Open Baffle musings

[charlielaub]

So, with all the talk about SL's LX521 system, I'm itching to try some kind of open baffle system. I want to bounce some ideas around here, so please feel free to deconstruct and criticize the following:

Open Baffle Project WAF-1
Drivers:

• 12" Eminence Driver: 60Hz - 300Hz
• 6" AE Speakers TD6M: 300Hz - 2500Hz
• up-firing SB Acoustics SB29RDCN ring radiator

Baffle & driver mounting:
rectangular 24" W, 36-40" H, 1.5" THK butcher block baffle
Eminence 12" near or just below midpoint
TD6M centered side-to-side in baffle, very close to top edge
SB29RDCN mounted at top of baffle, firing up into a "speaker spike" conical diffuser

Thoughts:

• I did some modeling of the positions of the woofer and midrange drivers, and it looks like these will work well in terms of the baffle response
• The Eminence driver was purchased from extra stock from Sausalito Sound - it was a special order for them. It has 10mm Xmax and a copper shorting ring. Le is 1.1 mH, Qt=0.42, Fs 30Hz. This looks like a good candidate for the low end (down to 40Hz - 60Hz) and the baffle should be heavy enough to keep the vibration down. Should be able to do 300Hz without any issues.
• The TD6M are drivers that I recently obtained and I think this will be a great application for them. Very low Le (0.044 mH). Should have good performance up to and above 3k Hz if needed (but would cross lower).
• With all of this talk about D/R sound and power response of the tweeter, I thought I would try something "different". The tweeter is a ring radiator, so the center of the dome is not moving. The tweeter would be mounted at the top edge of the baffle, pointed up. I would position a metal cone (like a speaker spike) with the point a few mm above the center of the dome. This should result in response that is independent of lateral angle. What happens with the vertical response is a big question mark, maybe just a lot of destructive interference... also very little high frequency energy would be available below the tweeter's mounting point, but I'm not sure that is much of an issue. I would definitely have to try this out alone before committing to it. Plan B would probably be a Neo3PDR.

So, what's the feeling on this concept?

-Charlie

[diy speaker guy]

Re: Open Baffle musings

So, what's the feeling on this concept?

-Charlie

I assume you are going active or else you wouldn't be using that woofer.

This concept is completely backwards compared to how active OB is trending, with narrow baffles and sometimes even baffleless to preserve dipole operation as high as possible in frequency.

I suspect this proposed concept will give you dipole operation only in the woofer range, above that I think it will get increasingly cardiod with the wide dual side by side mids and ending up omni in the tweeter range (as omni as a tweeter can be), basically the opposite of controlled directivity. If that's what you are going for I think you are on the right track. It doesn't seem to be what anyone else is going for though.

[JasonP]

Re: Open Baffle musings

Watch the bracing and amount of surface area you let be exposed on those panels. I learned the hard way with the Wavefront:


I even tried to break the panels up into three parts, didn't help. At loud volumes those panels have a sonic effect, and its not one you'd want. I'd brace them with some kind of glued on metal frame next time, but instead I'm making a design with a smaller radiating area and much more rigid wood (solid purpleheart).

Also, I want to start measuring the rear output of drivers used this way, since I think that has a large impact on perceived sound but little on direct frontal measurements - just an opinion at this point.

[jhollander]

Re: Open Baffle musings

Charlie, not sure why you would want to do an Omni tweeter with a dipole mid, you’re going to be out of phase on the rear.

Your mid on baffle measurements should determine the x-o points.

I didn't see dual mids?

[greywarden]

Re: Open Baffle musings

Cone thingy here

https://www.intertechnik.com/Shop/Accessories/Speaker-spikes-and-feets/_70350_0-Diffusorkegel-MT130_1768,en,18,115077

[charlielaub]

Re: Open Baffle musings

I assume you are going active or else you wouldn't be using that woofer.

This concept is completely backwards compared to how active OB is trending, with narrow baffles and sometimes even baffleless to preserve dipole operation as high as possible in frequency.

I suspect this proposed concept will give you dipole operation only in the woofer range, above that I think it will get increasingly cardiod with the wide dual side by side mids and ending up omni in the tweeter range (as omni as a tweeter can be), basically the opposite of controlled directivity. If that's what you are going for I think you are on the right track. It doesn't seem to be what anyone else is going for though.

Ah, I wondered if anyone would touch on that point (current trend towards narrow baffles). I understand the motivations behind this approach, however:
A. This is not a problem for the woofer
B. By mounting the midrange about as high as possible on the baffle, it is effectively "narrow", at least at or above the listening plane (40" off the ground) and I am hoping this will achieve the same thing

There are no "side by side mids" as you stated. Sorry for the confusion. There is a single open baffle cone midrange, located at the top of the baffle, near the center (laterally).

