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1. The static one From one or more symmetric sources,
emanating tones not music the eigenfrequencies (room modes) have a more or less
a regular form and almost ‘’absolutely’’ symmetrical... In this situation if we
put one or more ‘’bass absorbers - (the >classical< ones from various companies,
not eager to evolve)‘’ in the room, even at the calculated necessary points, the action from the mentioned absorbers , are a topically filtering , i.e.
producing notches or deeps in the spectrum , first locally and then in the
nearer field.
From the bibliography resulted that this kind of notches is like
an open vane in a piscine- the water will tends to go out from there and the
clear water surface will be disturbed. Another bass absorber at another place ,
calculated and built for another mode / bandwidth will again produce, there , in
his 3D area another locally disturbance. With just 2 such a distant low bass
absorbers, the room will have a serious modes distribution distorted. Think that
all this are for, say, sustained tones, or just sweeping in frequencies which
cover at least the left and right absorbers margins.
Supposing that the build up phenomenon will continue for few seconds more, then
the ‘’map’’ of all eigenfrequencies will be ‘’stretched’’ and the symmetry will
be lost. Like all phenomena in rooms, the reflected waves will adds more
anisotropy and overall, the new and continuing formatted modes ‘’map’’ will
stretch more the expected symmetry. Just putting more bass absorbers , centered
at another frequencies will disturb more the situation, and in the best
situation will produce an overall low frequency notch. Aurally this will be
sensed as bodiless or lack of energy. There is no sure relationship between such
low frequency absorption and Fletcher - Munson / Dodson- Robinson loudness
curves, simply because energetically, the massive or diaphragmatic bass
frequency absorbers will not follow our hearing capacity as shown in the
Loudness curves related with the source levels.
At
low levels, almost all bass absorbers – commercially or at the research level
available, will react little or very little with the low frequency energy. The
‘’stretched modes maps’’ will stay like that and because the Loudness curves,
statistically have proved as being true, there will be less proved ‘’work’’ to
our ears done by the bass absorbers. As the low level source increase, the low
frequency absorbers, the way they are mounted will interact more or less
efficiently.
The existence of more than one bass absorber in a room will have in
the build up time and after that a non symmetric action, resulting, for a
symmetrical two sources situation, an ‘’image stretching ‘’. Even for steady
tones or slow sweeping, the sweet spot will be gone.
More, turning slightly our
head left and right, the already non symmetric situation will be more disturbed.
Note that until now, at the research or practical level, there was not such a
construction able to ‘’filter down’’ or produce a notch exactly the same as
calculated. There will be always a lateral ‘’inflation’’ and preferentially
related with the source level and position. The resulted bass absorption will
differ enough from the calculated one.
Please note also, that we never used the
word music, searching only the symmetry situation. As you know, even in
electrical signal processing, the filters are never ‘’perfect’’. Even at this
stage of analysis, the far away, child - toy kaleidoscope memory will not stay
‘’absolutely’’ centered as our memory did.
2. The ‘’live’’ situation We have the same situation as
above, but replacing the tones or sweeping with music, just a 10-15 second from
a recording contains few instruments, and surely a contrabass or an electric
bass. With more than one bass absorber mounted on one or more of the room walls,
the field will tends to be steady stretched from one more powerful energetically
and level dependent absorption. Because there is impossible to have two bass
absorbers, for two spectrum part, being mounted in the same place, there will be
at least two moments in time – t1 and t2 , true, slightly different, because,
now we are in the music domain, and we are not listen music in infinite spaces.
The t1 and t2 [resulted form the different time that energetically the incident
waves enters and are ‘’processed’’ by our experience of at least two bass
absorbers] are still away from the threshold of more than 35 msec where the
preceding effect begin acting [two sources of a same signal separated in time
by more than 35 msec are perceived by our ears as different].
In small and
medium sized rooms, the preceding effect will tends to be perceived only if the
rooms are ‘’naked’’ empty, and even the listener bodies being absent, an absurd
situation. Note that some absorption will results from our bodies as listeners,
our clothes, small reflections from the equipment and loudspeakers.
Even in extreme situations like an empty room used for music
listening, the slight diffusion augments as the room become bigger and in the
opposite situation, as the room is smaller and smaller or a cube, the natural
diffusion will be covered by the more and more low frequency modes, and the word
boominess will becomes more frequently pronounced. That is, as the room decrease
in dimensions, the same sources producing no evident ‘’low frequency damages’’
in bigger rooms, will be a real problem.
