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More COVID speakerplanning - Trapezoidal 3-way top

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citizensc View Drop Down
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    Posted: 08 July 2020 at 12:56pm
Hi Guys

The city i'm currently living in has just gone back in to lockdown for at least 6 more weeks so I guess its time for me to design another speaker, a speaker I feel has been missing from the pool of commonly circulated plans. 

A trapezoidal 3-way horn-loaded mid-top; think Martin H3, Funktion One Resolution, turbosound TMS, you know what I mean. If this design works out well and I can find a means of funding it I may build a prototype. 

There have been some attempts to design such a cab on this forum but pretty much all of them don't make sense as a plan for the masses to build. They either require some special mid-horn no one can get, don't play low enough to meet many subs, the kick doesn't play high enough to comfortably meet most mid horns or are a bad size-performance compromise. 

The xtro is good, I have 4 of them and I like them but they are not perfect. The main issues are getting an XT8, build cost (about 700 pounds with out the mid horn, >800 pounds if you can find an XT8), size, weight and arraying a square box. I think they were originally designed as a one box a side solution. 

The PM90/60 looks good but it is expensive (about 920 pounds in drivers on bluearan), only plays down to about 100hz and is not trapezoidal.



My idea is a simple 1+8+15 using the MR8XTN as a mid horn. 

My design goals are: 
1. Trapezoidal, easy to array 2 boxes per side
2. Manageable weight, <50kg hopefully 
3. Sensible size, front dimensions of ~550mm*800mm and about 600mm-700mm deep  
4. Comfortably meet any sub that plays up to ~90hz, eg. Punisher, BG horn 
5. Minimal cost with out compromising sound
6. Have a decent kick, I like techno, don't judge 
7. Drivers integrate well
8. Components are easy to source 


The compression driver is up to personal preference and would be hung in the mouth of the 15 inch horn, similar to the Xtro. I would use a light weight neo like the DE400 on a TD164.

The 15 inch section is tricky, I want it to play low enough to meet most subs, about 90hz but high enough to meet the MR8XTN at about 400hz, this is >2 octaves which is a lot for a 15 inch folded horn. The PM90/60 manages more with 2x12 inch drivers so I think it is doable. I have found such a design is VERY picky with drivers, after reading the specs of literally every 12, 14 and 15 inch neo from every major manufacturer I have narrowed it down to the RCF MB15N351. 

The total driver/hornflare cost is 554 pounds on Blue Aran, I would consider this a significant saving relative to the previously mentioned designs. 

Anyway here is where I am up to with the design for the kick section, the fold would be 1/4 wavelength of the highest frequency I plan to produce. 1/4 wavelength at 400hz is about 200mm. 

My kick - Black 8ohm @ 2.83v , Xtro - Grey 4 ohm @ 2v


My horn

Xtro - Inputted as one horn then simmed as two parallel speakers 



Displacement with 650 watt, 72.11v @ 8ohm 

Let me know what you think, does this look like i'm on to something? Do you have any suggestions before I fold it? I kinda want to get it right rather than folding it literally 20 times like I did with the BG horn, especially as this cab will be trapezoidal. 








Edited by citizensc - 08 July 2020 at 1:05pm
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martinsson View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote martinsson Quote  Post ReplyReply Direct Link To This Post Posted: 11 July 2020 at 5:53am
Hello citizensc

This sounds interesting, I have thought about designing and building a scaled down homage to the tms2, based around the same mid-horn you are suggesting but using a 12" to better suit the width of the mid horn and limiting the downward extension to ~130Hz to keep the dimensions down overall, like the tm2 however, my thinking is to keep the footprint rectangular.

But this is not what you are doing and this is your thread and topic, I just wanted to relate a bit that's all.

A couple of reflections on your proposal:

If intended for the greater DIY community, and by that I'm thinking worldwide, perhaps the mid horn is a limitation as far as availability is concerned, but there are few options, the limmer 8" mid horn springs to mind, not sure if this improves availabillity though, or to resolve it completely design it to be built by the diy'er, but it is difficult to design.

