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-   -   Double Bass Array (DBA) - The modern bass concept! (https://www.avsforum.com/forum/155-diy-speakers-subs/837744-double-bass-array-dba-modern-bass-concept.html)

unretarded 08-27-2017 04:40 AM

Quote:

Originally Posted by AIA- (Post 48516865)
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.

markus767 08-27-2017 07:29 AM

Quote:

Originally Posted by unretarded (Post 54699676)
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.

https://www.avsforum.com/forum/155-di...ss-xxls12.html

mikela 08-27-2017 09:39 AM

&
 
another example:

see link below.

RoboAVS 08-27-2017 12:35 PM

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.

FoLLgoTT 08-27-2017 01:16 PM

Quote:

Originally Posted by RoboAVS (Post 54701266)
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.

Adhoc1 08-27-2017 03:04 PM

1 Attachment(s)
Quote:

Originally Posted by Tip24/96 (Post 54699604)
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

sdurani 08-27-2017 04:31 PM

Quote:

Originally Posted by Tip24/96 (Post 54699604)
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.

Adhoc1 08-28-2017 02:10 AM

@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.

sdurani 08-28-2017 07:21 AM

Quote:

Originally Posted by Adhoc1 (Post 54703620)
@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.

RoboAVS 08-28-2017 09:35 AM

Quote:

Originally Posted by FoLLgoTT (Post 54701418)
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

Adhoc1 08-28-2017 03:37 PM

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.

FoLLgoTT 08-28-2017 10:36 PM

Quote:

Originally Posted by Adhoc1 (Post 54707354)
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

jjcook 12-10-2017 07:44 AM

Quote:

Originally Posted by FoLLgoTT (Post 54709028)
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

Nils, a few questions:

1) For DBA, what is the minimum distance from listener to rear wall array? As I’ve gathered from this thread there may be some undesirable effects sitting too close to where the oncoming wave front is being cancelled. My room is only 10 feet deep (no depth for SBA) and so my single row listening position would only be about 1-1.5 feet from rear wall.

2) For L-shaped room of opposite orientation (source wall is the longest) would I instead put a cancellation sub on the wall where the room narrows?

SpinMonster 12-10-2017 12:46 PM

Quote:

Originally Posted by FoLLgoTT (Post 10416356)
Another interesting idea appeared at a german Hifi forum. The idea is to use only a Single Bass Array (SBA) on the front wall and to add a time shifted signal with inverted polarity to the original signal.
So the wave will be reflected at the rear wall exactly one time and then it will be canceled by the additional signal.

Sounds like something Bob Carver would have been all over.

jjcook 12-18-2017 12:17 AM

Quote:

Originally Posted by jjcook (Post 55292384)
1) For DBA, what is the minimum distance from listener to rear wall array? As I’ve gathered from this thread there may be some undesirable effects sitting too close to where the oncoming wave front is being cancelled. My room is only 10 feet deep (no depth for SBA) and so my single row listening position would only be about 1-1.5 feet from rear wall.

If its not bad form to quote myself -- I suppose there is no reason why I could not instead source the DBA from the rear of the room and sink it at the front wall (and thus far from my seating to avoid sitting in the cancellation "turbulence") -- so long as the crossover is set to avoid localizable frequencies.

And so long as I properly time align the sources to the MLP, I furthermore suppose with appropriate DSP support one could use the DBA with source in rear for low modal frequencies yet use the front subs (only?) as source for the localizable frequency range that would generally be above the DBA plane wave formation cutoff frequency assuming a modest array.

For my room, I'll have to start a thread to discuss how much woofage a standard construction 2x4 partition wall can handle...

Vince_B 03-30-2019 06:03 AM

3 Attachment(s)
Played around with this a little, this is not remotely a proper setup but I have two hs24 sealed at opposite ends of the room so I gave it a go. Very interesting. The room is 17'5" long, rectangular, couple of open doors, one to a large closet and one to the hall. Subs are front and rear center on the floor, distance between subs is 14'. Subs are not recessed in the wall, just sitting on the floor.

-The math is very simple, speed of sound is 1125 f/s, so the delay needed is 17.416 feet / 1125 feet/second * 1000 = 15ms
-Inverted the rear sub, didn't realize to dial down the rear level a little so they are at same volume.

Immediately the very low end is both less strong but also less muddy. Also the response through the room is notably more even. The rear sub just slurps up the bass that would be reflected. This effect would have to be way more effective with four subs front and four rear. It would be interesting to try ported cabs, or even better imagine stacks of horns front and rear :D

Overall spl, very interesting in the areas circled where you can see the modes neatly reversed and much better behaved. I took measurements in different areas but in general a cool thing is that the dba almost never makes the response worse. You will lose some low bass (and boominess) but this graph is pretty amazing to me, it would probably be impossible to boost that 108hz area enough to have that effect of reversing the null. Guessing that 86 hz is the floor to ceiling mode since the subs are on the floor, a real dba might fix that too.

https://www.avsforum.com/forum/attac...1&d=1553950554

Couple of waterfalls, the very low bass is the interesting part, and the very noticeable part in room

Here is the before, of course no eq, no audyssey, etc, 3ms delay, in phase

https://www.avsforum.com/forum/attac...1&d=1553950247

And after, 15ms delay, rear sub inverted

https://www.avsforum.com/forum/attac...1&d=1553950247

krholmberg 03-30-2019 06:50 AM

Quote:

Originally Posted by Vince_B (Post 57827428)
Played around with this a little, this is not remotely a proper setup but I have two hs24 sealed at opposite ends of the room so I gave it a go. Very interesting. The room is 17'5" long, rectangular, couple of open doors, one to a large closet and one to the hall. Subs are front and rear center on the floor, distance between subs is 14'. Subs are not recessed in the wall, just sitting on the floor.



