How do many transmitters share one broadcast across a large venue?

Why it matters

Large areas may need several transmitters. Makers describe their own receivers switching between them, while the Pilatus Arena test found different behaviour with phones and hearing aids^1,2.

What the evidence shows

• Specification work is under way. The Bluetooth SIG lists projects for extended Auracast coverage with several transmitters and for increased capacity³.
• Shared names are allowed, placement is not specified. The Public Broadcast Profile lets several transmitters carrying the same audio use the same broadcast name, so scanning devices can recognise them as alternatives; the profile sets no requirements for coverage, transmit power or latency⁴.
• What happened at an arena. In Pro Audito's independent test at a Swiss sports arena (three hearing-aid models and two headphones, with equipment owned by participants or lent free by makers), four transmitters shared one broadcast name. The system's own receivers switched automatically to the strongest transmitter, while phones and hearing aids listed four identical streams with no way to tell which was strongest (November 2025); developers told the testers this is expected to be fixed².
• Makers link transmitters in different ways. One links transmitters into arrays that share channels, so its own receivers switch by signal strength¹; another uses extender units that rebroadcast a master unit's audio with the same broadcast settings by default⁵; a third can feed one transmitter from another over the network at a nominal 5 ms latency⁶. None of these documents says how hearing aids or phones behave at the boundary.
• The coming standard is single-transmitter. IEC 60118-17 covers single-transmitter systems⁷.
• Delays add a constraint. Separate broadcasts with different delays for different areas have been proposed, but support above a 40 ms Presentation Delay is not required of receivers^8,9, and each Standard Quality stream uses about 11 to 22% of the airtime, so one transmitter can carry only a few streams¹⁰. The specifications do not say what a receiver should do with a Presentation Delay outside the range it supports¹¹; the SIG's receiver design guide advises using the nearest supported value rather than rejecting the stream¹².
• Range per transmitter is limited. One expert puts real range at about 30 m per transmitter¹³; in Pro Audito's independent test in a 75 x 57 m hall, with manufacturer-loaned equipment, no manufacturer funding, one transmitter placed for maximum distance and no significant interference from event equipment, 26 of the 51 transmitter-receiver pairs in the main reception comparison had dropouts or distortion from about 5 to 10 m and heavy dropouts from about mid-hall, while 16 received throughout the hall. The testers say this setup is not representative of other installations¹⁴.
• Codes add counters and captions. Where adopted, the 2024 International Building Code requires an assistive listening system at one or more ticket windows at each location in stadiums and arenas, and captioning of audible public announcements where there are 15,000 or more fixed seats¹⁵.

Where sources disagree

Little published disagreement; mostly an absence of published methods and tests. Makers' own receivers can switch between transmitters that share a name^2,1, but the cited field test does not demonstrate the same behaviour with phones and hearing aids.

What would settle it

The SIG's extended-coverage specification and deployment guide for public locations, and published tests of handover between transmitters in occupied venues with phones and hearing aids as well as dedicated receivers^3,16,2.

Planning while it is open

• Plan transmitter spacing from field results, since advertised ranges overstate real range: a Swiss expert advises keeping the farthest seat within about 20 to 30 m of a transmitter¹³, and in one hall test reception from a single transmitter depended strongly on the receiver¹⁴.
• Test walking between transmitter areas during commissioning, with phones and hearing aids as well as the maker's own receivers².
• Check what each installed product supports when extended-coverage specifications or updates arrive; the roadmap and the arena testers' report of a planned fix do not establish which existing products will be updated^3,2.

