What is the appeal of open baffle?

[Newman]

objective references for this claim (OB speakers interact "less" with the room)

Basically it is because, in the low range, an open baffle radiates like a 'figure 8' whereas a monopole radiates like a sphere. So the open baffle energizes the side wall and ceiling modes less.

Plus, as pointed out by someone a few posts ago, the front-rear cancellation in the bass obviously means less SPL for the room modes even if activated...

 

[puppet]

You could look at the improved bass w/OB this way ... considering (2) 15" drivers you actually have (4) sources working to even out room modes.

 

[Wseaton]

We need to narrow this down. Open baffle has different implications for tweeters, midrange and woofers.

We used to have a Legacy showroom nearby with the owner being a friend. I spent the better part of a day screwing with Bill Duddlestein's massive Whisper XDS design with each speaker housing 4x15" woofers in a back to front config that cancels out room reflections to a degree by directing the wave front. Bass transient response of the XDS rivals midrange drivers. Try that with a 12" woofer bolted to the front of a box.

 

[dc655321]

Basically it is because, in the low range, an open baffle radiates like a 'figure 8' whereas a monopole radiates like a sphere. So the open baffle energizes the side wall and ceiling modes less.

Plus, as pointed out by someone a few posts ago, the front-rear cancellation in the bass obviously means less SPL for the room modes even if activated...

Thanks. I am aware of the hand-wavey explanations, but I asked for objective references. Evidence.

 

[Newman]

https://www.linkwitzlab.com/rooms.htm#B

Perhaps when Linkwitz waves his hands, you won't call him hand-wavey. Same explanation though.

 

[dc655321]

https://www.linkwitzlab.com/rooms.htm#B

Perhaps when Linkwitz waves his hands, you won't call him hand-wavey. Same explanation though.

You ain't he.
Thanks for the link.

 

[OWC]

Could you please recommend some objective references for this claim? I would appreciate seeing the physics layed out for this oft touted rationale.

Well, for starters, it's kind of inherent to the dipole shape.

With full cancellation on the sides of the speaker, as well as having a front and backwave that are each others polar opposite.
But if you want to get a grasp on things, I would recommend reading Linkwitz' website.

 

[OWC]

https://www.linkwitzlab.com/rooms.htm#B

Perhaps when Linkwitz waves his hands, you won't call him hand-wavey. Same explanation though.

Linkwitz is not gonna wave any hands anymore unfortunately

 

[SIY]

Thanks. I am aware of the hand-wavey explanations, but I asked for objective references. Evidence.

There is a planar node in ANY dipole, whether acoustic (speakers and mikes) or antennas. This can be found in any basic text on vibrations and waves. Also see Beranek and Mellow's "Acoustics - Sound Fields and Transducers" for analysis.

 

[Jim Matthews]

You ain't he.
Thanks for the link.

Geddes posted some raw data regarding in room responses including dipoles. I suspect the emphasis on cardioid response misses the obvious aspect of OB designs - limited contribution from cabinet resonances.

After decades with panel designs (and the necessary positioning fussiness) I concur with Geddes conclusion and shifted to Constant directivity as my polestar to follow.

OB designs can be compared to ported cabinets, where considerable energy (at 180° polarity to the primary signal) is directed away from the listening position and arrives at the ear a significant time later.

This would be perceived as reverberation.

I leave it to our Gentle readers to determine if that is preferable.http://www.gedlee.com/Papers/papers.aspx

 

[OWC]

Geddes posted some raw data regarding in room responses including dipoles. I suspect the emphasis on cardioid response misses the obvious aspect of OB designs - limited contribution from cabinet resonances.

After decades with panel designs (and the necessary positioning fussiness) I concur with Geddes conclusion and shifted to Constant directivity as my polestar to follow.

OB designs can be compared to ported cabinets, where considerable energy (at 180° polarity to the primary signal) is directed away from the listening position and arrives at the ear a significant time later.

This would be perceived as reverberation.

I leave it to our Gentle readers to determine if that is preferable.http://www.gedlee.com/Papers/papers.aspx

I don't follow your first sentence.
One could make a cardioid basically on the same way as a dipole.
You just block the backwave with damping material or similar.
This is basically what the guys at Dutch & Dutch do.

It is also possible to make a carioid out of closed speaker (or BR for that matter), but the same counts for a dipole system.

There is no perfect, one way or another. They just have their advantages and disadvantages.
The constant directivity always counts, regardless whatever system you have.

