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Discussion Starter #1
Hi, i just picked up a 12" lms-4000 driver and i've been doing some modeling with winisd to try to find the "best" possible enclosure.

My goal is to get clean and accurate sound down to about 20 Hz (maybe a little lower). spl isn't an important factor for me as i've got a new baby in the house and my HT doubles as the family room.

i'm thinking about a 6.5 cu. ft. enclosure (after taking driver volume and bracing into account) tuned to 12.5 Hz with dual 4" ports (approx 32" long) and using an ep2500 to power it.

I'd like some feedback from those of you who've been doing this for a while as this is my first diy sub.

also, do i need to add any damping/padding inside the enclosure?

thanks, i appreciate the help.

Josh
 

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Hey there Josh,

The LMS-4000 drivers are great, but the one problem they present is that they prefer large enclosures. 6.5ft^3 is too small to tune to 12.5Hz unless you use a single 4" port. Now, I might do this since you say you don't care about spl, you shouldn't hear any chuffing with even a single 4" port especially because you'd be tuning so low.

Or you could just build a 4-5ft^3 sealed enclosure because with just a little room gain you'd be pretty close to, if not flat to 20Hz. But the 6.5ft^3 tuned to 12.5Hz with a single 4" port (I'd use the heavily flared PSP ports) or a slot port with sufficient port area looks pretty good in WinISD. You'd only need one channel of your EP2500 to power it well (assuming you already have it).
 

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Discussion Starter #3
WillyD,

Thanks for the response. I thought the winisd modeling looked pretty good for the 6.5 cuft too. what's the advantage of using a single port instead of 2? i was modeling 2 because it kept the port velocity down well below 27 which seems to be the (arguably) point where port noise starts to become an issue.

thanks again.

Josh
 

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Well the disadvantage of the two ports you used in your simulations is that they would have to be really long. You were correct in wanting to bring the port velocity down, but you neglected the port length. Your 1st port resonance would be low and you'd have to figure out a way to fit the ports in your enclosure.

So thats why I'd either go with a single well flared port, a slot port, or I'd go sealed.
 

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Discussion Starter #5
ok, gotcha. thanks again for the assistance.
 

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Discussion Starter #6
a question on damping/padding. is it necessary and if so then how much and how exactly does it affect effective volume. is this stuff necessary only in order to reduce box resonance in the event that it's insufficiently braced or is there another purpose?

thanks.
 

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The purpose of lining the walls is to dampen the sound and stop the sub from sounding "boomy". It does not change the effective volume. The panels of an insufficiently braced sub will still vibrate whether or not there is lining on the interior walls. Lining will not fix a poorly built box.
 

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Discussion Starter #8
thanks guys. i've revised my design and now i'm looking at about 8 ft3 internal after bracing, driver and port subtractions. looking to tune this down around 12 Hz with a 4" port. i'm thinking about the ep2500 for power, but haven't bought it yet so if there are any other suggestions i'd appreciate it. anyone see any issues with the design thus far? thanks.
 

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Discussion Starter #10
Mike,

thanks for the advice, i've been wondering whether or not that was going to create problems. at this point i think i'm going to drop a 6" port in there instead. it's a lot longer but that's really no problem since haven't started construction yet. It looks like the port should be about 60" long and has a 1st resonance around 112 Hz but since i'm planning on crossing over no higher than 80 Hz that shouldn't give me a problem right?
 

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If you plan on using a port of substantial length as you have mentioned (60") it is likely you would need to fold the port within your cabinet to achieve this length unless you cabinet is 60" in one direction of course. If you plan on taking the time and effort to create a slotted port I suggest rounding the corners within your slots to at least 3/4" radii to allow for minimum impedance of airflow.

This is the type of rounding I am referring to:
http://i184.photobucket.com/albums/x320/z38gm/Speaker build/SubwooferBuild017.jpg
http://i184.photobucket.com/albums/x320/z38gm/Speaker build/SubwooferBuild016.jpg
http://i184.photobucket.com/albums/x320/z38gm/Speaker build/SubwooferBuild010.jpg

Do note that any area where air would be sucked in or blown out has these rounded edges both in concave and convex manners depending on location.

