Connect Multiple Headphones Wirelessly – FM, Bluetooth, UHF

Why connect multiple headphones wirelessly

There are several reasons you may want to connect multiple headphones wirelessly (or speakers): Headphones party, watching TV with another person in the middle of the night (while neighbors sleep), a tour guide that want to talk with a group over the wireless headset. After some research – there is no simple answer.

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Tested Solution: FM Radio waves

Using FM Radio waves transmitter and several FM Radio waves receivers to connect multiple headphones wirelessly is probably the cheapest solution and will have zero delay in sound transmission, but not as reliable as digital solutions.

Zero delay in Audio playback from the source (Analog transmission)
Relatively high number of devices that can receive the signal at the same time

Could be illegal in some Countries, since you’re using their FM Radio waves
Distance can be short if using portable solutions
Signal is not reliable (Analog Transmission)
Not as comfortable as Bluetooth solutions, since you will connect wired headphones to the FM Radio receiver, unless you use wireless headphones that support FM Radio

If you are a tour guide with a group of people, probably this solution is for you.

The device that we used was “Niorfnio T300M” – portable 0.3 watt FM transmitter. This one has several audio signal input options: it can connect with USB to a PC as a sound card interface, analog 3.5 mm input (stereo AUX in or microphone), micro SD card. We tested several cheap receivers, but the stable signal range did not pass one meter. Overall, the signal went past 5 meters, but with heavy interference.

If you want something more stable, you should get more powerful transmitter (more than 0.3 watt). If you want something portable – that is another story. The more powerful the FM transmitter – the less portable it will be (no battery, bigger unit). Therefore, this is something you should consider. Try to purchase a transmitter and receivers for test in a store that you can return it if the results will not be satisfying for your needs. In addition, it is best to use FM radio receivers that support digital FM tuning rather than analog tuning wheel, since they are more precise and it will be easier for you to find empty FM wave.

Tested Solution: Bluetooth Wireless Transmission

Bluetooth Audio Codec Basics

There are several popular codecs: SBC, AAC, aptx, apt HD, aptx LL. With most of the codecs, the audio will have a delay of around 100 – 200 ms. This is relatively high when watching videos, since the audio will be delayed. The only codec that will have less noticeable delay is aptX LL.

SBC: the standard codec and the oldest. Latency around 200 ms (cheaper devices can go up to 500 ms).
AAC: used in Apple devices.
aptX codecs: Qualcomm proprietary

aptx: 16-bit / 44.1 (325 kbps) or 16-bit / 48 kHz (384 kbps). Latency 120 – 200 ms.
aptx HD: 24-bit / 48 kHz (576 kbps). Latency around 200 ms, which is higher than regular aptX because of better quality (hence higher bandwidth).
aptx LL (Low Latency): 16-bit / 44.1 – 48 kHz (352 kbps). Lowest latency codec available – around 40 ms.

Useful information:
Understanding Bluetooth codecs with SoundGuys
Qualcomm aptx codec information
SBC codec on Wikipedia
SBC vs aptX on RTINGS
Everything about aptX codecs on Wikipedia

Bluetooth Audio Transmitters

Check the ratings when you get the Bluetooth Transmitter. Would not recommend going lower than $30 for transmitter. Most of them support Bluetooth transmission and receiving. The cheap versions support 10-meter range. If you want more range, it will cost you more (around $70 – you can try some 1Mii and Avantree models), but basic features will probably be the same (maybe more different sound inputs). Also, consider if you want portable transmitter with a battery or not.

Most of the latest Bluetooth transmitters (Bluetooth 5.0 and later and some of the older Bluetooth 4 devices) will have an option to connect two headphones simultaneously (Dual Bluetooth). If you want two people to watch a TV in two headphones – one transmitter should be enough. Just make sure that both headphones support aptx LL and the transmitter can connect two headphones and can send aptx LL to both at the same time (critical). The best option would be to use two identical pairs of headphones.

There are two types of Bluetooth Wireless headphones / speakers: regular and TWS (True Wireless).

Regular Bluetooth Headphones / Earphones

In regular Bluetooth headphones, both left and right headphone / earphone connect with a cable to each other and act as single Bluetooth device. In most cases, the microphone will be on the cable, since it is closer to the mouth and the control buttons will be on the microphone.

More stable connection than FM Radio
Higher stable wireless range (no interference noise) for more portable size
Higher quality than the FM Radio

Any Bluetooth audio transmission will have a delay, unless you will use aptX LL devices (which will have the lowest 40 ms)
Will cost more for aptX LL devices
Less comfortable than the Bluetooth TWS earphones, since there is a cable connecting the left and right earphone
Only two headphones will connect to one Bluetooth transmitter (if you want to connect more you will need to split the analog audio signal and use several transmitters)

TWS – True Wireless Earphones

TWS (True Wireless) – each earphone (left and right) will not connect to each other with a cable. While connecting TWS earphones to a phone, in most cases, it is enough to connect only one side and the second will pair automatically. In most earphones, you can connect the left or the right separately, while the second earphone is off. This option gives you the best portability and comfort without using any cables at all.