Sources

1. Infinium system controller and transmitter user manual (MAN 297B). Williams AV, 2026. Manufacturer (Williams AV) ↩︎ https://williamsav.com/wp-content/uploads/2025/08/MAN-297B-Infinium-Controller-Transmitter-BA-CT1.pdf
2. Technical analysis of the Bluetooth Auracast system in the Pilatus Arena. Pro Audito Schweiz. Pro Audito Schweiz (in German), 3 November 2025. Independent (Pro Audito Schweiz, Swiss hearing-loss association; test devices were lent free by their manufacturers or owned by participants) ↩︎ https://pro-audito.ch/news/technische-analyse-des-bluetooth-auracast-systems-in-der-pilatus-arena/
3. Features in development. Bluetooth SIG, undated (read 9 October 2026). Standards body (Bluetooth SIG, an industry association funded by its member companies, which owns the Auracast trademark) ↩︎ https://www.bluetooth.com/specifications/specifications-in-development/
4. Public Broadcast Profile, version 1.0.2. Bluetooth SIG Audio, Telephony, and Automotive Working Group. Bluetooth SIG, 3 November 2025. Standards body (Bluetooth SIG, an industry association funded by its member companies, which owns the Auracast trademark) ↩︎ https://www.bluetooth.com/wp-content/uploads/Files/Specification/HTML/pbp_v1-0-2_1761252922/PBP_v1.0.2/out/en/index-en.html
5. Bettear CASTER user manual (firmware 1.0.8). Bettear. Bettear; copy hosted by the distributor Univox, 2026. Manufacturer (Bettear) ↩︎ https://univox.eu/wp-content/uploads/sites/2/2026/01/B-CASTER-User-Manual-1.0.8.pdf
6. Auri TX2N / TX2N-D transmitter datasheet. Listen Technologies and Ampetronic (Auri). Ampetronic, July 2025. Manufacturer (Listen Technologies and Ampetronic) ↩︎ https://www.ampetronic.com/wp-content/uploads/UP3B603-2_Auri_TX2N_Transmitter_Datasheet.pdf
7. IEC 60118-17 (in preparation): assistive listening system for hearing aid users based on 2.4 GHz audio streaming. IEC TC 29 WG 13. International Electrotechnical Commission, undated (read 13 October 2026). Standards body (International Electrotechnical Commission) ↩︎ https://tc29.iec.ch/tc-activity/standards-under-preparation/
8. Requirements for mass adoption of assistive listening technology by the general public. Kaufmann TB, Foroogozar M, Liss J, Berisha V. ICASSP 2023 Workshops, IEEE (arXiv 2303.02523), 3 May 2023. Independent (Arizona State University) ↩︎ https://arxiv.org/abs/2303.02523
9. Basic Audio Profile, version 1.0.3. Bluetooth SIG Generic Audio Working Group. Bluetooth SIG, 23 June 2026. Standards body (Bluetooth SIG, an industry association funded by its member companies, which owns the Auracast trademark) ↩︎ https://www.bluetooth.com/wp-content/uploads/Files/Specification/HTML/bap_v1-0-3_1782503972/BAP_v1.0.3/out/en/index-en.html
10. How to build an Auracast transmitter: technical overview, version 3. Bluetooth SIG Market Development. Bluetooth SIG, 16 September 2026. Standards body (Bluetooth SIG, an industry association funded by its member companies, which owns the Auracast trademark) ↩︎ https://www.bluetooth.com/wp-content/uploads/2024/05/2403_How_To_Auracast_Transmitter.pdf
11. Introducing Bluetooth LE Audio, 2nd edition (including Auracast). Nick Hunn. Nick Hunn; free digital edition distributed by the Bluetooth SIG, November 2024. Independent (the author's own book; free edition distributed by the Bluetooth SIG; the 2024 Broadcast Audio URI specification lists the author under GN Hearing, a hearing-aid maker) ↩︎ https://www.bluetooth.com/wp-content/uploads/2025/01/Introduction-to-LE-Audio-2.0.pdf
12. How to design Auracast earbuds. Bluetooth SIG Market Development. Bluetooth SIG (technical overview, version 1.1), 6 February 2025. Standards body (Bluetooth SIG, an industry association funded by its member companies, which owns the Auracast trademark) ↩︎ https://www.bluetooth.com/wp-content/uploads/2024/05/2403_Auracast_Earbuds.pdf
13. Bluetooth Auracast in theaters and event venues. Graf B (Pro Audito Schweiz). Proscenium no. 3, pp. 10-11, Swiss Association of Technical Stage and Event Industry; English reprint by the Center for Hearing Access, September 2026. Nonprofit advocacy (Pro Audito Schweiz, Swiss hearing-loss association) ↩︎ https://centerforhearingaccess.org/wp-content/uploads/Proscenium-Technical-article-Bluetooth-Auracast-in-theaters-and-event-venues-1.pdf
14. Auracast transmitter-receiver compatibility test (with data workbook). Pro Audito Schweiz, 6 October 2025. Independent (Pro Audito Schweiz, Swiss hearing-loss association; no manufacturer funding, test products lent free by manufacturers) ↩︎ https://pro-audito.ch/news/auracast-transmitter-receiver-compatibility-test/
15. 2024 International Building Code, Chapter 11 Accessibility: 1109.2.7 Assistive listening systems and 1112.4 Other signs. International Code Council. International Code Council (ICC Digital Codes), August 2023. Standards body (International Code Council) ↩︎ https://codes.iccsafe.org/content/IBC2024P1/chapter-11-accessibility
16. Auracast for public locations. Bluetooth SIG, undated (read 13 October 2026). Trade body (Bluetooth SIG marketing material; the SIG is an industry association funded by its member companies and owns the Auracast trademark) ↩︎ https://www.bluetooth.com/auracast/public-locations/

Change log

• 10 October 2026Published with 16 sources.
• 13 October 2026Qualified coverage and firmware expectations, clarified the delay requirement and cited evidence gaps.
• 13 October 2026Independent audit clarified the reception-test denominator and interference conditions.

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