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Sealed dual LMS 18" 5400 build

post #1 of 176
8/22/11 at 1:00pm
Thread Starter 
I currently have a 5400 + 2 VMP build that has plenty of 15-80hz output, but is definitely lacking in anything below 15hz. My goal now is to make some serious gains in the 5-10hz department. I guess you could say it's just the next step up for me.

http://www.avsforum.com/avs-vb/showt...0#post20514030

For sealed subs, this build definitely sticks out: http://www.avsforum.com/avs-vb/showthread.php?t=1314884

I like the design of the array layout since the depth of the cabinet is not excessive. The depth of my current cabinet being around 33 has been an annoyance and I've had to change the positioning of the main speakers and TV to accommodate and also not look so funny. I know there are advantages of the dual-opposed design, but due to cabinet size that's not in the cards right now.

I do have some questions regarding the array design since I won't be using the insane powerful LG clone amps like notnyt has.

First off, what are the advantages/disadvantages to having both drivers in one sealed chamber in the cabinet opposed sealing each off from the other?

notnyt is using one amp per cabinet since the power is there, so I can see why one large sealed chamber makes sense. What if I were going to use a pair of amps to drive the cabinet, like one ep4000 per driver, or run one larger amp in stereo like my Peavey 4080hz rated at 2k RMS per channel at 4ohm? Would I want to seal each driver from the other, or does that cause a decrease in performance?

Thanks!
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post #2 of 176
8/22/11 at 5:44pm
one reason to make a dual opposed cabinet is that it can be relatively lightweight and not vibrate. when the cabinet vibrates, you are losing energy that should be going to creating sound.

the most affordable way to get 5-10 hz content is with an infinite baffle type setup...essentially a very large sealed subwoofer where the drivers don't need giant motors because they aren't fighting internal cabinet pressures.

also with infinite baffle, you hardly need any power, again because you aren't fighting against internal air pressure of a cab.

you can read about many projects here: http://ibsubwoofers.proboards.com/index.cgi
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post #3 of 176
8/22/11 at 9:38pm
He wasn't asking about dual opposed, he was asking about having two drivers sharing the same air space, vs separating them.
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post #4 of 176
8/23/11 at 6:05am
Quote:


My goal now is to make some serious gains in the 5-10hz department. I guess you could say it’s just the next step up for me.

I think you need atleast 4 LMS5400s. I have 2 LMS5400s and even though they give me decent output down to 10Hz I believe its still not enough when it comes to having 10Hz performance that makes a real difference.
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post #5 of 176
8/23/11 at 6:15am
Will this me in addition to what you have now?
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post #6 of 176
8/23/11 at 6:31am
For now it means I have limited < 15Hz performance. Too many other projects but Im adding 2 x 30 amp circuits this week so who knows?? If I find a deal for 18" drivers, I might do it.

OP understands that 10Hz performance is 100% about displacement/power requirements. Displacement is Xmax * Surface Area which should be > 25 Liters to have enough output for 10Hz performance to be meaningful.
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post #7 of 176
8/23/11 at 7:55am
Thread Starter 
Quote:
Originally Posted by penngray View Post
I think you need atleast 4 LMS5400s. I have 2 LMS5400s and even though they give me decent output down to 10Hz I believe its still not enough when it comes to having 10Hz performance that makes a real difference.
Agreed.

At the moment I have ZERO performance at 10hz. Since my PR's are tuned to 16hz I have a subsonic filter at 15hz.

From what I've seen from graphs, before room gain, and IF both drivers receive 2k RMS each, I should be around 103-104db at 10hz. When the money is there I'd build an identical enclosure and get closer to 110db. After room gain things should be looking pretty good at that point.

So the question, do I seal each sub off from the other?
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post #8 of 176
8/23/11 at 8:03am
Thread Starter 
Quote:
Originally Posted by t6902wf View Post
Will this me in addition to what you have now?
I’m going to re-use the driver that’s in my current DIY build. However, the dual sealed LMS will be used in conjunction with two JTR Caps.
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post #9 of 176
8/23/11 at 10:18am
Quote:
Originally Posted by lukeamdman View Post
Agreed.

