What makes speakers "disappear " and can it be measured?

[sigbergaudio]

I mentioned in another thread: I have floor standing speakers that do a very good job of disapearing. But when I put spring-based pods under my speakers to decouple then from the wood floor they seemed to completely disappear in almost an electrostatic speaker way. The sound also tightened up in the bass and became cleaner and less congested seemingly throughout the full frequency range. It’s pretty amazing.
The thing is whenever I do this I am very pleased with the results but after a while I miss the sense of physical connection with the sound that I get when they are allowed to vibrate on the floor. There’s more physical presence and punch, so I take the spring footers back out.

We actually do listen with our body and feet as well. So if you have a non-solid floor (won't work with say concrete), removing your own feet from the floor may actually have a similar effect as your spring-based pods. You may get an impression of cleaned up sound and attentuated bass. It's quite fascinating

 

[Tangband]

Pleased to oblige with some highly simplified responses:
1. Speakers devoid of resonances and (larger?) frequency reponse irregularities. Probably certain frequencies are more revealing than others.
Detection thresholds of resonances are relatively independent of frequency but very dependent on the program material - pink noise is the most revealing. Low-Q resonances (least ringing) are more audible than higher Q for the same deviation in spectrum amplitude - counterintuitive, but evidence is that we don't attend to the ringing as much as we do to the spectral bump. See section 4.6.2 in the 3rd edition of my book, or Toole, F. E. and Olive, S.E. (1988). “The modification of timbre by resonances: perception and measurement”, J. Audio Eng. Soc., 36, pp. 122-142.
Re. cabinet resonances: they are included in the 3D spinorama measurements and are not better or worse than the equivalent resonant sounds radiated by any other component in the system.
3. Early refections at sufficient level are bad.
If the spectrum/timbre of a reflection is different from the direct sound it will be more easily detectable as a separate phenomenon. LEDE control rooms and the notion that lateral reflections must be eliminated came about as a result of loudspeakers having poor off-axis sound radiation. This seems to explain why loudspeakers with well behaved (smooth and fundamentally similar) off axis early reflected sounds (around 60 +/- degrees off axis) are awarded the highest sound quality ratings in double-blind listening tests - done in rooms with NO side-wall absorption. Here is an example of how bad things were when some of these practices were being added to the "rules" for good sound in control rooms, which migrated into homes. The UREI was a very popular monitor speaker of the period - obviously the far-off axis sounds need to be eliminated/absorbed before decent sound quality is possible. Fortunately things have greatly improved. With well-designed loudspeakers wide dispersion is generally much approved of, lending a friendly sense of space, especially for those soundstage components that are hard-panned to L & R speakers - i.e. mono sounds. See Section 7.4.2 in 3rd edition.
3 Ratio of direct to late reflected sound.
The important reflections need to have substantial time delays (longer than the short-delayed reflections in domestic rooms) to support illusions of great distance meaning that they need to be in the recordings. In stereo they don't get to be reproduced from the appropriate angles. This is the dominant advantage of multichannel - the difference in "envelopment" (the sense of being in a large space) can be profound.
4 Ratio of forward sound to side-wall reflections. See above.
5. Floor reflection. If present it may reveal position, especially height localisation. This will challenge your credibility. See Section 7.4.7 in the 3rd edition. The most definitive test I am aware of was done in the Fraunhofer Institute flexible acoustics room. They concluded: "Regarding the floor reflection, the audible influence by removing this with absorbers around the listener is negative - unnatural sounding. No normal room has an absorbent floor. The human brain seems to be used to this." Humans evolved with something reflective below the feet.
6. Lower treble - may relate to a more distant sound.
This would require familiarity with the sound at a known distance in order to recognize the sound at another distance. Air absorption is the physical mechanism responsible for the spectral change with distance - See Figure 10.12 in the 3rd edition. The perception of elevation is another case requiring familiarity with the sound, and even given some familiarity our precision in vertical localization is poor.

Thank you for very interesting reading .

Another question : In your experience - how important or destructive are the impact of SBIR ? Is there any need to do room-treatment on the wall behind the loudspeakers ?

 

[Thomas_A]

Imo the KEY to time-intensity trading working well is for the output of the near speaker to fall off smoothly (and rather rapidly) as you move off-axis. This way as you move off to one side, the far speaker becomes louder than the near speaker in part because you are moving more on-axis of the far speaker, but MOSTLY because you are moving well off-axis of the near speaker. You want that near speaker's off-axis response to stay smooth so that the center image doesn't wander with changes in pitch.

