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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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#429 ·
John with this type of burst testing even a 1" dome tweeter can withstand many kilowatts of input in certain frequency ranges. These same power inputs can cook even an LMS coil easily. It is only the very short duration that allows them. Every sub is going to be amplifier limited at a lot of frequency bands.


I like Ed's old charts. I had already been listing the limiting factor for long term signals on my Excel charts. It does make sense to include it for cea2010 as well.
 
#432 ·

Quote:
Originally Posted by Ricci /forum/post/20788760


The signal is the standard CEA2010, 6.5cycle duration, Hann shaped, 1/3rd octave bursts. 100 and 125hz are very short duration. Nothing more than a blip. The program usually just records them like that.


I ran out of amp at 16hz, 40, 50, 80, 100 ,125hz. There were driver distress noises that made me leery of extra level at 20,25,31.5hz despite low distortion results. Distortion limited 10 and 12.5hz and 63hz. That is if I remember all of this right.

Excellent results.


Is there a DIY version of this test, or was that a specific package that you used?


I'd love to be able to use the same methodology on my builds - there is a TON of information presented there.
 
#435 ·
"Is there a DIY version of this test, or was that a specific package that you used?"


a "behind the measurements" would make for a great technical article ricci, if you don't think that would be stepping past the line.


----------


"i would put this bad boy in a bedroom"


something about that statement doesn't sound quite right. :)
 
#436 ·
Mike,

The program runs under a software package called IgorPro. Powerful and very deep software for audio. It is sort of like a measurement and graphical presentation tool kit. What I mean by that is it is sort of open for the user to set up routines or experiments or setup what you want to do. It is $600 for a license if I remember right. The experiment that runs this was created by Don Keele. It is not available for purchase anywhere still. You would also need some other minimum equipment to run it foremost being an SPL calibrator.





Quote:
Originally Posted by mph33
over kill or not... i would put this bad boy in a bedroom lol
I will give the plans to anyone who wants to build it. All you have to do is pm me your email.


I would like to put 2 in the back of a shortie Astro van and see what would happen on a termlab at 16hz myself. Just for fun of course.
 
#437 ·

Quote:
Originally Posted by Ricci /forum/post/20563812



Now this is a real curiosity. When I first put the cabs together and applied power I took some close mic graphs. These all show a 100hz dip that was not apparent in the simulation. I then ran the pair lightly in a pa set-up for a few days. Fast forward...I get one of them outside to test it and lo and behold the 100hz dip is gone and between 90-110hz the response has changed. The 100hz dip is no longer there. I freak out thinking perhaps I had damaged something in this cab, or the driver, or both, which wouldn't have been out of the realm of possibility considering the beating bestowed on it, so i run inside and take a measure on the other cab and it is now missing the 100hz dip too. That one hasn't been used very hard at all. I thought that perhaps I somehow had EQ engaged during the original measurements but there is no way. The drivers were brand new and had never been above about 2v so perhaps they had a major break in and this is responsible but I find that a hard pill to swallow. The cabs are 13ply BB with pocket screws and are PL'd together and built by a professional cabinet shop who's owner owns DTS-10's and is familiar with speakers so I have a hard time believing that a panel came loose and shifted enough to cause the response change either. I am at a loss to explain it really. I have attached a couple of measurements illustrating this as well. The 100hz notch is easily seen in the original measurement. The other one is the current response where there is no longer a 100hz dip. Very odd.
Atleast it is a response improvement.








Attachment 214743
Attachment 214742

Just doing some catching up and noticed this post. Since I was reading through, I remembered this post before it:

Quote:
Originally Posted by Ricci /forum/post/20520984



Bentz,

These quick and dirties are with the mic positioned middle of the mouth and coincident with the plane of the side. The cab is rotated tall with the mouth off of the floor and the whole thing is on a furniture dolly rolled outside onto a dock.

It seems likely that your mic was exactly 1/4 wave distance from the floor (33-34") for your close mic graph and otherwise for the measurements that show no null at 100 Hz.


Without the dimensions, I'm just taking a probability stab at this. Maybe you can verify the distance of the mic-to-floor dimension in the 100 Hz null measurement vs the non-100 Hz null measurements?


To verify if this is the case, you could repeat the exercise (measure one with mouth up and mic centered in mouth).


Bosso
 
#438 ·

Quote:
Originally Posted by bossobass /forum/post/20847009


Just doing some catching up and noticed this post. Since I was reading through, I remembered this post before it:




It seems likely that your mic was exactly 1/4 wave distance from the floor (33-34") for your close mic graph and otherwise for the measurements that show no null at 100 Hz.


Without the dimensions, I'm just taking a probability stab at this. Maybe you can verify the distance of the mic-to-floor dimension in the 100 Hz null measurement vs the non-100 Hz null measurements?


To verify if this is the case, you could repeat the exercise (measure one with mouth up and mic centered in mouth).


