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25th March 2006, 05:46 PM  #1 
diyAudio Member
Join Date: Mar 2006
Location: Washington DC

Building Buschhorn MKII for 12 CM driver
I am interested in building a set of Buschhorn MKIIs. Can anyone give any insight as to how to scale the plan for a 11.512 cm driver like the Fostex FE126 as apposed to the 10 cm driver that the plan calls for? I have been trying to learn folded horn theory so I can modify the plan but it is taking time to find any good information and I am feeling frustrated about the situation. Any help would be appreciated! Thanks!

25th March 2006, 10:46 PM  #2 
diyAudio Member
Join Date: Apr 2004
Location: Winnipeg, Manitoba

This fellow planted the FE126E into the Buschhorn MkII.
New speakers It looks nice, but he did not comment on the sound. On a side note, The Horn Shoppe has used a number of drivers (401197, FE103E, FE108ES and now FE126E) in their popular horn design. From their website, it looks like the swtich to the FE126E is done by adding some damping to the compression chamber. Not quite a horn, but planet_10 has had some good results with the Fostex enclosure for the FE126E http://www.diyaudio.com/forums/showt...702#post831702 http://www.diyaudio.com/forums/showt...672#post834672
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26th March 2006, 05:45 AM  #3 
diyAudio Member
Join Date: Nov 2005
Location: Ontario

I've also looked at building both the original Buschhorn and the MkII using FE126 drivers. Initially the original Buschhorn looked like the way to go because its size and foldings appear to be so similar to the Hornshoppe Horn.
Both the original and MKII need to have the compression chamber's height increased to physically fit the driver. After changing the heights I modelled both designs with various compression chamber geometries and volumes using MJ King's older BLH worksheet The original Buschhorn seems to have too short a horn path length (I measured it to be approx. 62") and the Sthroat is also small in relation to the driver. The MkII also has a shorter path length that hampers its performance (I measured it to be approx. 76"). However after substantially decreasing the CC length and narrowing the area of the closed end the results were pretty good. I also tried modelling Ron's A126E design with much better results. Unfortunately I couldn't get a good handle on the parameters of the CC and had to guess about actual lengths etc. Despite this the A126E design seems to work much better and appears go at least one more octave deep in bass. The original had a very ragged freq. resp. between 100 and 100 Hz with SPLs ranging from 70 dBs up to roughly 102 dBs. (I don't know how Ed from the HornShoppe does it!). Unfortunately I don't find ithe A126E to be as visually appealing as the Buschhorn or MkII and it looks like it would be much more difficult to build. BTW I found that when modeling these designs that very small changes in the CC volume and geometry have a very large impact on the frequency response curves between 250 and 1000 Hz. No matter what I did I ended up with a ragged response (they are horns after all!) but I found it could be mitigated to some extent. The parameters I came up with to model the Buschhorns with the FE126E were: Original: Lhorn ~ 62" Sthroat = 0.265 Sd Smouth = 12.195 Sd Mk II: Lhorn ~ 76" Sthroat = 0.4 Sd Smouth = 9.8 Sd I couldn't come up with the expansion rate for either design so modeled all three types given in the King BLH worksheet (0=linear, 1=conical, 2=exponential). They both seemed to model the best with a linear expansion rate. I'd be very interested in hearing from anyone else who has tried modeling and then building these designs. (Let me know if I screwed up!) 
26th March 2006, 01:57 PM  #4 
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Join Date: Mar 2006
Location: Washington DC

My thanks to you guys for your response! All of this is very good information! If anyone else has ideas, I am open to them as well. In addition, does anyone have any good links to horn theory? I know of all the mathcad papers and of the great work of some of the horn designers out there, however, I want basic theory, not pages of math. I can do the math when I fully understand why I am goind it. Thanks in advance!
Tom "Peregrinari" Petz 
26th March 2006, 02:35 PM  #5 
diyAudio Member
Join Date: Jan 2004
Location: US

I'm a bit light on horn theory, but Dave (Planet 10) is reportedly working on a 126E horn with Ron from the Full Range Driver Forum. You might want to check out the ups and downs of modeling that went on in that forum post.
Kofi 
5th April 2006, 10:47 PM  #6 
diyAudio Member
Join Date: Dec 2005
Location: Berlin

Hey nice i have done a bit of research on that project, too! My first starting point was to build horns 'like' the hornshoppe ones. I had a discussion with Mr. Buschhorn himself on the design, it seems the folding is "similar" to his MK1, but with a bigger compression chamber. He suggested not to build a horn from the Mk1 design because of some design flaws, he recommended the Mk2 Buschhorn.
Another member of the forum had actually calculated the whole thing and recommended to increase the width of the MK2 from 16 to 20cm and then put the FE126E in it. I haven't really come any further since i have something else in mind now (Ripole sub with satellite horns), because i want to give the fullranges a little rest from low frequencies. Anyway, i would like to know where this leads you. Good Luck! Nils 
6th April 2006, 01:46 AM  #7 
diyAudio Member
Join Date: Nov 2005
Location: Ontario

Widening the MKII is a good idea that will increase both the throat and the mouth area. However the plans that I have from the Planet10 website (http://www.planet10hifi.com/boxes.html) show the width as 13.5 cm not 16 cm (?). Increasing the width to 20 cm should move the mouth size to about 11.2 Sd  an improvement but I suspect probably not far enough.
The FE126 will still be a tight fit vertically (less than 15 mm to play with). 
6th April 2006, 07:45 AM  #8 
diyAudio Member
Join Date: Dec 2005
Location: Berlin

@holdent: You are right, 16 cm was referring to the outer width. The INNER width would grow from 13.5cm to about 20cm in the new version, sorry for being confusing...
Have a nice day! 
6th April 2006, 09:43 AM  #9 
diyAudio Member
Join Date: Nov 2005
Location: Ontario

Just did some modeling of the FE126 in a MKII using King's MathCad worksheets (www.quarterwave.com). I started with the 20 cm width and then tried 25 cm. Next I modified the CC by closing up the throat end and putting the throat at the back of the CC that shortened to 4.5". (The height of the CC must now be increased to fit the FE126). Further I adjusted the driver end and the throat end so that they both have an area of 1.8 x Sd. For the FE126 that's 65 cm2 x 1.8 = 117 cm2.
So what did this achieve?!: The performance of the original modeled with a straight expansion attached. 
6th April 2006, 09:44 AM  #10 
diyAudio Member
Join Date: Nov 2005
Location: Ontario

Now the results with the modifications attached (I think!  I'm still under moderation so I can't check immediately).
Modeling the horn as a straight, conical, or various hyperbolicexponential expansion variants did not change the frequency ersponse much. The performance peak at approx. 60 Hz was raised to about 65 Hz and smoothened done a bit moving from a straight to conical to hyperbolicexponential expansion. The size of the mouth is still a limiting factor for the impulse response. Moving to a much better size of 18 Sd (or even better to 24 Sd) will improve this but not alter the freq response. Moving this high will require a change in the foldings as well (ie. abandon the MKII design). 
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