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MDD Multi Delays Diffraction (Multi TL, omnidirectional, single drive, ...)
MDD Multi Delays Diffraction (Multi TL, omnidirectional, single drive, ...)
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Old 21st April 2021, 12:53 PM   #171
claudiogan is offline claudiogan  Italy
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Default MDD3K240 Front acoustic load with triple Karlson profile

In this MDD3K240 project, the Karlson triple profile front acoustic loading replaces the aluminum MDDFL front acoustic loading of the MDD3H240 prototype. This project is also very cheap and simple to make.

The horizontal omnidirectional emission is generated in three areas.
1 - In the triangles there is a first emission by diffraction of all the frequencies arriving at the edge of the driver itself.
2 - The rectangular slits emit by diffraction in three lobes of approximately 180 degrees partially overlapping to cover the horizontal plane. Other coherent secondary sound waves are generated.
3 - The upper edge of the wave guide generates further coherent and delayed secondary waves of about 0.3 milliseconds by acoustic diffraction.
A fraction of the acoustic energy emitted is directed upwards and is subsequently reflected from the ceiling into the listening room.

Compared to the MDD3T240 prototype, there is the advantage that the front acoustic load has a rigid structure, resists shocks that could deform the acoustic paper transformer and change its characteristics. The frequency response does not depend on the deformation of the wave guide but only on the acoustic diffraction which is controlled by the geometry of the structure.

This is a first prototype to be improved but even with rough profiles it is very pleasant to listen to. It is ideal for omnidirectional economic systems. The shape and size of the profiles are able to influence the frequency response. Before studying the frontal acoustic load better I will try to eliminate the drop in frequency response between 150 and 160.

Claudio Gandolfi - MDD (Multi Delays Diffraction Loudspeaker)
MDD3A89
Attached Images
File Type: jpg 3kB803.jpg (158.0 KB, 211 views)
File Type: jpg 3kR810.jpg (104.5 KB, 241 views)
File Type: jpg 3K240 THD left.jpg (104.6 KB, 209 views)

Last edited by claudiogan; 21st April 2021 at 12:55 PM.
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Old 21st April 2021, 03:25 PM   #172
bentoronto is offline bentoronto  Canada
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MDD Multi Delays Diffraction (Multi TL, omnidirectional, single drive, ...)
A very nice FR and THD, although not super low yet. Maybe you have found a good rear-wave sequestering that is neither tuned (BR, TL) nor wastes the wave (sealed).

Might look odd is most rooms, but a great possibility is to think of the speaker as a sub and with the pipes spread around the room (or even just across the speaker wall). Might have the benefits of multiple subs that we are all keen to use. But with these flexible pipes, you can have them terminate anywhere on the wall, high and low, that you want. Certainly a perfect a multiple-sub concept.

(They look like vacuum cleaner hoses to me. In a previous house, I built a central vacuum cleaning system and bought many meters of the hoses so as to reach all corners.)
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Old 21st April 2021, 05:12 PM   #173
claudiogan is offline claudiogan  Italy
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You have well described the operation and potential of the MDDBL rear acoustic load. For each frequency there is a path of suitable length to effectively transfer the sound pressure from the rear compression chamber to the room. There remains the problem of the resonances generated by the room, the responses of the two channels are different.

I have to check if the minimum at 150 Hz is related to the material used for the waveguides. The spiral sheath is produced for external electrical systems, it has a minimum residual elasticity which could be the cause of the irregularity in the frequency response. The fastening of the guide is to be improved, I think that greater rigidity would lead to a reduction in distortion at the lower frequencies.
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File Type: jpg 3K240 THD left.jpg (104.6 KB, 194 views)
File Type: jpg 3K240 THD right.jpg (106.5 KB, 192 views)
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Old 8th May 2021, 06:24 PM   #174
claudiogan is offline claudiogan  Italy
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Default MDD3M150 Front acoustic load in aluminum and rear acoustic load in alveolar polypropy

The MDD3M150 prototype is a new combination of acoustic loadings made with the material at my disposal.

The MDDFL front acoustic load in aluminum and the base are the same used in the MDD3G100 prototype.

Change the length of the MDDBL rear acoustic load in alveolar polypropylene. With an Lmax of 1500 mm the frequency response is more extended than the MDD3G100 prototype (Lmax 1000 mm) and reduced compared to the MDD3H240 prototype (2400 mm).

The most interesting measure is the reduced distortion compared to previous prototypes.


https://www.claudiogandolfi.it/
https://www.claudiogandolfi.it/mdd3a89.html#m
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File Type: jpg 3M150 THD left.jpg (94.6 KB, 23 views)
File Type: jpg 3ML828.jpg (22.9 KB, 85 views)
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Old 12th May 2021, 02:44 AM   #175
Bigun is offline Bigun  Canada
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MDD Multi Delays Diffraction (Multi TL, omnidirectional, single drive, ...)
Default MDD microphone ?

>> Adventures In Science | Professor Mark Csele
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File Type: jpeg F81D1993-5055-4935-9D20-9179A65D94F0.jpeg (21.1 KB, 40 views)
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Old 12th May 2021, 08:02 AM   #176
claudiogan is offline claudiogan  Italy
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Thanks for this new report of structures similar to my MDD prototypes used for directional microphones. Other posts on the subject have been published in this thread:

MDD Multi Delays Diffraction (Multi TL, omnidirectional, single drive, ...)

MDD Multi Delays Diffraction (Multi TL, omnidirectional, single drive, ...)

The multiple waveguide structure can be used as an omnidirectional acoustic load on the entire audio band, the driver replaces the microphone directly. The only difference I noticed is the linear distribution of the lengths, in the acoustic loads MDD the distribution is logarithmic.

The single waveguide structure with side openings is not suitable for the reproduction of low frequencies. I think it can work well as a front acoustic load of the latest MDD3K240, MDD3T240, MDD3M150 prototypes. Before using it I still have to figure out how to optimize the size.
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Old 20th May 2021, 08:31 PM   #177
claudiogan is offline claudiogan  Italy
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Default MDD3N150 Triple Karlson profile front acoustic load, MDDBL in alveolar polypropylene

The MDD3N150 prototype uses the same front acoustic load as the MDD3K240 prototype with a triple Karlson profile. The MDDBL rear acoustic load in alveolar polypropylene and the base are the same used in the MDD3M150 prototype.

As in the MDD3M150 prototype the distortion is reduced, it is easier to build.
Attached Images
File Type: jpg 3NB850.jpg (142.0 KB, 55 views)
File Type: jpg 3N150 THD left.jpg (94.8 KB, 33 views)
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Old 25th May 2021, 03:39 PM   #178
claudiogan is offline claudiogan  Italy
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Default MDD3S150 Front acoustic load in rigid PVC and rear in alveolar polypropylene

The MDD3S150 prototype uses the same front acoustic load as the MDD3FE25d prototype with seven rigid PVC waveguides. The MDDBL rear acoustic load in alveolar polypropylene and the base are the same used in the MDD3M150 prototype.

The base is very versatile and allows me to try out many combinations with the acoustic loads I have made. Also in this prototype the reproduction is excellent. The greater length from the frontal acoustic load increases the range of delays emitted to almost 5 milliseconds, for me it is an advantage but it could be my subjective preference not shared by others.

Claudio Gandolfi - MDD (Multi Delays Diffraction Loudspeaker)
MDD3A89
Attached Images
File Type: jpg 3SB903.jpg (100.5 KB, 30 views)
File Type: jpg 3S150 THD left.jpg (89.2 KB, 23 views)
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Old 16th June 2021, 03:49 PM   #179
claudiogan is offline claudiogan  Italy
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Default MDD3J240

The MDD3J240 project has the same rear acoustic load as the MDD3H240 and also the same base.

Change the front acoustic load MDD tube , a single waveguide in PVC with a diameter of 80 mm on the outside that fits without modification to the rubber front seal of the Faital-Pro 3FE25 driver. The 9 mm holes at the base create an acoustic short-circuit that makes the system open at both ends of the waveguide. The four series of 5 mm holes generate by diffraction coherent secondary waves with delays from 0 to 1 milliseconds.

The reproduction is excellent even if it can still be improved.

Claudio Gandolfi - MDD (Multi Delays Diffraction Loudspeaker)
MDD3A89
https://www.claudiogandolfi.it/mddfl.html#j
Attached Images
File Type: jpg 3JL918.jpg (66.2 KB, 17 views)
File Type: jpg 3J240 THD left.jpg (89.4 KB, 19 views)
File Type: jpg 3JB911.jpg (131.6 KB, 18 views)
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Old Yesterday, 07:33 AM   #180
mondogenerator is offline mondogenerator  England
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The concept is very interesting.

The corrugated hose is a weak point. It generates its own "noise".

Take a length and swing it around. It will whistle.
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