audioguy
At least when it comes to the number of subs to drive the room uniformly (For rectangular sealed spaces only).   I have built 4 theaters in the last 10 years and assisted 3 or 4  others do the same.  In each case, I convinced the owner to place a sub as close to each corner of the room as possible.  

In the most recent case, the individual knew zip about a home theater so we were able assist in all of the component selections and room treatment recommendations.  We recommended four Seaton subs and given space restrictions, we wanted two pairs of the new F18 Master/Slave systems.

To cut to the chase, here is the FR of the subs with no EQ applied:



Here is the FR WITH Audyssey:



Can we say FLAT!!!  About 5db down at 6HZ !!!!!!

Here are a few photos of the room.  The only place he wandered away from our recommendations was the thickness of the wall panels (he did so for cosmetic reasons but I still think my approach would have looked and sounded better.)  This room is fairly small (11 x 19 x 10).  I finished the initial calibration today but want to return and play with the knobs that provides low end lift on the sub amps - to add a touch more "heft" on the bottom end.  But one thing was obvious, these new F18's are KILLER subs.  In fact, after hearing them, I need to find a way to buy 4 for ME and replace the two DIY 18 inch subs I have up front in my room.  Maybe I can start a "GoFundMe" project [biggrin] [biggrin]





By the way, my camera did not get the colors correct.  The upper panels and the diffussors are a blue color and the chairs and carpet are a dark gray/black!!

If 4 subs is not practical for financial reasons or even space reasons, an almost equally good approach is two subs in diagonal corners.  Again, this works for rectangular sealed spaces. 

Anyway, congratulations Mark for yet another amazing sub product!

Our Theater
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hifiaudio2
Very cool!  So you are getting better results from using the 4 corners over the 4 mid points? I had thought mid point positioning was considered the gold standard by Harman et al. over four corner placement...

Are the rear subs in the pics side firing in the last cut out along the side?   

And what treatments did you use?

Great looking room for a pretty narrow space!
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audioguy
If you re-read the referenced Harman paper, the 4 mid-points recommendation is only marginally [and in my mind, theoretically]  better than the 4 corners.  BUT, none of the rooms I referenced would allow mid-wall placement for ALL walls.  There are other sub placement options that can work as well but don't easily allow hiding all of the subs. CraigJohn has 3 SubMersives "randomly placed" and gets great response but hiding them would be tricky, to say the least.

And yes, the subs are in the rear most covered space.  The enclosures he built for the 4 subs are double thick MDF with Green Glue between the layers.  He did clips and channels for room isolation and upstairs (theater in basement) even directly above the theater, it is REALLY quiet.

Treatment: The first reflection points for the L + R speaker are diffussors (he built them from some DIY diffusor web site we found) as is the rear wall space behind the last row of seats and the rest of the room is absorption.  He was originally going to cover the diffusors with material but dfecided he liked the look of them - as do I.  The soffits are stuffed with fiber glass as bass traps.  He didn't want to do ceiling treatment as he is going to have it painted with glowing night sky with the lights he has in the soffit trim.  Since the room is so small, there was no practical way to do corner traps, so we didn't.  
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Mark_Seaton
hifiaudio2 wrote:
Very cool!  So you are getting better results from using the 4 corners over the 4 mid points? I had thought mid point positioning was considered the gold standard by Harman et al. over four corner placement...


Most also manage to skim over or forget the assumption made in the Welti/Harman papers assuming identical signals and subwoofers at each location.  No delay, level or EQ differences were applied.  I have measured more than a few rooms where the recommended Harman approaches resulted in huge nulls in the listening area.  The space has to align with the assumptions made in the study, and many do not.

Note this system has an F18+ & Slave at the front wall, and another F18+ and Slave at the rear wall.

Fortunately adding delay as a range of flexibility for the front/rear grouping of subs is often enough to achieve very positive results.  This assumes that the front and rear locations are reasonably complimentary and useful, which is most often the case for front wall and rear wall placements.  You could very likely slide either pair of subwoofers to the 1/4 & 3/4 width points with modest changes in the results.  A large delay is not always needed on the closer subs, and sometimes no delay is needed at all.
Mark Seaton
Seaton Sound, Inc.
sales@seatonsound.net
773-290-8436
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Mark_Seaton
audioguy wrote:
If you re-read the referenced Harman paper, the 4 mid-points recommendation is only marginally [and in my mind, theoretically]  better than the 4 corners.   


