Ported/Bandpass horn with a V18
Printed From: Speakerplans.com
Category: Plans
Forum Name: New Projects Forum
Forum Description: Forum for new speakerplans projects, in memory of Tony Wilkes, 1953 - 2014
URL: https://forum.speakerplans.com/forum_posts.asp?TID=67172
Printed Date: 19 April 2024 at 9:45pm
Software Version: Web Wiz Forums 12.06 - https://www.webwizforums.com
Topic: Ported/Bandpass horn with a V18
Posted By: kevinmcdonough
Subject: Ported/Bandpass horn with a V18
Date Posted: 19 May 2012 at 5:49pm
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hey Have my THAM15 build to be getting on with just now (been held up with my time being spent on house renovations, hopefully weekend after next have a long weekend off and will attack them then). But after that, the plan I've had in my head for my next build is to do a full horn loaded, fairly narrow dispersion system. For the tops im deciding between MT122 or MT130 (although leaning towards 130) with the BMS coax comp on a 40 degree limmer horn. Even with a very high sensitivity 12" driver the big comp will only be being tickled with one 12" section so will have a second in its own cab that can be stacked in to really open the whole thing up. For subs, as I mentioned in a previous post about ported horns this is probably the way I'm going. Wanna keep it 1 way if I can, but it only has to hit a solid 40Hz doesn't have to go super low as its mostly live music I work with. Needs to get to 120 or higher to meet the tops. Wanna get maximum power density so that I have have a fairly neat stack of 3 subs and two tops that will pump, and so am thinking of a bifrucated horn as Martin seem to have done with the MLA, allowing me to get two 18" drivers in one box that still has horn sensitivity. While a full FLH would be great you just cant get two drivers in without the box being ridiculous, so its ported or tapped. I may worked on a tapped horn in the future but while you save on the box volume taken up by the rear chamber, the path has to be longer and more complicatedly folded to fit the shape I want, and when it comes to the bifurcating stage this will be much more complicated as the second driver now introduced into the mouth area will take up volume and change things. The ported horn should be much easer when it comes to this point, and so this is where I started. Taking a little inspiration from Marc O's MPH-46 (http://hornplans.free.fr/mph46.html) I made the path length a little longer and mouth much wider (almost double) and played about with the front chamber volume to get this....... (Single horn, half space)  and this...... (same horn, changed to 0.5 pie to simulate 4 horns)  Bare in mind that you can add 3db to these because each box will have two drivers eventually (but the response will be the same as the main horn path and mouth area will be the same. The input perimeters for this were.....  Now this is only in very early stages of messing about but my reason for posting is I want people to pick holes in the design or suggest changes. While i've played with ported horns in the past I seem to stumble across these results far too quickly and they feel too good to be true. Excursion seems to be OK, little peak a 50 hz or so but nothing that's a problem, I do realise its a little TOO bassy at the lower end, 40 to 60 and I would have liked to bring that down a little. But while making the front chamber smaller done this it also seemed to INCREASE excursion a bit which I cant quite understand lol. k |
Replies:
Posted By: Teunos
Date Posted: 19 May 2012 at 7:21pm
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Is the sim made for half of the cabinet with 1 driver or for the whole cabinet with only one driver? Assuming the latter since half a cab with a mouth of 4000 sq cm is an afwully big cabinet, frequency response will not stay the same. It will change dramatically when adding a second driver. It is simmable by entering 2 parralel drivers in the Tools menu> driver configuration. It's very not true that you can just add 3db to the plots shown. ------------- Best regards, Teun. |
Posted By: Teunos
Date Posted: 19 May 2012 at 7:31pm
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About the increasing cone excursion. Basically a ported horn is a superposition of a horn and a helmholtz resonator. The mouth size, throat size but mainly the length of the horn will determine its lower cutoff frequency. Simming the excursion of your cab with an absent port will result in the cone excursion of just the horn. Then by adding the port the cone excursion will decrease around the tuning frequency which depends on the port area, port length, chamber volume and loading properties (the speaker combined with the load of the horn). Overlaying these two excursion plots will yield approximately the effective cone excursion. Decreasing the chamber volume whilst keeping the port area and length fixed will result in a lower port tuning frequency Thus increasing cone excursion between the tuning frequency of the port and horn. The thing to manage with a ported horn is to gain a good balance between the tuning frequencies of both the port and horn. Getting them too close together will result in phase incoherence, pressure loss and a one note honky sound. Getting them too far apart will result in excessive cone excursion destroying woofers and missing parts of the spectrum inbetween tuning frequencies. Also keep an eye out for the group delay as it can spike very high very easily. ------------- Best regards, Teun. |