Here is the moment to introduce the
complex phenomena of masking and dynamic masking. There is the ‘’war’’ of
searching to calm the low and very low modes culpable of ‘’ boominess’’ but
without reducing them so much in order to go the undesired direction of letting
the listener without the bass energy , from where the music takes the body and
contour and feeling of warmness. Seems a no way situation because one action
will tend to cancel the other.
The theoretical and practical way until now was even to
electronically process the signal going to the loudspeakers or actively merging
from them and electronically analyzing the acoustical result to continuously
treat the signal in again electronically, or, to treat the room as much and as
well as to have no disturbingly and annoying low modes, literally named ‘’
boominess’. The first, electronically way, even with good results, put the
listener in the ‘’absolutely centre statue’’ position, even the slight head
moving resulting in the stereo image loosing. The acoustical treatment have had
always better results , but because of not exact filters – bass absorbers
working there was always a more spectral energy absorption as needed.
Please
note, that we spoke nothing about the rest of the spectrum. If the bass gives
the ‘’hot’ feeling, the music contour, the mid and high frequencies contains the
music’s details. Search a radio station broadcasting a kind of low-fi music,
with very few mid and fewer high frequencies, and you, even ‘’understanding’’
the music will feel that something is lost. In the opposite direction, which is
much more frequently, meaning a real situation, if you are listening music from
a radio station broadcasting without enough or little low frequency contents,
you will feel more annoyed. The signal ‘’harshness’’ will keep you less time in
pleasure.
Hopefully enough, the [low frequency] missing fundamental
phenomenon - our brain salvation solution, will process the signal
‘’reconstituting’’ for us and our only ears, the not appearing low frequency
contents. This is a frequent situation from cheaper or small ‘’ transistors’’
when mainly the information is asked and the music will just ‘’ embrace’’ our
ears, as to the time will past nicer, a kind of pleasant ‘’residual noise’’.
From here to the HI-FI or HI-END situation is a very long road… So, we were in
the situation where cleaning the bass in a known [ until now ] way, so many
problems resulted and continue to result, that the music lovers will tends all
the time [influenced by myriads of articles from periodicals] to buy or change
the stereophonic equipments, a never ending situation...
For those accepting an aesthetical changing in their rooms [ when
THE wife agree ] , there is a solution. It is an elegant solution because
putting in the same reduced physical place all filters as bass absorbers and /
or diffusers [ which until now were mounted allover the room - being voluminous,
and so reducing the physical room dimensions ] will solve 99.9 % of problems.
Why is this solution elegant and essentially and practically SOLVING all the
acoustical room problems? Remember the times t1 and t2 for just two bass
absorbers. Dynamically, these times, by the complex way that the masking effects
(learn from our site what is masking), affects our hearing, results in the
simple named – forward and backward masking [ which are temporal ones ] and
other kind of masking as a spectral ones and the masking affecting
differentially our left and right rears, as a result from a stereo or a more
room distributed sources situation. As much as our hearing suffers from the
direct or indirect masking phenomena, the music perception will be disturbed,
there will be always a dissatisfaction feeling, difficult to cure and inertial
in time.
3. Explanations To not complicate further the
explanations, the way that our Roundffusor1 treats and solves all the above
phenomena is just this: being an adaptable low and very low frequency
absorption – the simple masking and dynamic masking phenomena are reduced so
much as not being perceived. The same object – the Roundffusor1, with a minimum
area and only 11 cm depth is simultaneously a powerful wide band diffuser and an
adaptable low frequency absorber. It solves the difficult problems – many
filters in the same physical place and diffusing down to the frequency limit
where the adaptable low frequency absorption begins.
It sounds simple but in
fact, from a theoretical point of view is so complicated that the actual
theoretical background level is not enough to fully explain the Roundffusors
functions. Research is done by the patent holder mostly in the psychoacoustical
domain , because there is the key and perhaps the answer. Until now , even with
the f MRI [ magnetic tomography - collateral research and interpretation of
work done by other researchers ] we hadn't found much more. But what's more
important: to have a real working device or ''absolute'' theory not practically
applicable ? The Roundffusor1 is patented and his design and functions are
indeed original. Being a native Romanian living in the last 24 years in Greece,
perhaps I was influenced in its design by the purity and simplicity of ancient
Greek art. As much as archeology unveiled the past, the ancient Greeks used no
absorptive materials in their theatres, just hard materials and ingenuity.
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