Double Bass Array concept, any thoughts?

[thadman]

Has anybody researched/investigated this concept?

Heres some info
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. 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.

In theory, it should work correctly. Right? Anybody see any flaws in the concept?

How high in frequency can this effect work? It seems like a substitute for DRC and dipole

[thadman]

Is there a formula available (such as those made available by Jim Griffin in his white paper for Line Arrays) that will calculate how high in frequency the DBA effect will dominate the listening domain?


FYI the dimensions are not exact.

I was wondering if the rear wall was necessary for the DBA effect, or if I could place the rear subwoofers at a predetermined distance in the room and cancel them at that point? I'd love to incorporate a double bass array into my HT/listening area, but since my listening room opens up it doesnt seem very desirable. Could I place the rear subwoofers at the mouth of the HT area and achieve the same effects as if a wall were there?

I'd also love to substitute this for a dipole and run them all the way up to 300hz (RSS390HF can handle extremely high crossover points, considering the first high amplitude breakup is in the 1700-1800hz region). What would be necessary and how many would I need to reach 300hz?

[Dennis H]

DBA is a cool concept but it will only work perfectly in a sealed rectangular room made of concrete. Doors, windows, odd room shapes, absorbant walls, furniture, it won't work as well anymore.

Is there a formula available (such as those made available by Jim Griffin in his white paper for Line Arrays) that will calculate how high in frequency the DBA effect will dominate the listening domain?

Keep the driver spacing below 1/2 wavelength.

I'd also love to substitute this for a dipole and run them all the way up to 300hz

If you want everything up to 300 Hz to be mono, and you want to buy enough drivers so the C-C distance is less than 2' (24 drivers for a 8'x12' front wall plus another 24 on the back wall) that could work. Otherwise forget it.

[thadman]

[QUOTE=Dennis H]DBA is a cool concept but it will only work perfectly in a sealed rectangular room made of concrete. Doors, windows, odd room shapes, absorbant walls, furniture, it won't work as well anymore.

If you need more specifics, 2 of the 5 walls in the room have concrete directly behind/beneath them. The HT viewing area has a "cabinet" built into the wall, which houses the TV and AV equipment. A concrete wall lies behind this AV cabinet. There is a large L shaped couch located at the mouth of the HT area, it is pressed against the upper wall (in the picture). The lower wall has a small room located behind it (plumbing, power, cable, everything is in here). The ceiling is directly beneath the kitchen which incorporates a stone floor. Could you take my specific circumstances into account when you extrapolate? I have the picture and information in my post for a reason.

[thadman]

Im sorry if I came off arrogant, if that was conveyed I am deeply sorry. You obviously have a better understanding of the concept than I, (the post over on AVS was pretty vague and the white paper is in German). I understand now that it can only operate in mono operation. At what point does stereo operation and seperate drivers become necessary, otherwise sound quality begins to diminish? Could I run mono to 150hz, without penalty?

DBA is a cool concept but it will only work perfectly in a sealed rectangular room made of concrete. Doors, windows, odd room shapes, absorbant walls, furniture, it won't work as well anymore.

To what extent? If its not demonstrated in a perfect room is the concept totally destroyed...or does it still do a fairly good job of destroying room nodes? I asked how the DBA effect would work in my circumstances, and was looking for an answer specific to my situation not a generalization of all situations. Thats the reason I provided a drawing and several details of my room.

[noah katz]

Google Harman white paper on multiple subwoofers.

[---k---]

I asked how the DBA effect would work in my circumstances, and was looking for an answer specific to my situation not a generalization of all situations. Thats the reason I provided a drawing and several details of my room.

Thad,
You got to understand that no one is going to be able to answer your question about how it specifically behaves in your room, without doing testing in your room. Way too many varibles. I think you are underestimating how much research went into the original white paper, and how much research remains to be done. Note that the author hasn't published a white paper on non-perfect rectangular rooms. They just aren't easy concepts thats can be easily transfer into your room.

So yeah, demanding answers for your room was a bit arrogant. The only way to answer your questions is to do the I in DIY and let us know how it turns out.

[thadman]

Thad,
You got to understand that no one is going to be able to answer your question about how it specifically behaves in your room, without doing testing in your room. Way too many varibles. I think you are underestimating how much research went into the original white paper, and how much research remains to be done. Note that the author hasn't published a white paper on non-perfect rectangular rooms. They just aren't easy concepts thats can be easily transfer into your room.

So yeah, demanding answers for your room was a bit arrogant. The only way to answer your questions is to do the I in DIY and let us know how it turns out.

Ok, I'm sorry if I came off as arrogant. I do not wish to detract from this marvelous forum at all, its been a blessing and a plethora of knowledge for me :B

I've got a question though concerning room nodes. My listening area is ~150" wide and 100" high. I am aware that a node cannot exist when the distance (wall to wall) is less than 1/2 wavelength of the frequency (150(2)=300, 13397/300=~45hz. 100(2)=200, 13397/200=~67hz). Dipole propagation thus should be necessary >45hz to cancel the width node and >67hz to cancel the height node. How will the length node effect the response in my room, considering my room opens up significantly and is very deep. I'm aware that my room wont pressurize :cry: until I reach VERY low frequencies. Will the length node be that virulent and would harm be done in crossing to a monopole woofer with a shallow slope ~45-50hz?

[capslock]

Does anybody have a link to that whitepaper?

Thanks

[---k---]

The math assusmes perfectly rigid walls, no openings, etc. Simple first step to understanding the issues would be to take your current sub and make a nearfield frequency resposne graph and a frequency response graph from your listening position. You just need a Radio Shack SPL meter to do this. You can use RoomEQ Wiz software or just test tones, like the ones you can download from realtraps.com. Do this with the sub in all the likely places, and post the graphs. It will tell you a whole lot more than any of our guesses would. This stuff isn't easy.

There is ray tracing software available to professionals that I believe can model what you are asking, but I've never seen anyone do this in the DIY arena.

[Dennis H]

Here's a link to Nils' build thread. He has a link to the DBA white paper in the first post. The paper is in German which obviously won't be a problem for Eric. I must say, Nils' 1/24 octave in-room response is mighty impressive.

http://www.avsforum.com/avs-vb/showthread.php?t=837744

[thadman]

Ok, I'm sorry if I came off as arrogant. I do not wish to detract from this marvelous forum at all, its been a blessing and a plethora of knowledge for me :B

I've got a question though concerning room nodes. My listening area is ~150" wide and 100" high. I am aware that a node cannot exist when the distance (wall to wall) is less than 1/2 wavelength of the frequency (150(2)=300, 13397/300=~45hz. 100(2)=200, 13397/200=~67hz). Dipole propagation thus should be necessary >45hz to cancel the width node and >67hz to cancel the height node. How will the length node effect the response in my room, considering my room opens up significantly and is very deep. I'm aware that my room wont pressurize :cry: until I reach VERY low frequencies. Will the length node be that virulent and would harm be done in crossing to a monopole woofer with a shallow slope ~45-50hz?

does anybody know???