Building a Bicycle Sound System

Bicycle Sound Systems (BSS) are growing in popularity. Anyone who has gone to a festival, seen or participated in a Critical Mass ride or watched the Skyride events in the UK will have seen a BSS in operation. The following is a description of what I have learnt over the years in the art of building a sound system attached to a bicycle.
Please note that all this is just my opinion; there are no rules. If it works and you or someone else is happy with the result then that is great. Duke Ellington once said, "There are two types of music, good and bad. If you like it, it's good music."
The first consideration before building a bicycle sound system is to ask yourself exactly what is it for? Now this may sound like a stupid question but consider:

1. Is the music for your own enjoyment, other cyclists riding with you, or members of the public watching?
2. Will you be riding the bike whilst the music is playing? (probably answered in the first question)
3. Would you like to play just your own music or have facilities, i.e. mixing desk, microphones, to make the system more flexible?
4. Would you wish to hire out the system at festivals and other events?
5. Where would the system be stored when not in use?
6. How would you get the system to the events?

Hopefully you can see the reason for asking these questions first. Once you know what the BSS is for, there are now a few more questions.

1. What is the budget?
2. How loud is the system to be?
3. Will you want to operate it in the rain?
4. Is it to be self-powered?
5. Would you want to use a trailer?

I am going to presume that the BSS is designed to have the music playing whilst being ridden. I have seen 'static' systems but I feel the whole idea of a BSS is that we have mobile music.
A top of the range BSS could run into thousands of pounds, especially if everything needed was bought new.
The volume of the system is probably the key to everything. The amount of power needed outside is far, far more than is needed inside; most of the sound from speakers inside a building is actually reflected sound. Take the walls away and the volume drops massively.
There has to be a balance between what is audible, the fidelity of the reproduction, what can be afforded, and what is practical. A super loud system can not only annoy the neighbourhood and attract the police but it becomes really heavy and is impossible to move. Remember there is not just the weight of the speakers, there are also batteries and amplifiers that have to be carried.
Again, how loud depends on the use, if it is just yourself and a cyclist next to you, 50 - 100 watts could be enough. In my opinion, 100 watts would be the absolute minimum. If you want many people to hear you and you want a proper bass response, the wattage must increase. I believe 600 watts is somewhere around the maximum, for both volume and weight.
Critically the amplifier must not be overdriven. This usually happens when the output of the amplifier is not enough for the situation. Everything is turned to max to compensate and there is distortion. We have all heard it, in cars, clueless DJ's, PA systems... The crazy thing is that turning it down just a bit will reduce the volume very slightly but everything can now be heard properly without distortion.
The question of waterproofing has to be considered from the outset. Placing plastic bags or sheeting over speakers, amps and players does not work; not only does it look terrible, water WILL get in. Another issue is at what point do the covers go on? In case it looks like rain or when it starts raining? The latter means carrying covers to hopefully quickly throw over the system (whilst it is running!) in the hope that nothing gets damaged. Although there are waterproof players out there, the connections are not waterproof. Waterproof speakers do not sound that good, they are small and low powered. I have never seen a waterproof amplifier.
Self -powered or not? This will come down to the volume of the system. An average cyclist can develop 100-200 watts for an hour. Moving the bike and sound system is going to use a certain amount of that power. There are losses involved in converting that power to usable electricity. Taking these factors into account, never mind the engineering problems in generating the electricity, we do not have much left for powering the amplifier. It can and has been done, the systems are not that loud and, in my opinion, are not that good.
Whether or not to use a trailer is again down to what the BSS is for. We have all seen the ghetto-blaster strapped to the side of a bicycle. It works but the sound is not too good and cannot be heard from more than a few metres away.
The main problem with getting a decent sound without a trailer is one of weight. That is why all the good sound systems I have seen use a trailer.
If it is decided that batteries will power the system, we then consider the amplifier. Although the best amplifiers, in terms of fidelity are the domestic, Hi-Fi amps, they run on mains, 110v or 240v AC. This means the battery voltage, most likely 12v DC, must be converted.
This causes all sorts of problems. The worst is that cheaper converters, or inverters, convert the DC into a square wave AC, this makes an amplifier hum. The other problem is the idea of having high voltages running around the system.
Even if these considerations were overcome, the next, probably terminal issue is that a domestic or PA amplifier would probably fall apart in a short time due to the battering bicycle sound systems get. And they do get a battering; cobbles, pot holes, kerbs, speed humps, all give these rigs a hard life.
These reasons are why every BSS I have seen use 12v automotive amplifiers; they are relatively cheap, easy to bolt down and provided a reputable make is used, are very reliable.
The fidelity of an amplifier on a BSS is not that critical. What is discernable inside a quiet living room will be lost outside. As long as there is no distortion, the most critical component of a bicycle sound system is the speaker(s)
The most important consideration when building any music system, whether a domestic Hi-Fi, car audio system, or public address (PA) is the choice of speakers. Over half your budget should go on the speakers. If top quality speakers are used, you can get away, to a certain extent, with cheaper amplifiers. Do it the other way round and there will always be a poor sound.
Speakers are difficult to get right. The different drivers, e.g. woofer, tweeter, must be matched with each other and they also must be matched with the correct crossover (the device that splits the signal into high and low frequencies). Not only that, the cabinet, or enclosure must also be matched to the drivers and the crossover.
A sound engineer told me that he once worked for a top speaker manufacturer in the UK. His first project was to discover why their latest speaker did not work as well as their previous model. In theory it should have sounded better but mysteriously sounded worse. After a week of messing about he discovered that the screws holding the rear cover on were slightly shorter in the new speaker. Changing the screws for the longer ones magically brought the speaker to life.
It is that story alone that makes the idea of building a speaker from DIY plans very much hit or miss. Yes, the speaker will work but will it sound fantastic, just OK or dreadful? The only advantage of building a speaker cabinet is that it could be made to fit a trailer, or be an integral part of the trailer.
The choice of speakers is massive. Generally, speakers can be divided into three types, Hi-Fi, car audio and PA.
Car speakers can be a popular choice for BSS as they are cheap. The biggest problem with them is that they have to be fitted into a cabinet. Often seen is the 'sub' bass, a 15" speaker already fitted into a cabinet. The problem is that a 'sub' bass is just that, subsonic, or very low frequencies only. Great for certain types of music and a cinema surround sound system but not good enough on its own for a sound system. There will be a need for proper bass drivers as well as a sub. Generally a sub is not needed, not only does it require huge amounts of power to drive it, most music sounds good without one.
Hi-Fi speakers can and are used. The disadvantages with them are:

