How can I set up a DBA

Double Bass Array - Practical Guide for Dummies

Postby Maxix »Tue Dec 22, 2015 10:38 am

Hello you professionals

Please read through once and then write down any additions / questions below.
Remember: It is for unsuspecting beginners who just want to have a DBA. Once you have built it, you will automatically deal with it more intensively
If everything fits, pictures will be added.


Double Bass Array - Practical Guide for Dummies

Hello and welcome to my practice guide for dummies. Briefly how it came about and then it should start.
I wanted to have more bass in the home theater because my satellites / shelf boxes didn't come deep enough. After listening to various floorstanding speakers, it turned out that this was not a final solution. So I decided on a subwoofer solution. In many cinemas, the Mivoc AW124 chassis I use are used as a kicker in the Double Bass Array (DBA). The approximate hardware can also be found quickly and thus nothing stands in the way of building.
And then?
Exactly. And then…?
That's why I decided to write this practical guide.
I am not an acoustics expert, have no experience in loudspeaker construction, no measuring equipment and I also don't know how to use it ... the guide is intended to give everyone who is interested an introduction and overview of what has cost me time and research. A small repayment to the community, which consistently support each other well.
The guide was created in December 2015, the prices here were also up-to-date.

What was used:
Four Tempest subwoofers roughly based on Emil Attlid (http://attlid.eu/p_tempest.html).
Behringer DCX 2496 DSP.
The t.Amp E4-250 power amplifier.
Denon X3100W AVR.
Heimkinoclub Munich Forum (home cinema report on Juju Magic).
Together forum.
Hornbach hardware store.

What did the fun cost:
Subs ~ € 100 / piece
DCX € 285
E4-250 € 298
+ Cables etc.

The construction:
According to Emil Attlid's blueprint (http://attlid.eu/tempest/tempest_woofer_fp.pdf) I had the 19mm MDF (medium density fiber, pressed wood chips, nicely dense) panels cut to size in the local Hornbach (make them on the mm , fit). In addition, there was Ponal Wood Glue Express (orange, small bottle is enough for everything), a piece of “25cm” 110 HT pipe from the sanitary department and a “bucket” of 750ml acrylic paint matt black of the private label. In total, that was a good 100 euros.
The necessary shapes were then sawed out with the buddy’s Bosch PST 900 jigsaw. There are special blades for hardwood and tight radii, so it went really well (T308BOF, 3 pieces, € 17, one might be enough for everything, we used another before ...).
110 holes were sawn out for the bass reflex tubes. Then we push the HT pipe in as far as it will go and mark it there. Later it is sawn off a little further up (hacksaw; manual operation was better than tiger saw ...) and hammered into the opening (put a piece of wood underneath so that you don't hit the front of the housing ...). This means that the pipe will also be a good 26.5cm long. That should be the case with the Emil Attlid housing to tune the speaker to ~ 34Hz.
When gluing the housing, it is advisable to have at least one screw clamp. This should be able to stretch 60cm. The glue picks up very quickly, the pressing was often done simply by placing other cut parts or the subwoofer chassis.
After the housings were glued, they were rolled with the acrylic varnish. Diluted with 1/10 water the first time, covering the second time. If you are good, you can get by with the 750ml. 1000ml would be better ...
To connect the connection panel to the chassis, I used approximately 60cm 2 x 2.5mm double wire. This is available from full copper in a transparent jacket as a hundred meter ring for ~ 70 € at Hornbach. It also use it to connect the subs to the power amplifier, so it made no sense for me to use 60cm 4mm inside ...
I soldered the line to the panels, and there are screw connections on the sub-chassis.
So that the chassis wouldn't put too much strain on the MDF, I sawed small pieces out of a 25x40mm wooden batten and glued them from behind to the previously drilled holes in the chassis (see Emil Attlid). To fasten these, 4x40mm screws were used (eight per chassis). The connection panels were 4x25mm, four per panel (without wood behind ...).
In my cinema, the subwoofer housings are on the round MDF cutouts of the large chassis holes. Why should you waste this MDF too ... The BR tube is on top, the chassis is on the bottom. So far, I've saved myself turning around to test.
I used the neutrik plug NL2 FX to connect the subs to the TSA 4-250.
I placed the subwoofers in my 520x540cm room with the membrane center at 125cm to the outer wall. With the back directly against the wall (as far as the connection panels allow).
The cables all have Nachamichi banana plugs, 20 pieces cost about 18 euros, good product!
After everything was connected, the DCX had to be set. I have carried out some measurements with a headset microphone (beyerdynamic MMX 300) and the CARMA 4 Pro (freeware), but apart from a little experience, that didn't bring me anything: D
It was much more useful to set certain basic parameters (how the settings are entered can be found in the manual of the DCX very well, this is then also very quickly from the hand).

