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|5th October 2010, 03:05 PM||#1491|
Join Date: Dec 2004
Location: Novi, Michigan
The "black hole" of damping is precisely what you would want to absorb any diffraction (but it won't change the diffraction from the baffle in any other way.) If it were not there then the diffraction would reflect back to the listener.
Earl Geddes Gedlee Website
Read about the highly acclaimed Geddes loudspeakers
|5th October 2010, 03:25 PM||#1492|
Join Date: Oct 2008
Hmm, I might have suspected, but I'm still trying to understand. Aren't wedges used in anechoic chambers because the sudden loss of energy causes a resultant backwave? and would it be even better to bring the foam forward in front of the baffle plane and even around the front edges a little?
|30th January 2011, 04:42 PM||#1494|
At the object based approach becomes possible, subtracting the playback room acoustics for direct wave and first reflections. Reverberation becomes generate in different way, from the impulse response, and equalised separately.
The procedure is described in WFS-Holophony , chapter 4.2. In that case, loudspeaker and room really are one system.
|15th February 2011, 02:30 PM||#1495|
Join Date: Mar 2008
Some unsorted thoughts on ceiling reflections and "sound from above"
Our ear/brain has developed even before speech and music came into human live.
Our perception system has developed to survive.
It's first aim is the identification of objects: Their nature, their distance,
their direction, their speed and direction of movement ...
OK, let's imagine our stone age huntsman passing a narrow cutting ... he is
being observed by someone who is able to move very quiet ...
But that sort of cat is not perfect either. Some pebbles get loose and begin to roll
down over the crag, causing some transient clicking noise ... got it ?
Where ? Exactly where, please ?
That fractions of a second decide whether our huntsman's plans for his future live
will be of any use or not.
Over 10.000 years later, that clicking noise might indicate an unlocked overhead bin
in an airplane with you sitting right underneath.
And if you did not know already, than i might be allowed to tell you, that luggage
falling out of unsecured overhead bins is the oftenmost cause for serious
insuries of aircraft passengers. Don't be afraid of flying in an airplane, but have
a closer look on the luggage please ...
So far so good ...
Human live - as well as killing and defence strategies - have been perfectioned.
Speech and musical culture have an omportant place also in human live.
There is still that frequency range around 8 Khz, which is associated with 'brillance'.
It is important for our perception and our ear conches are designed to give
that frequency range a gain of over 10 dB if coming from above. That gain is
lesser if the elevation angle is lower that 90 degrees from the median plane.
That 'directional band' is called the 'above' band according to Jens Blauert.
File:Akustik - Richtungsbänder.svg ? Wikimedia Commons
Now mixing some of my own (almost trivial) thoughts into the rules of the game:
- An acoustical 'object' or 'gestalt' is not complete without that 'brilliance' information.
- Sounds known to us miss 'sparkle' without that frequency range.
- The frequency range together with the 'presence' region below that 'above' band
has importance in detecting positions of 'sound objects' rather fine and make them
'real' even on a proximity level of perception. An object with 'no proximity' is not
a real (or realistic) object. For the 'realism' in a painting there are similar rules:
An object is embedded into its context/backround by perspective, oherwise it will
not occur to be real or realistic at least.
In the culture of music buildings have been designed for the purpose of listening to
music. A large fraction of sound energy in those buildings is reaching the listener
by ceiling reflections. A music pavillon e.g. has the purpose of protecting the
musicians and their instruments from a drizzle, but there is also an acoustic
purpose which may be even more important:
Structurae [de]: Bilder: ID 4226
How is that sound utilized, which is radiated upwards ?
Again i like to throw some unsorted thougts towards you:
- The sound reflected from the ceiling is utilized to give some notion of presence
and sparkle even to the more distant listeners, so the organizer can sell
some more tickets even for the distant seats at a reasonable price for both sides,
organizer and visitor as well.
- The ceiling reflected sound is utilized for 'spectral averaging' over a string
ensemble e.g. making the spectrum of sound more smooth as it would be the case when
sitting at the side of that ensemble without any reflections present ... you would
get the directional radiation patterns of the closest instruments in a dominant
manner then and the desired 'mixing', 'smoothing' and 'fusion' does not occur to
the desired extent.
Some agreement so far ?
Now the third set of unsorted thoughts, risking the leap over to our beloved topic
of discussion: The Loudspeaker (and its frequency dependent directivity characteristics.)
Today in the focus: The vertical plane.
How would a loudspeaker sound, which has balanced energy and also dispersion
say up to around 4 Khz and from there upwards has a significant narrowing
in vertical radiation angle thereby only keeping the sound pressure radiated
on axis constant ?
Instead of a verbose answer i send some pictures with listening impressions from
a rather 'wet' and small room:
|15th February 2011, 03:01 PM||#1496|
Join Date: Mar 2008
The "small line source" ribbon like tweeter is about 12cm in length.
The woofer has about 10cm diameter.
