34c9 a MDD full range speakers.

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MDD (Multi Delays Diffraction) is an innovative technology for loudspeakers.

MDD uses acoustic diffraction to emit coherent secondary sound waves, delayed by a few milliseconds at different points in space.
The 34c9 project is the first compact version made with MDD technology. Other features of the 34c9 project:
- zero internal acoustic reflections,
- sound insulation from the floor in the audio band,
- omnidirectional emission on the horizontal plane over the entire audio band,
- no damping material,
- 3FE25 speaker from Faital-Pro.

More information at links:
Claudio Gandolfi - MDD
34c9
Pinterest

My current working hypotheses are described on the page acustica.

The last projects reported in the full range and planars-and-exotics section:
MDD3A89 an MDD project with the 3FE25 driver
https://www.diyaudio.com/forums/planars-and-exotics/342677-mdd-multi-delays-diffraction-multi-tl-omnidirectional-single-drive-15.html#post6437638
other documentation is published at MDD3A89.

54m42 54m42 an MDD project (42 alveolar polypropylene wave guides on one driver)
other documentation is published at 54m42

66c9 66c9 a low-cost MDD project (paper waveguide for educational use)
https://www.claudiogandolfi.it/66c9.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.
 

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This is a pretty cool project
What’s the largest driver you have used ?
What’s the size of the driver you used for all of these? Could we try a 6.5” driver? There are so many great 6.5” drivers out on the market today. Do you think using a 6.5 or a 8” driver and using 3” down to 1” pipes would work? The larger pipe for lower hz and the smaller tubes for higher hz
 
What’s the largest driver you have used ?
What’s the size of the driver you used for all of these? Could we try a 6.5” driver? There are so many great 6.5” drivers out on the market today. Do you think using a 6.5 or a 8” driver and using 3” down to 1” pipes would work? The larger pipe for lower hz and the smaller tubes for higher hz

I only did tests with 3" drivers but the MDD technology can work with bigger speakers. The problems that occur with 6.5" and even more with 8" are mechanical. It increases weight and you need to find a fairly strong bracket to have an adequate subsonic resonance, greater weight requires a more stable base to avoid accidental falls.

Side-by-side waveguides must have the same section. There is the advantage of obtaining some guides from a single long tube, reducing the waste of material.

The rule I used in the prototypes is to have the sum of the area of all the sections of the waveguides equal to about the area of the speaker cone.

The resonance frequency depends on the length (no section) of the guides and I recommend having the shortest one half the length of the longest. The number can also be different from 9, it is important that the lengths are calculated so that the increments are logarithmic. 
 
What about using a 3 point spring mount?
So your saying that the tubes or pipes need to equal the same amount as the area of the driver ? so is a driver has a total of 20 in.² or 10 cm² of cone Area, then the pipes or tubes should equal to 20 in.² or 10 cm² ? Am I way off base on this? I really want to try this
I have some old full range drivers from the 50’s though the 70’s that came out of Console tube stereo systems, LOW power
Most of them are from 8” up to 15” drivers
And I’d like to use round pipes, like ones used in church organs. I’d really like to use as large as a 10” down to 1” pipes. And all copper or brass
 
What about using a 3 point spring mount?
The system with 3 springs can work, it must oscillate to a few Hz also ensuring stability. In the 34c9 project with a 3" loudspeaker that weighs 525 grams you get to a complete 2.2 kg system. An 8" driver weighs 2 kg, I think the total weight with the guides easily reaches 10 kg. Everything becomes more complicated to manage.

So your saying that the tubes or pipes need to equal the same amount as the area of the driver ? so is a driver has a total of 20 in.² or 10 cm² of cone Area, then the pipes or tubes should equal to 20 in.² or 10 cm² ? Am I way off base on this? I really want to try this
In the 34c9 project the external section of the guides is:
20 x 20 = 400 mm² (single guide)
400 x 9 = 3600 mm² = 36 cm² (total).
The internal section of the guides is:
18 x 18 = 324 mm² (single guide)
324 x 9 = 2916 mm² = 29 cm² (total)
The area of the cone up to the center of the foam gasket is:
radius = 32.5 mm
Area = 3318 mm² = 33 cm²

If the cone area is 20 in.² you can use 9 guides from 2.22 in.² but it should work well even with values between 2.0 and 2.5 in.²
If the cone area is 10 in.² you can use 9 guides of 1.11 in.² (1.0 - 1.25)

I have some old full range drivers from the 50’s though the 70’s that came out of Console tube stereo systems, LOW power
Most of them are from 8” up to 15” drivers
And I’d like to use round pipes, like ones used in church organs. I’d really like to use as large as a 10” down to 1” pipes.
I used rigid pvc round guides in the 227h project .
The easiest configuration to make is with seven guides, one in the center and six on the diagonals of a hexagon. In each diagonal three guides are aligned, in this configuration in a 6" driver you can use 2" guides, with a 15" you can use 5" guides (You can complicate the configuration using different diameters). With seven guides I suggest using this logarithmic series for the lengths: 552, 610, 673, 743, 820, 906, 1000 mm.

And all copper or brass

Copper and brass tubes (smooth inside) are suitable to work as acoustic waveguides, if you have them available it's fine. Given the value of the metals I would do before tests with rigid PVC which is less expensive. The system can be made adjustable by sliding cardboard tubes inside the rigid ones. Once I found a satisfactory configuration I would pass to the definitive one in metal. 
 

