looking at the image and skimming the text of the patent, seems your Dad's invention is not the same as this, but I recently bought a portable instrument speaker cabinet:
http://www.gollihurmusic.com/product/1197-EUPHONIC_AUDIO_WIZZY_12_SPEAKER_CABINET.html

Seems the general idea of multiple cone speakers is used in the example above, supposedly to increase frequency response.

Interesting- did he make any working prototypes to test his idea out?

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Hey ttt, thanks for the link
I ran into another product in that page called
"Wizzy 500 Combo Amp " and it explicitly advertises that:
The loudspeaker is actually a dual-cone device which simultaneously produces low and high frequency signals from a single voice coil. The transmission line enclosure has been painstakingly tuned for an aggressive but pleasing sound. There are no crossover components to distort or alter the response.

Not a new idea here. Back in the 50's and 60's, there were many dual-cone or whizzer speakers on the market.

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I also agree that the idea of utilizing multi-cone (dual cone) to produce sound is strikingly similar as my dad's invention...I don't know up to what extent his patent has effect but I should look into this more and talk to my dad about this.

Your Dad's design looks, to me, more akin to an isobaric design, although he uses one motor and isobarics are usually stacks of individually-driven speakers.

Kal

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Kal, I apologize for my ignorance in this field
Here is my dad's response:

Quote:
Kal, you're right. It is very similar to the isobaric but my
multi-cone type loudspeaker design utilizes multiple cones with a single magnet
instead of having multiple cones along with the magnets.
Since the cones do not have to be accompanied by magnets, you could save far more space with my design.
The accompanying cones could be double, triple, quadruple, or even more.
However, in my prototype model I was only able to stack up to triple cones.

Thanks,
Lord Kelvin

So, I figured. I did not have time to read the patent application but I fail to see, intuitively, the advantage of the multiple cones as they add their mass, their compliances and the trapped air volumes.

Kal