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Old 11th December 2008, 09:15 AM   #51
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Quote:
Originally posted by markus76
Welti has published multiple papers. His prior papers only considered what is referred to as "positional optimization" in his later paper. When people here discuss "Welti" or "Harmon" sub placement they're generally referring to this approach, not SFM. I believe this is the source of your confusion.

SFM has only appeared in his later papers. While there remain some differences, Geddes approach is clearly a pragmatic version of the same method with a human doing the optimization rather than software (naive exhaustive search vs shotgun hillclimbing with good heuristics if you want to be all grad student about it). I think Geddes discussion of his approach predates Welti's later papers, but I'm not sure of that.

In any case, it's not surprising that their approaches are converging, since they're solving the same problem largely under the same constraints.
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Old 11th December 2008, 09:50 AM   #52
MaVo is offline MaVo  Germany
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My subjective experience with multiple subs is a clearly less muddy sound. I was amazed once i heard 4 symmetrically placed subs. Even two, placed at the right position, was a "never go back to the state before" experience. So, my applause goes to people like geddes, who brought this approach to the diy world... i dont want to imagine how my room would have looked with oldschool fibrous absorbers for bass frequencies
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Old 11th December 2008, 10:17 AM   #53
youngho is offline youngho  United States
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My impression from reading Toole's book is that SFM has developed further since Welti's 2006 paper. Toole used the phrase "substantial signal processing"in describing it, hence my impression that it involved signal processing. What was I thinking?

Also, I did not get the impression that SFM searched for best subwoofer positions but rather ideal settings for level, delay, and one band of parametric equalization for subwoofers already positioned. Geddes' method seems to result in the nearest subwoofer being the loudest and the furthest being the softest, at least in terms of gain. If SFM's brute force search tended to provide similar setups, then the two approaches would indeed tend to converge, but the complexity introduced by seemingly endless possibilities for settings for gain, delay, and parametric equalization make me skeptical without proof.

Perhaps I am mistaken. If so, please enlighten me.
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Old 11th December 2008, 10:39 AM   #54
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Hi Earl

I may have missed this, but are the mains run full-range, to further spread the number of sound sources? The downside would be that you miss the opportunity to relieve the mid-woofers of low bass duty, and gain better sound from them . .

Also, I see why limiting higher output is desirable, eg by a bandpass. If a bandpass isn’t used for whatever reason, wouldn’t a reasonable alternative be a crossover?

Lastly, is sealed preferred because of the slower rolloff, ie more bass down very low, at the expense of typically less output c 30 – 50 Hz. Would a mix of sealed and ported spread the output best?

Thanks
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Old 11th December 2008, 10:40 AM   #55
breez is offline breez  Finland
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Quote:
Originally posted by youngho
My impression from reading Toole's book is that SFM has developed further since Welti's 2006 paper. Toole used the phrase "substantial signal processing"in describing it, hence my impression that it involved signal processing. What was I thinking?


An alternative approach involving a complex filter for each subwoofer was developed and compared to the thing we know as SFM.

Quote:
Also, I did not get the impression that SFM searched for best subwoofer positions but rather ideal settings for level, delay, and one band of parametric equalization for subwoofers already positioned. Geddes' method seems to result in the nearest subwoofer being the loudest and the furthest being the softest, at least in terms of gain. If SFM's brute force search tended to provide similar setups, then the two approaches would indeed tend to converge, but the complexity introduced by seemingly endless possibilities for settings for gain, delay, and parametric equalization make me skeptical without proof.

Perhaps I am mistaken. If so, please enlighten me.
I'm not sure if the SFM described in the paper allowed to choose from many possible subwoofer locations, but it would be a trivial task to allow such a possibility. SFM is amazingly simple due to brute force search and simple settings apart from the parametric filter. Only the filter option requires any intelligence from the algorithm.
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Old 11th December 2008, 10:40 AM   #56
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SFM does optimize for position. More specifically, you measure an individual subwoofer at some number of potential positions, and SFM selects a subset of those. However, in the 2006 paper I believe only one room had a large number of choices (8), the others just had 4 and the best found solution for those rooms used all of them. That may be what you're thinking of.

I don't believe Geddes method results in the closest being the loudest. Unless I misunderstand it the typical result is that the first subwoofer, placed in the corner, dominates the response. That said, following his approach you might end up with any number of subwoofers being the loudest depending on the room and what positions you try.
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Old 11th December 2008, 10:55 AM   #57
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Great discussion. I'm getting ready to try the 3- or 4 sub approach. What do you people use to parcel out the freq bands to the subs? I've seen some references to that JBL BassQ unit, any experience with it? What does that unit cost anyway?

Jan Didden
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Old 11th December 2008, 11:30 AM   #58
youngho is offline youngho  United States
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Thanks! I appreciate the information. If I understand correctly, the SFM approach tends to result in symmetric subwoofer setups, at least in symmetric rooms. The one very asymmetric example still had some symmetry of the two subwoofers with respect to the listening position. I imagine that Geddes' approach does not?
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Old 11th December 2008, 12:22 PM   #59
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Quote:
Originally posted by janneman
JBL BassQ ... What does that unit cost anyway?
$1200
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Old 11th December 2008, 01:09 PM   #60
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Quote:
Originally posted by markus76


$1200

Thanks Markus. Hmmmm. Maybe I should try first with my DCX2496 at $200

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