The comparison vs ported cabinets doesn't make any sense.
The port and speaker work as one, ports can also be on the front etc.
Also the frequencies from a BR are way to low to cause any reverberation.

Unless you're talking about the internal resonance/standing wave and bleed through from the port.
But that is a different story, and either just one small band or side effect.
A good engineer/designer takes care of that.

 

[Newman]

the obvious aspect of OB designs - limited contribution from cabinet resonances.

People do say that a lot. But, without going thoroughly into it, I would assume an OB's baffle would resonate more than most decent cabinets, due to the relatively flimsy restraint. Hence, an OB should be more prone to structural resonance.

 

[Jim Matthews]

People do say that a lot. But, without going thoroughly into it, I would assume an OB's baffle would resonate more than most decent cabinets, due to the relatively flimsy restraint. Hence, an OB should be more prone to structural resonance.

Paging Dr. Toole...

While making acoustically inert cabinets *is possible* waterfall plots reveal cabinets releasing significant energy, delayed from the primary impulse.

https://www.audiosciencereview.com/...vs-amirs-speaker-measurement-waterfall.21753/

 

[abdo123]

Way more unpredictable room interaction, but potentially more cancellation leading to a greater direct/omni SPL ratio than normal monopoles. Market advances in LF directivity control make it obsolete, in my opinion.

and by the market you mean five or six digit price boutique speakers?

 

[abdo123]

This is basically what the guys at Dutch & Dutch do.

This is not what the D&D do, they intentionally leak some cabinet sound pressure out, it's out of phase, and that's how they remove the back wave, no damping, damping at 100Hz would be insane.

 

[Jim Matthews]

I don't follow your first sentence.

The link to Geddes' articles is linked at the bottom.

One could make a cardioid basically on the same way as a dipole.
You just block the backwave with damping material or similar.
This is basically what the guys at Dutch & Dutch do.

No doubt. This discussion concerns the "appeal of open baffles" and I assert much of that stems from the response pattern.

The comparison vs ported cabinets doesn't make any sense.
The port and speaker work as one, ports can also be on the front etc.

Are you suggesting that port output is in phase or out of phase with the driver in the cabinet?

Also the frequencies from a BR are way to low to cause any reverberation.

What is a BR?

Unless you're talking about the internal resonance/standing wave and bleed through from the port.

Port output interferes with main driver output, both constructively and destructively. Placing the port on the rear of the cabinet necessarily induces a timing offset, which then interacts with room walls - including the wall behind the speaker.


https://sonicscoop.com/2017/12/14/the-1-speaker-placement-tip-speaker-manuals-get-completely-wrong/

 

[hex168]

Dipoles in room. Not hand-wavey:
http://musicanddesign.speakerdesign.net/roomgain.html
http://musicanddesign.speakerdesign.net/roomgain2A.html
http://musicanddesign.speakerdesign.net/Dipole_modesA.html

This is from a valuable site (thank you to Dave Ralph for preserving it):
http://musicanddesign.speakerdesign.net/tech.html
John Kreskovsky's site (archived):
http://musicanddesign.speakerdesign.net/products.html
All at Dave Ralph's site (other good stuff, too):
https://speakerdesign.net/

 

[OWC]

This is not what the D&D do, they intentionally leak some cabinet sound pressure out, it's out of phase, and that's how they remove the back wave, no damping, damping at 100Hz would be insane.

Right, you just described exactly the same thing.

fyi, the only way to make a cardioid is to dampening the backwave, otherwise it would be still a dipole.
fyi 2, I would highly recommend diving a bit deeper in the history of the 8c, were it came from and how it was constructed.

There are a lot of people and information on diyaudio as well as the Dutch ZBA forum.
Especially from a user called Jag.

 

[abdo123]

Right, you just described exactly the same thing.

fyi, the only way to make a cardioid is to dampening the backwave, otherwise it would be still a dipole.
fyi 2, I would highly recommend diving a bit deeper in the history of the 8c, were it came from and how it was constructed.

There are a lot of people and information on diyaudio as well as the Dutch ZBA forum.
Especially from a user called Jag.

I’m pretty sure the term you’re looking for is cancellation, damping is usually associated with absorbers.

 

[Jim Matthews]

Right, you just described exactly the same thing.

fyi, the only way to make a cardioid is to dampening the backwave, otherwise it would be still a dipole.
.

Not according to Linkwitz.

See figure 5 in the linked article.https://www.linkwitzlab.com/H-U woofer2.htm

As mentioned before, I prefer designs with fewer parts, less required equalization and more compact cabinetry.