[sfdoddsy]

Can anyone hazard a guess what the radiation pattern for an OB woofer section in a U frame with dual side-mounted woofers might be?

Like this:






And any advantage over a regular U frame?

[matevana]

Assuming the woofers are wired with the same polarity, it will likely throw an irregular figure eight pattern, which often requires more complex correction to address phase abnormalities. While you might be able to make an argument for force cancellation in a sealed enclosure, this would have little benefit in an open box.

[matevana]

What might be more interesting is an experiment wiring the woofers in push-pull. You would likely wind up with a dispersion pattern similar to that of the single woofer Gradient Helsinki. Many people seem to like this speaker.

[sfdoddsy]

Thanks. Upon further research Danny from GR Research is proposing something similar as a base for his OB speakers.

Is it really as easy as he makes out?

https://www.audiocircle.com/index.php?topic=126112.msg1331035#msg1331035

[matevana]

You would still wind up with an asymmetrical radiation pattern with heavy cancellation in the rear. This design seems to be purpose built as stands for mini monitors that are placed close to the front wall. The best sounding systems that I have heard seem to strive for symmetrical radiation throughout most of their range, along with ample space from room boundaries.

[sfdoddsy]

My long-term Orionish open baffles successfully used a flat baffle and then an H-Frame stuffed with big drivers well out from walls. Alas, for space and aesthetic reasons I'm not able to do that with this build.

I'm actually going for something that can be used close to a front wall to support (possibly physically) an OB mid-tweeter section from around 300 to below 80.

Sealed would be easy. My most recent speakers used a pair of sealed boundary woofers like the Lyngdorf DP1 but I'm not sure I can get that through again in our new home.

And I could just do a sealed mid-bass box with an OB panel above.

Tempting would be trying for cardiod with a slotted acoustic resistance enclosure like the Dutch and Dutch 8c.

The side mounted U frame felt like it might be somewhere in-between.

The ability to reverse connections and approximate the pattern of the Helsinki makes it even more appealing.

On the other hand, a simple U-frame can be sealed if it doesn't work.

Decisions.

[AJinFLA]

The side mounted U frame felt like it might be somewhere in-between.

The radiation pattern (cardioidish>dipole) is frequency dependent, including of course the baffle size. I have measurements somewhere of a design (from 2012ish) that used that exact layout, so I'll try to dig up for you.

[sfdoddsy]

Thanks AJ. I'd be most curious. Do you recall if they needed as much EQ as normal dipoles?

[AJinFLA]

Thanks AJ. I'd be most curious. Do you recall if they needed as much EQ as normal dipoles?

At lowest frequencies, because the baffle size is small relative to wavelengths, yes, or close to as much.
What bandwidth is your intended use?

[sfdoddsy]

250 down to 80hz or so.

[AJinFLA]

250 down to 80hz or so.

80?? That's a midbass Steve. 
Almost begs the question why an opposed U? How wide is the coax upper baffle? IIRC, you're going heavily WAF with these?
If 8.5" (215-220mm) is slim enough, you could get away with multiple front mount 8s and easily get good output to 80hz with minimal sides depth

[sfdoddsy]

Well, lower might also be nice.



The coax is the Seas C18, but I also have a set of BG Neo 10s and Neo 3s hanging around which would require a thinner baffle.

The mid-bass drivers in question will either be my exisiting RS225s or possibly Anarchies.

Mind you, I also have some SLS10s floating around somewhere.

[sfdoddsy]

The radiation pattern (cardioidish>dipole) is frequency dependent, including of course the baffle size. I have measurements somewhere of a design (from 2012ish) that used that exact layout, so I'll try to dig up for you.

Don’t make me nag you AJ!

[Openly Baffled]

Can anyone hazard a guess what the radiation pattern for an OB woofer section in a U frame with dual side-mounted woofers might be?

Essentially Cardioid but with 2 rear off-axis nulls.

The nice thing about the rear nulls is they reduce the bass boom effects from the rear corners of your listening room. This can eliminate or at least reduce the need for rear corner acoustic treatments.

The design also increases bass SPL compared to a simpler finite open baffle design.

However, I'm not a complete fan as, IMO, some of the impact and openness of open baffle bass is lost in this configuration.

I've experimented with H and U frames but I keep going back to a planar baffle with a combined Fc of about 200Hz - then actively equalize.

[sfdoddsy]

That's what I was hoping the layout would do.

Unfortunately Danny Ritchie built a pair and found they operated more like a slotted port.

https://www.audiocircle.com/index.php?topic=129161.msg1369962#msg1369962

Any thoughts?

[Openly Baffled]

That's what I was hoping the layout would do.

Unfortunately Danny Ritchie built a pair and found they operated more like a slotted port.

I think there is a lot going on with Danny Ritchie's design.

Most proponents of this set-up keep the shared air mass between the woofers to a minimum. There is a limit because you don't want the "port" air velocity too high otherwise chuffing (and distortion) will occur.

The offset design probably introduced additional reflections, turbulance and high air mass. Maybe this is why the results weren't so good.

I suggest you track down others who have made (and still use) these systems to get their feedback.

[rollo]

What might be more interesting is an experiment wiring the woofers in push-pull. You would likely wind up with a dispersion pattern similar to that of the single woofer Gradient Helsinki. Many people seem to like this speaker.

   A wonderful speaker. Everyone should hear it.


charles

[sfdoddsy]

I think there is a lot going on with Danny Ritchie's design.

Most proponents of this set-up keep the shared air mass between the woofers to a minimum. There is a limit because you don't want the "port" air velocity too high otherwise chuffing (and distortion) will occur.

The offset design probably introduced additional reflections, turbulance and high air mass. Maybe this is why the results weren't so good.

I suggest you track down others who have made (and still use) these systems to get their feedback.

Indeed.

I've been trying to track down those who use such a system

Hence my post here (and with the clever folk at HTGuide).

Alas, the answers have diverged.

I'm generally not a fan of Mr Ritchie's designs, and this one did not work as he claimed it might.

To his credit he admitted this.

The closest I could find elsewhere were the various SLOB discussions at DIYAudio and the Cardiod Bass ones which led to the Dutch and Dutch speakers.

You, however, seem to know folk who have tried such a system.

If you can direct me, I'm all ears (and fingers).

Otherwise I suspect I'll have to take the non-lazy route and do a test baffle and measure the damn thing.

[JohnR]

How close to the wall does it need to go?

(I'm a bit confused about the design goals).

[sfdoddsy]

About 50cm from the rear wall.

It's the bass section of a stand-mount open baffle to cover from 300hz down to 80Hz.