Bernabe, the speaker connector is on the left side. Please follow Dell's instructions (found [http://support.dell.com/support/edocs/systems/studio1557/en/SM/palmrest.htm#wp1186039|here]) in order to reseat the connection (Connector 6).
PS: That manual assumes that you have the Dell Studio 1557 or the 1558. If you do not have that model (Check the bottom), please respond with the correct model number and I can look for it.