sound system project

[LiFeCycle]

Finished product:

Just thought i'd post an update on a sound system i have built for my bike.

Having used an underpowered portable bluetooth speaker @3w, I decided to build a 30w speaker system run off my battery. I bought the following:

And assembled it. Initially, I have glued the speakers to a phone case just to hold them and see how it works. Then, I screwed, and liquid nailsed the bluetooth receiver to the top, and the amplifier upside down on the bottom of the left side of the phone case.

It took 3 or 4 coats of liquid nails to get everything secured in place. I just wanted to get it on with the minimum of fuss and weight. Found something to screw it to, and mounted it.

The output of the bluetooth modules is soldered to where the 3.5mm input socket of the amp is soldered to the board. You can still plug a 3.5mm plug into it if you want. The unit runs on a 12v dc-dc converter in the battery bag. $10 on ebay.

Here's how it looks.

[strike]I learned a few lessons. Don't put the speakers right next to each other. They interfere in a major way, causing you to hear the difference between the left and right channels rather than their actual content. It sounds really weird, and changes depending on the angle you listen. I just cut one of the speakers off and just run one channel so it actually sounds ok. So I ended up with 1x 15w channel on the amp, driving a single 15w speaker with pretty bad bass.[/strike]
<edit>When wired in phase, they sound great together.

It's quite loud though - especially at a standstill. Noticeably better than the portable unit.

But I rode home today at 40kph into a 40kph headwind, and you could barely hear it at max volume.
Overall, it's a cool little unit, which just unclips at the pack and the cord unplugs with a 2.1mm dc jack, and i can put it away if it rains.

[strike]I'm contemplating a build with a car speaker[/strike] to have a bit of oomph and better range. One could be easily constructed with a 200w class d amp, thats about the voltage that they run on your pack voltage without a dc-dc for those of us on 50 -60v.

Apparently this is a 'Class D' https://en.wikipedia.org/wiki/Class-D_amplifier - i.e. one in which an analog signal is converted into a high frequency square wave, which a mosfet can switch more efficiently. It requires less heatsink per watt than the one i used on my first build.

Then I would pair that with a car speaker over the back wheel.

Edit: Now that i've run the 30w one for a bit with a proper enclosure, the car speaker seems totally unnecessary.

 

[John in CR]

Your speakers need an enclosure to make bass, or at least a panel to separate the front and rear waves from cancelling below the frequency determined by the distance. The longer the distance to the edge, the lower the frequency. A "U" baffle achieves this in a more compact form...think something like mounted in the end of a piece of PVC for light easy and cheap.

When you ran both speakers and got little sound, they were probably wired out of phase and that's why they cancelled. Stereo sound shouldn't cancel just because the speakers are close together.

 

[LiFeCycle]

Thanks John. I'll try wiring the speaker the other way around and see if it makes any difference.

 

[flangefrog]

I'd highly recommend those TPA3116 amps. I have one based on that chip and the sound quality is amazing. You can find more info about them here: http://www.diyaudio.com/wiki/TPA3116D2_Boards

You could also consider the bluetooth amp boards or finished amps sold by Yan Jing Audio. You can find some of these on eBay.

 

[LiFeCycle]

Thanks again John. I fixed my rookie mistake of wiring the speakers out of phase. Now they sound great together.

So the next step is to build some sort of enclosure to help with the bass. If the bass was better, I think 30W would more than adequate for a bike.

But yeah, I would love to try those TPA3116 based amps and see how they go. Good to know that the sound quality is good. I'll keep these in mind for future projects.

I found another amp on ebay that could be alright for the car speaker setup too - a 200W mono class D amp board which runs on 40-60v! This would be great because I wouldn't need a DC/DC converter - I could run it straight off the battery.

 

[John in CR]

For more bass on a bicycle rig, an option is using software such as MaxxBass. Making real bass means moving lots of air, which isn't realistic to carry the equipment on a bike. Small speakers simply can't make much bass. The way the software works is that it enhances the harmonics of the lower frequencies included in the music, and the smaller speakers are capable of playing those harmonics. The result is that you hear the lowest octaves contained in the music without your speakers actually playing them.

I wouldn't worry about carrying around high wattage. All you need is high efficiency speakers and the power from high efficiency digital amps. Though I probably wouldn't mount any of mine on a bike, I have a number of high efficiency full range drivers that will put out 90db or more on a single watt at 1m. A pair with each getting a watt adds 6 decibels. That's why I'm able to get tremendous sound out of a pair of speaker with my little tube amps that put out only about 2 watts per channel. Add in the fact that your ears are less than a meter from the speakers and rock concert sound is possible with a tiny digital amp.

I've thought often about adding sound to my ebikes, but the only thing holding me back is safety, since I rely heavily on hearing what's around me. I have quite a few pairs of Fostex FE108ez's, so I could risk a pair on bike after some cone modding to make them at least somewhat resistant to water. OTOH I have a bit larger pair of good efficiency good sounding car speakers that I used to have in my Jeep. With a sub those would do ear splitting loud enough to drown out all other noise riding at highway speeds with the top off a big off-roading tires.

 

[Doctorbass]

But I rode home today at 40kph into a 40kph headwind, and you could barely hear it at max volume.

You probably had only 15W total :|

Why not choosed 4ohm speakers?.. these TDA amp chip usually give their rated power at that impedance.

byw those compact class D amp really rock! I installed one in my lithium powered RGB full color laser projector for the external speakers when making public laser show with sound. If you have great cooling they work fine otherwise they fall into output limitation when overtemp occur..

Doc

 

[LiFeCycle]

Fascinating stuff. I held a pair of envelopes up to create a temporary barrier between the waves in front and the waves at the back (which are interfering with each other), and the change in sound was dramatic. You could really start to make out the bass, and the full potential of the speaker was realised. So i knew john was right, and it was time for an enclosure.

I taped a few bits of foam out of an old phone case onto the sides and taped it all up. There were lots of places to tape to and make a pretty secure job of it.






I have to say, the sound is terrific from these now. It would just about be a recommended addition to an ebike. The space on the headstem is the perfect spot to deliver sound directly to your ears.

since you're not wearing any earphones you can still totally hear your surroundings.

And 30w is nothing for a battery of this size. Although I am fascinated, doctor bass at your idea of getting a lot of sound out of only a few watts. What is different about your speakers that allows you to do this? Are they horn type?

 

[Jonathan in Hiram]

I had one of these mounted to my handlebars for a while, sounded quite good but I decided I don't really want the distraction of music while on the bike unless I'm well away from traffic which is almost never.

They are made for a portable XM radio player but will work with an MP3 player or a phone, has the Maxx Bass technology mentioned above and digital amplifiers. For the price of $20 it's hard to beat, list was $149.

http://www.amazon.com/Altec-Lansing...=1445304294&sr=1-1&keywords=Altec+Lansing+xm2