Quote:
Originally Posted by
kingtut38
β‘οΈ
I had the opportunity to speak with Christian Hohendahl who is the designer of the BS-3D and we discussed it and the new 3D Holophonic system they are coming out with. He seemed really exciting about both but especially the new product. There should be a lot of buzz when it is released. It's price will be considerably more than I can spend but it's meant for high end users anyway.
I think I will continue to evolve my homemade dummy head and when I hear some other clips of the bs-3d evaluate my situation then.
So, I did a lot of digging on the web and found the foreign patent application for the Holophonics system as envisioned by Zuccarelli, and later, I fould the U.S. patent proper.
There are many, many things in the patent that scream 'binaural' and there appear to be (in my opinion) few, if any discriminators that clearly make the claimed holophonic process significantly different than a typical binaural as manufactured by Bruel & Kjaer, Head Acoustics, Neumann, Cortex et al.
In a nutshell, the U.S. patent describes both the idea of 'holography' as well as the process itself for making the mannequin head. The differences between what they refer to as 'other binaural' techniques comes down to this:
The process assumes that an x-ray (or series of x-rays) are taken of a human head in order to define its geometry. The mannequin head incorporates a sort of 'mass' like that of the human brain as well as nasal cavaties and such. What I can ascertain from the patent is that these things are all incorporated, but the mechanism by which sound is sensed is pressure transducers (i.e. an omni-directional microphone) mated to an ear canal (what they call the meatus) and that ear canal being part of an artificial ear. The patent also specifies that the ears should be made of something like silicone rubber (which is what is used in the B&K 4100, Neumann KU 100, the KEMAR, and the Cortex - only the Head Acoustics variants utilize an ear that more resembles a wedge than it does a pinna).
Basically, this like all true mannequin heads is
unlike a BS-3D in that the BS-3Dis a sphere and not more of an ovoid like a typical human head (and thus mannequin) shape and lacks ear-located pressure transducers at the end of an artificial ear canal. What Zuccarelli refers to as "holography" is IMHO simply a binaural mannequin.
At first I thought that somehow they were using the nasal cavity as part of the transduction scheme, but as far as I can tell in the patent these are really just 'place-holders' of anatomy. While he does speak to the idea that the skull should have human-like properties, this isn't really given specific parameters (i.e. optimal mass, stiffness, damping etc). I copied the image and attached it. If you look, you will see a tube, and at the end of each tube, a pressure transducer.
The patent continues:
"hair is also of considerable importance in spatial discrimination, allowing a precise perception of sound coming from the front or the rear by giving rise to an asymmetric hologram. In fact, bald persons have been observed to have somewhat reduced front-rear discrimination along the axis of symmetry of the head"
Quick poll: For those readers out there who are bald, do you find it difficult to know when a sound is in front of you or in back of you?
Frankly, there are numerous reasons why sounds directly in front / back are harder to localize that those slightly off axis, but mush depends upon a) boundary conditions (acoustics), b) source-to receiver distance, and c) spectral as well as temporal content. However, this straight ahead / straight behind localization is difficult for all humans, whether having hair or being bald.
My eyebrows arose when I read that, according to the patent, the mannequin is equipped with "a wig which serves to generate asymmetry for front-rear discrimination". No data are referenced / cited to support the 'hair' claim. Sure, hair can affect diffraction as well as absorption, but the type of hair, its absorption (which, lest we forget, is a
function of frequency) and such are all variables that are not defined in the patent literature. So, as far as I can tell, the purported difference on between a Zuccarelli mannequin and those of all others (on the outside) out there is that the inside elements of the head are reproduced (brain, nasal passages etc), and there's a wig.
Now, I can see how those endo-skeletal elements
might contribute to how the transducers react to excitation (airborne and structureborne), and certainly when we speak (all these things affect the timbre of our voice for instance, but this mannequin is not used for telephony and as such, does not radiate sound through its mouth), but keep in mind that the diaphragms of the cited pressure transducers react almost entirely to forces normal to or at some angle incident upon the diaphragm, but the diaphragm is mated to the closed-open tube; the diaphragm, like all microphone diaphragms, would thus be relatively immune to forces acting in shear (along the surface of the diaphragm).
