Beaming? Lobing? Directivity? René Of Acculution explains …

[hardisj]

In the audio realm we talk about “beaming”, “directivity”, “lobing” and “breakup” in speakers. But I find that few people understand what it means. So, I asked René Christensen of Acculution to join me and explain. In the video below, @René - Acculution.com breaks down the math and gives us practical examples, showing how cone geometry and materials can impact radiation and resonance in transducers.

Please leave a “thank you” for Rene in the video comment section and make sure to leave suggestions for future topics you’d be interested in seeing.

(FWIW, my “interview” videos are not monetized)

 

[DanielT]

Thanks to René and Erin for that video!

I'm just starting to look at it. Seems very interesting. This will be new knowledge and educational for me and I'm sure others will like the video.

 

[ppataki]

Thank you @hardisj & @René - Acculution.com for this video - mostly above my head but extremely good material!

If I may answer the question at the end here: yes, all these topics would be really interesting to hear about! I vote for all of them

 

[xaviescacs]

If I have to choose, I vote for Phase and Room modes.

 

[Bill Brown]

Great video. Thank you to you both. I am hoping you can settle a concept I have been struggling with in the concept of DIY speaker dreaming.

My long-time-ago reading lead me to believe that radiation above a certain ka and the resultant change in the driver's directivity was solely based on non-pistonic driver activity (it was in "breakup"). Contrary to this, of course, are driver data sheets for rigid diaphragms showing an absence of resonant behavior until a single prominent resonance peak very high up (beryllium tweeter the classic example), despite the fact that there are of course radiation changes.

So the conclusion, as demonstrated in the video (I think!), is that in the absence of breakup, the distances along the surface of the driver lead to differing radiation patterns by frequency (as shown in the video with multiple drivers interacting in an array). I had been thinking this was the case for some time now, but then a couple of images in the video made me again wonder.

In this image relationships between the pressures being generated is being demonstrated rather than diaphragm behavior?:

This one, too, as it is similar to images of a driver in breakup:

Thank you again for the video,

Bill

 

[mightycicadalord]

Wow what wonderful info. I know there is a lot I don't know buy my god, it's worse than I thought lol.

Some good reads on acculution website for anyone interested.

I noticed some of the visual aids of cone movement look pretty much exactly like some that you find on focals website. Any relation or just coincidence?

As far as future topics, yeah I agree I'd love to hear them all covered. I have a basic understanding of the choices there, but likely nowhere near what I could René reveal in a short time.

 

[MCH]

Fantastic explanation with the right level of complexity for someone that sometimes reads the speaker reviews here and starts to be familiar with the graphs but doesn't really know much more (like yours truly).
Highly recommended if you fall in this group.

Will be definitely watching for the phase, room modes and crossovers videos.

 

[alex-z]

Awesome stuff. The illustration of quadrature in the circular piston helps me understand the inherent loss of efficiency that real world drivers experience with higher frequencies.

I would love to have a video talking about Q value and transient behaviour. That could clear misconceptions about cabinet tuning, especially in subwoofers.

Additionally, if René has thoughts on optimizing ports with simulation, that would be excellent. A lot of port designs seem outright rudimentary, having extraneous resonances, and non-linear flow.

 

[fineMen]

... in the concept of DIY speaker dreaming.
... is being demonstrated rather than diaphragm behavior?:

Problem is, the topic, despite being not too complex, departs from all-day knowledge, the wording ("breakup") doesn't help either. Not the least, the challenges posed by not ultimately rigid cones are not in the working-field of the user. He would take what he gets.

And he should. You cannot do anything about it, but make the right choices. Always look at what comes out of the speaker, don't question how it gets in there as to say. To deal with drawbacks is enough of a task to accomplish for a speaker designer.

For instance, the main problem today is not the cone. It is the surround, especially with high(er) excursion drivers. The surround is the first and most sound destroying part of the driver. Often we see a soft dip of 3dB@600Hz maybe, and shrug our shoulders with neglect. If it is due to a resonant surround, though, that would easily generate 10..20..30% of intermodulation, once the cone has to move a fair bit, say +/-3mm. The IM is far more destructive to the sound than elevated HD could ever be.

The "Purify" models have these nasty surrounds for a reason - high excursion demand and the midband to be maintained clean. And a humble quite regular simple paper cone, hmm ...

 

[René - Acculution.com]

Great video. Thank you to you both. I am hoping you can settle a concept I have been struggling with in the concept of DIY speaker dreaming.

My long-time-ago reading lead me to believe that radiation above a certain ka and the resultant change in the driver's directivity was solely based on non-pistonic driver activity (it was in "breakup"). Contrary to this, of course, are driver data sheets for rigid diaphragms showing an absence of resonant behavior until a single prominent resonance peak very high up (beryllium tweeter the classic example), despite the fact that there are of course radiation changes.

