What is the ideal directivity pattern for stereo speakers?

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...tend to bring spaciousness - "images that fill a space (ASW)" (as opposed to pin points) which is a thing many consider necessary for realism of sound reproduction, for example Markus76 here, on diyaudio forum?


A solo voice with some space around is a setting which can be
reproduced quite nicely. If it is "realistic" i see no reason for artificially
"blowing it up".

Early reflections do not contribute to envelopment IMO.
Envelopment may be a desirable property, but one can have bloating
of phantom sources without creating any envelopment. That is what early
reflections tend to do IMO.


yes, perhaps some early reflections may affect tonality but do You know any detailed study of this question - of which reflections (with regard to their delay, angle, frequency response etc.), how and to what degree?

If you accept "informal studies", i built lots of similar 2-ways as i was
a student and placed them in different environments.

Listening distance and near side wall reflections (above the crossover frequency
to the tweeter) were dominant factors in changeing tonality. They had to be
compensated for, in case the placement could not be changed to statisfaction
(by toeing in, moving the speakers further away from walls, listening close enough).
 
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yes, perhaps some early reflections may affect tonality but do You know any detailed study of this question - of which reflections (with regard to their delay, angle, frequency response etc.), how and to what degree?

Soren Bech of the University of Denmark studied this for a number of years and wrote several AES papers on it.

He modeled a typical speaker in a typical living room by setting up a large number of loudspeakers (early KEF uni-Q) in an anechoic chamber. The typical reflections from floor ceiling and walls were accurately modeled as to direction, delay, frequency response and strength.

Once he had the room model set up he could turn up and down each reflection to see if it was typically noticed and what its effect was.

You should read the papers but his general conclusion was that the floor bounce for sure and usually the rear wall bounce were at a noticable level (caused coloration). Other reflections were below the detection threshold, although the corner reflections will determine the bass response.

Regards,
David S.
 
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to be more precise 0.2 is just a value I have found on one of audiophile pages. On the other hand on another page I have found that 0.5 is the "optimum midfrequency RT60" for a "broadcast studio" 0.5 is also typical/recommended RT60 for small rooms according to KTH handbook,
which relies in that regard on "textbook knowledge" and results of a KTH research project "Speech and Music in Rooms". For bigger rooms like 6x8 classroom size room it is 0.8

Ideal RT must always be tied to room size. bigger rooms should have a longer RT but they won't seem more "lively" because of it.

It is better to think in terms of average absorption. For example a wide range of cinema sizes can have ideal acoustics (with a wide range of RT) if the mean alpha is 0.4.

David S.
 
Soren Bech of the University of Denmark studied this for a number of years and wrote several AES papers on it.

He modeled a typical speaker in a typical living room by setting up a large number of loudspeakers (early KEF uni-Q) in an anechoic chamber. The typical reflections from floor ceiling and walls were accurately modeled as to direction, delay, frequency response and strength.

Once he had the room model set up he could turn up and down each reflection to see if it was typically noticed and what its effect was.

You should read the papers but his general conclusion was that the floor bounce for sure and usually the rear wall bounce were at a noticable level (caused coloration). Other reflections were below the detection threshold, although the corner reflections will determine the bass response.

Regards,
David S.
Interesting - so it looks as though it may be better to put the woofer close to the floor in a floorstander, even at the expense of lobing with the mid...
 
Interesting - so it looks as though it may be better to put the woofer close to the floor in a floorstander, even at the expense of lobing with the mid...

post-101654-1197498029.jpg


Roy Allison found it very important.

EDIT: And so does Peter Lyngdorf: http://www.lyngdorf.com/content/view/25/50/
 
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Interesting - so it looks as though it may be better to put the woofer close to the floor in a floorstander, even at the expense of lobing with the mid...

Yes, the Allison or AR approach still works. If the woofer is near the floor then the floor bounce frequency is high and out of the woofers range. If the midrange is well above the floor then the floor bounce frequency (for it) becomes low and below the crossover. In both cases you put the bounce frequencies out of their respective ranges.

Works great for 3 ways but not so good for 2 ways.

David S.
 
Wait - wouldn't the ideal solution be to put a wide-angle diffuser at the floor bounce location for typical listening positions? That way one can avoid the vertical lobing by keeping the woofer close to the mid.


The floorbounce typically occurs around 300 hz. Because of the large wavelengths involved, that means you'd need a huge diffuser to do anything useful.

I think the ideal loudspeaker should do something about the floorbounce dip. The Alisson method got rid of both the floor- and back-wall dips at once. Another way to mitigate the floorbounce dip is to use vertically spaced drivers. As such line-arrays work pretty well in this regard too.
 
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Yes, the Allison or AR approach still works. If the woofer is near the floor then the floor bounce frequency is high and out of the woofers range. If the midrange is well above the floor then the floor bounce frequency (for it) becomes low and below the crossover. In both cases you put the bounce frequencies out of their respective ranges.