Keep the design and build as simple as possible, a tricky balancing act concerning performance compromises, keeping the build simple makes a very big difference with regards to the reception an number of builds, which in turn correlates to the amount of feedback on the design.

Making the 15" flh section reach 500hz is perhaps doable if limiting the lower extension as per your proposal, but will it sound good, honest question, perhaps it will sound just fine, but my experience is a bit limited as to that application.

Just a few thoughts of mine on the topic, best of luck, keep us poted andstay healthy, br / Martinsson






Edited by martinsson - 11 July 2020 at 5:54am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote fat_brstd Quote  Post ReplyReply Direct Link To This Post Posted: 11 July 2020 at 8:01am
Looking at other similar boxes the classic selenium mid top (as used by many reggae sounds in JA) is a 15" on a short horn, 12" on a short horn and then a 2" and bullets, normally located in the middle with the 15" at the bottom and 12" at the top. The issue with a box like this is the size, they are massive compared to something as compact as an xtro.

My worry with your box is the 15" section, whilst it sims up to 400hz will it sound any good that high or will be the classic boxy sound you get. I have never really liked the way band pass boxes play up that high and if you are going for a front loaded horn with at 180 degree bend in it rather than a band pass assisted style that will also affect how high the box can play.

Have you thought about using a ported straight short horn instead of bandpass? If the intention is for this box to always be used with a sub then the extra extension gained from a band pass arrangement is unnecessary, and using a short horn that loads down to say 100hz with a port tuned to 75/80hz to get a boost at low end of the boxes frequency response and deliver the required kick sound for techno. Using a high efficiency, small voice coil driver with a sensible power handling (4-600 watts rather than a 1200 watt monster bass driver) will mean you get a lot of kick for not a lot of money.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote citizensc Quote  Post ReplyReply Direct Link To This Post Posted: 12 July 2020 at 12:37pm
Originally posted by martinsson martinsson wrote:

If intended for the greater DIY community, and by that I'm thinking worldwide, perhaps the mid horn is a limitation as far as availability is concerned, but there are few options, the limmer 8" mid horn springs to mind, not sure if this improves availabillity though, or to resolve it completely design it to be built by the diy'er, but it is difficult to design.

I was originally planning on designing and making my own mid-horn using the 10NSM76, I went as far as to learn how to use ABEC/AKABAK for BEM modelling. I drafted up a design and modelled it, the directivity wasnt even close to acceptable and I had no idea how to improve on it so I just gave up. I was a little disappointed as I working with fibreglass is no problem for me, I use it a lot at uni.

The MR8XTN is by far the most accessible mid horn in my opinion, it is very affordable for what you get and Blue Aran ship worldwide. I have ordered stuff from them to Australia, they were happy for me to organise postage but they can organise it for you if you don't want to worry about that. 

Being plastic also means it is very light weight, if you have ever picked up an XT8 you will know how heavy they are. 
Originally posted by martinsson martinsson wrote:

Making the 15" flh section reach 500hz is perhaps doable if limiting the lower extension as per your proposal, but will it sound good, honest question,
Originally posted by fat_brstd fat_brstd wrote:


My worry with your box is the 15" section, whilst it sims up to 400hz will it sound any good that high or will be the classic boxy sound you get. I have never really liked the way band pass boxes play up that high and if you are going for a front loaded horn with at 180 degree bend in it rather than a band pass assisted style that will also affect how high the box can play.

This is NOT a bandpass horn, you can tell by the very small front and rear chambers in the hornresp window posted above. I think that boxy sound is what you get when you try make a bandpass horn play over a large bandwidth. If i'm not mistaken, the point of a bandpass enclosure is to narrow bandwidth and increase efficiency with in that narrowed bandwidth so trying to get one to play over a wide bandwidth seems like a stretch. 

There are already designs that have no problem playing higher than 400hz with folded FLHs, including the MKH230. The PM60/90 plays up to ~750hz, that's almost a full octave higher, this cab has glowing reviews. I am aware this is a ported horn but 750hz isn't coming out of the ports, its passing through the horn, around the fold. 

