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BG Horn Mk1 - 36hz Front loaded horn

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citizensc View Drop Down
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    Posted: 22 June 2020 at 3:46am
Hi Guys

I have made this thread as a place to access the plans and ask questions about the BG Horn. 

PM me if either of the below links go dead.




What is the BG Horn? 
It is a 15 inch front loaded horn covering ~36-90hz. It is designed for the 15BG100. It has similar folding to a Punisher but is larger, more sensitive, plays lower, and should take more power. 

Why should you build the BG Horn?
-You need a FLH that plays below 40hz
-You want to build a FLH but other designs look too complex and hard to build
-You want a FLH that that is a manageable size and weight, the BG Horn is about 75kg loaded
-You would rather not spend big money on they types of drivers that are popular in DIY horns (pd.1850, V18-1000, 18sw115 etc.)
-You want to build a horn with a driver that is widely available and is likely to stay that way for some time
-You don't live in Europe or the US and find it difficult to get good quality 18 inch drivers due to air freight restrictions. 

Why shouldn't you build a BG Horn?
-You don't feel comfortable with building untested design. If you would like to give this plan a try, hit me up via PM or comment in this thread, id love to hear about it! 
-You plan to build less than 4 cabs, this may work okay with two cabs but is designed to work in groups of 4 or more. 
-You need a cab that is a one man lift (build single reflex cabs if you want this) 
-You are looking for a one-way bass solution that plays above 100hz. 


Here are some sims show where it fits - keep in mind that speaker design is about compromise, these cabs are all different size, efficiency, bandwidth and cost compromises. 

All sims are 2.83v @ 8 ohm (1 watt), 4 cabs grouped, 0.25 watt per cab. 

Punisher (12.00sw) Black, BG horn grey

1850 horn (pd.1850) Black, BG Horn Grey

WSX (V18-1000) black, BG Horn Grey

SBH (PD.1850) Black, BG Horn Grey

TH18 (18sw115-8) Black, BG Horn Grey




Edited by citizensc - 05 August 2020 at 7:54am
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KaphaSound View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KaphaSound Quote  Post ReplyReply Direct Link To This Post Posted: 23 July 2020 at 3:03pm
Very new to horn design and genuinely just curious, but what would happen if you cut the top sheet in the same style as the “eye shape” in the Danley BC218s and put 4 together in the same eye configuration? Would you be able to slightly increase the length of the horn this way and gain a bit of extra directivity due to the increased size of the ‘face’ of the stack?

Edited by KaphaSound - 23 July 2020 at 3:04pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote citizensc Quote  Post ReplyReply Direct Link To This Post Posted: 24 July 2020 at 2:20pm
This is an interesting question, I understand your thinking, I suspect directivity would be improved and you might be right about the slightly increased horn length. This is something I would like to try and measure. I guess I will have to add it to the list of things I would love to do if I wasn't a poor student locked down in an apartment away from my home city.

Would be interested to hear from anyone who has used the BC218.   
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KaphaSound Quote  Post ReplyReply Direct Link To This Post Posted: 25 July 2020 at 4:17pm
I’d love to help I’m just not 100% confident in hornresp yet, but to get close I assume you’d use 1pi to approximate the large face, then a bit of extra length to get around the final bend at the mouth, but here’s where I get stuck . Would you essentially need to calculate the total horn with 2 or 4 drivers so the combined S1 (S2 for OD) for the compression ratio, then I guess combined S3/4 to keep the expansion rate consistent? Then the total combined mouth size (S5), and then are there any other paramaters like VTC/ATC VRC/LRC that need to double/quadruple according to the number of drivers? I’m really hoping to pick up 4 15s to put under some EV ZLX 15ps as a first project and the B&C BG15 drivers were looking quite appealing. The goal was to make something capable of hitting 30hz, but after some reading I was realizing that’s near impossible in any kind of semi compact/lighterweight format, until I saw your design. So I’d basically love to see if the boundary compliant multiple horns one mouth method could even push f3 a bit lower if only by just a few hz.

Edited by KaphaSound - 26 July 2020 at 8:40pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote citizensc Quote  Post ReplyReply Direct Link To This Post Posted: 02 August 2020 at 10:03am
Sorry for the delayed response, been a little bit busy. 


Originally posted by KaphaSound KaphaSound wrote:

Would you essentially need to calculate the total horn with 2 or 4 drivers so the combined S1 (S2 for OD) for the compression ratio, then I guess combined S3/4 to keep the expansion rate consistent? 


I would keep it simple, I would sim it as 4 seperate horns, this is quite easy, just enter it as one horn, click calculate then click tools > multiple speakers > drag the sliders, for 4 horns I would go 2 parallel, 2 series, this way it will be an 8 ohm, this will give you 1 watt with the default 2.83v for Eg. You dont need to do anything fancy with changing chamber volume sizes to simulate multiple horns. 

The tricky part would be correctly modelling the last part of the horn, I think I know how I would get the correct length for the horn. I would just draw the path in sketchup and measure it. The mouth is a little trickier. 

Modelling the mouth area of this would be simple, it would just be the cross sectional area (LxW). 



But modelling this isn't so straight forward. 


The mouth actually looks smaller and I suspect it is smaller but the reduced mouth area compared to the last picture may be acoustically invisible at the frequencies we are talking about. Similar to hanging a compression driver and horn flare in mouth of a kick bin like an xtro. The horn flare may take up 30% of the cross sectional area at the mouth but does not have a significant effect on the output. 

Feel free to try sim it in hornresp and post it, will be happy to give my 2 cents. Might even get some input from other people. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jo bg Quote  Post ReplyReply Direct Link To This Post Posted: 02 August 2020 at 10:53am
The mouth on the BC subs is actually smaller as you noticed, the horn path restricts at mouth before suddendly increasing with the boundary loading.
So it's not easy to have a regular (expanding) flh act as a Bc sub when stacked, as there would be no such restriction.

The stack will still load better for the bigger mouth and size, but just stacking and a round exit will not make a BC sub.

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