The goal is the making of a multichannel soundsystem for sound and image performances autonomous (in electricity) and transportable walking.

Modularity : as much as possible, we try to split the whole circuit into building blocks, interconnectables, to have something upgradable and scalable, depending on the needs and also the means available at the moment of building/replicating.

We aimed at having a 8 channels system with 8 speakers, that can be used either altogether as an acousmonium, when setup on a specific spot. But also to be able to be able to use the speaker while moving, using several mediaplayers, at the cost of loosing syncronicity.

Explained stage by stage, we understand better the different elements needed to build a multichannel system.

Two differents trials for a general drawing :

We choose to have the same model for all speakers. First to have the same amplifier + powering combo for all, and to simplify the installation (no need to take into account the sound of each speaker to choose it's position). We go for full-range speakers, with a larger bandwith. We want all spot to be able to reproduce the more frequency possible (high and lows). This way it can be an acousmonium, but also used as many proximity speakers to cover a larger field with the same volume, but without blasting a whole field…

We liked the monitoring speakers in the category of the Yamaha S20X, which are powerfull, sturdy and compacts. We search something in the same style. Some questions about JBL Control 1 (bad feedback from Edouard and Sonia), but what about Control 23 ?

After several listening tests with two different groups in the summer 2023 (wandering seminary and Chantier Dispersés), with second hand equipment, we finally keep the JBL Control 1. They are less powerfull but nicer to our hears than the Yamaha S20X. We also compared with some hand made cubical speakers, with one voice, of a much lower quality. Also compared to another model similar [info missing ? ]

Subs

We talked about finding one or several subwoofer, which could occasionnaly replace a pair of speaker and bring some bass. We need to check if it doesn't drain the battery and if it's worth it. But even without this we are above the budget so…

We finally dropped this idea.

Speaker cables

Be carefull with the thickness of the speaker cable when there is a certain lenght, it starts to loose some power. Details here (in french) : http://www.sono-solution.com/section-dun-cable-haut-parleur/

[Power transmitted at the end of the cable in % to speakers in W withe a 100W amp]

Also pay attention to the metal used : normal coper (OFC) is a better conductor than copper-plated aluminium (CCA). Attention aussi au materiau utilisé : le cuivre normal (OFC) est meilleur conducteur que l'alu trempé dans du cuivre (CCA). Un autre tableau devrait indiquer la perte de puissance avec du CCA.

2.5mm 25m Leroy Merlin

We liked the amplifiers boards at Wondom : good price/quality ratio. But it's possible to get cheaper on any big seller platform.

We choosed to pair speakers on one stereo amp to save money. But one can also chose to use mono amp and potentially to have 8 autonomous backpacks instead of 4… Could be usefull for sound walk with larger crowds… But doing so you double amount of amp and power boards, as well as the lithium cells.

We choose standard 1/4“ jack cable between mixer and amps. Wireless is something that could be researched and added later…

Two boxes to send the audio signal to the 8 speakers, either from a simple stereo or even mono source, or from a multichannel device (laptop with soundcard).

We imagine theses possible sound sources :

• A stereo file read by a media player or a smartphone with a minijack (1/8”)
• 8 channels from one sound card (electroacoustic piece, live coding performance or whatever)
• Several electronic instruments on battery with a line level output : synthetisers, pedals, samplers, walkmans
• Sound from a projector 16mm modified or using a special DI box : the audio signal must be of a line level be careful!

We want to be as friendly as possible for both members of the “German” school (the artist directly works in multichannel) and fo the “French” scheel (the work is in stereo and the spatialisation is performed live on a mixer with fader… For this reason, we choosed to make 2 boxes :

First box is the “Matrix Mixer”. It allow routing and mixing audio signals with trimmer potentiometers. Vu-meters make it easy to control what is sent to the amps.

The other box is the “Spatialisatrice”. It allow to trim down manally each output to the amp with 8 faders. This box is a passive add-on, or plug-in, that can be added or not the matrix mixer.

Details of the construction of the Matrix Mixer and Spatialisatrice.

3rd residency :

The potentiometers…

We need linear pots for the matrix because, connected in serie, they turn into log (we've been told). And for the gain pot (or trim pot, to be correct), we need logarythmic pots. Depending on the brand/manufacturer they are marked A or B… so it's tricky.

