Gobel and the Bending Wave


An article at Stereophile regarding the Gobel Divin Noblesse speaker caught my eye recently:

https://www.stereophile.com/content/g%C3%B6bel-loudspeakers-cables-engstr%C3%B6m-pre-and-power-wadax...


Jason Victor Serinus made a simple mistake and listed the AMT tweeter as a "bending wave" transducer. He's corrected the error, but the "fix" was just as curious. According to the Gobel website, and JVS's correction, the midrange drivers, which for all the world look like FaitalPro 8" mids to me are "bending wave" transducers in this model.


http://www.goebel-highend.de/products/divin-noblesse.html


These midranges look nothing like the bending wave planar transducers used in the Epoque line, or described by their technology page here:

http://www.goebel-highend.de/technology.html

So, without being able to order and disassemble these $190K speakers, I'm really skeptical that this description of the midrange drivers is accurate.


That is all,

Erik
erik_squires
For historical context, the Ohm Walsh down firing drivers were some of the earliest "bending wave" drivers if not the first. There have also been other attempts at creating mega speakers from bending wave type of drivers like this one from Impact (long gone):

https://www.stereophile.com/floorloudspeakers/648/index.html
The Air Motion Transformer was a bending wave, so is the tweeter used in the High Emotion Audio loudspeakers. Very nice and fast, smooth due to no breakups?
Sorry, AMT is not bending wave, Atmasphere. It's motion is pistonic, although at an angle. :)

IMHO, to be a bending wave, the transducer must be excited at one end, and have the sound wave emit off the surface as the wave travels from one end to the other, or from a central point to the edge.

AMT's are driven across their entire length at the same time. There is no start and end to the wave across its surface.
Post removed 
Right, and I see no evidence that this 8" driver is being used in any other way than pistonic, especially given crossover points.

Mind you, these are very good parts and the speaker may be amazing. I'm just scratching my head over what appears to be shamelessly branding a standard 8" cone with "bending wave."
The model shown here ( Epoque Aeon ):

https://www.youtube.com/watch?v=Ipjahbc6QRE

looks like the seemingly hidden driver at the top could use the advertised bending wave principle similar to Manger speaker drivers. Pistonic motion would be radial with sound emitted at an angle to that.

The original and somewhat well known "bending wave" configuration that has been around for some time as mentioned is of course that of the Lincoln Walsh-style transmission line drivers where driver is mounted vertically with vertical pistonic motion. Original OHM A’s and F’s from years back did this fairly full range with a single physical driver, newer OHM Walsh model speakers do it similarly but just for the key mid frequencies using much more conventional (and robust) drivers. German Physiks DDD drivers do it for the higher frequencies. Dale Harder’s Exotic Speakers line (very hard to find) take the original OHM Walsh full range design and refine it with more modern technology.

BTW My understanding is that many otherwise conventional dynamic (pistonic) drivers can also function as bending wave drivers for certain frequencies, most perhaps just not very well unless designed to do so. They also do have to be mounted vertically though so the sound emanating at an angle from the rear of the cone is primarily what reaches your ears.

Are AMTs/folded ribbon drivers bending wave? I’ve never thought them to be as I understand it, though perhaps more unconventional in operation than most high frequency drivers, but in a different way. Same true of MBL speakers in general, unique configuration but technically not "bending wave" TTBOMK.


Are AMTs/folded ribbon drivers bending wave?

As I define it, the bending wave is defined by a membrane where one end or point is excited, causing a wave to form on the membrane which tavels to the extremities.


A cone, driven pistonically, endeavors to have the same relative motion at all points.

Ribbons, AMT's and ESL's are excited across their length simultaneously.  There's no wave which travels from point A to point B.

Quads however, as I understand them, are in fact bending wave transducers.  They are excited at the center, and the wave then travels to the outer edges.



Hmm well bending wave Walsh style drivers are essentially specially designed cones that operate pistonically just like traditional dynamic drivers.


"
Bending wave loudspeakers

Bending wave transducers use a diaphragm that is intentionally flexible. The rigidity of the material increases from the center to the outside. Short wavelengths radiate primarily from the inner area, while longer waves reach the edge of the speaker. To prevent reflections from the outside back into the center, long waves are absorbed by a surrounding damper. Such transducers can cover a wide frequency range (80 Hz to 35,000 Hz) and have been promoted as being close to an ideal point sound source.[62] This uncommon approach is being taken by only a very few manufacturers, in very different arrangements.

The Ohm Walsh loudspeakers use a unique driver designed by Lincoln Walsh, who had been a radar development engineer in WWII. He became interested in audio equipment design and his last project was a unique, one-way speaker using a single driver. The cone faced down into a sealed, airtight enclosure. Rather than move back-and-forth as conventional speakers do, the cone rippled and created sound in a manner known in RF electronics as a "transmission line". The new speaker created a cylindrical sound field. Lincoln Walsh died before his speaker was released to the public. The Ohm Acoustics firm has produced several loudspeaker models using the Walsh driver design since then. German Physiks, an audio equipment firm in Germany, also produces speakers using this approach.

