what effect does baffle have on open-baffle system?

[kappa546]

i'm sorry im pretty new to home audio so this may be a little sophomoric for some of you vets. i just sold my kef q35's and want to design a new set of speakers using my css FR125's in an open-baffle setup along with some dayton 12HF's.... just the two drivers taking care of everything. i read a little about how the baffle determines the low end extension but was left unclear what the determinants are. can anyone explain how different baffle sizes alter the FR of the system?


i also know alot of you guys have the css drivers and want to ask for any other possible configurations that might work better than my idea. i had thought about the 7L bass-reflex design on the css website or perhaps the AP design to save some space (does anyone know how these would compare?). i dont have any separate processor so everything would be run off my panasonic xr-55 receiver and some sub amp i guess.


thanks again,
Andre

[2litre]

Andre,

I'm fairly new to all this to but, having started out with open baffle AND having just recieved my FR125S's, I'll give you a sophomoric response.

Increasing your baffle size will indeed enhance your drivers low frequency extension. You could just use a tall x wide flat sheet of whatever material is handy or you could use a slightly smaller front baffle with short wings on the sides (or all around) or use an even narrower front baffle but with deeper wings. The latter two options give you the same effective baffle size but offer a smaller overall footprint.

I quickly put my FR's in a 13.5"w x 46"h front baffle with 9.5" and 11.5" wings bent back at 45deg (simply the panels alone without figuring in the bends = 34.5"x46") and they sound very good. [search author TomekZ, open baffle and FR125S] I'm not an expert but I have no doubt I'm hearing their rated 65Hz low tones in this configuration. And man do they have some excursion!

There is discussion about how much info the large flat panel hides from a listener. Some like the flat panel, some advocate a bent baffle. It will end up being your choice. I'm past the large x huge flat panel and am experimenting with the bent baffle idea. I'm just trying to find out how narrow of front baffle I can tolerate before the wings make MY sound to tunneled or boxy sounding.

I currently use a pair of 12" woofers in simple 24"x24" baffles bi-wired off my B channel for my LF. It really helps and I'm probably getting down an additional 15-20Hz with them playing. I switch between 15wpc and a 45wpc '70's vintage Pioneer recievers. More tinkering to do with the baffles as far as asthetics vs sound but that's the nature of the game I guess. Given the simplicity of the whole thing it sounds fantastic already!
I figure it can only get better from here. Just do it!

After exhausting your searches here you might also search the fullrangedriver forums for additional info.

R/

Jim

[Rudolf]

Originally posted by kappa546
can anyone explain how different baffle sizes alter the FR of the system?

The frequency a baffle supports is defined primarily by its area - not its width. Since real OBs stand on real floors, the baffle to floor interaction has to be considered. That´s were woofer distance to floor comes into play. Both effects can be calculated with xlbaffle, a tool by Thorsten Loesch:
http://www.t-linespeakers.org/downloads.html
xlbaffle is most useful for the frequency range below 500 Hz.

A dominant factor for a balanced SPL above 500 Hz is the optimal position of the driver on the baffle. This can be simulated with EDGE:
http://www.tolvan.com/edge/
Please keep in mind that Edge doesn´t care for floor effects or T/S parameters. So it´s simulations below ~ 500 Hz are quite meaningless.

So much for starters - plain flat baffles. Adding wings and folding them back changes everything and takes you beyond sophomore status

[kappa546]

thanks alot guys... i'll look into those programs, but i might ask you for some help rudolf.

another question, how far should i keep the back of these from a wall?

[kappa546]

yep... from lookin at them for a few minutes i'll definitely need some help. are there perhaps any proven designs about?

oh and can anyone explain baffle-step diffraction and anything else i might need to worry about? i know nothing about this but have seen it thrown around quite a bit.

[Rudolf]

Originally posted by kappa546
... another question, how far should i keep the back of these from a wall?

Common denominator is at least 3 feet, because then the reflection from the back wall will reach your ear late enough to be detected as an "echo" - and not "merged" with the original sound.

You could damp the back of the driver or the rear wall in some way and get away with a shorter distance.

For baffle step diffraction I would recommend starting from here:
http://www.t-linespeakers.org/tech/index.html

or with the explanation by SL:
http://www.woodartistry.com/linkwitzlab/faq.htm#Q8

And yes, there is more to dipoles than putting a loudspeaker on a plank. So you are right for sure to look for some proven design first.

Rudolf

[john k...]

(JPK) There is a fairly simple way to get a handle on this. If you look at a typical simulation of the baffle step for a sealed box type system you will see a region where the amplitude starts to roll off at 6dB /octave. It then levels off at - 6dB below the baffle step. With an open baffle the basic difference is that the response continues to roll off at 6dB/octave instead of settling at
-6dB.