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DIY bass horn build...Up next

69K views 462 replies 50 participants last post by  wireburn 
#1 ·
EDIT: This is for PA, not home audio or HT.



Ok. I've never built a bass horn yet and after experiencing Labsubs and lately the DTS-10's I've gotten the itch to give it a go. The ported 21's are about a week away from being wrapped up and I've finally decided on a horn simulation that I'd like to turn into a pile of sawdust and wood...I think.
I figure I'd better get the ball rolling if I expect to get this built before weather turns bad for the winter.


I've run through a ton of simulations in the last 6 months and there are about 20 possible scenarios that I like and about 8 that it was really tough choosing between for the build. I weeded that down to about 3 possibles by eliminating the ones involving drivers I don't already own. Why buy if you don't need to? I ended up deciding on a 380L net, 30hz FLH using the LMS 5400, over a 380L 30hz B&C FLH and a 30hz 380L B&C TH.

The performance of each is close enough on paper to make it a toss up really.


For the curious here's my thought process. The other contenders were involving dual xxx12's in a TH, TC's PA5100 and the 18sound 21NLW9600. The 18sound 21 and the B&C are VERY similar in performance when using the same enclosure, basically interchangeable IMO with very small differences in modeled performance, so that eliminated the 18sound because I already own the B&C. The PA 5100 also models very well, but differently in the same basic horn parameters as the 21's but obviously needs some changes in the overall form factor due to being a smaller diameter deeper driver. Again since none of them really showed a notable performance advantage on paper and I already own the B&C's...The dual xxx 12 sub I would really like to build (sub bass gargantua), but it's the most complicated, expensive, heaviest and largest. Maybe later. The LMS I decided on over the B&C, because it's the less obvious choice and more of a known quantity at this point. Plus I'm already doing a new build for the B&C's. The build I am doing will be leaving some of the LMS's potential on the table. It'd be better in a larger 20hz FLH or an 18hz TH, but I don't want to build anything so large and difficult to move first off. If I can't easily fit it in the back of my Jeep with the help of 1 other guy it was eliminated this is also why I ended up with a 30hz corner. The LMS doesn't like TH's so small tuned so high.





Anyway. This is what I've got. Nothing is set in stone yet. I need help reviewing the model for mistakes and I could especially use some help with folding the horn up. I've never folded one, so help or comments from more experienced guys would be much appreciated. All opinions are welcome.
BTW the model is intentionally a very basic single expansion rate conical (parabolic now) type to hopefully keep the folding and build as simple and straight forward as possible.




Input parameters
Attachment 183905


Phase and delay
Attachment 183906


1W into the minumum impedance in half space
Attachment 183907


124v input in half space
Attachment 183908


124v driver excursion
Attachment 183909




 
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#353 ·

Quote:
Originally Posted by Ricci /forum/post/20457407


Ho there stranger! Haven't seen you around lately.


Yes I too am concerned about the center section of the horn. We will see won't we?



You didn't miss the "other" horn. It is next in the pipeline.

Yeah, I've been pulled in other directions the last few months.


I know we have talked about it in emails, but for everyone else I'm not really worried about how it will work at "normal" levels. 105db-120dB peaks a couple of meters back in a median room. It is at war levels that I am interested in seeing how it works out. In high voltage PA applications, or the way some of the people around here abuse these things.


Glad to know I didn't miss anything else.
 
#354 ·
These cabs should be in tomorrow.


I will be getting a quote on the Otherhorn soon. Im just going to call it that. That one is for the 21sw152 and it is in a 24x36x36 cab. Its a TH and the cut off is 25hz. The response knee is at about 30hz. It is more of a typical pro sound type deal with about 10hz extra extension.


Mike,

Yes the horn provides the impedance matching with the air. That is where the lion's share of the potential efficiency gains come from. The throat is very important as well obviously. If your throat configuration is jacked up the horn is no better than scrap, but once you get the throat close to the range where it seems to bring the total response together all of the further tweaking in the world is not going to drag an extra 4db broad band sensitivity out of it. This cab or any other. I spent a LOT of time designing this thing. The horn is simply to small to to realize a 10db broad gain over the vented alignment I used for comparison. 6db average is what I could get. If you give me a cab 400% bigger than the vented then it is possible. In a cab of the same size as the vented I don't think you would get much more than 3db extra. Twice the cab seems to give maybe 6 db. Maybe its possible but I definitely don't see a 10db gain unless looking at specific frequencies in isolation. Certainly not at the vented enclosure tuning. If anybody has a simulation that pulls that off I would love to see it. I am by no means an expert on this stuff.
 
#355 ·
#359 ·
Just a small update. The cabs have been coated with duratex. 3 gallons for the 2 cabs. Hopefully I can get a driver loaded and get some preliminary measurements in the next couple of days. A close mic FR check should tell me a lot about how close these will be to the goal.