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Wow Claudio, this is indeed a radically different FR design, unlike anything I have seen on this forum. I would love to hear what it sounds. You chose a great driver – very affordable and sounds fantastic in the right enclosure. This should be a very cheap build. Aluminum is mined here, so the tubing is at least cheap in our country.

I am interested to see how this develops, and surprised that you have not received more interest, attention or comments here.
 
Thanks for the first "Wow" in a comment, I'm glad you appreciate the originality of the 34c9 project.

Since 2013 I have been building FR trying to optimize the emission of coherent secondary sound waves, delayed at different points in space. This is not easy if you also try to have a good frequency response and low distortion. I found nothing that documents similar research, I invented the acronym MDD to describe the technique.

At the moment I'm the only (maybe) who works on MDD technology, who wants to listen to it will have to be very patient. Alternatively, you can decide to experiment in a field where only my documentation is published. Until someone replies the 34c9 project, I will gladly provide clarifications on specific aspects of the implementation.
 
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I have first two questions - just to be sure how it is made (to clear my understanding of your description).

1. the square holder for the pipes has no bottom, the speaker is screwed directly on to the sidewalls. And the holes around the frame are sealed by a sealant - what would you recommend to use? I think silicone or hot melt glue should work.

2. the polyurethane ring at the base is a fit on the magnet, so when the whole thing swings, it slides on the magnet, to create a kind of seal. Is that correct? Do you have any suggestion where to get this foam from?

I put the pipes into an online alu dealer calculator (I can get only with 1.5 mm thickness) - and the cost will be slightly less than a pair of drivers, so that is not too bad, since there will be only a little wood and woodworking.

Thanks!
 
MDD (Multi Delays Diffraction) is an innovative technology for loudspeakers.

MDD uses acoustic diffraction to emit coherent secondary sound waves, delayed by a few milliseconds at different points in space.
The 34c9 project is the first compact version made with MDD technology. Other features of the 34c9 project:
- zero internal acoustic reflections,
- sound insulation from the floor in the audio band,
- omnidirectional emission on the horizontal plane over the entire audio band,
- no damping material,
- 3FE25 speaker from Faital-Pro.

More information at links:
Claudio Gandolfi - MDD
34c9
Pin by claudio gandolfi on 34c9

Thanks for the attention
Claudio


very original project!


btw, you are mounting 3fe25 from the bottom - for this mounting you should try Lavoce drivers, they are suitable for this AND italian (!!!)
 
I have first two questions - just to be sure how it is made (to clear my understanding of your description).

1. the square holder for the pipes has no bottom, the speaker is screwed directly on to the sidewalls. And the holes around the frame are sealed by a sealant - what would you recommend to use? I think silicone or hot melt glue should work.

2. the polyurethane ring at the base is a fit on the magnet, so when the whole thing swings, it slides on the magnet, to create a kind of seal. Is that correct? Do you have any suggestion where to get this foam from?

I put the pipes into an online alu dealer calculator (I can get only with 1.5 mm thickness) - and the cost will be slightly less than a pair of drivers, so that is not too bad, since there will be only a little wood and woodworking.

Thanks!

Attached are some photos that I also published on the site to better clarify the assembly. From the enlargements the defects of the manual workmanship can be seen well. The inaccuracies in the workmanship do not create problems if there is the air tightness between the loudspeaker and the guides.
  • the support is a wooden pipe with the internal sides slightly flared (2mm) to prevent the foam of the cone from coming into contact with the corner at the center of the inner side.
  • the speaker is screwed directly onto the sides, the four holes are visible.
  • I used a built-in steel sink sealer that always remains soft, it can be reused in case of disassembly by reshaping it. Trade names: butyl sealant, Sikalastomer, Elastuk, is similar to plasticine used by children. Silicone and hot glue must be replaced if disassembled. Attention, the hot glue is very tough and can break the gasket of the loudspeaker in case of disassembly.
  • The polyurethane ring has the aesthetic function of covering the crack, I have repeatedly started listening to music forgetting it and I have not detected any difference. It can be replaced with fabric, rubber or cardboard, the important thing is that it does not interfere with the oscillations of the guides.
  • Passing from 1 to 1.5 mm the internal section goes from 18x18 to 17x17, I don't think it produces detectable variations to listening. There is the advantage that you have more material to round the upper edge of the guide which can be sharp.
 

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very original project!
btw, you are mounting 3fe25 from the bottom - for this mounting you should try Lavoce drivers, they are suitable for this AND italian (!!!)

I have two problems with the test:
1- Time, I already have a series of outstanding tests to do with the 3fe25 (I have about ten available and it's also Italian).
2 - Costs, I have no plans to buy more material at the moment.

For those who have time and material I suggest trying to do this two ways. Just a cardboard and a tweeter turned upwards to verify the potential of acoustic diffraction. A normally directive driver becomes omnidirectional on the horizontal plane.
 

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so it's essentially the same concept as a shotgun microphone filter tube assembly used in reverse,no?

No filter. It is easier for me to list differences than analogies. The microphone is a strongly directive device that works using negative interference between sound waves for different angles from the one desired. The 34c9 project has an omnidirectional emission using the phenomenon of acoustic diffraction (Huygens principle).
 
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Great, now all is clear. I ordered a pair of 3FE22 on 50 % discount, the 25 were not in local stock. Also the square tubes are on the way. I have some leftover 18 mm pine planks that I will use for the holder and base instead of plywood. The sealant is called Butyrub here. I hope to have it put together in a few weeks.
 
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