What tests in particular are you criticising ? Informal tests on this forum ? The work of Toole and others ? Specific examples please.
Has not been proven in what way ?
Are you suggesting that we as DIY speaker enthusiasts must sit back and wait for some academic research to come along that "proves" excessive reflections in a small room are a problem before we have a valid reason to try building or using directional speakers ? What a load of pompous nonsense.
Anyone who has tried speakers of radically different directivity in typical rooms can hear the obvious differences in response. Which is preferable is the debate, not that the difference exists.
In the end it probably comes down more to the preferred direct to reflected ratio of the listener, and the whole "you are there vs they are here" dichotomy, rather than any arbitary directivity pattern being the "best", however directivity is a key tool in realising the desired result within realistic rooms, along with speaker placement and damping of course.
You say that excessive reflections have not been proven to be detrimental, but I would turn that around and say that it is you who must prove that they are not detrimental.
It's clear that the more the room influences the sound, the more the sound deviates from what is on the recording in a way that is largely unpredictable to the recording engineer. Prove to us that this is not a bad thing.
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DBmandrake,
Where did ScottG refer to "excessive reflections"?
By its very nature the word excessive means too much. Of course excessive reflecions are bad just as an overly dead room acoustic is ultimately bad for stereo reproduction, if not Home Theatre/Cinema.
Surely balance is the key.
The worst acoustics I have heard yet in a domestic setting used for listening to music and movies was an extremely large (by British/European domestic standards) square room with no soft furnishing apart from a couple of Sofa's, a room of Glass with no curtains or carpets and a very high ceiling. it was extremely reverberant and my mind was certainly not able to tune its effects out. Everything I heard was tainted by the room acoustics. Watching a movie in this room all the scenes appeared as if indoors, say in a Church (like the "wet" reverb sound effect settings on an EAX soundcard), even the outside ones, atrocious, no loudspeaker directivity could sort this. I would even have to choose an overly dead acoustic over this.
Where did ScottG refer to "excessive reflections"?
By its very nature the word excessive means too much. Of course excessive reflecions are bad just as an overly dead room acoustic is ultimately bad for stereo reproduction, if not Home Theatre/Cinema.
Surely balance is the key.
The worst acoustics I have heard yet in a domestic setting used for listening to music and movies was an extremely large (by British/European domestic standards) square room with no soft furnishing apart from a couple of Sofa's, a room of Glass with no curtains or carpets and a very high ceiling. it was extremely reverberant and my mind was certainly not able to tune its effects out. Everything I heard was tainted by the room acoustics. Watching a movie in this room all the scenes appeared as if indoors, say in a Church (like the "wet" reverb sound effect settings on an EAX soundcard), even the outside ones, atrocious, no loudspeaker directivity could sort this. I would even have to choose an overly dead acoustic over this.
What tests in particular are you criticising ? Informal tests on this forum ? The work of Toole and others ? Specific examples please.
Has not been proven in what way ?
Are you suggesting that we as DIY speaker enthusiasts must sit back and wait for some academic research to come along that "proves" excessive reflections in a small room are a problem before we have a valid reason to try building or using directional speakers ? What a load of pompous nonsense.
Anyone who has tried speakers of radically different directivity in typical rooms can hear the obvious differences in response. Which is preferable is the debate, not that the difference exists.
In the end it probably comes down more to the preferred direct to reflected ratio of the listener, and the whole "you are there vs they are here" dichotomy, rather than any arbitary directivity pattern being the "best", however directivity is a key tool in realising the desired result within realistic rooms, along with speaker placement and damping of course.
You say that excessive reflections have not been proven to be detrimental, but I would turn that around and say that it is you who must prove that they are not detrimental.
It's clear that the more the room influences the sound, the more the sound deviates from what is on the recording in a way that is largely unpredictable to the recording engineer. Prove to us that this is not a bad thing.
I think you are "reading in a lot more" than I wrote.
