[thxgoon]

Hey all, this is a great forum I've been reading it for some time now and I think its time for me to jump into this and build one of my own. I thought I'd get your input on the initial design and see if you think this will work. A little background...

I currently have an M&K MX350THX and it's a sweet sweet sub. I love the quality of bass that this puts out but in my current living situation the room is too large for it and I have to put it in a corner to get decent output. This virtually ruins the quality of sound. The response is terribly uneven. The loud frequencies resonate and really have no definition. So my options are, buy several more M&K's or build my own. Obviously, more M&K's would be hugely expensive and from the looks of things I might be able to build something better.

To overcome the room size and acoustic problems I think I'll take a 'sledgehammer' :bigsmile: approach and build something ridiculously huge, place it optimally in the room (even if the location doesn't give the most output) then eq out any remaining problems. I think I can do this for what I can sell my M&K for plus a small budget of my own. What I don't want is a loss of any quality. If my new sub sounds worse (even if it's louder) I will likely part it out and sell it at a loss and keep my M&K. So my requirements are high sound quality, and effortless reference output in my room.

I propose to build four sub boxes containing 2 each of Dayton's Titanic 12" drivers in push pull configuration. This will provide maximum flexibility in placement. I'll power them with a huge external amp capable of driving the woofers to near xmax. So far the QSC PLX series or a used MX series looks like a good option. Then I'll add an EQ like the beringer or rane to even things out. I was thinking of re-enforcing the box by coating it inside and out with concrete. Anyone do anything like that?

What do you think? The room is approx 30ftX22ft and basically rectangular. One thing I don't completely understand is the effect of Q. The books say I should aim for a Q of .707, but lower Q's seem to provide a flatter deeper response and require less power. What exactly would I lose by going to say a Q of .5? Box size is really of little concern. Thanks for any input you can provide, I'll keep this thread updated as I go on. Thanks for having such a great forum!

 

[Sonnie]

Hi goon and welcome to the Shack!

I don't believe placing your sub in the corner ruins the quality of the sound, but rather reinforces lower frequencies. Probably what's happening is you have some serious peaks in your response and placing the sub in the corner amplifies them. But take the sub out of the corner and you lose room gain, which is something that you probably need in that big of a room. A BFD on your sub would most likely help a lot, but with your room size I kinda doubt the M&K sub would be enough even if you got your response tamed.

My suggestion (and it may not be the best one you'll get) would be to download REW and measure the response of your sub in several locations. Let's see where you do get the best response from as well as it may help determine what and how you need to build your subs.

I don't know much about push/pull configurations, but I do know that two very popular and extremely effective DIY subs are the IB and the LLT. I don't believe IB will work for you if you are on a budget. I'm not sure the Dayton subs will do what you need for your size room, but I would suspect if you did something like a dual 15" driver LLT, you would be super well pleased, and I'd recommend something like the SoundSplinter RL-p15 drivers. You could probably accomplish flat response down to 15Hz reasonably easy and probably see some pretty good SPL as well, even with your big room. The quality has been proven to be exceptional with IB and with LLT.

 

[Exocer]

What exactly would I lose by going to say a Q of .5? Box size is really of little concern.

Everything looks good. But, why push pull? Is it that your MK subs are push-pull and you're after something familiar to the MK's?

Going to a Q of .5 from .707 will decrease power handling, require a larger box (which you say isn't a problem),cause a loss in output in the higher frequencies, and increase the danger of exceeding Xmech. The loss in output at the higher frequencies can be EQed back into the loop if you find it necessary.

 

[SteveCallas]

Glad you are taking the plunge, but why use 12" drivers? For not much more, 15" drivers offer a lot more displacement. And for not much more than that, there is now a very reasonably priced 18" driver that will give even more. The less a driver has to move, and the less power it need sto reach your desired output levels, the better for maintaining low distortion. So you should definitely be considering larger drivers.

 

[thxgoon]

Wow thanks for the great replys. I still have a lot of info to process. I hadn't really thought about an LLT but after reading the LLT Explained thread it has got me thinking about it. I'm still a bit skeptical at this point as I've never heard of this design before and I've never had a chance to hear an LLT sub, but would I love to have a couple of 18's! IB would be my first choice, but it'll be few years yet before I own a house I can poke big holes in.

Everything looks good. But, why push pull? Is it that your MK subs are push-pull and you're after something familiar to the MK's?
.

er.....guilty. That and a webpage I found describing different box designs said the push pull configuration was the most accurate and suitable for audiophile type listening. This is what I want, but big enough to stay that way at reference level. Also, compared to other subs I've not heard the M&K's match at quality of bass. I think it might be due to push-pull and its distortion eliminating design. Anyways, if I'm using more than one driver, why not?

but why use 12" drivers? For not much more, 15" drivers offer a lot more displacement. And for not much more than that, there is now a very reasonably priced 18" driver that will give even more. The less a driver has to move, and the less power it need sto reach your desired output levels, the better for maintaining low distortion.

