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Brahma or Shiva Iso? (1 Viewer)

Brian J Dupuis

Second Unit
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341
Hello,
First-time DIYer here looking to build a small but powerful sub. I posted earlier this year and was primarily steered toward an isobaric Shiva application. Now with talk of this new Brahma driver, I'm wondering if that advice holds true.
Essentially I need a very small enclosure (I'm sure my wife would love if I decided to get a Sunfire, if that gives you any indication). But, as usual, I want excellent performance. Good extension, tight, room-shaking :). My original thought was a shielded clamshell isobaric Shiva in about 27 liters (half the 54 liters of a Q = 0.707 enclosure). With everyone raving about the upcoming Brahma, I decided to see if someone thought a Brahma-based solution would be a better performer while maintaining that volume (or less if I can get away with it).
Those that would recommend the Brahma over the Shiva, what would you recommend for powering it? I have a room with quite a bit of cubic feet to fill (cathedral ceilings) and I've heard people talking about feeding it 1000 watts, but I have yet to find a plate amp with that rating.
Thanks.
 
A

Anthony_Gomez

if you are look at a small sub with all the boom for HT, then there are very few ways to go.

I would look into either the brahma or the BPD1203. Youwill be running these sealed and will REQUIRE either a linkwitz transform, or a shelving filter...and you most likely need a parametric EQ like the BFD. as long as the unperturbed qts is < say 0.707 (which you can easily do in a small enclosure) then you can actually use the BFD alone.

As for amps....I would look into getting a power amp. If you must have a plate amp, then adire has two that would probably work:

a750--just an amp...no XO or anything, so you would need either a seperate LP XO or use the reciever XO.

HS500--all in one plate amp
 

Jack Gilvey

Senior HTF Member
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Hi Brian,
As Anthony points out, and as was discussed in this thread , the BPD 1203 and Brahma do require quite a bit of power and eq. Plate amps need not apply, for the most part.
For more reasonable power requirements and no real need for eq (except for room problems, of course), the Shiva idea is a good one. You could also try two of these , which would require an even smaller box for the same Qtc.
Still, having only 1 12" driver to fill a large space is a tall order.
 

Brian J Dupuis

Second Unit
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Jul 8, 2001
Messages
341
Thanks guys.
Plate amps need not apply, for the most part.
For more reasonable power requirements and no real need for eq (except for room problems, of course), the Shiva idea is a good one. You could also try two of these , which would require an even smaller box for the same Qtc.
Still, having only 1 12" driver to fill a large space is a tall order.
Yeah, unfortunately I have no further room in the entertainment center "complex" for more equipment, so I was hoping for a solution with a plate amp. Do you feel that the HS500 is inadequate for driving either of these?
As far as filling a large space with this one driver, it is indeed a tall order. I'm going to start at the lower end of the spectrum size-wise and see how it goes. I figure if it doesn't meet our needs, I'll work my way up the size ladder. But I have to at least make the appearance of starting small to fill WAF requirements. Then, when she begins to feel that her pants leg isn't shaking quite enough, I have an opening for something a bit more serious :).
Thanks again.
 

AjayM

Screenwriter
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Dan Wiggins once sent me a file for LSPCad with the details on an Iso Shiva vented setup. Box volume was 57.6l (roughly 2cu/ft), had a single 4" port...but here's the kicker...the port needs to be 5ft long for a tuning of 16Hz (this will semi-closely emulate a Low-Q sealed box response). For a little better in the port area, tune to 20Hz and the vent length shrinks to 3ft.

Both of these are good for some decent SPL (LSPCad says around 105, give or take) with the Adire 250W plate amp (and you're bumping into excursion limits with the Shiva in that alignment).

Figure out what to do with the port and it would be a winner!

Andrew
 

Brian J Dupuis

Second Unit
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Interesting, though the port length (and indeed internal volume for that matter) make it somewhat infeasible for my application. That's over double the internal volume of the isobaric Q = 0.707 sealed enclosure (27L). What would the benefit of the ported enclosure be over the sealed enclosure?

Thanks for the input.
 

Jack Gilvey

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What is your goal, as far as SPL/frequency? Are you talking reference level movies?

In a 30L box, the Brahma or the 1203 look like they could get up to just 100db anechoic at 20Hz with the Adire HS500. In the same box, that PE 12" DVC can do about 96.5db @ 20Hz with 250 watts.
 

Brian J Dupuis

Second Unit
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Jul 8, 2001
Messages
341
What is your goal, as far as SPL/frequency? Are you talking reference level movies?