When it's working right (which ime is at normal listening distances as you have found), my understanding is that the earlier arrival TIME of the near speaker is approximately offset by the greater INTENSITY of the far speaker.

I have multiple customers who sold their center-channel speakers after buying left and right speakers I designed because the dialogue was still on-screen for viewers well off to either side of the centerline, while the timbre of the phantom center channel was superior to that of their physical center channel speakers. And I'm talking about high-end center channel speakers which cost as much or more than one of my full-sized speakers.

There is one situation in which time-intensity trading does not work well even with suitable speakers, and that is for people who have a hearing imbalance (one ear hears significantly better than the other). For these people, imo a dedicated center-channel speaker is needed to anchor the dialogue on-screen.

There is another issue as well and that is the primary reflection on the nearest wall. While sitting in the sweet spot there is no problem with the center phantom image or clarity. Moving along the listening positions the position of the primary reflection point on the side wall changes. To maintain the phantom center while seated in front of one speaker, the reflection can be attenuated either by less energy from the speaker or by damping at the wall at that specific position or a combination. I use a combination including almost 45 degree toe-in but importantly I do not damp the primary side wall reflection point when at sweet spot. Only at the wall position when seated in front of one of the speakers. So while having rather wide dispersion up to 8 kHz, this works well for maintaining a center phantom image for several listeners.

 

[Thomas_A]

Have you tried Auro3D for upmixing stereo? I actually upmix all my music with Auro3D now. IMO, I think it does pretty much everything better than pure stereo. It's not a huge difference(which is why I like it). I almost never listen to stereo anymore since getting it. Unfortunately it requires 4 height channels, and Auro2D seems to be a completely different algorithm that I don't like at all . In fact, I think I prefer stereo over every other upmixer. What I don't like about most of them is that they put parts of the mix behind and/or above you. I like that Auro3D leaves the stereo image basically untouched and just adds additional envelopment via delayed reflected sound. I also love how customizable it is. You can customize both the delay of the reflections as well as their strength.

I hate that it requires 4 heights though. That makes it a no go for most. I wish Auro2D used same algorithm(just without the heights).

No, I don’t have Auro3D on my Marantz NR1710. I have a pair of Dolby-enabled loudspeakers sitting on top of my main speakers which I think work rather poorly. The side speakers are a bit special though sitting higher up on the wall with woofer directed against listener seats and tweeter at the roof angled to bounce down to the listeners. This gives both side and height impression. For Atmos ”roof speakers” I need to make more experiments with positioning without placing them in the roof. Roof placement would be a big no-no here (WAF).

 

[Floyd Toole]

Hi Floyd,

is there an optimal distance between the reflective side wall and the wide-dispersion speaker? Too close, and it becomes a problematic early-reflection 'second source' instead of merely adding apparent width: too far, and the amplitude drops off along with the effect of width?

cheers

Hi, sorry but I will make this one a homework assignment, because the answer is a very long one . Section 7.6 "Perceptual Effects of Room Reflections" is 17 pages long and it takes you through the elements of what you are asking. The very short answer is that ALL reflections in typical rooms are above the detection threshold, meaning that they are contributing "something" that is audible. However, the "second-source" threshold is higher than any of the typical room reflections (Figure 7.30) - at least for second sources that are timbrally similar to the direct sound. The question is: What are they adding and it it a good or bad thing?

The answer involves some "hard" facts and the "soft" reality that humans adapt to rooms - after all, it is another evolutionary factor: caves to living rooms, all of which have not only floors, but walls and ceilings. An important metric of perception is speech intelligibility and there is much evidence that humans exposed to new acoustical spaces adapt very quickly to the new patterns of reflections and their speech intelligibility scores improve after brief exposures. Experiments showed that "the process underlying this effect are relatively rapid - on the order of seconds - and do not show longer term improvement". Personally, I believe I have experienced the effect when I have been away from my system for an extended period, like a vacation. When I first turn it on it sounds "strange" but in no time I "break in" again to the old circumstance and all is well. This is obviously how it is that double-blind tests of speakers done in very different rooms yield very similar results - the listeners "normalize" the rooms, up to a point at least. (Section 7.6.1 in the 3rd edition).

