Speakon Explained:
Common late model amplifiers and speaker cabinets are equipped with “Speakon” connectors. Typically one of two types of “Speakon” panel jacks are used on these newer amplifiers and speaker cabinets:
1) NL2MP
2) NL4MP
NL2 connectors explained:
The NL2MP panel jack is much less common than the NL4 type of panel jacks. The NL2 and NL4 panel jacks can look very similar. The NL2MP is a male gender panel jack with only two contacts in the jack. Genuine Neutrik NL2MP jacks are identified with white lettering with the model number “NL2” as shown here:
Only Speakon NL2FC cord-ends will function with NL2MP panel jacks. If your equipment is equipped with NL2 panel jacks then your cord must be equipped with NL2 cord ends since NL4 cord ends will not insert into NL2 panel jacks. Genuine Neutrik NL2FC cord ends are identified by the white printing stating “NL2FC” on the grey release ring as shown here:
Speakon
The NL2FC is a female gender cord-end and just like the NL2MP jack, is equipped with only two contact points. The NL2FC cord-end will insert into a NL4MP panel jack, and will pass signal on the two 1+ and 1- contact points. The NL4FC end will not insert into a NL2MP panel jack.
NL4 connectors explained:
The NL4 type panel jacks look very similar to the NL2 type panel jack. Also, the NL4 type cord-ends look very similar to the NL2 type cord-end. It is easy to mistake one for the other. The genuine Neutrik NL4 panel jack is not as easy to positively identify as the NL2 panel jacks. There is a variety of common NL4 type panels jacks, which are:
1) NL4MP: small square mounting flange style with solder or spade connector termination points
2) NL4MP-ST: small square mounting flange style with set-screw termination points
3) NL4MPR: large round mounting flange style with solder or spade connection termination points
The common NL4 type panel jacks are shown here:
Audiopile Pro Audio - Speakon / Powercon
The following inscriptions are located on the surface of the genuine Neutrik NL4 panel jacks:
1) Neutrik: This is raised lettering located on the surface of the inner-most ring. Note: the NL2 panel jack is also labeled in this same exact manner.
2) Liechtenstein: This is embossed in the lower left corner of the panel jack. Note: the NL2 panel jack is also labeled in this same exact manner.
3) The NL4 panel jack has no other front surface lettering except the Neutrik logo in the upper right hand corner. If the Speakon panel jack is black in color, and IS NOT labeled with the white NL2 label, then it’s most likely an NL4 panel jack. If in-doubt, check your owner’s manual or contact the manufacture.
In my experience, most modern amplifiers and speaker cabinets which are equipped with Speakon jacks, are equipped with the NL4 type Speakon jacks. The NL4 type Speakon jacks are equipped with 4 (four) ea. contact points, as opposed to the NL2 type Speakon jacks which are only equipped with 2 contact points. The NL4 type Speakon connector is capable of passing 2 different speaker signals; where-as the NL2 type Speakon connector is only capable of passing 1 single speaker’s signal. Many of the NL4 panel jacks mounted on modern amplifiers and speaker cabinets only utilize 2 of the 4 contact points. I believe the NL4 jacks are used because the cost is similar to the NL2 jacks, and the NL4 jack will accept either the NL2 or NL4 cord-ends.
The contact points on the NL4 connectors are labeled on the connector in various locations depending on the model of the NL4 connector, and can be difficult to read because the labeling is fairly small, and could be partially obscured by set-screws, but the labeling is as follows:
1) 1+
2) 1-
3) 2+
4) 2-
If the amplifier or speaker cabinet is equipped with NL4 jacks, and if only 2 of the 4 contact points are being used, generally it’s Pins 1+ and 1-. HOWEVER: This is not how all are wired. There is no “standard” for wiring NL4 connectors, although some configurations are more common than others. If the panel jack in the amplifier is wired for bridge/mono output, it’s possible that Pins 1+ and 2+ are being used. Many amplifiers have one (or more) of the Speakon jacks wired with both channels of the amplifier wired to the jack, which is generally intended for bi-amping purposes. If this is the case, channel 1 of the amplifier might be wired to pins 1+ and 1- of the jack, and channel 2 of the amplifier might be wired to pins 2+ and 2- of the jack. In virtually all cases, NL2 Speakon connectors are all wired the same; however, NL4 Speakon connectors could be wired in any of one of 16 (sixteen) different configurations on either the amplifier or the speaker cabinet. Just guessing what the wiring scheme would result in a 1 (one) in 256 (two hundred fifty six) chance of the amplifier wiring matching the speaker wiring.
If your amplifier and speaker cabinet are equipped with NL2 type Speakon jacks, then you will need an NL2 type speaker cable to hook them up. Generally all NL2 Speakon jacks and NL2 Speakon cable are wired the same and fully compatible.
If either your amplifier or speaker cabinet are equipped with NL4 type Speakon jacks, it's naive to assume the wiring scheme. To construct a proper cable, the panel jacks must be positively identified as being NL4 type and the pin-out configuration of both the amplifier NL4 jacks and speaker NL4 jacks must be known.
All I could say is WOW. 
