have a design here that I've been messing about with for the past couple of months on and off. Since I'm not gonna have any time to really develop it any further or make any sawdust any time soon, thought I'd stick it on here and see if anyone fancies taking a run at it. 

It all started when I read a thread about the Othorn (big 21" tapped horn based around the B&C 21SW152). I vaguely knew it existed before, but had never really paid it much attention. However one bored afternoon I read through the thread and was much more taken by it, and by the reactions people were having about it. It seemed like it was a MUCH better design than I'd initially thought, much more worthy of attention than I'd realised, so I started messing about with the design a little, trying some different drivers and things in it and imagining I might have time/money to build a big pile someday. 

However I've always been partial to ported horn designs and so had a quick mess about in Hornresp, thinking that I would see what I could do in a ported horn that was the same sized box and compare it to the tapped horn version. Using the B&C sw152 and a carbon coned 21" eighteensound driver (the ones I had been trying in the tapped horn versions I'd been messing with) I was getting decent results, but nothing that blew me away. 

However I read an article or a something about B&C's newest driver the 21DS115, something popped up on Facebook or whatever, and on a whim decided to try it in the ported horn design as well, just to see what would happen......

....and thought that cant be right!  That's significantly better than the Othorn, right across its frequency range! 

However having checked my sums and looked at everything, double checking all my stuff it seemed that yeah, this seemed to be a bit of a magic combination. 

Playing about with it and refining it a bit, I was able to shrink it down to a box that was a chunk smaller than the Othorn, shaving 40 or 50 liters off of the overall volume of the box, not having quite such a compression ratio for the driver saving a little pressure on the cone, while still having what looked like a much better response!.....

An ever so slightly lower corner, and much more sensitivity across the passband. And much more upper bass response too, will have a bit more kick than the Othorn while still having the same depth, so should hopefully work much better for live music as well as the deep electronic stuff. And no big spike in group delay like the tapped horn has, so should integrate much easier and cross over much easier into whatever tops were being used. 

Ultimately its not to say that its gonna have a much higher SPL when running at full tilt: both designs are really limited by excursion rather than power handling, and so will both reach similar overall SPLs at the end of the day. But with the higher sensitivity the ported horn will do it with less amp power needed and maybe a little more grace than the Othorn. 

When it came to actually trying to fold it, I messed about a few times and tried a few different layouts, but the one I ended up most happy with was the following. It's not a milimetre perfect following of the hornresp sim, but it's very close and gives a good place to start. 

The first, parallel section of the horn path would be a Martin letterbox style throat, so would have two angled pieces of wood put in expanding in the other plain. Where the dotted line starts would then be where the horn was the full height of the cab and then expands normally.

The port is on the other side, there is some play here in terms of how big to make it. I made it a 10cm shelf port with some flaring at both ends, but this then requires it to be an L shape to get the correct length. However this is much more area than some other designs, and there is probably some scope to reduce that a bit to make it a straight port if someone wanted. However being this big does mean that when you put handles in that side wall it shouldn't make too much difference to the tuning, less percentage of volume taken away from the port than it would be if it was smaller/thinner. 

The baffle piece that the driver is mounted too would have some holes cut in the 4 corners, similar to what Martin do with the WLX, so that the chamber takes up all of the white space, it opens up into both the section where the port feeds into and the section that the horn wraps around, and it all just becomes one big chamber to get the correct volume. 

Driver in the centre-ish keeps the weight fairly balanced and even for transport, and other than a bit of horizontal bracing in the port and horn path, all of the vertical bracing is really just taken care of by the construction and it should be a pretty solid cab. 

Hatch could be on the front piece of wood facing the audience, and if you really wanted to go crazy the magnet etc is close enough to it that there could be some scope for some heat sink fun to reduce power compression etc. 

Anyway, just a first go at a design and some possibilities, and as I said while I'd love to develop it further but not on the cards any time soon, so feel free to comment or suggest modifications or changes, or anything else. 

K

Very interesting design, though the layout is different and its a double, it looks quite similar to your design. In terms of port and horn size .

It was designed around the Ipal but other drivers also look promising.

How are multiple boxes comparing?

How you gonna make the first joint of the horn side?

Yeah, yeah had read up on the other designs he has came up with, including the Skhorn. Obviously the big difference is that the Skhorn is a double 21" horn, and while it could be split in half and made into 2 singles, each single would be a little smaller than the one I've designed above and wouldn't go down quite so low or be quite so sensitive. But it's also a great design.

K

Multiples look good. Obviously you don't get the same low end boost as you would with true horns, but it definitely still looks good. Here's 3 in parallel (against a single in grey).

If i were to get time to build some someday, then 3 stacked to get to a good height with a mid-top (or pair) on top is probably how I'd most commonly set up.

In both cases, it'd need a little touch of flattening around 50-60Hz, but with that added in and the crossover slope pulling things down around 100Hz or whever you set it, you'd be left with a pretty flat response all the way from 30 to up over 100Hz.

And not sure what you mean, which horn part?

K

aww ok, yeah its like 176 degrees lol, only a 4 degree angle. hadn't really thought about construction specifically at this stage, but would probably biscuit joint the two pieces together, clamped with plenty of glue, and then use lots of filler/sealant to make sure the join was airtight to keep the chamber and horn path separate. Once all done just fix them into place in the overall design as a single piece. 

K

https://ibb.co/g4rCJK

In simulation it gave incredible output. But when in use at some locations it did not work out well, it could be related to the placement. 

I did measure it, but I do not have the graphs anymore. If I remember correctly the horn part did his job, great output above 80 Hz, but below that noting special (just a regular bass reflex output). So at the end you still need an extra double 18" to get the low end on the same level as the midbass and could better have just 2 regular double 18"bass reflexes. 

