[kyrill]

Hi ppl

i feel this to be beginner OB questions, but that is what i am 
If i have an OB baffle of 20inch width what height do i need as minimum for the midrange driver to reach +/- 100 hz?

or when that is not possible behind the baffle a "U" frame which length is needed for the parallel "wings"?

I dont have programs to help me out
thx

[richidoo]

It all depends on the midrange driver specs.

This software will help you see what's going on, only $25:
http://www.quarter-wave.com/Models/MathCad_Models.html
Rich

[kyrill]

thx Rich
i actually mean regardless of driver
so what is the baffle response if the baffle "loss" (6db/oct) starts around 100 hz and lower

the link to 1/4wave is a bit too technical for me

[Graham Maynard]

Is James' Single Driver Website still running.
It gave a baffle size/frequency chart which might help kyrill.

There are also many pages of info here;-
http://www.linkwitzlab.com/faq.htm

Cheers ...... Graham.

[richidoo]

Is this what you're looking for kyrill?   

Linked from http://members.myactv.net/~je2a3/open.htm

-Rich

[Graham Maynard]

Hi Rich,

That is the chart I was thinking of, but I can't find James' website anymore.

Hi kyrill,

Try by going here -
http://uk.babelfish.yahoo.com/

Fill in German to English in the second window, remove the http:/ and copy/paste this address in for translation. 
http://www.dipolplus.de/frameset.htm
Wait for a few seconds and then use the website index on the left.

Much good info and inspiration.  Rudolf posts here too.

Cheers .......... Graham.

[kyrill]

Hi Rich

Yes i have that graph but it is for a perfect rectangular OB

it says in case of 100 Hz i need a rectangle of 32"x32"

this is very ugly in my eyes

so i will use a 20 inch width and more than 32"tall. I believe that it does not matter,
that i will still have a roll of beginning at those 20 inch width at 160 hz but when the baffle
is longer than 20 inch i will have a slower roll of say 4db/oct.


However if i stay at 20 inch i am short of 12 inch, that is  6 inches a side
If i make a Uframe behind the baffle ( a bit out of sight) i can regain those 6 inches.

Guitarretyp's OB baffle


Graham thx for the link I will try this out

[scorpion]

Actually 32" should be read as the smallest measure, certainly need not be quadratic. 32" width including wings would be OK.

/Erling

[kyrill]

thx  Erking, i was hoping for that

[tubamark]

. . . . Yes i have that graph but it is for a perfect rectangular OB

it says in case of 100 Hz i need a rectangle of 32"x32"

this is very ugly in my eyes
. . .

Pretty much the only dimension to worry about is the width, unless your baffle doesn't touch the floor, or is of really unusual proportions (like really tall and very narrow).  The vertical dimension is always effectively double due to mirror image in the floor.  IOW a 32" tall baffle is effectively 64" tall.

Simply modelling the baffle + it's floor image in EDGE will give an excellent idea of the rolloff of the baffle itself.  That chart above is handy for rough guide, but Edge is way superior, as it shows the midbass hump, which affects total response as markedly as the rolloff.

20" width + 6 inch wings (be sure to include the thickness of the baffle) should get you <100 Hz easy if your driver allows it.  This means more like 5" wings - very modest, shouldn't color the sound, especially if attached with corner blocks.

[kyrill]

Hi tubamark

that is excellent news, what are corner blocks?

[tubamark]

Hi tubamark

that is excellent news, what are corner blocks?

Vertical pieces of wood that help support the wings - fastened (glued) in the inside corner formed by the wing and the rear of the baffle.  Supports the wing structurally, and also gives some surface variation to the (otherwise) paralell sides the rear of the driver sees. 

For extra credit, these can be made triangular (45-90-45).
How large you make the blocks depends on how wide your driver is compared to the baffle width.  if your midrange is 8" on a 20" baffle, you can pretty much make said corner block as big as the wing.  in this case, a plank with mitered edges can be used (leaving a hollow cavity in the corner) instead of a hefty block.

Effectively, the front of the driver sees a large flat baffle, while the rear of the driver sees a 3-sided angled baffle.  It offers a little more "launch" to the front wave than a 3-sided hinged baffle does, and is structurally very solid.

'hope this make sense.
--- Mark