Whether its for a mobile bike party or a solar powered concert, a 12V or 24V sound system is the key. I recently built several systems for mobile bike parties and this article has a pile of details. You can also check my Easy Bike Party Sound System project if you want a simpler and smaller system and my Bike Party Sound Trailer for specific tips on a trailer design. If you want to just purchase finished speakers built according to the principles of this guide, we sell them at MonkeyLectric.
This article covers:
My friend Deep runs Flashdance, and we used his system as a reference point to compare our work against. Deep has an amazing tricycle setup that lets him bring the party wherever he goes. San Francisco has rather notorious hills though, so our goal was to see if we could cut the weight of his setup without sacrificing any of the sound. A big key to cutting the weight is to see if we can use something much smaller than a car battery - and that means being more efficient about power use.
This project is brought to you by MonkeyLectric and the Monkey Light bike light
Step 1: A word about Efficiency
The key to any battery-powered sound system is efficiency. Home and car sound gear is not designed to be efficient or light - it just isn't a concern in those applications. Low efficiency means you need lots of power to make the same amount of sound, and lots of power means a big heavy amp, a big heavy car battery, and maybe a big heavy inverter too. An efficient speaker can produce 5x the volume from the same amount of power. An efficient amplifier is 2x better than a standard one, plus its far smaller and lighter. Together this means that with a bit of attention paid to your component choices, you'll get way more output for the same amount of power.
Lets take a look at Deep's current system. He's got:
With auto-sound gear, you don't need an inverter but the problem is that it all the parts have very poor efficiency. I think this is due to marketing forces at work - the folks selling you this stuff learned that if the amp and speakers are bigger and have higher watt ratings, they make more money selling them. but, those high watt ratings are only needed because the gear is so inefficient.
Step 2: Efficient speakers
PA, DJ and "Live Sound" speakers are the best place to look for efficiency. You will find the efficiency measured as "SPL 1w/1m" in the spec sheets of most speakers. "SPL max" is different. Every 3 points of SPL means DOUBLE the efficiency: 90 is bad, 96+ is good.
Large speakers (both boxes and driver cone size) are nearly always more efficient than small ones. If you don't care so much about the weight get the biggest speakers (15" or larger woofers). If you do care, the weight and size of the speaker will be your main tradeoff in your setup
Think about going MONO! Stereo doesn't always make a lot of sense in an informal environment. Using one larger speaker you will have overall higher efficiency and lower weight than two smaller ones.
I built and tested systems using the speakers listed below. All but the smallest are rated SPL between 95 and 98:
Our tested results for these speakers: The Peavey and Pyle are the loudest with the same power input, and about equal to each other. The Behringer's are noticeably less loud. The B212XL and the Yamaha have noticeably better audio quality than the others. (more results later). The Gemini is by far the smallest speaker here - it will fit into a milk crate - its not as loud as the bigger ones but great for its size.
Bigger speakers (15" or 18" woofer) can get up to 100 or 101 SPL efficiency. With more expensive speakers you can find something a little more efficient, but mostly you are buying higher sound quality and a higher maximum power level. Running off batteries you likely will be well below the maximum power levels.
Where to find this stuff:
and others... (amazon.com has some of them)
Step 3: Efficient amplifiers
For amplifiers there is really only one choice: a Tripath-based amp, sometimes called a T-amp, Class-T amp, or Digital amp. These ultra-efficient wonders are inexpensive but obscure.
(a note on terms: "Class-T" is a marketing term. All T-amps are technically "Class-D" amps, sometimes refrerred to as "Digital" amps. There exist non-Tripath class-D amps, but all the ones I have seen are either very small or only for use with subwoofers (they are not "full spectrum").
T-amps are available in a couple of different sizes, based on different amp chips:
I bought and tested several of the common amps I found on ebay. Note that there are many vendors on ebay all selling the same amps (or copies of the same amps). The names of the amps get a bit confusing, its easier to go by the photos.
How to find these on ebay.com: search for the amp chip: TA2020, etc. You will find tons of these amps.