 

[Floyd Toole]

The info so far still does not explain the apparent fixed center phantom image when I am listening in the sofa in front of the left speaker. It falls apart when moving closer to the speaker, but at nominal listening distance the center phantom image is dead center between the speakers. Without a center speaker. Is it reflections and toe-in?

An interesting question. My PhD thesis was on sound localization and it quickly became clear that when the interaural time cues moved beyond the +/- 0.6 ms (or so) within which "normal" binaural image shifting takes place, there is another process. This one seems to be "central" - cerebral processing as opposed to occurring in the periphery of the auditory system - in what I called a "compromise" localization - a logical or plausible interpretation. Two ears - and a brain - do their best to make sense out of nonsense. These are fully sighted experiences, making the perceptions even more susceptible to visual factors which are profoundly dominant.

Something similar happens in many real life situations, like an orchestra in a concert hall. Back in the audience the direct-sound localization cues are seriously corrupted by the relatively strong reflected sound field. However, it takes only a few brief transient sounds for us to identify the position of certain instruments. Once localized they perceptually remain in those locations even when the real-time sounds are impossibly corrupted.

At least this is the best explanation I can offer at this time.

 

[Floyd Toole]

Have you tried Auro3D for upmixing stereo? I actually upmix all my music with Auro3D now. IMO, I think it does pretty much everything better than pure stereo. It's not a huge difference(which is why I like it). I almost never listen to stereo anymore since getting it. Unfortunately it requires 4 height channels, and Auro2D seems to be a completely different algorithm that I don't like at all . In fact, I think I prefer stereo over every other upmixer. What I don't like about most of them is that they put parts of the mix behind and/or above you. I like that Auro3D leaves the stereo image basically untouched and just adds additional envelopment via delayed reflected sound. I also love how customizable it is. You can customize both the delay of the reflections as well as their strength.

I hate that it requires 4 heights though. That makes it a no go for most. I wish Auro2D used same algorithm(just without the heights).

I too use Auro3D upmixing for almost all of my stereo program listening. It can be adjusted to add what is for me the right amount of very subtle envelopment - the perceptual element that stereo (a directionally and spatially deprived format) is most lacking. From memory it is not as good as an early version of Lexicon Logic7, but that is history. That did an excellent job of enhancing the missing sense of enveloping space while leaving the stereo soundstage alone. With real surround channels and speakers all this chatter about listening room reflections suddenly becomes almost irrelevant. It is time to move on. BTW, elevation speakers are not a firm requirement for success if one can find the right upmix algorithm.

 

[Floyd Toole]

After reading Mr Toole's response, would it be fair to say that older speaker designs emulated headphone design, with a particular emphasis for on axis and an emphasis on eliminating off axis sound? It seems to me that modern speaker design accommodates for the room, whereas in the past there was a concerted effort to eliminate the room from the equation.

The focus on direct sound is an historical relic, much influenced by professional recording and broadcasting practices (including BBC). A lot of their listening was done is quite "dead" rooms. That said, there were definitely some early speaker designers who made an effort to get the off-axis performance right. With improved access to accurate anechoic (real or simulated) measurements the situation has improved, and the contributions of modern research, including some of my own, have added fuel to the effort to make loudspeakers more "friendly" to real world rooms.

 

[Floyd Toole]

Good to see real data on room response and psychoacoustics. If home consumers can design rooms with good acoustic traits, speakers should follow soon after.

I suggest turning your statement around. "If home consumers start with well-designed loudspeakers room acoustics will be less of an issue - except at bass frequencies, where the room/loudspeaker/listener coupling dominates. Such loudspeakers now exist, and methods for refining bass performance are well understood.

 

[Floyd Toole]

We actually do listen with our body and feet as well. So if you have a non-solid floor (won't work with say concrete), removing your own feet from the floor may actually have a similar effect as your spring-based pods. You may get an impression of cleaned up sound and attentuated bass. It's quite fascinating

H-m-m-m, vibration isolators for footstools - I like it!

