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2x 18" LMS Ultra 5400 in 27 cubic foot 15hz vented enclosure


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Most of you are familiar with my current setup which is pretty over the top and think I'm crazy for wanting more. Regardless of that, I do want more. I feel the sealed enclosures I built left a lot on the table between 10-35hz that I can pick up by going with a vented alignment. I'm going to try to pickup a few sheets of ply tomorrow and get this build going. I'm starting with one enclosure to test and tune with, then will build three more.

The outer dimensions of this measure 48" long, 46" high, and 30" deep. Ports will be oriented on the sides as I will be stacking these.

Since there is some debate on the vent length, I'm starting it out at 40". I will test and add more as necessary, with the end goal being a 15hz tune. Do not try to build this until this is complete. I will update the dimensions/cutlist with the proper sized inner vent piece when complete.


This ended up being tuned to ~14.7hz with an effective port length of 55 inches.  Cut list is linked below.


I will not be adding any damping. The enclosure will be braced by 1" dowels and/or scrap ply. It will be a challenge getting bracing in while having the port in a position where I can add more length to it, but I'll figure it out when I get there. I'll be using some kind of 3/4" ply for the build. These are going to be heavy.

Sketchup file: download
Cut list: download


Visual stimuli below.

Modeled at 6200w with 13.5hz 3rd order butterworth highpass.


SPL compared to current sealed subs with 8000w input and 11hz 3rd order filter (I have massive room gain in this area, filter prevents over excursion below 7hz).







Port Velocity:














results vs sealed:


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Tomorrow I'll put some drivers in it and get the tuning proper.  I'll see about taking some outdoor sweeps, but not sure how possible that will be.  These things are really big and unweildy.  At least they fit through my door :)


I'm also going to spackle over the pocket holes in the port area.

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The bracing looks a little on the light side to me...I'll be interested to see if you note any resonance or flex issues once you get those to war volume. My guess is probably not. If you do you still have plenty of room to retrofit some threaded rod in those big ole cabs.   :)  


Your impressions compared to the old sealed setup will be very interesting I bet.

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Well, I tried measuring this in my garage, but that didn't go too well.  I'll have to bring this outside tomorrow.  Not much I can do at around 3AM.  The amp here is an unknown, no idea what the rolloff is like, but I assume it will work well enough that I can find the actual tuning frequency of this box.


mdat attached with two sweeps.  Green is with doors open slightly.


1/3rd octave smoothing with model overlay



1/3rd octave smoothing




no smoothing



group delay



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Looks like port length modeling in winisd is good even for slot ports.  I need to extend this port a bit now.  Will follow up later once that's done.


There's some obvious rolloff from this amp as well, but it's still apparent the corner is ~17hz.  The rise is probably from the stupid 'bass' knob on this amp as well.  Unfortunately, it's all I have available to easily test with.


Going to lengthen port 15" now.  This will be fun.



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