Abstract: The invention relates to an engine manifold having a plurality of branches connecting respective engine ports to ambient air. Each branch of the manifold is connected to pass through an acoustic coupling (10) formed by a chamber (12) of shallow depth having conjugate foci and defined by two closely spaced end plates and acoustically reflective side walls. The branch section (14) of the manifold leading to an engine port (20) is connected to the coupling (10) at one of its conjugate foci. The branch section (18) leading to ambient air being connected to the coupling (12) at a point remote from its conjugate foci, and an acoustic reflector (16) is connected to one of the conjugate foci of the acoustic coupling (10) to reflect sound waves propagating along the branch section (14) leading to the engine port back towards the same engine port (20).