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Old 30th August 2011, 09:25 AM   #11
graaf is offline graaf  Poland
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Quote:
Originally Posted by Humdinger View Post
Reflections will be there if you're in a room. The question is how can you work with that "mechanism", such that its damage is minimal, or in some cases an enhancement of the listening experience? (I knew I shouldn't have drank that coffee...)
yes, this is the question
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Old 30th August 2011, 09:39 AM   #12
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Originally Posted by graaf View Post

into the reverberant field because decorrelation occurs in the reverberant field

Side- or ceiling flooder approaches will not reliably provide a certain desired
decorrelation just by mainly utilizing a single reflection, which may be from
a flat and naked wall.

With such a device the "reflector" itself has to be part of the "scope of
delivery" to achieve somewhat reproducible results, as the "neutral direct
sound component" is completely missing in the passband of said
"transducer/reflector" arrangement.

Transducer and reflector have to make up a system, with the reflector to be mounted
in a defined way (at least a defined range due to distance and orientation) and the
group delay compensated in a tunable network.

Shape and material of the reflector would provide the desired amount
of decorrelation (diffusivity) and together with the transducer a certain
desired radiation pattern will build up.

Now a pair of speakers has to be placed in the room and a pair of reflectors
additionally ...

A suitably designed bending wave loudspaker optionally equipped with
means for dispersion control (narrowing)

- yields the desired dispersion and decorrelation
- is one single unit
- performs far more independent from idiosyncrasies of listening room and placement

- can be made without excessive group delay

(which e.g. is present in a transducer/reflector arrangement).

____

But - different approaches aside - i think Elias' post (including provided link)
is in no way off topic.
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Last edited by LineArray; 30th August 2011 at 10:00 AM.
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Old 30th August 2011, 11:07 AM   #13
graaf is offline graaf  Poland
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Quote:
Originally Posted by LineArray View Post
Side- or ceiling flooder approaches will not reliably provide decorrelation
just because they utilize a single reflection (which may be from a flat and naked wall).
in particular in case of a ceiling flooder You can have at least four ipsilateral first-order reflections - side-wall, front-wall, back-wall and - of course - ceiling reflection, no floor reflection

Quote:
Originally Posted by LineArray View Post
A suitable designed bending wave loudspaker

- yields the desired dispersion and decorrelation
- is one single unit
- performs far more independently from the properties of the listening
room and placement

- can be made without the excessive group delay

(of a transducer / reflector arrangement).
but is it real life option? can we diy such a bending wave loudspaker?
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Old 30th August 2011, 11:07 AM   #14
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Quote:
Originally Posted by graaf View Post

Originally Posted by speaker dave
The other view of the objective is "what balance between direct and reflected?" That is, are we in the direct field, or at a distance where direct and reflected are equal or perhaps well into the reverberent field?

(Graaf) into the reverberant field because decorrelation occurs in the reverberant field
You need to explain the term "decorrelation' that you constantly use. The reverberent field is a consequence of the direct sound so it is correlated with it. Not sure how a field (or how the treble of a speaker) can be "decorrelated" in a proper sense.
Quote:

Originally Posted by speaker dave
"Even if we speculate that a certain reflection pattern is ideal we may not be able to achieve it within the dimensions of our room. If it turns out we can achieve it then likely a small variety of speaker room combinations might achieve it equally."

(Graaf) both flooder and back-to-back configuration can achieve it in almost every room suitable for normal stereo, with one possible exception of acoustically overtreated audiophile room because it prevents the build up of adequate reverberant field
If the desired goal is low reflection level in the first 20 msec, then a wide dispersion speaker in a small live room will not be able to achieve it. The goal may not be how to achieve more reflections but how to achieve less, at least in the early period.

Quote:
total frequency response? can't it be equalized quite easily? on the other hand equalizing time response in room is more difficult
Definitely talking about achieving a particular time response. My assumption is that the direct response is flat. I haven't seen any evidence that the delayed reflections should have any particular frequency response but they should have a particular leval and delay. Frequency EQ is not the solution to a time based problem. This is what most of the DSP room EQ systems get wrong.


Quote:

(Graaf) I think David Moulton can be right: "My design philosophy for studios is: let's have a perfectly reflective space for 50 milliseconds and then let's have no reflections or reverb after that. So let's have all the early delays with as little frequency response change and as little amplitude loss as possible, and then nothing after that."
Really?, that is directly opposite what the research is saying, in terms of suppresion of the early reflections to reduce timbral effects. And how do we get a studio to be "perfectly reflective for 50 milleseconds and then no reverb after that"? Acoustic noise gates?

