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Discussion Starter #1
Hi,

So, I've been looking at various sub designs, which amps to use, etc., and so far, all I've managed to do is get to the point where I understand that I don't understand a thing about this.

So, first, the goals:

1) SQ is priority 1

2) High power handling will be needed, now that I'm running separate amps for my mains (500 wpc). Current plan is to use a sub controller module and EP4000 amps for their high power and fairly high damping factor. This also gets me past what will probably be a relatively low SPL design due to another requirement.

3) Mid-bass capability is not important. 2 x-over points will be used: 50 Hz while listening to music, 80
Hz during movies. I'll continue to use the 3 7" drivers in my mains for mid-bass (1st x-over point on mains is 125 Hz).

4) Lower -3db point of 8 Hz, or at least useful extension down to that point. Yes, 8 Hz. I like organ music, and a pipe organ can produce a fundamental tone of 8 Hz. Now that SACD and DVD-A are around, and now that engineers are putting 14-16 Hz effects on Blu-Ray, I want to be ready.

So, now the questions begin:
1) Basic design, ported or sealed? I understand that while you can tune a ported enclosure for any freq you want, roll-off is 12 db/octave below tuning frequency. So I'd probably have to tune to, what? Something like 4-6 Hz? Sealed is less efficient though, so I just don't know enough about the upsides and downsides of each design to make a decision. However, enclosures which exceed the available floor space of the room will be difficult to get past the wife. The wife is, however, an angel of tolerance when it comes to my little acts of folly in this area. As long as it looks good and sounds great, she accepts pretty much anything I do with minimal comment (yes, I am aware she's a keeper, and that I'm a very lucky moo to have found her).

2) Driver size. I'm trying to decide between 15 and 18. Again, SQ is the number one goal, and it seems like the bigger the driver, the higher the damping factor the amp would have to have in order to control the driver. Is there a significant difference in the damping factor requirements between 15 and 18 inch drivers? I have about 1500-1800 sq ft that I'm trying to pressurize, due to the fairly open floor plan of my house. I can place up to 4 subs in the listening area, depending on size (4 refrigerator sized enclosures probably won't work though).

3) What am I missing? I know there are things I have to be missing in this. As Donald said, what are the unknown unknowns?

That's all off the top of my head. I'm sure more will follow. It always does with me.
 

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I understand that while you can tune a ported enclosure for any freq you want, roll-off is 12 db/octave below tuning frequency.
Ported roll off is 24 db below tuning, sealed roll off at a rate of 12 db.

I can place up to 4 subs in the listening area, depending on size (4 refrigerator sized enclosures probably won't work though)
Define the maximum cabinet size that is acceptable and your budget for drivers and amps. That will determine if your goals are achievable.
 

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Discussion Starter #3
Drivers: 600-800 per driver. Could go to 1500 per driver if I really had to, but that would significantly delay this project. Amps, as I said, the plan is to use the EP4000, so that's the price range I'm looking at, plus 600-800 for the sub controller module.

Thanks for the correction. Obviously, that article was wrong.
 

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You need to understand what you're asking. There's no such thing as a small box that will have any meaningful extension down to 8 hz. 8 hz requires moving massive amounts of air. To do that you'll need 2 huge subs with 2 18" subs in each cabinet. Each cabinet would be 30 cu.ft. (approximately 30" x 30" x 70") Each pair of drivers would require 3000 watts.

The modeling shows 2 18" Maelstrom-X subs in 30 cu.ft tuned to 10 hz with 3000 watts input power. A subsonic filter is required at 11 hz to protect the subs from over excursion. With 2 of these subs you can expect 118-120 db at 8 hz with room gain.

The Maelstrom-X is $395 each, you'll need 2 amps capable of powering a pair of these subs, the EP4000 won't do it.

8hz.JPG
 

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Discussion Starter #5
You need to understand what you're asking.
Ok, so that's why I'm posting. Help me understand. You say I need 2 subs in each box. Why would 4 separate enclosures not work?

You say I need an amp capable of driving these. What kind of amp are we talking about? The EP4000 bridged @ 2 ohm seems to have the kind of power you're talking about. Or if not, then what are some suggestions for other amps that meet the required specs? Everything I've looked at seems to be of a spec very similar to the EP4000. If I need one to drive each driver, that can happen.

You have to understand that I'm utterly ignorant about this stuff, so if things need to change, they will. I'm also not trying to go cheap. I looked at those subs, but at that price point (remember, the number I cited is per driver, not total), at least compared to everything else I've looked at, I have to wonder just how SQ oriented it is. The price point is more in line with others that are strictly SPL oriented, despite whatever claims they make. A search shows no substantial reviews, and only one endorsement on the site for a driver that's been out for at least 1.5 years. This does not fill me with hope that this is what I'm looking for. But it's definitely in that direction. Or am I misunderstanding your post and this is pretty much my only option? Or just an example of what I'm after?
 

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4 separate subs will work, you didn't want 4 refrigerator sized subs so i thought 2 would do. :bigsmile: My mistake on the EP4000. It can't be bridged into a 2 ohm load, but each sub can be wired for 2 ohms and each channel of the amp can feed each sub. So that will work.

