Double Bass Array (DBA) - The modern bass concept! - Page 13 - AVS Forum | Home Theater Discussions And Reviews
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post #361 of 372 Old 08-27-2017, 04:40 AM
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Originally Posted by AIA- View Post
I think this video explains well in an easy understandable way what is said in this post
https://youtu.be/pdM57_C-OEE

How would one construct a back wall like that is completely non bass reflective as shown in that vid and is it even realistic that it is possible.


I understand how the DBA does this, but that back wall in the vid doing what it shows needs some clarification.

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post #362 of 372 Old 08-27-2017, 07:29 AM
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Originally Posted by unretarded View Post
How would one construct a back wall like that is completely non bass reflective as shown in that vid and is it even realistic that it is possible.


I understand how the DBA does this, but that back wall in the vid doing what it shows needs some clarification.
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post #363 of 372 Old 08-27-2017, 09:39 AM
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&

another example:

see link below.
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post #364 of 372 Old 08-27-2017, 12:35 PM
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I may be the only skeptic I guess. I can only see the waterfall from the first post but it has a huge dip around 70hz....that isn't a cancellation? and then the response measurements....there is one taken in the middle of the room without a couch? I guess I am confused, as the waterfall shows cancellation due to a room mode.

Putting delays on subs in the back makes sense, I suppose the twist here is to have a reversed polarity for the back subs to absorb sound, versus absorption on the back wall which will...absorb sound.

How does one measurement prove this theory? Shouldn't there be 20 measurements throughout the room to show this works?

I'm no superstar but I have subs delayed in the back and flat measuremnts in spl and waterfall without the dip.

In theory, I understand having subs up top, but nobody is up there...and having good bass in the entire room would be awesome but what proof is there, did I miss it? Cool theory but it sounds more like a giant set of cancelling headphones which....only sort of works in a almost perfect environment....headphones.

It's nobody's job to convince me but I see no benefits here.
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post #365 of 372 Old 08-27-2017, 01:16 PM - Thread Starter
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Originally Posted by RoboAVS View Post
I may be the only skeptic I guess. I can only see the waterfall from the first post but it has a huge dip around 70hz....that isn't a cancellation? and then the response measurements....there is one taken in the middle of the room without a couch? I guess I am confused, as the waterfall shows cancellation due to a room mode.
The reason for the dip in my measurement is that the outer subwoofers are angled to the listener. In fact there is space behind them which leads to a not completely cancelled width mode. I BEM-simulated this situation and have several solutions for this error (different delay, gain for the outer subwoofer etc.). A SBA/DBA with flat subwoofers on the wall doesn't have this problem.
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post #366 of 372 Old 08-27-2017, 03:04 PM
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Originally Posted by Tip24/96 View Post
Would it be possible to use four of the Dayton PA460's in a DBA configuration, with two on the front wall and two on the rear wall?

My room is roughly 14ft wide x 14ft deep x 8ft tall. So the optimal mounting locations would be; (front wall) one mounted at 3.5ft from a side wall and 3.5ft from the ceiling? Then the second sub mounted at 3.5ft from the ceiling and also 3.5ft from the same(?) or opposit side wall from the other front sub?

Can someone help me understand the optimal locations in a 14ft x 14ft x 8ft dedicated HT room?

I already own the drivers, just haven't built enclosures for them yet.
Yes. Check out "1.5 Controlled Acoustic Bass System (C.A.B.S.)" in enclosed pdf. It would be better to have more than 2+2 subs at their proper places but one may have to bend to practicalities in one's room ... Regarding misplacement for practical reasons, the DBA / CABS can still work quite OK, misplacement sideways or up/down can be acceptable but lengthwise is a definite no no: http://webistem.com/acoustics2008/ac...les/000837.pdf
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post #367 of 372 Old 08-27-2017, 04:31 PM
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Originally Posted by Tip24/96 View Post
Would it be possible to use four of the Dayton PA460's in a DBA configuration, with two on the front wall and two on the rear wall?
If you put the PA460 in a box, it will radiate sound omni-directionally (like an expanding sphere). If you install a PA460 flush on a baffle wall, it will radiate semi-spherically, like an expanding bowl travelling along the length of your room towards the back wall. The tricky part of doing a DBA is that you need to cancel the bass wave when it arrives at the back wall. How do you time delay the cancellation signal to the back wall subs: timed for when the leading edge of the bass wave arrives or timed for when the trailing corners of the bass wave arrives OR somewhere in between?

One way around this dilemma is to flatten out the bass wave so that ALL of it arrives at the back wall at the same time. Using more than one sub will make the hemi-spherical wave into a planar wave. The number of subs and their spacing will determine up to which frequency the wave will be flat. In your room, using two subs across the front wall, the bass wave will be flat up to 71Hz vertically and up to 81Hz horizontally. That's not a lot of wiggle room for crossing over your subs to your speakers, but it's better than nothing.
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post #368 of 372 Old 08-28-2017, 02:10 AM
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@sdurani ; From the text and math in the pdf under the headline "1.5 Controlled Acoustic Bass System (C.A.B.S.)" (post 366), I get an upper frequency cut off versus width of about 160 Hz (with 7 feet / 2,13 m between the speakers.) Have you come across another document on this?

