:
I agree with you that on-axis response should be flat, so having the forward axis pointing straight at you should yield good results. That's sort of the most obvious condition to me, a starting point, if you will. Most any good speaker should sound right when pointed directly at you, and if it doesn't, something is wrong.
However, this listening position - where a stereo pair of speakers cross their forward axis - defines a pinpoint spot. I think this is the optimum listening position for most speakers, and if the listener moves in any direction, sound quality degrades.
What I've described in the link above is a setup that offers good imaging over a much wider range of listening positions. It allows the listener to move in their chair without detracting from their listening experience, and also allows them to share that same good quality sound with others sitting nearby. However, one caveat is that it requires speakers that provide constant directivity.
Wayne Parham said:
Wayne,
I have my speakers set up in the manner described in your link. Being able to listen any where in the room is delightful. For instance, my listening room also doubles as my office, and I really appreciate being able to listen in the sweet spot, but also getting good sound at my desk which is a few behind the sweet spot. Highly recommended!
If I'm not mistaken this is also the setup described here:
http://www.gedlee.com/downloads/Cum laude.pdf
In the formation of the phantom image only the direct sound from the drivers is useful. Reflected energy is destructive. The reason for getting away from the walls is mainly to do with the timing of reflections not the amplitude, the ear responds to delayed reflections by ignoring them after a certain time, a few tens of milliseconds I think, whereas early reflections cause both timbre shifts and confusion of the phantom image. A symetrical room and speaker layout helps. So does listening with the speakers toed in 45 degrees each side and listening close up where the tweeter axes cross. One of the better tests for phantom image construction is mono sound played back through both channels, the desired result is that the speakers seem to disappear and the sound comes only from a point midway between the speakers.
Ted
Ted
I think this is the HOLY GRAIL of sound reproduction. Taken from stereophile: 
What had wowed me? A total absence of "electronica." An enormous addition of lushness, texture, harmonics, and warmth, especially in the massed strings. And, at the same time, a major extension in air, detail, and transparency, coupled with a sensation of phase coherence that I describe as "acoustic jell." Usually you can get improvements in warmth and textures or more extension, air, detail, and transparency. Here, simultaneously, were both: a gigantic floating apparition of detail, delicacy, air, and texture, and an even greater diminution of glaze, glare, etch, and artifact. Usually you can get rid of those with the tonal cover-up of a high-frequency rolloff. With the TARA Mystery Wire, the artifacts were gone, yet the top-end extension and openness were greatly increased.
Each note on the celeste became a full-fledged, tripartite event: first a fully defined, cleanly rendered attack; then a three-dimensional, body-defining sustain; and finally a cleanly defined, effervescent decay into blackness. That holy trinity of live sound—believable attack, sustain, and decay timed out to perfection—more or less describes the dramatic improvement the TARA IC had wrought in my system. That, and the pitch-black backdrops against which all this sonic drama was played out, was what had me yelling "Wow!"
You can't beat "Acoustic Jell"
What had wowed me? A total absence of "electronica." An enormous addition of lushness, texture, harmonics, and warmth, especially in the massed strings. And, at the same time, a major extension in air, detail, and transparency, coupled with a sensation of phase coherence that I describe as "acoustic jell." Usually you can get improvements in warmth and textures or more extension, air, detail, and transparency. Here, simultaneously, were both: a gigantic floating apparition of detail, delicacy, air, and texture, and an even greater diminution of glaze, glare, etch, and artifact. Usually you can get rid of those with the tonal cover-up of a high-frequency rolloff. With the TARA Mystery Wire, the artifacts were gone, yet the top-end extension and openness were greatly increased.
Each note on the celeste became a full-fledged, tripartite event: first a fully defined, cleanly rendered attack; then a three-dimensional, body-defining sustain; and finally a cleanly defined, effervescent decay into blackness. That holy trinity of live sound—believable attack, sustain, and decay timed out to perfection—more or less describes the dramatic improvement the TARA IC had wrought in my system. That, and the pitch-black backdrops against which all this sonic drama was played out, was what had me yelling "Wow!"
You can't beat "Acoustic Jell"
tedr said:
Yes, and NO
A small amount of reflection is good...its a matter of finding the right amount fore that particular speaker in that very room
Absorbers should be used very carefully, its NOT a matter of more is better
My previous room was quite empty, with carpet on the floor...and it still needed some carpets behind and between the speakers
My present room is stuffed with all sorts of things, that should cause lots of destructive reflections...and wooden floor with NO carpets
I dont say is optimal and couldnt be improved...but I can only say it works perfectly, no problems whatsoever
There are no general thumb rules
one things also is how the wave react with each other
for there will be waves that will cancel each other, and you have waves that at redirecting parts of the air motion in different directions even as they come out of the speakers. I like the MTM or TMTM designs for the middle tweeter gives a good transient response that would be lacking in the true way that a high definition wave. My speakers project many mode points for imagining. I believe that is why Bose has for a long time using direct/ direct-reflecting approach. For when you are at a live performance you have sound bouncing from many directions. Plus just the movement of the air in the room like air conditioning, since it is all about how the air is vibrated.
for there will be waves that will cancel each other, and you have waves that at redirecting parts of the air motion in different directions even as they come out of the speakers. I like the MTM or TMTM designs for the middle tweeter gives a good transient response that would be lacking in the true way that a high definition wave. My speakers project many mode points for imagining. I believe that is why Bose has for a long time using direct/ direct-reflecting approach. For when you are at a live performance you have sound bouncing from many directions. Plus just the movement of the air in the room like air conditioning, since it is all about how the air is vibrated.
tinitus said:
There is a difference between reflections and reflections. It's all about perception. Early reflections ( < 10-20 ms) should be minimal, but a reverberant field is necessary. Listening in a completely dead room is not very enjoyable. In a dead room, there is only the reverberant field information recorded in the source material and not from the room, but it will not be perceived as a reverberant field.