Regarding SQ, Exodus products are quality products. In a properly designed sytem these drivers will do what is required of them. For the SPL levels in the 20 hz and lower range your biggest issue will be room interaction problems. The SQ that you're after will involve using the REW program to see where the dips and peaks are in the response and correcting them. Add to that the job of finding all the buzzes and rattle in the room and eliminating them. Building the subs is the first part, properly integrating them is the second part.
 

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Discussion Starter #7
I'm at least familiar with REW. I even went with the SB X-fi because when I tested, it's -3db point was 2.2 Hz. :)

You are indeed right on the EP4000. I was thinking it could be bridged into 2 Ohm, but so 2 kw into each driver will give useful SPL at that freq? What about an enclosure design of about 12 cu ft? And is using a passive radiator an option in this application? Or am I better off maybe even doing a tube design?

What did you use to create that graph? Is there a package out there that would help with formulating the parameters for these?

And I think I can get away with 4. If they're a bit shorter, I'll try passing them off as really loud end tables :)
 

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so 2 kw into each driver will give useful SPL at that freq?
Yes, the amps will do fine.

What about an enclosure design of about 12 cu ft? And is using a passive radiator an option in this application?
12 cu.ft. would make the port to long for the tuning frequency .I'll model some PR's and see what the results are.

Or am I better off maybe even doing a tube design?
Probably not. The length of the port would benefit from a folded slot port design to minimize any port resonance issue that may be created by a straight port.

What did you use to create that graph? Is there a package out there that would help with formulating the parameters for these?
WinISD Pro is the program. There is a tutorial here:

http://www.hometheatershack.com/forums/diy-subwoofers/6330-winisd-pro-tutorial-download-detailed-guide-how-use-winisd-pro.html

The WinISD file for the Maelstrom-X is here:

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

The file for this sub is the "Gen.II".
 

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Have you thought about a transmission line? Whilst they are not easy to design without proper software like AJHorn and they need some fine tuning to really get the best out of them, they tend to give you really good bass extension. Maybe even a tapped horn might work for you.

Visaton have a plan for such a transmission line. Whilst this one only goes down to 18Hz it still is an intersting example.

On the other hand, why not just get 2-4 21" woofers, build big vented enclosures and maybe use some digital speaker management to add the needed output?

Have you considered that your room might not be suited for playback of such frequencies? Will room modes not most probably mess with your response considerably?
 

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Discussion Starter #11
I've never heard of transmission line. I'm just starting to get into a lot of this stuff.

Basically, the plan at this point seems to be 4 big vented enclosures with 18s. I do plan on using a sub management system, because if for no other reason, I need something to control the phase since I will have a sub on each of 4 walls.

I have considered that the room might not be capable of it, but I'm also starting room treatment and hope that I can find a way to make it work. If nothing else, the size of the room won't change, and I would at least be able to get a solid 12-14 happening, which will be good enough for the vast majority of music as well as doing pretty well for HT. I'm already seeing semi-useful extension down to 16 Hz (-6 db point) just by using REW, an FBD 1124, a pair of M&K V-125s, and a lot of patience from my wife while I move subs around the room, but no room treatment as of yet. And those subs are spec'ed as having a -3 db point of 20 Hz, which matches up with that I see in REW pretty well.
 

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Since you have all the extra room for the subs, I would look at going with an IB and multiple drivers like the DPL15. For 8 of them you get more SPL and sensitivity than going with 4 18" subs.
 

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Discussion Starter #13
IB?
 

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Infinite Baffle.

There is another section on the board which discusses it and there are many people who are hard line for and against them.

I myself like the IB and have designed my theater to incorporate one that is much larger than I really need, my addiction.

If you do a google search for the words Cult Infinite Baffle you will find a web site which is dedicated to the topic.

You just need to read and make up your own mind.
 

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Putting one woofer into each corner is quite a good idea. Have you thought of building a triangular enclosure to put into the corners? Looks really nice cause it blends into the wall and is pretty simple to build.
Your woman will love this, 'cause there are no boxes standing around! :T

Take a look at this calculator, it's in German (so it's metric!), but you'll get the gist of it without understanding the words. Basically you enter the width, length and height of your room into the three fields above and the modes for your room will be shown. Click on the checkboxes to select the frequency and look at the simulation on the right. The darker the shade, the louder the bass will be. It'll be clear when you see it. :)
 

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It may have high WAF appeal but you will lose the capability of putting bass traps in the corners and may find some bad nulls in the room because of this positioning.
 

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It may have high WAF appeal but you will lose the capability of putting bass traps in the corners and may find some bad nulls in the room because of this positioning.
Even if he's just using these below 50hz with movies? If he had one in each corner he should be able to excite multiple room nodes. I'd imagine the gain from the corners would be substantial as well. He stated that "4 refrigerator size subs probably wont work" so I think integrating them into the corners might be a good idea.

IB might be a good option but he logistics of it might inhibit the actual application. He'd need substantial space behind the woofer and 18" holes would require a severe amount of room alteration. Not to mention the bracing required to support such a thing.

Rob, are you going to be building this on your own? Sounds like a fun project!
 

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It's a little more complicated than that but as a general rule I think that's alright. It's also frequency dependent.
You are correct. It is a function of frequency along with the absorption rate of the material around, the temperature and a whole slew of other things.

That is why I stated it as simplistic as I did. It is a general rule of thumb.

Other things to consider is the size, shape and volume of the room. There are many factors that go into the SQ of any system and until you REW it you never know exactly how it will behave.
 
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