The German firm, Manger, has designed and produced a bending wave driver that at first glance appears conventional. In fact, the round panel attached to the voice coil bends in a carefully controlled way to produce full range sound.[63] Josef W. Manger was awarded with the "Diesel Medal" for extraordinary developments and inventions by the German institute of inventions."
@mapman

You should read your own posting. Your quoted text directly contradicts your first sentence.
No contradiction. The driver modulation is pistonic with sound produced via wave bending as described. The current Walsh model speakers produce lower frequencies pistonically and the higher frequencies through the midrange via wave bending.

That is my understanding. I have two pair of Ohm Walsh in my home for many years that demonstrate it. It was discussed to some degree a few years back on the Ohm Microwalsh who’s heard them thread. Should still be on the record. One of the contributors was Dale Harder who designs Walsh style speakers and is probably  about as much of an expert on Walsh drivers these days as there is.
I don’t have a problem with the text regarding Ohm Walsh. I have a problem with this self contradictory line:

Walsh style drivers are essentially specially designed cones that operate pistonically just like traditional dynamic drivers.

Pistonically means the cone acts like a rigid piston. You can’t be pistonic and bending wave at the same time, but you can be pistonic for some frequencies and bending wave at others.
It would seem apparent that for wave  bending the cone cannot be a "rigid" piston.  
it woukd seem apparent that the cone cannot be a "rigid" piston.

In that case, we do not describe it as pistonic. :)

The term comes from the theoretical ideal of having a piston with a flat, infinitely rigid surface, exactly like a piston, operating in a cylinder.
That’s fine theoretically but in practice the bottom ported Ohm Walsh driver produces sound both pistonically and via wave bending at the same time.  
I didn't know Lonesome George Goebel could surf.
That’s fine theoretically but in practice the bottom ported Ohm Walsh driver produces sound both pistonically and via wave bending at the same time
.  

But not at the same frequencies. That's what I mean by simultaneously. It is a bending wave transducer to a point, below which it becomes pistonic.

Sorry, AMT is not bending wave, Atmasphere. It's motion is pistonic, although at an angle. :)

IMHO, to be a bending wave, the transducer must be excited at one end, and have the sound wave emit off the surface as the wave travels from one end to the other, or from a central point to the edge.
The Linaeum tweeter is a flexible membrane and is excited at the center with the sound wave emitting off the surface as the wave travels from the center to the edge. I have a set- and they are very similar to the High Emotion Audio tweeter. I've spoken directly to the engineer that designed the latter (Mike Shields) who said that his design is a bending wave and also similar to the Linaeum. So what am I missing? Is the Linaeum tweeter not also the AMT?
The Linaeum tweeter is a flexible membrane and is excited at the center with the sound wave emitting off the surface as the wave travels from the center to the edge.



Right, and if that is accurate, the Linaeum would be a bending wave device but by contrast, AMT’s are excited across the length of each pleat simultaneously. I found this article which was interesting and included more on the subject:

http://www.soundimage.dk/Different-col/Bending.htm

AMTs are conspicuously absent.


I think the only similarity is really in that pleat. Lineaum uses a single pleat as the motor, AMT’s use multiple pleats. AMTs work not by moving back and forth towards the users, but by squeezing air in and out from between the pleats, more like an accordion.

More here:

https://en.wikipedia.org/wiki/Air_Motion_Transformer

And here:
https://www.audioholics.com/bookshelf-speaker-reviews/monoprice-monolith

But there’s no description for an AMT I’ve ever read where one area of the membrane is excited at one location, and then a wave is transmitted on the surface. Instead, each pleat is like a ribbon’s conductor in a magnetic field.
Ah. I had thought that the Linaeum AMT was also the Linaeum bending wave tweeter, but apparently they are different. You can see the Lineaum bending wave tweeter in the first link you provided above.
@atmasphere -

I'm not a Linaeum historian, the only tweeter I know them from was the butt-cheek like driver made famous by Radio Shack.


If they also made an AMT that would be news to me. Let me know if you find a link to one.


Best,
E
Erik, I have a pair of that Radio Shack speaker, named the Optimus Pro LX5. The Linaeum driver was used as a dipole in that model, and as a direct radiator in an even cheaper model.
Hey bdp24

This is staring to sound familiar. Honestly, I'm more than a little surprised that this tweeter design didn't last well into the late 20th and early 21st century. I don't remember hearing it, but it's' innovative design should have made it a long lived classic.


Best,

E
HI Erik- the bending wave driver IS alive and well.  The original designer of the Lineaum tweeter and later the Impact speakers (Paul Paddock) has designed a HUGELY impressive new speaker called the Forty 10 for a company named MCAudiotech (http://mcaudiotech.com) which I have heard several times and it is VERY impressive indeed.
Hello @jwpstayman


Very cool. :) I met the folks from Impact I had no idea there was a connection to the Lineaum.
I like the look of it too, I wonder if you could project images on that screen?

Best,

E
Just as I thought we had covered the bending wave speaker in all its commercial forms another vendor, Audionec (yes, NEC, not NET) popped up on my radar.


Pretty impressive designs, especially the modular version.

http://www.6moons.com/audioreviews2/audionec/1.html 

File these under #Unaffordable but #Cool and #I_have_not_heard_them