Stand alone amps (amps with a plastic or metal case):
Step 4: Notes on the Sure Electronics TK2050 100W amps
I got 2 different TK2050 amps from Sure Electronics - their original 100W system and the "improved" 100W system. These are both "bare board" amps. At $40-$50 for a 2x100W amp with 85%+ efficiency, these are amazing deals under any circumstances. I recommend the "improved" amp because its umm - improved! ok here's the deal:
Step 5: Mixers
If you want to have a microphone or any 2nd input in addition to your mp3 player then you need a powered mixer. Also, the higher-power 100W amplifiers need a powered mixer just to boost the signal level from the mp3 player. Without the signal boost you just can't get maximum volume out of the amp.
There are a couple of different suitable mixers available around $50. I've been using the Rolls MX51s, which calls itself a "stereo powered mini line mixer". you can get it from parts-express.com, amazon, and others. there are some other brands with nearly identical products.
How to use the mixer:
Step 6: Power, Batteries and Chargers
for the smaller TA2024 and TA2020 amps, a 12V battery is needed. To get full power from a big TK2050 amp you need 24V, although it is possible to run the amp on 12V at reduced power.
12V SLA batteries (also known as "gel cell" or "sealed lead acid") are very convenient for a battery-based sound system. They come in many sizes and are inexpensive. If you need 24V, just get two 12V batteries and wire them in series. SLA batteries are widely used in electric scooters, emergency exit lights, "UPS" computer back-up power supplies, etc.
Free batteries! You can often find SLA batteries free at your local recycle center. I've found that the UPS systems are often disposed while the battery inside them is still in good condition and easily removed.
If you want to just buy a new 12V SLA battery, they run $20 to $45 depending on the size. Amazon.com and batterywholesale.com have many sizes, just search for "12v sealed lead acid battery".
For a TA2024 or TA2020 system, you can also run on 8 or 10 AA batteries. Use rechargeables since it will last 3 to 5 hours. You can get a 10-AA battery holder from mouser.com part number 12BH310.
Capacity: SLA batteries come in a wide range of capacities. For a smaller systems a 4Ah to 8Ah battery is good and will be 3 to 6 pounds in weight. Figure on 1 to 2 hours runtime per Ah with a smaller amp. For a larger system or multiple speakers, you probably want to think about how long you need to run your setup for as compared to any weight consideration. With my setup I have 9Ah batteries for a single TK2050 amp, and 18Ah batteries for a dual-speaker setup, both of those will run for 6 or 8 hours at full volume, all day if i turn it down just a little. A standard car battery is around 50Ah. rechargeable AA's are about 2.5Ah capacity.
Charging: 12V SLA batteries can be charged with a small car battery charger, you can also get small and inexpensive chargers designed specially for them. Many electric scooters run on 12V, 24V or 36V, so conveniently you can find $10 to $15 chargers with all 3 of these voltage choices. You can get these $10 scooter chargers at Amazon, just search for "12V SLA charger" or "24V SLA charger" or "36V SLA charger". They come with a connector that you can just cut off and replace with crimp-terminals.
Weight: gel cells are heavy, but you'll still save a lot of weight compared to a car battery just because your setup is efficient so you won't need as big a battery. A car battery is 40 or 50 lbs, and my gel cell is half that weight and powers an equally loud setup. Lithium packs are the lightest, but much more expensive than SLA. You can get some good big lithium packs from all-battery.com.
Step 7: The Elements
Depending on your application, you may want to improve the waterproofing or vibration proofing of your gear.
Waterproofing - if you are re-cycling a home audio speaker, you probably want to paint it. a PA or DJ speaker normally has a waterproof box. In either case, i found the woofer cone is often made of unprotected stiff paper. You can easily waterproof this by coating it with a thin layer of a water-based urethane wood finish - such as Varthane - from your home improvement store.
