Double Bass Array (DBA)

[StigErik]

3 dB per doubling of distance was intended to be used to find how much the rear array should be attenuated. I started out at a calculated value of 8.5 dB, and ended up very close to that with 9 dB.

 

[daverosenthal]

3 dB per doubling of distance was intended to be used to find how much the rear array should be attenuated. I started out at a calculated value of 8.5 dB, and ended up very close to that with 9 dB.

Huh, that's weird. I was under the impression that in these setups the front and rear arrays should play at (or very near) the same volume, regardless of distance. (In theory there should be minimal losses from a LF plane wave as it travels across the room because it's not expanding at all.) It's hard to argue with the results posted, though! Can you confirm that the rear array is physically playing 9dB quieter than the front?

 

[Hayabusa]

Crazy idea: What about making this with two speakers...
One 3 by 5 meter wall filling electrostatic speaker and one on the back wall

 

[StigErik]

Huh, that's weird. I was under the impression that in these setups the front and rear arrays should play at (or very near) the same volume, regardless of distance. (In theory there should be minimal losses from a LF plane wave as it travels across the room because it's not expanding at all.) It's hard to argue with the results posted, though! Can you confirm that the rear array is physically playing 9dB quieter than the front?

I tried that. Don’t work in my room at all. Maybe it works in a room with no loss, like a concrete bunker? Dunno….

I have to correct myself again. The actual difference is 5dB, not 9.

 

[daverosenthal]

I tried that. Don’t work in my room at all. Maybe it works in a room with no loss, like a concrete bunker? Dunno….

Can confirm that the rear array is about 9 dB quieter. Will show measurements!

Thanks for the confirmation! That’s an interesting data point for sure. 9dB is quite a lot of loss for one traversal of the room. By some rough math (7m / speed of sound) * (60 dB / 9dB) that implies a room RT60 time of 135ms, which would be very low for LF. A bit of a mystery

 

[StigErik]

See previous post. It’s 5 dB. My bad

 

[StigErik]

I got confused by having amps with different gain for front and rear array, as well as different number of speakers on each amp. My math was not correct, obviously…

 

[Sokel]

I got confused by having amps with different gain for front and rear array, as well as different number of speakers on each amp. My math was not correct, obviously…

Yep,5db more for 2000as2 and on top of that probably different loads.

 

[voodooless]

Huh, that's weird. I was under the impression that in these setups the front and rear arrays should play at (or very near) the same volume, regardless of distance.

The idea is to extinguish the wave at the rear wall by adding the exact inverse to it. Since you have losses from front to rear, the rear needs to be attenuated to make that happen. So, this is exactly as expected.

 

[StigErik]

Impressive result, do you have a picture of the arrays?

Sure. It looks like ***, but sounds very nice!

Front end - including MG 3.7 with 4x12" midbass dipoles, MG 3.6 center channel with two 4x10" midbass dipoles. The whole thing is usually hidden behind drapes and a projection screen, so it's a bit less ugly than this (see pic #2).

Rear end, also showing the surround speakers - MG 3.6 plus 4x12" midbass dipoles - and hush-box for my projector. The large stack of firewood is actually "skyline" diffusors.

 

[voodooless]

Well, there goes all my hopes of implementing this in a stealthy way for a living room

 

[ppataki]

Well, there goes all my hopes of implementing this in a stealthy way for a living room

Couldn't one flush mount all the drivers in a gypsum board wall maybe? (Like cutting 50-50cm from the room in the front and the back)
That would make it kind of an infinite baffle I guess.... just an idea, not sure if/how DBA would work then

 

[Flaesh]

not sure if/how DBA would work then

This will work. I used to have a front array in an infinity baffle. This has all already been discussed in other threads.

(Like cutting 50-50cm from the room in the front and the back)

It could be much less. In real life, windows and doors can interfere with this dream)). For example, I don’t have a single wall without doors or windows.

 

[voodooless]

Couldn't one flush mount all the drivers in a gypsum board wall maybe? (Like cutting 50-50cm from the room in the front and the back)
That would make it kind of an infinite baffle I guess.... just an idea, not sure if/how DBA would work then

Sure, two blind walls that house the woofers and covering would do. It’s just curious to have two bare walls in your living room…

 

[badboygolf16v]

Bravo!

 

[voodooless]

Sure, two blind walls that house the woofers and covering would do. It’s just curious to have two bare walls in your living room…

Or suspend drywall panels fitted with bass shakers instead of woofers. With enough surface area this would probably work…

 

[goryu]

what is the frequency range covered by the DBA, the 12" mid bass arrays in front/back, and the 10" mid bass arrays at the front?

 

[StigErik]

DBA is used below 80 Hz.
All midbass arrays 80 to 550 Hz.

The Magnepans are crossed over like this:
Bass panel : 550 - 1500 Hz
Midrange panel : 1500 - 5000 Hz
Ribbon tweeter : 5000 Hz ->

 

[goryu]

what does the system response look like with just the DBA and all the mid bass arrays? A bit surprised at how high you cross to the bass
panels.

 

[StigErik]

I cross that high because the MG bass panels have increasing distortion levels below 500 Hz. They loose a lot of sensitivity as well, as much as 10 dB difference between 500 Hz and 100 Hz.