So for your case, hopefully the 30-70 Hz part is as strong as the >70 Hz region. 

I ended up making the speaker 5cm wider overall. While the driver could just about squeeze onto the baffle and line up with entry into the horn, it left the holes a little small that feed from the baffle into the other parts to make one big chamber. Especially on the side that feeds into the port side, they were pretty small to the point they would have had some sort of tuning/resonance of their own. While playing with this at a future date and creating some sort of double tuned double chamber design might also be fun, for this one I wanted it just to be a more basic ported horn. So the holes are as big as possible on the baffle and should make all three areas act as one big chamber......

Then a little more detail of the horn expansion. Initially the sidewalls of the horn are parallel and the horn expands vertically with the two slanted pieces until it gets to the full internal height of the cab. After that then the expansion is made by the changing angle of the wood so it expands horizontally as normal....

 

Obviously to be a viable product it'd first need to be tested (especially the port tuning and length. The flared ends add some unpredictability to the tuning and it won't match exactly to calculations, as will the fact that it's along a sidewall so the length is virtually extended a little on the inside entry. So it'll be a little trial and error to get that right) and it'll need a lot more detail in terms of hatch design on the front face panel, handles added, castors and stacking things, pole mount hardware etc etc. But it's a start. Not something I'll get to any time soon, but maybe next summer.

K

mobiele eenheid wrote: Don't forget about adding a spacer ring or a double (or triple) baffle, so the driver can hit Xmax freely and preferably Xmech before it hits the wood.

An extra 8 mm space sounds like it might allow the 21DS115 to hit the wood and Xmax simultaneously, which sounds to me like an expensive mistake.

You can double up the baffle in the other direction too (where the horn is). Look, 15 or 18 mm less horn length isn't gonna be noticeable in a measurement but 15 or 18 mm more excursion is a huge difference.

Johan

 

Thanks for the kind words.

I really enjoy the Skhorn sub and it was a long journey to get there and to this type of cabinet alignment using the newer types of long xmax, low Qts drivers. I eventually got frustrated with both FLH's and TH's size, folding and response limitations and found this type of design for the M.A.U.L. and Skhorn towards the end of 2014 as I recall.

 

If I might offer some advice...Make sure you are doing your simulations with complex Le or Le simming engaged in HR. Either will be more accurate than not.

 

Good luck with the cab design.

hey

as I said in the initial post, it was an idea that I was playing about with, but I'm realistically not gonna have the time to take it any further any time soon, hence putting the plans on here to allow someone else to run with it if they want.

K

Was discussing it on another forum we bounced about a few ideas, and there was a suggestion that making it an offset horn would put less strain on the driver. Modeling it up and considering a few possible layouts it actually seems like it's a better design this way, easier to construct at the very least. While I've tuned it slightly higher and it doesn't drop down quite as low as the other design, just about touching 30Hz at -3db is more than enough for the work I do (live music mostly) and think it's better overall. 

Another discussion was about port area. Around 400cm2 as is in this design (two 6" pipes) is about as big as you can go before starting to think about having to fold things, but people suggested it was very small for a big capable 21" driver such as the 21DS115. I'd like to ideally see a bigger area too, but it doesn't seem all THAT small when you compare it to other commercially available designs. Many of Void's designs use a series of 3 or 4 smaller pipes that give about the same, if not slightly less, port area, and things like Martin Audio's various ported horn designs also use ports that around the same size give or take. 

BassBox Pro, the program I most often use for reflex speaker design work, seems to think it's ok, and thinks that at 1700Hz, it's RMS, it'll only be pushing air at around 21m/s in the ports. You need to push the power up to over 5000w before you begin to hit what it considers the danger limit of 34 m/s.

I'd be interested on hearing people's thoughts on the port size, but I suppose it's something that can only really be answered for definite with a prototype and some testing, which I might try and do over the summer if I get a chance. 

I'm also not massively precious about the design. While I don't have any actual plans or cutsheets drawn up on paper, I'd be happy to zip up the solidworks file as it is for anyone who has access to that software, and they can get all the panel sizes and routing details and could have a go at a prototype if they wanted. 

(design is shown compared to the Othorn tapped horn in grey)

Oddly I never managed to get a similar design to look good in simulation using an 18".

Im No designer, but this is a design i could be tempted to have a go at. 

But when you mention port size and air velocity being on the edge, i do get some concerns.

But as you state, its getting a problem with 5kw of power. Thats alot of power! 

Would love to have a go at this mate!

... although slightly lower corner at 27 Hz would have been perfection 

1) larger chamber all else the same

2) larger chamber and horn extended through 90 degrees (over the port exits) and along width of box. Assume ports are relocated + ignore external dims for now. 

3) Same as above but with chamber remaining the same.

Asking a lot I know - until lockdown is over I can't jump on a buddies laptop to try myself. 

Not asking for sims just interested in bouncing ideas around.

TIA

Looks like a similar idea:

In all other quick sims, I can not reach such 2,83V sensitivity figures.

According to the measured response peak sensitivity is around 111/112dB @+-150Hz, which does fall out of the desired bandwidth but still is pretty high.

If I may ask, which design are you talking about regarding the vent also tapping in the horn mouth?

Isnt that very unlikely, since you need lab horn size for real 30 hz horn loading (in multiples of four!!)

I would have guessed the reverse 

Which Martin model do you refer to? I'm not aware of any similar design.

2,6m seems doable with those dimensions.

I'm toying with the idea of designing something of a similar nature, and have been considering attempting a larger double 15" loaded design following the design principles of the skram.

I'm not too experienced in cabinet design, so would appreciate any input.

In my head this could be more cost effective power density, and potentially higher sensitivity? Or is this a silly goose to chase...