The secret appears to be correct driver selection and putting the fold as close to the throat as possible, 1/4 wavelength at the highest frequency produced at a minimum. This isn't limited to bass horns, there are Danley products that use this principle with compression drivers up to 16khz. 


Originally posted by fat_brstd fat_brstd wrote:


Have you thought about using a ported straight short horn instead of bandpass? If the intention is for this box to always be used with a sub then the extra extension gained from a band pass arrangement is unnecessary, and using a short horn that loads down to say 100hz with a port tuned to 75/80hz to get a boost at low end of the boxes frequency response and deliver the required kick sound for techno. Using a high efficiency, small voice coil driver with a sensible power handling (4-600 watts rather than a 1200 watt monster bass driver) will mean you get a lot of kick for not a lot of money.

I don't really have any experience with ported horns, I don't think I have ever heard one, I do have a lot of experience with FLHs and I love the way they sound. 

As far as driver selection goes, I pay no attention to things like power rating or VC size. I only look at T/S parameters. I have a spreadsheet based on the Leache paper that finds optimal T/S parameters based on the type of system you are trying to build. I am aware the voice coil diameter affects BL and Mmd which affect Qes, Fs, Vas etc. but I wont make a decision based on voice coil diameter. If a suitable driver happens to have a large power rating and a large VC then great, it will take more power and exhibit less power compression. 

Originally posted by fat_brstd fat_brstd wrote:

Looking at other similar boxes the classic selenium mid top (as used by many reggae sounds in JA) is a 15" on a short horn, 12" on a short horn and then a 2" and bullets, normally located in the middle with the 15" at the bottom and 12" at the top. The issue with a box like this is the size, they are massive compared to something as compact as an xtro.


I have only just started experimenting with layouts and have one that is 20L smaller than an Xtro, I expect to make some improvement on that as it has a lot of wasted space. 



The major issue i'm having is packaging. I think a trap cab is ruled out, a 15 inch driver is quite wide and getting it close to the fold is physically impossible if the cab tapers in at the back. 

Another issue is that the rear chamber of a FLH is quite small, my current iteration is 18.5L which is tiny compared to a BPH, this may sound like a space saving but it makes it impossible to package it in such a way that includes the back of the mid horn in the same chamber. 

The last issue is that the MR8XTN is actually quite small and a 15 inch driver doesnt fit through the baffle cutout... i'm still figuring out how to give access to the driver. 



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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mikkel Quote  Post ReplyReply Direct Link To This Post Posted: 12 July 2020 at 1:48pm
isn't that rcf 90x90 dispersion? Might not be ideal for 2 aside.

i know this is preliminary design stage and all that but 3000cm2 mouth is like 60x50cm, which a huge aperture to fit into any kind of box. considering the path length is 80cm too you might struggle to fit that into a single fold.

As others have said it may not play well up so high but all that depends on how you intend on folding the horn and how sharp the bends are.

Im interested in seeing what you come up with in any case. Good luck with the project!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote citizensc Quote  Post ReplyReply Direct Link To This Post Posted: 12 July 2020 at 2:09pm
Originally posted by Mikkel Mikkel wrote:

isn't that rcf 90x90 dispersion? Might not be ideal for 2 aside.

i know this is preliminary design stage and all that but 3000cm2 mouth is like 60x50cm, which a huge aperture to fit into any kind of box. considering the path length is 80cm too you might struggle to fit that into a single fold.

As others have said it may not play well up so high but all that depends on how you intend on folding the horn and how sharp the bends are.

Im interested in seeing what you come up with in any case. Good luck with the project!


The horn is made by Sonitus... who ever they are, its 60x40, apparently it sounds quite good. The RCF component is the 15inch driver for the kick. 

Yes i'm aware that mouth is huge, I did have a trapezoidal cab with a wide mouth in mind when I came up with that. As i'm going to compromise and do a square cab, the mouth is shrinking substantially. 

I forgot to add, I have no intention of putting a 180 degree fold in it. It will be a 90 degree fold very close to the throat. 

Here is a pic of my current draft layout, its still 2d as im figuring things out. Its just to give an idea of where my head is at. Please keep in mind that this will likely change a lot, there is still a lot of improvement to be made. 