Posted By: kevinmcdonough
Date Posted: 20 May 2012 at 9:44am
hey Yeah the plot above would be for (almost  ) the whole cabinet. Bifrucated horns is something I'm just beginning to investigate just now, but from my understanding the theory is that you design one 'half' of the horn and then when you combine them, the idea is that even though they share a common horn section each one only 'sees' its own path to the mouth and so you essentially have the same response (as each horn still sees the same expansion etc) but just twice the pressure. Pics may be easier. This is a horn that Charden on here tried.  Its a dual 15" bifrucated design. Its not exactly what i'm looking at, obviously the driver here is reverse mounted and mine is intended to be ported, but its close enough in layout for the example. From the limited information I can find on it the idea is that you design a single horn, and then lay it out like this so that each sees one copy of that single path.   So the left driver would see the green path, and the right driver would see the blue path. Even though you have two horns, you don't get the lowering of frequency response that you get by placing two completely separate horns together, because obviously your not doubling the mouth area. But you do get the increase in SPL because you are doubling the drivers, and as each one sees the same expansion as it would in a single horn then response stays the same....... .....at least in theory As I say there isn't a huge amount of information on this on the site and I know charden wasn't massively impressed with this prototype so there is some fudging and experimentation needed, particularly I would assume around the joining point. So yeah I figure if I just go straight to doubles and there is a difference between the sims and the measured results, i wont know if its the original horn design thats the problem, or the act of joining them. So my plan is first to design a single horn and build a prototype or two, get it to where I'm happy with it, and then start to experiment with joining. That way least I'll know that the problem is with the joining and not the initial design and can start to modify accordingly see if I can get it fixed. k |
Teunos wrote:Posted By: rich, ind.st
Date Posted: 20 May 2012 at 11:21pm
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that is very reminiscent of the decware wicked one design, i should imagine it will hoof ------------- music is god |
Posted By: ceharden
Date Posted: 20 May 2012 at 11:45pm
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Incidentally, that design was a big flop. Not necessarily because of the bifurcation bit, I think I just got the whole horn tuning wrong. Front chamber was too big etc. I still think the bifurcation bit is worth playing with though. However the ported horns I went on to design were a much bigger success and much simpler.  I've had a few attempts to design an 18" version like some of the Martin Audio designs but never got the simulations to look good enough to be worth building. |
Posted By: ceharden
Date Posted: 20 May 2012 at 11:51pm
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I think you might be better using Akabak rather than Hornresponse and thus modelling the bifurcation properly. It might look scary if you haven't played with it before but actually it's not too difficult to write the input scripts. |
Posted By: kevinmcdonough
Date Posted: 20 May 2012 at 11:56pm
yeah well that's the idea As I say, within one cabinet, even though your doubling the drivers you don't get the increase in low end cos overall your still having the same mouth area overall (though I'll be running 3 a side of the final design so will get some extension over the single double driver cab, although not much cos of the ported nature more just an evening out and a reduction in ripple). But long as your response is OK from that one cab, you do get the increase in sensitivity from the double driver so by the time you have it up at full power so your getting the extra 6db for only 1.5 times the cab size rather than 2x, because they're sharing the largest part of the horn. Yeah I remember you weren't happy with the design chris that's why I wanna have a good play with the cab as a single first and make sure that's working OK before trying to double it. If I cant get the single to work properly in my own "from scratch" design I do have in the back of my head to have a look at the WLX design and take some inspiration from that, already a proven ported horn and pretty much the same overall volume as this design, and work from there adjusting a little to suit my needs. However is basically down to cash, the B&C drivers that work in that are in the £300-350 range and if I can make a design work the way I want using a £200 V18 instead, then over the twelve drivers I'll need to buy that a noticeable saving (enough to just about cover the 4 big BMS coax comps i'll need for the tops!  ) and means I have a spare one here already for initial testing.k |