At the moment I have ZERO performance at 10hz. Since my PR's are tuned to 16hz I have a subsonic filter at 15hz.

From what I've seen from graphs, before room gain, and IF both drivers receive 2k RMS each, I should be around 103-104db at 10hz. When the money is there I'd build an identical enclosure and get closer to 110db. After room gain things should be looking pretty good at that point.

So the question, do I seal each sub off from the other?
You have a decision, do you just want to maximize output or do you want the ability to possibly smooth out the in room bass response.

The only reason you would go with separate sealed designs is because you want placement flexibility. If you are going just have the subs stacked together then put them in one box for maximum output, minimum vibration (ie. sealed dual opposed). Of course if you like the looks of a single box dual woofers facing you then go that route (ie. Gotta love what Notnyt built )

You just have to decide what your priorities are.

Do you want to see those cool looking LMS5400 drivers?

Do you want to maximize output?

Do you want to try and smooth out in room response?

FWIW, you really need > 110dB at 10Hz to make it meaningful. Will your room gain give you that? Who knows.
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post #10 of 176
8/23/11 at 10:26am
Something else to consider. You mentioned you wanted to dig down to 5hz. I did some testing with my system to see where meaningful output stopped. Once I started to go below 7hz, it became hard to notice the output. Doors would be shaking and stuff would be rattling, but below that there wasn't really much tactile sensation at all. Because of that, I added a steep HPF to prevent over excursion below 7hz.
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post #11 of 176
8/23/11 at 12:20pm
Thread Starter 
Quote:
Originally Posted by penngray View Post

You have a decision, do you just want to maximize output or do you want the ability to possibly smooth out the in room bass response.

The only reason you would go with separate sealed designs is because you want placement flexibility. If you are going just have the subs stacked together then put them in one box for maximum output, minimum vibration (ie. sealed dual opposed). Of course if you like the looks of a single box dual woofers facing you then go that route (ie. Gotta love what Notnyt built )

You just have to decide what your priorities are.

Do you want to see those cool looking LMS5400 drivers?

Do you want to maximize output?

Do you want to try and smooth out in room response?

FWIW, you really need > 110dB at 10Hz to make it meaningful. Will your room gain give you that? Who knows.

This is hard to explain and I'm obviously not asking in a clear enough manner

I have a performance (SPL) question in regards to this: Take the dual drivers in a single cabinet like notnyt's build (both drivers are in the same cabinet with no divider in between. If you push on one driver the other will move since they're in the same sealed compartment). What would the difference be if he put a divider in between them so that even though they're in the same cabinet, their sealed air space is separated. Would there be a performance (SPL) disadvantage?
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post #12 of 176
8/23/11 at 12:47pm
Your question was clear and the answer is no, their will be no SPL differences.

BUT as Penn clearly pointed out, there are performance differences when two independant enclosures are used with different placement over one, large enclosure. Given the response curve of a sealed system without eQ, the difference in room response could be substantial. In other words, build two.
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post #13 of 176
8/23/11 at 1:21pm
Quote:
Originally Posted by mayhem13 View Post

In other words, build two.

I hope by that you meant build two seperate duals. God forbid that he lose the cool factor of an upright dual driver sealed enclosure.
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post #14 of 176
8/23/11 at 2:44pm
Thread Starter 
Quote:
Originally Posted by mayhem13 View Post
Your question was clear and the answer is no, their will be no SPL differences.

BUT as Penn clearly pointed out, there are performance differences when two independant enclosures are used with different placement over one, large enclosure. Given the response curve of a sealed system without eQ, the difference in room response could be substantial. In other words, build two.
I definitely intend on building two, but each will have dual drivers

Until I have enough money for the second I already have two other subs to even out the room response.
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post #15 of 176
8/23/11 at 4:01pm
Quote:
Originally Posted by lukeamdman View Post
I definitely intend on building two, but each will have dual drivers

Until I have enough money for the second I already have two other subs to even out the room response.
Then build four instead.
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post #16 of 176
8/24/11 at 8:07am
Thread Starter 
Quote:
Originally Posted by notnyt View Post

Something else to consider. You mentioned you wanted to dig down to 5hz. I did some testing with my system to see where meaningful output stopped. Once I started to go below 7hz, it became hard to notice the output. Doors would be shaking and stuff would be rattling, but below that there wasn't really much tactile sensation at all. Because of that, I added a steep HPF to prevent over excursion below 7hz.

