Does the first reflection point actually matter??

Aj523 wrote: 

" 5. Tame from "40 cycles - 7000 cycles" as he calls it with eight (8) carbon panel CPs at $750 per panel. And since each panel weighs 150lbs, its about $1,000 for shipping. So all in $7,000." 

I agree with the frequency region he focuses on.

We see that serious acoustic treatment is expensive. That seven thousand dollar figure is an argument for taking loudspeaker/room interaction into account from the beginning, as imo there are more cost-effective solutions.

Duke

"You could easily circumnavigate the laser point and it would be much much better than merely putting panels on that point."

I don’t think I’ve ever advocated a "reflection POINT" paradigm; I think I’ve been talking about a reflection ZONE.

"And that unless you are in a small home recording studio, where you can touch the left and right walls at the same time, the correct placement being off 6" here won’t matter."  

Are we actually within six inches of agreement?

Duke

@erik_squires wrote:

"I believe most audiophiles would be unable to tell if those treatments were at the reflection points or not, and that in many cases 4 panels of 2’x2’, no matter how well placed, would be unable to effect an audible improvement."

and

"By ["treat"] I mean to alter the [room] surfaces by increasing the absorption and decreasing the ability of those surfaces to throw a coherent reflection by both absorption and diffusion."

Thank you Erik.

My reservations about using absorption on the entire surface, rather than just on the places where it has the most beneficial effect, are twofold.

First, to the extent that absorption is more effective at short wavelengths than at long ones, it will change (darken) the spectral balance of those first reflections. That may still be a worthwhile net improvement if the room is overly reflective, but in general it is desirable for the reflections to have approximately the same spectral balance as the direct sound.

Second, absorption continues to be effective long after the first reflections... ALL subsequent reflections which strike the absorptive material have their spectrum and overall loudness altered accordingly. So treating entire room surfaces can result in an overly dead room.

Reverberation time is seldom an issue in small rooms unless they have a slap-echo issue, and even then treating the entire wall with absorption is probably unnecessary. (Some argue that the term “reverberation” is actually inappropriate for small rooms because discrete reflections dominate, but I think it conveys a useful concept.)

As has been mentioned, loudspeakers are not true point sources, nor do we normally sit with our heads sufficiently in a vice that a 1 foot square treatment panel is what anybody is advocating. So I think "first reflection zones" is a more useful concept than "first reflection points."

I think you and I disagree on whether the timing and magnitude of reflections matters. If not, then neither does it matter where your absorptive panels go. If it does, then where they go also matters.

As I stated before, imo your assumptions are valid for large rooms (wherein the reverberant field is uniform enough that the reflections average identically at any given location) but not for small ones (wherein we have discrete reflections at any given location).

It sounds to me like you want to use enough absorptive acoustic treatment panels to make a significant difference throughout the room. Imo that would make sense ONLY if the speaker’s off-axis response is so bad that the reflections are generally detrimental. If the reflections are beneficial, weakening all of them and degrading their tonal balance with absorption would be detrimental. I’m not saying absorption has no place in home audio, but I am saying that the less of it we "need", the better.

Imo there is an alternative approach which starts out with the design of the loudspeakers themselves, and which does not call for anything remotely approaching treatment of entire room surfaces in order to get good results. Briefly, the loudspeaker sends spectrally-correct energy in directions which minimize early sidewall reflections, and the reverberant energy is allowed to decay more or less naturally, perhaps using diffusion, as opposed to being rapidly absorbed. If anyone is interested I’ll go into detail.

Duke

Mahgister wrote: "how will you create ideal listening conditions in your own room?"

That would take a while for me to answer and would de-rail or hijack the thread.

I get the impression that you have something you’d like to share:

"The best is the cheapest way to create a stunning audio experience is not upgrading your audio system to a more transparent one at prohibitive cost, but transforming your room in a positive player...The rewarding is astounding and the cost very low....

"This is my experiment...This is my point.... "

It sound like you are very excited about something you have done in your room. Maybe you could start a thread about it?

Duke

Mahgister wrote: " We must NEVER forget that acoustic preparation of a studio recording room has no relation at all with what must be used in a play back audiophile room.... "

Please note that I said "control room", not "live room", the latter being the room where the musicians perform and the actual recording is made.

The goal in the control room are not dissimilar to home audio: To clearly hear what’s on the recording, without any masking or other undesirable signature from the playback room.