I've never looked at it this way before. It's always been my understanding that bigger drivers were more massive and harder to control thus less accurate. Every 15" sub I've ever heard has sounded like a car sub gone wrong. Has anyone here ever built a sub and put it against top quality commercial subs and noticed an improvement? Is it really possible for a big driver to deliver good transients? At this point I am beyond convinced that it is possible and getting more excited by the minute.

As for the Q, it sounds like if I build a box that is too big, I will end up with a Q lower than .707 and the only problem that causes is the possiblilty of botteming the woofers and needing to eq the midbass a little. Is that correct? If so that makes life a **** of a lot easier. Thanks again for all the info, I will try to post some sketches of my design and my room when I find some time. btw.. What is REW and BFD?

 

[Exocer]

BFD: Very affordable parametric equalizer. Will be able to help successfully EQ mid bass back into your sub (although if you don't go way below .707, you may not even have a desire to EQ the mid bass...its when you get to below critical Q of .5 that you'd really need to start worrying about mid bass deficiencies)

REWrogram used in conjunction with a mic/spl meter to measure frequency response in your room so you can get an idea of what needs to be EQed or how flat/peaky your frequency response is.

Click below to find out more.
http://www.hometheatershack.com/forums/bfd-rew-forum/

Steve is right about going with larger drivers. The only drawback of going with larger drivers is that they will usually require a slightly larger box than the smaller drivers. These quality larger drivers are just as articulate as their smaller relatives when placed in the right size box. Often people buy 15" subs, don't know anything about Qtc, and throw these drivers into small itty bitty boxes this causing the final Qtc to be above the magical trade-off point of .707 (the tradeoff is between transient response, low frequency efficiency).

My Avalanche 15" sealed subwoofer is ~around .55 Qtc. At this point there is no reason to boost the midbass and it crosses over just fine to the rest of my system even up to 80hz without sounding empty in the midbass. It doesn't sound like a car sub in the least

 

[SteveCallas]

It's always been my understanding that bigger drivers were more massive and harder to control thus less accurate.

It's just the opposite - the larger the driver (all else equal), the lower the distortion and the more accurate the reproduction.

Has anyone here ever built a sub and put it against top quality commercial subs and noticed an improvement?

Yes, more people than I can keep track of.

Is it really possible for a big driver to deliver good transients?

Not only good, but better than smaller drivers.

 

[thxgoon]

Thanks for all the great replys. You've got me seriously considering an LLT with 18" drivers. How do you model an LLT in Unibox or WinISD? Do you 'pick' a frequency and design from there or does that frequency come from other constraints? Lastly, I've been scouring the internet for 18" drivers and there doesn't seem to be any available. Anyone know where to look? Thanks again!

 

[SteveCallas]

FiCar Audio is selling the Q18 driver which is nicey suited to a LLT. I gave some tips towards the end of my "LLT Explained" post on how to go about designing a LLT. For that Q18, I'd take a look at ~625 effective liters with an 8" port that is 25" long being fed with 800-1000 watts.

 

[thxgoon]

That Q18 looks awesome! I've done some initial Unibox modeling and the results are a bit puzzling. For a sealed alignment I'm loving what Unibox is spitting out for this driver. Very flat and great output. 20hz at -7db! Wow. The vented alignment is set for an Fb of 15hz and this is where it gets puzzling. The output and response is substantially worse. Here are the graphs.

Sealed alignment:

Vented Alignment:

Also in the sealed alignment (no matter what driver I use) I get an excursion graph that looks like this:

Why don't you think the drivers are anywhere near xmax?

Box sizes for these 18's are getting pretty big. I'm thinking 2 LLT sonotubes will be the best route But while I said size was of no concern, I was hoping not to have to corner off a whole section of my room for the sub. So I did some basic math. Since output is related directly to displacement of the drivers I compared the Titanic 12 to the Q18. Using their published xmax values:

With 8 12's I get a displacement of 1331 cubic inches.
With 2 18's I get a displacement of 1078 cubic inches.

So in theory the 12's should extend deeper and play louder than the 18's in a sealed alignment. Going back to the 'bigger driver equals lower distortion' theory, here the 12's have a lower xmax so won't be traveling as far and they have less mass. Wouldn't one think this would give a more accurate sound? It would also allow me to build smaller boxes and give me more flexibility in placement. At this point the graph of the sealed 18's is very exciting and I like the idea of LLT. I'd like to get some accurate modeling of an LLT before taking the plunge....