Bosso


Well....That is a possibility I guess. I am stabbing at the distance from the floor to the mic but it was probably around 40 to 45". I wouldn't expect the reflection to cause that strong of a cancellation but maybe so. I also had a thought about a reflection from the mouth back into the horn which would also be 45" or so. I only plan to do one more test on these that requires me to drag one outdoors. If I remember I will try to check this again. Right now these are under JBL 4675-c's which aren't too easy to lift down off of them.
 
#439 ·

Quote:
Originally Posted by Ricci /forum/post/20845666


Mike,

The program runs under a software package called IgorPro. Powerful and very deep software for audio. It is sort of like a measurement and graphical presentation tool kit. What I mean by that is it is sort of open for the user to set up routines or experiments or setup what you want to do. It is $600 for a license if I remember right. The experiment that runs this was created by Don Keele. It is not available for purchase anywhere still. You would also need some other minimum equipment to run it foremost being an SPL calibrator.

Hmmmm, that looks like some seriously COOL software. Unfortunately, the price tag and limited availability sorta puts it out of my league.... I don't think I have invested $600 for all of my acoustic measurement gear, including the laptop.


Maybe I can grab some spectrum screengrabs in REW and overlay the CEA2010 limits? I'll have to look into alternatives. Shipping them down to you for testing might get a little expensive, not to mention placing more of a burden on you (which is just uncool....). I would like to know how my designs measure up, and CEA2010 is as good a standard as any.
 
#441 ·
That would be awesome. I guess I could make that request. I have already generated some cosine-gated CEA test tones with GoldWave using the instructions from Linkwitz's site.


Working on tabulating the thresholds. I think I can actually do this with Excel and the SPL measurement tools I have already if I can get a FRD-style text dump of a spectrum measurement.


Edit - and--- it looks like I can from REW.


Will post results as soon as I get this sorted.
 
#443 ·
Good luck Mike but I am not sure how close the results would be. There has been significant differences shown between even the "official" setup used by different parties. I tried to use ARTA and a peak hold setup to capture something similar previously and that was just not the same. Some of the results were quite close and others were way off between the 2 different ways. If you want to try I would suggest getting the signal correct first. Good luck!
 
#445 ·
Ricci what kind of Hpas would be needed for this sub if used in a home with a Pi18?


I doubt anyone would ever need a Hpas in a home environment but I wanted to ask. I have been looking at maybe getting a pair of the Pi18's and building a monster like this would be a good way for me to finally be able to hear which I would like to have. (Pi18 sealed or TH)


And should I send you a PM for the plans when closer to a build?


Thanks
 
#447 ·

Quote:
Originally Posted by maxmercy /forum/post/21341206


For steadystate tones, this ROCKS.


All we need now is to be able to track distortion components in REW like HolmImpulse can....


JSS

Agreed. I mentioned this to John long ago. If he can get harmonic distortion measurements during the sweeps implemented that would be huge for me. I use ARTA for that now. STEPS is great but way too brutal for high power. The other thing that I asked him about was beefing the generator up even further and allowing multiple sine wave output. Similar to NCH tone generator. Also the ability to do ascending or descending sweeps for measurements would be cool. REW has come a long, long way already.
 
#448 ·

Quote:
Originally Posted by chrapladm /forum/post/21340709


Ricci what kind of Hpas would be needed for this sub if used in a home with a Pi18?


I doubt anyone would ever need a Hpas in a home environment but I wanted to ask. I have been looking at maybe getting a pair of the Pi18's and building a monster like this would be a good way for me to finally be able to hear which I would like to have. (Pi18 sealed or TH)


And should I send you a PM for the plans when closer to a build?


Thanks

Something near 14Hz and 18 or 24dB octave roll off would be recommended.


Sure.
 
#450 · (Edited)
@Archaea


you probably know, but the gjallarhorn has a constant width, so all the internal panels are whatever width the cab is less the two side panels.


ricci posted the plan.
all that needs to be calculated are the panel lengths depending on which panels you want to but up against which panel at the panel intersections, though somebody who has built one may have the panel dimensions already on hand.





since it is a scale drawing, you could always 'front projector' it onto a piece of paper at 100% scale, trace it, and simply measure with an old fashioned yardstick. :)


there is also a gjallarhorn v2 if you like a center located horn exit.
 
#451 · (Edited)
@Archaea, @Gorilla83

Here is the v2 template from the print. If either of you want I can just send you the print PDF or DXF if you want. If you can handle large assemblies or parts files there are all sorts of options there as well. I'd need you to pm me your email though. I have a couple of guys I need to send the plans to next time I get a chance anyway.

Also I just read back through this thread and there is some great discussion going on at the beginning. I've learned so much since then. Also realized that the Gjallarhorn version 1 is now 4 years old. Dang.
 

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#452 ·
Also I just read back through this thread and there is some great discussion going on at the beginning. I've learned so much since then. Also realized that the Gjallarhorn version 1 is now 4 years old. Dang.
My Gjallarhorns had their 1 year birthday a couple of months ago. I am amazed that more people haven't built them with all of the bassheads we have running around here on AVS. This has to be one of the best gifts to the DIY community - thanks again for sharing, Josh. I just bought a couple of UXL18 in case I need to build two more (probably will)
 
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