Alright here is the deal. I have a 12" Brahma MKII dual 2 ohm sub. Then I have a set of 15" Acoustic Elegance 15" 1050g Passive Radiators. I am looking to make a sub for home use with good low end extension. As of now I don't know what I am going to use power wise but most likely run my current car amp off a DC power supply while I get money for a Plate. I'm new to PR design so any help would be appreciated. I am trying to keep the enclosure as small as possible.

The Brahma Specs are as follows.

Fs: 28hz

Qms: 5.1

Qes: .47

Qts: .43

Vas 38L

Re: 1.4 Ohms per coil

Le: .9mH per coil.

BL: 15.9

Sd: 436 sq. cm.

Xmax 29 mm

And the PRs specs are as followed.

Fs: 4.9hz

Qms: 51.96

Vas: 978L

Mms: 1080g

Cms: 1 mm/N

Sd: 830 sq. cm.

Xmax: 25 cm.

So far I modeled out an enclosure that was 3 cu. ft. internally with both PRs. It has an F3 of 19hz, although it isn't super flat. The 0dB point is right around 42 Hz and it has a 1.7dB peak at about 73hz and a 1.65dB peak at 22hz then rolls off at like 28dB per octave. Guesstimates mostly. If I use a single PR it is a lot more peaky.

Any suggestions or comments would be greatly appreciated.

Here is a FR chart that i was looking at on BBP6

Should I go ahead and build or make changed to the design.

Edited May 28, 200817 yr by todd.brust

What's the Fb? What will this sub be used for, music, movies or both? Percentage of each? How big is the room it is going in?

As of now I don't know what I am going to use power wise but most likely run my current car amp off a DC power supply while I get money for a Plate.

Not a good idea. You would spend more for a proper AC to DC power supply than you would for a plate amp.

-Robert

What's the Fb? What will this sub be used for, music, movies or both? Percentage of each? How big is the room it is going in?

As of now I don't know what I am going to use power wise but most likely run my current car amp off a DC power supply while I get money for a Plate.

Not a good idea. You would spend more for a proper AC to DC power supply than you would for a plate amp.

-Robert

x2

get a plate, or pro audio amp. You will be 100,000,000,000.3917% happier with the end result.

get a plate, or pro audio amp. You will be 100,000,000,000.3917% happier with the end result.

I thought about suggesting a pro amp as well but he needs something with an SSF. Unless he uses a Reckhorn crossover or an Elemental Designs EQ.2, a pro amp will play too low for a PR enclosure.

-Robert

No idea how to determine the Fb. I'll have to find my copy of LSDC and read up on PR systems.

But this sub system would be used 99% of the time for music.

The room size....uhh I haven't moved in yet but if I had to guess based off my memory....15-17 ft. length and width and 10ft ceilings.

What would you guys recommend for an amplifier?

Edit: I think I figured the Fb to be between 21 and 23 Hz. Do those numbers look right at all?

Edited May 29, 200817 yr by todd.brust

If you are going to use the sub for action movies the other 1% of the time, then I suggest a plate amp with an SSF set at 18hz to 20hz. The 500w Dayton model from Parts Express would be perfect for this. It also has a one band parametric EQ that can help tame room response. The Fb in the low 20's seems right.

-Robert

Perfect timing on my part here!

I was looking at those Dayton plate amps. I just need to sell my Car amp so I can get funds to buy a plate. I love being broke!

The 500w BASH amp from 0 Audio is another choice. But since it has an adjustable SSF, I would tune lower. You don't want an Fb of 22hz and an SSF at 16hz. The BASH from PE is another option as well but you have to replace 2 resistors to change the factory SSF.

-Robert

That Bash is more in my price range. I'll have to mess around with the design a little more and tune it lower. I'd like to add mass to the PRs, but the process for it is somewhat critical from what I have been told. Unlike the Variable mass PRs, like the ones TC sold, these have to had lead or some type of filler material to be filled into the back of the cone. What are the other selectable SSF levels on that BASH?

I'll do some messing around with it. What do you think would be a desirable Fb? Do you think I am really going to need extension that low?

I'd like to add mass to the PRs, but the process for it is somewhat critical from what I have been told.

Measure out the weight, glue it one the back of the PR evenly. Washers, nickles, etc. Account for a few grams of glue as well. Or you can glue a large bolt into the cardboard "voice coil" of the PR. That will add some weight and allow you to add more as needed.

What are the other selectable SSF levels on that BASH?

http://www.oaudio.com/500W_SUBAMP.html

The PE BASH has infinite possibilities based on the values of 2 resistors that you replace.

I'll do some messing around with it. What do you think would be a desirable Fb? Do you think I am really going to need extension that low?

I know you mentioned 99% music. Wait until you watch a movie with a real sub. It is very addictive. My wife and I watched Transformers over the weekend. Average movie but both the visual and audio special effects were great. I'll re-watch it after I install my 18's in the home theater.

-Robert

I've been busy lately with moving and whatnot but I got some good news yesterday and that is that the Passive radiators are mine for sure. On another note, the buddy with the PRs had a DC power supply, a small one that I can use temporarily until I can afford to get a plate amp. Even better news is that I may have my amp sold so I may be able to buy a plate soon! WOOT! As of now, the Bash seems like my best bet to fit my budget. I haven't gotten a chance to mess with the design since I don't have a computer to access whenever I need to .

As for adding weight to the PRs, the method of adding weight is by using lead and actually filling the cylinder on the back of the PR. I could always experiment with with washers and glue, but I don't really want to risk messing up the matching parameters I do like the idea of adding the bolt and adding more weights as needed. My question is how much would I need to add to get that extra low end extension without drastically changing the overall "flatness" of the FR.

Thanks for the help though Robert. Any more help would be appreciated

I finally got MS Excel installed and can run the Unibox spreadsheet.

Modeling your driver and 2 PR's in an 85L (~3.5cf) box, I get a perfect EBS response graph when I add 1,000g of weight per PR. The Fb is lowered to 17hz. So a 15hz SSF would be a perfect match. At 500w, the driver is only hitting about 20mm of excursion max. The PR is reaching xmax at 15hz. Make sure that the PR's are on opposing sides of the box. 2,050g (4.4 pounds) is a LOT of weight to be moving back and forth. Having them on opposing sides will counteract each other so that the enclosure doesn't move at all.

-Robert

Sweet! I may have to look into adding some weight then. Maybe this could double as a HT sub!

I think that if I do this, I will use the lead as opposed to gluing washers/bolts. The buddy who is getting me the PRs has instructions on how to add the lead properly so the weight is as accurate as possible.

I just found it on the AE forum and it goes like this.

"The best way to add mass to these is to mix up some lead shot and a 2 part epoxy, then pour it into the tube. Set the PR face down and level while doing this. "

But the washers seem a lot easier to me though

Edited June 3, 200817 yr by todd.brust