An exhaust duct assembly for conveying exhaust gases emanating from a combustion zone to atmosphere is disclosed. The assembly includes: an exhaust gas outlet for exhausting exhaust gas into the atmosphere; and an acoustic duct portion located upstream of the exhaust gas outlet, the acoustic duct portion having a peripheral wall defining a through-passage arranged and constructed to promote propagation of sound there-through. The acoustic duct portion has a length in a flow direction that is at least 50% of an average hydraulic diameter of the through-passage.

A honeycomb filter includes a pillar-shaped honeycomb structure having a porous partition wall disposed to surround a plurality of cells and a plugging portion, wherein a thickness of the partition wall is 152 to 305 m, a porosity of the partition wall is 35% to 70%, an average pore diameter of the partition wall is 7 m to 24 m, a porous body constituting the partition wall has a communication pore which opens to the surface of the partition wall and communicates with a pore inside the partition wall, and the communication pore has a narrow part where the diameter is partially narrowed, and in a virtual single pore obtained by virtually dividing the communication pore at the narrow part, an average of a ratio (X/Y) of a minimum width X (m) to a maximum width Y (m) passing through the center of gravity of the virtual single pore is 0.51 to 1.00.