An apparatus for spatial audio signal decoding associated with a plurality of speaker nodes placed within a three dimensional space, wherein the apparatus is configured to: determine a non-overlapping virtual surface arrangement, wherein the virtual surface arrangement comprises a plurality of virtual surfaces with corners positioned at least three speaker nodes of the plurality of speaker nodes and sides connecting pairs of corners configured to be non-intersecting with at least one defined virtual plane within the three dimensional space, wherein the non-overlapping virtual surface arrangement is determined by the apparatus being configured to divide the speaker nodes into parts, wherein at least one part comprises speaker nodes located to one side or on the defined virtual plane, and at least one further part comprises speaker nodes located to the other side or on the defined virtual plane; determine virtual surface edges for the at least one part and virtual surface edges for the at least one further part; and combine the virtual surface edges for the at least one part and the virtual surface edges for the at least one further part to generate the plurality of virtual surfaces and therefore determine the non-overlapping virtual surface arrangement; generate gains for the speaker nodes based on the determined the virtual surface arrangement; apply the gains to at least one audio signal, the at least one audio signal to be positioned within the three dimensional space, wherein the apparatus is characterized by being configured when dividing the speaker nodes into parts, to divide the speaker nodes into an additional part comprising speaker nodes located on or close to the defined virtual plane, wherein the apparatus, when determining the virtual surface edges for the at least one part is further configured to virtually connect speaker nodes for the at least one part comprising speaker nodes located on or close to the defined virtual plane. determine a non-overlapping virtual surface arrangement, wherein the virtual surface arrangement comprises a plurality of virtual surfaces with corners positioned at least three speaker nodes of the plurality of speaker nodes and sides connecting pairs of corners configured to be non-intersecting with at least one defined virtual plane within the three dimensional space, wherein the non-overlapping virtual surface arrangement is determined by the apparatus being configured to divide the speaker nodes into parts, wherein at least one part comprises speaker nodes located to one side or on the defined virtual plane, and at least one further part comprises speaker nodes located to the other side or on the defined virtual plane; determine virtual surface edges for the at least one part and virtual surface edges for the at least one further part; and combine the virtual surface edges for the at least one part and the virtual surface edges for the at least one further part to generate the plurality of virtual surfaces and therefore determine the non-overlapping virtual surface arrangement; generate gains for the speaker nodes based on the determined the virtual surface arrangement; apply the gains to at least one audio signal, the at least one audio signal to be positioned within the three dimensional space, wherein the apparatus is characterized by being configured when dividing the speaker nodes into parts, to divide the speaker nodes into an additional part comprising speaker nodes located on or close to the defined virtual plane, wherein the apparatus, when determining the virtual surface edges for the at least one part is further configured to virtually connect speaker nodes for the at least one part comprising speaker nodes located on or close to the defined virtual plane. <EOS>