Double Bass Array (DBA) - The modern bass concept! - Page 9 - AVS Forum
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Old 01-27-2014, 07:08 AM
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I think one of the beauties of this concept is that it is actually better to use a bunch/lot/s****load of cheaper drivers then a couple of expensive drivers. You don't get room gain that you do with normal subs below the primary mode (~40hz) but you do get added efficiency of lots of woofers working together. I'd personally opt for a good quality but reasonably affordable (in qty) woofer that preferably had shorting rings so that I could use the cluster up as high as possible (maybe even a little above 80hz) to tackle as many room modes as possible.

This guy seems like a reasonable candidate. http://www.parts-express.com/dayton-audio-um15-22-15-ultimax-dvc-subwoofer-2-ohms-per-coil--295-514

I like the idea of making a false wall will the array of subs and then an acoustically transparent screen in front.

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Old 01-27-2014, 07:12 AM
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Actually, I think I like this one better and a little bit cheaper.

http://www.parts-express.com/dayton-audio-rss390ho-4-15-reference-ho-subwoofer-4-ohm--295-469

It likes a smaller box so easier to array more of them.

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Old 01-27-2014, 08:43 AM
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What I'd like to see tried is using smaller band limited subs in the rear. I don't see why it would be vital that the rear array's extend below the lowest null and why they would need to be identical to the front subs. They would need to match the output capability of the front subs, but that is easier over a smaller bandwidth.

This would allow the use of much smaller and possibly shallower subs but would still have the same potential effect. The back subs are just active absorption and you don't need it below 20-30hz in most rooms.

Something like 8 of these shallow subs in enclosures designed to be high passed around 25hz: http://www.parts-express.com/pioneer-ts-sw251-10-shallow-mount-subwoofer--297-290

My room has angled walls at the back so I'm not sure if this would work.
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Old 01-27-2014, 08:49 AM
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That is a very good point!

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Old 01-27-2014, 10:23 AM - Thread Starter
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Quote:
Originally Posted by AudioJosh View Post

You don't get room gain...

This is not true. I have to correct the statement I made a few years ago. A DBA has room gain as every other subwoofer system does. I measured it a few months ago. I was just wrong on that. rolleyes.gif



I think the explanation is that both waves benefit from boundary gain.
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Old 01-27-2014, 11:44 AM
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Nils, what do you think about limiting the bandwidth of the rear subs in order to use smaller enclosures?

Also, do you think the rear walls need to be parallel to the front wall in order for them to work?
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Old 01-27-2014, 11:47 AM - Thread Starter
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Originally Posted by coctostan View Post

Nils, what do you think about limiting the bandwidth of the rear subs in order to use smaller enclosures?

I've never tried it. If done well it could work I think.
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Also, do you think the rear walls need to be parallel to the front wall in order for them to work?

Yes, I think so. But again I never tried a DBA in such a room. Maybe the result is better than expected...
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Old 01-27-2014, 11:48 AM
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Yep, I guess I would just have to test it.
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Old 01-27-2014, 12:00 PM
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I think the non-parrallel back wall should work fine. It just means you have an averaging effect for your primary mode (slightly lower on the longer depth than the shallower depth). Non parallel sides would be tougher to predict I'd think.

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Old 01-27-2014, 01:03 PM
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I've finally completed my single bass array setup and made the first few measurements. I've not started on the back wall treatment yet, and I've not done any kind of EQ so far. Even without this it looks very promising.

Looking forward to getting the back wall finished and start working with the EQ.
The FR on the different measurements are almost the same, as they should be according to the theory, so I hope the EQ job will be easy.

The array is build with 4x2 Dayton HO 12" drivers and they are powered by 2 Crown XTI-2000.
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Old 01-27-2014, 04:36 PM
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Very nice width response similarity!!

JSS
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Old 01-28-2014, 08:51 AM
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Im curious. In a SBA setup, could you place diffusers on the back wall infront of the absorbtion material without interfering with it too much? If so, how big could the diffuser be?

Edit: Thinking something like Perry R's diffuser, just on the backwall, maybe slightly wider depending on room width.

