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Re: Speaker placement [message #18667 is a reply to message #18665] Wed, 29 March 2006 07:20 Go to previous messageGo to next message
Earl Geddes is currently offline  Earl Geddes
Messages: 220
Registered: May 2009
Master
"Perhaps randomly placed midbass drivers will smooth the sound field in the midbass, up to 120Hz. It's a reasonable suggestion. Then again, your proposed configuration is relatively complex with several woofers and crossover points. I also think having multiple distant and randomly placed sound sources run up through the upper bass to lower midrange might yield another set of problems. That's getting into the audio range where vocals, piano, guitar, cello, trombone and other wind and string instruments begin."

This is simply incorrect. So that we can get our terminology straight, to me, midbass lies above 100 Hz. Everything below 100 Hz. is simply bass and there are precious few musical instruments which have fundamentals in this region.

In the modal (bass) region things like distances to the sources crossover frequencies and the like have little to no real meaning. And talking about 100 Hz (the upper limit of my multiple sub implimentation) as being "run up through the upper bass to lower midrange" is ridiculous. In the modal region the complexity of multiple subs is Exactly what one wants.



Re: Speaker placement [message #18671 is a reply to message #18667] Wed, 29 March 2006 09:30 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18297
Registered: January 2001
Illuminati (33rd Degree)

You can make up your own definitions for bass, midbass, midrange, overtones and treble. Those are loosely defined regions, so it's probably more accurate to discuss specific frequency ranges. But 100Hz to 1000Hz is midrange to me, since that's where vocals and many other instruments lie. I identify the range from 1000Hz to 5000Hz also as midrange, but I like to call it the overtone region because that's what is usually present there, the harmonics generated by vocals and instruments. Treble is 5kHz and up, with 10kHz to 20kHz as the top octave. I consider everything under 100Hz to be bass, with content under 30Hz as deep bass and above 60Hz as midbass. Those are my definitions, so when you hear me use one of those phrases, you'll know what I'm talking about.

http://audioroundtable.com/misc/FreqGraph.gif

You can move the edges of your definition of "bass" and "midrange" up or down a half octave or so, makes no difference to me. To me, the midbass to midrange, the area between about 60Hz to 180Hz or so, is a transition area that makes it harder to deal with. The modes are growing increasingly denser as we near the top of this range, but at the bottom the modes are still sparse and need smoothing. But this is also an area where localization becomes possible and you definitely want close integration with the mains. I tend to think the woofers used in this range should be spaced relatively close to the mains, just a few feet away, and probably should be symmetrical with respect to the mains. Deeper bass can be sent to subs placed further away, but midbass woofers should be nearer. Remote subs - especially distant ones - are better crossed down low.

Re: Speaker placement [message #18672 is a reply to message #18671] Wed, 29 March 2006 09:55 Go to previous messageGo to next message
Earl Geddes is currently offline  Earl Geddes
Messages: 220
Registered: May 2009
Master
The summing is complex, thats exactly the point. The more complex it is the smoother it becomes. Simple summing (like subs close together) yields highly periodic and pronounced irregularities in the spatial and frequency response. You keep trying to apply HF concepts to the modal region and that simply does not work. And now you are contradicting yourself if you recommend the Welti approach because, if what you say were to be true then even the Welti's recommendations would not be acceptable.

Re: Speaker placement [message #18675 is a reply to message #18672] Wed, 29 March 2006 11:10 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18297
Registered: January 2001
Illuminati (33rd Degree)

The whole philosophy of multi-subs is to introduce dense interference. My point is whether or not the deep bass range should be covered by randomly placed subs or symmetrically placed subs, I think the midbass sound sources probably should be symmetrical and closer to the mains. You can't run a distant sub up too high, but you do want multiple sound sources throught the entire modal range. That includes some frequencies that are really too high for distant subs, in my opinion. It's a competing set of priorities at the high end of the modal range.


Re: Speaker placement [message #18679 is a reply to message #18675] Wed, 29 March 2006 13:25 Go to previous messageGo to next message
Earl Geddes is currently offline  Earl Geddes
Messages: 220
Registered: May 2009
Master
I noticed that you completely avoided my point about Welti - care to explain your way out of that? Do you or do you not remember claiming that you recommend his approach? If so then what about his approach at 100Hz? And don't try and tell me that he was only interested in much lower frequencies because that is not at all the case.

