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What makes speakers "disappear " and can it be measured?
- Thread starter Pearljam5000
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I don't think it's that simple. While wide dispersion can minimise the effect of speaker position (increasing the ratio of reflected/direct sound in the room), you also need to take care of any detrimental reflections occurring in the vicinity of the speakers. In-wall speakers or near-wall speakers comes to mind.
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... and then you would increase the ability to localize, no? What comes to mind with peanuts suggestion is using reflections to confuse the source. I suppose that can work but as SPL increases the room might seem to get overwhelmed at some point. I've had dipoles in such a configuration and it's not for me.
In terms of a stereo pair of speakers, I think apparent imaging and speakers disappearing are primarily a function of symmetry.
Speakers need to have as close to the same frequency response (mag and phase) as possible. And is measurable.
And have the same directivity response, which can be taken as a given since using a pair of same speakers.
Room needs to have as symmetric a response at listening position as possible in terms of reflections, modal effects, etc. Measurable but more difficult.
In terms of a single speaker, i think flat mag and phase, with acoustic centers as close as possible, along with minimizing diffractions that give audible location clues, all together allow the speaker's apparent image to expand, thus making the speaker itself seem to disappear.
Ironically, strictly in pursuit of stereo imaging, i think the whole symmetry thingy dominates single speaker correctness.
And is hard to achieve
And is a big reason why nearly all subjective impressions of imaging, speakers disappearing, and sound fields, need to be heavily discounted imho.
Speakers need to have as close to the same frequency response (mag and phase) as possible. And is measurable.
And have the same directivity response, which can be taken as a given since using a pair of same speakers.
Room needs to have as symmetric a response at listening position as possible in terms of reflections, modal effects, etc. Measurable but more difficult.
In terms of a single speaker, i think flat mag and phase, with acoustic centers as close as possible, along with minimizing diffractions that give audible location clues, all together allow the speaker's apparent image to expand, thus making the speaker itself seem to disappear.
Ironically, strictly in pursuit of stereo imaging, i think the whole symmetry thingy dominates single speaker correctness.
And is hard to achieve
And is a big reason why nearly all subjective impressions of imaging, speakers disappearing, and sound fields, need to be heavily discounted imho.
Not sure what you mean but an in-wall speaker with wide even dispersion will be half-sphere and not omni. The remaning of the equation will be related to the room, symmetry and the listening distance to the speaker.
I'm a little surprised no one has mentioned a lack of resonances. That is one of the most important qualities for a speaker to avoid revealing itself as a wooden/metal/plastic box. It modifies timbre, can make a note stand out in the time domain, and just sticks out like a sore thumb.
Directivity is important for sure when it comes to the spatial presentation aspect, and I find wider directivity speakers are usually a bit more likely to have this disappearing effect, but having minimally audible resonances is paramount.
Per toole:
"If resonances exist in loudspeakers, either in the transducers or in the enclosures, they are added to those in the program, changing the timbre. These changes are monotonously added to all reproduced sounds: voices, musical instruments and so forth."
Furthermore, these resonances actually become more audible in a reflective environment, not less as some might assume. You're less likely to hear a resonance in, say, a nearfield setup with ample room treatment than you are in a typical living room:
"An interesting fact is that reflected sounds are perceived as “repetitions” of the direct sound, and the result of the accumulated “looks” at the sound is that low- and medium Q resonances become more audible. Consequently two contrasting events follow: flaws in loudspeakers are more obvious (bad), and subtle timbral cues in music are better revealed (good) (Toole and Olive, 1988). Listening through headphones or in a dominant direct sound field (a dead room) make us less sensitive to low- and middle-Q resonances, possibly explaining why some headphones with unimpressive measurements are tolerable, at least with pop music."
Edit: All from chapter 4 of Toole's book.
Directivity is important for sure when it comes to the spatial presentation aspect, and I find wider directivity speakers are usually a bit more likely to have this disappearing effect, but having minimally audible resonances is paramount.