Vibration proofing - i'm making mobile bike systems, these get vibrated a lot. amps often have some larger components in them that may or may not be well attached to the amp board. take a look and glue down anything that looks flimsy. hot-melt glue and silicone glue both work well to glue down any wobbly parts in your electronics. some of the T-amps are ok. the ones from arjenhelder_electronics needed some anti-vibration glue (see the photo). the original TK2050 from sure electronics also needed a bit of help.
Step 8: Just do it now!!
ok there's an easy way and a hard way for everything. If you want the easy way, here it is:
read the previous steps. get an efficient speaker (or 2), get an effiicient amp, a battery, and plug them together. done!!
(my article about a simple rear-rack mounted bike party sound system shows an example of the 'do it now' option)
the steps after this show how to make an Active 12V speaker - a speaker with integrated battery-powered amp. This allows slightly improved efficiency, lower weight and a more convenient package, but it is also more complex to build.
Step 9: The fully integrated Active 12V-24V speaker
Along my quest for speaker efficiency I started thinking about Active speakers (also called Powered speakers). This is the term for when the amp is built into the speaker. Most active speakers are built for 120V wall power - it means you just plug in your active speaker and plug the mp3 player straight to it. very convenient.
I looked around for a while for an active 12V speaker - one with an integrated 12V amp - but there's really not much out there. just a few subwoofers for cars, nothing full range. so lets make one! the benefits:
inside your speaker are normally 2 or 3 "drivers" - the things that make the sound. the low-frequencies are made by the big cone, called the woofer. the highs are made by a smaller horn called the tweeter. sometimes there's a 3rd midrange speaker. the efficiency of each of the 2 or 3 drivers is not the same. in a PA/DJ speaker the woofer might have a 96 SPL rating, while the tweeter might be around 103. that's a big difference! when you have your amp outside the speaker (as in any home or car stereo setup), there is just 1 signal sent to the speaker. inside every speaker is a "crossover" circuit that splits the sound up - it sends the low frequency part of the sound to the woofer and the high frequency part to the tweeter. just doing this at all incurs perhaps a 5% or 10% efficiency loss. But - what if the tweeter is much more efficient than the woofer? if all the crossover did was split up the sound, then the efficient tweeter would play all the high-pitch sounds way too loud compared to the low-pitch sounds played by the less efficient woofer. so the crossover has a 2nd job - it equalizes the sound by reducing the volume on the tweeter. but, the way that this volume adjustment happens in the crossover is by blowing off the excess power as heat - another efficiency loss. in an active speaker we have the opportunity to fix this - active speakers use a separate amp for each driver - one amp for the woofer and one for the tweeter, and we can just turn down the volume on the tweeter's amp. that's an efficient way to reduce the tweeter volume instead of the inefficient way the crossover does it. Since our T-amps are so cheap, this also won't cost much to do, and we'll end up with our amp neatly mounted inside our speaker.
Step 10: What you need
to make the fully integrated 12V amp + speaker, you need:
- stereo amp
Check the system diagrams below.
When the crossover comes after the amp, then it has to be big to handle the full amplified signal, and it has to waste power to equalize the tweeter and woofer volume. But, we always need to split apart the highs and lows from the mp3 player and direct them to the tweeter and woofer. So the secret to a good integrated amp setup is that we put a small crossover BEFORE the amp. this gives us an un-amplified tweeter signal, and an un-amplified woofer signal. we route one of those to the left channel input of the amp, and the other to the right channel input of the amp. Then on the amp output side we wire the left channel direct to the tweeter, and the right channel direct to the woofer.
When we put the crossover before the amp, we can also use it to adjust the volumes of the tweeter and woofer, and also to combine stereo to mono if we want to. operating on the un-amplified signal these can all be done without power waste.
So, to make the integrated 12V amp + speaker you need:
- 1 stereo amp per speaker
- 1 crossover per speaker
The stereo amp can be whichever T-amp you like. My build photos mostly show the TK2050 amps.
The crossover - I made my own circuit for this - see my monoXover project. It is a fairly simple circuit so you can build it yourself from parts. If you would be interested in buying a monoXover DIY kit, let me know. Another option is to use a mixing board. Some small mixing boards in the $50 to $100 range can provide this crossover functionality, i haven't tried this myself but it looks possible.