Crossover frequency is around 900Hz.
Since there is little directionality in the crossover region, that speaker
does not have the usual "2-way woofer/dome discountinuity" in the
crossover region and sounds rather homogeneous from midrange to
But it has a problem too: While the vertical directivity of that tweeter
increases with frequency, the horizontal directivity is not changing
significantly with frequency.
With tweeter on ear level, the speaker sounds as brillant at 180 degrees
as on axis, but mind the vertical plane ...
The poor guy who designed and built that little bugger around 10 years
ago had to find a compromise between flat energy response and flat
sound pressure on axis, so the speaker is designed to be listened
from a vertical angle around 10 degrees vertically relative to the
center of the tweeter.
If you listen to that tweeter on ear level if will drill a 'brilliance hole'
into your cochlea ...
If you adjust vertical angle right, it is quite balanced. That makes the
speaker a rather bitchy thing.
There is another problem: The brilliance information is there, but
it does not balance properly with the presence region, no matter
how you adjust angles or turn your head.
A measuring microphone 10 degrees vertical off axis will tell you
that everithing is pretty flat ... but that is only a small fraction of
the truth. My ears tell me, that the speaker is bitchy and it stays
The same speaker turned by 90 degrees, has a different flavor and
is far less bitchy. There is sparkle at nearly every listening position.
A deviation in horizontal listening angle from axis - which
was the super critical vertical axis before - can be put away
quite easily - subjectively.
Of course, everyone would mount such a tweeter vertically,
because of the more even dispersion in the horizontal
plane, imaging issues etc. ... right ?
There is only one from these speakers in the world, so i
cannot verify a stereo setup unfortunately.
Possible that the horizontal alignment would couse some
irregulararities in localization when listening out of symmetry ...
But nevertheless i fear the horizontal setup is superior under
that certain conditions in terms of homogeneity and simply
being less bitchy.
|15th February 2011, 04:48 PM||#1497|
Previously: Kuei Yang Wang
Join Date: Nov 2002
Location: Somewhere nice on planet earth where censorship of Ideas is frowned upon
Certain sounds etc. cause a mild (one hopes) version of the fight/flight reflex, flooding the body with adrenalin, giving a high (one can also take certain drugs for the same effect magnified).
I recently talked with someone about audio who has tastes running rather counter to mine.
Now to me the adrenaline high combined with music that is not supposed to elicit it by itself is a "bad thing". at the same time this Gentleman considered it "always a good thing".
This may explain the different reactions people have to things like ceiling flooders... It would literally be an issue of emotional response and reaction to (brain internal) drugs.
|15th February 2011, 04:59 PM||#1498|
Join Date: Mar 2008
The difficulties of audio reproduction
Conventional loudspeaker reproduction cannot create such an experience because the right box is only approx. 30 degrees off from the median axis. However, more tight spacing causes more correlation and is, consequently, less attractive. In the center of the concert hall the ceiling reflections are hardly contributing to an improvement of spatial impression. Such reflections in line with the center are counterproductive, normally. "
It seems to me, that proper localization of phantom
sources can hardly be achieved by designs which
radiate the presence to brillance region predominantly
towards the ceiling.
But: If a system lacks balanced dispersion in that
frequency range and the energy response drops, a
radiation of that range towards the ceiling might
increase the amount of presence and sparkle detected
by our ears and a more consistent and balanced
'color' of the sound allover the room might me achieved.
There might be also an improved "spaceousness" with
some systems as the speaker itself is less detectable
as a sound source. Nevertheless localization of phantom
sources will presumably suffer.
On the other hand, for the design of predominantly
direct radiating speakers, a consistent directivity
pattern in the vertical plane seems as important as
in the horizontal plane.
Reflections from the ceiling should have approximately
the same spectral "fingerprint" like the direct sound,
especially from upper midrange to brillance region.
If the localization of phantom sources can rely on
balanced direct sound (and uncolored lateral reflections),
a moderate presence of - also uncoloured -
ceiling reflections might improve "spaceausness"
but not seriously disturb localization of phantom
That amount of energy from above in "presence and
sparkle region" might also contribute in the listener
being less restricted to the sweetspot and give the
a more "homogeneous" experience allover the room.
IMO consistent ceiling reflection may also contribute in
'depth' of imaging.
|15th February 2011, 05:25 PM||#1499|
Join Date: Mar 2008
i agree that dumping and reaction to brain internal
drugs may be a serious distinguishing mark between
Nevertheless concerning the ceiling flooder approach
i have to admit, that
@graaf: "there is something to it".
Not sufficient for me to make ceiling flooders in future,
but the discussion points to the importance of consistent
radiation even the vertical plane IMO.
|15th February 2011, 05:53 PM||#1500|
Join Date: Mar 2008
depending on the crossover frequency i would say
it is a "presence to brillance flooder" ...
And i can imagine that design to have its own
qualities compared to products of the time ...
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