So the conclusion, as demonstrated in the video (I think!), is that in the absence of breakup, the distances along the surface of the driver lead to differing radiation patterns by frequency (as shown in the video with multiple drivers interacting in an array). I had been thinking this was the case for some time now, but then a couple of images in the video made me again wonder.

In this image relationships between the pressures being generated is being demonstrated rather than diaphragm behavior?:

View attachment 203174

This one, too, as it is similar to images of a driver in breakup:

View attachment 203175

Thank you again for the video,

Bill

Without any break-up, you will have the issue with beaming as demonstrated. Modal behavior will change the displacement phase from point to point, so that will also affect radiation patterns, since now you have phase changes from distance and from general variation over the cone.

 

[René - Acculution.com]

Wow what wonderful info. I know there is a lot I don't know buy my god, it's worse than I thought lol.

Some good reads on acculution website for anyone interested.

I noticed some of the visual aids of cone movement look pretty much exactly like some that you find on focals website. Any relation or just coincidence?

As far as future topics, yeah I agree I'd love to hear them all covered. I have a basic understanding of the choices there, but likely nowhere near what I could René reveal in a short time.

I have not seen any Focal plots that look like what I show, and a quick look at their webpage did not reveal any such plots.

 

[Colonel7]

Thank you @hardisj & @René - Acculution.com for this video - mostly above my head but extremely good material!

If I may answer the question at the end here: yes, all these topics would be really interesting to hear about! I vote for all of them

View attachment 203040

Phase and crossovers! Then again any of these would be great

 

[TimVG]

Very interesting video, thank you both.

Since many people tend to focus quite a bit these days on the estimated in-room response, it's interesting that any but coincident (coaxial) loudspeakers that do not have some sort of dip in the crossover region, (in the spinorama) tend to feature an asymmetrical vertical lobe.

As René rightfully points out, with such a loudspeaker design, going above and below the main listening axis quite quickly creates either a cancellation or amplification (departing from flat) depending on the design. However when measured from a distance, it 'averages out' so to speak and there seem to be many people who focus on this 'average'. I would love to see a discussion about this. I have my own views of course, but would love to hear others, and it is probably useful for the readers/viewers.

 

[René - Acculution.com]

Very interesting video, thank you both.

Since many people tend to focus quite a bit these days on the estimated in-room response, it's interesting that any but coincident (coaxial) loudspeakers that do not have some sort of dip in the crossover region, (in the spinorama) tend to feature an asymmetrical vertical lobe.

As René rightfully points out, with such a loudspeaker design, going above and below the main listening axis quite quickly creates either a cancellation or amplification (departing from flat) depending on the design. However when measured from a distance, it 'averages out' so to speak and there seem to be many people who focus on this 'average'. I would love to see a discussion about this. I have my own views of course, but would love to hear others, and it is probably useful for the readers/viewers.

I guess MTM would also work (but I imagine that the lobe then becomes narrow, although I haven't looked into it)

 

[fineMen]

... that any but coincident (coaxial) loudspeakers that do not have some sort of dip in the crossover region ... when measured from a distance, it 'averages out' so to speak ...

Toole mentions this in his well-known book. Mitigation is available with the averaging. But only so, if the dispersion is wide enough to facilitate an averaging. Which, due to the very nature of the problem isn't the case *g*.

Another problem, in the same frequency range, is the cancellation of mono signals due to the listener's two ear distance around 2kHz. The affected frequency range is determined not only by the ears' distance. Off the perfect symmetry it drops significantly. Who grants for the sound-engineer's accuracy with positioning himself?

Many more--one might argue, that 'cone break up' is one of the lesser problems in stereo design. I mentioned the necessarily flexible surround already, only to bring the sacred recipes of cone design into some perspective. "Purify" follows the route to radically re-design the surround while deploying a middle-of-the-road paper cone.

Of course this critique is not ad hominem. I would anyway say, that the expert is in charge to chose a topic of real interest. What is the use of knowing how a cross-over works? Leading to the topic of lobing? Finally encourage to chose speakers that deal with it? But is it actually necessary? With the latter question in the row the education would be on target, me thinks.

<edit> The industry advertises a product with special features, like non-resonant cones. The audience might want to understand how a non-resonant cone would benefit the product. Because the consumer wants to understand the advertising. Isn't that the wrong way round? Shouldn't it be so, that the consumer should understand what his benefit from the final product was, in his home? Better to start to explain what is really relevant in the data of the final product. That was Toole's way, and I like it.