Duke

The first sidewall reflection point matters in the design of a recording studio control room. Those I have been involved in used angles which direct the reflections away from the normal listening position.

In rooms where that’s not an option, apparently the first sidewall reflections still matter... or at least, what one does at these locations matters. @erik_squires on the subject:

"To my experience, as others here have noted, diffusion at the 1st reflection points are a better idea [than absorption]. They enhance imaging."

One significant difference between diffusion and absorption is, diffusion doesn’t significantly change the spectral balance of the reflected energy, while absorption does. And absorption keeps on having its effect on everything that hits it, not just those first reflections, for better or for worse. Both reduce the amount of early sidewall reflection energy which arrives at the listening location, but diffusion does so more benignly.

Early sidewall reflections have benefits. They DO increase the apparent source width... in other words, they can make the soundstage wider, but some image precision and soundstage depth is lost in the process, along with some clarity. So it’s a tradeoff. If not absorbed, that first sidewall reflection energy lives on to come back as later reflections which convey spaciousness (hall ambience) with no significant downside.

Earl Geddes on the subject of early reflections, which typically include the first sidewall reflections:

"The earlier and the greater in level the first room reflections are, the worse they are. This aspect of sound perception is controversial. Some believe that all reflections are good because they increase the listeners’ feeling of space – they increase the spaciousness of the sound. While it is certainly true that all reflections add to spaciousness, the very early ones (< 10 ms.) do so at the sake of imaging and coloration... the first reflections in small rooms must be thought of as a serious problem that causes coloration and image blurring. These reflections must be considered in the [loudspeaker] design and should be also be considered in the room as well."

Duke

Mahgister, it sounded to me like you have created a "stunning audio experience" by doing something to you room, but I have absolutely no idea what you have done. I have no idea what your "change of perspective" is, but would like to. You seem to be very excited about it.  Have you discovered something new?

It also sounds like you may feel offended by something I said, which was not my intent. If you want to talk about that too, feel free.

Which Floyd Toole article are you referring to? I’m somewhat familiar with his work on sound reproduction, and on the acoustics and psychoacoustics of loudspeakers and rooms.

Duke

Mahgister wrote:  " I related my 2 years journey in my thread... 

"Miracles in audio....." 

Thank you very much.  And thank you for the link to the Audioholics article,    I'll look at both. 

Duke

@erik_squires wrote: " For the purposes of this argument, alone, I want to argue that first reflection points don’t matter, ever."

Early lateral reflections contribute to spaciousness and expand the "apparent source width", according to Floyd Toole.

When "presence" is lacking the earliest reflections are the most responsible, according to David Griesinger.

So apparently early sidewall reflections are neither entirely beneficial nor entirely detrimental. They do some things which are desirable, and some which are undesirable.

Earl Geddes is aware of both the benefits and the detriments of early reflections, and here is his thinking on the subject:

"The earlier and the greater in level the first room reflections are, the worse they are. This aspect of sound perception is controversial. Some believe that all reflections are good because they increase the listeners’ feeling of space – they increase the spaciousness of the sound. While it is certainly true that all reflections add to spaciousness, the very early ones (< 10 ms.) do so at the sake of imaging and coloration. There is no contention that reflections > 20 ms are positive and perceived as early reverberation and acoustic spaciousness within the space. In small rooms, the first reflections from an arbitrary source, mainly omni-directional, will never occur later than 10-20 ms (basically this is the definition of a small room), hence the first reflections in small rooms must be thought of as a serious problem that causes coloration and image blurring. These reflections must be considered in the design [of the loudspeakers] and should be also be considered in the room as well."

My own investigation (controlled blind testing, but nothing peer-reviewed) leads me to believe that early reflections are strongly involved in conveying a sense of the playback room’s boundaries being nearby. The weaker the early reflections, the less "small room signature" the playback room superimposes atop the recording venue’s acoustic signature, whether it be real or engineered or both.

I have been involved in several professional recording studio projects, in which the acoustician has designed angles into the sidewalls which geometrically preclude early sidewall reflections at the mix position. This is to facilitate clearly hearing the acoustic signature which is on the recording, without the mixing room’s signature being dominant.

So imo what happens (or doesn’t happen) at the first sidewall reflection points makes a difference. Whether or not this difference "matters", and if to so what extent, is, I suppose, a judgment call.

