[opnly bafld]

I finally did it,
45"x20" baffle,
top to bottom,
B200 + tube amp fullrange,
B200 + tube/fet 12 mH inductor,
Hawthorne Augie + ss  80hz/24 dB.
Can easily have too much bass.
Below 40hz still a problem, but with a baffle not much wider than the Augies expected.
I have a few ideas to try to coax a little more low end grunt out of the Augies.
No comments on the overall sound yet, I need to dial it in and listen some more.
If this seems complicated, you should have been the one to wire it all up.

Lin

[JohninCR]

Lin,

What size is your room?  You may be running into the steep dipole drop off below room resonance.  Also, do you have the ability to adjust the slope on that Augie XO?  My guess would be a low pass at 30-40hz with a 12db/oct filter.  Multiple low pass filters like that will likely result in some phase issues that you'll need to address to get it optimized.

Now you're having fun.  Good luck with it.

[opnly bafld]

Hey JohninCR,
Room is 22' at the front (where speakers are) and 12' at the rear x 18' length.
shape is                       22'
                       xxxxxxxxxxxxxxxxxxxxxx
                       xxxxxxxxxxxxxxxxxxxxxx
                 18'   xxxxxxxxxxxx/w dining room^
                       xxxxxxxxxxxx/a kitchen<
                       xxxxxxxxxxxx/l
                       xxxxxxxxxxxx/llllll
                       hallway------------------------------
                       l     12'       l
x's at top right dining room- blank area bottom right kitchen with a wall to separate from livingroom - it seems to act like one big room with regard to bass.

No adjustment for slope now, but I am planning on getting 2 plate amps from PE (out of stock and why I have been putting off trying this) w/12dB slopes for Augies.

Lin

[JohninCR]

Lin,

I asked about the room because John Kreskovsky, in his tech studies at www.MusicAndDesign.com tells us that dipole bass rolls off steeply below a room's fundamental resonance.  I'd have no idea how to compute that for an L shaped room like yours.  I've tried to discuss this topic with him in a couple of threads over at the DIYAudio forums, because he talks about dipole being limited because it can't pressurize the room (but somehow cardioid, as in U-baffles can).  I don't doubt his test results, but I think the wording of the conclusion may be incorrect.

I believe the extension limitation of dipole bass is based on the on axis[/b] room mode, not necessarily the fundamental mode.  I believe the answer doesn't lie in pressurization, because I don't see how a U-baffle can create any pressure vessel gain.  Instead, once you get to the on axis mode the baffle size ceases to be the limitation and the room itself takes over.  In simple terms, 1/2 wavelength of the front and rear waves no longer fits in the room, so the reflections of the 2 wavefronts cause much more cancellation than the 6db/oct dipole roll-off.  Think about it like you are creating 2 standing waves, but they are directly out of phase, so cancellation is great.  U-baffles avoid this effect because the on axis response is primarily the front radiation only.

In your case, your room is large enough that probably isn't your problem in the 40hz range, as your 18ft distance should enable you to get down to near 30hz before encountering problems with dipole extension.  It's more likely a combination of your baffle size, the B200's rolling off much more steeply down there, and too high an XO point.

I'm going to be testing an active PC solution for XO very soon, my first try at an active XO.  Not only will I have complete flexibility for filter points and slopes, but I'll also have EQ, time alignment, and even phase correction.  If it's as transparent as the beta testers are reporting, then we're talking about a whole different league from anything I've done yet (time aligned flat response combined with the coherency of a fullrange driver, but with perfect phase).  Because everything is handled in the digital domain, the limiting factor will be reduced to the DAC used. 

[opnly bafld]

I tried U-baffles 12" deep in this and another smaller room with no discernable differences from a flat 26" wide baffle, other than I liked the sound better with the flat baffle, maybe because I was crossing it over higher (150-170 24dB) to reach just 1 B200.

Thanks,
Lin

[JohninCR]

I've had the best success with lower filter points and shallower slopes.  My objective has always been to try to match the roll-off of the augmenter(s) to the decreasing response of the main driver.  That's probably why you and others have success with the added B200 to augment the bass using just a coil.  The phase change is minimal and the B200's very gradual roll-off is difficult to match with an augmenter and a steeper sloped XO , especially if you leave the B200 running full range.  I can't wait to hear the B200 relieved of low bass duties and a touch of EQ to pad down the top end.

Regarding U's- They require damping and, most importantly, significant bracing if you are generating bass.

[hurdy_gurdyman]

Good morning all. I hope I'm coherent this Monday morning. I've spent the weekend at a music fest sustained with a prednisone (steroids) boost to keep me going. I feel like I've been run through an old fashioned washing machine ringer this morning.

I use a simple 1st or second order slope with bass agmenters on any open baffle driver I've used over the last five years or so, including vintage 8", 10" and 12" fullrangers and modern 15 inch coaxials. John is right about crossing low. Even with my 8 inch EV fullrangers, which plumented below 80 Hz, the bass augmenter was crossed about 40 Hz or lower. This seems to blend well with most OB configurations. Currently, with my 15 inch SI coaxials, when I even use bass augmentation, it's crossed down around 25-35 Hz. I actually find first order easier with any of these drivers to integrate than second order, as long as you cross very low. It just sounds cleaner.

Dave

[opnly bafld]

Thanks for your input HG Dave.

Lin