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Old 01-28-2014, 10:44 AM
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Quote:
Originally Posted by mos6581 View Post

I've finally completed my single bass array setup and made the first few measurements. I've not started on the back wall treatment yet, and I've not done any kind of EQ so far. Even without this it looks very promising.

Looking forward to getting the back wall finished and start working with the EQ.
The FR on the different measurements are almost the same, as they should be according to the theory, so I hope the EQ job will be easy.

The array is build with 4x2 Dayton HO 12" drivers and they are powered by 2 Crown XTI-2000.

mos6581,

Very encouraging and impressive!
Am looking forward to how you are handling the rear wall, also how you will EQ those 8 drivers?
Do you have a build thread for this project?

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Old 01-28-2014, 10:58 AM
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Quote:
Originally Posted by eXa View Post

Im curious. In a SBA setup, could you place diffusers on the back wall infront of the absorbtion material without interfering with it too much? If so, how big could the diffuser be?
I think you should download and play with the great QRDude program to get an idea how large diffusers need to be for LF.
Long story short: diffusers are not the solution, but a large depth of absorption might.
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Old 01-28-2014, 11:55 AM
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You misunderstood the question. I dont want to replace the absobtion on the backwall, i want to place a diffuser infront of it.
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Old 01-29-2014, 01:37 AM - Thread Starter
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Quote:
Originally Posted by eXa View Post

You misunderstood the question. I dont want to replace the absobtion on the backwall, i want to place a diffuser infront of it.

A friend of mine placed a diffuser similar to yours in front of his absorber. It still works. But I have not seen measurents from him without the diffuser. I think you just have to find out yourself.
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Old 01-29-2014, 06:29 AM
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Quote:
Originally Posted by eXa View Post

Im curious. In a SBA setup, could you place diffusers on the back wall infront of the absorbtion material without interfering with it too much? If so, how big could the diffuser be?

You'll be fine.

Typically, the SBA LF wavelengths involved wouldn't be significantly impacted by such a diffusor. It's a prudent approach and common practice in studios and mastering rooms, ie., effective LF treatment faced with diffusion/scattering, redirection.

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Old 01-29-2014, 09:24 AM
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Exa, although it will technically work, I doubt it will fit in a practical room. Between the exceptional depth needed to absorb the SBA, the depth needed to do an effective 1d diffusor, and the distance you need to sit from said diffusor it just isn't practical. I think Follo has 20"+ of absorption at the back of his room. Add on ~6" for the QRD's and the need to sit a minimum of 4' away from them.

A better solution would be very deep RPG BAD panel clone. It acts as low profile quasi-diffusor and allows you to sit much closer. It is basically just a random pattern of holes placed over the absorption. They do more of a controlled scatter and mitigate what would be overabsorption of the highs by scattering. RPG builds them up to 4" deep, but you could do it much deeper. You might also try a limp membrane in the middle of the panel to increase the effectiveness of the insulation depth. Oh and they are much easier and cheaper to build and can be covered in cloth for aesthetics.
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Old 01-29-2014, 12:24 PM
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Originally Posted by cuzed2 View Post

mos6581,

Very encouraging and impressive!
Am looking forward to how you are handling the rear wall, also how you will EQ those 8 drivers?
Do you have a build thread for this project?
The rear wall will be built as a false wall with about 20cm of air gap and 30cm of rockwool. I've done some simulation with a online porus absorber calculators, and with the locally available rockwool with a flow resistivity of 9000-11000 it's not much to gain by making a thicker wall. And i also have a door to consider. I'll also use some QRD diffusors on the rear wall.
I'll use the EQ on my Crown amplifiers. If the rear wall works as intended I'll only use a shelving filter to compensate for the roll of from the sealed subwoofers and two bands to reduce the remaining peaks related to the length nodes of 31 and 62hz.. I'll also run ARC on top of this to remove any smaller irregularities in the FR.
I don't have a build thread on avsforum just a small thread on a Norwegian forum.
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Originally Posted by eXa View Post

You misunderstood the question. I dont want to replace the absobtion on the backwall, i want to place a diffuser infront of it.
As some other people have answered, this should in theory not be a problem due to the wave length. To be one the safe side I would use diffusors made of EPS and not wood. At least this is what I'm going to do smile.gif
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Old 01-29-2014, 02:41 PM
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@Coctostan: Something like 6-7 feet from the back wall. Doesnt sound so bad. But you got some good points and alternatives.

