This　work　establishes　a　novel　direct　time-domain　artificial　boundary　method　for　acoustic　wave　problems.　The　proposed　method,　called　scaled　boundary　perfectly　matched　layer　(SBPML),　is　more　generalized　and　flexible　than　the　conventional　perfectly　matched　layer　(PML).　This　work　originates　from　an　extension　of　recently　proposed　SBPMLs　for　wave　problems　in　solid　medium　and　fluid-saturated　poroelastic　media.　The　acoustic　SBPML　is　constructed　by　combining　the　scaled　boundary　coordinates　transformation　inspired　by　the　scaled　boundary　finite　element　method　(SBFEM)　with　the　complex　coordinate　stretching　technology　from　the　PML.　This　method　directly　constructs　the　complex　coordinate　stretching　function　in　the　scaled　boundary　coordinates,　eliminating　the　reliance　of　existing　PMLs　on　the　global　coordinate　system.　As　a　result,　this　method　can　accommodate　artificial　boundaries　with　general　geometries　and　consider　planar　physical　surfaces　and　interfaces　that　may　exist　in　infinite　acoustic　domains.　Moreover,　it　also　can　be　described　as　a　second-order　mixed　unsplit-field　form　of　the　acoustic　pressure-velocity　field　in　time,　which　can　be　seamlessly　coupled　with　the　finite-element　equations　of　the　bounded　domains.　Numerical　examples　are　presented　to　demonstrate　the　accuracy　and　potential　of　the　proposed　method　in　dealing　with　the　interaction　problems　in　infinite　acoustic　domains.