I’ve been reviewing all manner of things at Wirecutter, from phone cases and tablets to selfie sticks and barware, since 2014.

Wirecutter senior staff writer Brent Butterworth conducted lab measurements of all the transmitters we tested to make sure the devices reproduced the full range of sound and had no excess latency. Brent has 30 years of experience reviewing audio gear and is one of a very small number of journalists who are equipped to measure Bluetooth devices.

Bluetooth wireless headphones and earbuds are rapidly becoming the preferred choice in headphones, especially as more smartphone makers remove the headphone jack. But if you want to use your pair to listen to an audio source that doesn’t have built-in Bluetooth—such as an in-flight entertainment system, the equipment at the gym, or an older smart TV—you just can’t do it.

Bluetooth transmitters provide a solution to that problem, essentially adding Bluetooth to devices that lack it. They connect to the source via an audio cable and wirelessly broadcast the audio to your headphones or even to a Bluetooth speaker.

Some models are small and portable, with a built-in battery, while others are designed to be stationary and used with your TV so that you can listen to what you’re watching without disturbing others or keep listening as you leave the room.

You can find a ton of inexpensive Bluetooth transmitters on Amazon, and most of them are relatively similar to one another in functionality, design, and price. Because they’re all so comparable, we focused our search on transmitters that included a few more-advanced features:

• aptX Low Latency: Many Android devices, and some headphones, support this streaming audio codec, which can reduce latency to below 40 milliseconds. This means that if you’re watching a video, the audio is synced up to the character’s lips, without the disorienting lag that can happen with Bluetooth codecs such as SBC. For you to enjoy the benefits of aptX Low Latency, both the source device and the receiving device must support it. Notably, Apple devices, including iPhones and AirPods, don’t support aptX Low Latency.

• Multi-device pairing: Because most of the models we researched can connect to two Bluetooth receivers at once (your headphones and your partner’s, for example), we eliminated any that connected to only one device.
• Both transmitter and receiver modes: Although all these devices can beam audio to your headphones, some of them can also receive audio from your phone and pass it through to wired headphones, a speaker, or a car stereo. Since the prices of transmitter/receiver combos were in the same range as those of transmitter-only models, we decided to limit our test to those that included both modes for added convenience. Even so, this guide focuses on the Bluetooth transmitting function; if you’re looking specifically for a Bluetooth receiver, we have other guides for that—namely, guides to the best Bluetooth headphone adapter and the best Bluetooth audio receiver for your home stereo or speakers.
• A long battery life (for portable models): A long-lasting battery means you’ll be able to use your portable transmitter on trips or throughout the week without having to be constantly charging, and there’s a better chance that the device will be ready to go whenever you pick it up. We saw advertised battery life ranging from eight to 20 hours among these models; even the low-end figures are pretty good and wouldn’t exclusively disqualify a transmitter. Some of the TV-based models also have batteries, but that’s simply a nice-to-have feature, as such models are most often used in a semipermanent, stationary position.
• Optical output, audio pass-through, and simultaneous output (for TV-based models): We noted a few additional considerations for stationary models intended for use with a TV. We chose to test only those transmitters that had both an optical audio input and output, allowing the audio to pass through to your soundbar (or other audio device), if you use one, rather than hijacking the signal altogether. And we wanted them to be able to play audio through the TV or soundbar at the same time they broadcast the audio wirelessly.

The above criteria helped us narrow down our list of transmitters to test. We then used the following criteria to evaluate each transmitter:

• Ease of connection: We started by pairing, or attempting to pair, a set of headphones with each transmitter. Some connected instantly, as we expected, but a shocking number simply didn’t, even after repeated attempts. Although Bluetooth can be somewhat finicky, and a failure here doesn’t mean a given model will never work, you need to be able to rely on a consistently smooth process. After pairing the headphones, we then paired a Bluetooth speaker to the models that connected successfully to see how they handled outputting to two devices.
• Controls: Despite the relative simplicity of these accessories, their controls varied widely. Some offered only one button and one light for us to control everything and see the status, while others had more advanced (and easier-to-use) systems. We quickly found that we preferred the less ambiguous control schemes, especially when pairing to multiple devices.
• Latency: Latency refers to the time delay between the audio and video parts of the signal. When latency is too high, you can see that the audio doesn’t properly sync with the video. We measured the audio latency by sending signals to two different Bluetooth receivers: the Sony HWS-BTA2W, which supports only the laggier SBC codec, and the Aluratek ABC53F, which supports the aptX and aptX Low Latency codecs.
• Frequency response: Next, we took frequency response measurements using pink noise and a spectrum analyzer, with the transmitters beaming to an Audioengine B1 Bluetooth Music Receiver. This test showed us how evenly each transmitter replicated all sounds across the audio spectrum, an empirical measure of the audio quality.
• Sound level: To make sure these transmitters didn’t reduce the sound output level, we measured the output of the Audioengine B1 sending a 250 mV, 1 kHz signal into each transmitter, with the transmitters’ volume controls (where available) set to maximum.

