66c9 a low-cost MDD project (for educational use)

[claudiogan]

The 66c9 project is the cheapest that uses MDD technology. The 66c9 project is also the most sophisticated cabinet made only with paper, adhesive tape and glue.

It is designed for educational applications. With just a few euros you can make a speaker that exploits the potential of modern class D amplifiers. For a stereo system to be used in a classroom, you need: a smartphone, an amplifier with BT interface, cables and 66c9 speakers.

My site is: Claudio Gandolfi - MDD
My current working hypotheses are described on the page acustica.

The last projects reported in the full range and planars-and-exotics section:
54m42 54m42 an MDD project (42 alveolar polypropylene wave guides on one driver)
other documentation is published at 54m42

34c9 Compact aluminum project
34c9 a MDD full range speakers.
https://www.claudiogandolfi.it/34c9.html

22D7 Two drivers per channel for a 3D effect
22D7: four MDD systems for a 3D effect with omnidirectional speakers
https://www.claudiogandolfi.it/22d7.html

22M7 Simple and inexpensive wide-band rigid PVC project.
https://www.diyaudio.com/forums/pla...nidirectional-single-drive-4.html#post6006473
other documentation is published at 22M7.

22C71L8 One driver per channel with waveguides applied to the two sides of the cone.
https://www.diyaudio.com/forums/pla...nidirectional-single-drive-5.html#post6017746
other documentation is published at 22C71L8.

MDDHX135 an MDD project with the HX135 driver
https://www.diyaudio.com/forums/pla...nidirectional-single-drive-6.html#post6124020
other documentation is published at MDDHX135.

MDD3FE25 an MDD project with the 3FE25 driver
https://www.diyaudio.com/forums/pla...nidirectional-single-drive-8.html#post6170069
other documentation is published at MDD3FE25.

 

[twocents]

Hi Claudio. This is really a fascinating concept and radically different from any other design I have seen on this forum. I am a noob with very limited knowledge of speakers and speaker design, but here is my opinion anyway. If I understand correctly these are omni directional speakers and you give more details in THIS thread. Although you use a single Full Range driver, I think your posts might be more appropriate (and attract more attention) in the Planars & Exotics section where omni directional speakers are discussed. This MDD technology you are referring to does not seem relate anything to audio – so this is all very new. Using words like 34c9 or MDD in the title of your posts does not attract any attention – maybe using the word omni directional might catch more attention. Furthermore, it is very difficult to imagine what these speakers sound like because you have not compared it to any other known speakers or something I can relate to.

I am certainly very interested in how this develops and what other member’s finding might be in the future, since I like the simplicity and small from factor of these speakers. I think these speakers could certainly also be made from foam core, and should be more sturdy than paper or cardboard?

 

[pelanj]

I agree with twocents, I first completely ignored the 34c9 thread, but when I opened it, I found a great little project. Making the thread title a bit more eye attracting would definitely get more attention which this concept deserves.

It should take only a few more afternoons to finish it (need to polish the tubes, make the base with a nice finish, etc. I trust these will sound good, so I need them also to look good. They might be even admitted into the living room by my wife🙂

This is something that could be put together in a few hours and I really see the potential for a class project. I value the out of the box thinking!

 

[claudiogan]

Hi Claudio. This is really a fascinating concept and radically different from any other design I have seen on this forum. I am a noob with very limited knowledge of speakers and speaker design, but here is my opinion anyway. If I understand correctly these are omni directional speakers and you give more details in THIS thread. Although you use a single Full Range driver, I think your posts might be more appropriate (and attract more attention) in the Planars & Exotics section where omni directional speakers are discussed. This MDD technology you are referring to does not seem relate anything to audio – so this is all very new. Using words like 34c9 or MDD in the title of your posts does not attract any attention – maybe using the word omni directional might catch more attention. Furthermore, it is very difficult to imagine what these speakers sound like because you have not compared it to any other known speakers or something I can relate to.

I am certainly very interested in how this develops and what other member’s finding might be in the future, since I like the simplicity and small from factor of these speakers. I think these speakers could certainly also be made from foam core, and should be more sturdy than paper or cardboard?

I reported the projects in the "... alternative technologies" section
MDD Multi Delays Diffraction (Multi TL, omnidirectional, single drive, ...)

I am curious to hear the results of replies, I think it is unlikely that my limited tests have already identified the optimal configuration.

All materials capable of confining sound waves in waveguides can be used. For the foam there are two things to watch out for.

The greater thickness compared to paper, aluminum or polypropylene must not reduce too much the free area in which the sound passes. It is best to try it in speakers larger than 3 ".

The deformability of the foam can generate undulations on the surface that flow upwards at the speed of sound. The undulations emit a series of secondary waves and the sound could also improve. The problem is that if the deformation is not perfectly linear the distortion with sound pressure rapidly increases.

 

[CraigSu]

Claudio, thank you for openly sharing your findings. I’ve looked over your threads and website and noticed all of your waveguides (pipes) are the same dimension except for length. It will no doubt add some complexity but have you considered using different sizes of square tubing or diameters of pipe in addition to logarithmically scaled lengths, and how would that affect frequency response? The most obvious comparison is to pipe organ ranks so I’m interested in your thoughts on this design twist. Would it introduce unnecessary complexity into your designs or would it be beneficial?

 

[claudiogan]

Claudio, thank you for openly sharing your findings. I’ve looked over your threads and website and noticed all of your waveguides (pipes) are the same dimension except for length. It will no doubt add some complexity but have you considered using different sizes of square tubing or diameters of pipe in addition to logarithmically scaled lengths, and how would that affect frequency response? The most obvious comparison is to pipe organ ranks so I’m interested in your thoughts on this design twist. Would it introduce unnecessary complexity into your designs or would it be beneficial?

Now I have no reason to modify the logarithmic series of lengths or to vary the section of the tubes. Having tubes with the same section reduces costs and simplifies purchases.

Modifying a length or a section would certainly have effects on the frequency response but this (complex) search makes sense only if measurements in an anechoic chamber can be made. Now I detect the answer in a domestic environment and I would go to correct the answer in a specific room.

Changing lengths not only changes the response to low frequencies but also to high frequencies. With the logarithmic series we have all the differences between neighboring tubes distributed on an octave, we avoid the emission of sibilanting sounds that occurs with a linear series.

 

[CraigSu]

I was not implying a change to the logarithmically scaled lengths as this is key to your designs. Rereading my post, however, made me realize how poorly I worded it. Thank you for your reply. Clearly, adding complexity without measurable benefit is something to be avoided.

 

[claudiogan]

I discovered that there is a world day of teachers on October 5th.

I take this opportunity to report an update of the (ultra-economic) educational version of the MDD speaker. With a steel wire, subsonic support can also be added to the 66c9 project.

Link: 66c9

 

[grindstone]

Late to your cool project, Claudio. Thank you for sharing. Stimulates a lot of thoughts. Kind of looks like a very hip vacuum cleaner. My mind raced to see if Freddy or Moray will be the first to cut k-slots in them or that Horst hasn't been using enough horns (or too many drivers) 🙂