Got my answer tho, some kind of diffuser on the back wall should be fine. smile.gif
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Old 01-31-2014, 08:18 AM
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*mildly related tangent*

The thing I like about threads like this is the focus on quality of bass rather than what seems typical on this forum of an obsession over quantity and a bass arms race. Not to be dismissive of that goal but rarely does it seem that much attention is paid of quality and tackling room modes. Granted if you are focused on max SPL below the primary mode, say 40hz, down to single digits then modes aren't the major factor but really the midbass region 40-200hz is a very critical region for quality audio reproduction and where the room matters.

DBA/SBA aren't the only solutions. HK"s 4 middle walls solution, Geddes' spatial averaging solution, etc are also very good solutions although maybe a bit harder to setup originally as it requires measurement and iterations. I'd just wished more bass threads spent more time focusing on the quality aspect in addition to the quantity.

*tangent off*
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Old 02-02-2014, 08:01 AM
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Josh-

I agree completely. In fact there are many cases when people keep adding capacity when it is a response issue they really need to address.
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@Coctostan: Something like 6-7 feet from the back wall. Doesnt sound so bad. But you got some good points and alternatives.

Got my answer tho, some kind of diffuser on the back wall should be fine. smile.gif

You have 6-7ft from the rear wall to the nearest listening positions? Is that with or without that 2' of absorption and 6-8" of diffusion? It depends on the diffusor used, but typically time based diffusion really needs you to sit a good distance away or the effect can actually be detrimental. How far depends on the diffusor design.

The BAD panels eliminate the depth of the QRD and also allow you to sit closer due to the fact that they are amplitude based.

They also allow frequencies under 1khz to be absorbed by the insulation behind the panel whereas a typical QRD with solid backing will act as a hard surface over a bandwidth from about 300hz to 1khz before doings job (this depends on design and materials). It is much more difficult to integrate a 1d or 2d diffuser with bass trapping behind it.
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Old 02-13-2014, 07:40 PM
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Bit slow to answer.

I have nothing atm, well. a livingroom setup wich is not at all suited for DBA/SBA. This is more of a learnig process.
But with a dedicated room with say 20'ish length (my livingroom now is 21.5') i dont see any problems in sitting 7-8feet from the back wall, even if i move the front wall 2feet out to hide speakers and such. Dont think i would want to sit any closer anyways. That is actually very close to my current situation (i have the the 100" screen and speakers almost 3' into the room because of all the windows on the front wall.)
I think i modeled a 1d diffuser to work down in the 500hz range for my current livingroom, no point to go lower than that because of distance and depth. But IF you should sit abit closer, it isnt like it stops working at all, just not as good.

But yeah, again. Very good alternative. Sounds easier and got the benefit of beeing able to sit closer. So probably the best solution in a SBA setups since you already got alot of absorbtion there anyways.
Only drawback is that i like the looks of a big 1d diffuser better tongue.gif But looks is not a big priority in a dedicated room anywas so moot point. (in my opinion anyways)

Edit: Actually, now you got me thinking about 2 RPG BAD panels on my back wall (in my living room). Seems much easier and cheaper to build than 2 big 1D diffusers. Need 2 big ones 1400-1500mm wide, because there is a opening to the kitchen in the middle. Gonna read more about them (found some on gearslutz)

Edit2: When i think about it, 1200x1200mm is much more sensible since standard sheets here in Norway is 1220x2440mm. Would only need 1 sheet for the 2 of them smile.gif
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Old 02-13-2014, 11:34 PM
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I don’t know where you live in Norway but Optifusser may be an option for you. Very good performance and cheap for the size and can also be combined with a panel absorber behind for a very low mode problem frequency. Info: http://www.resonatorstockholm.com/Optiffuser/Optiffuser_Manual.pdf Size 2,88 m², 4 pcs, each 1200x600x220 mm, costs about 2800 Sw. kronor (about USD 412:- ) at Emusic here: http://www.emusic.se/Product/17813/Resonator-Stockholm-Optiffuser. (If I had had room for it, I would have gone for that one instead of the BADs I made, as these take considerable time to DIY.)