Erik again: "if you take a dozen panels placed around evenly in a room, I don’t think you could tell that the 1st reflection points do anything more special than the rest."

This would be true in a large room, but not in a small room. In a large room the reflections paths are much longer and there are so many reflections that the reverberant energy is effectively uniform throughout the room, such that WHERE you place acoustic treatment doesn’t matter - the net effect is the same. But in our small home listening rooms, we experience discrete reflections. And the earliest and loudest of those reflections are the ones which have the strongest effects, whether their effects be beneficial or detrimental or both.

Duke

Erik wrote: " We shouldn’t spot treat surfaces. We should treat the surface. That is, putting 2’x2’ panels in exactly the side, rear and even floor reflection points is practically useless. What does work is to treat the floor, side and rear. "

So if I understand correctly, you are saying that treating the relatively small area where a reflection occurs is "practically useless" - instead, we should treat the ENTIRE room surface - the entire wall, or the entire floor, and/or the entire ceiling.

Am I understanding you correctly?

And, just so we’re on the same page as much as possible, can you describe what you mean by "treat"?

Thanks!

Duke

Erik wrote: " Which I agree with, but is subtly, different than what I am arguing about. :)"

I guess I missed that subtlty. Could you rephrase it? Pretend like I’m really dense... or don’t pretend, as the case may be... 

;^)

Thanks.

Duke

Hsw wrote:  " Is this discussion only limited to lateral reflections? It seems to me the floor is the largest first reflection. "

The floor bounce usually is the strongest early reflection, but perceptually is is not as detrimental as its magnitude seems to imply.

The floor bounce doesn't have a strong spatial effect, as it occurs in-line with the direct sound from each speaker.   

The floor bounce does result in a cancellation (comb filter) notch in the  frequency response at the listening position at the frequency were the reflection arrives 1/2 wavelength behind the direct sound.   

From a perceptual standpoint, the floor-bounce notch can be filled in by energy which arrives within a few milliseconds, such as by the ceiling bounce.  The ceiling bounce and the floor bounce will have different notch frequencies and will tend to perceptually fill in one another's bounces.   

The floor bounce notch is most audible when there are no soon-arriving reflections to fill it in. An example of this situation would be when talking with someone outdoors.  There will be a lower midrange frequency response notch from the bounce off the ground or pavement, with no other reflections arriving to fill it in.  Walk indoors to continue the conversation and the timbre of the person's voice noticeably warms up, and I think this is at least in part due to the floor bounce notch being filled in, perhaps largely by the ceiling bounce.   

The argument has also been made that our ears are so accustomed to the floor bounce notch and other naturally-occurring comb filter effects that we largely tend to ignore them.  That's NOT to say that there is no benefit from minimizing or removing them - only that they do not tend to cause colorations which draw attention to themselves.   

Imo there IS benefit from reducing the magnitude of the floor and ceiling bounce notches, or otherwise breaking them up.  But it is also my understanding is that they tend to be perceptually relatively benign in a home audio setting.   

Duke

@erik_squires wrote:

" What matters is that portion of the wall, and the overall, average results. For instance, covering 20% of the wall with absorption and 5% of it with diffusion, as needed. "

It sounds like you are still looking at small rooms as if they were large ones, where 20% wall coverage has the same effect no matter where that 20% is located. And I disagree, because in a small room the earliest reflections will not only be the loudest but also the most likely to be detrimental, therefore THOSE are the ones we should pay the most attention to.

And I think that in general you lean more towards absorption, whereas in general I lean more towards diffusion, because I want to preserve the spectral balance of those reflections. If their spectral balance is inherently bad (because of poor radiation pattern control), that’s a different situation - then we would be using room treatment in an attempt to FIX a problem which ORIGINATES with the loudspeakers. And that is not easy to do well because room treatments are generally not frequency-region-specific enough in the RIGHT regions; room treatments generally paint with broad brushes, so to speak.

I’ll go along with the "AS NEEDED" part, with each of us obviously having a different idea of what that means.

Duke

" My gods we are being so literal."

Let’s not descend into arguing about arguing.

" I’m saying that if best acoustic principles call for 20% absorption on a wall surface near the speakers, whether those panels EXACTLY cover a reflection point which works for exactly one seated position is irrelevant. "

I understand what you are saying.

And I disagree.

Imo "best acoustic principles" in a small room includes correct PLACEMENT of acoustic treatments. 

Duke