Sennheiser Flex 5000
Sennheiser Flex 5000If you like to crank the TV while others sleep, listening on headphones is a good solution. Except for the cable. Most viewing positions will be too far away for even a three-metre cable to reach the TV, and besides, many TVs these days have ditched the analogue headphone socket, so there’s nowhere to plug a headphone cable anyway.
One obvious solution is to use wireless headphones. And some TVs can send via Bluetooth direct to Bluetooth headphones. The problem there may be latency — the delay inherent in Bluetooth transmission can be enough to throw the audio out of sync with the picture, especially if there’s codec conversion or analogue-to-digital sampling in the process, or if you’re sensitive to such delays (as are we).
One of the best solutions we know for listening comfortably to TV on headphones is Sennheiser’s RS range of home wireless headphones, the second generation of which was released two years ago. Rather less pricey, though, is this new solution from the German headphone meisters — the $349.95 Sennheiser Flex 5000.
Send and receive
The Flex 5000 comprises a transmitter and receiver pair. The transmitter is the larger of the two, resembling an oversized remote control, with socketry at its top, and a magnetically bonding space for the smaller receiver unit at the bottom. 
So this might sit near your TV (as pictured above)receiving either an optical cable from your TV, or a minijack cable from your TV’s headphone socket (both cables are included). Bear in mind that TV headphone outputs are generally cheap circuits, and any nasties will be forwarded to the Sennheiser unit, whereas an optical connection will pass both conversion and audio duties to the hopefully superior Sennheiser circuits.
The receiver is a smaller unit, just 83 by 25mm, with volume controls on the front and a clip on the back to fix it to your clothing of choice, while on the bottom is the minijack headphone output. So you are thereby freed to sit on the couch or wander with your headphones of choice plugged into the wireless receiver unit.
The receiver is designed to dock in the mains-powered transmitter when not in use, and it clamps in with significant magnetic force! Usefully this means that, as with the higher RS headphones with their charging stands, the receiver is always fully charged, and not something you have to remember to plug in every night after use. It’s quoted for 12 hours of use between charges (three LED segments light up to show how much charge is left, four hours each), but it’s hard to foresee the receiver ever being off the charger for that long, unless left accidentally clipped to clothing after use.
Noting only the minijack rather than the quarter-inch socket on the receiver, you’re free to use any suitable headphones, though Sennheiser does generously include a pair of MX 475 in-ear phones in the box, which normally sell separately with an RRP of $44.95. Even if you don’t use them with the Flex, it’s always useful to have a spare pair of half-decent buds around. Those with hearing aids can also use an induction loop if the hearing aid supports an induction coil (T-coil).
So there are two main things to be reviewed here — the wireless transmission quality and range, and the actual sound quality of the headphone output stage in the receiver unit. In practice, you can’t separate the two, of course. Happily both turned out to be impeccable. 
Set-up is pretty much idiot-proof. We gave the Flex 5000 an analogue input from a recording loop on our hi-fi amplifier, thereby allowing us to feed any source through. We also attached our TV using the optical output from our LG TV. Once slight inconvenience — there’s no way to switch between these two inputs; you have to disconnect the analogue cable to use the optical one. 
Sennheiser Flex 5000Then, after giving the receiver a couple of days to get its charge maxed up, we took the receiver unit off its transmitter dock and plugged in our favourite AKG headphones (we have favourite Sennies too, but the point here is the ability to mix things up). Pressing one of the volume control buttons also serves to turn on both receiver and transmitter together, and as the sound faded up, the quality was immediately clear. The Flex 5000 seems to use the same transmission system as the RS range of headphones — not Bluetooth but a true CD-quality digital transmission system (8-FSK modulation on a 2.4-2.4835GHz carrier frequency). The quality seemed indistinguishable from being plugged direct into the hi-fi amp (which has an excellent headphone stage itself), other than having some sort of automatic gain circuit in there somewhere. We were nervous of this, as some of Sennheiser’s first gen of RS headphones had an aggressive auto-gain which couldn’t be turned off, and it made listening to classical music particularly unbearable, as it would pump up during the quiet sections and then limit the loud bits. Here it seems a once-off decision based on its initial input — give it a low level and it’ll add gain, but it won’t subsequent pump as things change. It doesn’t compress the music. 
Beware, however, the side button on the receiver, all too easy to press and invoking ‘speech intelligibility’ mode, in which “annoying background noise is effectively reduced, speech becomes clearer and easier to understand”. Sennheiser, to its credit, does say not to use it with music, and you’re unlikely to do it by mistake, as it collapses the stereo image and softens everything (the main LED on the transmitter also turns blue instead of white). Is this mode useful for movies, then? Well, it does seem to tame overzealous mixes; we switched to optical (by pulling out the analogue cable) and span up Indiana Jones and the Temple of Doom. This franchise’s rather incessant wide-panned orchestral music was dropped back significantly to the slight advantage of dialogue, but that dialogue was also softened and the overall effect rather unpleasant — definitely deleterious to the intended excitement of it all. We’d suggest leaving this button well alone, unless to hold it for two seconds to turn off the receiver. But docking it turns it off anyway.
There’s more sound manipulation available via three ‘hearing profiles’ on the main transmitter. Don’t go near these unless you actually have a hearing problem that requires correction, or have some seriously compromised source material. They all invoke compression, and range in effect from making everything dull to making it all thin. Learn what the LED indicators mean so you can be sure you have them turned off (though again, your ears will tell you pretty sharpish). You can also shift the balance from left to right, again if you have flawed source material or a hearing deficiency. Otherwise, not required.
Two other notes on the optical input. Firstly if you can’t hear anything, try changing the digital format on your TV or digital source to PCM, not bitstream. (If you’re playing high-res music, the optical input is good to 24-bit/96kHz.) Secondly, latency — the potential delay from digital-to-analogue conversion and then transmission — could potentially put your audio out of sync with the TV. Well, the Flex 5000 specs claim latency below 60ms, and we experienced no notable latency at all (we’ll rather sensitive to this, so we were impressed). 
So for most users there’s superfluous sound-tweaking stuff here, but the fundamentals are thrilling. The wireless range matched the best RS models — expect 15 metres without drop-outs, less if you have lots of concrete, more if you’re nicely open-plan. Sound quality is as good as, say, a midrange hi-fi amp head-phone socket, and there’s plenty of level for normal sensitivity headphones. Best of all, of course, is the freedom to move, to have cable-free headphones, and to use headphones of your choice. 
We hope people ignore the confusions of its sound profiles, and grasp these excellent fundamental abilities, though we gather neither of the major electronics chains in Australia did, so the Flex 5000 may be rather hard to find here. That’s a great shame, as it deserves to be a big success for Sennheiser, and it made us far happier than the bloke in their publicity pics (below). 
Sennheiser Flex 5000
Sennheiser Flex 5000          $349.95
Transmitter inputs: minijack analogue; optical digital (PCM 16/24-bit, 32-96kHz) 
Receiver output: minijack headphone (900mV at 32 ohms, minimum 16 ohms)
Headphones included: MX 475
Quoted range: up to 30 metres (line of sight)
Audio latency: < 60ms
Dimensions (whd): 50 x 270 x 42mm (transmitter); 29 x 87 x 25mm (receiver)