AVS Forum banner

1 - 20 of 28 Posts

·
Registered
Joined
·
4,029 Posts
Discussion Starter #1
Ok. Just like the title suggests, what can be advantageous IB placement options with 2 or more manifolds that each house multiple drivers? My options are pretty much entire ceiling surface area for attic manifolds, behind front screen, and partial sections of rear wall (has limitations for treating wall if used. Will explain below).


I asked about an IB system that used both the front and rear walls quite some time ago but never got any solid feedback on such a system. I would imagine that two IBs that literally send a wave towards each other (or as much of a wave as can possibly produce) would have some anomalies, maybe?


I have had doubts about creating an IB behind my AT screen when the design calls for the drivers to be directly behind the fabric. I have up to 18" of room between the baffle and screen to work with. I currently have all my drivers arrayed horizontally below the screen (18' of speakers side to side) with one stacked on the outer most drivers next to each left/right wall. This sealed setup is pleanty loud across the front two rows but the FR is all jacked up below 38hz. I literally have a plateau from 38hz on up with a little bump around 20hz which I assume is room gain or some other room interaction.


Are there any strategies for multi manifolds in attic placement only? In attic plus front or rear or any combination of the three?


My front wall has aprox 700cuft to work with. Rear wall has three sections that could each house 60cuft but this would leave me unable to heavily treat the rear wall. FOH has given me a lot of advice to help me come up with a plan to use as much depth on my rear wall as possible for trapping. So I think the back wall may need to be spared for treatment unless there is a design which uses the rear wall specifically paired with other manifolds as my two stage riser is a bass trap designed by D.E. it does some good but I'm sure a bunch of well placed mass across the rear wall will show greatly improved results.


All my current drivers are 21s and am trying to get pallet shipping quote on the 24s which would be 8 drivers. I'm not in any hurry because I have to update my LCRs first so the 24s price increase may push me to other IB capable drivers. But total IB displacement of drivers will be equal to aprox 10 21s and 8 24s.


Just curious as to how you all would lay out several manifolds. With my limited 700ish cuft behind the front baffle I could possibly place some drivers behind the screen since there wouldn't be more than 6-8 of them. I just fear an unwatchable screen from screen movement. I'm working on a plan to even further decouple my false screen wall from the concrete floor/stick framing but enough air movement will make it flutter no matter what I guess. I've thought about going rear projection when update my LCRs and completely hold off on the sub upgrade just for vibration reasons alone but fear the cost of the glass/screen! I'd also have to cut a hole into the structure for throw reasons/reduce the cost of such short throw mirror system. Ok off of fantasy land rear projection. The fact that I fear screen vibrations is quite clear lol.


So what would someone like D.E., Seaton, Danley, YOU scientifically read AVSers design?


This next little bit is more fantasy land but doable if would really be worth it.


I still would like to build atleast 2 FLH 21s before my ht endeavors are over but 4 would be even better! 4 of these modeled with the Mal 21s with more SPL than all 10 of my sealed 21s. I don't know if the design will work with the FTW 21 and I only have two Mal 21s left. I know there are some that have mixed horns with both sealed and ported subs with good results but just don't know about it with IB/overall sub redo. The horns would spread across front wall under the screen from 1/4 point to the other 1/4 point with 4 of them.I want to truly be done after this! I don't need flat response from seat to seat throughout all three rows but would like as close as possible without limiting the two center seats of rows 1 & 2. The "only" reason I brought this up is because I would never build the FLHs for any other room other than the HT so essentially its within the IB build or most likely never.
 

·
Registered
Joined
·
530 Posts
I am not one of the acoustic experts here but I do follow the info that I learn on the forum and this is what I have done...


I recently built a baffle wall and put 4 dual IB's (2 sets of 15" drivers and 2 sets of 18") and 2 quad IB's (all 15" drivers) as close to the 1/4 rule as possible (some info here but there was a big discussion about it somewhere that I cannot find at the moment) http://www.avsforum.com/t/1457166/s-e-o-s-r-mega-build/1200_50 . Mine are about 16"-24" behind the screen depending on which baffle it is as my baffle wall has angled ends so the LR point to the LP. I supplement these with a Crowson TD and cut the IB's at about 15hz. They don't seem to produce an air wave as I have been told a ported sub does (which could move the screen), but I have never had ported subs.


I have not seen my screen moving altho I suppose there could be some movement I am not seeing since there is usually a lot of action on the screen when these high bass scenes are played.


Before this I had a mix of IB in ceiling and FLH subs and it was a real pain to get them to work together. And even tho the response between these and the IB's looked the same on the REW sweeps the IB's sounded and felt stronger. Also the ceiling IB's had much more severe dips in FR than the baffle wall IB's do now.


Hopefully some of the experts will come on here and correct/verify my info.