As to the tests I'm referring to (within the context I presented).. take your pick from Tooles book.
BTW, I'd always advocate experimenting!
As for me proving to you.. I have recommended at least one (relatively simple) test (that at least partially concerns this topic) - (within I think this thread no less) to make your own conclusions. As to where it is.. err.
(..and I'm not going to go on "search about" either). 
I have made this point before, but I can see that I need to make it again. Almost nothing in audio is "proven", at best its based on some weak data. So are we to do nothing as a result? Well thoise who need "proof" can sit and wait for it, but don;t hold your breath.
We use the best data, experince and intuition we have to get to the best compromises of a vast complex of competing requirements.
What is NOT acceptable, and happens all the time, is to believe things that are completely contradicted by the evidence. There is not much sense to that.
For the most part I find those that look for "proof" are simply trying to stall a discussion that is not going the way they would like it to.
We use the best data, experince and intuition we have to get to the best compromises of a vast complex of competing requirements.
What is NOT acceptable, and happens all the time, is to believe things that are completely contradicted by the evidence. There is not much sense to that.
For the most part I find those that look for "proof" are simply trying to stall a discussion that is not going the way they would like it to.
Hmm. You are in great danger, you realize. As you become increasingly learned, this effect will extend to lower and lower frequencies until you reach the final state of education where you hear all sounds as emanating from discrete speakers.
Your post suggests that you could once hear HF phantoms but this is no longer so? Perhaps one ear has become a bit deteriorated or at least different from the other ear.
..and as a point of clarification to my prior (apparently problem) post:
-the intent was to provide *caution*.
The tendency is to think the naturally obvious is correct, but the fact is that the obvious isn't always correct.
The "obvious" in this instance is that reflections (not part of the original signal) created by the room, would degrade the signal with stereo reproduction.
Of course taken to a natural conclusion such an argument would wind-up recommending anechoic chambers for listening rooms. There is of course a fair bit of research, yes - generally considered sufficiently "proven", to refute such a conclusion. Of course almost everyone takes this for granted now, but it does show that caution is prudent (..and even does so in this particular context of discussion).
My point with Tom's comment that:
"..you can’t get there if the listening room is a strong contributor, it is then a “special effect” you can’t turn off..
-is that: what is a "strong contributor", and *why* is that way?
Additionally, might it not be a strong contributor with a different pair of loudspeakers - perhaps either with more or less directivity?
Furthermore, while there are obvious differences with loudspeakers of substantially differing directivity, are those differences primarily attributed to a reduction in room influence? Again, the obvious answer is yes (particularly in a thread with this topic) - but is that correct (or even mostly correct)?
-the intent was to provide *caution*.
The tendency is to think the naturally obvious is correct, but the fact is that the obvious isn't always correct.
The "obvious" in this instance is that reflections (not part of the original signal) created by the room, would degrade the signal with stereo reproduction.
Of course taken to a natural conclusion such an argument would wind-up recommending anechoic chambers for listening rooms. There is of course a fair bit of research, yes - generally considered sufficiently "proven", to refute such a conclusion. Of course almost everyone takes this for granted now, but it does show that caution is prudent (..and even does so in this particular context of discussion).
My point with Tom's comment that:
"..you can’t get there if the listening room is a strong contributor, it is then a “special effect” you can’t turn off..
-is that: what is a "strong contributor", and *why* is that way?
Additionally, might it not be a strong contributor with a different pair of loudspeakers - perhaps either with more or less directivity?
Furthermore, while there are obvious differences with loudspeakers of substantially differing directivity, are those differences primarily attributed to a reduction in room influence? Again, the obvious answer is yes (particularly in a thread with this topic) - but is that correct (or even mostly correct)?