-The math is very simple, speed of sound is 1125 f/s, so the delay needed is 17.416 feet / 1125 feet/second * 1000 = 15ms

-Inverted the rear sub, didn't realize to dial down the rear level a little so they are at same volume.



Immediately the very low end is both less strong but also less muddy. Also the response through the room is notably more even. The rear sub just slurps up the bass that would be reflected. This effect would have to be way more effective with four subs front and four rear. It would be interesting to try ported cabs, or even better imagine stacks of horns front and rear :D



Overall spl, very interesting in the areas circled where you can see the modes neatly reversed and much better behaved. I took measurements in different areas but in general a cool thing is that the dba almost never makes the response worse. You will lose some low bass (and boominess) but this graph is pretty amazing to me, it would probably be impossible to boost that 108hz area enough to have that effect of reversing the null. Guessing that 86 hz is the floor to ceiling mode since the subs are on the floor, a real dba might fix that too.



https://www.avsforum.com/forum/attac...1&d=1553950554



Couple of waterfalls, the very low bass is the interesting part, and the very noticeable part in room



Here is the before, of course no eq, no audyssey, etc, 3ms delay, in phase



https://www.avsforum.com/forum/attac...1&d=1553950247



And after, 15ms delay, rear sub inverted



https://www.avsforum.com/forum/attac...1&d=1553950247

Have you read the Harmon papers on subwoofer placement? One of the conclusions was the best locations for two subs is centered front and back, but not out of phase. Your experiment is fascinating! Thank you for showing meaningful data. I'm wondering... if you used an EQ to boost the lower frequencies (a house curve), would you gain back the low end that's missing with the subs out of phase while still having less dips in the response? I'm guessing here but with such very capable subs, you likely can have your cake and eat it, too!

Sent from my Pixel 2 XL using Tapatalk

mikela 03-30-2019 06:52 AM

Quote:

Originally Posted by Vince_B (Post 57827428)
Guessing that 86 hz is the floor to ceiling mode since the subs are on the floor, a real dba might fix that too.

Agreed...not quite a "planar" bass wave.

Vince_B 03-30-2019 07:43 AM

Quote:

Originally Posted by krholmberg (Post 57827624)
Have you read the Harmon papers on subwoofer placement? One of the conclusions was the best locations for two subs is centered front and back, but not out of phase. Your experiment is fascinating! Thank you for showing meaningful data. I'm wondering... if you used an EQ to boost the lower frequencies (a house curve), would you gain back the low end that's missing with the subs out of phase while still having less dips in the response? I'm guessing here but with such very capable subs, you likely can have your cake and eat it, too!

Thanks! You can definitely boost the low end back up. Below 40 hz it looks like about a 5-6 db average loss. That makes sense because each sub has it's own amp channel so -6db would be the prediction from turning off one sub. I would have guessed there would be more loss from losing room gain but then again this isn't a true dba. I'm going to play with it some more and try running audyssey before and after just to add that factor. Since I started playing with the bass eq thread stuff, it encourages you not to have lots of eq going on in the minidsp, so I've experimented with just not eq things, let audyssey do it instead. It actually does a pretty good job, so with the dba, if you can clean up the bass that way, then run audyssey it is probably a pretty compelling outcome.

Quote:

Originally Posted by mikela (Post 57827638)
Agreed...not quite a "planar" bass wave.

it would be pretty interesting to try this with some of the 12" black friday woofers or something to see, that might be a great application for those and get closer to the ideal wavefront.

Vince_B 03-30-2019 09:31 AM

5 Attachment(s)
Set up the mic in one spot, about ear height, about 70% back in room, roughly centered side to side. Ran a sweep with and without dba, and then again after running audyssey one pass. Mic never moved during this process.

Also set audyssey for one sub, to make sure it doesn't monkey with the front vs back eq.

Before and after audyssey, no dba, 3ms delay, subs in phase

https://www.avsforum.com/forum/attac...1&d=1553963035

Before and after audyssey, dba, 14ms delay, back sub out of phase

https://www.avsforum.com/forum/attac...1&d=1553963035

Post audyssey, dba vs not. It's actually impressive what a good job audyssey does, I didn't think to check the crossovers it set, that would have been good but it probably did the same. My denon won't show the sub eq, but I bet it took a lot more eq to fix the non-dba setup.

https://www.avsforum.com/forum/attac...1&d=1553963035

Spectrogram of the post audyssey plots, note the dba has about -2 ms earlier peak energy, that seems good?

Not dba:

https://www.avsforum.com/forum/attac...1&d=1553963035

dba:

https://www.avsforum.com/forum/attac...1&d=1553963035

eXa 05-27-2019 04:29 PM

1 Attachment(s)
@FoLLgoTT

Hey, i saw a question in a FB group about a SBA setup in a room with slanted ceelings. Do you have any idea if DBA/SBA would work, and the minimum amount of drivers needed?

FoLLgoTT 05-27-2019 11:37 PM

Quote:

Originally Posted by eXa (Post 58105836)
Hey, i saw a question in a FB group about a SBA setup in a room with slanted ceelings. Do you have any idea if DBA/SBA would work, and the minimum amount of drivers needed?

No, I don't have a solution yet. I suggest to use ABEC to find the optimum arrangement. When I have time I will play around with such a room shape. It is much manual work in the simulation.

eXa 05-28-2019 08:23 AM

1 Attachment(s)
Another picture, to help illustrate. May look like something like 2 up and 4 down would be the best geometry if only 6 drivers are to be used (as OP is planning).


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