As always YMMV
,

Moto


Edit: OK, here is more info: http://www.avsforum.com/t/1501074/si-24z-build-8-of-em/100_50
 

·
Banned
Joined
·
3,677 Posts
Have you considered doing a double bass array? That is probably a great option if you are able to do 1/4 wall placement on both the front & rear wall.


Another worthy option is to go with ported enclosures on all of your subwoofer drivers. That would gain you some massive bass effects around the 15hz to 30hz region, and would likely be a very noticeable upgrade from sealed.
 

·
Registered
Joined
·
4,029 Posts
Discussion Starter #4

Quote:
Originally Posted by MX48  /t/1521217/multiple-ib-manifold-questions-scenarios#post_24446008


I am not one of the acoustic experts here but I do follow the info that I learn on the forum and this is what I have done...


I recently built a baffle wall and put 4 dual IB's (2 sets of 15" drivers and 2 sets of 18") and 2 quad IB's (all 15" drivers) as close to the 1/4 rule as possible (some info here but there was a big discussion about it somewhere that I cannot find at the moment) http://www.avsforum.com/t/1457166/s-e-o-s-r-mega-build/1200_50 . Mine are about 16"-24" behind the screen depending on which baffle it is as my baffle wall has angled ends so the LR point to the LP. I supplement these with a Crowson TD and cut the IB's at about 15hz. They don't seem to produce an air wave as I have been told a ported sub does (which could move the screen), but I have never had ported subs.


I have not seen my screen moving altho I suppose there could be some movement I am not seeing since there is usually a lot of action on the screen when these high bass scenes are played.


Before this I had a mix of IB in ceiling and FLH subs and it was a real pain to get them to work together. And even tho the response between these and the IB's looked the same on the REW sweeps the IB's sounded and felt stronger. Also the ceiling IB's had much more severe dips in FR than the baffle wall IB's do now.


Hopefully some of the experts will come on here and correct/verify my info.


As always YMMV
,

Moto


Edit: OK, here is more info: http://www.avsforum.com/t/1501074/si-24z-build-8-of-em/100_50

Thank you

Wow. Yeah that is deffinately useful and would like to hear others' views about the attic situations.
 

·
Registered
Joined
·
4,029 Posts
Discussion Starter #5

Quote:
Originally Posted by Martycool007  /t/1521217/multiple-ib-manifold-questions-scenarios#post_24446050


Have you considered doing a double bass array? That is probably a great option if you are able to do 1/4 wall placement on both the front & rear wall.


Another worthy option is to go with ported enclosures on all of your subwoofer drivers. That would gain you some massive bass effects around the 15hz to 30hz region, and would likely be a very noticeable upgrade from sealed.

Yea I've thought about a bda and ported.


I don't know that there is enough room to place multiples on the back wall since the space is only 60-70cuft per space. I have a column at both 1/4points on rear wall that house rear surrounds so the spaces would be between each column and to their sides.


I would love to go ported and pick up crazy amounts down where I'm having issues but afraid that wont really be possible since the 21s would require too much space to fit them anywhere other than where they are now so would most likely still have room interaction issues.
 

·
Registered
Joined
·
19,671 Posts
Sealed will always sound better to me if and only if you have enough output to match the output of the ported subs around tune. I am using a bass array IB in my baffle wall and my screen does not move that I can tell.
 

·
Registered
Joined
·
539 Posts
Try flipping the room upside down by temporarily spacing four box subs on your floor, including 1/4 x 1/4. Then run measurements about 3' (seated height) down from the ceiling above your LP. If that works, put the IB subs directly above where they perform best.
 

·
Registered
Joined
·
897 Posts

Quote:
Originally Posted by MX48  /t/1521217/multiple-ib-manifold-questions-scenarios#post_24446008


I am not one of the acoustic experts here but I do follow the info that I learn on the forum and this is what I have done...


I recently built a baffle wall and put 4 dual IB's (2 sets of 15" drivers and 2 sets of 18") and 2 quad IB's (all 15" drivers) as close to the 1/4 rule as possible

So that's (12) 15" drivers and (4) 18" drivers? That sounds like it doesn't suck!
What drivers did you go with and how many cu.ft. of space do you have to pressurize?
 

·
Registered
Joined
·
530 Posts

Quote:
What drivers did you go with and how many cu.ft. of space do you have to pressurize?

My room is 24.5 x 18.5 x 9ft. About 4000 cubes.


the 12 15" drivers are the sellout MFW's, wouldn't be my first choice but they were cheap and seem to be doing a fine job. I have enough where I don't have to push them hard. The 18's are the Ficar IB318's, which were my 1st choice.

I wouldn't want to push these down to 5hz as I am sure they would start bottoming which is why I have the Crowson to handle that.
 

