open baffle shape

[smak]

i'm now in a position to mount my ciare ch250's to a baffle.

i have a W frame housing two 15's handling anything below 90hz or so, and was wondering what the consensus seems to be regarding the shape of open baffles for medium low response.

would mounting this driver to a 2 foot wide by 5 foot tall board be equivelant to any other configuration with 10 square feet of surface area?

i'd imagine they would respond very differently.

this in mind, i'd like to keep the width of my baffle as narrow as possible due to spade limitations in a high traffic area, and would also like to have the driver at least 3 feet from the ground.

i gotta say though, i'm very imperssed as it is with just the drivers hooked up and sitting on the boxes they came out of. and the sub of course its hard to imagine any setup i put these drivers into would not kick ***.

[Rudolf]

smak,

a lot of the bass you get from an OB stems from the floor reflection/assistance. With a small footprint and a driver quite high up from the floor (like you want to have it) I have my doubts whether you can expect enough bass left at 90 Hz.

What about dividing your W frame into two N frames, integrating them in the bottom of your OBs and taking them to an X-over at 120-160 Hz? Even if you power the subs still mono, they will integrate quite well.

The Ciares should work perfectly in those OBs above ~120 Hz.

Rudolf

[Paul W]

smak,
There are a lot of tradeoffs involved. In the 90 Hz range, response is heavily dependent on front/back path length so you could "fold" the baffle into a "U" shape for a smaller visual footprint. However, the parallel walls of a U can introduce audible midrange resonances. Also, the shape of the baffle influences diffraction at higher frequencies so try to avoid 90 degree turns...avoid sharp edges.

Google for "pvconsultants" and use Paul V's baffle diffraction simulator to help evaluate alternative baffle shapes. SL's site includes a calculator that will help you with LF.

The baffles shown here are "C" shaped, but I've also had good results with "V" baffles. The Vs (45 degree wings) are relatively easy to build.
Have fun!
Paul

[smak]

2x5 with the driver located 3 feet off the ground was just an example.. i can easily put to use a design that is closer to an ideal OB configuration.

i think i'm going to try a 80cm tall baffle by 40cm wide.. and locate the drive at about 65cm from the ground. i'll use cheap stock to build with until i tune to a design i really like.

hope that will leave some 90hz to work with. i dont have alot of room to place the driver away from the wall which may help a bit also, but sacrafice the waves interacting like they should.

my mono w-frame dipole serves double duty as a nice table stand in between two theatre seats i use when watching dvd's. i'd like to keep it in the back of my room due to space restrictions.

thanks for the http://www.pvconsultants.com/audio/frdgroup.htm tools.. if i had a windows/dos box handy it would come in handy ;P wouldent happen to have any online cacluators handy eh? i'll hold onto that link though

will try and post pics of results when i get something nice together.

[smak]

i was looking for a chart in the past that displayed OB size vs bass response and finally came across the link again. its pretty nifty although i dont know how accurate it is considering that it doesent take into account a drivers distance from the ground and Qts.

http://www.angelfire.com/electronic/...oncept-1b.html

anyways i setup my caire ch250's with a "shelving" kit i found at the local home depot. $8 a side with nicely trimmed edges. i cut them down a bit to size and ended up with about 34 inches of height by 12" width.

according to the linked chart, i shouldent be getting lower than 260Hz or so but the sound i'm getting seems nice and full so i'm a bit baffled (no pun intended) as to what to think.

i found a set of supertweeters were defianty required for high frequencies and i've got some Foster 025N47 8 Ohm's playing that duty with solen .47 caps in line. they were kinda slapped on as an afterthought but enrich the aural experience quite significantly.

quickie photo of my setup, not sure if i'm going to use completely new baffles later on or just widen these by adding glass around the perimiter.

thnx for the help sofar all.

[ultrachrome]

Larry Selmer talked me into building non-parallel H/U frames. Not the prettiest thing to have in your living room but they work well.

[paulspencer]

When it comes to OB size and shape, I believe the main issues are:

* fequal where the SPL is the same as the driver in a sealed box, below this point there is an extra 1st order rolloff due to cancellation

* polar response

both relate mostly to width rather than to area

you can add wings, although many comment that better sound is achieved with out wings, or small ones, although tradeoffs need to be made here

[smak]

i dont know about adding wings to the baffle.. i really enjoy the simplicity of a flat baffle design and think it works well in the room. i'd rather add a bit of width than wings for now.

with those pyramid type speakers though, why not have the two lower woofers play in dipole as if they were in an h-frame, and then have the midrange/ribbon cover higher frequencies?

if i had a bit more room it looks like a design i'd like to give a shot.. although i'd probably get another couple pyle 15's and some ribbon tweeters to do the job right

[paulspencer]

Wings need not be big. Look at Linkwitz dipoles, in particular Phoenix, they have very small wings. They also give the baffle more apparent thickness, bracing and concealing the basket a bit better.

[ultrachrome]

Originally posted by smak
with those pyramid type speakers though, why not have the two lower woofers play in dipole as if they were in an h-frame, and then have the midrange/ribbon cover higher frequencies?

if i had a bit more room it looks like a design i'd like to give a shot.. although i'd probably get another couple pyle 15's and some ribbon tweeters to do the job right

Actually, the two 12" woofers are dipole and the tweeter is a NeoPro5i ribbon.

I don't think there's anything wrong with keeping the baffle narrow. A bigger baffle reduces or eliminates the need to compensate for dipole roll-off. If you use a smaller than ideal baffle, you just need to compensate with a shelving low pass filter. I guess you still need to make sure the driver can handle the increased excursion that will result.

As paulspencer points out, the Orion baffles and wings are pretty shallow. Linkwitz uses a shelving low pass filter to compensate for dipole roll-off with both the mid and the woofer.

http://linkwitzlab.com/orion_asp.htm

I assume you're going active, right?