2x15" front loaded horn F2B |
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snowflake
Old Croc Joined: 29 December 2004 Location: Bristol Status: Offline Points: 3118 |
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if you make all the parts in red out of solid timber that baffle is going to incredibly well braced. you could make that 6mm baffle piece even thinner to wrangle 2mm or 3mm extra. I assume the original design had flares expaning the letter box in the vertical dimension in that first few centimetres of the throat. maybe make the 18mm baffle piece smaller and removable with the driver. that way if you ever want to use a different driver with different sized cutout, bolt pattern, or want to increase excursion clearance above 18mm, you can just make a new baffle. fix it into the solid timber points with eight large threaded inserts and should be solid. you need to be careful rebateding that much out of the panel behind the driver. going from 18mm to 8mm reduces the stiffness by a factor of about 11. it's not a massive area but it could be enough to reduce the Q of the rear enclousure and affect the system efficiency. How about using an aluminium plate for the access panel - aluminium is about ten times stiffer than plywood. its an extreme, but for an example system - if Qmc falls from 20 to 5, system efficiency goes down from 46% to 35%, which reduces thermally limited max output by ~2dB Edited by snowflake - 28 May 2020 at 1:55pm |
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ceharden
The 10,000 Points Club Joined: 05 June 2005 Location: Southampton Status: Offline Points: 11776 |
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Not to mention that having the panel that thin makes it liable to external damage.
I would normally want to stiffen a panel in the rear chamber, not weaken it. The pressures are quite significant. 8mm aluminium would be good and act as a heat exchanger.
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snowflake
Old Croc Joined: 29 December 2004 Location: Bristol Status: Offline Points: 3118 |
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also you need to place some recessed bar handles - only place they can really go is on the rear chamber. fit them with gaskets and mounting plates to get them totally airtight and stiff. and even more heatsinks!
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citizensc
Young Croc Joined: 16 October 2015 Location: Perth,Australia Status: Offline Points: 532 |
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One of my main goals for this is to keep it easy to build. Part of that is keeping the bill of materials and list of skills required to build it short.
Having said that these are some good ideas. A member is building two of these as we speak, will suggest he start conservative with removing material behind the driver. In the next version of the plan (to come after feedback from the builder) I will point out that there are options to improve on a simple plywood design eg. aluminium access hatch and using solid timber to make all the parts in red. Thanks for the feedback. |
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snowflake
Old Croc Joined: 29 December 2004 Location: Bristol Status: Offline Points: 3118 |
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I just realised something about this F2B horn. leaving the first few centimetres of 'rubber throat' aside, even if you calculate a hyerbolic horn with M=0 it still doesn't expand quite as slowly at the throat and as quickly near the mouth as this horn. I was wondering why none of my designs based on Leach's reactance annulling came anywhere close to the F2B. So what is the theory behind this?
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Digbethdave
Registered User Joined: 16 November 2018 Status: Offline Points: 406 |
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You got to remember this was all designed as a system. Part flown. Part ground stack.
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djeddie
Old Croc Joined: 26 April 2004 Location: Bristol Status: Offline Points: 4125 |
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And?
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Chas n Dave : it's like Drum and Bass but with beards. E=mc² ±3dB
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tilla
New Member Joined: 07 July 2020 Location: London Status: Offline Points: 6 |
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Hey guys, great thread! Thanks for sharing all the knowledge and info here, enjoyed reading all.
Just recently, I bought 4 of the F2Bs unloaded and now I am debating what to load them with. I d like to ask you guys to help me out to have a good idea of what would be the best ( most cost effective as well of course) option. I have two pairs of PD156s which I could use in two of them , they will just about to fit with a little modification to the mounting area in the box. What do you guys think how will this sound ? I also have a pair of RCF L15P-200/a which i m thinking to fit in the third one and maybe get a pair of these to the forth F2b. I understand that the above may not be ideal and of course all boxes with the same matching drivers are the real deal. This may be on the radar next year but for now i need to work with what I have. Whats do you guys think ? |
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Digbethdave
Registered User Joined: 16 November 2018 Status: Offline Points: 406 |
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Also a good reason for 1/4 pack. I don't personally think ythe F2B needs redesigning, to the extent it now becomes something different. It's a good box, it is what it is. And I applaud people like jimmer who use it for what it is.
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madboffin
Old Croc Joined: 03 July 2009 Location: Milton Keynes Status: Offline Points: 1537 |
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To be strictly accurate, it was specifically designed to be as versatile as possible, and equally usable stacked or flown.
Anyway I have found another picture, mixed stacked and flown, using the retrofit Technique fly bar system for the mids and tops: http://www.spamabyss.net/pictures/F2NNSL.jpg Edited by madboffin - 08 July 2020 at 9:39am |
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snowflake
Old Croc Joined: 29 December 2004 Location: Bristol Status: Offline Points: 3118 |
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those drivers won't be terrible but you would do a lot better getting eight matching: or have a think about bolt patterns and whether it will be easy to upgrade to other drivers in future. Edited by snowflake - 08 July 2020 at 1:12pm |
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concept-10
Young Croc Joined: 17 May 2016 Status: Offline Points: 1292 |
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those drivers won't be terrible but you would do a lot better getting eight matching: or have a think about bolt patterns and whether it will be easy to upgrade to other drivers in future. Edited by concept-10 - 08 November 2020 at 8:46am |
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