 
#361 ·
ricci, that 45 degree lip really gives it a finished look. little details sometimes really make the difference.


looney, compliance may not even be on the spec sheets, i don't recall. i've noticed that i often have to work backwards from the derived parameters to get to it (of course, i let winisd do the math).
 
#366 ·
so whats the result? Don't keep us waiting !!!!!!!!
 
#368 ·
Nice, that 4x10 aluminum Hartke cab is one of my faves....what preamp you driving that CE4000 with?
 
#371 ·
Scott...LOL! p



Guys I don't really have a whole lot on this yet. I got it buttoned up at about 11:30pm last night just in time for the nightly tornado warnings and lightning storms.
I ran about 5 sine sweeps through it, some pink noise, played a couple of sines at specific frequencies and ran about 3 songs through it.


I did get a close mic FR. Here it is compared with the simulated response.







Well in some ways I am a little disappointed that the top end is not as good as hoped, which would've been merely rough to begin with instead of plain old beat up. I was hoping for it to be useful up to 110hz maybe with help from EQ. On the other hand I am quite happy that it is as close as it is. I've never designed a horn before and this is a big and complicated one. I had no rough draft so it might not have worked at all! I could've gotten much worse. Also I had to expect that the sheer amount of turns in the middle section would have a detrimental and somewhat unknown effect. I'd suspect that these plus the internal resonances formed inside by the cab geometry have some large part in it as well. On the other hand as I had suspected it would the actual cab tuning came in a little lower than designed. This measurement was really rough and quick and at a pretty hot level, so I have no idea how the actual 1W efficiency will stack up. After I measure the other cab and do an outdoor gp test with a known voltage input I will have a better picture.



Here is a quick measured impedance. This wasn't really calibrated so the exact impedance magnitude may be a bit off but it shows that the peaks are close to the simulation and that the actual loading is a little bit lower in frequency than as designed. I did not recalibrate and I was using much longer leads than usual. I will have to redo this later with a proper calibration as well.







Some other quick observations are that these will definitely need a good dose of eq applied as mandatory and /or crossed over low like 60hz or lower. The cab does not want to let go of some notes. I do not have any damping at all in the cab currently I think there is a need for some. I can only reach the throat and the final 2 corners but I will see if this helps out at all. Also the cab is solid as a rock except for the bottom by the access panel where it is quite resonant. I knew this would be the case since the nature of the design didn't really allow any bracing in there and it is right by the driver back wave. The positive about that is that it is the bottom of the cab and in my application will be sitting on the floor with the full 300lb? weight on it. It won't be a problem in that case. I didn't wring the thing out but I did give it a little juice and thus far it doesn't appear that there will be any broken cone from horn pressure shenanigans. Its an angry little beastie. It slappa da bass around like it just don't care mon!
. I can't really say that I am surprised by much of this. Par for the course so far.
 
#373 ·
I am not sure what the cause of the 100hz null is. 100hz is a roughly 11.25 ft long wavelength. This is a 22 ft long horn with many turns and sections. It is most likely some interaction with the cabinet dimensions causing a cancellation. Maybe it is the driver placement relative to a return reflection. Perhaps I can determine it later. That is actually the main thing that bugs me is the suck out at 100hz. Peaks can be cut heavily but nulls are not so easily dealt with.


I did throw some rough eq on it last night to beat down 63hz and 91hz and slapped an 80hz bw 4th order on. That made a big improvement in cleaning up the sound. Output is not a problem. I am starting to wish that I had a way to watch movies in there so I can give it LFE channel to sink its teeth into. Music just doesn't have much for it. Hopefully outdoor gp testing will be next weekend.
 
#374 ·
Blah blah...



I tried out a few things to see if I could get some worthwhile improvement yesterday.


I tried adding a reflector panel at 45 degrees in the last corner before the driver to see if it would affect the upper end response and perhaps help out at 100hz...No dice. Negligible impact. Scratch that from the list.






While I was at it I tried some damping in the throat behind the driver and a generous amount in the last 2 corners before the driver. The throat damping did nothing of note really other than sapping about a db of efficiency. With all of the damping in both corners and in the horn throat it did clean up the response some and knock down the horn resonances at 63hz and 90hz quite a bit. However it also caused an efficiency loss of nearly 3db across much of the bandwidth!
No thanks. I don't think the slight improvement is worth the hefty loss of output which is what these big guys are all about. I'd rather just use EQ to knock the edges off. It would be needed with or without the damping anyway. You can see the efficiency losses in this graph.






Here is the effect that all of the damping had on the decay of the horn. It did improve it somewhat but once you bring the level back up to match what it was prior to loseing the efficiency it isn't as much as hoped. Again not worth the efficiency sac IMHO.

 
#377 ·
I lose 3db damping my dual THTs with pillow stuffing in the mouths. But I gain no cavernous reverberations from the mains that are close by....Audyssey calibration is a nightmare of reverb. I run them with very little power anyway, so no big loss, I listen at around 10db below reference to preserve my hearing...


JSS
 
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