Which SEOS for near-wall placement? - AVS Forum
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post #1 of 16 Old 11-13-2013, 12:41 PM - Thread Starter
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My sub build is finished, mains are up to bat and I need some direction. I'm looking at the SEOS12/360 with AE 12(?) as the LCR to work with my two Gjallarhorns in my living room HT/music listening area. The room is vaulted, there are several openings to other rooms. The L and R will be right next to the side walls floor-standing, or can be in the upper corners. If they are in the upper corners, they will need to be smaller obviously, but I worry about losing some low end. If the mains are in the upper corners, one will be very close to the mouth of the G-horn. The G-horns will be venting from the right upper corner of the vault, and 1/4 space to the left. I prefer running my mains at FULL. The L side will be right in a doorway if on the floor, so it needs to be against the wall. Anyways, my head spins with all of the options and I appreciate any input from you guys. I'm open to be the guinea pig for new configurations, ie an MTM with 10s that was mentioned recently -wink, wink.

My pertinent gear:
Onkyo 818, running 7.1
two G-horns
60" LED
MiniDSP and UMIK
Room is 13'9" x 19'5" x 12'10" at peak of vault. 2781 ft^3
LP at 12'10" from screen wall




Here is the room showing the screen wall, scheduled for demo Dec 1. with installation of 5/8" rock to the walls with soffit at 9'

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post #2 of 16 Old 11-15-2013, 05:40 AM - Thread Starter
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Bump - which SEOS design would work well near-wall, and as described above?
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post #3 of 16 Old 11-15-2013, 06:43 AM
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Bump - which SEOS design would work well near-wall, and as described above?
All speakers are subject to Allison Effect. Where the distance from the speaker to the wall behind it is 1/4 wavelength there will be a cancellation notch. For example, taking 80Hz as the crossover frequency from the mains, where 1/4 wavelength is 3.5 feet, that means the subs must be closer than 3.5 feet to the wall, and the mains further away than that, to avoid any cancellations. The other option with mains is to wall mount with the 1/4 wavelength distance from the baffle to the wall being above the baffle step frequency. That means making the cab as shallow as possible, and the baffle as large as possible, within the constraints of the box volume.

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post #4 of 16 Old 11-15-2013, 07:15 AM
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Originally Posted by Bill Fitzmaurice View Post

All speakers are subject to Allison Effect. Where the distance from the speaker to the wall behind it is 1/4 wavelength there will be a cancellation notch. For example, taking 80Hz as the crossover frequency from the mains, where 1/4 wavelength is 3.5 feet, that means the subs must be closer than 3.5 feet to the wall, and the mains further away than that, to avoid any cancellations. The other option with mains is to wall mount with the 1/4 wavelength distance from the baffle to the wall being above the baffle step frequency. That means making the cab as shallow as possible, and the baffle as large as possible, within the constraints of the box volume.

I planned on wall mounting my Fusion-10 pures and fusion-8's onto 6" converted monitor arms.

What kinds of problems should I expect because of this?
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post #5 of 16 Old 11-15-2013, 07:26 AM
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I planned on wall mounting my Fusion-10 pures and fusion-8's onto 6" converted monitor arms.

What kinds of problems should I expect because of this?
How far are the baffles from the wall, and what are the baffle step frequencies?

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post #6 of 16 Old 11-15-2013, 07:28 AM
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How far are the baffles from the wall, and what are the baffle step frequencies?

Wish I knew what a baffle step frequency was...

Baffles are about 17.5 inches from the wall
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post #7 of 16 Old 11-15-2013, 08:47 AM - Thread Starter
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Quote:
Originally Posted by Bill Fitzmaurice View Post

All speakers are subject to Allison Effect. Where the distance from the speaker to the wall behind it is 1/4 wavelength there will be a cancellation notch. For example, taking 80Hz as the crossover frequency from the mains, where 1/4 wavelength is 3.5 feet, that means the subs must be closer than 3.5 feet to the wall, and the mains further away than that, to avoid any cancellations. The other option with mains is to wall mount with the 1/4 wavelength distance from the baffle to the wall being above the baffle step frequency. That means making the cab as shallow as possible, and the baffle as large as possible, within the constraints of the box volume.

Makes sense Bill. I guess it doesn't really matter what type of speaker it is. Would toe-in/out in relation to the LP will be the easiest way to handle it, along with a diffuser right next to it to spread out the reflections? I don't completely understand how these magic waveguides work, but I like what I hear about them. I want to make sure they will work for my application as well or better than a traditional 3 way design. None of my speaker placement for this room is ideal.
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Wish I knew what a baffle step frequency was...