The 4 mid-wall locations also give up a small bit of VLF efficiency in their comparisons, but again this is where some fine tuning in real rooms while taking real measurements can yield significant gains. 

Quote:

And yes, the subs are in the rear most covered space.  The enclosures he built for the 4 subs are double thick MDF with Green Glue between the layers.  He did clips and channels for room isolation and upstairs (theater in basement) even directly above the theater, it is REALLY quiet. 


I can't recall from when this was being planned, but I thought the subwoofers were behind the lower fabric on the back wall?  Hifiaudio2 was asking if they recess into the left and right walls near the rear corners.
Mark Seaton
Seaton Sound, Inc.
sales@seatonsound.net
773-290-8436
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zdoggz
I also recall in one of Floyd Toole's papers that it was noted how much output efficiency is typically lost (or not gained/realized rather) in the midwall positions vs corner placements,... so much so as to require 2 subs at each wall midpoint (8 subs total) to equal the overall output capability of 4 corner subs.
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paw
Here's a practical question. Where's the door into the theater?
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audioguy
Mark_Seaton wrote:


The 4 mid-wall locations also give up a small bit of VLF efficiency in their comparisons, but again this is where some fine tuning in real rooms while taking real measurements can yield significant gains. 



I can't recall from when this was being planned, but I thought the subwoofers were behind the lower fabric on the back wall?  Hifiaudio2 was asking if they recess into the left and right walls near the rear corners.
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audioguy
The plot with no eq does have delays set for the rear (closer) subs. The gain knob on front and rear is set to the same place at about 12:00. And the "rear" subs are on the sidewall but in the corners recessed into the wall - so they are about as "corner-ish" as possible
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Stereodude
Mark_Seaton wrote:
Most also manage to skim over or forget the assumption made in the Welti/Harman papers assuming identical signals and subwoofers at each location.  No delay, level or EQ differences were applied.  I have measured more than a few rooms where the recommended Harman approaches resulted in huge nulls in the listening area.  The space has to align with the assumptions made in the study, and many do not.

I think that paper has led as many people astray as it has helped.  It would be nice if they were to revisit it and at the least consider time alignment (delay).
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audioguy
paw wrote:
Here's a practical question. Where's the door into the theater?


Right wall, front of room. [Not shown].  It is covered with the same diffusors that are on the left wall!
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Gibroni
Where are the subs aimed? Is either set out of phase?
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audioguy
Gibroni wrote:
Where are the subs aimed? Is either set out of phase?


The front subs are "aimed" toward the rear of the room and the rear subs are "aimed" toward each other.  There is no "phase" knob on the subs and the delays on the subs is set to zero but we used the delays in the Denon to even out the response.  A phase knob adjusts phase for a specific frequency whereas altering the delay, changes the "phase" at all frequencies. 

I'm not sure what you are trying to get at with the question about "aiming" but given the wave lengths reproduced, aiming doesn't do much.  Where is can come into play, for example, would be to alter the distance to the mic. 

In my room, when I had single driver subs in the rear of the room, I got different response with the sub facing into the room vs being rotated 180 degrees and facing into the wall.  Why?  Because once rotated toward the wall,  the driver was now about 22 inches further away.  This made a difference at "around" 100HZ.

Hope this helps.
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audioguy
(Very) Short Update:

4 F18's (and about 8000 watts) in less than 2100 cf is just stupid good.  The bass is very tight, very deep and very clean.  Each time I talk to the home owner, that is the one thing he keeps bringing up.  And his kids absolutely love it.  Great job (again) Mark. 

I said in an earlier post (in May of this year) that I wanted to find a way to get 4 F18's in my room to replace my last two DIY's.  They (hopefully) ship this week [biggrin] [biggrin].  I will be placing them in the front two corners, hidden by a a column that will also include corner bass traps.
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audioguy
Another example of four being the perfect number.  These are my two SubMersive's new playmates.  There will be a stack of 2 F18's in each of the front two corners and the two SubMersives will be at the rear.  The only bad news is that these guys will be hidden in the corners - visually but certainly not audibly [biggrin] [biggrin].