Posted By: kevinmcdonough
Date Posted: 20 May 2012 at 11:58pm
yeah I was thinking that once I get into the bifrucating port I should move to there. I've played with it a little before and its not to bad, I pretty much had my head around the way it works and with asking a few q's on here as I go I should be able to manage it. LOL biggest pain is having to spend some time installing an XP virtual machine to run it  k |
Posted By: Teunos
Date Posted: 21 May 2012 at 7:20am
About the bifurcation, i doubt that what you have sketched is what happens in reality. When you would put a panel down the middle of the horn, the whole cabinet is basically two halves put together. I think you should be simmulating half of the horn and treat that to be half of the cabinet. e.g. the left situation should be equal to the right in my opinion. ------------- Best regards, Teun. |
Posted By: snowflake
Date Posted: 21 May 2012 at 10:43am
| you can sim multiple drivers in hornresp so just model the full cab to save confusion |
Posted By: Teunos
Date Posted: 21 May 2012 at 11:56am
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Could you upload a drawing of the cab (with measurments) to see how you actually came up with the parameters? Just using the multiple drivers tool will too probably give incorrect resultst, as it's highly unlikely the total throat area for the two drivers combined is 470sq cm. Like this it's just a game of guessing.
------------- Best regards, Teun. |
Posted By: kevinmcdonough
Date Posted: 21 May 2012 at 12:47pm
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hey Well, this is the mystery of bifurcated horns There isn't a huge amount of info on the forum about them and when i came up before I i tried to ask no one seemed to know. On the one hand there is the theory that each driver sees a single path to the mouth as I outlined above. Seems to be born out at least in looks by the few bifurcated horns there are like the Wicked One and the Martin Philishave. So you need to design the horn as a single first witth a single driver (which is what my posting for the V18 is above) and then keep the same expansion rate so the horn interacts with the drivers TS specs in the same way and hence gives the same frequency response, but gets double the pressure and hence the increase in SPL from the second driver. On the other hand there is the idea of do you just double everything, the full mouth area and horn path, for the two drivers so you end up with a horn twice as wide all over. This to me would seem to be expanding a bit too quick and so would change the response of the cab, but maybe I'm thinking about it wrong. Or is the answer indeed somewhere inbetween? LOL k |
Posted By: kevinmcdonough
Date Posted: 21 May 2012 at 12:49pm
yeah but the problem is (and I could be wrong I'm certainly no expert on it) that i dont think it has the facility to have this type of design where the drivers have their own chamber, ports and initial horn section, but then feed into a final horn section for the rest of the path? k |
Posted By: Keen
Date Posted: 26 April 2013 at 12:07pm
cheers |
Posted By: kevinmcdonough
Date Posted: 26 April 2013 at 12:31pm
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hey double click on the actual word (Hyp, Con etc) and it rotates through the options. k |
Posted By: Keen
Date Posted: 26 April 2013 at 12:58pm
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cheers kev, but only con, exp, par. no hyp |
Posted By: Centauri
Date Posted: 26 April 2013 at 1:34pm
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Press the "H" key when the field is highlighted. |
Posted By: PavelP
Date Posted: 26 April 2013 at 10:18pm
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It seems to me there's negative expansion near middle triangle. |
Posted By: infrasound
Date Posted: 26 April 2013 at 10:36pm
Yes, this is right - divide down the centre.
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Posted By: infrasound
Date Posted: 26 April 2013 at 10:50pm
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The pressure from each driver will average out in the middle of the hornpath. If one driver fails, then you can have the situation seen in your blue and green pictures. Although, you'll have more problems than that, as the failed driver will start to absorb some energy - and not equally at all frequencies. The only reason you would put something in the middle is bracing, aside from cabinet resonance - it doesn't affect the acoustics - if perpendicular to wavefront and at low frequencies. If you were to put a brace in the middle, you'd have to brace the brace (ooer) as it would tend to resonate a little lower than liked (cross brace). Unless you were sensible and used 20mm of alu rod - can be just as effective, lighter and won't resonate
 . You'd have to be clever with fixing the ends though |
Posted By: Keen
Date Posted: 26 April 2013 at 11:59pm
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