Articles and whitepapers

HomePlug Powerline Carrier Technology for Audio Distribution (3/12/2007)

By Michael Stein, Russound

A new wave of avid music listeners is entering the home-owner market. With it comes an opportunity to increase business by giving this growing segment the products and technologies that allow it to access its favourite sounds anywhere in the home.

Raised on MP3, P2P, iPods, podcasts, MySpace, and an overall explosion of digital content, these new music aficionados bring expectations of ubiquitous access to their music. PCs and portable players are just two of the myriad devices that serenade consumers as they travel through their day, inspiring new expectations for the installed residential audio systems they choose to install in their homes.

Once relegated to jury-rigged adapters for listening through a boom box or car stereo system, the iPod and its competition (such as it is) are now being welcomed into the most elaborate home entertainment systems. New digital transport technologies are creating opportunities to install advanced systems in existing structures, even in markets like Europe where retrofitting centuries-old homes can be a challenge at best.

IP technologies, including MOCA, HomePNA, Wi-Fi, DS2, and HomePlug are opening new markets to the custom installer, with a wide selection of products incorporating most of these new technologies.

The HomePlug advantage

In studying the above options, we at Russound decided to use HomePlug for our retrofit audio system solutions. This decision was based on the system's ubiquitous access to AC power throughout the home as compared to coax (MOCA) or phone wire (HomePNA), not to mention reliability issues concerning Wi-Fi.

It is important to remember when retrofitting audio systems that the audio amplifier requires power. If the system is to be installed in the wall, then Wi-Fi, MOCA, and HomePNA solutions will require additional wiring to power the amplifier.

Europe is especially challenging for Wi-Fi-based solutions due to the concrete construction found in so many buildings. HomePlug has proven itself as more ubiquitous than coax or phoneline solutions, and more reliable than Wi-Fi, being less susceptible to dropouts that are commonplace when Wi-Fi is used under the same roof as microwave ovens and cordless phones.

Put simply, HomePlug uses the home's power wires to carry IP data from point to point. Initially, this was used for data applications such as Internet and printer sharing, but this powerline carrier (PLC) technology can be used for much more.

HomePlug operates much in the same way as a typical data network, which includes two or more devices that plug into a PC (or router) Ethernet port and an AC outlet. These devices now appear to be on the home LAN.

Example of a PLC system using AC outlets to network devices.

A HomePlug audio system is no different. In its simplest form, an audio system may consist of two small devices. One with stereo audio input, and one with stereo audio output. These devices can be placed anywhere in the home and can transmit audio through the AC wires from the transmitter device to the receiver device.

 
The Russound Avenue PLC system comprises a Hub (left) and multiple Points (right). The Hub is designed to mate with the Russound CAV6.6, which controls up to six wired zones. The hub receives six stereo audio inputs and control information from the CAV, converting and transmitting signals via PLC to the Points which are compact enough to be hidden under furniture or on top of shelves. Each Point is connected to an AC outlet and functions as a 20W per channel stereo amplifier.

A comprehensive system may include user interfaces, the ability to play time-synchronised audio in multiple locations, built-in amplification, and bridges to other content choices.

The Russound iBridge Dock PLC bridge from iPod to a multiroom system.

The IP advantage

One of the big advantages of IP-based music systems are their scalable nature. An analogue system is typically based on an audio multiplex (MUX). MUX has a fixed number of inputs and outputs, making them cost effective only when all zones of the MUX are used. In other words, a six-source by six-zone analogue system is very cost-effective when all zones are used, but not so when only one or two zones are used. Scalable IP-based systems on the other hand, are built in a modular fashion. A single-zone system is just as cost-effective as a ten-zone system.

Installation

Installation requirements of a PLC-based system depend on the overall system itself. In its simplest form, installation is the same as any other audio system except that the long wires are replaced with the power lines. An audio output is plugged into an encoder, transmitted over the powerlines, and decoded by another module plugged into the powerline.

Of course, a custom installer would want to also install keypads, UI controls, built-in speakers, etc. The addition of powerline technology should have little impact on these other devices other than the benefit of having long wires replaced by PLC.

It is important to note that some systems may require connection by a licensed electrician. After all, these systems connect to the power inside the walls instead of a connivance outlet, and are thus suited for a fully built-in system typical of the type associated with professional electricians rather than typical custom installers.

Practical considerations

Since PLC (or any data network) imposes a limit on available bandwidth, the limitations of such a powerline system will depend heavily on what is available in every home. HomePlug 1.0 operates at 14Mb/s, HomePlug Turbo at 85Mb/s, and HomePlug AV is at 200Mb/s speed at the Physical layer, though actual throughput is much lower than Physical layer speed. This available bandwidth affects the level of required compression and the number of simultaneous listeners.

Latency is also an issue with any IP-based audio system. Additional time is required to digitise, transmit, error correct, and create an analogue signal. This is not an issue when playing MP3 files, but the opposite is true if the audio is to be used with an analogue video signal since the latency can cause lip-sync issues.

Synchronisation between multiple zones is also an issue with IP-based systems. Many ignore this consideration altogether, but a good system should allow the same music to be played throughout the house, without an echo effect.

As with any retrofit technology, PLC is not yet as reliable as a dedicated wire. In rare circumstances, an appliance in the home may require a plug-in filter to keep it from interfering with the PLC signal. Additionally, some outlets (or electrical branches) may run through a subpanel or other source of attenuation. Both of the above are rare. In any case, a complete site survey should be performed before installing PLC systems to identify any problem circuits before holes are cut in the walls.

Conclusion

Any technology that shares a medium may one day find the medium has become hostile to its existence. This is true of all the available retrofit solutions including Wi-Fi, MoCA, and HomePNA. HomePlug (IEEE 1901) however, is an internationally recognised protocol and continues to allow coexistence of 1.0, Turbo, and AV technologies on the same powerlines. Russound maintains that HomePlug will continue to assure future products will not interfere with these existing implementations.

Michael Stein is Director of Research and Technology for Russound, manufacturer of a complete range of multiroom audio-video systems, multichannel amplifiers, and loudspeakers.

www.russound.com