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We compare products from their published specs and features; the verdicts below are our independent editorial opinions.
Updated: 2026-09-17 · 7 min read · Independent comparison
• Sennheiser Consumer Audio BTD — biggest strength: Bluetooth 5.2 with aptX codecs, low latency and a USB-A dongle plus a USB-C adapter, so it fits either port on a computer and keeps audio and video in sync.
• Sennheiser Consumer Audio BTD — biggest trade-off: It is a computer-oriented dongle. It is not a battery-powered transmitter for a 3.5 mm headphone jack, and it does not let two people share one audio source.
• Avantree Relay — biggest strength: It turns a wired 3.5 mm output into Bluetooth, supports two pairs of headphones at once, and runs up to 25 hours on a charge with onboard volume controls.
• Avantree Relay — biggest trade-off: It is transmitter-only, has no microphone, and Avantree explicitly says it is not meant for phone calls, TVs, hearing aids, musical instruments, or receiving audio.
• Pick the Sennheiser BTD if your problem is "my laptop won't talk to my Bluetooth headphones properly."
• Pick the Avantree Relay if your problem is "two of us want to watch the same in-flight movie with our own earbuds."
The BTD 600 is a very small black dongle — roughly 0.61 x 0.31 x 0.78 inches and about 0.04 kg — and its whole job is to give a computer a proper Bluetooth audio path. You plug it into a USB-A port, or into a USB-C port using the included adapter, and pair your headphones to it. That is the entire setup. Sennheiser calls it plug-and-play, and the design backs that up: one port, no battery, no charging, no app.
What makes it interesting for a buyer is the codec and latency story. Bluetooth 5.2 plus aptX audio codecs is a combination aimed at higher-definition music, clear calls, and video that stays in sync. If you have ever watched a video on a desktop with generic Bluetooth and noticed the lips landing a beat after the words, that is exactly the annoyance this dongle is built to remove. It also passes media and call controls through to your headphones, so you keep using the buttons you already know instead of hunting for on-screen controls. And because it stays paired, you can move it from one machine to another and your headphones reconnect without a fresh pairing dance.
Who should skip it: anyone trying to get sound out of a 3.5 mm jack, anyone who needs to feed two listeners at once, and anyone who wants a battery-powered transmitter they can carry on a plane. That is simply not what this device is.
Avantree Relay: Who It's For
The Avantree Relay starts from a completely different problem. Airplane seatback screens almost always hand you a 3.5 mm socket — and if you travel with AirPods or Bluetooth headphones, that socket is useless to you. The Relay plugs into that jack, pairs with your headphones, and transmits the audio wirelessly. Avantree describes a three-step process: plug in, put your headphones in pairing mode, connect. A dual-prong airplane adapter is included, which is the piece you need on older aircraft that use the two-pin socket.
The headline feature is Dual Link. Two pairs of Bluetooth headphones can connect to one Relay, which means you and a travel partner can both listen to the same movie without splitting a cheap pair of airline earbuds. If you have ever passed a single earbud back and forth on a long-haul flight, you already know why this matters.
The second headline is battery. Avantree rates it at up to 25 hours of playtime with a clear battery indicator and onboard volume controls, and a full charge takes about 2 hours via the lithium-polymer cell. For a long-haul itinerary that is comfortably more than a single flight, and the volume controls mean you are not stuck reaching for the seatback buttons. On the audio side it uses Qualcomm technology with aptX Adaptive and aptX HD support, plus Bluetooth 5.3, so with compatible headphones you get stable, detailed sound rather than the thin, hissy result you get from budget transmitters. The enclosure is ABS plastic in a Sandstorm Beige finish.
The trade-offs are real and Avantree is upfront about them. This is a transmitter only. There is no microphone, so it cannot be used for phone calls. Avantree also states it is not intended for TVs, hearing aids, musical instruments, or receiving audio. It is built for one narrow, specific job: sending audio from a 3.5 mm source to Bluetooth headphones.
Side-by-Side: Which Should You Choose?
• Best for PC and Mac audio → Sennheiser Consumer Audio BTD. USB-A with a USB-C adapter, Bluetooth 5.2, aptX codecs, and it stays paired across devices.
• Best for travel and in-flight sharing → Avantree Relay. 3.5 mm input, dual headphone support, and a bundled dual-prong airplane adapter.
• Best for battery life → Avantree Relay. Up to 25 hours of playtime with a battery indicator; the Sennheiser has no battery at all because it draws power from the USB port.
• Best for low-latency video sync → Sennheiser Consumer Audio BTD. Low latency and aptX are the core of its pitch, and it keeps audio and video aligned for streaming and calls.
• Best for two listeners at once → Avantree Relay. Dual Link is the deciding feature; the Sennheiser connects one set of headphones.
• Best for calls → Sennheiser Consumer Audio BTD. It supports media and call controls through your headphones. The Relay has no microphone and is not made for calls.
• Best for a no-charge, leave-it-plugged-in setup → Sennheiser Consumer Audio BTD. No battery to manage, no charging routine.
• Best for wired 3.5 mm sources → Avantree Relay. That is its only input. The Sennheiser has no analog jack.
In my opinion, these two barely compete — they solve different problems, and the right answer depends entirely on which problem you actually have. If you want better Bluetooth audio on a computer, I would buy the Sennheiser Consumer Audio BTD: it is a focused, no-battery, plug-and-play fix with aptX and low latency, and it does exactly one thing well. If your real pain is a long flight and a seatback screen, I would buy the Avantree Relay: 25 hours of battery, dual headphone support, and a bundled airplane adapter make it the obvious travel pick. Buy the one that matches your problem, not the one with more features on paper.
The Avantree Relay is the one built for that. It takes the airplane's 3.5 mm output, sends it to your Bluetooth headphones, and supports two listeners at once. The Sennheiser BTD 600 plugs into a computer's USB port, not an airplane jack.
No. Avantree states the Relay has no microphone and is not intended for phone calls, TVs, hearing aids, musical instruments, or receiving audio. For calls, the Sennheiser BTD 600 is the appropriate pick, since it supports call controls through your headphones.
No. It is a USB dongle with no battery and no plug. It draws power from the port it is plugged into. The Avantree Relay, by contrast, runs on a lithium-polymer battery rated for up to 25 hours and takes about 2 hours to charge.
The Sennheiser Consumer Audio BTD. Bluetooth 5.2, aptX codecs, low latency, and the USB-A plus USB-C adapter cover the common laptop and desktop situations. Compare the current prices on Amazon before deciding, since that is the one thing that can shift the math.
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