Multiple Small Subs - Geddes Approach - Page 176 - diyAudio
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diyAudio Member

Join Date: Dec 2004
Location: Novi, Michigan
Quote:
 Originally Posted by weltersys Earl, Are you saying that there is no difference in room modal excitation whether the radiator is a dipole or a monopole?
Of course there is a difference, but you cannot view it as a directivity response problem. In a room that has discrete modes the wave is restricted to move in only one direction per mode (well actually two orthogonal directions). The idea of directivity requires the response of a source along a variable direction, but the sound cannot travel away from the source in an arbitrary direction if there are discreet modes. As Markus says it is best to view LF sources of all types as sums of discrete sources separated in space and phase. This is always safe, but looking at it from a directivity standpoint is dangerous.

It is this kind of thinking that leads to false concepts like "Dipoles excite fewer modes." which is false. You can see this if you view a dipole as two sources out of phase and separated by a distance. The dipole will actually tend to excite more modes, which of course is desirable, not the other way around.

diyAudio Member

Join Date: Jan 2008
Quote:
 Originally Posted by gedlee The idea of directivity requires the response of a source along a variable direction, but the sound cannot travel away from the source in an arbitrary direction if there are discreet modes. As Markus says it is best to view LF sources of all types as sums of discrete sources separated in space and phase.
Agreed.

As Markus also said:
"The direct sound is swamped by the room response. So the radiation pattern isn't exactly meaningless but just one parameter in getting smooth response in frequency and time."

After further review of the tests posted in #1730, appears that time alignment has less to do with smooth response at my listening position, and "luck" at choosing the right place to put my couch in relation to the room modes more .

One interesting finding was that opening the rear room doors increased LF +8 at 33 Hz at the listening position.

diyAudio Member

Join Date: Jan 2008
Location: Toronto and Delray Beach, FL
Quote:
 Originally Posted by gedlee As Markus says it is best to view LF sources of all types as sums of discrete sources separated in space and phase. This is always safe, but looking at it from a directivity standpoint is dangerous.
My traces in #1713 illustrate nicely the complex interaction of enduring modes arising from room shape and the influence of seat location. The room modes are clearly enduring, but the two traces are distinctly different as well. (If you wanted to name the major artifacts, you'd name the room modes.)

Without even whispering a word about human hearing that might give a major twist to this discussion, it is easy to fall in fallacious thinking by confusing the simplifying assumptions and inspirational diagrams used to propel analysis with the sound of music introduced into a room. We all simplify to analyze, I'm just saying (pending better and better 3-D waterfall charts) there's a big step between that and the final audition.

Although thinking about the complex sound of dipoles might give the more analystic among unipole fans the heaves, it sure seems to fill-the-bill for dipole fans. Ditto for the topic of this thread: multiple subs.

Ben
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For several months now, nearly all my entries have been stalked by a certain humourless "guy" who never tires of lambasting me with long-winded screeds. Sad fellow. HiFi aspirations since 1956.

Last edited by bentoronto; 26th October 2013 at 06:36 PM.

diyAudio Member

Join Date: Dec 2004
Location: Novi, Michigan
Quote:
 Originally Posted by bentoronto Without even whispering a word about human hearing that might give a major twist to this discussion, it is easy to fall in fallacious thinking by confusing the simplifying assumptions and inspirational diagrams used to propel analysis with the sound of music introduced into a room.
Huh!?

 1st July 2014, 03:37 PM #1755 diyAudio Member   Join Date: Nov 2002 Location: Hyderabad, India Does multi sub approach also work in smaller rooms? Hi Earl, Will the same multi sub approach also work in smaller rooms, something like 15x13x10? The reason why I ask is that in OptimalPlaybackInSmallRooms.ppt you have defined a small room as 20x14x10. Some rooms may be smaller like above. Thanks, Goldy __________________ Audio enthusiast/hobbyist
diyAudio Member

Join Date: Jan 2008
Location: Toronto and Delray Beach, FL
Quote:
 Originally Posted by goldyrathore Hi Earl, Will the same multi sub approach also work in smaller rooms, something like 15x13x10? The reason why I ask is that in OptimalPlaybackInSmallRooms.ppt you have defined a small room as 20x14x10. Some rooms may be smaller like above. Thanks, Goldy
The smaller the room, the more pressing are bass issues. For example, room modes are in more audibly detectable ranges. So having another bit of control (by working with multiple subs) is better. Of course, the smaller the room, the harder it is to decorate your room with many subs.

Aim for heterogeneity of box types too.

B.
__________________
For several months now, nearly all my entries have been stalked by a certain humourless "guy" who never tires of lambasting me with long-winded screeds. Sad fellow. HiFi aspirations since 1956.

diyAudio Member

Join Date: Dec 2004
Location: Novi, Michigan
Quote:
 Originally Posted by goldyrathore Hi Earl, Will the same multi sub approach also work in smaller rooms, something like 15x13x10? The reason why I ask is that in OptimalPlaybackInSmallRooms.ppt you have defined a small room as 20x14x10. Some rooms may be smaller like above. Thanks, Goldy
Multiple subs always works regardless of size. The specifics of each room are so widely varied that you really need to simulate the situation using something like the software on my site.

diyAudio Member

Join Date: Jan 2008
Location: Toronto and Delray Beach, FL
Quote:
 Originally Posted by gedlee Huh!?
I'm sorry to have neglected any comment from Earl, even if just "huh."

My favourite example of relying on your eyeballs instead of your ears-on-music is comb filtering. Few diagrams are as dispiritingly horrible as comb filtering. But there's reason to doubt comb filtering spoils music much or at all.

Ben
__________________
For several months now, nearly all my entries have been stalked by a certain humourless "guy" who never tires of lambasting me with long-winded screeds. Sad fellow. HiFi aspirations since 1956.

diyAudio Member

Join Date: Jun 2012
Location: Appalachia, in the middle of nowhere.
Quote:
 Originally Posted by bentoronto SNIP...... . Few diagrams are as dispiritingly horrible as comb filtering. But there's reason to doubt comb filtering spoils music much or at all. Ben
I have built a number of 4 element column speakers, improving each design over time.
My latest has 4 Dayton PA-130's and a small horn.
I cross them to woofers and then subs at 153 Hz BW4.
I think they sound great.
They are so efficient I can not tolerate full volume with a 40 watt amp.
.
My Daughter comes over and says "How can you stand all that swish, swish"

I guess everyone has their own expectations and hears what they want to.
Subjectivity seems to swamp reality.

P.S. I fully subscribe to the Multiple Sub approach.

Dave

Last edited by Shadydave; 1st July 2014 at 07:53 PM. Reason: Spelling

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