The 1Mii ML300 is the best portable Bluetooth transmitter because it matches the audio features of every other device we tested and actually does everything it claims to do, which wasn’t always the case with other transmitters we tested. It pairs with two sets of headphones at once, and its flat design, light weight, and decent battery life make it easy to use on the go.

The ML300 supports aptX Low Latency for improved audio and video sync. In our tests, when using the standard SBC Bluetooth codec, we found that the lag was 139 milliseconds (the average for all the devices we tested was about 132 ms, and you’re not likely to notice that 7 ms difference). This isn’t a problem if you’re only listening to audio, but the lag is noticeable if you’re watching video.

On the other hand, when we used the aptX Low Latency codec, the latency measured a much more acceptable 29 ms, just under the 31.4 ms average. At that rate, there won’t be a noticeable lip-sync lag. But remember, your headphones must also support aptX Low Latency to get that low number.

In terms of both frequency response and gain, the ML300 matched the rest of the contenders, as well.

The ML300 delivered consistent performance, which was not a given in our testing. You may read the ML300’s results as “it does what it says.” That’s correct, but it’s also more than what similar models can offer. For example, the TaoTronics TT-BA08 is also supposed to pair to two devices, but we simply couldn’t get that to happen, no matter how many times we followed the instructions in the manual to the letter.

This category is a race to the bottom in terms of both price and features, and while the ML300 didn’t absolutely “wow” us, at least it delivered on what it says it will.

This isn’t the smallest portable Bluetooth transmitter we tested, but it is slim enough to fit in most pockets. The ML300 is a 2.1-inch-by-1.5-inch rectangle with rounded edges, and it measures only about half an inch thick. And since it weighs only 0.63 ounces, it won’t weigh you down.

In addition to the 3.5 mm auxiliary port and the USB-C charging port, the ML300 has a switch to move between transmitter and receiver modes or to turn off the device, a multifunction button for pairing, and a button to switch to aptX HD. The transmitter comes with a 3.5 mm audio cable, a USB-A–to–USB-C charging cable, and a carrying case.

1Mii says the ML300 has a 12-hour battery life in transmitter mode (we didn’t independently test this figure). That’s long enough for many flights or a week of trips to the gym, but it falls short of the figures that some pricier models promise. If you need a longer-lasting battery for lengthy flights or any other reason, consider Aluratek’s ABC01F or Twelve South’s AirFly Pro.

Flaws but not dealbreakers

The ML300’s controls could be a bit more intuitive. This transmitter isn't as easy to control as our previous favorite, the now-discontinued Mpow BH259A. You’ll likely need to use the instruction manual to get everything set up, especially if you’re pairing to two devices.

There’s only one button that serves multiple functions, including power and pairing, so you have to use a Morse-code-like system of clicks and holds to connect your headphones, and the only real indicator of success is a flashing LED light that’s equally ambiguous. It’s not obvious when you have things in pairing mode, nor when you get that second set of headphones connected, unless you’re closely following the manual.

1Mii’s warranty is unclear. The company’s website states that “all quality-related defects on items sold directly by 1Mii or 1Mii’s authorized resellers are covered by an extensive warranty, starting from the date of purchase,” but it doesn’t specify what that “extensive” warranty period actually is, and our emails to the company went unanswered.

The ML300 is more affordable than similar models, and there’s not much that physically can break, but if you’re concerned about support, consider one of the models in The competition.

If you’re looking for a stationary transmitter to use with your TV or another home audio source, we recommend 1Mii’s B03. It has the same features as the ML300, including good audio quality, aptX Low Latency, support for up to two pairs of headphones, and a receiver mode. But it adds features that are tailored to TV use, including an optical digital-audio input and output so you can pass audio through to a soundbar, an AV receiver, or powered speakers.

The B03 had lower latency when using the aptX Low Latency codec than any transmitter we’ve tested. Our resident audio expert Brent Butterworth described it as a “screamingly low” 10 milliseconds. That may not guarantee perfectly lip-synced video, but it’s as close as you’re going to get with one of these devices. To get this low number, though, your Bluetooth headphones or speakers must support aptX Low Latency, too.

When using the SBC codec, we measured latency at 120 ms. That’s still laggy when you’re watching TV, and you may be bothered seeing people’s lips on screen being out of sync with the audio.

