Mackie HD1521 Owner's Manual - Page 11

Appendix B: Connections "XLR" Connectors The HD1521 has one female XLR input that accepts a balanced line-level signal. When connecting a balanced signal, be sure it's wired per AES (Audio Engineering Society) standards: XLR Hot (+) Pin 2 Cold (-)Pin 3 Shield (Ground) Pin 1 Balanced XLR Connectors There is also a male XLR connector on the HD1521 labeled loop out. This is also wired according to the AES standards listed above. The loop out connector allows you to connect several HD1521's. Simply plug the signal source (i.e., mixer output) into the input jack, and patch that speaker's loop out jack to the next speaker's input jack, and so on, daisy-chaining multiple speakers. See page 4 for a visual example of daisy-chaining. There is a limit to how many you can daisy-chain together. A general rule is to maintain a load impedance ten times or more than the source impedance to prevent excessive loading on the source. For example, if your mixer has an output impedance of 120 ohms, then you can daisy chain up to nine HD1521s. This is a load of 1222 ohms (HD1521 input impedance=11 kohms; 9 of these in parallel=1222 ohms). Since microphones typically have a higher output impedance, you should limit daisy-chaining from a mic source to two HD1521s. The loop out jack is wired straight from the main input connector - there is no electronic circuitry between - so the signal coming out of the loop out jack is exactly the same as the signal going in. Owner's Manual 11 Owner's Manual