[oz_audio_todd]

Help me (just imagine Mila Johoval..etc etc etc saying the line in 'The fifth element').
Soon to move into an apartment and I am really concerned that my neigbours will not like my more than reasonable bass levels as much as I do.
From what I have read about OB Bass, it is supposed to be better to listen to and not load the room with bass as much as other designs (hopefully my neighbours rooms as well     ).
I have a couple of subs that I am not using that I figure I could take a stab at using in an OB Bass set up.
My question is: Are there driver specs that are better suited to OB (Vas, Qts, Qes etc) or definitely not suited to OB? (I had a look through 11 pages of this forum, didn't find the answer and decided to just ask the question at that point).
As my only common wall will be the wall my HT screen will be set up on, I was kind of thinking that if I was to may be run 2 separate subs facing my seat (somewhere in the range of 45 - 90 degrees off axis), with the plane of the baffle directed at my common wall and with the speakers as far apart as possible to try to futher cancel out radiating bass waves (Dam! I have put just way too much thought into being considerate here!  )
Could this work or have I missed something basic (I have been known to do that     )?

Any help you can give me will be appreciated.

Thanks,
Todd
Sydney Australia

[mcgsxr]

Welcome my Aussie friend, to the world of OB bass!

I should start a sticky, about drivers and specs.

http://www.audiocircle.com/index.php?topic=66676.0 should get you started, and points out specs that matter, and my thoughts.

As for your suggested implementation, it will take experimentation, but sounds valid to me.  I would start with one sub built and placed as you describe, and then move to multiples if req'd.

[oz_audio_todd]

Wow, that's a lot of info! Thanks for that. Sounds like I may just have to try them as I now cant find what I did with the specs any way.
Another quick question though: If I plan to use these for bass only (<80 Hz (may be lower still)), is there a baffle width that I should be trying to achieve? and are there pros and cons with thin vs wider baffles?
Thanks again   

[mcgsxr]

When the focus is bass only, effective baffle width becomes the main issue.  The wider, the better, to speak in sweeping generalities.

You can "fold" the baffle into U and H shapes, as many have, or you can use a very wide baffle, as other have.

I know that Martin King has done significant amounts of work around this topic, and as I recall the U baffle is his current fav, to blend good bass, with a minimum visual baffle width.

As for how wide to shoot for, there are math calcs out there to guide you through how wide a baffle equates how deep a bass note is supported.

For the record, with my OB 12 inch woofers, I am using an effective baffle width of 36 inches.  It has wings, so it is not 36 inches wide, it is 15 inches where the driver is, and has a 6 inch wing on one side, and a 14 inch wing on the other.  I know that only adds up to 35, but the width of the piano hinges makes up for the loss of baffle width due to cutting with a table saw!

[mcgsxr]

Oh yeah, what subs are you looking to use?

[Telstar]

I plan to use the Beyma 12BR70. Anyone else has used this before in OB?

mcg, my baffles will be similar to yours but I wont use asymetric wings, but sloped ones (in the middle). I got the idea on dyiaudio forum, it should work well

[oz_audio_todd]

Hey Mark, thanks for the reply
I was kind of thinking that i might get a few sheets of 18mm (3/4" in America speak) that are 600mm wide (24" or so) and use 3 of them to make a H shape. May be a bit off set the middle panel to the front to get the magnets in the centre of the footprint to make them as stable as possible. And I guess 1200mm high (48") may be with the speakers at the base with the sub plate amp mounted above it. I figure that should give me a bit more stability than a flat baffle. Does that sound like reasonable theory so far?
Can you let me know where might I find these baffle width vs bass freq equations pls? (I soooo should have used the word 'newbie' in my subject title!     ). I must admit that wide baffles make sense for bass but Mr Danny Ritchie's designs (GR Research in case people don't know him) look to be not much wider than his woofers, no idea how he gets down to 20Hz with them, but If he says he gets 20Hz, I believe him.
I found the specs on the subs that I have. They are probably just Taiwanese or something like that. I bought them from an electronics supplier called Jaycar here in Oz.
The 12's that I have are Carbon fibre cones,8 ohms, 200w power handling, Qts of .35, Vas of 230L, 93dB of sensitivity and an Fs of 22Hz.
The 15's were a little cheaper, but the program that I found on the net suggested that if I dropped 2 of them, mounted isobaricly into a 200L box, with some massive ports I could get a -3dB of 18Hz! That sounded most adequate to me but I never got around to building the boxes. Pretty sure my neighbours would have hated them any way 
They are 4 ohms, 250watts, 88dB, Qts of .5, Vas of 151L and a Fs of 26Hz.

I have the Sub plate amps and two of each of these woofers already, so I was hoping that they might be suitable.

Also, as I said, I am a total newbie, and just trying to wrap my head around the theory, but with your set up, wouldn't your lower bass capabilities be limited by your 6" wing, and hence the 14" side have 8" not adding much to the situation?

Thanks again for all your help   

[mightym]

You need to read this:www.quarter-wave.com/OBs/U_and_H_Frames.pdf

All the issues mentioned so far are addressed here.

should answer your questions.

IIRC, baffle measures should be from driver edge to driver edge all the way around from front to back. EG. a 20" baffle with 6" wings  from center to center would measure 32"

John

[oz_audio_todd]

Looks like some tough reading, but i printed off the article and will have a go at it tonight. Thanks for that John (no doubt I will be back with more questions soon though!       )

[mightym]

Most of the math in the paper went over my head like an F-16.  with a couple of readings I began to Grok.

This may help too, remember " ideal " tuning in a box is considered to be .707.  The OB woofer has no box to interact with, only the air in front and back to damp it.  Most OB designed bass drivers will have a min. .7 Qts.

John