Yes, I would execute this as an (all) active system.

-Charlie

[charlielaub]

Re: Open Baffle musings

Watch the bracing and amount of surface area you let be exposed on those panels. I learned the hard way with the Wavefront

The baffle that I will be using is pretty solid stuff. The glue between the blocks stiffens it. It's usually used for countertop... and it's not as lively as MDF.

For bracing, I would use a single "leg" up the rear. This would form a "Tee" shape that adds stiffness. I can also brace the rear of the woofer as part of that structure.

-Charlie

[charlielaub]

Re: Open Baffle musings

Cone thingy here

https://www.intertechnik.com/Shop/Ac...8,en,18,115077

No, I would NOT use this:


This shape flares out too much and there would be reflections back at the dome. I'm thinking of something more like this:


The width is approximately the same as the dome width.

-Charlie

[Deward Hastings]

Re: Open Baffle musings

B. By mounting the midrange about as high as possible on the baffle, it is effectively "narrow", at least at or above the listening plane (40" off the ground) and I am hoping this will achieve the same thing

It really isn't (effectively narrow), and it won't. The thickness of the baffle only makes it worse. You won't like the midrange.

The planked woofer will work, but at 36" wide it will . . . impose. Do you have a room big enough for that? 300Hz is a bit high to cross off of a driver at floor level (especially to a mid over two feet above it), but if you move it up on the baffle you lose some floor coupling (gain) and other problems will appear.

You will simply fight the tweeter until you give up on it . . . if you could get it to work as an omni it would still be wrong on a dipole.

There are very good reasons that both SL and John K have gone 4-way . . . I'd expect that trying for a 3-way, especially with that driver selection and baffle, is just an invitation to disappointment. You'll get better results from that tweeter as a "normal" monopole, from the mid on a narrow (and much thinner) baffle, and from the Eminence as a subwoofer in a box. Look for something additional to serve as a dipole woofer/lower mid . . . it will make your life easier and the speaker both physically smaller and more likely to succeed.

[jhollander]

Re: Open Baffle musings

Plugged the drivers into ABC Dipole. Looks like the woofer needs some help

[Pete Schumacher]

Re: Open Baffle musings

No, I would NOT use this:


This shape flares out too much and there would be reflections back at the dome. I'm thinking of something more like this:


The width is approximately the same as the dome width.

-Charlie

The top one is much better than your second option. Most of the tweeter radiation at the lower end will not even see the narrow cone. Only the highest frequencies will intercept the cone, but even those will be directed upward.

The more drastic looking diffusor above is actually something that would probably provide better measured response in the horizontal plane.

But as others have pointed out, going omni on the tweeter and dipole on the mid is just plain not a good idea.

You'd be better off putting another tweeter on the back of the baffle. At least you'd have some semblance of a dipole radiation pattern to compliment the open baffle drivers below.

[charlielaub]

Re: Open Baffle musings

Plugged the drivers into ABC Dipole. Looks like the woofer needs some help

Yup. I'm well aware of that, thanks.

[charlielaub]

Re: Open Baffle musings

Deward, Did you listen to this WWF OB system at BA (F=Fostex fullrange):


I thought it sounded pretty nice, although I only had about 30 seconds to listen to it. It's two woofers on a wide baffle plus a small full range near the top. I am proposing something that is like that, but with an omni tweeter.

Why are y'all's panties in a bunch over this?

What is the big deal with going from dipole to omni, just for the top end sparkle?

And I still think that the "effective baffle" width will be "narrow" with midrange driver positioning. It's true that below the level of the driver, the baffle will appear wide, but no one listens to the speaker while lying on the floor! So mostly the listening position will be at or above the mid, and there will be short paths from front to back from that perspective. This is what my sims are telling me...

Anyway, here is a quick sketch. Baffle dims are 24"W, 36"H:



-Charlie

[charlielaub]

Re: Open Baffle musings

Charlie, not sure why you would want to do an Omni tweeter with a dipole mid, you’re going to be out of phase on the rear.

Hmmm, I hadn't thought about the "out of phase on the rear" thing. But maybe it's not such a problem... the tweeter is mostly radiating up, and is above the mid. The mid may not have appreciable radiation "up" towards the tweeter in this range, and so being out of phase might not be important. Anyway, even if it was an issue, I could use a very steep filter to minimize interactions, no?

-Charlie

[edlafontaine]

Re: Open Baffle musings

May want to review Dan N's creations.