 

[Wes]

https://journals.physiology.org/doi/full/10.1152/physrev.00026.2009

 

[hex168]

I too use Auro3D upmixing for almost all of my stereo program listening. It can be adjusted to add what is for me the right amount of very subtle envelopment - the perceptual element that stereo (a directionally and spatially deprived format) is most lacking. From memory it is not as good as an early version of Lexicon Logic7, but that is history. That did an excellent job of enhancing the missing sense of enveloping space while leaving the stereo soundstage alone. With real surround channels and speakers all this chatter about listening room reflections suddenly becomes almost irrelevant. It is time to move on. BTW, elevation speakers are not a firm requirement for success if one can find the right upmix algorithm.

This is a dumb couple of questions, but I am curious. I have Harman Logic 7 in my car. 1) Does it have much of a relationship to the Lexicon Logic 7 you are referring to? And, 2) My subjective impression of turning the Logic 7 on in my car is that the sense of space is better but the upper midrange becomes harsher. Anything similar for the home system? Thanks!

 

[More Dynamics Please]

I feel like I've stepped into a time machine and gone way back to my college days listening to the most interesting and informative Q&A session with Professor Toole. How fortunate we are that he continues to be so willing to freely share his vast experience and knowledge with us in this forum.

 

[Thomas_A]

https://journals.physiology.org/doi/full/10.1152/physrev.00026.2009

Thanks, will read in detail later. Regarding floor bounce I am still hesitant. As shown floor bounce gives spectral cues. If these are embedded in the recording I don’t think they should be added again in your room.

 

[Pearljam5000]

I feel like I've stepped into a time machine and gone way back to my college days listening to the most interesting and informative Q&A session with Professor Toole. How fortunate we are that he continues to be so willing to freely share his vast experience and knowledge with us in this forum.

I still can't believe he's participating in a thread I started

 

[Frgirard]

Thanks, will read in detail later. Regarding floor bounce I am still hesitant. As shown floor bounce gives spectral cues. If these are embedded in the recording I don’t think they should be added again in your room.

In concert, when the venue is full the floor bounce doesn't exist. It's not an issue. I set on my floor japanese tatamis with a rug. 7 cm thick. I will not change.

 

[Sancus]

From memory it is not as good as an early version of Lexicon Logic7, but that is history.

The SDP-55 has a "Logic 16" that is supposed to be an updated version of that, I don't know if it's coming to the SDP-75. And I don't know anyone who has tried it/heard it because apparently it's been bugged since the release of that processor. But I'm very curious how well it works if they ever fix it...

There is also a Lexicon cinema processor that includes something called "QuantumLogic" which is also a successor to the Logic upmixing. But it's less than ideal for home use, and quite expensive just by itself.

 

[Floyd Toole]

Thank you for very interesting reading .

Another question : In your experience - how important or destructive are the impact of SBIR ? Is there any need to do room-treatment on the wall behind the loudspeakers ?

With forward-firing loudspeakers the sound radiated to the rear is dominated by bass frequencies - as loudspeakers tend towards omnidirectIonality at low frequencies. This means that any absorbing material must be effective at long wavelengths, so "fluff" would need to be impractically deep, and membrane absorbers tend to be frequency selective, although a few commercial products are fairly broadband. Not simple. It turns out that

Thank you for very interesting reading .

Another question : In your experience - how important or destructive are the impact of SBIR ? Is there any need to do room-treatment on the wall behind the loudspeakers ?

Section 9.2 in the 3rd edition addresses the issue of adjacent boundary effects. It is essentially an issue of radiated energy which is amenable to equalization based on a generous spatial average. But it cannot be completely eliminated. What remains seems to be accommodated by adaptation.

 

[Floyd Toole]

The SDP-55 has a "Logic 16" that is supposed to be an updated version of that, I don't know if it's coming to the SDP-75. And I don't know anyone who has tried it/heard it because apparently it's been bugged since the release of that processor. But I'm very curious how well it works if they ever fix it...

There is also a Lexicon cinema processor that includes something called "QuantumLogic" which is also a successor to the Logic upmixing. But it's less than ideal for home use, and quite expensive just by itself.

Quantum Logic is a totally different process intended to construct "new" listening experiences, not to subtly enhance stereo. Dr. David Griesinger, the brains and good judgment behind the original Logic 7 is retired. I know nothing about the current offerings - I too am retired.

 

[Thomas_A]

In concert, when the venue is full the floor bounce doesn't exist. It's not an issue. I set on my floor japanese tatamis with a rug. 7 cm thick. I will not change.

yes aometimes it is not embedded in the recording. Sometimes it is. In either case, adding a new one is of no benefit IMO.