[JeffB]

I am interested in possibly trying an open baffle experiement, but I have a couple of problems.

My room layout forces a baffle no wider than 12".  11" is probably better.
I am not constrained by height, although I would like to keep it to about 60" or less.
I would like bass down to 100Hz, preferably 80Hz.

Does the narrow width constrain me to a frequency cutoff closer to 260Hz or does the height some how compensate?

I would try the Visaton B200, except I hear it rolls off at 200Hz in open baffle.

I am willing to use a coaxial driver to get a driver that will go lower, but I don't know a good driver for this purpose.  I am actually contemplating an Alpine car audio coaxial.  They have a 6.5" that they rate to 35Hz and a 6x9 they rate to 30Hz.  I have no idea how they would perform in open baffle.  But if I were to try this is there any point going with the 6x9 over the 6.5.  Will the baffle width completely defeat the lower response of the 6x9 or might the 6x9 still give me a little more bass.

I plan to call alpine to get the thiel small parameters before deciding.

And if I went with the 6x9 should I mount it horizontally or vertically?

[Rick Craig]

I am interested in possibly trying an open baffle experiement, but I have a couple of problems.

My room layout forces a baffle no wider than 12".  11" is probably better.
I am not constrained by height, although I would like to keep it to about 60" or less.
I would like bass down to 100Hz, preferably 80Hz.

Does the narrow width constrain me to a frequency cutoff closer to 260Hz or does the height some how compensate?

I would try the Visaton B200, except I hear it rolls off at 200Hz in open baffle ...

Without equalization it will be difficult to achieve that low of a cutoff. You would need a woofer with a high Q and fairly low Fs which means very low sensitivity. The taller baffle won't help because the width predominantly is going to determine the cutoff.

[JohninCR]

That's easy.  You just need swept back wings.  Every inch that you make the rear wave travel backward is worth 4" of width (2" on each side).  You need to experiment first and different length "wings" is important.   If you are using near wall placement then you will need some polyfill batting and/or open cell foam in the cavity.  Top caps are often needed to prevent funneling the rear wave toward the ceiling.

The general opinion that OB's have to be big is simply incorrect.  Let's take an example:  Use an 8" driver such as the B200 with a front baffle just large enough to fit the driver.  Use one 8" wing and one 10" wing and angle the wings so you have your 11-12" maximum width at the rear.  The 2 speakers need to be opposites with the 8" wings to the center.  You do lose some floor effect due to the overall narrow width, but otherwise this small form is equivalent in terms of bass extension to a flat baffle that is equal to a flat baffle that is over 40" wide.

Car speakers can work surprisingly well.  You want those designed for rear deck (IB) use, not for small box use.  The main problem with multi-way car speakers is in the XO and tweeters, which are generally poor.