LTE interference to wireless headphones

Dr. Harald B. Karcher, July 2013

LTE 800 user equipment can disturb wireless headphones if they are both radiating in neighboring frequency areas.
When you do LTE-Downloads, you can often hear sizzling sounds in the wireless headphone, and with LTE-uploads, it can even come to painful screaming and scratching sounds, if the LTE user device is operating very close by.

Can LTE user equipment such as LTE routers and LTE smartphones disturb the wireless audio connection between the 3D-HD-Philips-TV-Set 47PFL and the wireless headphone Sennheiser HDR 119 II on short distance? Yes, they Can! 
(Source: Dr. Harald Karcher)

This article summarizes the findings of a 70 page study on LTE interference to wireless headphones. It explores, in which situations the sound quality of wireless headphones is being disturbed and interfered by LTE user equipment. For this reason, the sound of HDTV programs was transmitted via a wireless headphone into the ear of the tester, sitting in the same room. The interference SOUNDS were recorded and documented. Interference between LTE 800 user equipment and the TV-VIDEO-Signal also possible, but this was not documented in our headphone study.

In this summary we only considered LTE user equipment with Vodafone-LTE-SIM-Cards, as Vodafone had the broadest range of LTE user equipment in the German market in May 2013. Vodafone downloads are being transmitted between 801 und 811 MHz and Vodafone uploads range from 842 to 852 MHz. For uploads, we expected stronger interference, because the upload band is closer to the “headphone band” than the download frequencies are. The original study also contains some more interference tests with LTE from Deutsche Telekom and Telefonica o2.

The wireless headphone system „Sennheiser RS 119 II“ transmits the sound in the frequency spectrum between 863,35 and 864,75 MHz. You should not transfer the following findings on other frequency areas without further tests and studies.

The uplink frequencies of the German LTE 800 providers Telefonica o2, Vodafone and Deutsche Telekom are closer to the „wireless headphone band“ than the downlink frequencies.
(Source: APWPT)

LTE interference to wireless headphones

Now let’s come to our findings: Almost all tested LTE user equipment does spoil and damage the wireless headphone sound with painful screaming and scratching, as long as it radiates very close by to the wireless headphones headsets. Most LTE user equipment stops interfering the headphones after a distance of 10 to 15 centimeter. Only very few LTE 800 user equipment devices can disturb the wireless headphone sound even in 70 centimeter distance, as for example the oldest LTE 800 router at all, the „Huawei B390s-2“ alias „Vodafone B1000“. In my tests, I reduced the loudness of the headphones, so you can hear the interference better and louder in the following audio recordings.

The interference sounds in the headphones were much more screaming and scratching in the LTE uploads than in the LTE downloads. The transmission of photos and videos from an LTE router or LTE smartphone up to Facebook or YouTube could be such a typical LTE upload in real life. It can last for minutes or even longer, depending on the size of your photos and videos, on the speed of your LTE user device, and on the current performance level of your providers LTE network.

Older LTE user equipment causing stronger interference

When it comes to interference, we can see differences between different LTE user equipment. So the LTE device manufacturers seem to have some scope for design to reduce the interference potential to wireless headphones.

* The first commercially available LTE smartphone in Germany was the „HTC Velocity 4G“. In our tests, it caused stronger interference to the wireless headphone than the younger 4G phones „Nokia Lumia 920“, „Samsung Galaxy S3 LTE“ or „Samsung Galaxy S4“. The Velocity successor „HTC One XL“ also caused less interference to the headphone than the firstborn „HTC Velocity 4G“.

* With LTE routers, we had a similar situation: The oldest device caused the strongest interference. The first commercially available LTE 800 router in Germany, the „Huawei B390s-2“ is known under different names like „o2 LTE Router“, „Telekom Speedport LTE“ and „Vodafone B1000“. As all German LTE providers sold this „Huawei B390s-2“ under their own brand names, it should have a considerable geographical distribution in Germany. We only tested the Vodafone version B1000, as all the different Huawei-B390-OEM models are technically very similar to each other.

Modified headphone with audio output cable

We connected the base station of the wireless headphone system „Sennheiser RS 119 II“ with the analog headphone output of the HD-TV-Set. In our tests it was very close to the TV screen. Sennheiser calls the headphone base station „TR 119 II transmitter with audio connecting cable“.

In our tests, the wireless mobile „Sennheiser HDR 119 II headphones“ were sitting on the testers head, so we had a real live situation in our interference experiments. The right speaker of the headset was modified with an audio output cable by Sennheiser just for our interference tests. So we were able to connect a mobile audio recorder and to record the regular TV sounds together with the LTE interference sounds as MP3 audio files in 192 Kbps quality. Now everybody can listen to our recordings and get an own interpretation of the recorded interference sounds.

LTE smartphone HTC Velocity 4G

The Android smartphone „HTC Velocity 4G“ was the first LTE smartphone in the commercial German cell phone market. Right from the start in spring 2012 it covered LTE 800/2600 MHz, HSPA/WCDMA 900/2100 MHz und Quad-band GSM/GPRS/EDGE 850/900/1800/1900 MHz.

The early HTC Velocity 4G may only have reached the most innovative early adopters in Germany. So it may not have a too broad distribution in the German field. (Source: Dr. Harald Karcher).

The tester makes sure, that the LTE smartphone is in the 4G LTE 800 operating mode, in order to get the most interesting interference results.

In zero centimeter distance from the right speaker of the headset, the 4G smartphone caused painful screaming and scratching sounds to the headphone in very unpleasant frequencies. The spoken word from the TV Program became almost incomprehensible.