·
Registered
Joined
·
897 Posts

Quote:
Originally Posted by MX48  /t/1521217/multiple-ib-manifold-questions-scenarios#post_24447770


My room is 24.5 x 18.5 x 9ft. About 4000 cubes.


the 12 15" drivers are the sellout MFW's, wouldn't be my first choice but they were cheap and seem to be doing a fine job. I have enough where I don't have to push them hard. The 18's are the Ficar IB318's, which were my 1st choice.

I wouldn't want to push these down to 5hz as I am sure they would start bottoming which is why I have the Crowson to handle that.

Nice setup -- I own some of both of those drivers myself. The Vd of the 12 MFW's (a beefier Dayton DVC385) equals the 4 FI's...60 liters of displacement is a nice place to be! I bet the Crowsons really complete the experience; is your room on a concrete slab?
 

·
Registered
Joined
·
4,029 Posts
Discussion Starter #11

Quote:
Originally Posted by MKtheater  /t/1521217/multiple-ib-manifold-questions-scenarios#post_24446508


Sealed will always sound better to me if and only if you have enough output to match the output of the ported subs around tune. I am using a bass array IB in my baffle wall and my screen does not move that I can tell.

Yea I've kept up with your room but my screen will move now with the subs firing under it so can't imagine how it wouldn't move with them directly behind it. That might just have to be a compromise though. Keeping the pj stationary was also a feat that somehow worked out with the help of the framer's experience.
 

·
Registered
Joined
·
4,029 Posts
Discussion Starter #12

Quote:
Originally Posted by pnw  /t/1521217/multiple-ib-manifold-questions-scenarios#post_24447076


Try flipping the room upside down by temporarily spacing four box subs on your floor, including 1/4 x 1/4. Then run measurements about 3' (seated height) down from the ceiling above your LP. If that works, put the IB subs directly above where they perform best.

I have some av123 mfw 15s that could try this with but the ceiling has soffits and the floor has three levels so.....? How well would this work? I'm sure it would be better than nothing but truly wonder if the results would be optimal?
 

·
Registered
Joined
·
530 Posts

Quote:
is your room on a concrete slab?

Yes. Thought about building a riser under my chair several times but just never got motivated to do it. Won't happen now as I just don't want to mess with it.
 

·
Registered
Joined
·
4,029 Posts
Discussion Starter #15

Quote:
Originally Posted by pnw  /t/1521217/multiple-ib-manifold-questions-scenarios#post_24448362


"Optimal" is tough. Perfect results from an imperfect mirror, not likely.

Yep. That's how I see it as well.


I wonder if I did find the mirrored place to work similar to the tests if the size of the manifold would make much difference. Like if ran four in a square verses having the manifold 2 drivers long but opposed to each other?


In other words, I wonder how constrained of the space would affect the results. Once more drivers are added and the point source so to speak gets larger. I understand subs aren't point source drivers but the interactions surely would show a difference at a certain size increase.
 

·
Registered
Joined
·
539 Posts
I'd expect many dual opposed manifolds spaced across the ceiling to provide the most even response. In other words, my guess would be to use driver pairs (for force cancellation) and spread them out.
 

·
Registered
Joined
·
1,722 Posts
With certain frequencies, my screen does noticeably vibrate, but you cannot see this when the room is dark and something is projected on the screen. The only time I notice the screen waving is when my screen wash lights above the screen are on with nothing projected on the screen.
 

·
Registered
Joined
·
1,722 Posts

Quote:
Originally Posted by audiovideoholic  /t/1521217/multiple-ib-manifold-questions-scenarios#post_24447972


Yea I've kept up with your room but my screen will move now with the subs firing under it so can't imagine how it wouldn't move with them directly behind it. That might just have to be a compromise though. Keeping the pj stationary was also a feat that somehow worked out with the help of the framer's experience.

By the way, with a huge IB system, I think your screen is going to move a bit no matter where in the room your subs are. If the subs can shake your pant legs from across the room, they can certainly shake the screen.
 

·
Registered
Joined
·
4,029 Posts
Discussion Starter #19

Quote:
Originally Posted by stockmonkey2000  /t/1521217/multiple-ib-manifold-questions-scenarios#post_24453475


By the way, with a huge IB system, I think your screen is going to move a bit no matter where in the room your subs are. If the subs can shake your pant legs from across the room, they can certainly shake the screen.

I completely agree but would like to eliminate as much as possible. The screen frame shaking the entire screen is what's going on now in my room. The AT material on Stewart's frames seems to be stretched plenty tight but with air directly hitting I assume it would move even more. BUT would it move in a different manner (like back and forth) that would make it less obvious during viewing or more obvious? I have no idea!


It will most likely just end up being a compromise that will have to live with unless someone recommends a great way to scatter out all the manifolds in the ceiling. I'll still place some behind the screen unless convinced I can get superb results with just the ceiling scenario.
 
1 - 20 of 28 Posts
Top