I believe this forum doesn't have a thread dedicated to Double Bass Array (DBA), so I'm creating one.
Wikipedia article about DBA :
https://en.wikipedia.org/wiki/Double_bass_array
(Images below are taken from the Wiki article)
To create a DBA we must set up an array of at least four loudspeakers on the front wall, and a similar one on the rear wall. The rear array must play in reverse phase to actively absorb the plane wave from the front wall.
A simple way to understand what a DBA does can be described like this:
- The front array creates a plane wave which should cancel standing waves in the height- and width plane of the room (up to a certain frequency)
- The rear array shall actively absorb standing waves in the longitudinal plane
The result of this is that no standing waves should be exited, and you get a frequency response that is completely flat, and a decay without resonances. In theory at least. With some tweaking, it's possible in practice as well.
There are requirements and limitations of course:
My own room doesn't meet any of these requirements. Even so, I was able to create this result with a lot of tweaking. The decay is very short down to about 30 Hz, where the neighboring room starts to contribute to the decay we see on the measurements here.
Wikipedia article about DBA :
https://en.wikipedia.org/wiki/Double_bass_array
(Images below are taken from the Wiki article)
To create a DBA we must set up an array of at least four loudspeakers on the front wall, and a similar one on the rear wall. The rear array must play in reverse phase to actively absorb the plane wave from the front wall.
A simple way to understand what a DBA does can be described like this:
- The front array creates a plane wave which should cancel standing waves in the height- and width plane of the room (up to a certain frequency)
- The rear array shall actively absorb standing waves in the longitudinal plane
The result of this is that no standing waves should be exited, and you get a frequency response that is completely flat, and a decay without resonances. In theory at least. With some tweaking, it's possible in practice as well.
There are requirements and limitations of course:
- The room should be rectangular with a flat ceiling (relatively easy to accomplish)
- The room should have very stiff surfaces. Concrete is good. Japanese paper walls are not.
- Apart from the loudspeaker arrays, the room should ideally be empty. Any objects disturbing the wave fronts will alter the result.
- Digital delay and EQ is required
- Measurements during setup is required
My own room doesn't meet any of these requirements. Even so, I was able to create this result with a lot of tweaking. The decay is very short down to about 30 Hz, where the neighboring room starts to contribute to the decay we see on the measurements here.
That is an very lovely low end response there.
I wasn't aware of this sort of array years and years ago when my friend and I would throw house parties with silly amounts of pa bass bins in small rooms. We always had trouble getting low end coverage in small spaces, I mean come on if people see a big subs they expect to hear and feel them.
Thought some testing we found putting subs on both ends of a room and inverting the phase of one group pretty much solved all our problems. I ended up taking things further and would hire out pa rig to select electronic events and I employed that sort of technique in spaces where I was able to with great success. Kinda cool to see that there some rhyme to our reason.
I wasn't aware of this sort of array years and years ago when my friend and I would throw house parties with silly amounts of pa bass bins in small rooms. We always had trouble getting low end coverage in small spaces, I mean come on if people see a big subs they expect to hear and feel them.
Thought some testing we found putting subs on both ends of a room and inverting the phase of one group pretty much solved all our problems. I ended up taking things further and would hire out pa rig to select electronic events and I employed that sort of technique in spaces where I was able to with great success. Kinda cool to see that there some rhyme to our reason.
Placing your listening position in the middle of the room is usually a bad idea. This is where you will get the worst bass response. With a DBA however, it does not matter. In fact, the middle of the room may be the best location.
Here's my room layout. As you can see, the room is rectangular, but the ceiling is not flat. I also have a lot of acoustic tuning and large dipole panel speakers in the room.
Here's my room layout. As you can see, the room is rectangular, but the ceiling is not flat. I also have a lot of acoustic tuning and large dipole panel speakers in the room.
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As you probably can see from the room layout drawings above, I have twelve subwoofers in each array. They are SEAS L26ROY in small closed boxes, about 35 liters each. This gives us this response:
Since the subwoofers are placed close to the front and rear walls there is a lot of room gain, so the resulting response do look a lot different. I will show some measurements a bit later.
Since the subwoofers are placed close to the front and rear walls there is a lot of room gain, so the resulting response do look a lot different. I will show some measurements a bit later.
The first thing we need to do when configuring the DSP, is to set the correct level and delay for the rear array. This can be a bit tricky, and may require some adjustment under the way. A good rule of thumb is to set the delay equal to the path distance between the front array and rear, including the reflection off the rear wall. Like so:
In my case, I set it to 21.5 ms, which is equal to 7.18 meters. My room is 7 meters long.
The level must also be experimented with, but if you calculate the SPL loss for your distance, you won't be far off. I ended up with -7 dB on the rear array.
Also, the rear array must have the phase inverted. This can be done in the DSP or simply by switching + and - on the speaker terminals.
In my case, I set it to 21.5 ms, which is equal to 7.18 meters. My room is 7 meters long.
The level must also be experimented with, but if you calculate the SPL loss for your distance, you won't be far off. I ended up with -7 dB on the rear array.
Also, the rear array must have the phase inverted. This can be done in the DSP or simply by switching + and - on the speaker terminals.
It seems like the home cinema crowd is more concerned with their low end than those bound to 2-channel music playback? 
I’m a bit of both - so my room and setup was built to offer the best possible sound, regardless of source type, and with high-end picture as well (4K projector and 130” screen).
To answer @Frank207be ’s question : there is no other furniture in the room than a 3-seater sofa and two small tables. However, there are som very large speakers in the room that will obstruct the wavefront from the DBA. No windows, just a door.
I’m a bit of both - so my room and setup was built to offer the best possible sound, regardless of source type, and with high-end picture as well (4K projector and 130” screen).
To answer @Frank207be ’s question : there is no other furniture in the room than a 3-seater sofa and two small tables. However, there are som very large speakers in the room that will obstruct the wavefront from the DBA. No windows, just a door.
Subjective Preference of Modal Control Methods in Listening Rooms
This compares a number of different multispeaker bass arrays, including various forms of DBA.
Also available free as an attachment on another audio forum -- search for it.
This compares a number of different multispeaker bass arrays, including various forms of DBA.
Also available free as an attachment on another audio forum -- search for it.
Wow! So if I count right that's 24 subs? (each sub position in the top view has 3 subs on different heights?)
I assume you run bass in mono?
So it only works at frequencies where the spearation of the walls is less than the quarter wavelength?
dave