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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 13th September 2019, 08:36 PM   #1
claudiogan is offline claudiogan  Italy
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Default MDD Multi Delays Diffraction (Multi TL, omnidirectional, single drive, ...)

I was suggested to indicate in this section my projects that actually fall under alternative technologies.

I am Claudio Gandolfi and since 2013 I have been listening to music reproduced with unconventional self-built speakers. The innovation of the projects is the generation of coherent secondary waves, delayed by a few milliseconds emitted at different points of the space. I didn't find anything similar on the Internet and I invented the acronym MDD to describe them.

The MDD technology simulates the presence of the musical instrument in the listening room. The emission is omnidirectional, it has many secondary sonorous fronts generated in different points, delayed and consistent. The secondary sound fronts and reflections of the listening environment mask the reflections of the environment in which the recording took place. Music feels good all over the room, you can move, dance, listen or watch a movie together. The recorded sounds are always easily recognizable.

When the amplifier sends a signal, the first sound front coming to the ear is the one emitted from the back side of the speaker, the sound comes from the lower side near the floor. This primary emission is omnidirectional and is attenuated at high frequencies.

The energy of the frontal emission is fractionated and confined in the waveguides, it rises upwards and is re-emitted in the environment exploiting the sound diffraction with delays of 2 - 4 msec. The delayed secondary sound fronts are coherent in phase with each other because they are generated by the same speaker. Each waveguide is omnidirectional on the horizontal plane and emits all the mid and high frequencies.

At low frequencies things get complicated because a waveguide can create constructive or destructive interferences at frequencies with the wavelength of the same order of magnitude as the length of the waveguide. Things also change in view of the fact that the waveguide has one or two open sides. The waveguide lengths are calculated so that they are distributed over an octave, each low frequency always has paths available to transfer its energy into the listening environment.

As with all technologies, it is not ideal, works better or worse than others under certain conditions. Even personal tastes and habits have their influence.

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

The last three projects also reported in the full range section:
54m42 an MDD project (42 wave guides on a driver)
54m42

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

66c9 a low-cost MDD project (for educational use)
https://www.claudiogandolfi.it/66c9.html
Attached Images
File Type: jpg ondeSecondarie.jpg (117.5 KB, 204 views)
File Type: jpg 54m42 13 right.jpg (81.1 KB, 204 views)
File Type: jpg 54m42 16 right flangia.jpg (184.2 KB, 208 views)
File Type: jpg 34c9 L alto 15.jpg (93.9 KB, 205 views)
File Type: jpg 34c9 AVG ZFR 03.jpg (66.9 KB, 209 views)
File Type: jpg 66c9 25 left top.jpg (181.5 KB, 81 views)
File Type: jpg 66c9 13 right top.jpg (107.6 KB, 68 views)
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Old 14th September 2019, 12:35 AM   #2
planet10 is offline planet10  Canada
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MDD Multi Delays Diffraction (Multi TL, omnidirectional, single drive, ...)
Some of that looks interesting. The ripples in the impedance denote each individual pipe, some damping might help. These can also be seen in the FR.

This concept looks a lot like it is related to Hedgeman’s work on speakers, but with the TL termi outside the box.

dave
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Old 14th September 2019, 12:11 PM   #3
pelanj is offline pelanj  Czech Republic
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I wonder if a spiral arrangement (with the longest pipe in the middle) would work in the same way as the standard zig-zag for the square aluminium tube version.
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Old 14th September 2019, 05:38 PM   #4
claudiogan is offline claudiogan  Italy
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Quote:
Originally Posted by planet10 View Post
Some of that looks interesting. The ripples in the impedance denote each individual pipe, some damping might help. These can also be seen in the FR.

This concept looks a lot like it is related to Hedgeman’s work on speakers, but with the TL termi outside the box.

dave
To eliminate the series of impedance peaks I prefer to increase the number of waveguides, the frequency differences between the peaks are reduced and overlap. The result is visible in the project impedance graph 54m42 with 42 wave guides. The use of damping material undoubtedly eliminates the individual peaks but risks attenuating the high frequencies that pass through the waveguides before being diffused in the listening environment. While listening, I am unable to detect the presence of peaks in the impedance and the effect of the geometry of the listening environment is much greater in the course of the FR.

