34c9 a MDD full range speakers.

[Squeak]

Hi Claudio

here's a 1940 patent I bumped into when searching for stuff related to the Bose "K-tube" patent.

https://patentimages.storage.googleapis.com/24/a6/f6/243bee1170b78f/US2225312.pdf

Please share your findings.
What is the Bose K-tube?

 

[freddi]

Hi Squeak

That Bose patent is basically the same thing that Karlson did with the X15 speaker (introduced fall 1965). Karlson was not referenced perhaps as his patent was for microwave application.

Ive used K-tube as tweeter for 20 years or so.

Below are a few links showing a K-tube.

Sadly, I've not been able to experiment with MDD.

Best,
Freddy


BOSE patent

US8351630B2 - Passive directional acoustical radiating
- Google Patents

PRIOR ART. ( both microwave application)

1944:

https://i.imgur.com/ZitUIP1.jpg

Karlson’s Opem End Waveguide Antenna - similar was used in his
1965 X15 2-way speaker.


US3445852A - Open end waveguide antenna
- Google Patents


A FEW K-TUBE THREADS at Diyaudio

Fieldcoil + K-tube

a few pics of Karlson and K-tube

 

[claudiogan]

In that patent, fig 2, there are lot of holes between the tubes. Actually one can make such spiral with paper without the tubes. As sound doesn't have to find a tube to move through, the job would be the same.

The behavior in the frequency domain would change considerably. The part with the shorter wall would create an acoustic short circuit which would make the presence of the longer part of the spiral wall almost useless.

Using the guides as a microphone would lose directionality.

Using the guides as acoustic load of a driver would attenuate the low frequencies and the delayed sound fronts emitted by diffraction would be concentrated in the short part of the system.

 

[claudiogan]

That Bose patent is basically the same thing that Karlson did with the X15 speaker (introduced fall 1965). Karlson was not referenced perhaps as his patent was for microwave application.
Ive used K-tube as tweeter for 20 years or so. ...
Sadly, I've not been able to experiment with MDD. ...

Hi Freddi

the MDD prototypes have in common with the acoustic lenses designed by Karlson the use of diffraction to optimally distribute the pressure generated by the driver over an area larger than the driver itself.

Designing the exponential profile that does not generate unwanted tubing is complicated. In the MDD prototypes the wave fronts travel along separate guides and cannot interfere with each other.

In the MDD prototypes the length can be easily increased to generate emissions with delay of 1-6 milliseconds. With the K-tube acoustic load the short length does not generate appreciable delays.

A few more days for a post with a new prototype that is easier to build than the last MDD3FE25.

 

[claudiogan]

The prototype MDD3A89 is ready on diyAudio:
https://www.diyaudio.com/forums/pla...idirectional-single-drive-15.html#post6437638