He has invented a speaker that gives wide horizontal dispersion and now he needs to justify it. This is a popular notion that I see running through this thread and throughout the forum: "If reflections are just the same response as the direct sound then everything is okay." I've never seen any research to support this. If we have direct response and a single delayed reflection making the reflection flat in spectrum doesn't change the comb filtered mess of the combined response. It just determines the extent of the combing. Bech shows that an angular related hole in the reflection might just depress it below audibility. It is frequency selective directivity and in this case directivity was a good thing.
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Old 30th August 2011, 11:13 AM   #15
graaf is offline graaf  Poland
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Quote:
Originally Posted by DBMandrake View Post
As you say, 3ms can give a satisfactory result, if overall reflectivity and reverberation are kept down to a manageable level.
yes, bathroom is no good place for a listening room
I believe that if overall reflectivity and reverberation are kept down to a manageable level then just anything above say 1.5 ms can bring satisfactory results

Moulton:
Quote:
let's have a perfectly reflective space for 50 milliseconds and then let's have no reflections or reverb after that. So let's have all the early delays with as little frequency response change and as little amplitude loss as possible, and then nothing after that.
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Old 30th August 2011, 11:22 AM   #16
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Quote:
Originally Posted by graaf View Post
Originally Posted by speaker dave "doubling the distance from listener to the CD horn system would give the same direct to reflected ratio as the wide dispersion system. Who can proclaim that one is universally more desirable than the other, at least without talking about the room and listening distance?"

but the listening distance is pretty typical and depends mainly on typical room sizes
The point was that even with speakers of widely different directivity a reasonable seating distance difference could equalize their direct to reflected ratio.
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Old 30th August 2011, 12:07 PM   #17
graaf is offline graaf  Poland
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Quote:
Originally Posted by speaker dave View Post
You need to explain the term "decorrelation' that you constantly use.
less IACC and less IACC = spaciousness and envelopment

Quote:
Originally Posted by speaker dave View Post
The goal may not be how to achieve more reflections but how to achieve less, at least in the early period.
why may not be?? who said so? Roman Pontiff?

Quote:
Originally Posted by speaker dave View Post
Really?, that is directly opposite what the research is saying,
oh yeah! with minor exception of Dr Floyd Toole for example

Quote:
Originally Posted by speaker dave View Post
how do we get a studio to be "perfectly reflective for 50 milleseconds and then no reverb after that"? Acoustic noise gates?
this is ideal of course, a goal to be pursued (just like an anechoic chamber is such a goal/ideal for many audiophiles) and here is about what can be done in real life:
Moulton Laboratories :: The Real World of Project Control Room Monitoring

here is about how it sounds in opinion of Bob Olhsson (from gearslutz forum):

Quote:
Dave Moulton did a simple demo for me in a bare room that turns most of what we thought we knew about acoustic treatment and imaging right on its ear.

He had designed some speakers that deliver a flat response across 180 degrees. The imaging in the bare room was holographic, among the best I've ever heard. His conclusion is that early reflections aren't any problem at all but early reflections that don't have a flat frequency response are a big problem because they change the perceived tonality of the speaker.

Something that led him to this was the fact that many of the best translating control rooms a lot of us "old timers" ever encountered did not have any early reflection treatment while some of the worst have been certified LEDE rooms.

The problem with room tuning and early reflection absorption is that they are oversimplifications that have little to do with how we actually hear. Dave actually has serious academic credentials in addition to having been an engineer at Columbia Records. He also, last I heard, wasn't in the room design business.
neither is Mr Moulton in the speaker design business, so it is not true in his case that:

Quote:
Originally Posted by speaker dave View Post
He has invented a speaker that gives wide horizontal dispersion and now he needs to justify it.
Mr Moulton's business is "music production, orchestral recording in stereo & surround, mixing and mastering for a variety of clients." and also "educational and technical writing, multichannel music composition and synthesis, acoustical and psychoacoustical research and consultation, and education"

Moulton's Takes
KIQ Productions

Quote:
Originally Posted by speaker dave View Post
we have direct response and a single delayed reflection making the reflection flat in spectrum doesn't change the comb filtered mess of the combined response. It just determines the extent of the combing. Bech shows that an angular related hole in the reflection might just depress it below audibility.
and Dr Toole says that comb filtering is a measurement artifact, not audible at all
so, who knows? ...without trying...
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Old 30th August 2011, 12:10 PM   #18
graaf is offline graaf  Poland
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Originally Posted by speaker dave View Post
The point was that even with speakers of widely different directivity a reasonable seating distance difference could equalize their direct to reflected ratio.
yes, but the point is that usually it is not an option in practice, one just cannot move one's listening chair from three meters distance from the speakers to six meters, and so one cannot equalize anything in such a way
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Old 30th August 2011, 12:14 PM   #19
graaf is offline graaf  Poland
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Quote:
Originally Posted by DBMandrake View Post
10ms to first reflection is a complete fantasy for anyone living in Europe, even 6ms is impractical.
Quote:
Originally Posted by speaker dave View Post
Which is why you want speaker directivity or room treatment to help to deal with those early reflections.
and Moulton says no need to worry because

Quote:
it should get better in small rooms
because

Quote:
if you take a look at what's really going on in recordings, playback rooms are generally small and the early reflections happen very quickly-whereas in a recording space (or simulation of a recording space that we do with artificial reverb), those reflections are much, much later in time.

What happens is that the early reflections of the playback room carry information about the recording room
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Old 30th August 2011, 01:02 PM   #20
graaf is offline graaf  Poland
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ps.

Quote:
Originally Posted by DBMandrake View Post
10ms to first reflection is a complete fantasy for anyone living in Europe, even 6ms is impractical.
in fact, if You are a RFZ-believer and You have room size constraints making this >6 ms impossible to obtain, then a flooder in Beveridge placement is really the way to go for You

with a flooder in Beveridge placement You can have all early reflections delayed more than 6 ms easily
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