There's a good chance that the unmanaged switch doesn't understand 802.1q trunking. That being said, if you on the managed switch have a port where vlan 1 is native (untagged) and tagging vlan 4, connect the unmanaged switch to said port, all traffic will ingress on the untagged vlan 1 on the managed switch, because the unmanaged switch has no concept of vlans. Now if the managed switch port is in Access mode on vlan 4, and the unmanaged switch is connected to this port, all traffic on the unmanaged switch will ingress on vlan 4 of the managed. I hope that made sense. The negative effects of an unmanaged switch is that you really have no chance to configure features on it, debug network issues etc. Chances are also that it doesn't support any safeguard measures, so you stand the risk of bringing the entire network down, or if someone with little networking knowledge connects a cable to two ports on the same unmanaged switch (introducing a network loop). Also QoS can not be done on a unmanaged switch, so traffic can not be priorotized on the unmanaged switch. Only on the managed switch.
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