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post #331 of 341 Old 09-10-2014, 08:50 PM
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The effective DBA/SBA frequency range for your room dimensions are 80Hz horizontal and 70Hz vertical. Assuming you are crossing near that you should be OK.
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post #332 of 341 Old 09-11-2014, 03:19 AM
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Ok, thanks guys!

So from the graphs that JackNC just posted in post #330 , it looks fairly smooth all the way to 80hz and down to around 30hz it starts to get a massive hump? I am new to reading graphs, so please, bear with me!

With my room width being 14ft wide, and all four of my full sized MartySubs being 2ft wide by 2ft tall by 4 ft deep, and assuming that they will all go behind my baffle wall,,where should each enclosure be place in order to get the 1/4 & 3/4 distances from each of side walls, and the ceiling and floor?
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post #333 of 341 Old 09-11-2014, 04:24 AM
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Quote:
Originally Posted by Martycool007 View Post
Ok, thanks guys!

So from the graphs that JackNC just posted in post #330 , it looks fairly smooth all the way to 80hz and down to around 30hz it starts to get a massive hump? I am new to reading graphs, so please, bear with me!
That's just a simulation. Reality might look very different. You would need to measure. The peak you see isn't "massive". Or are you talking about the vertical line? That's just a marker showing a modal frequency.

Quote:
Originally Posted by Martycool007 View Post
With my room width being 14ft wide, and all four of my full sized MartySubs being 2ft wide by 2ft tall by 4 ft deep, and assuming that they will all go behind my baffle wall,,where should each enclosure be place in order to get the 1/4 & 3/4 distances from each of side walls, and the ceiling and floor?
Well, at 1/4 and 3/4 of 14ft. Try to get the driver as close to the wall as possible.

Markus

"In science, contrary evidence causes one to question a theory. In religion, contrary evidence causes one to question the evidence." - Floyd Toole
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post #334 of 341 Old 09-11-2014, 09:20 AM
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Just to be clear - to me, the sims just mean that those positions are worth trying. This thread is all about the quarter width/height position and demonstrate how good it can be but the sims show that the corner is as good if not better and corner has advantages for the mains. Corners are known good positions for woofers as well as full range speakesers. I plan to use a couple of helper subs along the sidewalls near the back in conjunction with corner full range 3-ways, with woofers at the heights illustrated in the sims.

No matter what I do, I always end up with some sharp nulls around 150Hz. These seem to be ceiling bounce related and I'm hoping these will be taken care of by overlap between mids and woofers. The simple REW room sim doesn't allow that to be modeled.

Marty: If you see a peak, you can be fairly confident in being able to knock it down with EQ. Nulls/valleys need to be filled in by helper subs or choosing another position for a helper sub or the listening position. I think its lots easier to move icons around on a screen than 75 lb+ subs. Still these are just simulations and reality will be different. The simulations assume the drivers on the front wall are embedded in absorber, which takes care of boundary reflection nulls and no doubt affects baffle step. You may need to bring some of that absorber, not the full thickness but 2-4" around the corner and up the side wall a few feet.

Jack
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post #335 of 341 Old 09-11-2014, 09:48 AM
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Question for you guys:

I have 4 subs in my sealed, rectangular room. So far, I have experimented with corner placement and 1/4 3/4 placement on the front and back walls.

I don't have any nulls, and I get good seat to seat consistency. I do have a big 20db peak at 37hz caused by the length of the room, which I am addressing with EQ.

Experimenting with a DBA in REW's simulator, that eliminates the 37hz peak, but everything else stays pretty much the same. Would fixing that be worth sacrificing half of my power for?

If the main listening position is centered (with equal time alignment), perhaps room EQ that addresses impulse response would still be able to cancel out the front-back reflections and remove that energy from the room. I suppose I would lose time alignment with the mains for other seats, though.

Do I have this right?
Any suggestions?
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post #336 of 341 Old 09-11-2014, 10:02 AM
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Quote:
Originally Posted by rcohen View Post
I don't have any nulls, and I get good seat to seat consistency. I do have a big 20db peak at 37hz caused by the length of the room, which I am addressing with EQ.

Experimenting with a DBA in REW's simulator, that eliminates the 37hz peak, but everything else stays pretty much the same. Would fixing that be worth sacrificing half of my power for?
No, if the EQ fixes the ringing at 37Hz for the listening area in question.
Got some measurements to share?

Markus

"In science, contrary evidence causes one to question a theory. In religion, contrary evidence causes one to question the evidence." - Floyd Toole
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post #337 of 341 Old 09-11-2014, 11:20 AM
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Quote:
Originally Posted by Martycool007 View Post
With my room width being 14ft wide, and all four of my full sized MartySubs being 2ft wide by 2ft tall by 4 ft deep, and assuming that they will all go behind my baffle wall,,where should each enclosure be place in order to get the 1/4 & 3/4 distances from each of side walls, and the ceiling and floor?
Hi Marty,

Your subs should be centered at 3.5' from the side walls and 2' from the ceiling and floor respectively.

Mike
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post #338 of 341 Old 09-11-2014, 11:26 AM
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Quote:
Originally Posted by JackNC View Post
This thread is all about the quarter width/height position and demonstrate how good it can be but the sims show that the corner is as good if not better and corner has advantages for the mains. Corners are known good positions for woofers as well as full range speakesers.
Jack
One of the virtues of the DBA/SBA array is the uniformity of response for more than one position. Check out Nils' SBA thread to see just how effective it can be. FoLLgoTT's build: 18 x Peerless XXLS12 See post 53

Last edited by mikela; 09-11-2014 at 11:32 AM. Reason: Added reference to Nils' thread
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post #339 of 341 Old 09-11-2014, 11:31 AM
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Originally Posted by markus767 View Post
No, if the EQ fixes the ringing at 37Hz for the listening area in question.
Got some measurements to share?
Here's the last time I did measurements, before and after EQ. I've been moving some stuff around, so this isn't actually current. Conveniently, the REW simulator's predictions are surprisingly accurate for me.


Also, here are a couple layouts I'm experimenting with in the sim, with and without DBA. (None of these match the measurement layout, although the first one is the closest.)


BTW, my "bass array" is just made of speakers on the floor, so there's nothing to help with ceiling reflections. I'm hoping to eventually add some sort of ceiling treatment, perhaps as part of a dropped ceiling.
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post #340 of 341 Old 09-11-2014, 12:23 PM
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^
That Dirac after graph is a calculation not a measurement. You would need to measure at multiple points throughout the listening area to verify the peak is gone and doesn't ring anymore.

Markus

"In science, contrary evidence causes one to question a theory. In religion, contrary evidence causes one to question the evidence." - Floyd Toole
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post #341 of 341 Old 09-11-2014, 12:33 PM
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Quote:
Originally Posted by markus767 View Post
^
That Dirac after graph is a calculation not a measurement. You would need to measure at multiple points throughout the listening area to verify the peak is gone and doesn't ring anymore.
10-4. Measuring after Dirac can be tricky. So far, I've only managed to get that to work once, but when I did, it was very consistent with the after graph (much closer than the REW sim, which is just roughly consistent). I can try again, and see if I get lucky.
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