Unibox issues, need help w/brahma 12" 4 theater

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Unibox issues, need help w/brahma 12" 4 theater

I'm not new to building sub boxes and such but I could use some help here.

I have an Adire Brahma 12" DVC driver and I want to make a box for home theatre use.

The room is 30 x 30 with 9ft ceilings. Do I go ported or sealed?

I got advice to build a 3 cubic ft box ported tuned to low 20s. When I put the numbers in Unibox I get a rediculous port length. I can't figure out where I'm going wrong. I need box size and port size. Help appreciated!

Im not particular about the box size. I want the best sound for my application. Any help?
Brahma 12 mk I: RE= 2.6
Z=4
Le=1.7
Fs=28
Qms=5.30
Qes=0.49
Qts=0.45
Vas (L) 41
SD (sqr cm)=436
Xmax (mm)=27.3
Pmax =1600
SPL (1W 1m) =84.3
Dual Voice Coils, params in series

Now lets talk amps: I have an Adcom 545 but I think its under powered for the driver, even bridged. The driver has dual 2 ohm voice coils so I need to do one channel at 4 ohms. I need some power to move this monster (it can take up to 1200 Watts). Any opinions on a decent amp? Maybe a plate amp?
 

GM

Member
Joined 2003
Re: Unibox issues, need help w/brahma 12" 4 theater

Greets!

Considering the driver's Xmax and Pe, a corner loaded sealed alignment would be high SQ and best for soundtracks that have <16-20 Hz content, but then if getting anywhere near DD reference out of it you'll need some type of ported alignment.

Right, small box tuned low with lots of power = TL size/length vent, so one of two alignment types are obvious choices, TQWT or some type of horn, either of which are going to be pretty big.

If you go the tapped horn route, then at most you'll only need ~450 W (half space loading) or as little as ~100 W (corner loaded).

Here's a pi space (mid-wall location since your room's so big) loaded simple conic expansion ~494.4 L (net) TH at 450 W without exceeding Xmax till <15 Hz, so shouldn't have any problem hitting DD reference at low power/distortion over most of its BW once EQ'd ~flat in-room:

GM
 

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More info please

Thanks for your assistance. Im not as well versed on the vocabulary here...

So what are the construction details here? (box size?) and do you have suggestions on where to get a tapped horn? What size horn?

Also I was mistaken on the amp. It is is an Adcom 555II, I should get 600W out of it bridged at 4 ohm. Voicecoils in parallel. It was forever ago when I bought it!
 

GM

Member
Joined 2003
Re: More info please

Right, though for home apps in particular you ideally want to keep the vent mach to < 5%, so you don't want to use too small a diameter. If you did you can always 'stick a sock in it' or other means of damping it to quell it's noise, though it will roll off its response to a degree.

GM
 

GM

Member
Joined 2003
Re: More info please

bradonline said:
Thanks for your assistance. Im not as well versed on the vocabulary here...

Greets!

You're welcome!

This is a DIY forum, so you build your own ;): http://www.diyaudio.com/forums/showthread.php?s=&threadid=97674

Anyway, I only know of two companies selling THs, the inventor's and a Canadian licencee: http://www.danleysoundlabs.com/tapped_horn.html http://www.yorkville.com/products.asp?type=29&cat=38&id=317

The box dims, driver position are here in the top half of the window: http://www.diyaudio.com/forums/attachment.php?s=&postid=1395683&stamp=1199858165

Simplest layout and data field definitions: http://www.diyaudio.com/forums/showthread.php?postid=1397610#post1397610

GM
 
Be carefull, that amp isn't designed for 2 ohm stereo/4 ohm mono loads, you may end up smoking it. If you put the coils in parrellel you'll end up with a mono 1 ohm load... Really bad for that amp....

A ported box will be difficult with that driver, it works best in a box that isn't big enough to handle a sufficent vent size... Kind of a drawback to the design, it wasn't really ever intended to be in that type of alignment, even though it is a killer Home Audio driver. I have built several H/T boxes using MkI and MkII Brahma 12s, and Sadhara subwoofers....

You'll just have to get creative with the vent if you go that route. It may end up being that a good amount of your overall enclosure is volume used up by the vent...

I wouldn't bother going sealed with that driver, just my opinion...

I put the Brahmas and Sadhara in larger (4ft3 ish, IIRC) boxes and tuned them really low, like 18-20 Hz. They don't need much power here at all, I completely trashed the suspension on one of them with 500 watts, those big boxes are really efficient and the Brahma has a real linear suspention, even above tuning you don't need a ton of power.... 200-300 watts is plenty with that sub in a big vented box, having a bunch more power is great, just be carefull... I ran the 250 watt P/E plate amp on the Sadhara and absolutely got down, plenty for an average H/T...

I never tried any other alignments with those drivers, I was going to try a T-Line with the Sadhara, I think it would have worked well there, I'll never know though....
 
bradonline said:
95Honda:

Thanks for the input. I'll check my wiring. It's been a while and I need a refresher course!

Since you are experienced with this particular driver can you give me some build details of your most successful design?

For the sadhara I pretty much copied the Adire design with a Sonotube and a pair of 4" flared ports. You might still be able to dig up the white paper on it somewhere on the web, I don't know. I was downfiring and I had it 4" off the floor, it worked great.

The Brahma 12 that sounded best was in a pretty straight forward vented box, around 4 cubes with a tuning around 20Hz. It was a front firing slot vent, I think about 24in2 of vent area, vent along the bottom and then up the back of the box, all 1" MDF construction with a shelf brace inside and lined with 2" fiberglass. The plate amp was not mounted on that box due to the vent running along the inside of the back, IIRC. The dust cap came off of that sub when I first started using it, the glue failed. When I glued it back on I decided to add some mass to see if it would make a difference, lowing the Fs a bit. I squirted a big glob of silicone on the cone under the duscap, it added a fair amount of weight. I couldn't tell much of a difference.....

Sounded great, that XBL2 motor made the best sounding subwoofers I have ever used, I love those subwoofers.
 
I remember seeing that Sadhara project and I have been looking for it on the web as it was my plan to build it. Adire's site is down and I can't find it elsewhere.

I will mimic your Brahma box project. To clear up the port measurement: Is the area of the port basically the sum of the inside surface areas of the port?
 
I don't remember, but I was pretty sure it was around 24-27in2 of area, and in a 4ft3 box, just model and see. I think it was pretty long, maybe 40-50" or so, I can't remember, just run the numbers on a calculator and see. Vent went along the bottom and up almost the whole back of the box, but it only had to make one 90 degree turn at the bottom of the box, I like that alot better than making a bunch of turns and folding the vent on one end of the box only.

24in2 seemed to be enough area for the Brahma 12 and Tempest 15 tuned low and not give much noise from vent velocity. It is roughly equal to a 6" PVC pipe, and that is a decent vent for almost any 12 and most 15s out there, even tuned fairly low.
 
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