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Discussion Starter #1 (Edited)
Hi all,

I've built a couple of pairs of speakers before (floorstanders & bookshelves), and have decided it time to tackle the sub that they both want/need.

I want fairly tight and accurate bass for music and HT is secondary, so i've decided a sealed sub should do the trick. I'm building a modular hifi cabinet and the sub will just be an extra box, so the volume is limited to about 2.2 cubic feet.

I am down to the Dayton RSS315HF-4 or the slightly less well known CSS SD12, with a 300W Oaudio bash amp.

From what i've read the oaudio and PE bash amps are really similar, though the oaudio are by default better suited to sealed arrangement because of the (was it 30hz?) boost. and I think the caps on the inside are slightly bigger, though i've got no idea what that means.

It's quite hard to find details on the CSS driver.
 

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Discussion Starter #3
Re: Opinion on Ported 12" Sub

What "details" are you looking for?
Mainly just looking for those that have used the driver for various alignments and how it has compared to similar drivers, especially the Dayton RSS315HF. I can't seem to find anyone that has used the sd12 in a sealed sub.
 

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Re: Opinion on Ported 12" Sub

I had ported SD12 in 4cf enclosure tuned at 18Hz and 500W amp. It was very very capable in HT in small/medium living-room. My brother on the other hand has two SD12 drivers in 3cf sealed enclosure. It is much musical that way and with 2 drivers matches the output of one ported.

If the choise is HT application then I'd recommend one ported SD12 (if two sealed is out of the question as I think it is).
 

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Discussion Starter #6
Re: Opinion on Ported 12" Sub

Yeah, sticking to single driver for the budget. Mostly for music, which is why I think sealed is the go for me. After i'm screwed by postage costs, the SD12 is only $10 more, so the price difference is obviously a non-point.

Mike do you think given it's more for music than ht that the linearity of the dayton might be of importance?

I've modelled the two on linearteam.dk, and they both are -12db at 20hz, though the roll off of the dayton starts at about 60hz while the sd12 starts rolling off from 90hz.

i have no real idea which is preferable, especially after a 5db or so boost at 25hz, which the amp provides.
 

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Re: Opinion on Ported 12" Sub

I'm willing to bet you couldn't tell the difference between the two subs. Both subs model the same SPL wise. The model shown is with an assumed high pass filter at 18 hz and 5 db of boost at 25 hz. Where did you find the boost info? I can't seem to find it on the O-Audio website.

SD12.JPG
 

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Discussion Starter #8
Re: Opinion on Ported 12" Sub

Ok, so it looks like i'll go with the SD12, a little more xmax can't hurt, and modelling shows next to nothing in it.

Good point Mike, it looks like i've spent a few too many nights scouring forums and got a little confused on the 500W version vs the 300W, and also getting references to the PE bash and oaudio bash confused.

Which is a tad annoying because I should think I would be wanting SOME boost down around 25hz. Given how similar this and the PE bash apparently are, I wonder if you can modify the resistors...

Either that or step up to the 500W O-audio...

Any thoughts on the best way to get a bit more output around 25hz?

Cheers
 

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Discussion Starter #9
Re: Opinion on Ported 12" Sub

I've looked but can't find anything on resistors in the oaudio units.

So I guess that leaves me with the PE 300W bash with a resistor mod, or the o-audio 500W (which I would choose over the PE 500W Bash).
 

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Re: Opinion on Ported 12" Sub

Yellow is with the O Audio 500 watt amp. The HPF is set at 20 hz which also has about 4 db of boost. Using the amps EQ to cut the boost down a bit will keep the sub within its Xmax.

Green is with a Bash 300. HPF at 20.7 hz and 2 db of boost in the 25 - 30 hz range. The amp runs out of power well before Xmax. The O Audio 500 is definitely the better choice.

SD12.JPG

excursion.JPG
 

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Discussion Starter #11
Re: Opinion on Ported 12" Sub

Thanks for that Mike.

I think i'll probably just go large for fifty cents extra and invest in the o-audio 500w, just need to nail the final couple of details.

I assume those excursion graphs must be when the amp is at full power - Does this occur when gain is at full? - or does gain work differently?

I ask because I imagine with a 500W amp in my listening room i'd be hard pressed to need much if any gain and am wondering if this would allow me to do some further flattening of the response curve with the parametric EQ?

I tried running some simulations using winISD (alpha & beta) but couldn't get your curves.

I don't really understand the power consumption of subs and their relation to frequency boosts and gain. anywhere good to look for a good breakdown?
 

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Re: 12 Inch Sub

I assume those excursion graphs must be when the amp is at full power
Yes, with the HPF at 20 hz and the 4 db of boost that comes with it has been modified to 2 db.
Does this occur when gain is at full? - or does gain work differently?
Gain is dependent on the input voltage feeding the plate amp. The higher the input voltage the less gain it takes to bring the amp to full power.

