Originally Posted by amirm
. I showed the experiment that Dr. Toole ran to arrive at ETC showing completely wrong results. You all dismissed that with no real response. So we have another researcher here warning you that such measurements can be quite misleading. You can argue all you want .
Incorrectly constructed multi-source experiments that prove thatt the operator is unaware of ways to minimize and eliminate sources of error in a flawed experiment.
Congrats! Yup, but rather than prove how the the technique is flawed per your predisposed bias you have simply conclusively proven that you and the others lack the understanding necessary to employ such a fundamentally simple technique.
And in 1983 as well! He should have been at SynAudCon and learned how to properly use the tool - and MUCH more! - Heck, he could have learned from Heyser hilmself, or Don Keele, or Don Davis or Russ Berger or Peter D'Antonio or perhaps even Everest.
But please, humor us and cut and past some more as you as you apparently feel inadequate to prove your incompetence all by your self. But hey.misery loves company and you have managed to find all 3 people in the last 30+ years to maintain that a measurement that is industry standard in every major acoustics platform is flawed. But one thing yo have established with certainty! You have conclusively proven that it can be misapplied in poorly constructed experiments violating nest practices.
Can we say OPERATOR ERROR?
You might want to become intimate with that term, as if you only knew how to do them yourself, being the self proclaimed expert that you are!
Amd how can we ignore this chestnut " There were no measurement systems used in that graph. "
Are you serious? OF COURSE you are! Yes, NO measurement systems were employed to collect the data that was complied into your chart.
PLEASE do us all favor and go back to school and take a basic instrumentation and measurement course, as you embarrass yourself every time you make such asinine claims. And you went to school WHERE? I suspect they would appreciate that you do not advertise the fact...
For anyone still reading an edited cut and paste presentation of Toole by one who has “several days” exposure to the concepts, you might want to examine as aspect that he erroneously posits as equivalent and which displays an astounding lack of understanding of actual acoustical behavior.
It is rather fascinating as he makes it a cornerstone of his analytical mission.
When you electronically modify a direct signal you can modify its frequency composition in myriad ways. And after all is said and done, that is all you have done.
When this signal is played over a well designed loudspeaker it will exhibit the polar pattern consistent with the design of the speaker.
For our intents and purposes we will assume a speaker with an ideal power response per Toole – one that renders the output essentially uniform in a cardioid pattern devoid of polar lobing. (the first polar pattern “A” posted below)
Unfortunately, the behavior of the signal that he imagines is being replicated is anything but a uniform polar distribution.
And one even vaguely familiar with the concept of the superposition of spaced sources out of phase knows that what appears as a comb filtering pattern on an oscilloscope or a frequency response graph is merely the symptom of what is called polar lobing – of spatial regions where the effective signal is MISSING – not there – and regions where the signal is indeed distributed. In other words, what is modified is not the frequency response which our friend mistakes for reality, but it is the POLAR DISTRIBUTION – the actual distribution of the energy in space – that is different. The frequency composition of the direct signal does NOT exhibit ANY comb filtering! The direct signals can both be linearly ruler flat – ideal if you will.
What varies is the regional distribution of the signal energy in space, as there are literally regions of space where the pressure based energy, when the two arriving sound fronts intersect or superpose, the negative pressure and the positive pressure effectively restore the region to the ambient pressure – which results in there being no apparent pressure differential to hear as sound – it is ‘canceled’.
So, is a signal that exhibits variations in its constituent frequency composition that is reproduced in a uniformly distributed polar pattern identical acoustically to a signal whose frequency content is unmodified but whose spatial distribution is significantly modified such that entire regions lack any effective energy presence?
Heck no! The two scenarios are NOT EQUIVALENT in any way shape of form.
His example is flawed as a result of a VERY fundamental mistake very common to those who come from the world of 2 space small signal analysis – EE. He and his friends make the fundamental error of equating a 2 space uniformly distributed signal exhibiting variations in frequency with a signal whose spatial distribution has been radically altered and where the null regions lack the frequency content by virtue of active noise cancellation (superposition). But the frequency content of the source signals has never changed. Only the fat that where the spaced source signals combine out of phase at a particular frequency manifest in a spatial null is the ACOUSTICAL environment substantially modified.
Below you can see a graphical polar measurement of the result of two spaced sources whose arrival time varies by ONLY a difference of .283ms or 3 inches. The frequency content of the source signals from each speaker or of the direct and reflected indirect signal has not changed – it is whatever the source material provided – which for our example is a linearly flat full range signal from 0 Hz to gamma rays in frequency.
Note specifically how the polar pattern is significantly modified by the combining (superposition) of two or more separate ‘offset’ signals.
Note also that the signal that merely has its frequency content modified exhibits the uniform polar response of the of te non-offset signals for ALL frequencies.
Also, hopefully not to confuse this much further, but to point out another important factor with which to be aware, in the second case where ‘spaced’/out of synch signals are combined, that the polar pattern changes with frequency, and there will be not simply the one polar pattern pictured, but that with the increase in frequency you will have an increase in the number of nulls and lobes – so that what looks like a constant distribution pattern, changes with frequency – and also with ones movement within that soundfield!!!
