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Old 6th March 2012, 12:03 PM   #1
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Default Directivity characteristics - what's the effect?

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Directivity is an interesting topic, but has it been discussed in detail? The topic comes in many forms and as with all speaker questions it merges into other areas as well.

But considering a plain 2-way speaker. Its directivity pattern is determined by the drivers respective phase and CC distance.
Now consider different height of the speaker (height up to right between tweeter and bas/midrange). 3 different alternatives:
1) at the sime height as listening height
2) higher than listening height
3) lower than listening height

One of the other areas it merges in to, is the reflections from e.g. the ceiling! Without dealing with the reflection (no acoustical treatment on the ceiling) it becomes even more important that this angle is a perfectly summed angle.

Are there any studies within this area/topic?
What are your experiences?
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Old 6th March 2012, 01:31 PM   #2
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Directivity is an interesting topic, but has it been discussed in detail?
I think it was kicked around a little.

What is the ideal directivity pattern for stereo speakers?

David S.
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Old 6th March 2012, 03:14 PM   #3
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Originally Posted by speaker dave View Post
I think it was kicked around a little.
Your knack for understatement is astounding.
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Old 6th March 2012, 03:33 PM   #4
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Originally Posted by speaker dave View Post
I think it was kicked around a little.

What is the ideal directivity pattern for stereo speakers?

David S.
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Old 6th March 2012, 04:36 PM   #5
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Originally Posted by EngelholmAudio View Post

Directivity is an interesting topic, but has it been discussed in detail? The topic comes in many forms and as with all speaker questions it merges into other areas as well.

Are there any studies within this area/topic?
What are your experiences?
Directivity is an interesting topic, I'm obsessed by it and I've written a lot about it.

But what you are showing is not an important issue in this regard IMO.

Basically looking at the directivity of pistons is kind of simplistic because real sources don't act much like pistons. You need to look at real source directivity data. Pistons are a decent source of examples for learning the basics, but don't try and extrapolate that too far.

And IMO, the polar lobes created at the crossover are usually in the vertical direction - the horizontal directivity is much more important and completely dependent on real source directivities. Sure there is a lobing issue right at crossover bewteen any two non-coincident sources, but this is pretty easy to deal with. Getting the horizontal directivity right across the full bandwidth from real sources is another problem all-together. (And "pistons" cannot do it.)
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Old 7th March 2012, 07:47 AM   #6
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Originally Posted by gedlee View Post
Directivity is an interesting topic, I'm obsessed by it and I've written a lot about it.

But what you are showing is not an important issue in this regard IMO.

Basically looking at the directivity of pistons is kind of simplistic because real sources don't act much like pistons. You need to look at real source directivity data. Pistons are a decent source of examples for learning the basics, but don't try and extrapolate that too far.

And IMO, the polar lobes created at the crossover are usually in the vertical direction - the horizontal directivity is much more important and completely dependent on real source directivities. Sure there is a lobing issue right at crossover bewteen any two non-coincident sources, but this is pretty easy to deal with. Getting the horizontal directivity right across the full bandwidth from real sources is another problem all-together. (And "pistons" cannot do it.)
Sure pistons can...but you need a 5-way speaker or so... I built a 4 way speaker and by inserting the Accuton C44 driver I managed to get an excellent directivity pattern.

For sure the simulation is a simplistic view - its validity in this thread is shear schematic, to show the principle.

I agree that lobes are most dominant in the vertically aspect. I'm interested in your comment:
"Sure there is a lobing issue right at crossover bewteen any two non-coincident sources, but this is pretty easy to deal with"
Hmm...yes - they are easy to deal with. Adjust the phase and/or CC distance. But what to aim for, others than a "perfect sum"?

Not all speakers have a listening height leveled tweeter/midrange. Should the loob point at the listening position? If not, should it be positivly or negativly phase shifted? How much?

Also a big thank's to speaker dave. Will read.
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Old 7th March 2012, 08:42 AM   #7
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Originally Posted by gedlee View Post
And IMO, the polar lobes created at the crossover are usually in the vertical direction - the horizontal directivity is much more important and completely dependent on real source directivities.
If direct sound is all that counts, yes, but is direct sound the whole story? In a free field, yes, but we tend to listen to speakers in rooms. So we first would need to answer the question "how do we perceive sound in an enclosed spaces?". There's not much we know about it.
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Old 7th March 2012, 08:49 AM   #8
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If direct sound is all that counts, yes, but is direct sound the whole story? In a free field, yes, but we tend to listen to speakers in rooms. So we first would need to answer the question "how do we perceive sound in an enclosed spaces?". There's not much we know about it.
But he says that "the horizontal directivity is much more important" which - in my interpretation - says exactly that it's much more than direct sound.

If I continue interpreting, gedlee says that horisintially originated reflections are more important than vertical ones. If interpreted correctly, I am curious as to why.

Not selldom, my measurements of hifi rooms shows a ceiling reflection absolutly to dominant in magnitude as well as to close in time. This makes me conclude that also vertical directivity is important.
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Old 7th March 2012, 09:05 AM   #9
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Not everythig we can measure is perceptually relevant. In my opinion the status quo in room acoustics gives the right answers to the wrong questions, i.e. there are effective products for problems that don't exist. This stems from the fact that the development was and still is driven by measurements and not by psychoacoustics. The AES paper "50 Years of Sound Control Room Design" by Jan Voetmann is a good read.
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Old 7th March 2012, 09:21 AM   #10
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Originally Posted by markus76 View Post
Not everythig we can measure is perceptually relevant. In my opinion the status quo in room acoustics gives the right answers to the wrong questions, i.e. there are effective products for problems that don't exist. This stems from the fact that the development was and still is driven by measurements and not by psychoacoustics. The AES paper "50 Years of Sound Control Room Design" by Jan Voetmann is a good read.
I belive we're fighting for the same thing, Markus. I do room acoustic treatment with the greatest respect to psychoacoustics. I do not look at the RT60, but rather e.g EDT and trying to maintain a positive reverb in the room.

But in order to do that, one must have total control of the speakers directivity, as well as total the rooms acoustic behaviuor.

So please stay on topic and contribute!
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