Which 15 or 18 ınch woofer- best for open baffle

I Need 15 or 18 ınch Sub Bass for Open baffle I prefer RCA -B&C or BEYMA ( I can find easy in our country)
Will you please send me your comments...

None of these!

All of the pro drivers from these companies (as far as the models that I am aware of here in the US) have Qts that is too low and Fs too high for open baffle use. Look for drivers with Qts of 0.5 or higher. The exception would be if you can connect them to an amplifier with controlled output impedance, and set that to some "high" value (e.g. 8+ ohms) to cause Qts to increase.

Have you seen the studies of open baffle speakers by Martin King?
http://www.quarter-wave.com/OBs/U_and_H_Frames.pdf

He uses Eminence drivers (Alpha 15) with Qts > 1.0 with very nice results. Can you get those in your country?

-Charlie
 
I am by no means an expert, but a mid qts with very low fs (<30Hz) is what I'd be looking for. Much easier to find. Mms would be the third factor, depending on how high you want them to play.

Either very large diameter - 30" I'll guess or very heavy membrane = low SPL.

An OB will probably never go lower that 40 Hz, unless you have a very large room, and will need heavy eq., or very wide baffle.
 
I'm using AE Speakers --- Superb Quality, Unforgettable Performance, Definitely. , in my case the LO15 a combination of a Dipole 15 motor and TD15M. This version has OB low extension and is usable to a higher crossover point than the Dipole 15 (crossing is at 800hz tot SEOS-15).

If you only need dipole base <500hz the Dipole 15 is a very good choice (I also used the Dipole 12, very good).

Also used Ciare 15NdW in the past.
 
This all depends entirely on the operating bandwidth.

The lower you go, the more excursion you need - a LOT more excursion. OR you need more surface area (..i.e. more drivers). OR of course a combination of the two. (..close-coupling to the floor can also help somewhat.)

The notion that you "need" a higher qts driver is not correct. You can also equalize the system for increased pressure at lower freq.s. You can also achieve something of a hybrid approach via a dual voice coil design. One coil gets main signal, the other gets the eq at lower freq.s..

Frankly I don't think an open baffle dipole is necessary at lower freq.s., nor have I found it to be "better". There is a tactile sensation that goes somewhat missing with an open baffle design. I prefer a transition from mid-bass to bass at around 70 Hz.