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2x15" front loaded horn F2B

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snowflake View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 28 May 2020 at 1:45pm
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 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ceharden Quote  Post ReplyReply Direct Link To This Post Posted: 28 May 2020 at 9:30pm
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 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 28 May 2020 at 10:05pm
Originally posted by ceharden ceharden wrote:

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.


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 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote citizensc Quote  Post ReplyReply Direct Link To This Post Posted: 29 May 2020 at 6:36am
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 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 29 May 2020 at 9:26pm
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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Post Options Post Options   Thanks (0) Thanks(0)   Quote Digbethdave Quote  Post ReplyReply Direct Link To This Post Posted: 30 May 2020 at 11:14pm
You got to remember this was all designed as a system. Part flown. Part ground stack.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote djeddie Quote  Post ReplyReply Direct Link To This Post Posted: 31 May 2020 at 1:00pm
Originally posted by Digbethdave Digbethdave wrote:

You got to remember this was all designed as a system. Part flown. Part ground stack.



And?
Chas n Dave : it's like Drum and Bass but with beards.             E=mc² ±3dB
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