Auracast transmitter placement and mounting height

What the Bluetooth SIG says

The SIG's transmitter guide gives three placement rules:

• Centralize: "as central as possible within the intended coverage area."
• Height: as high as possible above the occupied area, "ideally on a ceiling, lowest high beam, or high on a wall."
• Avoid obstructions: keep clear of beams, rafters and other electrical equipment, and avoid "enclosures such as cupboards, or behind metal partitions or counters."

It also notes that people in the room affect range, and that "placing the Auracast transmitter above head level will minimize this effect."

Why height matters so much

At 2.4 GHz, a human body in the path takes a large share of the signal. In one study, a single person shadowing the transmitter added about 10 dB of measured path loss, and simulations showed more loss the closer the receiver was to the body. A transmitter above the audience sends its signal down over people's heads instead of through them. Our deep dive on walls, crowds and 2.4 GHz has the numbers.

What two manufacturers advise

These are each maker's guidance for its own products, not a standard. They differ in the numbers (above 1.8 m for Auri, 2.5 to 4 m for Bettear) and agree on the principle: high, central, facing the listeners, clear of obstructions.

Overhead or on a wall

How a unit spreads its signal depends on its antennas, so follow the maker's mounting drawings. Auri, for example, shows a different orientation for ceiling and wall mounting, with the logo facing the coverage area.

• Overhead (on the ceiling, a beam, a pendant or a high bracket): the unit looks down over the seats. Good for a room with seats all around.
• On a wall: the unit faces into the room. Aim the front at the seats. Good for a long room served from one end or one side. The wall behind it also reduces what reaches the next room, though it rarely stops it.

Awkward rooms

• Very high ceilings (churches, halls, arenas). A unit 10 m up is nearly 9 m above a seated listener's ears before it covers any distance across the floor. A pendant, a beam or a high wall position aimed at the seats is often better than the ceiling itself; the SIG guide's "lowest high beam" points the same way.
• Tiers and balconies. Each level needs a clear view of a transmitter. Auri lists balconies and mezzanines among the layouts that affect signal propagation, and notes angled mounting may be needed for tiered seating. Expect the seats under a deep balcony to be cut off from a unit mounted above it.
• Behind solid walls. Side chapels, overflow rooms and lobbies behind brick or concrete may need their own transmitter. Bettear's rule of thumb is that a solid wall means a new zone.
• Near equipment. Not in the AV rack, not in a cupboard, not behind a metal grille, not next to a Wi-Fi access point.

More than one transmitter

• Give every transmitter carrying the same program the same broadcast name. The SIG's transmitter guide says transmitters in one venue carrying the same audio "should use the same Broadcast_Name", and the Public Broadcast Profile notes that a shared name lets a phone or app recognize them as the same program.
• Overlap neighboring coverage areas so there is no gap. Auri suggests about 20 % "on the coverage for the least sensitive receiving device"; Bettear suggests 10 to 20 %.
• Moving between transmitters may need a short re-join on some receivers. The Bluetooth SIG's standard method for coverage with several transmitters is still in development, so do not promise seamless movement.

Before you drill

Where the room is unusual, put a transmitter on a stand or a temporary bracket at the planned position and walk the farthest seats with a receiver. It takes minutes and settles arguments about whether the far corner will work. Then follow the full commissioning walk test once the units are fixed.