So we get to listen to the one trick pony interpretations of Toole now adamantly opposed to early reflection treatment stating that "When we look at examples of how sounds arriving from specific angles are modified, a very different picture emerges, and it is one that strongly suggests that a naked wall may be a better option than thin absorbing panels."
Yeah, as he repeatedly states that ANY treatment that is NOT sufficiently broadband ADVERSELY MODIFIES THE SPECTRAL CONTENT OF THE REFLECTED ENERGY!!!!
Meaning ANY treatment MUST be sufficiently broadband!
This is further reinforced by admonitions from Toole consistent with what ALL of the best minds have advocated about treatment for what seems like forever:
"7.1.2 Obviously if the purpose of the absorbing material is to attenuate the reflection, the material should be equally effective at all frequencies. Given the duplex nature of sound fields in small rooms, it seems reasonable to expect similar performance at all frequencies above the transition region.
9.2.1 Any device inserted into a reflected sound path— reflector, absorber, or diffuser—should perform uniformly well at all frequencies above the transition frequency region, say, 200–300 Hz. This is in order to preserve the spectral balance of the loudspeakers, to uniformly attenuate the full spectrum of reflections, and to ensure that the precedence effect is maximally effective.
Thus from the perspectives of maintaining the excellence in sound quality of good loudspeakers, rendering an unwanted reflection inaudible, and preserving the effectiveness of the precedence effect, there are reasons not to alter the spectrum of reflected sounds. One is free to redirect them with reflectors or diffusers, or to absorb them with lossy acoustical devices, but in each case, the process should not alter the spectrum of the sound above some frequency toward the lower side of the transition region in a small room. It seems reasonable to propose, therefore, that all acoustical devices used in listening rooms— reflectors, diffusers, and absorbers—should be uniformly effective above about 200 Hz. For resistive absorbers this means thicknesses of 3 inches (76 mm) or more."
A fly in the ointment being that what many persist in believing is adequate performance is predicated on data based on flawed measurement procedures.
The irony being that measurements utilizing the heretofore accepted absorptive test standards ASTM-C423 and ISO-354, as a result of Ron Sauro's recent research, have been rendered politely "inaccurate at best" (as are the methods for calculating scattering coefficients as specified in ISO-17497-1).
This is further complicated by a testing methodology assuming a diffuse energy field that is not applicable to situations common to our usage where the incident sound is limited to more directionally restricted oblique angles of incidence and where edge diffraction of ALL edges, including non-incident edges, are not at play; in addition to he old measurements ignoring the important factoring of the anisotropic nature of the material - meaning that absorbent material functions differently depending upon its physical orientation, as the material structure is not random, but distributed in patterns where incident energy directed in one direction is effected differently and less well than energy directed from other directions.
(A simple example that may make this much more easy to envision is a 1D QRD diffusor. If sound is indecent perpendicular to the 'grooves/wells', the diffusor functions optimally. If the incident sound is parallel to the wells, the wells are almost totally ineffective. Such is the case with typical oriented semi-rigid Fiberglass as well.)
Now I am not expecting most to simply go, "oh, of course" as many of you express frustration with any reference to technical issues. So the larger point here is that much of the heretofore test results commonly cited are NOT what they seem to be. They are overstated not only by virtue of their ability to have absorption coefficients greater than 1, but they have been rendered flawed and are currently in the process of revision to render them more accurate as their accuracy has been successfully challenged!
But results using the new methodology are available on a more limited basis. And a few object to the use of Soundflow and the more advanced models, techniques and considerations being used as it contradicts and or modifies those old vested assumptions. (Yup, and just listen to someone here tell us what Soundflow is based upon; someone who was not even aware of it until we pointed it out, and who remains ignorant of the use of gas flow resistivity values being used in the calculations, let alone as to the myriad models that are cross correlated in the results... And where does this nonsense about calculations assume a perpendicular incidence when it is able to be specified and explored for any angle? Especially when they cannot even get Toole's own admonition that such purely resistive absorptive material be at least 3" thick based upon out of date data!)
And if you accept Toole's premise which also agrees with just about every other major school of thought that has preceded him, that means that 'almost good enough' treatment is NOT a sufficient solution!!!! It means that 'almost good enough' treatment is NOT a partial solution, but that it instead merely moves the problem around and makes it worse!
But let's take all of this one step further.
So what does Toole offer the average person here???
He states over and over again that merely treating a room is not satisfactory!
Unless one has 'ideal' speakers with a uniform power response, they are basically hosed.
So, folks, let's see a raise of hands who has ideal uniform power response speakers?
Hmmmmmm....A bit underwhelming, wouldn't you say? So it looks like we are left trying to figure out what the vast majority of you can do.
And who has an ideal room that will not adversely affect the symmetry or spectral balance of the reflected energy? Why do I get a feeling that the results are about the same as for those who lack ideal power response speakers?
And I suspect that this group also includes all of you who have cried out so loudly that adequate broadband treatment is simply not in the cards...as how there are so many real world mitigating conditions sufficient to cause one to compromise one's treatment....
So, per Toole, if you do NOT have ideal uniform power response speakers, and you cannot apply spectrally neutral treatments effective over the full specular bandwidth beginning at ~200 Hz, you are exaggerating the problems.
The reality need not be so draconian nor bleak.
One CAN largely address the problems caused by non-uniform power response speakers - the ones the vast majority have.
And for some, there will be a tradeoff due to the need to use adequate treatment.
