Corner position dipole option

morayjames · « **on:** 25 Oct 2006, 10:14 pm »

Thought that I would post this link to the Linkwitz site. This would make a great experiment with the GOLDWOOD GW-212/8 12" OEM WOOFER 8 OHM for instance. It is a simple woofer, PE's price is $ 18.95, but it has TSPs suitable for OB use. or other 15 or 18 inch driver with suitable specs. The bigger the driver the lower the Qts can be so you could probably get away with values as low as 0.3 - 0.35 with dual 18 inch drivers.
http://www.linkwitzlab.com/faq.htm#Q30

JLM · « **Reply #1 on:** 28 Oct 2006, 12:34 pm »

Wouldn't the front and back waves (being that close to each other) just cancel each other out?

JohninCR · « **Reply #2 on:** 28 Oct 2006, 05:15 pm »

JLM,

You're exactly right. I can't believe SL has a link to that on his website.
I guess he didn't think it through, and the guy with the test baffle probably
measured it only nearfield. The travel distances for the + and - waves are
too close to equal, so it would be like listening very near the baffle axis and
have very little bass.

A better idea is even more simple, is to use a single piece of wood on a 45
degree angle in the corner. Then corner loading can work to your advantage.
I've seen one similar design used near corners where the builder reported great
results. A setup like that would be appropriate when near corner placement
is unavoidable, because firing the rear wave of a dipole directly into a corner
is problematic.

U-Baffles are less problematic near corners, but they require a little more effort
in design and tuning, which IMHO is worth it.

opnly bafld · « **Reply #3 on:** 28 Oct 2006, 05:28 pm »

Quote from: JohninCR on 28 Oct 2006, 05:15 pm

JLM,

You're exactly right. I can't believe SL has a link to that on his website.
I guess he didn't think it through, and the guy with the test baffle probably
measured it only nearfield. The travel distances for the + and - waves are
too close to equal, so it would be like listening very near the baffle axis and
have very little bass.

A better idea is even more simple, is to use a single piece of wood on a 45
degree angle in the corner. Then corner loading can work to your advantage.

Are you sure John?
Have you tried it?

Lin

ooheadsoo · « **Reply #4 on:** 28 Oct 2006, 06:16 pm »

Would that be me?

My verdict - bass is great! Depth of soundstage...not so much. Watch out for ceiling reflections/ground reflections depending on where you place it, they're really bad.

ooheadsoo · « **Reply #5 on:** 28 Oct 2006, 07:26 pm »

Yes I saw that. I packed fiberglass behind my baffles to try to alleviate the problem. Can't say that it was a success.

JohninCR · « **Reply #6 on:** 28 Oct 2006, 07:47 pm »

ooheadsoo,

Interesting. Make your corner immediately behind the driver an outie using
a triangular box stuffed with your fiberglass so the box doesn't resonate. This
will likely cure at least most of the resonance problems with your arrangement.
It would divide the rear wave in half and guide the 2 halves out toward your
openings instead of reflecting around in that corner. Don't make it a right
triangle, though, because too much pressure is directed back to the cone. You
won't get as much bass, but I'm pretty sure it will sound better.

Turn your baffle 90 degrees, so one edge is in the corner and the baffle is sticking
out at 45 from each wall. We had a woofer in mind, but with the right material
on the wall as a reflector and the right listening position relative to the corner,
you might be able to turn your B200 into a direct reflecting OB speaker and even
tone down that top end in the process.

Lin,
I'll leave it to you to try the cab in the original post. I have enough projects in
mind that I'm pretty sure will work to try something that I'm convinced won't work.

ooheadsoo · « **Reply #7 on:** 28 Oct 2006, 07:53 pm »

Hi John,

Actually, I also have eighth nerve corners in there in addition to a few wads of fiberglass. In any case, that setup now belongs to a friend of mine who will utilize them as proper dipoles. Thanks for the advice though - but if I were to ever do it again, my entire ceiling would have to be treated before I would consider it. The reflections from the top were far too strong.

JLM · « **Reply #8 on:** 28 Oct 2006, 07:58 pm »

If you look back into the earlier pages of the Darkstar thread you'll see that I proposed the baffle across a corner, extending to near the floor and ceiling, to create a sort of cross between open and infinite baffle. At that time we envisioned damping/reflectors behind the driver, like many box designs (and now open baffles, especially those with "wings"). The whole idea was to boost bass response relative to mid/high frequencies.

Thanks ooheadsoo for your impressions.

scorpion · « **Reply #9 on:** 28 Oct 2006, 10:38 pm »

JohninCR,

What do you mean in your first post ?

/Erling

JohninCR · « **Reply #10 on:** 28 Oct 2006, 10:43 pm »

Quote from: scorpion on 28 Oct 2006, 10:38 pm

JohninCR,
What do you mean in your first post ?
/Erling

Not my post, Moray's (or is it James?).

scorpion · « **Reply #11 on:** 28 Oct 2006, 10:49 pm »

JohninCR,

Certainly not, your first post, not the first post !

