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post #331 of 357 Old 09-11-2014, 04:19 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 #332 of 357 Old 09-11-2014, 05:24 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.

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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 #333 of 357 Old 09-11-2014, 10:20 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 #334 of 357 Old 09-11-2014, 10:48 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 #335 of 357 Old 09-11-2014, 11:02 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

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post #336 of 357 Old 09-11-2014, 12:20 PM
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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 #337 of 357 Old 09-11-2014, 12:26 PM
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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 12:32 PM. Reason: Added reference to Nils' thread
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post #338 of 357 Old 09-11-2014, 12:31 PM
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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 #339 of 357 Old 09-11-2014, 01:23 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 #340 of 357 Old 09-11-2014, 01:33 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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post #341 of 357 Old 03-06-2015, 09:20 AM
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post #342 of 357 Old 03-06-2015, 09:27 AM
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Wow. That shelf must be strong!

Krister
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post #343 of 357 Old 03-06-2015, 10:07 AM
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Awesome!

I am going to try, very soon, a SBA in my basement theater. If that doesn't work as well as I hope then I'll try out the Geddes solution of spatial smoothing. But I have limited placement of my subs and the back wall subs are out of the question.

JoshK on most other audio forums
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post #344 of 357 Old 05-22-2015, 03:58 PM
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It looks like this thread has been dormant for a while, but I was wondering if I could reactivate it to ask a simple DBA question - would a DBA approach work in a slightly L shaped room? My room is 17 feet wide at the font, and 14 ft. 4 in. wide at the rear. Intuitively, this leads me to think the modal cancellation of a DBA would not be as complete or as smooth as it is in a rectangular room. Do you think it's even worth trying?

Thanks!
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post #345 of 357 Old 05-22-2015, 11:36 PM
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I think your L-shape is so subtle that it is very much worth the try.
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post #346 of 357 Old 06-18-2015, 11:41 AM
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post #347 of 357 Old 06-18-2015, 12:32 PM
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That looks great! How are other seats?
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post #348 of 357 Old 06-19-2015, 03:20 AM
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Holy **** that shape is perfect!
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post #349 of 357 Old 06-19-2015, 10:59 AM
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@eng-399 check out this thread. The 4 subs you have on the front wall make up half of the equation here. You may get a better frequency response by adjusting the height of each of the subs....
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post #350 of 357 Old 06-19-2015, 12:15 PM
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@eng-399 check out this thread. The 4 subs you have on the front wall make up half of the equation here. You may get a better frequency response by adjusting the height of each of the subs....
Thanks Pete going to read it now.
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post #351 of 357 Old 09-03-2015, 01:27 PM - Thread Starter
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I simulated a bit with alternative DBA arrangements. I think the results could be useful for people who have a door or a window in the wrong place.

The documentation is written in german, but I think the diagrams are self-explanatory.

Alternative DBA arrangements
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post #352 of 357 Old 09-03-2015, 06:06 PM
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nice. thank you.


have you ever measured the effective 1w sensitivity of your bass array at your seating position? I'm just kind of curious what the effective increase in sensitivity (relative to a 2pi model/measurement) such an arrangement provides.

Listen. It's All Good.
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post #353 of 357 Old 09-03-2015, 11:18 PM
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What would you guess the increase db spl of an array of 4 vented sub is compared to the same 4 sub spaced out in a room? I would assume in some modal issues are minimized with an array that would also add to the spl.
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post #354 of 357 Old 09-04-2015, 07:06 PM
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Hi Nils!
What do you think about front array in IB with rear array in closed boxes?
Front [sub]woofers actually is 2*18" at about 1/4H from floor and 1/4W from side walls (another pair at 1/4H from ceiling may be added if necessary).
Length modes .5 and 1 wave is most significant\annoing now.
It's highly desirable to limit rear BA with 2 subs at 1/4H from ceiling.
Will it work good enough?..
Room is 4.2W*4.8L*3H.
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post #355 of 357 Old 09-06-2015, 12:52 AM - Thread Starter
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Quote:
Originally Posted by Flaesh View Post
What do you think about front array in IB with rear array in closed boxes?
This should work as long as the frequency response of the two arrays is equal. But a Linkwitz transform (biquad) can do this. E.g. MiniDSP has this feature.