Works great for 3 ways but not so good for 2 ways.
Do you think there is an optimum crossover frequency range (and slope) for this approach from a psychoacoustic perspective ? Eg, lets ignore for the moment the optimal crossover frequencies of specific driver combinations, and examine only the factors that affect perception of imaging and focus, interaction with the room etc.

My feeling is that for this type of design (very low woofer, very high midrange) the crossover frequency should be no lower than 200Hz but also no higher than 300Hz, and not less than 12dB/oct, but I'd be interested to see other peoples thoughts.
 
Do you think there is an optimum crossover frequency range (and slope) for this approach from a psychoacoustic perspective ? Eg, lets ignore for the moment the optimal crossover frequencies of specific driver combinations, and examine only the factors that affect perception of imaging and focus, interaction with the room etc.

My feeling is that for this type of design (very low woofer, very high midrange) the crossover frequency should be no lower than 200Hz but also no higher than 300Hz, and not less than 12dB/oct, but I'd be interested to see other peoples thoughts.

I'm not sure what psychoacoustic factors will come into play. Even the seperation of sources is likely to be inaudible since the angular split is fairly low and it is in a vertical orrientation where we aren't very discerning.

Best frequency range? I'd have to do some simulations for that. The Allison picture shows a typical arrangement with the woofer center maybe 9 or 10 inches off the floor and the midrange just below a tweeter at the usual 40 inches up. Simulate or measure that and it will show you where the crossover needs to be. Note that for both drivers you will get a comb filtered response. For the woofer all the comb filtering can be in the stop band and thus ignored. For the mid the comb filtering is in the pass band so your hope is to ignore the first or second null and use it in a region where the response has settled down.

David S.
 
To start I think. Directivity we can not hear.

We can hear directivity interacting with the room causing interference of the original sound-level.

So I would say to get the play back original to your ears the directivity can be small to prevent room reflections to distort. Ideal would be a speaker acting as a earphone not influenced by room reflections.

You always have room reflection of low frequencies so use it in your design to optimize the result.
 
My recipe these days is for mid and hf horns with tightly controlled directivity oriented relatively on axis at my listening position. (60 degrees or less of dispersion in the horizontal plane, and 40 - 60 degrees in the vertical plane.


Wow! I've never discussed speakers with you but we use exactly the same directivity angles. The horns I've been working on are 60 X 40. This gives me good horizontal coverage without involving the room too much. 40 degrees vertical keeps floor and ceiling bounce to a minimum. I find this gives me the best clarity possible in my room. Very interesting we came to the same solution.
 

ra7

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It always amazes me when people say that reflections are bad. Reflections are necessary for proper localization of the phantom image. In an ideal anechoic chamber, with no reflected sound, where do you think the phantom image from two sources will form? It will form inside your head, just like in the case of headphones. It is the room reflections that tell your brain exactly where the image is.

With narrow dispersion, the image forms way in front of the speakers. The brain is not receiving enough information to locate the phantom image. With wide dispersion, or even moderate dispersion, the image forms behind the speakers, is much better defined and localized. These are my observations.

I would imagine that wide dispersion is, in general, better. I believe each one of speaker dave's suggestions in the first post are exactly spot on. Late reflections (I'm not sure how much time should elapse before a reflection is considered late) should be avoided, but early reflections should not be seen as a detriment to good sound or good soundstaging.
 
It always amazes me when people say that reflections are bad. Reflections are necessary for proper localization of the phantom image. In an ideal anechoic chamber, with no reflected sound, where do you think the phantom image from two sources will form? It will form inside your head, just like in the case of headphones. It is the room reflections that tell your brain exactly where the image is.

With narrow dispersion, the image forms way in front of the speakers. The brain is not receiving enough information to locate the phantom image. With wide dispersion, or even moderate dispersion, the image forms behind the speakers, is much better defined and localized. These are my observations.

I would imagine that wide dispersion is, in general, better. I believe each one of speaker dave's suggestions in the first post are exactly spot on. Late reflections (I'm not sure how much time should elapse before a reflection is considered late) should be avoided, but early reflections should not be seen as a detriment to good sound or good soundstaging.

bolds are mine
now this was great post! :D a bit overgeneralising but basically I agree with everything that You have written!
 
Wow! I've never discussed speakers with you but we use exactly the same directivity angles. The horns I've been working on are 60 X 40. This gives me good horizontal coverage without involving the room too much. 40 degrees vertical keeps floor and ceiling bounce to a minimum. I find this gives me the best clarity possible in my room. Very interesting we came to the same solution.

Recently found something for the extremists: Limmer 126 40x40 and Limmer 243 40x30
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What do you think about the 033? Looks unusual.
 
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