Dimensions are 640x750x500, its actually quite compact. Obviously the mid horn goes above the mouth. 


And the hornresp inputs for it:



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Post Options Post Options   Thanks (0) Thanks(0)   Quote MattStolton Quote  Post ReplyReply Direct Link To This Post Posted: 12 July 2020 at 2:41pm
What about the bottom end like the RCF 4pro 6001?

Twin 12, may help keep dimensions compact, whilst going high enough to reach mid horn, enough spl and potential for it going low enough to meet bass box.

Single 15 has merits, perhaps as a bass reflex, but a lot of draw backs, when horn loaded, mostly size and horn length related?

Given price of watts to get spl, and bandwidth, is cheap, BR 15 could work?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote citizensc Quote  Post ReplyReply Direct Link To This Post Posted: 13 July 2020 at 11:20am
Blue Aran sell flatpacks of a 15+8+1 with a reflex 15, I do see the merit to it but it doesn't meet my design goals, I really doubt the kick from that has more impact than a well designed FLH. I also really doubt that the reflex 15 would keep with with the 8 inch horn. 

A twin 12 may have the SPL but it would be more expensive to build and again, it wouldn't have the horn-loaded sound that I like. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post Posted: 13 July 2020 at 1:22pm
I'm not an expert by any means but wouldn't it be better to model in 4π for what is essentially a low-midrange device?
I'm thinking that the wavelength of even 100Hz is 3.4m, so unless your stack will be arranged in such a was as to keep this box within 0.85m of the ground, it won't really be in half space. That would result in an awfully low position for your upper mid and HF, so I'm assuming your stack would end up higher?

FWIW,
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Post Options Post Options   Thanks (0) Thanks(0)   Quote citizensc Quote  Post ReplyReply Direct Link To This Post Posted: 14 July 2020 at 8:36am
I have been thinking about 4pi vs 2pi, I have come to the conclusion that its probably somewhere between. You are correct to say that it wont be with in 1/4 wavelength of the ground and therefore it isnt true 2pi. It isnt a horn mouth floating in free space either, there are the panels surrounding the horn, the cabs it is likely stacked on top of and if its an indoor venue, there are walls and the ceiling to take in to account. I have decided to stick with 2pi because the xtro models badly in 4pi and I know from real world experience it works well. 

Hornresp is a rather simple modelling software, this is great because you can whip up a model much quicker than you can build a cabinet. More complicated software like COMSOL can be used to generate a closer to real world model but for the time it takes to build a model, a lot of people would rather just build a speaker and measure it. 

The simplicity of hornresp does limit the control you have over the model and as a result it may be less representative of the real world. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote smitske96 Quote  Post ReplyReply Direct Link To This Post Posted: 14 July 2020 at 9:35am
Just to add a bit on the PM90/60. You can also use the RCF ND950. It is significantly cheaper then the BMS/B&C coax.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MattStolton Quote  Post ReplyReply Direct Link To This Post Posted: 15 July 2020 at 9:52am
Originally posted by citizensc citizensc wrote:

I do see the merit to it but it doesn't meet my design goals... 


Just thinking out loud, and considering what others have done as solutions.

Unless you are amazing, finding genuinely new solutions is unlikely, but putting a 15" in a horn, with your choice of compromises will yield a new version of kick solution, so carry on. Iterative evolution of the subject is as valid as massive steps.

I see how the Merc/Racing Point brake ducts as an interesting case. At first glance, especially if you are as cynical as me, looks like straight plagiarism, or shared technology. Money is probably involved somewhere, it usually is.

However.

If you are trained to use a wind tunnel, and you are tasked with developing a duct, and you are constrained by strict rules about the location and size and every other variable on the duct, it is likely that a competent engineer will design something quite similar to another competent engineer?

Same with a 15" in a horn, simmed in HR? You have less FIA rules to adhere to, but you are adding your own constraints and rules. If you're competent, which it sounds like you are, for the set of variables you start with, should generate an almost predetermined output!

Effectively your speaker is already designed, so crack out the wood!!
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