mitre angles in the mt122 flare

oh come on, i can't believe that you all just planed them to fit or for that
matter put up with ill-fitting pieces. somebody must have at least a vague
idea...

2 degrees? 3 degrees? 3.5?

james.

hi julz, thanks for heeding my anguished cries. i suppose i should scan a
drawing of the bit i mean to describe it better. i shall try and get this
together tomorrow morning but i need my housemates help to host it,
and thus post a link to it.

i am utterly convinced that the inner pieces of the horn flare both need to
have their 'hypotenuse' edges cut at a slight angle because they don't sit
at a perfect right angle to the top and bottom flares. not much, but some.
arguably we've gone about these boxes in a fairly arse about face way,
but they are prototypes in terms of suitability to driver model and choice
of material.

they are using mckenzie c10-150gp cones because i have 12 of them,
just as the selenium horns will use mckenzie c15-400lrs because i have
16 of them. 4 in use, so 6 bass horns, 4 mid and one 1 rcf compression
driver a side with a choice of 18" xb scoops or 12" wicked ones doing
subs. it may prove mis-matched but we shall see what gives.

mdf has been used as it's the only way we can afford to hear what 4 a
side sound like this side of christmas, they are a tad weighty though, and
i despise it generally as a material. i think the seleniums will have to be
ply for weight reasons. in addition to the seleniums being more of a
proven desighn they are by all rights easier to construct than a 10" single
variant of the mt122, and we are seriously counting on them not taking
anything like as long.

this small pile of drivers has been sat for an age whilst we deliberate over
designs, finally urgency to upgrade the feeble eminence 12" beta lt
loaded horns became overwhelming so we set about making these 10s.

james.

hi jeth,

thanks for your help, but i think we aren't thinking about the same joint. i
think you are talking about where the horn flare (inner vertical section)
reaches the baffle which i would agree would be 12 degrees. i mean
where that piece meets the top and bottom flares. at first glance you'd
probably not think it requires mitring (sp!) but practical experience
indicates the necessity.

i will draw a sketch this weekend. promise.

james.

James...i see the bit you mean now...but really can't
see why this needs mitreing though...it is afterall all
in the horizontal plane, that is, the side flares meet
the top/botttom sections at right angles..Surely?

james, ind.st wrote: i am half convinced that if i sat down with a clear head i could do the maths and work the damned thing out, but i dread it as my last attempt was so clearly wrong i fear i have forgotten the basic rules of geometry.

hmmm.  Now you're dredging up painful memories....  i innocently thought along the same lines.  Surely a maths degree + a pen, paper and some basic trig could sort out my cutting list...  After narrowly escaping a brain embolism I gave up and opted for trial and error...

ok, sketch still pending, but then i have college tomorrow so i figure it
will get done in class. did some cutting today though and did about 3
degrees on the trapezoidal edge.

it is very nearly enough, there is the slightest gap between the two pieces
on the inner faces. i shall try 3.25 next.

although i have already cut all my outer horn flares, hence how i know
they need a taper to fit, i would have figured they would need mitring on
their trapezoidal edges to about 6.5 degrees.

james.