There is a problem with TWS technology – you cannot connect two pairs of TWS earphones to a Bluetooth transmitter that supports Dual Bluetooth. This is TWS technology limitation and not always stated by Bluetooth transmitter manufacturer. You should be familiar with this fact when building your setup. Therefore, if you want two people to watch a TV with having two pairs of TWS earphones, you will need two separate Bluetooth transmitters. It is best to use the same pair of earphones and two same Bluetooth transmitters to achieve the same latency.

Another problem, since you will have two Bluetooth transmitters and you have different models of earphones – you will have different delay. For example: first set a TWS earphones that supports aptX LL codec have latency of 40 ms, while the second set of TWS earphones that support aptX LL have delay of 50 ms resulting in different audio delay signal between the two people. While, 10 ms difference is not really noticeable, it can be problematic if one person have earphones with aptX (140 ms) and another one have earphones with aptX LL (40 ms). Again, the best way to avoid difference in audio signal is to buy identical Bluetooth transmitters and identical TWS earphones.

Same Pros and Cons as regular Bluetooth headphones Plus:
Pros: They are more comfortable than the regular Bluetooth headphones, since there are no cables
Cons: you will need one more Bluetooth transmitter if you want to connect two TWS headphones, since TWS do not support Dual Bluetooth.

As a side note about TWS – most latest portable Bluetooth speakers will support it. Meaning, you can connect two identical portable speakers in TWS mode – one will act as Left and the second as Right. Before buying two identical portable Bluetooth speakers – check that they support TWS.

Additional thoughts on Bluetooth Audio Transmission

1. All the Bluetooth codecs that are available today has a standard in specification, but depend on manufacturer implementation. Meaning, that each model of Headphones / Earphones of any manufacturer will have different audio latency. There are folks that tested several devices and provided a table with Bluetooth audio latency findings at RTINGS. Therefore, if you want to connect several headphones / earphones to one audio source you will better have the same ones.

2. If you want to use your specific wired headphones wirelessly, you can purchase two devices of the same model that transmits and receives the Bluetooth signal. Set one to TX (transmit) and one to RX (receive) and connect your wired Headphones to the receiver.

Our test system to connect multiple headphones wirelessly

We wanted to connect two pairs of Bluetooth TWS earphones and two Bluetooth speakers (not in TWS mode). The speakers control light changing on two LEDs controllers. Meaning we needed to connect 4 devices to one audio source.

Headphones Amplifier: Moukey MHAMP1.
You can get any 4-channel Headphones amplifier. Off course if you want to connect more than 4 headphones, you will need more outputs on the headphone amplifier. This specific device has one analog audio input and 4 audio outputs. Input and each output can be controlled with dedicated volume control. This is useful when you want to change volume for each device separately or for all at once if you change the input. All the inputs / outputs have 1/4″ TRS connector. If you want to connect regular 3.5 mm connector, you will need 1/4″ to 3.5 mm adapter for each input / output.
The audio output from PC connects to input of headphones amplifier. Three outputs from the amplifier connect to three Bluetooth Transmitters.

Bluetooth transmitters: MPOW BH259A, BlitzWolf BW-BL3.
All support SBC, AAC, aptX, aptX HD, aptX LL, are portable, and have a battery. BlitzWolf have indication of exact codec is currently used unlike MPOW that shows only one of two options: if it is SBC / AAX or aptX / HD / LL.
Each cable connects to the AUX analog audio input of the Bluetooth transmitter. Each transmitter is set to TX (transmission mode). Two MPOWs pair with two pairs of TWS Bluetooth earphones (each transmitter pairs with one pair of TWS earphones, since we cannot use Dual Bluetooth connection for TWS earphones). BlitzWolf transmitter pairs with two identical Bluetooth speakers (since this is regular Bluetooth speakers not connected through TWS – we can use Dual Bluetooth connection of one transmitter).

We are not specifying the Earphones / Speakers models, since it is out of the scope of this article. While playing the source, there was slight delay between the earphones and the speakers, but this was expected. Since the speakers were at low volume, just to control the LEDs, this delay was not noticed. Off course if you want minimum delay and difference between all the devices, you will have to use speakers and earphones that support aptX LL codec.

Solutions that were not tested to connect multiple headphones wirelessly

1. There are wireless Headphones that support other technologies rather than Bluetooth. Potentially they will have less audio latency. You can check the Non-Bluetooth Wireless devices table with latency scores on RTINGS. Though this is not directly related to connect multiple headphones wirelessly – some of the solutions may be combined with other available products.

2. You can use UHF Radio wave devices. FM Radio operates in VHF (Very High Frequency) range: 30 – 300 MHz. UHF (Ultra High Frequency) operates at much higher range: 300 – 3000 MHz. UHF range also includes Bluetooth, ZigBee, GPS, WLAN 2.4 GHz. This frequency should be more stable for operating Radio devices for higher range. “Retekess” has relatively cheap UHF Transmitters and Receivers that you can test. They also got ready Retekess bundles for tour guides.

3. Try Avantree TR2403. You can read about Avantree TR2403 1 Transmitter to 100 receivers on their site. The basic set contains 1 Transmitter and 3 Receivers with relatively low audio latency of 9 ms with 30-meter range (without potential quality loss).

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