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Post by lonelyraven on Dec 7, 2009 9:15:13 GMT -7
OK, long story short, I have a living room/theater that's a very open floor plan. I have a large subwoofer box in the front of the room with a 21" driver in 16cu ft sealed powered by an EP2500.
I'm thinking about adding an IB to this home theater for more effortless bass...maybe even use the same driver as my sealed box.
So the only place I can install an IB, is the BACK of the room where there are stairs down to the lower level, and I have a large storage closet built in under the stairs. There happens to be a flat space in the floor between the stairs and the back wall where I could easily install a manifold, and put a grill on it so the cats don't fall asleep in there.
My concern is about timing and phase compared to the mains and sub in the front of the room. I remember reading a long while ago here in COTIB that IB in the back of the room are a terrible solution....is this true, and if so, what sort of device would I need to blend in the IB with the rest of the system?
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Post by weverb on Dec 7, 2009 10:43:27 GMT -7
raven, Welcome to the forum.  Having the ib in the rear is bad if it is the only source of bass. Since you have the 21" mael up front, it is a different situation. Did you want them to play together or different ranges? Have you tried the mael in the spot where you can place the ib to see what kind of response you get? You can use REW and then average the two results to see what the final out come might look like. Also, make sure you use reading with no filters applied. What are you using for sub eq now? |
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Post by lonelyraven on Dec 7, 2009 11:41:30 GMT -7
This is what I'm looking at now. Measured at seating position, REW calibrated at 75db, sound card calibration loaded, and generic Behringer mic cal loaded. It almost seems too good to be true, so I'm going to run it again later this week and try to prove/disprove this measurement. Currently, I have zero EQ. It's just Onkyo 805 to EP2500 bridged to 21" woofer.  No way possible to move the current sub into potential position of the IB, as it's a tight spot, and the 21" box is HUGE. 21" Maelstrom-X (in final position it faces forward for the measurement above)  And space by the stairs, back of room (photo taken when we were still shopping for the house)  And the space under the stairs (now has some "stuff stored in it). The space is larger then the photo looks, because there are two half-flights of stairs, one you see, and one around the corner. There is plenty of airspace down here, and I could open/close the door to vary the airspace as needed...though there is no door to separate the upstairs from the downstairs.  In that last photo, the manifold would go just to the left of the door. I wouldn't be able to have the drivers mounted opposed unfortunately...that is, unless I cut out some walls in the basement...hmm... |
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Post by chrisbee on Dec 8, 2009 4:52:30 GMT -7
It would be very simple to place your box sub somewhere behind you to test whether you can actually live with a rear sub. The understair space looks tiny to me. Unless there is serious volume somewhere we cannot see I doubt there is enough. Treat the stairs as two prisms and they are easy to calculate their separate volumes: Base/2 x Height x Length. Then add whatever other spaces are enclosed by the same volume. No point in cheating on the maths. It's your sub. Not ours. It is difficult to judge whether opening the door will provide a sufficient path length for the drivers to function as a true IB rather than a hybrid. Only testing the frequency response will tell you about this. If it were me I'd place the 21" driver in a temporary baffle using the understair volume to check whether it's worth going ahead with this idea. Just use any old bit of ply, MDF or chipboard to get a real feel for the potential of this rear IB. After all, it is only you who has to live with it there. If it becomes a real build then this thread really ought to join the projects section of the forum. It just makes it easier to access all the build information in one place. |
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Post by lonelyraven on Dec 8, 2009 8:02:26 GMT -7
That's a good idea, Chris...I should just build a temp baffle and drop the M-21" in there. I have a feeling it wouldn't fit the spot without building a proper manifold though...I think there is only 18" of width where the manifold would be.
The space under the stairs is about the same air space as two small closets you'd have at your front door for jackets and boots. I'd have to crawl under there for measurements, but off the top of my head I could easily see 2500 Liters of airspace. That's big enough for a pair of 21" Maelstrom-X to see it as IB I think.
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Post by ThomasW on Dec 8, 2009 9:28:12 GMT -7
Ok I'm back with a reliable broadband connection so here come the questions...
The sub in it's existing position is messing up the imaging from the left main speaker so it's not in an optimal position.
If the picture is correct the room has no bass traps?
If you want to properly integrate front and rear subs you need to measure the phase differences between them, doing this takes an oscilloscope. After making the measurements then you need a device with the ability to adjust phase. Matching phase can only be done for a single position in the room and it will match only at the crossover point.
So the answer is yes you can put subs at the rear of the room but it's not a simple undertaking.
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Post by chrisbee on Dec 10, 2009 0:46:29 GMT -7
So the answer is yes you can put subs at the rear of the room but it's not a simple undertaking. Welcome back to civilisation, Thomas. It's good to hear you so being positive after your holiday. ;D |
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Post by ThomasW on Dec 10, 2009 9:07:07 GMT -7
It's good to hear you so being positive after your holiday. ;D I prefer to be positive, unfortunately more often than not the situation requires the opposite tact, aka 'reality bites'......  |
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Post by lonelyraven on Dec 12, 2009 8:42:10 GMT -7
Ok I'm back with a reliable broadband connection so here come the questions... The sub in it's existing position is messing up the imaging from the left main speaker so it's not in an optimal position. If the picture is correct the room has no bass traps? I have three in fact. The very large cloth covered thing, floor to ceiling in the front left corner is filled with OC703. And around the corner I have two CWAL type basstraps from Decware.com plans (which I am skeptical about, though I truly heard and measured a different in my old apartment). I'm working on pulling the racks and speakers forward, and treating all the space in the corner between wall and floor, plus I have a 5' tall corner in the back left of the room I can do another super-chunk. I will do my best to trap in this room, and I have the ear of one or two experts over at GearSlutz offering me some guidance on how to improve what I have. If you want to properly integrate front and rear subs you need to measure the phase differences between them, doing this takes an oscilloscope. After making the measurements then you need a device with the ability to adjust phase. Matching phase can only be done for a single position in the room and it will match only at the crossover point. So the answer is yes you can put subs at the rear of the room but it's not a simple undertaking. OK, so there is no gear that will help me automate this? Should I give up on this plan altogether then? |
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Post by ThomasW on Dec 12, 2009 9:25:16 GMT -7
I'm working on pulling the racks and speakers forward, and treating all the space in the corner between wall and floor, plus I have a 5' tall corner in the back left of the room I can do another super-chunk. I will do my best to trap in this room, and I have the ear of one or two experts over at GearSlutz offering me some guidance on how to improve what I have. Good sounds like you're going in the right direction.. I'm sure there is some multi thousand $$$ gear that will do this automatically. Something from Tact, Lyngdorf, or Dolby Lake would do the job. For mere mortals Room EQ Wizard has an oscilloscope function. That will let you see how much difference in phase there is between the front and rear subs. Who knows you maybe one of the lucky one where the dimensions of the room, combined with the placement of the subs, and the location of listening position all work out so no electrical adjustment is needed. If you need phase adjustment the Elemental Designs eD EQ2 has such an adjustment and is a pretty reasonable $100. At least one of the Behinger EQs, the DEQ2496 IIRC has an adjustable delay fuction. Thing is you'll never know unless you try it.... The space at the back of the room will work for a rear IB. Were it my room I'd be tempted to put the 21" Mael in the back of the room just to eliminate the huge box. Then use a couple smallish sealed box subs (12" or 15" drivers possibly) in the front. |
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