We choose lithium batteries, much lighter and durable than lead, necessary for the transportability of the system. For the amp we want to use, we'll need to provide 24V.

We think about taking boards handling the protection (BMS) and the charge of the cells, using the same brand as the amps to reduce the task of sourcing and developping. They exist with Li-ion cells 26650 or 18650. Still need to check which are the easiest to source for free. Probably the 18650. The boards vary from 1 to 6 cells. We should evaluate the amount of cells that allow amps to work more time (one night), or the highest consumption if we use subwoofers.

For 6 cells : https://store.sure-electronics.com/product/PS-BC12127

If one wants to build the battery on it's own with collected cells, donc forget the BMS ( carefull, it's DANGEROUS, fire and explosion hazard)!!

Fabriquer un pack lithium de A à Z

https://www.youtube.com/watch?v=Wyq8xqA9wHQ

https://passionelectronique.fr/bms-fonctionnement-choix-18650-lithium/

Recycling lithium battery : scooter, e-bike etc.

Otherwise, you can by them here :

https://ozo-electric.com/fr/233-cellules-lithium

https://ozo-electric.com/fr/cellules-lithium/565480-cellule-lithium-18650-36v-lg-mj1-3500mah.html

We need a model : 3.6v (ou 3.7v ? ).

1 bike produce enough power for the whole system which run with ~ 65w
35w for videoprojector
20w for amps driving 2 speakers
Energy is produced and accumulated into super capacitors. Super capacitor advantage is that you can keep it unused long time without damage by discharge. Battery advantage over super capacitor is that you can get much more energy.
But as the aim of CinéCyclo is to sensibilize on energy uses, it's an advantage to stop the system when energy is not produced anymore.

2 types of inputs, DC or AC motor.

AC motor for microtractors produce 13v 14A.
DC motor is cheaper but not brushless.

About DC-DC converter
at optimum point, ~ 15% energy loss

Common mode issue : noise produced by input, solution is an audio isolation transformer neutrik NTE1 for each input (12,90€ from Thomann).

Session 1 - Febuary 2023

• define goals and needs
• elaborate the device theoritecally
• researching solutions
• first budget

Interval 1

• buying for a prototype : (amps, BMS) / Antoine's mission
• everyone search for speakers on it's side
• Ask Terence for ideas about the mixer / Antoine's mission

Session 2 - July 2023

• Building 1 Matrix (schema to be made & parts to be bought)
• building 4 speakers (tests from leftovers) + bags
• testing / using 2 stereo amp (antoine's)
• testing / using Lithium cells (antoine ?)
• writing plans/schematics for spatialisatrice

Interval 2

• Pierre debugging and solving some issues on the matrix and the spat between july and september 2024
• Antoine repairs one amp with a discharged cell which was not charging in august 2024

real budget from the budget n°2.

Détails Budget #3.

To save money, we go for 4 stereo pairs instead of 8 independant monos. When walking, there is only 4 backpack and 4 points moving with sound.

TOTAL = 1649

Détails Budget # 2

• Version “Luxe” (with cheap cables) = 2239 €
• Version Eco happy = 1239 €

Détails Budget #1

JBL Control One seems to have a pretty fragile suspensions. We had to change half of them, probably beacause we bought all the speakers second hand (somes sellers said they changed suspensions before selling), and also because the Octoploc is producing loud plocs while being tested…

We bought suspensions on this online shop.

When pot is turned down, noise is feeding the output… Weird measurement of resistance on the matrix itself. Total confusion !

Finally it's been discovered that decoupling capacitors where missing. Warning : The abscence of print on the PCB makes it easy to forget when you are not focused and not reading the words on the schematics !

After having them, everything is more stable. But it might not be the only issue to adress to solve noises.

As the line level we have out of commonly used audio device is very variable, we decided to rise the gain of the matrix.

The feedback resistor (Rf) was changed on the output buffer board. Instead of a 10k we placed a 20k in order to have gain of 3.

Powering schematic has been revised in order to have the switch for general power on the + and not on the negative, as recommanded by Flo Kaufmann.

Initially the vu-meter were powered by the vcc out of one of the buffer board. When all the led of all the vu-meters were lit, an alarming smell was getting out the 9v regulator. The total consumption on these was above 1 amp.

Connecting the vu-meter power rail directly to the + bus of the battery, after the switch, is safer, especially for musicians and dj's who fancy analog distortion and constant red lights on their table.