End of OT.rolleyes.gif
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Old 02-14-2014, 01:13 AM
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That is actually quite good to know. The price is really good. Ive calculated the price in wood for making some 1D diffuser that would fit for me... and i couldnt do a diffuser that big for the price they are asking smile.gif And that isnt taking in account all the hours it would take to build it.
Bookmarked. Thank you.
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Old 02-14-2014, 08:43 AM - Thread Starter
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Quote:
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I don’t know where you live in Norway but Optifusser may be an option for you. Very good performance and cheap for the size and can also be combined with a panel absorber behind for a very low mode problem frequency. Info: http://www.resonatorstockholm.com/Optiffuser/Optiffuser_Manual.pdf Size 2,88 m², 4 pcs, each 1200x600x220 mm, costs about 2800 Sw. kronor (about USD 412:- ) at Emusic here: http://www.emusic.se/Product/17813/Resonator-Stockholm-Optiffuser. (If I had had room for it, I would have gone for that one instead of the BADs I made, as these take considerable time to DIY.)

Thank you very much for this hint! These diffusers are cheaper than Vicoustic's Trap Fuser and there is a sales discount for large numbers. Maybe I should start a group buy to Germany... smile.gifrolleyes.gif
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Old 02-14-2014, 03:13 PM
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I guess you already know Nils (?); the guy behind these diffusers is the same Jens who has been active in your SBA thread on Gear Slutz. (In my view, one of the better advising acousticians at GS.) The used Styrofoam is quite tough and sturdy, not like the fragile light weight stuff you find at the lumber yard for common insulation purposes.

Personally I’m not too fond of the aesthetics so I would hide the diffusers behind a perforated or stretched metal sheet (open area should be above 65% not to degrade the diffusive properties), like here behind the sofa and part of the side walls: http://www.component.se/forum/index.php?showtopic=12725&page=24#entry188396
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Old 03-19-2014, 03:12 PM
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Hi All,

 

First post here so be gentle!  I am quite taken with the idea of the DBA, however I cannot get my head around its transient response.  Imagine if you will a transient sound played by the front array.  For the sake of argument let's say the 'distance' between arrays is 15ms and the seating position is 2/3 of the room length from the front array.  Said transient will arrive at the ears after 10ms, however the delayed rear signal will take 20ms (15ms added delay plus 5ms from rear array to ears).  Does this have any noticeable effect?  Clearly this problem does not occur with the SBA, so is the latter setup superior?

 

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Old 03-19-2014, 04:08 PM
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^
The delayed signal of the back wall array "cancels" the signal from the front system when it hits the back wall.

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Old 03-19-2014, 11:03 PM
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Quote:
Originally Posted by Klinkenborg View Post

Hi All,

First post here so be gentle!  I am quite taken with the idea of the DBA, however I cannot get my head around its transient response.  Imagine if you will a transient sound played by the front array.  For the sake of argument let's say the 'distance' between arrays is 15ms and the seating position is 2/3 of the room length from the front array.  Said transient will arrive at the ears after 10ms, however the delayed rear signal will take 20ms (15ms added delay plus 5ms from rear array to ears).  Does this have any noticeable effect?  Clearly this problem does not occur with the SBA, so is the latter setup superior?

Cheers, Carl Klinkenborg.
The idea is that the action of the rear array is the exact inverse of the pressure wave arriving from the front array. Therefore, because the resultant pressure is zero, there is no wave propagation from the rear array toward your ears. You should perceive nothing at 20ms in your example. It's the same kind of idea as noise canceling headphones. You can't detect the inverse signal they're playing, because its energy has been completely cancelled by the incoming wave.
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