Per toole:
"If resonances exist in loudspeakers, either in the transducers or in the enclosures, they are added to those in the program, changing the timbre. These changes are monotonously added to all reproduced sounds: voices, musical instruments and so forth."
Furthermore, these resonances actually become more audible in a reflective environment, not less as some might assume. You're less likely to hear a resonance in, say, a nearfield setup with ample room treatment than you are in a typical living room:
"An interesting fact is that reflected sounds are perceived as “repetitions” of the direct sound, and the result of the accumulated “looks” at the sound is that low- and medium Q resonances become more audible. Consequently two contrasting events follow: flaws in loudspeakers are more obvious (bad), and subtle timbral cues in music are better revealed (good) (Toole and Olive, 1988). Listening through headphones or in a dominant direct sound field (a dead room) make us less sensitive to low- and middle-Q resonances, possibly explaining why some headphones with unimpressive measurements are tolerable, at least with pop music."
Edit: All from chapter 4 of Toole's book.
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In my specific question, the assumption is that he speaker itself is good enough not to reveal itself by peaks and resonances in the frequency response. A slightly lower energy in the 3-4 kHz range and 7-8 kHz range may however give the impression of a more laid-back, smoother and distant sound which may contribute to the ”invisible speaker”.
I was replying to your comment re:wide dispersion and treating reflections.
thewas
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True, although in the end such resonances are also secondary sound sources like I mentioned before.
My experience there is the opposite, higher directivity loudspeakers disappear more for me, as they give a higher percentage of direct sound at the listeners position, similar to listening in nearfield were you suddenly "leave the listeners room and enter the recording". Wide directivity loudspeakers might give me also a wider soundstage but I can still locate them more as sound sources.
I have been conducting double-blind subjective tests starting in the late 60s and when listening to single loudspeakers behind a screen there is no “stereo effect” to confuse the situation – it is a single source of sound. It turns out that the loudspeakers receiving the highest sound quality ratings are those with the smoothest, flattest, on-axis frequency response curves, and smooth, gradually changing, off-axis performance indicating that reflected sounds would have timbral similarity to the direct sound arriving at the listening position. It is all explained in great detail in the 3rd edition of my book, “Sound Reproduction; the Acoustics and Psychoacoustics of Loudspeakers and Rooms”, Focal Press, 2017 – end of commercial message, sorry.
It turns out that the dominant factor detracting from sound quality is resonances. These audible features stay with the loudspeaker, and when, during the listening tests, the sound is switched from one speaker to another for comparison our brains very quickly associate the distinctive resonant colorations with the individual speakers. The speaker with the least audible colorations wins the tests, and here is the interesting bit: they tend to “disappear” behind the screen – the sense of distance is closer to whatever was in the recording.
It seems that any audible defect that remains in place with changes in the recordings is associated with the loudspeaker and we localize to the speaker – it makes its presence known. The sense of depth and the stereo soundstage are compromised. Resonances, non-linear distortions and certain kinds of diffraction effects fall into this category (most don't because they change with angle). Room-reflected sounds are much less destructive than is commonly believed if they also are free from these defects, so off-axis performance of loudspeakers is very important. In a multichannel system, having surround and immersion speakers of similar neutrality to the front speakers is a huge advantage. Two ears and a brain can tell the difference – the walls “disappear”. I open my eyes and I am in a small room.
It turns out that the dominant factor detracting from sound quality is resonances. These audible features stay with the loudspeaker, and when, during the listening tests, the sound is switched from one speaker to another for comparison our brains very quickly associate the distinctive resonant colorations with the individual speakers. The speaker with the least audible colorations wins the tests, and here is the interesting bit: they tend to “disappear” behind the screen – the sense of distance is closer to whatever was in the recording.