Input A receives the signal from the AVR, here are the settings I made:
Routing: Mono, I have designated all positions as subwoofers.
Side 1: Gain = 0db
Side 2: Delay = off
Page 3: EQ = off
Page 4: Dyn EQ = off
Page 5: unchanged (Attack 100mS, Release 501mS)

Output 1 + 2 are the front subs for me, outputs 3 + 4 are the rear ones.
In the DCX there are eight pages per output, here are the set values:
Output 1, 2, 3 and 4:
Side 1: Input A, Gain = 0db, subwoofer
Side 2: Type = BUT24 (for both), Freq below = 32Hz, Freq above = 100Hz
Page 3: EQ = On, Type: LP, Freq 100Hz, Gain = 3.0db
Page 4: Dyn EQ = off
Page 5: unchanged (Attack 100mS, Release 501mS)
Page 6: Limiter = off
Output 1 + 2 (front):
Page 7: Pole = normal, phase = 45 °
Page 8: Delay = off, short = 0mS, long = 0m = 0mS
Output 3 + 4 (rear):
Page 7: Pol = inverted, phase = 45 °
Page 8: Delay = on, short = 0mS, long = 5.4m = 15.72mS

The outputs of the 4-250 are at medium strength for me.

After everything has been set, an Audyssey calibration with the AVR is due (with the subwoofers switched on, of course). After this measurement, you know during the first test why you put four subwoofers in the booth; D.
I find recommendable, for example:
Batman: The Dark Knight, scene after the motorcycle hunt when the Bat flies out of the alley.
Die Hard 4: Scene when the gas pipes at the power plant explode. When Bruce jumps into the helicopter with the copcar and it "lands".
Metallica - Through the Never BluRay: Enter Sandman
And a thousand more ...
The distance between the subwoofers in the AVR ~ should be the same as that of the front speakers. Depending on the AVR, there are many setting options here, too much for me to recommend.

When everything is set up, the "bass enjoyment" can begin.
From here on it goes to the fine-tuning, as can be seen below, it was heavily by ear. After investing in a DBA and the first 10-20 films with it, you should treat yourself to a professional measurement, either reading it yourself and buying the equipment or having it done by professionals / experienced users.

Here are a few general tips, explanations and hints:
DCX 2496:
The DCX is passive, so it doesn't make any noise.
It has no rubber feet (is also intended for installation in a 19 “cabinet).
The delay of 5.4m and 15.72mS results from the space. If this were now 6 meters, you would enter 6m accordingly (the mS then result automatically). Trying it out doesn't hurt here either.
My subwoofers currently have a phase of 45 °. This came about just by trying it out. I haven't heard all of the options yet; )
With a correct measurement you can definitely get a lot more out of it.
I still had the 3dB gain at 100Hz in the settings after measuring with the beyerdynamic, they don't break anything with me ...

The t.amp 4-250:
The power amplifier is active, it has a very loud fan and should therefore not be in the listening room if possible. 4 XLR (male-female) cables are required for connection to the DCX. I took 30cm and placed the DCX directly on the power amplifier.
The 4-250 weighs ~ 10Kg and has good rubber feet.

Costs:
The total cost is around 1000 euros.
Compared to the rest of my cinema, that's okay. You get four! Subwoofers that can be completely adjusted to the room. Even with a single, finished DSP sub, you won't get such a balanced bass. Of course, a little more space is needed, but if you are building a cinema you should plan this:)

Next Steps:
Continue to work on the settings and measure them professionally.

Greetings!
Last edited by Maxix on Wed Dec 23, 2015 10:50 am, edited 1 time in total.