In the hi-def era, all audiovisual signals travel over one cable. But things get tricky when that cable has to cover a long distance. By Glenn Derene
Let’s give the HDMI cable some credit. It helped clean up the tangled mess of wires behind our TVs, gave us a way to quickly link a stunning range of devices with a new generation of displays and provided a sturdy backbone for the HD revolution. But for everything this unassuming all-in-one cable can handle, sometimes it comes up short.
Like many video, audio and data cables, HDMI cords can suffer from signal degradation at longer lengths – 15 m is generally considered the maximum reliable length. And it’s rare to see an HDMI cable longer than 8 m in a store. Even online, cables more than 15 m long can be hard to find. If your TV, set-top box and other AV equipment are all on the same piece of furniture, this isn’t much of a concern. With a collocated setup, you’ll probably never need more than 2 m of cable at a time.
But HDTVs have introduced a whole new way of arranging home theatre gear. Flat screens are increasingly thin and lightweight, and their picture-frame profiles make them perfect for hanging on walls. Similarly, HD home theatre digital projectors are now affordable enough for non-millionaires to set up a home cinema. A clean installation of either of these setups generally requires a bit of in-wall wiring, sometimes even from one room – an AV cupboard, for instance – to another. And when you’re fishing wires up into ceilings, over doors and under floors, the necessary spool of cable gets long quickly.
Here are the alternatives.
Cat 6 piggyback
One commonly used solution to cablelength limitations is something called HDMI over Cat 6. Steven D’Addone, coowner of Intra Home Systems, an installer of high-end audiovisual systems, swears by the technology. “We only run Cat 6,” he says.
Here’s how it works: a video source, such as an HD cable box, is connected to a small device – a “balun”, in the parlance of the trade – with a short HDMI cable. The balun usually takes the form of a small, router-like box or a wall plate. Its job is to pass the HDMI signal along to one or more Cat 5e or Cat 6 cables. (These are the same cables used to wire Ethernet networks – Cat 5e is a more common cable, but the newer Cat 6 standard is preferred by AV installers for its higher bandwidth.) At the receiving end, a similar box passes the signal back onto an HDMI cable, which then connects to your display.
Now, all HDMI over Cat 6 baluns are not created equal. Some crudely bridge the HDMI and Cat 6 cables by relying on the signal power of the original video source; this limits the range considerably. Others compress and then decompress the HDMI signal, but this can cause hardware compatibility problems. D’Addone recommends a third type of system. “What seems to be the most reliable are products that are high-bandwidth and powered on both sides,” he says. These boxes, which can be found for about R700 each, create a direct bridge between HDMI and a pair of Cat 6 cables, but provide extra power to ensure the signal can travel close to 50 metres.
Best of all, powered HDMI over Cat 6 preserves the quality of video and audio signals. And given the low cable price, HDMI over Cat 6 makes the most economic sense for longer throws.
Copper and fibre
For distances up to 100 m, similarly priced adapters are available that make use of coaxial cable. One catch: HDMI over coaxial solutions usually require a minimum of two coax cables, and often as many as four. This means that existing household coax installations, which generally make use of only a single cable running to each connected room, won’t be of much use. For even longer runs, you’ll have to leave the world of copper for fibre optics. While the fibre itself is cheap, adapter hardware is pricey. In addition, DIY installation is a complicated and difficult proposition, and professional installation makes the setup even more expensive.
What if you’d like to lug your TV into the backyard for the big game? Or maybe you rent your home and aren’t permitted to drill holes for cables in the walls. In these cases, you can bypass wires entirely. “Wireless HDMI” is a phrase thrown around a lot, but it doesn’t refer to an official standard or even a specific technology. Rather, it’s a blanket term for a variety of wireless products that transmit video signals using proprietary wireless standards. These work by stationing a transmitter near the video source and a small receiver by the TV.
Wireless HD systems can be useful, but they have limitations. In most products, broadcast ranges top out at around 15 metres. Unlike HDMI over Cat 6, wireless HDMI solutions tend to degrade image quality – not fatally, but enough for a discerning eye to notice. Signals are also prone to unpredictable interruptions, just like you sometimes experience with Wi-Fi.
Lastly, these devices aren’t cheap: to get reasonable reliability, range and image quality, you’ll probably want to go with a major brand – Philips or Sony – and spend at least R2 000.
Good old HDMI
Before dropping a couple of grand on HDMI extenders or wireless transmitters, make sure it’s really necessary. For runs of 15 m and under, an HDMI cable is still your simplest option. And don’t go for the high-priced cables found in retail stores; rather spend a little while on the Web. HDMI can be installed in-wall almost as easily as coaxial or Cat 6 cable. (Although, thanks to HDMI’s security features, you cannot cut the cable to an exact length and apply fittings yourself, which means you generally have to overbuy and leave a bit of slack in your walls.) So be sure to measure out the distance between your equipment and TV before you invest in a complex system. It may turn out that an HDMI cable is the cheapest and easiest solution after all.