Step 11: Remove the speaker back
First remove the speaker back plate. this may be easy or difficult depending on the speaker. If its impossible, you can remove the woofer instead to get access to the inside.
Inside the speaker (usually attached to the plate) is the built-in crossover. Remove this and note the labels on the wires: you want to identify the "+" and "-" wires for both the woofer and tweeter. usually it is also labeled on the woofer and tweeter itself if you need to double-check.
cut the wires to the crossover and remove it.
also, check around for where you have enough room to mount your amp and crossover. on the Peavey PR12N, the plate is big enough to fit the amp. The Pyle PPHP121 has a really big plate, easy to work with. On the Behringer B212XL, there is no back plate at all, so i'll glue the amp inside the box somewhere.
Another option if you have no back plate - you can route all 4 wires from the woofer and tweeter outside the speaker, and attach the amp on the outside.
Step 12: Prep the back plates
we need to attach both our crossover and our amp to the backplate (or elsewhere inside).
the photos show the mounting on a Pyle PPHP121 plate.
- remove the built-in crossover
- remove some of the input jacks that came with the speaker if needed
- put a power jack into the back (i used one of the existing holes, or just drill a new one)
- drill mounting holes for a pre-amp crossover. (i'm using my monoXover crossover). i also put 2 holes so i can adjust the tweeter and woofer balance knobs from the outside.
- drill mounting holes to match my TK2050 amp
Step 13: Attach the pre-amp crossover
Step 14: Attach the amp
this shows a TK2050 "improved" model amp from sure electronics.
notice i removed the fan from the amp. when used inside the speaker, the woofer will create plenty of air flow to cool the amp, and the fan is not needed.
Step 15: Wire it up
- if you are using my monoXover crossover, the woofer output will be "out2" on the amp and tweeter will be "out1" on the amp.
- if you aren't sure which output has the high frequencies and which has the lows, test each output with a regular unmodified speaker to hear it.
- attach the woofer and tweeter to the amp. NOTE: depending on the type of crossover you use, you may need to FLIP the tweeter cables. if you are using my monoXover crossover (or any 2nd order crossover), you need to flip the tweeter: connect the tweeter's "+" to the amp's output "-". the woofer is always connected "straight up" to the amp. if you used an off-the-shelf mixing board, connect both of them "straight up".
- attach the power wires from the power jack to the amp
- attach an audio cable from the crossover to the amp input
- attach an audio cable from the crossover input to the outside of the speaker (use a jack if you want, my photo doesn't have a jack yet, but i'll put one in later)
Step 16: Put the plate back on
Step 17: Additional build photos
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i built some more setups with other speakers, here are some photos of those. check the photo notes for more info.
Step 18: The sound-off
We tested all the speakers. Our reference is Deep's set of 120V active powered Yamaha's. Deep has been using his mobile dance party setup all over san francisco for the past couple years so it is a good comparison.
Our active 24V speakers measured up! I made 3 different systems all with 100W TK2050 amps. The Yamaha reference speakers have a much higher power rating, but they are also less efficient.
At full volume, all the speakers were fairly close to each other, the B212XL was a bit quieter. The Yamaha and the B212XL have notably better sound quality than the others.
In terms of power use, it was no contest. with equal volume levels, all the 3 setups with TK2050 amps used about 1/3 the power of the Yamaha setup (with an inverter).
With 1/3 the power draw, it means we don't need a car battery to power these systems. They run great on a much smaller and lighter gel cell. plus no inverter is needed.
Step 19: More ideasI haven't tried building my own speaker boxes yet. it's rather time consuming. i'm not sure if you can improve efficiency by making your own box, but you can reduce weight. searching around instructables and the web you can find many projects about building your own boxes.
along with building your own box, you can also buy whichever woofer and tweeter you like best - including some very efficient ones. you could also swap the woofer in one of the cheaper plastic PA cabinets for a better one.
Step 20: Creditsthanks to: