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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 3rd January 2021, 02:10 PM   #161
jzagaja is offline jzagaja  Poland
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Join Date: Jun 2004
Location: Szczecin
MDD Multi Delays Diffraction (Multi TL, omnidirectional, single drive, ...)
What I would like to do next months is to use 5FE120 and compression driver that can be opened on the back and 3D print:

1) MDD with back and front loading
2) Compound horn

Both bent like a spiral or U-shape (see below). Compound horn mouth straight up to first 50cm. MDD is interesting in the bass range as you use multiple resonators. Here author used only two resonators:

Hornlautsprecher
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Old 3rd January 2021, 06:41 PM   #162
claudiogan is offline claudiogan  Italy
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Location: Sassari
I enclose a diagram for realizing the acoustic loads for a 5” driver. When I have time I will try them with the Ciare HX135 driver. I don't have a suitable 3D printer available so I will use 10mm honeycomb polypropylene.

Each acoustic load is a matrix of 10 x 10 guides. Each guide has a section of 10 x 10 mm. The guides are organized in four symmetrical blocks of 25, the highest guides in the center and the lowest on the outside. The scheme can also be reorganized according to aesthetic needs.

The front acoustic load has Lmax = 8 Lmin = 1000 mm, the rear acoustic load has Lmax = 2 Lmin = 1500 mm. Measurements can be changed in scale.

The section of the single waveguide of 10 x 10 mm derives from the availability of alveolar polypropylene of that size. I have verified that 5 mm is few. With a 3D printer you could also do tests with other measures, the best could be 8, 12, 15 or ?? mm (to be checked at the SPL levels you need).

I have never used a compression driver, with the 3D printer a fitting must be made to adapt the driver output to the input of the front MDD acoustic load.
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Old 13th January 2021, 06:15 PM   #163
claudiogan is offline claudiogan  Italy
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Default MDD3C89

The MDD3A89 and MDD3B89 projects use alveolar polypropylene with reduced thickness. With 5 mm and 2.5 mm the section of each wave guide is less than the length of a half wave so that the diffraction emission has a spherical shape. The reduced sections increase the acoustic impedance with the result that the high frequency emission is attenuated. In the MDD3C89 prototype the front acoustic load is made of 10 mm thick alveolar polypropylene. The medium and high frequency emission increases by a few dB. The frequency response is more balanced and the positioning is less critical for the reproduction of low frequencies. The 10mm honeycomb polypropylene is also stiffer and reduces the problem of spurious waveguide vibrations.

The waveguides of the front acoustic load are made by gluing 5 appropriately shaped 10 mm honeycomb polypropylene panels. In the same panel, 6 wave guides are obtained. The waveguides of the rear acoustic load are made by gluing 10 panels of alveolar polypropylene with a thickness of 5 mm. About 25 waveguides are obtained in the same panel.

In the frequency response there remains a depression between 3 and 4 KHz, probably in relation to the geometry of the waveguides. In the next prototype I will increase the total section of the front load and I will change the geometry of the system, the aim is to recover a few more dB on the mid and high frequencies.

Link:
Claudio Gandolfi - MDD (Multi Delays Diffraction Loudspeaker)
MDD3A89
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Last edited by claudiogan; 13th January 2021 at 06:17 PM.
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