THE WIFI SPEAKER SYSTEM
The WiFi Speaker System is an audio system that utilizes a TI BeagleBone Black running a Debian Linux distribution and a uPnP renderer as a Plug-and-Play wireless audio system through the use of the Advanced Linux Sound Architecture (also known as ALSA) and a 32-bit stereo DAC, a Burr Brown (owned by TI) PCM5102. The amplifier uses an active crossover utilizing several TI NE5532 and two National Semi (now TI) LM3886 Class AB monolithic amplifier chips per amplifier. The amplifier is completely integrated on to a plate amp which also holds a power transformer. The crossover includes baffle step compensation for lower frequencies, and a time delay circuit to achieve the best phase performance across frequency. The power supply uses a LM317 (NS) and a LM237 (TI). The system also features a relay to protect the speaker drivers from transients from turning the speaker on or off (also known as turn-on thump). The relay is driven by a TI Darlington pair IC with integrated flyback diodes, the ULN2003. Should the speaker be used without the uPnP renderer, the input may be left channel, right channel, or balanced (which is typically used in professional settings to increase CMRR). The input is selected through the use of a switch on the board. A Burr-Brown (owned by TI) INA134 takes the balanced signal and converts it to a single ended signal for use by the amplifier. All of the signals are transformer isolated and then buffered by a NE5532 and output into another 1/4" stereo jack. This allows for paralleling as many identical speakers as desired to increase the volume. The amplifier includes circuit board mounted transformers that eliminate ground loops that can be introduced through the interfaces between audio equipment and present an annoying hum that is very difficult to eliminate. Since these transformers have a high impedance coupling from the power transformer and nearby equipment, the amplifier has a novel circuit that loads the input when it detects there is no music playing. This eliminates the hum. The board has holes along the edge to allow for mounting of the amplifier to an aluminum plate that also acts as a heatsink for the power LM3886s. Overall the WiFi speaker system is an audio system that can not only compete with other lower bitrate options like Bluetooth, but beats them in almost every way. Please refer to the PDF in the attached zip file for full documentation.
Here is a video explanation of our project.
The analog portion of our project. Board design, layout and soldering by Ben and Rich.
The resources are attached in the zip file below.
Below are the steps to building your own Hi-Fi Wi-Fi Speaker System. Refer to the PDF in the zip file attached for full documentation.
WHY IT'S BETTER THAN BLUETOOTH
At some point we have to answer the million dollar question, "How could this possibly be better than Bluetooth?" If you're a true audiophile, you already know the answer. There are several reasons. First we have to introduce the concept of bitrate. From a very high level, bitrate is the amount of data that it takes to describe an audio waveform. When audio is recorded in the recording studio, the information is captured through a microphone and then turned into 1's and 0's and then recorded onto a computer for post-processing. Music is recorded at this stage is "lossless," the highest bitrate possible. When companies such as Apple and Spotify go to sell their music, they take the data that was generated after post-processing and actually remove a bunch of the 1's and 0's (this is called lossy compression) in order to make the filesize smaller, reduce the bitrate, and use less bandwidth when people download or stream their songs. A clever reader may wonder, "Can you actually tell the difference between lossy music and lossless music?" The answer is yes. It has been shown time and time again in double-blind tests that people can indeed tell the difference, notably that lossy music doesn't sound nearly as clear and crisp as lossless music. The most reliable way to get lossless music is to buy the physical CD and rip it to a lossless format such as FLAC or use a lossless streaming service such as Tidal. A clever reader may also wonder, "What do Apple and Spotify have to do with this?" Turns out, the same thing happens when you stream over Bluetooth. Your device, usually a smartphone, takes some of the 1's and 0's and strips them out, giving you a lower bitrate, in order to use a lower bandwidth. Again this dramatically reduces the quality. Still confused? Think of lossy compression like reading an abridged book. The story's still there, but it's worth it to read the full version. Even if you use lossless music, streaming it through Bluetooth will reduce the quality.
The second reason is battery life. Anyone who's had a smartphone has noticed that their battery life is significantly shortened when Bluetooth is turned on. This is because Bluetooth is continuously pinging other Bluetooth devices in the area and looking for known devices to connect to. In addition, when Bluetooth is streamed, it pulls data from your phone and continuously streams that data to the speaker. This is a great way to be tethered to the wall at 3 in the afternoon. On the other hand, with uPnP, a very common setup is to have a network server (such as a NAS or network-attached storage) stream data to the renderer, in this case, a BeagleBone. The streaming is then done from the server, which is plugged in to the wall, to the BeagleBone, and dramatically extends your phone's battery life. With this setup, the only time when your device communicates with the system is when you pause, play, change the volume, or change the playlist, all of which require no streaming. Our setup increases battery life by not forcing continual streaming from your device to the amplifier.
The third reason is the quality of the physical equipment. Most Bluetooth setups just don't have very good equipment. The amplifiers used just aren't of very high build quality. The speakers are cheap and not tuned properly. Many setups come with a preset equalizer that pumps the bass up to unbearable levels and leaves the higher frequencies as an afterthought. Our approach is simply to use good quality equipment. We tune the drivers and keep the frequency response as flat as possible and listen to the music as the artist intended. It's as simple as that. If you don't have good quality equipment, then you for sure won't have good quality sound.
So why does Bluetooth get all the hype? The answer, of course, is marketing. The amount of money that is poured into plugging Bluetooth is astronomical. Because of this, unfortunately Bluetooth will be in the market for a while to come.
The digital portion of our project - From left to right, Isolation transformers, BeagleBone, Stereo USB DAC, Powered USB Hub, Prototyping board (only used for low noise 5V power)
BILL OF MATERIALS
Below is the BOM for two boards (left and right). Most parts come with enough for you to mess up at least one and still have enough.
Over the course of the project we discovered quite a few errors in the board layout and schematic to change in future revisions. These are listed below.
THANKS AND ACKNOWLEDGEMENTS
Thanks to Eric Estes for being our mentor for this project. Thanks to MDBU-IMC for some last minute funding help. Thanks to John Caldwell for writing an amazing app note that was the basis for this project (TIPD134). Thanks to Kasey Arceri, the organizers, and the judges for making this competition possible. Thanks to the VT AMP Lab for their support throughout the school year. Thanks to Bob Lineberry from Virginia Tech for his undying support, help, and third pair of eyes.
Richard Dumene and Benjamin Wengert - August 2016
This project won Best Beaglebone Project at DIY with TI: Intern Edition 2016
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