/Erling

JohninCR · « **Reply #12 on:** 28 Oct 2006, 11:29 pm »

Sorry Erling,

A temporary brain fart on my part. The baffle shown in the initial link
puts the listener very near the null plane at almost any point in the
room. The +6db coming out of the center compared to either side is
completely offset by the boundary gain at the sides. I've got a name
for the design, "The almost no output OB corner sub". The reason it
can't have much output other than the very nearfield is that the travel
distance differentials for the + and - waves are extremely short because
the listener must be relatively close to the axis of the baffle plane, kind of like
listening to a flat baffle 75 degrees off axis. Corner loading nil is still nil.
My guess is that the guy how tried it, measured in the nearfield for him
to say it shows promise. In the very far field I believe output would
approach zero in any listening position due to those wall boundaries.

scorpion · « **Reply #13 on:** 30 Oct 2006, 05:06 pm »

John,

You are of course right about distances but wouldn't there be a lot more reflections, diffusion and wider spread compared with the situation with a simple wall reflection ? But that might not apply to bass-wavelenghts ?

/Erling

JohninCR · « **Reply #14 on:** 30 Oct 2006, 07:01 pm »

Here's a link to the original stuff. http://www.geocities.com/larryselmer/DRL.htm
Near the bottom of the page are some very interesting corner bisected ideas.
I really like the U-baffle one, which will force the area of greatest null away from
center and toward the side walls, perfect for a wide room. In my narrow deep
room the other orientation might work best, keeping the null near the front of the
room. Now I have something new that I must try.

scorpion · « **Reply #15 on:** 30 Oct 2006, 08:10 pm »

Yes, I found that link from Rudolf's original too and Dunham didn't go so far into the corner.

/Erling

opnly bafld · « **Reply #16 on:** 31 Oct 2006, 03:36 pm »

I tried the corner dipole thing, the way it is shown in the top view, with 2 Hawthorne Augies on a 45 degree V baffle 20" wide.
It had about half as much output(maybe less) as 1 Augie on a 20" wide flat baffle well out into the room.

I am glad it was an easy experiment for me, considering the underwhelming performance of the corner V baffle.

Edit: I used OB -not dipole in enclosures, so my experiment does not mean much.

Lin

Rudolf · « **Reply #17 on:** 31 Oct 2006, 10:52 pm »

Lin,
I believe Larry Selmers proposition on the Linkwitz´ site would qualify as a longitudinal quadrupole - with all the bass crushing effects of that design. You seem to be the first one actually trying this AFAIK.
Quadrupoles have been mentioned recently in http://www.audiocircle.com/index.php?topic=32731.10
Look for AJinFLA s reply 14.
What Larry actually built was a corner bisecting dipole as mentioned by JohninCR. That design looks quite promising - a valuable alternative for people with free room corners.
It seems to me that you have built a corner bisecting OB on a 20" wide triangular baffle with one 15" driver and found its output half as much as the same driver on a 20" width rectangular baffle out in the room. Is that correct?

Rudolf
www.dipolplus.de

opnly bafld · « **Reply #18 on:** 31 Oct 2006, 11:42 pm »

Rudolf,

I thought the side view looked like the drivers were enclosed, but the top view showing the angles seemed to indicate they were OB.

If I would have read the comments more carefully I would have realized it was suggesting dipole only, not OB.

I tried 1 driver OB on a rectangular baffle, as well as 2 drivers OB on a rectangular V baffle.(45 degrees)

Lin

JohninCR · « **Reply #19 on:** 3 Nov 2006, 11:20 am »

I'm sorry I missed these posts the other day. I'm glad someone gave it
a try just to be sure we we're missing some magic formula. You guys
are confusing me with the dipole vs OB thing though. I look at it as
OB, Open Baffle or Open Back, as anything with the front and rear of
the drivers open to the world. Dipoles are a subset of OB's where the
front and rear are equal, the simplest implementation being a driver
mounted on a flat baffle.

It sounds like what you did Lin is use 2 drivers, each mounted on a
rectangular baffle (2 dipoles), and stick them in a corner with one edge
joined and the baffles splayed at 45 degrees, just like the original diagram.
Then as long as your wiring was correct, drivers firing at each other in
unison, you tested the design perfectly.

Lin,
If you still have the Augies on those flat baffles, you may want to try just
one stuck in the corner, bisecting it. I can see that working as long as
your listening position isn't near the plane that bisects the corner.

I think the guy originating this approach was trying to use corner loading
to our benefit and conserve some of the energy that is wasted in the bass
region with our typical OB implementations, as well as hide some of the in
the corner. I have a feeling the concept may work very well with the right
room and listening position using one of the bisecting approaches near the
bottom of the more detailed link.

My hat's off to you Lin for giving it a try.