I did a quick search on Hedgeman's work but found only some photos and nothing on the internal structure, if you can indicate some links to deepen it I would facilitate the search. I can't say anything for now.
Attached Images
File Type: jpg 54m42 33 L09 FRZ.jpg (87.5 KB, 50 views)
File Type: jpg 54m42 34 R09 FRZ.jpg (85.6 KB, 27 views)
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Old 14th September 2019, 05:41 PM   #5
claudiogan is offline claudiogan  Italy
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Quote:
Originally Posted by pelanj View Post
I wonder if a spiral arrangement (with the longest pipe in the middle) would work in the same way as the standard zig-zag for the square aluminium tube version.
It depends on the level of acoustic reflection of the wall behind the speakers. If you have a wall, or other, acoustically reflective, the energy emitted in that direction at high frequencies arrives at the listener with any arrangement of the tubes.

I tried the zigzag arrangement to direct (by reflection) part of the acoustic energy at high frequencies towards the listener. The intention is to remedy the attenuation of the high frequencies that I have encountered in environments treated acoustically with absorbent materials.

A driver with a flat axis response is normally directive at high frequencies. This implies that the sound energy emitted in the listening environment at high frequencies (concentrated in a frontal lobe) is lower than that of the medium and low frequencies. If the same driver is configured as perfectly omnidirectional, a drop in high frequencies is inevitable, in certain environments it may be perceptible. The advice is to do tests.
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Old 14th September 2019, 07:52 PM   #6
bentoronto is offline bentoronto  Canada
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MDD Multi Delays Diffraction (Multi TL, omnidirectional, single drive, ...)
Just like with stereo movies, I think the stereo concept of home music is over-blown. Two speakers sound greatly better than one no matter where you sit or face backwards even. Spatial localization is only one small piece of music quality production.

And the sound of stuff is as much "social construction" as the ancient paintings of horses in caves. You can't truly capture any but the littlest instruments and bring them into your room with the stereo concept.

So, I think Claudio is asking the right questions.
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Old 15th September 2019, 05:32 PM   #7
mattstat is offline mattstat
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Quote:
Originally Posted by claudiogan View Post
To eliminate the series of impedance peaks I prefer to increase the number of waveguides, the frequency differences between the peaks are reduced and overlap. The result is visible in the project impedance graph 54m42 with 42 wave guides. The use of damping material undoubtedly eliminates the individual peaks but risks attenuating the high frequencies that pass through the waveguides before being diffused in the listening environment. While listening, I am unable to detect the presence of peaks in the impedance and the effect
Certainly extensive damping/absorption would attenuate the high frequencies. You may be able to employ something less aggressive to tame the resonances though. Thin felt may be an option.

In general, you may find audiophiles reluctant to embrace techniques that use highly resonant structures. The assumption is that energy storage and release obscures detail. This kind of coloration isn't always obvious at first. Direct comparison to highly resolving speakers or headphones can help highlight them. A high resolution distortion sweep is worth trying also.

Please don't take any of the above as criticism of your approach. I don't have direct experience with your design, so can't say how it sounds. Even if it has theoretical issues, the benefits could outweigh them. There are always trade-offs.
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Old 15th September 2019, 06:29 PM   #8
planet10 is offline planet10  Canada
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MDD Multi Delays Diffraction (Multi TL, omnidirectional, single drive, ...)
Quote:
...reluctant to embrace techniques that use highly resonant structures
The DML is looking like it might be a counterexample. And fullranges above a certain point operate in a “resonant” manner. How good a FR is is often how well those resonant structures are controlled.

dave
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Old 15th September 2019, 07:07 PM   #9
scottjoplin is offline scottjoplin  Wales
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Originally Posted by planet10 View Post
fullranges above a certain point operate in a “resonant” manner. How good a FR is is often how well those resonant structures are controlled.
How do you mean?
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Old 15th September 2019, 07:17 PM   #10
planet10 is offline planet10  Canada
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MDD Multi Delays Diffraction (Multi TL, omnidirectional, single drive, ...)
Below a certain point A FR acts as a piston, above a certain range the goal is for a growing part of the cone disengaging from reproducing the signal. The higher frequency behaviour is “resonant behaviour”, how well a FR does up top is a measure of how well the designer did on getting the resonant part of the behaviour to behave in a smooth manner.

dave
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