It seems that any audible defect that remains in place with changes in the recordings is associated with the loudspeaker and we localize to the speaker – it makes its presence known. The sense of depth and the stereo soundstage are compromised. Resonances, non-linear distortions and certain kinds of diffraction effects fall into this category (most don't because they change with angle). Room-reflected sounds are much less destructive than is commonly believed if they also are free from these defects, so off-axis performance of loudspeakers is very important. In a multichannel system, having surround and immersion speakers of similar neutrality to the front speakers is a huge advantage. Two ears and a brain can tell the difference – the walls “disappear”. I open my eyes and I am in a small room.
eddantes
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Welp - you can't get a more authoritative answer than that.
But I am curious about di-pole/bi-pole/omni speakers then... if resonances and other "artifacts" are the things that destroy the illusion and not reflections, then do these types of speaker (if well constructed) contribute to the illusion of space and stage or no? If a multi channel system is more effective at creating a stage, would a "more reflective" system also be more effective?
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This makes sense with PAP open baffles…I am convinced you can’t have big air moving woofers mounted to baffles without the entire assembly resonating. The woofers need to have independent mounts to the baffle to avoid it.
All the above ”tricks” you are mention are the result of using loudspeakers with bad directivity, ie loudspeakers with for example a big midrange unit ( 8 inch ) with the crossover to a tweeter of 1 inch.
The off axis response of such a loudspeaker will have peaks at those frequencys , wich needs compensation on axis.
Not a good way to create a good loudspeaker.
My own experiments to make a loudspeaker dissapear in the soundstage is like this:
1. Flat on axis frequency response
2. Good directivity at different angles.
3. No resonances
4. putting the loudspeaker away from reflextions within 5 ms, wich is exactly the same as you do with microphones when you are recording live music. Early reflections within 5 ms sound bad. Its the same with loudspeakers.
5. Using reflections in the room with a delay of 20 ms or more, to fill up the ”flawed” stereo 2-channel system, thus creating a better illusion from the recording event.
6. Correct installation of the loudspeakers.
Thanks for this! My question is however the other specifications; having a speaker devoid of such audible resonances, you can still easily detect position or have a tilted phantom centre if you are close enough to one of the speakers in a stereo setup. I believe the ratio of reflected vs. direct sound has an effect on the phantom image position, as well as set-up in term of toe-in of speakers. Also, reflected sounds help to diminish the flaws of the stereo system and even out the dips and peaks due to comb filtering always present in stereo.
All of the above are fine by me. However, delays of 20 ms, or 6.8 meters, and avoiding shorter ones to fill up the gaps and peaks will not be possible in most rooms.
Ok, I think I understand. All reflections are not the same - those coming from e.g. side-walls comes in an angle and not from the direction of the speakers. Reflections from the "speaker wall" side that comes with a short delay are not beneficial IMO. The only "early delayed reflections" coming from that side should be those encoded in the recording itself. Having an omnidirectional speaker you can diminish this by placing speakers >4 meters from the wall or use speakers designed to be very close to the wall, ideally in-wall.
Exactly! This is my main question here. It concerns the ratio of reflected vs. direct sound and "speaker invisibility". While you can extract the ambience and use surrounds to increase reflections from the recording venue, you can also increase the side-wall reflections by e.g. heavy toe-in to increase the enveloping sound.
tecnogadget
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Yes indeed, toe-in will undoubtedly have an effect on phantom image position (as explained on the pdf I uploaded). The way I see it, or at least I’ve empirically perceived, about the ratio of reflected vs direct sound, is that it affects the soundstage, how wide, how much depth or how much “3D like” the presentation feels.
My subjective appreciation after testing:
Direct sound: more like “in studio sound”, very focused or pinpoint, and not so big sound stage. Reflected: wider, like a “wall of sound”, bigger sound, livelier.
The thing about phantom image shifting if you are close enough to one of the sepakers is that since you are closer...sound time arrival is earlier than the other speaker, and our brain cares about that, so there isn’t any work around that, it’s the physics of listening to Stereo.
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