In the electronically modified signal, this does NOT happen. Its spatial distribution is ‘constant’ throughout the spatial region meaning that there is no polar lobing due to the signal itself.
And anyone with half a brain can discern that an environment with e ‘radically’ modified spatial dispersion is going to be perceived DIFFREENRTLY than one whose spatial dispersion is uniform and which only features a uniformly modulated signal!
Does anyone wonder why the perceived signal is hardly noticed with such a flawed substituted stimulus??? The two scenarios they imagine to be equivalent are NOT in any way acoustically equivalent.
You see, the REAL problem here is that a few cannot properly discern what behavior is real, and which is merely an aberration on a measurement display that, while symptomatic, is NOT what is actually happening. And full range signals whose polar distribution in space is radically altered by regions where the energy is effectively ‘no longer there’ is SIGNIFICANTLY different from that a signal that is uniformly distributed over the space but which merely exhibits frequency modulation.
In ACOUSTICS, as opposed to electronics, comb filtering is a pattern in a frequency response measurement display. It is not ‘real’. In acoustics, what is REAL is the variation in the polar distribution at the different frequencies that vary with position in space – in the room. It is this REAL variation in the spatial distribution that manifests itself as simply a symptomatic pattern in the frequency response.
Also note that the polar distribution changes for the two spaced direct and indirect signals with position, as the timing/spacing relationship between the two arriving signals varies, resulting in the nulls ‘changing’ frequency. The nulls do not actually in reality change frequency, but rather their distribution varies in space, and as you move, you move into and out of the regions of spatial nulls.
And here we have learned folks making claims about the insignificance of such polar distribution with regards to perceived psycho-acoustics as they erroneously assert the equivalency of a uniformly distributed modulated signal with that of a complex spatially lobed distributed signal featuring no frequency modulation.
But hey, life is good when a reflection is a reflection is a reflection and when you can simply, by decree, ignore physics. But let’s be kind, as superposition is a complex concept and we really can’t expect an EE, let alone an entire coterie of EE’s, to have a firm grasp on something they may not have spent much time in school studying!
That is hardly equivalent to a frequency varying signal that is uniformly distributed in space whose polar pattern remains uniform for all spots featuring the exact same frequency response with the same artificially induced frequency variations distributed uniformly!
And nope, as he tells us, one would NEVER discern a subjective perceived difference in such a substantially modified polar distribution! You see, early reflections impart only a pleasant subjective difference. LMAO! The fact is that very early arriving high gain sparse reflections result in significant polar lobing and a very discernible modification of the perceived direct signal.
So, while getting one’s head around difference in how they function in the physical universe may seem a bit confusing a first, it is nowhere as confused as those who fail to make the distinction and as a result make a MISTAKE.
Originally Posted by amirm
This is the reason why in Clark’s test even a huge 2 foot by 3 foot reflector that caused reflections as strong as the signal itself yet it was “barely noticed.”
…And a "HUGE 2' x 3' reflector"? And he imagines this “HUGE reflector” to be not only broadband, but IDEAL, not allowing ANY indirect energy to not be reflected back to the listening position. NONE!!! Again the EE has no idea that sound has size and that unless the wavelength is SMALLER than the object, it is NOT reflected but that it diffracts around he "huge" object! It’s truly a shame that EEs effectively stop their study of physics with the several chapters limited to the first year second semester of physics dealing with electromagnetism and fail to stray far.
But it gets better, as not only does he assume that this “HUGE reflector” is broadband and IDEAL, but look at the measured results. What happens is even more astounding than the assumption about the “HUGE reflector”!!!!!!
What actually happens is that the indirect energy is GREATER in gain than the direct energy, of which it is simply redirected after incurring an apparently lossless boundary incidence, greater travel through the air (with apparently no additional loss) and in the process it has actually GAINED energy!!!!!!
This is astounding! In fact, this makes the cold fusion claims of the University of Utah in the early 90’s pale by comparison! In fact, forget acoustics, this guy has answered all our questions regarding the future of energy on earth!
All you need is a 'greater than ideal' "HUGE 2' x 3" reflector" able to reflect more energy than is generated by the direct source and a group of 'his friends' capable of making such a mistake! Who said there is no such thing as a free lunch?!?!?!?!
Not bad for a couple of folks who make such fundamental errors as assuming the equivalency of radically different acoustical spatial dispersions of signals simply because they focus solely on a frequency response comb filtering pattern while totally ignoring the actual 3 space spatial manifestation of their imagined 2space wave form, but they also image a “HUGE” 2’x3’ reflector to be an IDEAL broadband reflector capable of reflecting and redirecting more energy back to the listening position than was even incident upon it – and that is after literally ignoring the additional sources of resistive, reactive incidence losses as well as the addition air resistance loses due to a longer path of travel! These folks have transcended the limitations of physics on earth and traveled to the equivalency of Uranus where they are INDEED kings!
.Edited by dragonfyr - 7/9/12 at 4:06am