@All
Here comes the long awaited solution for L-shaped room! Yes, it works!

Double Bass Array in L-shaped rooms (please auto translate from german)

You just need to simulate the plane wave of a rectangular room by adding scondary sources. These sources are delayed and fire when the plane wave passes the edge of the L. Simple, but highly effective.
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post #356 of 357 Old 09-06-2015, 02:18 AM
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Thanks Nils for posting this.

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 #357 of 357 Unread Today, 01:39 PM
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Originally Posted by FoLLgoTT View Post
I'm really surprised to see that the "Double Bass Array" (DBA) is not very popular outside Germany. I searched for key words, but found only one thread in the AudioCircle forum.

Maybe someone is interested in this concept, since it is by far the smartest way to get a linear frequency response and completely get rid of room modes.
The DBA was described first in a paper from Klein+Hummel which unfortunately exists only in german. I hope my english is good enough to give a small overview here.


Configuration

A DBA consists of two identical arrays of subwoofers. One on the front and one one on the rear side.
The subwoofers have to be mounted on special positions on the wall. For example if you have 4 drivers in one array (that means overall 8) ranged in a square, their correct place is at 1/4 and 3/4 of the wall's width and height. Like this (my room in an early stage):
 

 


The side walls work like mirrors and have the same effect like more equidistant bass sources. This completely eliminates the room modes between the side walls and between floor and ceiling.
With this order the front array produces a plane wave which propagetes through the room. When it arrives on the rear wall the second subwoofer array creates the same signal but with inverted polarity. So both waves compensate each other and no reflection on the rear wall occur. The bass is completely free of modes!

Of course it only works, if the rear array is delayed by the time the sound needs to travel from the front array to the rear (delay = speed of sound / room length). Such a delay can be achieved by using cheap DSP equalizers like the Behringer Ultracurve 2496.
The level of the rear array usually has to be a bit lower than the level of the front array, since there is always a bit loss in real rooms when the wave propagates. But with measuring equipment the best setting is easy to find.

The subwoofers itself should have a low depth so reflection from the mounting wall get minimized. Ideally the drivers are build directly into the wall.

Of course a DBA also works with more or less drivers per wall. It is only important that the distance between 2 drivers is twice as long as the distance between the driver closest to a side wall and the side wall itself.
Both dimensions can be considered completely independent of each other.
For example if you want to use only 2 drivers per array, they have to be mounted on 1/4 and 3/4 of the room width and on the middle between floor and ceiling.
Denser driver grids conclude in a higher frequency where a plane wave will still be formed. With common room dimensions 4 drivers per array are enough to ensure a plane wave up to the LFE cut-off frequency.


Conclusion

The big advantage of this concept is to be completely free of room modes and to get exact the frequency response of the simulation. The maximum sound pressure of the DBA is defined as the number of subwoofers in one (!) array times the maximum sound pressure of one single subwoofer.
Another advantage is that the bass is fine on a large area and not limited to one seat. This makes it suitable for large home cinemas. Also the subwoofers can be integrated perfectly because of their small depth. A simple curtain is enough to hide them completely (my front looks like this now). I have seen other solutions which integrates them into self-built shelves in the living room.
And with a DBA playing "Sokoban" at home is over!

The only disadvantage I know of is the adaption to the front speakers, since their sound pressure usually lowers with 6 dB when doubling the distance and DBA's sound pressure stays constant in the whole room. So if you adjust a linear frequency response for the first row of seats the second will get slightly more bass (or in fact lower sound pressure from the fronts).

The costs of a DBA strongly depend on the components you want to use. My solution is a very cheap one with about 1100€ for the whole setup. But with more and bigger drivers the costs can easily explode to a multiple of that.



Frequency response of the Simulation (with same lowpass and equalizing like the real one):




1/3 octave smoothed measurement in the middle of my room (looks like a fake, but it is not! ):




The waterfall shows no sign of first order modes:

I think this video explains well in an easy understandable way what is said in this post
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