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Old 10th December 2008, 09:38 PM   #41
Pallas is offline Pallas  Pakistan
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Quote:
Originally posted by gedlee
The "above the centerline" is not a dictum, but a recommendation. I've often done without it, it just worked better that way in the simulations. But the real world is more complicated and we can never get such a clean setup as in a simulation.
Fair enough on the dictum vs. recommendation point. I thought I detected a change in your position over time on that, after finding that your high sub wasn't working in your room or something like that.

In my previous home and in the previous iteration of this system, I did use a high sub as well as a second "broadband" sub. In my previous home, it was easy to hide the high sub. In this one, it was ugly. Eventually I got tired of looking at it, and ended up replacing both of my "broadband" subs with something much prettier.

Quote:
Originally posted by gedlee
I don't think that you will get the optimum without some measurements, although listening can be sufficient at times.
I would think it an assumption that anyone serious about getting the bass (or any other part of the spectrum) right in a room relies heavily on good measurements taken in situ.
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Old 10th December 2008, 10:23 PM   #42
gedlee is offline gedlee  United States
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Quote:
Originally posted by Wayne Parham
Both have moved some, but Geddes, in particular, made it a point to suggest that the two approaches were different.
I think that I pointed out that in a practical application the two approaches where almost identical. The differences are pretty small. Three versus four is the biggest difference.
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Old 10th December 2008, 10:23 PM   #43
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Great discussion, and more of it than I expected to see when I arrived home!

Hello Wayne! Long time, no see. As you can tell, I've abandoned the huge basshorns for home and heading for the multi-sub approach. The bass horns are pretty spectacular, but better suited for other applications. I am sold on the idea of more uniform response rather than spectacular dynamics at this point. Multiple subs do a fine job still and don't sacrifice integration in the process.

A lot of good thought coming out of this topic, with some really great minds involved. Looking forward to learning more with regards to individual unit symmetry/non symmetry and room placement in both the horizontal and vertical plane.

Jerrod
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Old 11th December 2008, 12:55 AM   #44
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Good to see you Jerrod, yes, it has been a while.

I tend to hang out mostly on AudioRoundTable.com and the Pi Speakers forum mostly. I come here from time to time too.

Not much new to report on my end. Still the same basic models. They pretty much do everything right.

Four Pi mains with three Pi subs in my main living room.
Two Pi towers in my bedroom.
Seven Pi cornerhorns in my office.
A warehouse full of 12Pi hornsubs, some out for for rentals.

Plans are still free, kits damn near.
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Old 11th December 2008, 01:12 AM   #45
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Yes, when you've got something that works, keep workin' it! Still got lots of really good parts here. Two Pi towers in the garage. Many itterations of midhorns, enough JBL parts to do several "pro Pi" speakers, big custom Fitz horns, really big dipole's with 5 15" drivers a side, and a bunch of other really fun stuff. After many horn variations, been doing high efficiency open baffle stuff for a few years. Been helping with some crossover work, testing, tuning, etc. for the Hawthorne Audio people. Been working with lots of the same old great parts, just different implementations(yeah, a few new parts too!....) Will have to drop in at ART and pull up a seat!

Back on topic
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Old 11th December 2008, 02:02 AM   #46
soongsc is offline soongsc  Taiwan
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Default Re: Re: Multiple Small Subs - Geddes Approach

Quote:
Originally posted by Cal Weldon
I am yet to hear a multi sub system that didn't sound cluttered and muddy. I will stick with one bass unit thank you.

I'll take two.

Quote:
Originally posted by markus76
Horizons, multiple subs is the best and only method to smooth the low frequency response when you can't install (any more) low frequency absorber. I've documented it here:
http://www.mehlau.net/audio/multisub_geddes/

Best, Markus
The main issue with multiple subs is that you excite multiple room modes. This translates to the muddiness that Cal is referring to because now the low frequency energy cannot decay fast enough.
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Old 11th December 2008, 03:28 AM   #47
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Default Re: Re: Re: Multiple Small Subs - Geddes Approach

Quote:
Originally posted by soongsc
The main issue with multiple subs is that you excite multiple room modes. This translates to the muddiness that Cal is referring to because now the low frequency energy cannot decay fast enough.
So what's the alternative solution?
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Old 11th December 2008, 04:13 AM   #48
youngho is offline youngho  United States
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I think the fundamental approach between Geddes' and Welti's original papers were different:

1. Welti's recommended setups in the Harman paper used the passive approach of node placement and/or active approach of mode cancellation. The main problem I had with this paper were the use of only a single real-world room for an investigation, which for the record, did have a door, and which generally supported the modelled results (I always point out that the single corner subwoofer did surprisingly well in this investigation).

2. Geddes' original approach (four subwoofers randomly placed, including one off the ground) in his white paper was a bit of a blunt force approach relying on random differences in phase and distance to excite modes in different phases. The problems I had with this paper was the location of the listener in the center of the room and the focus on a single listener, as I recall.

Obviously, both have modified their approaches since then. As noted, Sound Field Management relies on signal processing, which wasn't part of Welti's Harman paper but his subsequent one. Geddes' approach now relies on spatial averaging that wasn't discussed in his original white paper.

I imagine a future where the room shape and dimensions are entered into a computer, a subwoofer is placed into one of the room corners, someone walks around the room with a wireless microphone to record frequency response below 80 Hz, subwoofers are then placed into the primary horizontal nodes, the computer suggests volume and phase settings depending on the subwoofer characteristics, and signal processing takes care of the rest.
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Old 11th December 2008, 04:50 AM   #49
youngho is offline youngho  United States
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Quote:
Originally posted by youngho
I imagine a future where the room shape and dimensions are entered into a computer, a subwoofer is placed into one of the room corners, someone walks around the room with a wireless microphone to record frequency response below 80 Hz, subwoofers are then placed into the primary horizontal nodes, the computer suggests volume and phase settings depending on the subwoofer characteristics, and signal processing takes care of the rest.
Sorry, can't edit posts, meant to say that the computer suggests placement (which may be the primary horizontal modes), volume, and phase settings; more spatially averaged measurements are done at the listening position; and signal processing takes care of the rest.

The SFM device from JBL seems to work with already positioned subwoofers. Anyone had experience with it?
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Old 11th December 2008, 08:09 AM   #50
breez is offline breez  Finland
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Quote:
Originally posted by youngho
Obviously, both have modified their approaches since then. As noted, Sound Field Management relies on signal processing, which wasn't part of Welti's Harman paper but his subsequent one. Geddes' approach now relies on spatial averaging that wasn't discussed in his original white paper.
SFM is very light on signal processing and apart from the single parametric eq filter applicable the approach seems pretty much identical to Geddes'.

I'm interested in creating a software tool implementing SFM's brute force search for best combination of subwoofer positions with gain and delay settings. What's the deal with patents and stuff? Could I release such a software for free?
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