Re: Speaker placement [message #18680 is a reply to message #18679] Wed, 29 March 2006 14:16 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18297
Registered: January 2001
Illuminati (33rd Degree)

This has moved from a discussion about subwoofer placement into a more general discussion about subwoofer crossover frequencies and integration with mains.

There are two issues here. One is the use of dense interference to smooth room modes. The other is of integration with mains, considering crossover points and slopes and distance between subs and mains.

Dense interference can be accomplished at 100Hz using closer spacing than is required for dense interference at 35Hz because of the wavelengths involved. I'm saying I think probably it is worthwhile to have closer-spaced overlapping midwoofers for modal smoothing, and further spaced subs. The further subs might be arranged symmetrically as Welti suggests, or randomly as you suggest. But the nearby overlapping midwoofers should probably be symmetrical, to provide better imaging. They're the transition drivers, used up to the end of the modal range. They would work something like a traditional line array, but used only up to the Schroeder frequency.

I think I understand your concept, its strengths and weaknesses. How about you? Do you understand what I am saying?


Re: Speaker placement [message #18683 is a reply to message #18680] Wed, 29 March 2006 15:23 Go to previous messageGo to next message
Earl Geddes is currently offline  Earl Geddes
Messages: 220
Registered: May 2009
Master
I understand what you are trying to say, I just disagree with it.

"I'm saying I think probably it is worthwhile to have closer-spaced overlapping midwoofers for modal smoothing, and further spaced subs." i.e. non-Welti, or Geddes, a sort of Parham arrangement.

Below 100 Hz "integration with the mains" is irrelavent - it is insignificant. Thus, to me, your "issues" are simply not relavent. And your argument for symmetric placement is weak because it will always yield a higher spatial and frequency variance than a random or partially random placement will and there are no "integration" issues.

Re: Speaker placement [message #18684 is a reply to message #18683] Wed, 29 March 2006 16:36 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18297
Registered: January 2001
Illuminati (33rd Degree)

If we were discussing crossover below 100Hz, I might agree with you that integration with the mains was less troublesome, although I certainly wouldn't consider it to be irrelevant. But you have already indicated that you crossover above this point. That's where we disagree, as I see it. I would be more concerned with close spacing and symmetry as we get closer to the Schroeder frequency, where the sound field transitions from modal to reverberent.


Re: Speaker placement [message #18685 is a reply to message #18684] Wed, 29 March 2006 17:22 Go to previous messageGo to next message
Earl Geddes is currently offline  Earl Geddes
Messages: 220
Registered: May 2009
Master
Wayne - things would go a lot better if you would just READ what I write.

I never said that I "crossover" above 100 Hz, and I don't know where you got this idea. The only "crossover" would be at 50 Hz from the Summas to the VLF sub. The other subs don't crossover anything, they just augment the mains and simply fade away being down by about 6 dB at 100 Hz. with a very steep fall above about 120-150 Hz. So there is no potential for the things that you are ranting on about. This was all in my previuos posts, maybe not this concisely stated, but it was there. You seem to make up a lot of things that I never said.



Re: Speaker placement [message #18686 is a reply to message #18685] Thu, 30 March 2006 09:06 Go to previous messageGo to previous message
Wayne Parham is currently offline  Wayne Parham
Messages: 18297
Registered: January 2001
Illuminati (33rd Degree)

OK, so you don't have electrical crossover to rolloff your subs. You depend on the electro-mechanico-acoustic properties of the subs to roll them off instead. The distinction is irrelevant; The point is that there is output from multiple randomly-placed distant sound sources as high as 150Hz in your proposed configuration. That's pretty high frequency for subs - 130Hz is C below middle C - Definitely getting into the midrange at that point. I would not want that coming from multiple randomly-placed distant sound sources, not at all. I think it's worse than the room modes it tries to correct. Better to use a different configuration, in my opinion.

But I'm open minded. I plan to model your configuration as well as several others with CARA. I'll have to setup a system like that too; I'd like to hear what it sounds like.
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