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21" Ported Horn design idea

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kevinmcdonough View Drop Down
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    Posted: 22 August 2018 at 12:19am
hey all


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! LOL

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!.....

(ported horn in black, Othorn in grey)








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


Edited by kevinmcdonough - 22 August 2018 at 12:30am
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Speaker Sol View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Speaker Sol Quote  Post ReplyReply Direct Link To This Post Posted: 22 August 2018 at 12:49am
Have you checked out the Skhorn designed by the same designer as the othorn. 

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.


Edited by Speaker Sol - 22 August 2018 at 12:52am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote gen0me Quote  Post ReplyReply Direct Link To This Post Posted: 22 August 2018 at 1:47pm
How are multiple boxes comparing?
How you gonna make the first joint of the horn side?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kevinmcdonough Quote  Post ReplyReply Direct Link To This Post Posted: 22 August 2018 at 1:52pm
Originally posted by Speaker Sol Speaker Sol wrote:

Have you checked out the Skhorn designed by the same designer as the othorn. 

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.

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
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kevinmcdonough Quote  Post ReplyReply Direct Link To This Post Posted: 22 August 2018 at 2:02pm
Originally posted by gen0me gen0me wrote:

How are multiple boxes comparing?
How you gonna make the first joint of the horn side?

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






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Post Options Post Options   Thanks (0) Thanks(0)   Quote gen0me Quote  Post ReplyReply Direct Link To This Post Posted: 22 August 2018 at 4:27pm
Where 2 parts of plywood join at around 170°
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kevinmcdonough Quote  Post ReplyReply Direct Link To This Post Posted: 22 August 2018 at 4:40pm
Originally posted by gen0me gen0me wrote:

Where 2 parts of plywood join at around 170°

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
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Post Options Post Options   Thanks (0) Thanks(0)   Quote needmoresound Quote  Post ReplyReply Direct Link To This Post Posted: 22 August 2018 at 8:16pm
I look forward to measurements. I did made something similar some years ago, but double 18" and way higher tuned (-3db at 45hz). 
double 18 ported horn
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. 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote kevinmcdonough Quote  Post ReplyReply Direct Link To This Post Posted: 25 August 2018 at 1:05pm
Threw together a quick Solidworks model, some 3d pics......






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

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Post Options Post Options   Thanks (0) Thanks(0)   Quote mobiele eenheid Quote  Post ReplyReply Direct Link To This Post Posted: 25 August 2018 at 2:36pm
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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kevinmcdonough Quote  Post ReplyReply Direct Link To This Post Posted: 26 August 2018 at 7:00pm
some bracing and detail added.....





Originally posted by <span style=: rgb251, 251, 253; font-family: Arial, Helvetica, sans-serif; font-size: 15px; font-weight: 700;>mobiele eenheid 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.

Yeah I redesigned the baffle slightly differently after thinking more on this. have not resessed the driver any, so the driver is screwed flush to the wood, but then have taken out a circle 8mm deep where the edge of the actual surround and moving cone would be. This in effect creates an 8mm spacer. Whether that would be enough space would needed to be tested, but the driver already doesn't have loads of room before the magnet is touching the hatch door, so hopefully that should do it. 

k



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Post Options Post Options   Thanks (0) Thanks(0)   Quote mobiele eenheid Quote  Post ReplyReply Direct Link To This Post Posted: 26 August 2018 at 9:11pm
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
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