However, when early reflections cannot be avoided it is probably the best if they are spectral copies of the direct sound from at least a few hundred Hertz up, so that the human hearing perceptually masks them and does not identify them as a wavefront from a different source. Nevertheless, even these reflections will affect virtual source localization (imaging) as they are cues of the position of the speaker itself.
Also, as Dr. Geddes points out in one of his papers, early reflections may cause comb filtering which will affect the perceived frequency response.
A flat power response is also preferable for a neutral sounding reverberant field.
a_tewinkel said:
I'm a little less inclined to make that statement today because of some discussion with Dr. Toole about his book and further investigations.
Very early reflections < 10 ms can fuse with the direct sound to create an image ambiguity (poor image) - the shorter the delay the worse, which makes cabinet edge diffraction and nearby object diffraction a major issue. Good imaging requires a perfectly clean direct signal and impulse response for at least the first 5-10 ms. After this the reflections become masked by the precidence effects and it then appears that comb filtering effects are not significant. Floyd Toole still suggests that all reflections are perceived as positive, although this might be bacause they increase the stage width and the feeling of spaciuosness. There is likely a real tradeoff between spaciousness and image for very early reflections - one gets better only at the sake of the other, although there may be an ideal. I believe that the ideal exists when the first few ms range is completely free of reflections and diffraction, but after that ALL reflections only add spaciousness without a loss of image. Controlling the first reflections without reducing later ones is the key.
Which is why I fill the tweeter faceplate screw holes with black wax...makes quite a difference
It is also known that the "edge" around the dome on a Vifa XT25 should be rounded
I believe new models are all nicely rounded at this point
Its all only logical to be that way...I mean, noone would ever think of mounting drivers without countersinking
Funny that professional driver designers should learn that from DIYers
Wonder when they will take the next step getting rid of ALL chassis screw holes...they should know by now thats its not just a cosmetic thing
a_tewinkel said:
Nicely summarized! I'm glad we're drawing a disctinction between early and late reflections.
One thing I've noticed with waveguides is that you can bend the rules a bit. For example, you wouldn't want a conventional speaker too close to the walls. But with a waveguide it's possible if the wall forms a boundary with the waveguide.
For instance, I used to have my speakers set up in a very small room. With the speakers perpendicular to the rear wall, the image lacked spaciousness. But the sense of spaciousness increased dramatically when I oriented the speakers so that the mouth of the waveguide formed a boundary with the side wall.
It was quite amazing to turn the lights off and hear a soundstage which extended beyond the confines of the room!
Of course this isn't ideal, I really needed a bigger room. But if you're cursed with a small room, waveguides can offer unique advantages if you use room boundaries to full effect. (The same thing applies to cars also, and it's the reason waveguides sound excellent in a vehicle.)
Excuse Me, Dr. Geddes:
(1) Is it safe to assume that the Hass Effect window is predominate in the auditory region utilized for speech ( approx 170 - 4Khz ).
(2) Is there a perception vs frequency analysis?
(3) The 5 - 10ms window would imply that there should be no reflecting surfaces within 40cm of a speaker?
Thanks again
( I have my eraser with the safety off just in case )
(1) Is it safe to assume that the Hass Effect window is predominate in the auditory region utilized for speech ( approx 170 - 4Khz ).
(2) Is there a perception vs frequency analysis?
(3) The 5 - 10ms window would imply that there should be no reflecting surfaces within 40cm of a speaker?
Thanks again
( I have my eraser with the safety off just in case )
Patrick Bateman said:
I dont know about other conventional speakers...but my "conventional" speakers doesnt seem to have any problem with sidewalls or any other things around them, none at all...I would say its mostly a matter of crossover, but it may be that its easier with "born" directive transducers like waveguides, ribbons and such
Hiquephon seems to take the diffration issue more seriously than the competition...unfortunately there still is a very small sharp edge left
Attachments
HK26147 said:
I think of the Haas effect as existing in time not frequency and I'm not sure what data there is on the effect with frequency mixed in. From what I know all auditory effects are at their maximum in the speech range, but I would consider this somewhat higher than 170 Hz. Maybe 300 Hz. 300-3 kHz is what the phone company considered was necessary for speech. I think that they were right.
I would think that most of the time issue are pretty constant with frequency within the speech range, but I am not positive about that.
The 40 cm is a delta - a path length difference. I'd have to calculate what this meant in terms of absolute distance to a reflection. I think that its much larger.
gedlee said:
Recently I upgraded from three subwoofers to seven, and I noticed an improvement in imaging in my mains. I have a theory about this; bear with me.
Previously there were three subs were mounted in the three corners of the room. They had a cutoff of 80hz. My theory is that reflections from the *subwoofers*, not the mains, could have muddied the image.
Even with an 80hz cutoff there's third harmonic distortion present at 240hz. Even worse, with the subs in the corners that distortion at 240hz gets a nice reflection off the ceiling, two walls, AND the floor!
(I believe this is one of the reasons that subs should be physically separate from the mains, right? Even with a 100db filter at 80hz they will muddy the image due to 2nd and 3rd harmonic distortion.)
Long story short, the imaging on the mains has improved noticeably, and I didn't touch them. All I did was add subs.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.