With first port resonance at about 112Hz you could create potential issues, but with proper planning you shouldn't have any issues. With use of a sufficiently high order crossover you will be able to stop any leakage into this realm. With my now complete build I will be using a 4th order crossover at 80Hz to achieve this end and my first port resonance is at about 118Hz. Another step you could take to combat port resonance with a port of this size is taking dowels with 3/4" radius and placing them sparingly within the port*. This will increase rigidity slightly while having minimal effects on air flow.

*To give you an example if I were to have used dowels in my build pictured above there would be two pieces per fold.
 

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I didn't model anything, but maybe a PR system would work better for you?
A passive radiator system would likely decrease build complication due to lack of the need for a slotted port. In terms of sound quality, if a properly designed slot port is used there will be virtually no audible differences between the slot port and a properly implemented PR system.
 

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Discussion Starter #14
Ava,

thanks for the input. right now i'm mulling over doing a cylindrical 6" port within the cabinet or designing a slot port to accomplish the task. i was very impressed with the work you did on yours and that's encouraging to me but this is my first diy and i'm trying not to get too big a head in my ambitions. that said i may ignore my inner doubts and go for the master piece on the first attempt cause apparently the ego is winning. at any rate i'll keep you all in the loop and start posting pix as i start cutting. thanks.

JJ
 

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Ava,

thanks for the input. right now i'm mulling over doing a cylindrical 6" port within the cabinet or designing a slot port to accomplish the task. i was very impressed with the work you did on yours and that's encouraging to me but this is my first diy and i'm trying not to get too big a head in my ambitions. that said i may ignore my inner doubts and go for the master piece on the first attempt cause apparently the ego is winning. at any rate i'll keep you all in the loop and start posting pix as i start cutting. thanks.

JJ
I would strongly suggest the slot port. It is good experience and results in a higher quality design technically and in certain cases [high SPL at tuning frequency] audibly. The secret to any quality build is planning, planning and well planning. The build I linked was my first as well, before that I was simply a student of theory as I wanted to ensure my design was optimal before I cut a single piece of wood.
 

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Discussion Starter #16
thanks ava. what were the dimensions of the port you made? the more i think about it the more i like the idea of the slot port.
 

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thanks ava. what were the dimensions of the port you made? the more i think about it the more i like the idea of the slot port.
Sorry for the slow response I missed your post. I used a 12.5" wide x 3" deep x 56" long (total) port. Since the port was folded over I just calculated volume and ensured the two were the same.

Just like with regular round ports the length will be very specific to the cabinet and driver you are using. I would suggest making the port as long as possible while ensuring your port resonance will be out of the passband (don't forget that crossovers leakage). Also, another step that I suggest taking is using at least 3/4" rounds on all edges within the port that could inhibit airflow in either direction (in or out).

If for some reason I ignore a question again feel free to PM me and remind me to answer ;).
 

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Discussion Starter #18
Ava,

Thanks again for the update. I've done a little bit more modeling in WinISD and given the size of the box i'm planning, i'm looking at a slot port with dimensions of 24" x 1.25" x ~55". This gives me an area just slightly larger than a 6" cylindrical port so port velocity is reasonable and the port resonance is around 110-120 Hz which ought to be fine with an 80 Hz crossover i think. Does this sound right to you? thanks.
 

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It should be fine, as I think I previously said you might want to put a few wooden dowels in the port for extra support just in case. I braced my port in another way which allowed me to comfortably not use them.

One thing to note with port resonance at around 110-120Hz you will need to use a fairly steep crossover, such as a 4th order crossover, to insure no leakage into the range of port resonance. Other than that there are no issues with it as that is where my first port resonance occurs as well.
 

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Discussion Starter #20
i was thinking that i'd probably throw a few dowels in there just for added support, though i'm planning on bracing them up pretty well anyways. it's all starting to come together in my head now so hopefully pretty soon i'll actually get to start cutting! thanks for the advice.
 
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