I ask because I imagine with a 500W amp in my listening room i'd be hard pressed to need much if any gain and am wondering if this would allow me to do some further flattening of the response curve with the parametric EQ?
The EQ on the O Audio amp is "cut" only. It's effective range is 18 - 80 hz. The 4 db of boost at 20 hz would drive the sub past its Xmax, using the EQ to cut the boost down to 2 db results in the sub staying within its Xmax, as shown in the graph above.

I don't really understand the power consumption of subs and their relation to frequency boosts and gain.
A 3 db boost reqiures twice the amplifier power and has a profound effect on a subs excursion, especially at the lower frequencies. You can download the SD12 file here:

http://www.hometheatershack.com/forums/diy-subwoofers/14410-downloadable-winisd-pro-files.html

Save the file to the Drivers folder in WinISD.

Use WinISD Pro. Input 500 watts. Under the filters tab add a high pass filter, 2nd order at 20 hz. Switch to the cone excursion graph, add a Parameteric EQ filter with 4 db at 20 hz with a Q of 1. See the effect it has on the excursion. Modify the Eq filter to 2 db, the excursion will be within Xmax.
 

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Discussion Starter #13
Re: 12 Inch Sub

Wow, that is brilliant, through a bit of experimentation I finally get a lot more of the power relations now and how everything relates, and I can see how you are modelling it now. Thanks for that. Will keep you posted on progress.
 

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Discussion Starter #14
Re: 12 Inch Sub

Just an update.
I now have the sub and the amp, if the whether holds out (not likely) I may be able to build the box this weekend. The SD12 is 14kg - quite surprised when I picked it up.

The only thing I would like to be able to fine tune is the boost at the cutoff point, as you mentioned Mike I can use the PEQ to tame it within allowable excursion, but then I can't fix any room gains elsewhere in the response.

Not a big drama at this point, I will wait and see what it sounds like when it's in the box, though I am wondering if I might be able to change the boost associated with the high pass filter.
 

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Re: 12 Inch Sub

but then I can't fix any room gains elsewhere in the response.
Room gains and nulls can be determined by using REW and then using a BFD for any possible corrections.

I am wondering if I might be able to change the boost associated with the high pass filter.
There is no public documentation on making any changes to the O-Audio amp that I'm aware of. You could try contacting O-Audio, but from my experience with them about getting information, don't get your hopes up.
 

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Discussion Starter #16
Re: 12 Inch Sub

One sub now complete. :whew:

I am very happy with the final result, every aspect of the project turned out better than I had hoped for. The sub sounds amazing - it integrates beautifully with my DIY towers, seems very accurate and tight, certainly no ill defined boominess to speak of.

As I didn't have a sub in place before, and haven't heard other subs in the same listening environment i'm not about to make any valueless claims or comparisons. I can say that this sub has blown me away, and I am keen to try some rather expensive subs to compare. As it's sealed i'm sure it won't go as low as some, but for my application, accuracy beats volume hands down.

A few notes on construction, for those interested.

I used 12mm ply for all the boxes, but lined the sub box with 18mm MDF on the back, double 18mm on the front, and 12mm for the rest. The front baffle ended up being 48mm thick, as I wanted some grab after the 20mm rebate for the driver. I also rebated the amp in the back. All up the sub weighs around 40kg.

After feeling the weight of the magnet, I decided it best to use the bracing design from the sealed SD12 plans on the css site. The vertical brace tightly fits around the magnet, whilst the horizontal brace meets the magnet with some high density foam. When you tighten the bolts this foam condenses and creates considerable tension between the front and back of the cabinet.

For the feet I cut square aluminium tubing, and t-cut vulcanised rubber to fit inside, then screwed them in from the bottom.

I left a 4mm recess on the front panel from the edges as I am going to build a grille that wedges into that 4mm.

The finish is a stain / matte varnish with stain / matte varnish, varnishing done with a spray gun.

A Big thanks to those who helped, below are a few links to images.

http://aeski.net/inside_layout.jpg
http://aeski.net/almost_built.jpg
http://aeski.net/sub_back.jpg
http://aeski.net/empty_set.jpg
http://aeski.net/final_setup.jpg

inside_layout.jpg

almost_built.jpg

sub_back.jpg

empty_set.jpg

final_setup.jpg
 

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Discussion Starter #18
Re: 12 Inch Sub

it's the same boxes in the 4th and 5th images, just filled with records and hifi gear.
Though i'm thinking I might put the hifi box under the record player as the cd's rattle on the carousel being that close to the sub when turned it up.

I find that the gain at a bit under half way is more than adequate in my open plan living area (lounge is about 6x5 meters).
 
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