DigiSpeaker is a purely digital whole house audio system. It is capable of obtaining and delivering purely digital music directly to the speakers installed throughout a home or business. Only at the very last moment is the music converted to analog sound. All sourcing, transportation, processing and amplification of the music signal is done digitally. Because of this, DigiSpeaker is an extremely versatile and efficient system for playing music throughout a home.
Each DigiSpeaker is a self contained network node, audio processor, 100W amplifier and speaker device. DigiSpeaker is designed to be installed in the walls and ceilings of homes. Or, optionally, it can be configured as a standalone unit that can be placed in a room. Each DigiSpeaker exists as a node in a network of DigiSpeakers that share information wirelessly or via cable. DigiSpeaker only requires standard house power. No other connections to the unit are necessary although some connections are desirable depending on the installation.
The 100W amplifier contained in each DigiSpeaker is a Class D stereo amplifier. It can be configured in a dual Bridge-tied Load (BTL) configuration for maximum power transfer to the speakers. Or, it can be configured as four Single Ended (SE) outputs that individually drive the woofers and tweeters of two speakers. In the BTL configuration, DigiSpeaker can deliver up to 50W of power per channel. In the SE configuration, the gain curves driving the four individual speakers can be adjusted to achieve near perfect crossover from low to high frequency.
The 100W amplifier is driven by a 48 bit digital signal PWM processor. The basic function of this processor is to convert the pulse code modulated (PCM) stream of music into a stream of pulse width modulated (PWM) pulses. These pulses are then amplified and filtered by the 100W amplifier stage of DigiSpeaker. However, the digital signal processor does a lot more. The processor can digitally control the volume, treble, base and loudness on each channel. Mute and low volume operations are implemented with a combination of digital and power supply voltage control to eliminate low volume noise. Each channel has up to seven biquadratic filters so the gain curve of the channel can be customized to the music and listeners preference.
The audio processor is fed the music signal from a general purpose processor. The general purpose processor sits at a node in the house network and helps to shuffle music and control commands around the network. Each node is fully capable of sourcing and/or sinking music. That is, each node can be connected directly to a music source such as the internet, digital music device or legacy analog device and each node can playback any song with it audio processor and amplifier. The general processor also has plenty of storage for favorite songs so DigiSpeaker can play music even when the network or external music source is not available.
All DigiSpeakers have several gigabytes of storage for caching songs. When several DigiSpeakers are installed in a single location, they share their storage space with one another effectively making the entire home into a single large distributed disk drive. This eliminates the need for a central server for music storage because the music is stored within the network and distributed around the house. Of course, individual DigiSpeakers learn the playing habits at a certain location and keep the most favorite music local.
DigiSpeaker has four separate controls that allow the user to do simple things like volume control all the way up to complicated things like organizing music and customizing the amplifiers. At the simple end of things, DigiSpeaker can be control by 'smart light switches' and infrared remotes. These devices send simple signals to the DigiSpeaker via power lines or airwaves and are handy for quickly changing the volume and/or selection of the music. At the more complicated end of things, DigiSpeaker can be controlled by a web browser or web browser enabled wifi device (like the Nokia 800). When using a web browser, a collection of DigiSpeakers present a unified view that shows the user what music they have, what sources they have, how the music is organized (playlists, artists, albums, ...etc), how the music should be processed, ..etc. Using the web browser interface, the user can configure and control every aspect of their audio system.
The power supply and amplifier used by DigiSpeaker are both highly efficient. Each component is better than 90% efficient so the heat sinks and overall size of the devices is much smaller than traditional designs. The 120W power supply used is a so called 'green mode' power supply. It is rated for both the European and Japanese markets where power supplies are required to be highly efficient, electrically quiet (low EMI) and burst capable (low current with low load). Furthermore, the high quality Class D amplifier used in DigiSpeaker is very efficient because it runs the internal components of the amplifier at their most optimum states.
Finally, DigiSpeaker is an open project. Every aspect of DigiSpeaker construction is open to the public. All electrical schematics, board layouts, parts lists, software, algorithms and processes are documented on this web site. The advantage to the public is obvious. No aspect of DigiSpeaker is a mystery. Although much of this information is difficult for the uninitiated to absorb, there are many people that visit DigiSpeaker that are capable of understanding and expanding on the information. Indeed, many projects that open up the design and development of their product to the public benefit from user innovation. DigiSpeaker is no different. Users are encouraged to 'fiddle' with the design and produce their own variants that improve on the concepts outlined here.