A whole slew of basic questions

**robh** · **09-05-09, 09:59 AM**

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.

**Mike P.** · **09-05-09, 11:54 AM**

Quote:

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.

Quote:

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.

**robh** · **09-05-09, 01:03 PM**

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.

**Mike P.** · **09-05-09, 02:59 PM**

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.

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**robh** · **09-05-09, 03:23 PM**

Quote:

Mike P. wrote:

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?

**Mike P.** · **09-05-09, 03:54 PM**

4 separate subs will work, you didn't want 4 refrigerator sized subs so i thought 2 would do.

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.

**robh** · **09-05-09, 05:46 PM**

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

**Mike P.** · **09-05-09, 06:35 PM**

Quote:

so 2 kw into each driver will give useful SPL at that freq?

Yes, the amps will do fine.

Quote:

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.

Quote:

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.

Quote:

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/foru...inisd-pro.html

The WinISD file for the Maelstrom-X is here:

http://www.hometheatershack.com/foru...pro-files.html

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

**Mike P.** · **09-05-09, 06:47 PM**

Modeling shows that PR's won't be an option, 14.5 hz is the lowest tuning I can find.

**noeffred** · **09-13-09, 05:57 AM**

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?

**robh** · **09-13-09, 12:05 PM**

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.

**chadcummings** · **09-13-09, 12:14 PM**

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.

**robh** · **09-13-09, 12:22 PM**

**chadcummings** · **09-13-09, 12:31 PM**

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.

**noeffred** · **09-13-09, 02:37 PM**

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!

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.

**chadcummings** · **09-13-09, 02:44 PM**

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.

**StereoClarity** · **09-13-09, 04:06 PM**

Quote:

chadcummings wrote:

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!

**chadcummings** · **09-13-09, 04:10 PM**

If I remember correctly, you gain +3db off each wall so each corner give you +6db per sub.

**StereoClarity** · **09-13-09, 04:24 PM**

Quote:

chadcummings wrote:

If I remember correctly, you gain +3db off each wall so each corner give you +6db per sub.

It's a little more complicated than that but as a general rule I think that's alright. It's also frequency dependent.

**chadcummings** · **09-13-09, 04:31 PM**

Quote:

ItalynStylion wrote:

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.

**StereoClarity** · **09-13-09, 04:37 PM**

Quote:

chadcummings wrote:

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.

Then we're certainly on the same page

**chadcummings** · **09-13-09, 04:40 PM**

We have reached an accord.

**robh** · **10-06-09, 09:48 PM**

I got pretty distracted researching the IB stuff. I don't see how I can make that work, as the only place I could put the manifold would be in the attic, and in Texas, that would be likely cause the subs to fail pretty soon, since my attic, in the summer, hits over 140F. Even if I do a bunch of upgrades, which as much as they'd help my cooling bills, will take quite a bit of time and be rather cost prohibitive to get done on the time frame I'd like to get this completed in (<12 months). I could probably get 4 boxes the size of mini-fridges past the wife though. She's amazingly tolerant when it comes to this stuff. I haven't given up on IB yet, and it does sound like an IB sub could deliver the performance I'm after. I'm also investigating the room node stuff, since I hadn't given the amount of consideration to that that I should have.

I have the 2 subs I have now placed in the corners and it's working fairly well, but I did have to add in a bit of boost on a few frequencies to get a flattish response from them via the BFD.

I will be building this on my own, but I'll either be buying the tools to build the subs myself (justified since I'll be doing other home improvement projects where they'll be put to use) or going out to my father-in-law's who has a full wood working shop.

I looked at that German site, but it's somewhat limited. My roof, for example, slopes quite a bit, so it's about 10 ft at the front wall where the mains are, but about 15 ft. at it's peak. I also have this weird little section that juts into the room where a small enclosed area is that is serving as our after-dinner sitting area. It makes a corner, and I'm fairly certain I need a bass trap at least there. Or I have the option to put subs in 3 corners and one standing on the other side. Both the back subs would be even with the couch. But coming back to the site, I assume the dark and light areas are areas of minimum and maximum pressure, with the dark areas being maximum pressure? So where would I want to locate a speaker in relation to those?

I'm also thinking that to minimize phase problems that I should go with downward firing subs. The house is built on a concrete foundation, so coupling and resonance to the rest of the house is still minimized. Does that at least make sense?

And many thanks to those how have replied. I'm very much looking forward to making this happen, though my neighbors may be less than thrilled when I get this going.

**Ryan Anderson** · **10-06-09, 11:02 PM**

with the budget you have, it would be nice to see several 21" Maelstrom-X drivers implemented. it looks like you've been reading up and doing your research, check out XBL^2 technology. These subs, IMHO, are as good as it gets for sound quality, as well as move the most air to be able to reach down to "Bottom C". I too was going to atempt this at one time and planned on using 18" Maelstrom-X's, until the big one came out. Unfortunately, no matter what driver/alignment... tapped horn, TL, ported, sealed... to get 8Hz... it's got to be BIG. I sure hope you go for it and take a lot of pics. It would be my favorite build log if you did. Has anyone ever gone for "Bottom C", other than in an IB?

**robh** · **10-07-09, 12:06 AM**

I haven't ruled out an IB based sub. I'm just saying it's going to be challenging to put one in that won't burn up. I did have an idea about what I might be able to do for heat management: if I put in another small hole next to the the one(s) for the sub and mount a 12cm PC fan connected to a piece of dryer duct that then blows down into the top of the manifold, and I mount the subs magnet-in, I might be able to keep them cool enough to avoid both killing them and losing a large chunk of efficiency during the day.

It'll also take a lot of research to verify that the very limited placement options will give me a decent response curve so I'm not eq'ing the out of it.

Hmmm... but now I just realized I could do a combination of a linear array and a manifold, with the manifold just deep enough to hold a sub faced magnet-in, and 4-6 subs long in an array mounted at the front of the room in the ceiling.... hmmmm... Need to talk to the IB guys, I guess.

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