@Tip24/96 : Came to think about something. -With 14 feet / 4,26 m between front and backwall, you need to have a delay of roughly 12 ms for the theory to work and cancel out the arriving bass wave. Some of the cheaper miniDSPs only have about 7 ms as max delay if I remember correctly, so they cannot be used.
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post #369 of 372 Old 08-28-2017, 07:21 AM
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Originally Posted by Adhoc1 View Post
@sdurani ; From the text and math in the pdf under the headline "1.5 Controlled Acoustic Bass System (C.A.B.S.)" (post 366), I get an upper frequency cut off versus width of about 160 Hz (with 7 feet / 2,13 m between the speakers.) Have you come across another document on this?
Haven't looked at the C.A.B.S. pdf, but if you Google "double bass array" (the topic of this thread), the formula for the cut off frequency for the planar wave is the speed of sound divided by two times the distance between subwoofers. In this case: 1130 ÷ 2x7 = 81Hz.

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post #370 of 372 Old 08-28-2017, 09:35 AM
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Originally Posted by FoLLgoTT View Post
The reason for the dip in my measurement is that the outer subwoofers are angled to the listener. In fact there is space behind them which leads to a not completely cancelled width mode. I BEM-simulated this situation and have several solutions for this error (different delay, gain for the outer subwoofer etc.). A SBA/DBA with flat subwoofers on the wall doesn't have this problem.
thanks for the reply

i can see how it would be a good potential starting point.
it uses geddes theory but tries to solve issues without treatment

however put 4 or 8 subs in any room i think its a mostly flat response but not decay
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post #371 of 372 Old 08-28-2017, 03:37 PM
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Well, I had hoped you had a reference handy, so I wouldn’t have to google around for it.

If one puts 2 subs right up at against the front wall, each sub at ¼ distance versus room width, the lowest 3 width modes will be attenuated across the whole room width, -good for people in a sofa. The 4th mode will be reinforced at room centre but will in a common room size be above the subs frequency range. Assumed here is the same signal to the subs (=mono, not stereo subs) and rigid side walls. If side walls are dissimilar or studded ligth weight drywalls, one has to figure out the acoustical width of the room, not go on the physical internal width for the placement. It will be the same versus height modes. 2+2 subs at front wall will create an endless mirror imaging of subs versus width and height. In Tip24/96 14 feet wide room, the first 3 width modes would be around 40, 80 and 120 Hz (with rigid side walls).

Double Bass Array and C.A.B.S. (Controlled Acoustically Bass System) is one and the same thing for attenuating bass modes. Double Bass Array may be the more ”popular” name. C.A.B.S. the more ”official and correct" one as the idea goes back to Adrian Celestino’s Ph.D thesis: http://vbn.aau.dk/files/12831869/AC-phd.pdf (Allthough there have been previous works by other people, references are often made to Celestino’s thesis.)

From the thesis: ”The working frequency range of the system extends as the room size decreases. The smaller the room the fewer loudspeakers needed. CABS .2.2 could be applied to sound reproduction systems in small enclosures (e.g. automobiles, small music studios).” and: ”As seen in the results CABS .2.2 worked fine in the IEC Room up to 100 Hz and in the ITU Room up to 90 Hz. Indeed if the system is integrated to a full range reproduction system it must include a low pass filter to attenuate frequencies above these limits.” Something to consider; what is more precious in a moderate sized room? Money for more subs and amplifiers or lost real estate for effective huge bass traps?

Both the IEC and ITU room is a lot larger than 14x’14’x8’ … On page 92 in the thesis it is summarized how the system with subs work depending on room size. I put my money on the info in the C.A.B.S. pdf for cut off frequency.

RoboAVS, the DBA / C.A.B.S works in the time domain, so decay rates should go down if correctly implemented.

Last edited by Adhoc1; 08-28-2017 at 03:41 PM.
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post #372 of 372 Old 08-28-2017, 10:36 PM - Thread Starter
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Quote:
Originally Posted by Adhoc1 View Post
Double Bass Array and C.A.B.S. (Controlled Acoustically Bass System) is one and the same thing for attenuating bass modes. Double Bass Array may be the more ”popular” name. C.A.B.S. the more ”official and correct" one as the idea goes back to Adrian Celestino’s Ph.D thesis: http://vbn.aau.dk/files/12831869/AC-phd.pdf (Allthough there have been previous works by other people, references are often made to Celestino’s thesis.)
Anselm Goertz already presented his paper about the Double Bass Array in the year 2003 which is 4 years before Celestino.


@All
I updated my document about reduced and optimized DBA arrangements. I even added the "pseudo DBA" (or "virtual DBA") which uses only the front array which also fires the delayed and inverted signal (but it doesn't work well though). The "Stereo DBA" may also be of interest.

Reduced DBA arrangements
DBA in L-shaped rooms
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Last edited by FoLLgoTT; 08-28-2017 at 10:48 PM.
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