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You'll definitely reduce the impact of some early reflections with narrow pattern speakers. It would be hard for me to argue that wouldn't remove the most significant effects of the room from the sound. I'd have to argue against studies without meaningful evidence to support my view. Using convolution reverbs is so enlightening. I need to devise a way to make this into a useful demonstration. Any ideas would be appreciated. I can put sound files up in a couple locations around the web and start the impulse convolution at any point in time after the original sound. I Can even move the late reverberation back to help isolate the early reflections. Maybe I should open up an account just for audio demos to deepen the understanding of aficiana(u)d(i)os.
suggestions welcome. This is something I've wanted to do for a while now in order to stifle arguing. It will take some time however.
Dan
suggestions welcome. This is something I've wanted to do for a while now in order to stifle arguing. It will take some time however.
Dan
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That's interesting. You have the Nathan, right?
An externally hosted image should be here but it was not working when we last tested it.
Then maybe there is something about Earl's room that makes it very different from yours and mine. In my experience strong early reflections can help to make the sweetspot wider, but that's of course not their sole effect.
Yes.
That's why I'm asking Earl from time to time if he would be so unbelievable kind to provide some measurements of his room.
FWIW, I had a huge sweet spot when I had narrow pattern speakers crossfired. I mean huge! The whole room pretty much. Everywhere you'd reasonable be. The 'bad' spots were fairly close to the speakers-say within 2 meters. You needed to be very well centered that close. My speakers were not any of Dr. Geddes'. Their biggest issues were not much bass and slightly harsh treble. When you got close, the treble seemed more harsh. The speaker just generally sounded bright.
Dan
Dan
I wonder whether we are talking about the same amount of 'image sharpness'. JoshK on audiocircle did a review on the Summa, both in Geddes' living room and his HT room:
Source: A Visit to Dr. Geddes: Summa
JoshK says that the image is not razor sharp. The HT room is not very wide, based on the picture approximately 3.5 to 4 meter, which reminded me of an experiment I did with El Cuerno. Normally I listen to El Cuerno in this position:
but for this test I rotated the setup 90 degrees clockwise and posted my findings on the 'zelfbouwaudio forum' (nice to have a forum to document things
). The most important difference was that the image was not as sharp as in the normal position but it was more stable on the couch (so wider sweetspot). But, a negative side-effect was that Q-sound effects (Roger Waters - Amused to Death) did not work anymore. I like to do this test because it is easy to find out if the speakers are set-up correctly.So I wonder if this is also the case in the HT-room of Dr Geddes?
I have "matrix" which is non steered with the usual center summed and surround difference. Also Dolby PL and DTS Neo6.
Any of these modes would do this if you configured as "no surrounds". Surround material would fold to the fronts.
I have tried all the modes and in the end the simple matrix is as good as any (someone else said the same thing a few pages back). I suspect that all the steering modes are primarily meant to enhance the measurable channel seperation. If you walk up to any channel you can hear the crosstalk or hear the steering, but from a listening position it is much less noticable.
The primary observations are that a derived center gives a much more centered image (when it should be centered) for a listener off axis. I also notice a less "phasey" presentation with matrix than with stereo.
The only downside compared to an SACD (discrete multichannel) is that it tends to give everything the same broad sonic space whereas an SACD can be both spacious or discrete as called upon by the signal.
I think a derived center is worthwhile. Why don't you try a passive derived version?
David S.
Hmmm it didn't, took me to 1800 odd... http://www.diyaudio.com/forums/mult...y-pattern-stereo-speakers-53.html#post2737644 see if this one works...
Did you click on the post number itself? if it was just that page, then I have my posts set at 50 per page (not the default).
So I decided to do some more measurements tonight. I think that they pretty clearly show the asymetry of my room. This time I used swept sine with holm impulse. very similar to the results with pink noise in REW.
I think that the second graph showing the left and right is quite telling, you can very clearly see the different reflection times in the impulse response.
I had the mic within a few milimeters of dead centre based on the impusle (third pic).
The left is the speaker that is close to the wall The phase at frequencies below 500Hz is all over the place, no wonder I loose the correlation below that frequency!