1. To mount them properly they must either be strapped or screwed down. Screwing them means introducing screws into the cabinet, the cabinets are not designed for this and the material can be weakened. Also see above for the effect of the 'wrong' screws.
2. They are meant to be used in static situations. The electronic crossovers in them are not rugged enough for mobile use and can fail.
3. They are vunerable to damage.
4. The connections are unreliable for a mobile application.

I believe the best speaker for a BSS are professional PA speakers for the following reasons:

1. They are very robust, built for a life on the road. The cabinets are usually made from tough ABS plastic and the speakers have protective grills over them.
2. They often have handles built into them which makes assembling and transporting the system easier.
3. The crossovers are built in and are made for rough use and to handle high power.
4. They have professional Speakon connectors, these are very quick to connect and cannot work loose.
5. A speaker from a quality manufacturer will have designed the drivers to work well together at high wattages reliably
6. The cabinets usually have threaded inserts making it easy to fix them to a trailer. (remember the story about the wrong screws; start screwing into a domestic Hi-Fi speaker at your peril. That is why speaker wall brackets just clamp onto the speaker).

Another aspect of speaker choice comes back to the intended use. Stereo or mono? Stereo only works when the speakers are in the correct position in front of the listener. This is not going to happen with a BSS. Another consideration is placement. Front, side or rear facing?
An advantage of a mono sound is that the amplifier can be bridged. Most car amplifiers can be bridged. Bridging an amplifier has the effect of increasing the output of the amplifier. When bridging an amplifier into two speaker cabinets, extreme care must be taken to ensure the impedance of the combined speakers does not go below the minimum rated impedance of the amplifier otherwise a sorry mess of blue smoke will ensue.
Having carefully chosen the amplifier and speakers. The question of getting it all to fit together must be considered.
There is the choice of trailer and battery. The trailer often comes down to budget and availability. Just make sure it is strong enough to support the combined weight of everything.
Do not use 12v car batteries. They are designed to give a large current in a short burst to operate the starter motor. They are not designed to go flat - a flat battery is anything less than about 12.5 volts. Once they have gone flat they will never recover. Each re-charge will result in a lower and lower final voltage until the battery will fail.
The cheapest form of usable battery is the lead acid 'leisure battery'. These are designed for caravans and wind charger and photo-voltaic systems; they can be re-cycled (recharged) many times before failure.
Always use a fuse after the battery!
Use proper crimped connectors, battery terminals etc. Try to avoid jamming wire under bolts. The vast majority of failures in all electrical systems are loose or bad connections.
Try to use locking compound on screws and other fittings.
Large output amplifiers that are bridged running in an enclosed space can be prone to overheating. A good amplifier will have an automatic shut-down if this happens. Overheating can be easily avoided by using computer cooling fans blowing across the amplifier. Stick-on heat sinks can help. Computer fans operate at 12v and can be found very cheaply on eBay.
Put all the electrics into an enclosure that is waterproof. Have an air inlet at the bottom to let cool air in and an outlet at the top for the warm air to escape.
The speakers can be protected by a cover over the top and some sort of material (printed fabrics are cheap and look good) across the front of them. As long as the material is a few inches from the front of the speakers they will remain dry.
The music player for simplicity and water protection can be mounted near the amplifier. The obvious disadvantage is that it cannot be controlled from the bike. One solution is to mount it in a small box on the handle bars. We have found the best way is to use a plastic lidded box turned upside down with the box attached to the lid with a hinge. As long as the player is mounted above the base (lid) it will remain dry. Obviously if it is raining hard try to avoid opening the box!
Finally, appearance. Briefly, if the system is just to please you and your friends probably the last thing to worry about is its appearance. After all, there is something to be said about the aesthetics of a functional device. However, if you want to hire the system out or use it on paid-for events, the appearance can be a more important consideration than its performance.
So there you have it. I hope you have found this interesting and informative.
Thanks for reading this!

We at Bicycle Sound Systems have been making bike sound systems for about six years. We were originally asked to make one for the Skyrides in the UK and have gone on to make systems for other people and ourselves.
If you would like to see details about our latest 600 watt rig or would like to hire one of our systems or even like us to make a sound system to your specifications, visit us at http://www.BikeSoundSystems.com
If you would like add your own thoughts about bicycle sound systems, visit our blog at http://newbie-online.com/money/?p=8. We would love to hear from you!

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