How to build a mobile Soundsystem for protests/raves [34c3]
Either for a proper squat rave or for a demonstration - to empower people to reclaim space in the city, they need the right and cheap tools to do it. To achieve this, i want to share my recent experiences in building a loud and cheap (
- http://oscillating.space/ • A short overview on the history of soundsystems • Motivation for free open air partys • Components of a soundsystem • Power supply • Amplifiers • Speakers • Additional stuff • Example cost calculations • Workshop: Build a soundsystem
soundsystems • Beginning in the 50s in jamaica – Disko on wheels – Reggae, Jazz, Blues • Since mid 70s in northamerica with Hiphop&Disko – Ghettoblaster • (Illegal) Rave culture in europe since end of 80s – UK – Germany • Freetek, Teknivals get massive police repression • Nice Arte Docu: Sound System - Tontons du sound
Lots of power to use – Standard power plugs • Disadvantages – Burning old dinosaur shit to get power - WTF?! – Smelly and leaking liquids – Forbidden in parks - Ordnungsamt can sue you instantly – Heavy (but you can also get small ones)
car batteries – Acid liquids can leak – Bad stuff – Advantage • Cheap – Disadvantage • If not standing vertically it can leak acid • Acid is unhealthy and environmental hazard • Need to refill with liquids from time to time
Batteries – Gel- or AGM-Batteries – Sealed to prevent leaking – Advantages • No leaking • Without maintainance (no refill) • Resistance against deep discharge – Disadvantages • Expensive (approximately 2x as standard)
Power is in a Battery? – Amount of power in Ampere Hours (Ah) – Discharge curve – State of charge readable by Voltage of Battery – Discharge until 11.8V is ok – Below 11.8 the battery gets destroyed slowely – Destroyed battery irreparable – Only 70% of capacity usable
– Recharge batteries – Sustainable energy • Disadvantages – Only usable in the sun – Additional cost (Solarpanels + Inverter) – Not good usable without batteries • Cost – Depends on the power but > 150 €
mobile music batteries are the best • Additional cost for Solar or generator is too high • Buy only new batteries • Solid material batteries because they are leakfree • The bigger the batteries the smaller is the price for the power ( € / Ah ) • Use good chargers for AGM-Batteries (highvoltage) • Bicycle Generators are nice but complicated
the efficiency – The more efficient, the less power gets wasted to heat – Heat needs to get cooled with even more energy – If amplifier gets too hot it turns off / gets destroyed – Good amplifiers have more than 80% efficiency – Class D / digital amplifiers have a good efficiency – Old analgue Class A / B amps got ~60%
– The only right rating is Watts RMS / Sinus! – Watt PMPO: fake power rating • Also called „Pure Mystic Power Output“ • Its the power you can put on the speaker before it catches fire – Ohm load of the rating is also important: • Example: – Power rating: 50W RMS @ 4 Ohm – Matches: 25W RMS @ 8 Ohm
build for heavy usage longer than 2h – Additional heatsink or fan is needed – Use thermal paste for better thermal connection – Use a huge area to connect the heatsink to the amplifier – Use a efficient 12V fan (high airflow / watt)
car amp • Get a Digital amp with high efficiency (>80%) • Get a used amp from ebay / Kleinanzeigen to save money • No high power rating necessary for each output – 20W / 8Ohm for a small soundsystem – 100W / 8Ohm is enough for a big soundsystem • Analogue amps only good for small soundsystems because they generate too much heat
in the soundsystem • Different Setups possible – Classic 2.0: • Two fullrange speakers • One amp with two outputs – Additional Subwoofer 2.1: • Two speakers as mid-/high-Speakers • One subwoofer as low-Speaker / bass • Crossover needed to split the frequencys • Two separate amps necessary
of speakers is NOT equivalent to the loudness of a speaker • Sensitivity / „Wirkungsgrad“ is the important value – Given as dB/w/m in the technical specs – It says how loud is a speaker in a distance of 1 meter if you put 1W RMS of power from an amp to the speaker • The higher the sensivity, the longer the battery lasts at the party!
needed ? – Loudness measured in dB – „Discoloudness“ = 100dB – Berghain = approx. 110dB – Speaker with 85 dB/W/m • 100dB: 32 W RMS • 110dB: 300 W RMS – Speaker with 94dB/W/m • 100dB: only 4 W RMS! • 110dB: 50 W RMS Loudness examples with Distance Loud ness dB Jet airplane in 30 m 140 Pain threshold 130 Discomfort threshold 120 Chainsaw @ 1 meter dist, 110 Disco @ 1 m infront speaker 100 Dieselmotor @ 10 m dist. 90 At a busy street 5 m dist. 80 Vacuum @ 1 m distance 70 Normal talking @ 1 m dist. 60 Normal flat quiet 50 In a quiet library 40 Quiet sleepingroom by night 30
by efficiency • Speakers should have > 92 dB/W/m efficiency • Match Watt RMS to power rating of the amp • Consider the ohms of the speaker (see amps) • Used speakers are ok to buy and cheap • DIY possible and very cheap – Speaker is basically just a wooden box – Wide-range speakers play bass/mids/highs – Lots of plans in the internet (see links)
prevent deep discharge of the battery – Dont pay more than 5€ – Reminder: After 11.8V change the battery to prevent harming the battery • Equalizer for the soundsystem – Adjust the bass to avoid police – Adjust the highs
from 12V DC – Different types of inverters: • Rectangle • Sinus – Sinus for audioequipment – Pay attention to efficiency: higher than 80% ! – Advantage: Use regular 230V equipment – Disadvantage: Unnecessary voltage conversion which costs power and therefor hours of music – Needs to get cooled !
because they need way less power – Battery powered LED light strings • Laptops – Use laptop battery – If battery is over, remove battery and use only the laptop power supply (very inefficient to charge laptop battery from another battery) – MacBook Trick: Block middle pin of charger with ducktape to prevent loading of battery • DJ Mixer: use 12V Mixer (eg. Xone 22)
spec in a mobile soundsystem • Use leakfree batteries • Dont do deep discharge of the batteries • Important to look after the efficiency of the amp that there is less need to cool it • Use crazy good efficient speakers to get the loud music for a little of power and for a long time!
– Efficiency of a lot of amps http://amp-performance.de – Overview small amps: http://www.hifi-forum.de/viewthread-118-2855.html • Speakers – Pages with plans: Hififorum, Jobst Audio – Plan for Visaton BG20 Partyboombox: http://www.lautsprecher-berlin.de/partybox.html • Shops for soundsystem stuff: – Speakers: Geizhals.de – under „Lautsprecher“ filter with „Empfindlichkeit ab 92dB“ – Pollin.de & Reichelt.de for electrical parts, batteries and speakers • Inspirations for soundsystemconstruction: – https://www.hedonist-international.org/?q=de/node/414 – http://www.hifi-forum.de/viewthread-118-1591.html