A polarised two-pin unshielded connector, designed for connecting a loudspeaker to a power amplifier (or other device; many of the earlier shoebox style tape recorders used them), is known as the DIN 41529 loudspeaker connector. It exists as a panel-mounting female version, and line-mounted male and female versions. The male version has a central flat pin, and circular pin mounted off-centre. The circular pin is connected to the positive line (red) while the spade is connected to the negative line (black).[4] The panel-mounting female version is available with or without an auxiliary contact that disconnects the internal speaker of the device if an external speaker connector is inserted. Most common is a three-hole female connector with one circular hole on either side of the spade hole, one of them with an aux contact and one without, which provides the option to leave the internal speaker connected by inserting the plug twisted by 180°.
It is now mainly found on older equipment, such as 16 mm movie projectors. The Becker radio found in many Mercedes-Benz automobiles uses this connector. The same connector is used on some halogen lamps to connect the bulb to the power supply. While all other versions of the DIN plug are generally very reliable, the two-pin DIN plug is considered inferior in some ways - the lack of the outer sheath means far less force is required to disconnect the plug accidentally, makes it more prone to bending or shifting of the pins during use, and also not as solidly seated in its socket - worn two-pin speaker plugs on audio equipment are notorious for being very unreliable, often requiring only the slightest nudge to break contact. There are also a three- and four-pin version of this loudspeaker connector used for example by Bang & Olufsen.
Application：A four-channel cord wired in this way is sometimes simply called a DIN cord, a DIN lead or a DIN cable. For mono interconnections, the 3/180° plugs are sufficient. When a mono plug is inserted into a stereo socket, it mates with the left channel. This interface was rare in the U.S. market, and has progressively disappeared on new equipment, both in Germany and worldwide, since the 1980s, in favour of RCA connectors.