I's been a while since I have updated this log, not because there has been no work done, but because I have so little free time for me to document the progress. Lets begin. To start, the Amp/Audio assembly has been fully assembled. The following pictures show the testing setup of the completed audio assembly:
Testing off of battery and Boost Converter (for sub amp):
One of the things that I did not realize when purchasing these amps is that the minimum voltage rating is not the minimum voltage for maximum output. If the proper voltage is not supplied, then the amp will simply clip at a lower gain value than its advertised value. In other words, the recommended voltage is required for ideal operation. Since my power source was to be the 20-29v laptop bricks/battery packs, not enough voltage would be provided for the subwoofer amplifier to operate properly. I ended up getting a boost converter, which is a high efficiency dc-dc converter that boosts the voltage. I was able to bring the voltage up to ~40v and increase the gain without clipping to the proper output power. While I was at it, I also got a buck converter for the 12v bluetooth receiver and active crossover. This is similar to the boost in operation, but lowers and regulates voltage as long as the input is grater than or equal to the desired output.
It may be hard to see here, but notice the molex connectors at the end with the wires sticking off (also seen in picture above). This is going to be used to establish a connection between the audio assembly, power assembly, and the speakers themselves when installed in the electronics area:
Testing with power and fan assembly (notice the molex connectors):
This reminds me of a short story I would like to share about this project in this stage. I ended up taking this speaker back to my dorm to store wile the lab I was working in was closed. While there, I had it setup just like in the picture above for testing and listening purposes. Apparently, one of the supervisors doing health and safety inspections thought that this resembled some sort of bomb, so much so that they invited a police officer to come visit my room. Luckily, I was present downstairs before the cop showed up. Upon arrival, he stated to the supervisor that if there was a threat in the building, that it must be evacuated and then a bomb crew sent in to "detonate" it. At this point, I offered to show him pictures of the project to prove that it was not in fact a bomb and that it was simply an engineering project. Thankfully, that resolved the issue and I decided to not bring the speaker back to my room until it had no loose external wires. Anyway, back to the build log.
After listening to it for a few weeks with content that I was very familiar with, I determined that the amplifier for the subwoofer was not powerful enough for my liking. I ordered the 500 watt variant of the original 200w amp that I had. This was the same form factor, but required slightly higher voltage to operate. This was not a problem as the voltage coming from the boost converter was a quick adjustment up to 50v.
Another change I made to the existing design was replacing the main full range drivers. I attended the local maker fair here in Orlando, and got talking to some guys about the speakers they had built. The speakers looked like typical floor standing speakers, but with two low end drivers and this little 1.5" speaker. They sounded quite good and when I asked them what they had the crossovers set to (expecting them to say the little thing was a tweeter and the woofers took care of everything else) they said the little thing does 200-20,000hz and the woofers are 20-200hz. I didn't believe them at first but they quickly convinced my by covering the little one with their hand. All of the rich sound, the detail, everything diapered! I asked them what it was and they explained how it was a new technology called BMR. Anyway, long story short, I found some of them on parts express here: http://www.parts-express.com/tectonic-elements-tebm46c20n-4b-bmr-3-full-range-speaker-4-ohm--297-2157
. As soon as I got them, I mounted one in a tin can and tested it out. I couldn't believe my ears! The sound this thing makes in such a small form factor is insane! I rebuilt the speaker boxes for them and installed them into them with a filter capacitor at 200hz.
Also a ton of work was done on the electronics portion. The batteries were wired up to the management boards and the chargers wired to that. I seemed to be having problems with the chargers charging them if left hooked up, so I had to take it apart to charge them. I have recently tried putting diodes in line of the positive of the charger to prevent back flow into the charging circuit. This seems to help, but the chargers still seem to overcharge the cells. Here is a picture of the electronics assembly.
I know this post covered a lot and a lot of detail was missed, but the log is now caught up and I will update it as soon as work is done on the speaker from now on.