Line-out symbol. PC Guide color lime green. Line outputs usually present a source impedance of 100 to 600 ohms. The voltage can reach 2 volts peak-to-peak with levels referenced to −10 dBV (300 mV) at . The frequency response of most modern equipment is advertised as at least 20 Hz to 20 kHz, which corresponds to the conventional range of human hearing. Line outputs are intended to drive a load impedance of 10,000 ohms; with only a few volts, this requires only minimal current. Connecting other devices Connecting a low-impedance load such as a loudspeaker (usually ) to a line out will essentially short circuit the output circuit. Such loads are around 1/1000 the impedance a line out is designed to drive, so the line out is usually not designed to source the current that would be drawn by a 4 to 8 ohm load at normal line out signal voltages. The result will be very weak sound from the speaker and possibly a damaged line out circuit. Headphone outputs and line outputs are sometimes confused. Different make and model headphones have widely varying impedances, from as little as to a few hundred ohms; the lowest of these will have results similar to a speaker, while the highest may work acceptably if the line out impedance is low enough and the headphones are sensitive enough. Conversely, a headphone output generally has a source impedance of only a few ohms (to provide a bridging connection with 32 ohm headphones) and will easily drive a line input. For similar reasons, "wye"-cables (or "Y-splitters") should not be used to combine two line out signals into a single line in. Each line output would be driving the other line output as well as the intended input, again resulting in a much heavier load than designed for. This will result in signal loss and possibly even damage. An active mixer, using for example op-amps, should be used instead. A large resistor in series with each output can be used to safely mix them together, but must be appropriately designed for the load impedance and cable length. Line in Line-in symbol. PC Guide color light blue. It is intended by designers that the line out of one device be connected to the line input of another. Line inputs are designed to accept voltage levels in the range provided by line outputs. Impedances, on the other hand,