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Thomas_Smith
audioguy wrote:
At least when it comes to the number of subs to drive the room uniformly (For rectangular sealed spaces only).   I have built 4 theaters in the last 10 years and assisted 3 or 4  others do the same.  In each case, I convinced the owner to place a sub as close to each corner of the room as possible.  

In the most recent case, the individual knew zip about a home theater so we were able assist in all of the component selections and room treatment recommendations.  We recommended four Seaton subs and given space restrictions, we wanted two pairs of the new F18 Master/Slave systems.

To cut to the chase, here is the FR of the subs with no EQ applied:



Here is the FR WITH Audyssey:



Can we say FLAT!!!  About 5db down at 6HZ !!!!!!

Here are a few photos of the room.  The only place he wandered away from our recommendations was the thickness of the wall panels (he did so for cosmetic reasons but I still think my approach would have looked and sounded better.)  This room is fairly small (11 x 19 x 10).  I finished the initial calibration today but want to return and play with the knobs that provides low end lift on the sub amps - to add a touch more "heft" on the bottom end.  But one thing was obvious, these new F18's are KILLER subs.  In fact, after hearing them, I need to find a way to buy 4 for ME and replace the two DIY 18 inch subs I have up front in my room.  Maybe I can start a "GoFundMe" project [biggrin] [biggrin]





By the way, my camera did not get the colors correct.  The upper panels and the diffussors are a blue color and the chairs and carpet are a dark gray/black!!

If 4 subs is not practical for financial reasons or even space reasons, an almost equally good approach is two subs in diagonal corners.  Again, this works for rectangular sealed spaces. 

Anyway, congratulations Mark for yet another amazing sub product!



It seems that using the 4 corners over the 4 mid points is probably better right?
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audioguy
Thomas_Smith wrote:


It seems that using the 4 corners over the 4 mid points is probably better right?


Not really "better" but usually more practical.  The midpoints can interfere with, for example, a center channel under a screen, furniture placement, or pathways through the room.  In each of my theaters, at least one of the 4 wall center positions would not have worked.  And in my case in my current theater, I have chosen to hide my F18's in the corners.  In the room above, it was way too small to have subs at the wall midpoints.

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audioguy
EDIT:  As you might notice, all of my photos are gone thanks to Photobucket.  

The title of this thread should be changed to "Four is the perfect number" to "Four is the perfect number ........but Eight is even more perfect".

I now have 4 F18's split in 2 stacks of 2 in the front two corners AND placed in the rear of the roomF18s.JPG  F18s in Bed.JPG  have just added 4 more 
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zdoggz
I can't say I'm surprised to see this. Lol. Is it a matter of time before you go to 12? Haha

Do u still have your HPs?
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audioguy
zdoggz wrote:
I can't say I'm surprised to see this. Lol. Is it a matter of time before you go to 12? Haha Do u still have your HPs?


I can assure you, 12 won't happen. As it is, with full frequency sweeps, I can reach almost 125dB before any kind of distortion/compression starts to take place... which translates to peaks much, much, much higher than that in a real world application.  And I had never experienced that level of sound before (test sweeps)  in a confined space and it is really loud.  Furthermore, I am in a converted loft so even with this much horsepower, I wonder about the structural integrity of the room.  And going from 8 to 12 would only buy me about 3 more dB of output.

And no, I don't have the HPs any longer. I wanted a solution where I had the same amount (and kind) of subs in the front and rear of the room.  So I got rid of the 2 HPs and got the 4 F18's --- 4 in the front and 4 in the back.  

The only downside to my room makeover is that I have hidden all of the subs - and I really like the looks of the F18s.  




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BrolicBeast
Dude---I also worry about the structural integrity of the room.  After experience the awesome power of eight F18's in my room, I started to wonder about things like "will screws securing the multiple drywall layers to the clips and channel on the ceiling hold up with all of this bass?" Also: "Will pipe fixtures in the joists above the theater begin to separate at the thread/lamwick joints?" I've never had such concerns before....ever. And although I'm sure they are unfounded...the mind wanders! 
Home Theater is a Way of Life
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audioguy
audioguy wrote:
Do you still think you will need your seat activators with those 4 18's in the rear so close to your seats?
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