In a 30L box, the Brahma or the 1203 look like they could get up to just 100db anechoic at 20Hz with the Adire HS500. In the same box, that PE 12" DVC can do about 96.5db @ 20Hz with 250 watts.
Now we're getting somewhere! You're saying the 1203 is a better performer for the same volume, yes? I'd like to get the best performance for the size, so performance is the most important thing. I can justify the added expense of the 1203 or Brahma (I'm assuming the 1203 and Brahma drivers are similar in characteristics?) if it means increased performance.

I realize I'm probably not going to get reference levels at 20Hz with this displacement, but I'd like to get as close as possible with whatever driver/alignment provides the best performance.

Thanks again!
 

Jack Gilvey

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Now we're getting somewhere! You're saying the 1203 is a better performer for the same volume, yes?
At low bass frequencies, output will be displacement-limited, and the 1203 has a sizeable advantage in Vd.

The 1203 is a "better performer" with some help in the form of eq and lots of power. Unassisted, I'd rather have that PE 12".
 

Brian J Dupuis

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341
Unassisted, I'd rather have that PE 12".
Would you rather have the PE over the Shiva? BTW, I assumed it was the PE you were referring to in your first post, but both links pointed to the same post so it was hard to tell ;).
Interestingly enough Jack, you were the one who answered me the last time I had questions back in July... you're a prolific helper. Many thanks.
 

Brian J Dupuis

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Just so I don't misunderstand, are you suggesting an isobaric clamshell Dayton application? I think that's what you're saying, but want to make sure we're on the same sheet of paper. So an iso pair of Daytons in 30L should make me smile, eh? Anyone have a project page of one I could go by?
 

Brian J Dupuis

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Wow, thanks Jack. Actually with a bit more finger walking, I've found quite a bit of info on some projects with the Dayton, including your Mini Sub :). Looks nice!
Sorry for all the questions, I'm just having a hard time making a decision on what would ultimately be best. I want something that I'll be happy with for at least a little while, you know? Do you feel that the 30L Dayton provides a decent sub for the size? Would you still recommend this over the iso Shiva for performance?
 

Jack Gilvey

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Do you feel that the 30L Dayton provides a decent sub for the size? Would you still recommend this over the iso Shiva for performance?
Yeah, it's a nice little sub, I like it. Looking at Unibox, the Qtc of an isobaric Shiva setup in 30L would be the same as a single Shiva in a 60L box. That is, slightly lower than the DVC in 30L stuffed. I believe, however, that efficiency in an iso is lower than a single driver. And, of course, you're not getting any more output over a single. In this case, I don't think there'd be much to gain from dual-Shivas over a single DVC.
 

Brian J Dupuis

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Sounds like a winner. And it should save me a bit of cash going with a single driver.
So, looks like I'm going to be placing an order for a Dayton DVC 12" and the Adire ADA250 amplifier, for something very much like what you came up with for your little Mini Sub. You wouldn't have happened to keep any design drawings for that thing, would you have? ;)
Thanks for all your input!
 

Vince Bray

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Oct 4, 2000
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Jack (expectedly) gave you some good advice and I thought I would throw in another viewpoint, likely not as appropriate, but just my experience. I have gotten very good WAF numbers from end-table subs. If you can rest a lamp and a drink on it you're more likely to have more leeway. Also, 24" or so is a great height for an end table. Doesn't have to be that wide. Maybe this is not the best placement for your room, or maybe there's a chair on your front wall that could use some companionship from a good-looking table. Veneer it. Make it pretty.

Now you've got 2-4 cubic feet of volume to play with, and what do we do with that? A 15" woofer of course! Better effiency, more spl, and if you really want to shake a room, you need a 15".

Just my .01 (recession)

Vince
 

ThomasW

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Nov 6, 1999
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Also, being a first-time DIYer, I'm not up to speed with why these guys require the equilization. I've been reading, but my inexperience is getting the best of me.
High excursion drivers require EQ because the impedance of the voice coil is high. That causes the driver to play louder as the frequencies go up. This means that there is more output at 70Hz than say 50Hz. So EQ is needed to flatten (decrease) the output at the higher frequencies, so the sub doesn't sound like one of the "Boom, Boom, Boom" cars you hear on the streets.

The EQ is also helpful to boost the very low frequencies and tame any in-room problems that might arise.
 

Jack Gilvey

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Mar 13, 1999
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Wouldn't a passive radiator based design give you good extension with a smaller enclosure?
PR designs can be considered as you would vented ones, (although a PR can be tuned lower than a vent practically could in a relatively small box). As such, I wouldn't go smaller than 2.5 ft^3 or so. It does look like a very good idea with this driver, though, but the size needs to be larger.
 

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