Multichannel solutions are increasingly used to cope with the problem of low capacity in sensor networks resulting from high contention during wake-up periods of nodes. We can consider wake-up schedules as virtual channels, because nodes using different schedules cannot communicate with each other. In this paper, we show that multiple virtual channel solutions come at the cost of an increased energy consumption in broadcasts. We analyze the problem of broadcasting over multiple virtual channels under different classes of MAC methods and propose Clustered Virtual Channels (CVC), a new network structure that limits the number of frames needed for maintaining multiple virtual channels synchronized. Our simulation results show that CVC reduces the cost of maintaining synchronization and increases capacity while making all types of broadcasts possible.