So, in my engineering opinion, it cannot be acoustically affected by the nasal passages nor the brain (in the mannequin) in the mannequin because there are no acoustic paths between the nasal cavaties and the artificial ear canals. This leaves only structure-borne as a potential contributor. However, one would have to know the relative mass and compliances of the human brain, nasal cavity, and ear (auditory) system if one wanted the vibration characteristics to be correct. This is, from a structural point of view, or paramount importance because the mass, stiffness, and damping values would define the equations of motion and thus, the frequencies at which the physical system is efficient at passing them along, and the frequencies that are likely to be attenuated.
That...is a very tall order, and...to my knowledge, I don't know of any published data that cites the normative distributions of mass, stiffness, and damping of the human brain, nasal passages, and auditory system, but assuming one could in fact get these data, and assuming that one could faithfully execute a 'representative' compliance, mass, and so forth, then a representative skeletal structure and skin would also be required to accurately complete the system. Since the purported argument seems to be that the pseudo brain and nasal passages play a role, then one would have to make the surrogates in the mannequin head possess a representative mass, compilance, and damping, because if there is transmissibility to the ear mechanism, that transmissibility, which is a function of frequency, is goverened by those equations which have those elements in them (like any spring-mass-damper system). I know that work in audiology has been done on cadavers, but even so, I am not sure how the compliance and damping of the things inside the human head (brain, ear, nasal passages) change when we are not living (i.e. such as a cadaver). So, one would really have to know the properties of these living tissues. I'm reaching the limit of my knowledge here, and perhaps there is a database / a bunch of published work in peer-reviewed journals about the compliance and damping of these oragns and their measured transmissibility to the ear...but I really don't know how one would accurately measure such things.
Now, all of the other binaural mannquins out there (and I have used all but one variant) have a lot in common, but a big one is that they are all heavily damped. That is, rap one of them with a knuckle and you hear a decidedly dead 'thump' radiate from them. Clearly the idea among all manufacturers of commercial recording as well as research-based binaural mannequins is to minimize the structure borne element of the head, and thus prevent the sound from being 'colored' (having its frequency response affected) by any structure-borne vinration, leaving the mannequin's ears to react to the pressure perturbations incident upon each diaphragm.
So, we have a lot of claims being made, and it would seem the way to answer them would be to
measure the system in a controlled test environment so that the claims could be substantiated. This would tell us a great deal, and in fact, along with the complex FRFs observed, the impulse response of the systems would tell us pretty much everything we need to know. That is, if they are mathematically highly similar (they will never, ever be the exact same - even two mannequins by the same manufacturer will be slightly different due to manufacturing tolerances) then they will sense sound in highly similar ways. This priniciple is why every sm57 sounds alike or why every BS-3D sounds alike - because according to their complex FRF and impulse functions, they basically are the same.
If you want another trial, a
subjective trial, then simply record the test sounds with each system, and perform a structured juried listening test - even if paired only, ABX would so. Of course, for a third variant, place a wig on each binaural mannequin...and go from there...but...
what's the correct wig???
The one thing that I can see as being a possible unique approach is how the ear canals are implemented. There is some discussion in the patent about the geometry of the ear canals, and it would stand to reason that these would in fact affect the frequency response of the pinna / canal / transducer system. However, even taking these possible factors into account, it is still ostensibly a binaural process based on pressure transducers inside a replica of an ear, inside of an artificial head. I really can't find any real details in the patent as to the oto-radiation properties that are claimed by Zuccarelli.
Bottom line (IMHO), this is binaural, but may be different than other binaural systems due to changes in equalization. That's my best guess as to what this really is. Then again, I could be dead wrong...but I don't think I am.