Tony.
Attachments
Isn't the steering also designed with movie sound tracks in mind ? Eg there will tend to be isolated discrete sounds happening quite often, so the active steering is an attempt to reduce the spill-over into other channels when there is a loud sound from one primary direction.
I read somewhere that Prologic I tended to mangle music a bit because of its simplistic steering, and one of the design goals of Prologic II was additional "smarts" added to the steering algorithm that was better able to cope with music, presumably by recognising the different channel distribution of music vs sound effects and tending towards a more passive matrix.
In any case, from what you say it does seem like a non-steered matrix is just as good if not preferable for music, and that steering is really only useful for movies.
That's encouraging to hear. One thing that occurs to me when you say there is a "less phasey" presentation with the derived centre, is that perhaps the centre channel helps fill in the comb filtering of two speakers by providing a 3rd source with some deliberate channel crosstalk from a simple matrix.
My initial worry with a derived centre was that 3 front channels with phase correlated material might actually make comb filtering effects even worse. (As far as I know the centre channel on a DVD movie sound track is not usually correlated with left and right ?)
Comb filtering with 2 stereo speakers is somewhat reduced due to our HRTF occluding the opposite speaker at high frequencies, but in theory comb filtering between a centre speaker and a side speaker both playing phase correlated material would be worse because there would be far less crosstalk cancellation at the near ear between a directly ahead sound and one to the side than sources to each side.
This would be the case for example if you had discrete 3 channel material where panning was achieved by a simplistic 3 channel extension of pan-potting - Left goes to Left only, positions between Left and middle go to left and centre speakers in varying ratios, middle goes to centre speaker only, positions between middle and right go to centre and right speakers in varying ratios and so on.
I realise now this would work poorly because at most any given sound source location is only being produced by one or two speakers at a time, never three.
Hard left and right would be produced by their individual speakers, centre by the centre speaker, none of which would exhibit comb filtering, but any partial panning between centre and one side would be reproduced only by the centre channel and one side - which I expect would cause severe comb filtering.
An unsteered matrix on the other hand is always going to have some crosstalk between the three channels for partially panned material, and this may in fact be a good thing for music, not a bad thing.
What I mean by this is if you only have two sources of the same sound, one with a small time delay, deep notches can form from comb filtering, however if you add a 3rd (or more) simultaneous sound source(s) with yet another different delay, deep notches are unlikely to form because at any point where two of the sources are 180 degrees out of phase and roughly equal amplitude, the 3rd source is likely to be at a semi-random in between phase, and will thus largely fill in the hole. (In fact even if the 3rd source was in the same phase as one of the other two it would partially fill in the hole by unbalancing the cancellation...)
An example of this is if you were to measure lower midrange floor bounce of a speaker outdoors where there is only a "floor" and no walls or ceiling, even at 3 metres you should have no trouble measuring it, as you only have direct + one time delayed reflection.
However try to measure it at that distance in a room and you usually can't. Why ? Because there are 3rd (and more) reflections with different time delays from side-walls, front-wall etc that tend to fill in the holes, at least above the Schroeder frequency.
As you move off centre with a 3 channel matrix with significant (-6dB?) cross talk the smoothing effect of having 3 channels active (vs two) should be significant.
What would be very interesting to try is to feed mono, correlated pink noise to all three front channels without processing, and of equal amplitude, to see how much comb filter "swish swish" is noticed when moving laterally from the sweet spot, and whether there is less, or more than experienced with only left and right speakers operating. In other words does the addition of a third speaker reduce perceived comb filtering when all are playing the exact same correlated sound.
Anyone up for that test ?
Edit: And maybe also try the same test but with left and right channels both 6dB lower in level than the centre channel, which is more representative of what a passive matrix might derive from a mono signal...
Passive as in non-steered matrix ? Or passive as in some sort of passive network at line level ? Unfortunately I don't have a 3rd speaker to test with at the moment.
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