Interesting and good to know!

On my SMS I'll put a 7hz/48db crossover on it.
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post #17 of 176
8/24/11 at 8:22am
Quote:


Then build four instead.

Then atleast you can still stack them on top off each other.
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post #18 of 176
8/24/11 at 10:38am
Quote:
Originally Posted by gperkins1973 View Post

Then atleast you can still stack them on top off each other.

Why would you want to do that?
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post #19 of 176
8/24/11 at 10:59am
Maybe, Save floor space??
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post #20 of 176
8/24/11 at 11:40am
Thread Starter 
lol, I think perkins thought I was building single driver cabinets instead of the 48" tall duals
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post #21 of 176
8/24/11 at 11:56am
I was thinking along the lines off 4 singles vs 2 duals. Then you would still have the option off stacking the singles to get 2 duals which would give you more flexibility. Hope that makes sense now.
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post #22 of 176
8/24/11 at 11:59am
Im definitely with GP on 4 single boxes. It gives him maximum flexibility. I would never build a dual box myself considering a single LMS5400 4 cuft box weighs almost 200lbs already, real life flexibility is completely gone building those monsters.
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post #23 of 176
8/24/11 at 12:12pm
Thread Starter 
Just out of curiosity, what is the recommended box size for a dual opposed 5400 build? Typical 200L/7 cu.ft?
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post #24 of 176
9/21/11 at 8:42am
Thread Starter 
My current plan is to make the box 22x44x21 for around 4 cu.ft per sub. The front baffle, as well as the top and bottom of the cabinet will be 1.5 thick. I'll add 4lb's of polyfill per chamber.

Each sub will be powered by its own Crown XS1200 for what I'm guessing is around 2,500 RMS each?
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post #25 of 176
9/21/11 at 3:36pm
With 2,500W per driver, I would not worry too much on a HPF for the LMS's. Those drivers can take up to 4,000W or so in a 100L box, so you have no excursion issues to worry about. If you want a little more low end efficiency and considering your power (2,500W per sub), you could give each sub 6cf or so each if you have the space.

Do you know how much room gain you have? Also, mixing your LMS's sealed and the PR Captivator subs you have might give you integration issues.
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post #26 of 176
9/21/11 at 8:14pm
Thread Starter 
I may just pull the trigger on a LG clone amp.
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post #27 of 176
9/23/11 at 7:56am
Thread Starter 
Placed an order for a FP14000 today!
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post #28 of 176
9/23/11 at 7:57am
Did you send $$ direct to them or through someone else?
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post #29 of 176
9/23/11 at 7:59am
Quote:
Originally Posted by lukeamdman View Post

My current plan is to make the box 22x44x21 for around 4 cu.ft per sub. The front baffle, as well as the top and bottom of the cabinet will be 1.5 thick. I'll add 4lb's of polyfill per chamber.

Each sub will be powered by its own Crown XS1200 for what I'm guessing is around 2,500 RMS each?

Did you build the box already?? I would recommend keeping that length down closer to 36inch so that the 1/4wavelength is not close to the operation ranges of the sub.

I use boxnotes.exe to show me what issues I can have with any set of dimensions.
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post #30 of 176
9/23/11 at 8:44am
Thread Starter 
Quote:
Originally Posted by penngray View Post

Did you build the box already?? I would recommend keeping that length down closer to 36inch so that the 1/4wavelength is not close to the operation ranges of the sub.

I use boxnotes.exe to show me what issues I can have with any set of dimensions.

Sorry, I should be more clear on the dimensions. And no, I have not built the box yet.

It will be 22" wide, 44" tall, and 21" deep.
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