At which frequency? Every division brings quadruplication, you know...digital plants have a root (mean) square
Yes, u are right. At the driver's Fs is what should be more meaningful, maybe, assuming that the Eminence Alpha 15a has an Fs of 42 hz for example.
Juhazi, i highly appreciate your point of view as well as your assurance. Yes, i am working on a domestic hobby based system for personal use, in a room L×W×H = 22 ft. X 16 ft. X 12.5 ft. Given this, i think i should need to feed it with up to 20 watts/channel and yet ensure that the 8" midbass remains well within its excursion limits of 3mm. I am aiming for a long term SPL of 99-100 dB at 1 metre, which i suppose is a reasonable expectation for personal use.
So if i reframe my query, is there a set of criteria (eg: Cms, etc.) that i should look for in an 87 dB/watt/metre sensitive 8" midbass driver to suit an open baffle (or probably a very lightly loaded.... Vb=Vas*4 sized sealed enclosure) ?
Even an approximate set of values should be of GREAT help to me in extrapolating a bit and eventually work my way to reach the desired target!
Thanks and regards,
Sujat
Ok, i take the clue as to the 8" driver. Thanks for the link, Kjeldsen! I am confident that should provide me a very useful base to work upon!
Btw, how does a wider baffle help? I mean, what is the Physics involved?
@ gadut:
I appreciate your input showing the suggested design flow. Thank you for responding.
You have a lot to learn! Yes, physics and acoustics!
Tech
Equivalent Baffles
A, B, C, Dipole
Electro-acoustic models
Electro-acoustic models
http://www.dipolplus.de/
http://www.dipolplus.de/thema11.php
http://gainphile.blogspot.com/
Of course, Juhazi, of course! I do have a lot to learn and understand! 
Thanks a lot for these links. They will help me a lot. I have gone through Linkwitz lab website, but i am sure i must have missed much due to my being mathematically challenged. Nonetheless, i will go through these links and try to gather as much as is explained in words (algebraic equations are a wall that stops me dead!).
Thanks again!
Warm regards for the severe winter to follow!
Sujat
Thanks a lot for these links. They will help me a lot. I have gone through Linkwitz lab website, but i am sure i must have missed much due to my being mathematically challenged. Nonetheless, i will go through these links and try to gather as much as is explained in words (algebraic equations are a wall that stops me dead!).
Thanks again!
Warm regards for the severe winter to follow!
Sujat
Wide baffle is equal to a longer path for low frequency. This is equal less cancelation of low frequencies. An u baffle will du the same, but also introduce resonance so only good for bass.
Thanks, Kjeldsen. I understand the first part about the longer path lowering the frequency at which front-rear energy cancellation will begin.
I can understand the transmission line resonance in case of a 'U' or 'H' baffle, which is obvious.
Is this the same thing Juhazi was indicating? I thought he was indicating something more subtle which i wasn't yet aware of.
Anyway, i feel thankful for responses from all of you, Kjeldsen, Juhazi and all!
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I've only tried it with an Alpair 12P pair for a "single" rear channel, to compare discrete surrounds to a Hafler style single rear ambience channel.
I prefer the stone age Hafler channel, btw. I just use an amp with stepped volume pots to adjust the level, fed it's own line level signal.
For music, it was pretty good, when wired for l/r signal, perhaps because it has less interaction with room boundaries.
My first post.
Open Baffle rules!
I own a pair of PAP Trio 15’s with the W81808 fullrange, and have been extensively investigating them for over a year. Have come to some unusual conclusions and look forward to comparing with others.
I have two 15” neo woofers in W-W-FR configuration. They are crossed at 120hz 48db L-R and are driven from a minidsp2x4 hd using one dsp channel with a mixed L+R channel.
Spaced 4’ from back and side wall and separated by 7’.
The FR has a vertical baffle extension to support its ability to deliver down to 120hz. That driver is weak below about 225hz in OB, and I am convinced a new baffle shape would help.
I use FIR filters exclusively on the FR, getting phase as close to zero as possible. I wish I had more FIR taps. With FIR filters, I have almost entirely eliminated the scratchiest of the tangband at high volumes. More work to do here.
I would love to hear from any OB and minidsp owners on how they tame their fullrange.
I use reconditioned amps...bas driven by a Hafler 220, fullrange by a Hafler xl.
There are a couple of fundamental issues with the PAP trio 15...
a) fullrange is not physically aligned with bass drivers, there’s a 5 cm time delay due to this.
b) fullrange baffles are wider than they should be for best image, and not wide enough to support low crossover frequency easily
c) frame resonances aren’t isolated from fullrange
...but that said, the bass resolution is astoundingly great. And the image with FIR is convincing!
Open Baffle rules!
I own a pair of PAP Trio 15’s with the W81808 fullrange, and have been extensively investigating them for over a year. Have come to some unusual conclusions and look forward to comparing with others.
I have two 15” neo woofers in W-W-FR configuration. They are crossed at 120hz 48db L-R and are driven from a minidsp2x4 hd using one dsp channel with a mixed L+R channel.
Spaced 4’ from back and side wall and separated by 7’.
The FR has a vertical baffle extension to support its ability to deliver down to 120hz. That driver is weak below about 225hz in OB, and I am convinced a new baffle shape would help.
I use FIR filters exclusively on the FR, getting phase as close to zero as possible. I wish I had more FIR taps. With FIR filters, I have almost entirely eliminated the scratchiest of the tangband at high volumes. More work to do here.
I would love to hear from any OB and minidsp owners on how they tame their fullrange.
I use reconditioned amps...bas driven by a Hafler 220, fullrange by a Hafler xl.
There are a couple of fundamental issues with the PAP trio 15...
a) fullrange is not physically aligned with bass drivers, there’s a 5 cm time delay due to this.
b) fullrange baffles are wider than they should be for best image, and not wide enough to support low crossover frequency easily
c) frame resonances aren’t isolated from fullrange
...but that said, the bass resolution is astoundingly great. And the image with FIR is convincing!
I have been building OB's for many years and am on 6th iteration.
Current setup is
Alpair 12P magnet mounted on a spine, baffle is mounted to spine with rubber grommets for de-coupling and felt is applied to the front of the baffle.
Woofers are W frame with cavity resonance set at about 400hz. Drivers are Visaton W300 12" 2 per cabinet. Bass is fantastic and on movies will shake the floor. Bass guitar on Fleetwood Mac Dreams can be felt.
FR is sat on top of woofer box de-coupled with felt. I did try a separate stand for the FR over the woofer but this made no improvement. The felt is used to control baffle vibration and edge diffraction.
XO is active line level analog. I did use a miniDSP to determine XO parameters. Use the natural roll off the FR and keep XO freq away from resonant freq.
I have tried many FR drivers (numerous Fostex and Dayton Audio) and the Alpair 12P's are the best I have used, I have no driver taming in the signal path. Baffle step correction is done with baffle size , driver placement and XO freq. All the other FR drivers had peaks that needed to be tamed by some sort of filter, the Dayton Audio PS-220-8 were the worst and very shouty, I hated them.
Hope this helps..........
I too own a pair of 12P, and like them a lot.
A buddy had Planet 10 make him a pair of Onken like cabinets for him with 12PW Alpairs.
He claims the 12PW are a better driver, with the -3db point of 15000 hertz a moot point, since most people 50 or older can't hear that high anyways.
Anyone have experience with the 12PW drivers?
I mean in open baffle; they do sound very good in cabinets.