Know Your Cables and Connectors
Thursday, January 1st, 2009
It’s the beginning of 2009, and best wishes for the New Year! A good new year’s resolution for musicians would be to become more technically knowledgeable in the upcoming year. I’m here to help with that goal, so let’s get started. Today we’re going to discuss cables and connectors used in electronic music and in pro audio.
A good place to start is the type of cable used in various applications. There are three major categories of cables used in the music business: balanced microphone cables, unbalanced shielded instrument cables, and speaker cables. One of the biggest problem areas I see in my work is when the wrong cable is used for an application. Now, this usually isn’t a problem with microphone cables, since their XLR connectors are a dead giveaway as to their purpose, and because the only products which utilize those connectors are microphones, direct boxes, mixers, etc. If the plug fits, you’re in business. It’s hard to make a mistake with microphone cables.
On the other hand, it can be very easy to make a mistake and confuse unbalanced shielded instrument cables with certain types of speaker cables. If you utilize the wrong cable for an application in this area, the quality of your audio will suffer and it may even cost you money for the repair of damaged equipment. So, here’s a quick tutorial on the finer points of speaker cables and instrument cables.
First, let’s talk about unbalanced shielded instrument cables. These are commonly referred to as “guitar cords”, because that is certainly one of their primary applications. In addition to connecting guitars to amps, they are also used to connect keyboards, synthesizers, electronic percussion, etc to their respective amplifiers. Shorter lengths are used to interconnect floor effects units (“stomp boxes”) and rack-mounted audio effects processors. They are characterized by their ¼” phone plugs on each end, and shielded cable is used as the audio highway. Shielded cable means that one conductor is concentric, or wrapped, around the other conductor. The problem is that many speaker cables also utilize 1/4” phone plugs on each end – the difference is that speaker cables use unshielded cable. Unfortunately, it may be hard to distinguish between the two, and therefore easy to use the incorrect cable for an application.
What happens if you should use a speaker cable to connect an instrument to an amplifier? In a word – hum, and lots of it. Cables which connect to the inputs of amplifiers (or interconnect devices which then in turn connect to the inputs of amplifiers, such as effects units) need to be shielded cables. Generally, no damage occurs should you inadvertently use a speaker cable in place of an instrument cable (unless you have the volume on the amp set so high that the hum is overpowering and damages your speakers before you can power down the system).
But what happens if you use a shielded instrument cable to connect a speaker to a power amplifier or powered mixer? This is especially bad, because there are no immediate telltale clues that you’ve done anything wrong. The speakers will work – but, unknown to you, there will be considerable signal loss in that instrument cable. Instrument cables use conductors that are quite thin, because they are designed to carry only a very small signal, and don’t really need to be very large. When used as speaker cables, you could easily be losing 10% to 30% of the output power of the amplifier in that instrument cable. Where does the power go? It is dissipated in the form of heat within the cable itself. Heating the cable actually increases the resistance of the cable, which in turn increases the signal loss – a vicious cycle. You will be setting your mixer and amplifier volume “by ear” to get the right sound level in the room, and so you will be turning up the level even louder, forcing more power through the cable. Now you have another vicious cycle on your hands. You may not even realize that you are running your equipment nearly wide open to achieve a decent volume in the room. Your PA system itself is running very warm, cranking out the watts that you are demanding that it deliver. Sooner or later, something has to give. The cable may melt down internally, causing a short circuit on the output of the amplifier. Or, the power amp or powered mixer itself may fail from its own overheating. Either way, your gig may be suddenly interrupted by the loss of audio, and you’re going to be out some big bucks for the repair.
If your PA system uses 1/4” – 1/4″ speaker cables, be absolutely certain that the cables you have for that application are indeed speaker cables, and make sure you do not intermingle them with instrument cables. I need to clarify one point on this issue. If you have powered speakers (speaker cabinets with a built-in power amplifier, meaning that the speaker cabinet must be connected to 120V AC in order to operate), then you should use instrument cables to run the output of your mixer to the powered speaker. This is a low-level signal, and the powered speaker requires shielded cable to its input. A better choice is an XLR-XLR microphone cable, if the powered speaker features an XLR input, and if your mixing board has a balanced XLR main output.
Today, many newer systems have eliminated the use of 1/4″ - 1/4″ speaker cables in favor of other types of connections. This is a definite improvement, as it eliminates the possibility of error in grabbing the wrong cable. Plus, 1/4” connectors were never designed for the amount of current needed by today’s high wattage systems. Here are some other types of connectors found on speaker cables today:
Speakon is a type (and brand) of multi-pin connector developed by Neutrik which is commonly found on speakers and amplifiers with high wattage ratings. Speakon connectors offer a very reliable connection, can handle extremely high power, are very durable, and are relatively low cost compared to other connectors.
A banana plug is an electrical connector designed to join audio wires such as speaker wires to the binding posts on the back of many power amplifiers or to special jacks called, of course, banana jacks. A common configuration of banana plugs is to have two of them molded together and spaced 3/4″ apart, which is also the spacing of the binding post receptacles on the back of power amps. Technically this assembly is referred to as a “double-banana” plug. An advantage of banana plugs is the relatively large metal surface area used for the connection, which virtually eliminates signal loss at the connection point. Disadvantages include the ease in which the plug can accidentally be reversed (turned over), causing speakers to be out-of-phase with each other. Also, the banana plug can be easily pulled out of the banana jack should you accidentally yank or trip on the cable on stage.
Bare wire is the most basic (and least recommended) way to connect audio. It consists of dual-conductor cable, stripped of insulation at the ends to expose the individual conductors. These can be inserted into binding posts or hooked around screw terminals that are then tightened down. Besides the general “messiness” of bare wire, you must always make sure to match the “hot” and “ground” conductors of the cable on the outputs of the amp and the inputs of the speaker to prevent phasing problems. We don’t recommend this type of connection other than in an emergency.
Some systems require a combination of these connectors, so a hybrid cable is needed. For example, your power amp may have banana jacks only, and your speakers have Speakon connectors – in this case, you’ll need speaker cables with banana plugs at one end and Speakon connectors on the other end. The good news is that with these type of cables, you’ll never inadvertently connect an instrument cable in place of a speaker cable – the connectors won’t fit.
Finally, what is the best type connector for speaker cables? I would enthusiastically recommend Speakon connectors at both ends, if compatible with your equipment. Speakon connectors have good contact area for minimal loss, are twist-lock by design so they can’t be accidentally disconnected, and are durable. Definitely a good choice for the new year!
Frank the Tech Guy