But before they tune out and give up or simply complain some more, for those who so loudly lament the requirements for the thickness of purely porous absorption, that you face your constraints and pursue low Q hybrid porous/'membrane' absorbers that can achieve similar results using a thinner hybrid construction, that will in most cases cost more for the increased sophistication of the design, unless you are willing to spend a bit of time to learn the physics of the behavior and construction of such tools. And the most practical of these may be a 4" layer of porous material faced with a binary amplitude grating providing a combination of low frequency absorption with moderate degree of mid high frequency diffusion, thus resulting in greater lower frequency control coupled with the retention of the mid-high energy. Just realize the practical constraints of this topology, and it can offer significant benefit. Likewise one might also pursue a broadband VPR topology sandwiching a membrane between two porous material layers.
So let's review the basic behavior we are dealing with if you have non-ideal power response speakers...
A typical speaker with a non-uniform power response features what is commonly known as 'collapsing polars'. this means that the low frequencies are low Q, meaning that the lower in frequency and the longer in wavelength, the greater they spread out quickly in an almost cardioid pattern.
The mid range tends to beam in a medium Q pattern, somewhere in between a wide floodlight like distribution pattern, and the high frquencies tend to beam in a high Q pattern, rather like a spotlight. In other words, as you increase in frequency, the more narrow and focused the spatial power radiation pattern.
That means that ONLY in the narrow Q region of the tweeter are all of the frequencies present covering the same region evenly. And with decreasing frequency, you are becoming more and more weighted to the mids and finally the low frequencies in the off-axis regions.
As a result, assuming uniformly reflective walls over the specular bandwidth from ~200 Hz up, since the polar distribution of energy from the speakers is not even, the resulting reflections will not be uniform and will result in the coloration (effective EQing) of the frequency content of the direct sound.
Can we address this? Yes.
But it requires a few things. And it does have a few tradeoffs.
First, what does it require?
It requires that all treatments for reflections be effectively broadband. Meaning, as said earlier above, that all treatment must be effectively broadband, and able to control all energy over the FULL broadband bandpass, especially the long wavelength energy down to ~200 Hz.
You see, if it is able to handle the low frequency long wavelengths, it is generally pretty easy for it to handle the high frequency short wavelengths as well.
So by using the large thick absorbers s necessary to control the low specular frequencies, the mids and highs are 'automatically addressed'.
So, by identifying the incident patterns on the boundaries, one can surgically treat the points where such incidence is a real problem, and help control the uneven power response of a non-ideal speaker, as it is the low and low-mids that create the 'non-uniform' spectral portion of the spatial dispersion.
By making the treatment broadband, it will control the worst that may occur, while easily dealing with the mids and higher frequencies.
But if you only use thin limited treatment, you will only control the high frequencies and leave the even more critical low-mids and lows to wreak havoc with the response and color the sound, as well as to adversely affect the imaging, localization and intelligibility of the direct signal.
And while you never want early arriving sparse (non-diffuse) high gain reflections in any case, you also do not want significant early arriving reflections whose spectral balance has been modified by the wall surface or by inadequate treatment spectral balance will them also color the sound of the direct signal.
So, the way you deal with this situation is to use BROADBAND absorption (or diffusion in limited cases which are beyond he scope of this already too long post) that effectively can be used to even out the typical speaker's (and the room's) non-uniform power response, treats it adequately, and results in a direct signal whose integrity is preserved.
And without a plethora of well-controlled diffuse early reflections (of not too high gain or sparse a nature), you may not have a wide fuzzy less well defined but BIG image, but instead you will be 'stuck' with a more accurate (as in identical to what was recorded), more precisely defined image. And heaven knows that there are worse things!
But this tighter more defined imaging is precisely what Toole complains about (and which most recording engineers prefer - further supported by the fact that the users of Blackbird Studio C have covered the MEGA side diffusors with packing blankets, rendering them absorbers of early arriving energy, to thus tighter up the image in accordance with their professional PREFERENCE...) as it is not found as pleasing by some who like larger fuzzier images in multi-channel sources.
So, if you do not have ideal power response speakers, and you do not have perfect room, you are basically stick making selective surgical adjustments. And Toole's all or nothing admonitions that are essentially akin to the admonitions of communists advocating the perfect ideal classless society. Given the pre-requisite assumptions of a diffuse well behaved early arriving soundfield are achieved by both the room AND by uniform power response speakers, you are good to go.
But if you lack EITHER, you have big trouble in River City.
You are stuck with a non-uniform power response distribution, either because of the speakers, AND/OR as a result of the inadequacy of the room boundaries AND due to insufficiently broadband treatment.
So, you are faced with a rather obvious choice:
Follow Toole's advice and buy new speakers and completely redo your room that either preforms optimally without treatment or utilizes approriate adequately broadband treatment (an no more complaining about 'thick' porous panels if you choose to stick with porous absorption) (which if you could do that, I doubt you would be here...),
...or take measurements, determine the actual dispersion pattern of your speakers and the actual points of incidence of specular energy on the boundaries, and treat them APPROPRIATELY with adequate broadband treatment in order to correct for the real world uneven power response of your speakers and for the geometry of the room while being prepared to listen to the Toole camp repeatedly tell you that your speakers suck and that your room and treatment are inadequate - something you already know is you are here looking for solutions.
And given the later choice where an early arriving diffuse soundfield is not an option due to room and/or speakers, an achievable well behaved tighter more defined and accurate imagine is not such a bad alternative, coupled with a later well-behaved laterally arriving diffuse exponentially decaying soundfield that provides a complimentary sense of spaciousness and envelopment. All in all, such an achievable result may not be such a bad thing after all compared to a design basically telling you cannot get there unless you buy new speakers and heavily modify your room such that you do not need fancy treatment - although that which you do use, MUST be broadband.
It IS your choice.
Just ponder those professionals who have access to Blackbird, opting to place blankets over those absolutely amazing diffusors... Someone desperately needs to tell them about how large amorphously defined fuzzy imaging is preferred by some...