 

[SteveCallas]

The vented alignment is set for an Fb of 15hz and this is where it gets puzzling. The output and response is substantially worse

Yeah, something is off in your model - it should look like the attached.

Since output is related directly to displacement of the drivers I compared the Titanic 12 to the Q18. Using their published xmax values:

With 8 12's I get a displacement of 1331 cubic inches.
With 2 18's I get a displacement of 1078 cubic inches.

Ok, but each 12" Titanic is $160....that means you couldn't even get two for the price of one Q18. Using your numbers, one Q18 can displace 539 cubic inches and one 12" Titanc can displace 166 cubic inches. $310/539 = about 58 cents per cubic inch displacement. $160/166 = about 96 cents per cubic inch displacement. If you intend on going sealed, size shouldn't really be an issue with either option.

 

[WillyD]

The Q18 has a linear displacement of about 399 cubic inches.So that is about 78cents per cubic inch of displacement.

And a driver I would consider is the 15" TC-1000. It has a linear displacement of about 234.5 cubic inches. That is about 73cents per cubic inch (including shipping).

 

[SteveCallas]

Well ****, if it's all about displacement and nothing else, multiple MJ18's would take the cake, no? onder:

 

[WillyD]

Not by enough for me to choose them over the TC's, but hey, whatever floats your boat. :dumbcrazy:

 

[thxgoon]

I was actually beginning to look at the TC1000, I just don't like the silver. Whatever... in the sonosub design you wouldn't see it anyway.

I finally got a good model of a Sonosub LLT and wow! If it really performs the way these graphs show it will and sounds as good as you all claim, then this is going to be an absolute winner. I may not even need to build a second one. Here's some pics.

This is the Q18 LLT (green) vs 4 12" Titanics (yellow)

Here is max SPL with rated power..

The 12's are obviously louder in the >30hz but who cares, this is not necessarily where I'm looking for the oomph. But check out the response for the LLT. WOWOWOW

Something I'm a bit concerned about is the group delay. I don't know much about it so maybe someone can shed some light on it for me. In this picture you can see the delay for the sonosub rises dramatically as frequency reaches tuning.

What do you think? As of now my only concern is that of building this mega structure. sonosub.exe specifies a 9 foot enclosure with a 24" diameter! That won't even fit in my room. How big do they make those things?

 

[thxgoon]

Ok, so after a little research I found that as long as the group delay is less than 1 or 2 cylces of the driver, it is not detectable by the human ear. The group delay for the LLT is under this threshold by 100% so we're good to go there. Out of curiosity I decided to model an LLT with 4 12" driver. I thought maybe by doing this I could get away with a smaller box and I was right. Check out these graphs. Yellow is the Q18, green is 4 12" Titanics in an LLT tuned to 16.7hz.

Ignore the red graphs, that is a sealed enclosure for comparison...

The 18 has the flatter response but check out the box size. 400L vs 838L. With the 18 I was looking at a sonotube taller than the ceilings in my basement and 24" in diameter. I can get 4 12's in a box half the size of the 18 and according to the SPL plot I can get the same level of output with rated power. In addition I can mount them Push-pull and potentially get more accurate sound. The Dayton's might be a bit more expensive but I was willing to pay this in the first place. If it means the same or better performance in half the box size it would be worth it to me. Am I wrong in these assumptions? What do you think? Thanks.

 

[SteveCallas]

Why is your Q18 design so big? Try 625 liters with an 8" port that is 25" long and 800-1000 watts.

 

[BoomieMCT]

Yeah, a 800+ liter enclosure might be "optimal", but the reduction in performance might not be as big as you think to use something smaller. Since you are planning on investing at least a few hundred dollars into this play around with the volume and tuning a bit more to find somethat that does what you want in the space that you have.

 

[Brian Bunge]

The magnet controls the cone movement. So assuming the driver has a properly designed motor system it will have equal if not better sound quality than a smaller, lighter cone. You have to look at the entire desig, not just one or two parameters. It would be like saying my Civic is faster and quicker than a Corvette because it's smaller and lighter, which we all know is not the case.

 

[thxgoon]

Thank you all for your great replys! The information on this forum and on the AVS forum is invaluable!

I think the final design will look something like this.

2 sonotubes each with:
15" TC1000
400L Sonotube
15.6hz tune (6" dia 18" length)
EP2500
BFD
Some really cool bassy movies:bigsmile:

Size and budget got the best of me. While I'd love to build a dual 18" setup, it would just take up way to much room. A dual 15" setup will work much better and is well within my design constraints. 8 Titanics were a little expensive. I talked with TCSounds yesterday and they said the 15" TC1000 should be shipping again next week. What do you all think?