If your wireless headphones lack aptX Low Latency support and you notice AV sync issues, you can try connecting the Bluetooth transmitter directly to your AV source device (if it has a 3.5 mm or optical audio output), which may cut down on some lag created when the signal has to pass through the TV’s audio processor. Or, consider dedicated wireless TV headphones designed specifically for this purpose.

The B03 supports audio pass-through. In addition to its 3.5 mm audio input, the B03 has two optical digital-audio ports: one input for connecting to your TV and one output for connecting to a soundbar or other audio-playback device. This setup allows for audio bypass, meaning you don’t have to unplug the B03 when you want to listen to sound from your external speaker or soundbar; rather, you just toggle a switch.

Other competitors offer a similar setup, but what makes this one different is that you can transmit to Bluetooth at the same time the audio plays out loud, instead of having to choose one over the other. You might want to do this if you’d like to keep up with the audio of a game while you move from room to room, for example, or if someone in your family needs a higher volume level through headphones to hear the dialogue in a TV show.

The overall performance was solid. The B03’s frequency response and gain were on a par with the results from the rest of the units we tested. The B03 is also one of the few models we found that support the aptX HD codec, which offers higher-fidelity audio if you have compatible headphones.

The B03 is physically larger than our portable pick, but it’s not meant to travel along with you, so that’s okay. It has a footprint of just 4.5 by 3 inches, and it’s only about 1.5 inches tall at its highest, so you should be able to hide it in almost any home theater setup or living room.

The lack of a battery means the included Micro-USB cable needs to be plugged in at all times, but the USB port on any modern TV should provide enough power. This transmitter also comes with an optical audio cable, a 3.5 mm audio cable, and an RCA adapter.

The B03 doesn’t have built-in Dolby or DTS decoding, so you should change your TV’s sound output to the PCM setting when using it. If you don’t, you won’t be able to stream from services that offer Dolby Digital output, such as Netflix. The PCM setting downmixes the stream to stereo; in our tests, we didn’t notice any quality differences.

Flaws but not dealbreakers

Much like the ML300, the B03 lacks any defined warranty, so you’re taking your chances with service if something goes wrong.

Here are our thoughts on the other Bluetooth transmitters we tested.

Portable models

Aluratek’s ABT05F doesn’t support a receiver mode. The BC01F is more expensive than most of the models we tested in this category, with the only benefit being its 15-hour battery life.

Monoprice’s Premium Bluetooth 5 Transmitter and Receiver (38071) is more expensive than our pick, and while it has a longer battery life, it doesn’t have any additional features, and it often goes out of stock. It’s also quite bulky for a portable transmitter.

TaoTronics’s TT-BA08 doesn’t support aptX HD, and we simply couldn’t get it to connect to two devices at once, no matter how many times we tried.

Twelve South’s AirFly Pro is the best-looking portable transmitter we tested, but it’s also the most expensive. Its controls are frustratingly unintuitive; you get only a single button to control everything, so you need to follow the right combination of clicking and holding to set everything up, and you have to decode the color and pattern of the status light to know whether you’ve connected things properly. The AirFly Pro is also the only model we tested with a permanently attached audio cable—if it breaks, you’ll need to replace the whole unit. We do appreciate that it uses USB-C for charging rather than Micro-USB like the rest, and the claimed 25-hour battery life is the best we found.

Home models

1Mii’s B03Pro+ looks and functions like our top pick, but it adds a digital-to-analog converter (DAC) while eliminating the ability to hear from both a soundbar and headphones at the same time. The DAC will affect only the device’s performance as a Bluetooth receiver, so it was not a meaningful addition for our purposes, and we think the B03’s features are more useful.

Avantree’s Oasis Plus is our former favorite TV transmitter. We particularly like its easy controls, supplemented by spoken confirmations. But it has a higher latency than the B03, plus it costs more.

The Avantree Orbit is only a transmitter with no receiver mode, but we decided to test it because of its unique LCD display. While we found the screen useful and the frequency response mostly flat, the latency was problematic. We measured 70 milliseconds in aptX Low Latency and 170 ms in SBC, far greater than the 10 ms and 120 ms the 1Mii B03 delivers in the same tests. The Orbit is also much more expensive than the B03.

MEE Audio’s Connect Hub is expensive, yet it doesn’t offer any obvious benefits over the rest of the field.

TaoTronics’s TT-BA014 worked well in our tests, but it can’t transmit audio through a TV or soundbar and over Bluetooth at the same time (there is a bypass toggle).

This article was edited by Adrienne Maxwell and Grant Clauser.