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

Claudio, thank you very much for your generosity in sharing knowledge.
I took advantage of a spreadsheet for calculating musical notes and did not adjust the frequency calculation formula. I'll do it.
This last answer of yours complements everything I need for the moment.

To contextualize I will report why your project interests me so much.

I'm a choral conductor. I have noticed for decades that when unmicrophoned choirs are accompanied by a keyboard and a conventional speaker, there is not a good mix between the sound of the voices and the sound of the speaker(s).

Intuitively, I've almost always aimed the speaker at a nearby wall (when location permits), or at some irregular object. This way the direct sound is minimized and I get a more consistent blend of choir and keyboard sound.

When I found your project I immediately said: this is what I need!

It bears a resemblance to the pipe organ. On the very rare occasions when it is possible for the choir to be accompanied by a pipe organ, the mixture of the choir's voices with the sound of the organ is extremely organic. The same does not happen with a keyboard connected to speakers. Unmicrophoned choir accompanied by a keyboard connected to a speaker is the situation that happens most often.

My questions about dimensions are to adjust the proposal to the venues and also to think about the aesthetics of the set.

I know that some of the questions I've asked are pretty basic for a high-level forum like this one. So, thanks again for your patience and willingness to teach.
 
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Hi jaq775,
Este é um fórum de língua inglesa. Se você for postar em outro idioma, certifique-se também de postar a tradução em inglês.
This is an English speaking forum. If you are going to post in another language, please also make sure you post the English translation.

You can use Google Translate to do this. Here is your post in English ...
Greetings Claudio! I'm at the stage of putting together the budgets for the executive part. I have 2 practical questions: (1) Should the longest tube be a maximum of 3400mm so that the delay remains capped at 10ms? (2) For this limit of 3400mm I noticed that the total cost of the tubes is lower the greater the number of octaves (when the number of guides remains the same) What is more acoustically advantageous in the MDD: more octaves or less octaves? Thanks in advance for your willingness to respond.
 
Greetings Claudio!

I'm at the stage of putting together the budgets for the executive part.

I have 2 practical questions:
(1) Should the largest tube be a maximum of 3400mm so that the delay remains limited to 10ms?
(2) For this limit of 3400mm I noticed that the total cost of the tubes is lower the greater the number of octaves (when the number of guides remains the same). What is more acoustically advantageous in MDD: more octaves or fewer octaves?

Thank you again in advance for your willingness to respond.
 
Hi jaq775

for me You are the first to make a MDD system with a 30cm driver, good job.

It is a prototype, it will almost certainly require modifications, so the first advice is to save money. I prefer the sound of paper or cardboard waveguides over PVC or other plastic materials, I have been putting off the replacement of the MDDBL load of the MDD3ZC350 V2 prototype (now in pvc) for months. You can use telescoping square post tubes to build the rear sound load, round tubes are fine too.

1 – For the rear acoustic load MDDBL Lmax = 3400 mm is not binding and neither is 10 ms. You can use any Lmax by changing all lengths proportionally. Lmax changes the lowest frequency that the system can reproduce, approximately: Lmax=1000 mm (80 Hz – 3 ms), Lmax=2000 mm (40 Hz – 6 ms), Lmax=4000 mm (20 Hz – 12 ms). Another thing I haven't tried is using an MDD loudspeaker in a large venue (theatre, church, ...). If there are acoustic problems, the larger the dimensions, the greater the multiple delays must be.

2 – To reproduce the bass well MDDBL must work only on one octave, to save money you can try to reduce the number of waveguides to 5. I enclose the table for one octave and 5 waveguides, with two examples of length. For the frontal acoustic load MDDFL the delay distribution is more important to make the source non-point-like, I use 3 octaves. In large rooms with high ceilings I would like to try the effect of Lmax greater than 2000 mm.

As with all loudspeakers, the most important thing is to prevent fixing defects from generating unwanted vibrations as power increases.
 

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Claudio, thanks for the tables and drawing. I made simulations with the tube diameters available in local stores (25, 40, 50 and 75 and 100mm) Here, pvc tubes are cheaper than cardboard tubes. Probably because the demand of cardboard in the interior of the country is low and the distribution centers are about 800km away. I was able to reproduce your calculation table and now the values are matching yours. Some questions: (1)Can I use more tubes over the speaker? In that case, what precautions do I need to take? I didn't quite understand when he said "it is advisable not to exceed two cm on the side" . In the diameter of the speaker? (2)Can I use a bigger cabinet than what you proposed?
I made two drawings, one considering a 2-speaker cabinet in which I remove one to place the waveguides (3)And another in which I distribute it in a similar way to what you proposed. What considerations do I need to take into account in these cases?
 

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(1) The number of waveguides can change. I used 5, 7, 9, 12 and tens with alveolar polypropylene. My favorite material is paper but you can get excellent results with other materials too. I remember one thing that I forgot in the last few posts. The MDDFL frontal acoustic load has an open base, it is mounted approximately one cm above the center of the driver cone. The best height must be found empirically by raising and lowering the waveguides. You can think of the end of the waveguide as an upward pointing tweeter, if you go beyond 2cm at around 10KHz it will become upward directional. With the square section, horizontal emission lobes can also be formed.

The rear acoustic load MDDBL must be airtight as in a transmission line. The MDDBL is a multiple TL with distributed resonances. If you use pvc pipes with joints for plumbing you can make a prototype with variable lengths, you will use the maximum length only if you have to play music with a lot of bass.

(2) All the compression chamber measurements can be changed, they do not derive from calculations, using values from the Fibonacci series is my habit. I think the prototype will be quite large and you will need to build a base with adequate stability. The internal walls should be covered with foam rubber or other sound absorbent.

(3) For the drawings, choose the one that is more rigid and/or easier for you to make.
 
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