Baffles are about 17.5 inches from the wall

I posted a link below that explains it somewhat. I understand it as this: The XO design takes in to account the baffle step frequencies that are part of the overall design of the drivers, box, XO, and placement. The baffle step frequencies have to do with the sound waves out of the driver and their reflections at different points on the speaker baffle (and other things) on the way to your ear, ie,a tweeter floating in space is not affected by it. If they reflect at the wrong place at a certain frequency as they are designed, it will gain several db. My last speakers I built were wider than the designer intended, so the guys at meniscus used the BSC calculations to change up the some of the XO components so that they sound as they should. Speakers like the Statement are designed to have the mid at a set distance from the back wall to use the reflections to benefit the sound. This type of placement is the exact opposite of what I can use.



http://sound.westhost.com/bafflestep.htm
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post #8 of 16 Old 11-15-2013, 10:29 AM
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Originally Posted by goonstopher View Post

Wish I knew what a baffle step frequency was...
Where the smaller baffle dimension is one wavelength.
Quote:
Baffles are about 17.5 inches from the wall
That makes the 1/4 wavelength frequency 195Hz or so. The smaller baffle dimension would have to be about 5 feet to avoid any dip.
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Would toe-in/out in relation to the LP will be the easiest way to handle it, along with a diffuser right next to it to spread out the reflections?
Toe in might broaden the dip frequency while lessening the depth. It would take a very large baffle extension to do much. I got around Allison Effect with my line array mains that have a triangular shape that provides a natural toe-in, which along with corner placement results in zero baffle to wall distance. Flush in wall mounting does the same, but doesn't give toe in. You can mount in wall with toe in and use a filler between the wall and the edge of the cab the extends out of the wall. You can see how they got around Allison Effect as early as 1935 in pictures of the Shearer Horn, over twenty years before Roy Allison gave his name to it.

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post #9 of 16 Old 11-15-2013, 10:42 AM
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Guess I'll toe in and just deal with the dip... Hope the OP finds a better solution
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post #10 of 16 Old 11-15-2013, 11:08 AM
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Absorption on the wall behind the speaker will help. I have the same issue, and am planning on installing some eventually. 4" rigid fiberglass with a 4" air gap from the wall was mentioned as an excellent option. I might not go with that much air gap depending on how much space I have to give up, but I wouldn't go with less than a 4" panel.

Sounds Good to Me... keeping track of my audio projects.

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post #11 of 16 Old 11-15-2013, 12:06 PM
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I have 3" panels behind mine... will help some hopefully
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post #12 of 16 Old 11-15-2013, 12:06 PM
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Absorption on the wall behind the speaker will help. I have the same issue, and am planning on installing some eventually. 4" rigid fiberglass with a 4" air gap from the wall was mentioned as an excellent option. I might not go with that much air gap depending on how much space I have to give up, but I wouldn't go with less than a 4" panel.
That's an option, though not one that will pass WAF in a living room. I'd forget about the air gap, since it forces the speakers to be four inches further from the wall it's counter-productive, as the longer the wavelength you want to damp the more material it takes to do it. IME the worth of an air gap in adding effectiveness to traps is overstated by its adherents.

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post #13 of 16 Old 11-15-2013, 01:13 PM - Thread Starter
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Refer to the top pic for a sec - the L main will be directly under the round mirror. I could build an in-wall 4x4' absorber next to the speaker between the studs, fill the wall with insulation, cover with fabric, make it flush with the wall. I could put the cabinet right up against the wall. WAF!
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post #14 of 16 Old 11-17-2013, 06:07 AM - Thread Starter
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I'm sold on the td12m and seos 12/360 for my LCR. Robotbunny was nice enough to demo his for me yesterday and I have the same positive review as everyone else about this design. I think it will be great for my space and I'm in love with the smooth, detailed sound. We talked a bit about how to make this into a full-range speaker maintaining the incredible mids crossed over at 80 by adding an additional driver that can dig deeper, such as the td 12x. This would be a tall ported mtm. I'm going to restrict the driver size to 12" to keep the cab a slim as possible. I want to start putting together parts and build a 3 piece box for testing so I can try the 3rd driver in different arrangements.
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post #15 of 16 Old 11-20-2013, 08:08 AM - Thread Starter
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Where should I tune these to work with my Gjallarhorns?
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post #16 of 16 Old 11-20-2013, 08:25 AM
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Try to get 50-60Hz extension...GH's really should be rolled out at 50 to 60Hz because the response gets nasty above that point.
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