In the first audio recording, we put the display side of the “HTC Velocity 4G” on the right speaker of the headset: You can hear brutal download sounds starting at second 7 and very screaming UPLOAD sounds starting at second 18:

In the second audio recording, we put the back side of the “HTC Velocity 4G” on the right speaker of the headset: You can hear brutal download sounds starting at second 6 and very screaming UPLOAD sounds starting at second 14:

When the tester outstretched his right hand to the maximum distance, the high-tech cell phone was about 70 centimeter away from the right speaker of the headset and the LTE throughputs only caused very light screaming and scratching sounds to the headphone. They got a little louder, when the aluminum covered back side of the cell phone looked towards the tester. They got weaker, when the display front side of the cell phone looked towards the headphone.



LTE smartphone Nokia Lumia 920

The innovative Windows Phone 8 cell phone „Nokia Lumia 920“ operates in the following frequency areas:

* GSM Quad-Band (850/900/1800/1900 MHz)
* UMTS Quad-Band (850/900/1900/2100 MHz)
* LTE Penta-Band (800/900/1800/2100/2600 MHz)

As we see, it can handle all three German bands: LTE 800/1800/2600 MHz.

The noble “Nokia Lumia 920” covers all three German 4G bands: LTE 800/1800/2600 MHz. (Source: Dr. Harald Karcher).

In the first audio recording, we put the display side of the “Nokia Lumia 920” on the right speaker of the headset: You can hear download sounds starting at second 3 and UPLOAD sounds starting at second 16:

In the second audio recording, we put the back side of the “Nokia Lumia 920” on the right speaker of the headset: You can hear download sounds starting at second 3 and UPLOAD sounds starting at second 16:

LTE router Vodafone B1000

By the end of 2010, the LTE 800 router “Huawei B390s-2” alias “Vodafone B1000” came into the early German LTE networks, when there still was very little 4G traffic in the air.

In those almost empty LTE 800 networks, we got LTE downloads up to 50 MBit/s and pings around 20 milliseconds with the “Huawei B390s-2”.

The oldest LTE 800 router „Huawei B390s-2“, alias „O2 LTE Router“, alias „Telekom Speedport LTE“, alias „Vodafone B1000 LTE W-LAN Router“ caused the most painful interference sounds to the wireless headphone system „Sennheiser RS 119 II”. (Source: Dr. Harald Karcher).

The “Huawei B390s-2” can only handle one LTE modus: LTE 800 MHz. No GPRS, no EDGE, no UMTS, no HSPA, no LTE 1800, no LTE 2600.

In our Vodafone 4G LTE 800 tests with 12 different LTE devices, the “Huawei B390s-2” caused the most unpleasant interference to the headphones. Even in 70 cm distance of the Sennheiser RS 119 II head set, this LTE router caused pulsating interference sounds in the LTE UPLOADS. Only the B390-successor „Huawei B593u-12“ alias „Vodafone B2000“ caused very similar interference sounds.

In the first audio recording, we put the front side of the “Vodafone B1000” on the right speaker of the headset: You can hear painful download sounds starting at second 4 and screaming scratching UPLOAD sounds starting at second 27:

In the second audio recording, we put the back side of the “Vodafone B1000” on the right speaker of the headset: You can hear painful download sounds starting at second 3 and pulsating scratching UPLOAD sounds starting at second 17: Please listen to the audio recording to get your own impression:

Twelve LTE devices in the original study

In the original study from May 2013 we tested twelve LTE user equipment devices:

Apple iPhone 5, AVM FRITZ!Box 6810 LTE, AVM FRITZ!Box 6840 LTE, AVM FRITZ!Box 6842 LTE, HTC One XL, HTC Velocity 4G, Nokia Lumia 920, Samsung Galaxy Note II LTE, Samsung Galaxy S3 LTE, Samsung Galaxy S4, Vodafone B1000, Vodafone B2000.

A PDF of the full study with 70 pages can be downloaded here: DrKarcherFinalReport21072013 [2.395 KB] (German)

Tester and sponsor of this LTE interference study

The tester and author, Dr. Harald B. Karcher, works as an independent mobile device expert in Munich, Germany. As soon as LTE started in the German mobile networks in 2010, he also started testing all compatible LTE user devices. His LTE tests were published in media like CHIP, Connect, Computerwoche, CNET, ZDNet, FOCUS Online and many more.

360°communications GmbH is a full service PR agency located in Munich, Germany. The company advises the Association of Professional Wireless Production Technologies (APWPT).

APWPT is an international non-profit organization, which is representing the needs of all users of the Programme Making & Special Event (“PMSE”) sector. Members of APWPT include PMSE organizations, users and manufacturers. The APWPT directly and indirectly represents far over 25,000 members of the PMSE community in Europe and beyond.

Additional remarks from the APWPT

Additional remarks from the APWPT

We want to thank Dr. Harald Karcher for his remarkable work which is an enrichment for the technical section of our homepage.

We also want to say that his LTE-to-headphone interference scenario gives a first glance onto a real live situation. Nevertheless, this contribution should be continued with more scenarios and additional studies.

In this respect we also want to point towards the actual work of the ECC/CEPT study group SE 24. They are just doing an international study on the “Impact of SRD applications used in the band 862-863 MHz on applications in the band below 862 MHz (LTE) and on the cordless audio applications operating in 863-865 MHz."

We report as soon as we have further information.

Do you want to bring in your own experience or do you have any questions? Please write to info@apwpt.org