Big changes made. Information from a variety of posts is now summarized here.
well, submaximus has taken a turn...hopefully for the better. after farting around with this for several hours, a pretty simple plan emerged. i was shooting for something that would be simple and doable, yet be big and have big performance. it is still quite large at 2x4x4.75 feet, but not too many internal panels and 3 of the 6 panels are at simple 90 degree angles to the walls. bracing of course would be required and is not shown. the corner deflections would be a good idea for the first few turns from the mouth into the horn, but it is tough to say how much difference they will make after the first few.
there are at least 2 folks who have expressed interest in this one, which is why i am bringing it back from the dead.
this horn was optimized for the uxl18 driver, so it probably works equally well with the lms ultra (but we can check that), and it works pretty good for the stereo integrity ht18. i haven't checked the um18, but that driver probably requires something a little different. 2200 watts takes the driver right to 30mm at the first excursion peak above the low corner. for the si18ht, 1100 watts takes it to 23mm at the same place. destiny must have had a hand in this one. :-)
it is an exponential horn with a straight last section (no expansion). this is one way to bring up the bottom end by a few db vs. a full exponential horn.
excursion minimum occurs at around 18hz and the -3db off the corner point is about 15hz, so i'm not quite sure what to call it...maybe a 16hz horn?
one interesting thing about this design is it holds response pretty well down to around 30hz, which is where many rooms tends to start benefitting from frequency dependent room gain. so in an average room the rolloff down to 16hz or so might actually be pretty flat. won't know until it is built and measured.
consider this a "first draft" and not a final plan. if anybody can double check it as much as possible, i'd appreciate that.
for those who aren't familiar with how the hornresp models translate to actual performance, the peaks in the response tend to not be quite as pronounced in the actual results as they are in the model.
so without further delay...re-introducing
SUBMAXIMUS!
response, 2200 watts into 4 ohms, 2 pi space 1m (smushed):
fold/plan:
the idea with the fold plan is to "section" off the expansion into 4 flare rates. with 4 rates calculated to provide an exponential flare rate, changing the hornresp model to "par" will provide the same results as "exp". of course, we are one leg short in hornresp, so i'll have to manually calculate the appropriate expansion for leg 1 (purple). otherwise, we should be on target. 7.4 cm appears to be the cross section with an exponential flare rate at that point. L23 is a combination of the purple and the blue.
hornresp numbers:
response 1w1m 2 pi space:
response with 1100 watts into 4 ohm SI18HT driver 2 pi space 1m:
excursion uxl, 2200 watts into 4 ohms:
excursion si 8ht, 1100 watts into 4 ohms:
here is the submaximus horn with uxl driver vs. the uxl driver in a sealed enclosure of about 6 cubic feet.
at 16hz, the low corner of the horn, the horn has about 15db more sensitivity than the sealed enclosure. at the upper end of the bass, the gain is about 8db sensitivity.
here is the sealed enclosure max spl at 30mm and/or 2200 watts.
at 16hz, the max spl is about 107db. submaximus with uxl peaks at about 124db at the same frequency.
compression ratio is 3.4:1. my guess is that this is fine, but would like input there.
also, actual width is about 25.5 inches depending on material thickness. the 4x4.75 are exact outter dimensions. the 2 feet width is internal. bracing is not shown, but is REQUIRED!!
final scale drawing:
internal measurements and color coded boards to see how the butt joints work:
one method for arranging the panels on 4x8 stock. extra for bracing would be required. the corner deflectors are not included in the cut plan.
bracing is not shown either. the particular method for bracing doesn't matter as much as that it is well braced. this guy is going to generate a lot of pressure, so brace it very well!
the final model came out about 1db lower in sensitivity with 0.75" plywood. not different enough to repost all the plots. if really well braced, thinner stock can be used, but the cut plan is for 0.75", so keep that in mind. a little adjustment here and there would be require if using half inch for example.
the side panels completely enclose the other panels. in other words, start with a side panel on the floor. draw the pattern on it. place the panels on the side. when all panels and braces are in place, the other side with be placed on top to close it up.
there are only three panels on an angle. all other panels are right angles.
(c) 2014 LTD02. All Rights Reserved.
if you want to use this plan for a commercial design, please drop me a note first. otherwise...have at it!
comparison of full martysub with 18ho driver 1100 watts (red), submaximus loaded with 18ho driver 1100 watts (black), and submaximus loaded with uxl18 driver 2200 watts (blue). the effect of the stronger motor on the uxl can be seen in not just providing a higher total response, but also a different shape. the 18ho loaded submaximus looks pretty good though too... :-)
OLD & OUTDATED
Original post for posterity:
As the title says, this is a first rough draft of a large front-loaded horn for the Stereo Integrity HT 18" driver. It seems to be a pretty darn good value, so I was curious to see what it could do in a large horn.
This one is 4 feet tall, 5 feet deep, and 2 feet wide (similar in size to
the one that Myggpower's buddy in Germany built a while back
second pic). It appears to work well. With 1100 watts power, excursion is in check everywhere except just below tuning.
The low corner is around 16hz or so. Sensitivity is pretty good at 95db 1w-1m-2pi space at 32hz and still at 90db 1w-1m-2pi space at 16hz.
Bracing isn't shown. Interior fold isn't too complicated either.
Frequency response would need a little e.q. to take care of a couple of upper bass peaks, but no big deal there.
With typical room gain kicking in around 30hz, this one should be pretty flat down to 15hz or so where a highpass filter would be advised around 15hz or so (there is a short note on how to do this with the iNuke DSP or the DCX2496).
Two of them should be able to provide upwards of 130db bass down to 16hz or so in even a largish room. Not bad for two drivers that cost a couple hundred bucks each, a cheap Behringer amp, and some wood.
Anyway, here are some notes. This is a first draft and as always there may be errors, so comments/criticisms are welcome.
I guess that I have to give it a name...so this one shall be called
SubMaximus!