Rectangular connectors to the rescue!

A simple change of shape and size could be the key to increased reliability

BY JODY WILLIQUETTE
Harting, Elgin, IL
http://www.harting.com

Lack of reliability in certain types of circular connector designs threatens live sound and broadcast productions in a wide range of venues. That’s the consensus of both users and designers of cable assemblies and connectors, including product engineers, manufacturers, technicians, and professional sound engineers.

The reliability issue is particularly acute for concert tours and festivals, sporting events, performing arts centers, sound stages, and movie sets (see Fig. 1 ). Since most of these venues require a unique setup for each event, and many rely on rental equipment and services, the equipment installation, startup and troubleshooting can be fraught with problems..

Fig. 1. Cable connectors play a big role in the reliability of stage setups.

Hardware problems

A good place to start thinking about connector selection is on the audio trunk cables. Since an installation team often assembles each run from standard lengths of such cable, several connectors must be mated. The prevailing use of large multi-pin circular connectors for these assemblies has always been problematic. For instance, just the simple task of connecting multiple trunk line segments can take quite a bit of time in threading connector shells together and time is usually a premium.

Although circular connector designs vary, those that are most widely used rely on the threaded shell, particularly for audio applications. These legacy connectors typically have a key and slot design, but the mating is not foolproof. Often, the twisting motion on the connector’s shell places torque on the pins before the pin housing key engages its mating slot. The results are bent or broken pins and connection failures. The more pins, the more likely it is to happen, since a large pin count typically requires small-diameter pins to keep the connector size manageable.

Another irritation and time consumer is dealing with threaded shells that are easily bent. Similarly, threaded shells are vulnerable to connection difficulties due to cross threading, as well as dirt or corrosion in the threads. So with screw-type circular connectors you’re not always sure that contacts are completely engaged, and troubleshooting connection failures can be difficult.

Because of their size, small pins also make connector repair in the field difficult. Pin replacement can be very troublesome, even for crimp style connections. Disassembly of a connector housing, removal of a small diameter pin, and replacement on a small-gauge wire all require a good deal of dexterity. This is one reason why designers of newer connectors have moved toward larger pin sizes. Another reason is more contact surface area resulting in a higher-quality connection with better conductivity).

Rectangular connectors

Sensible use of rectangular connectors with appropriate design features can eliminate or reduce many of these difficulties. However, the thought of changing to a new connector design is not something a rental company or user would take lightly when they have standardized on one of the circular styles. Nevertheless, adopting one of the newer rectangular designs on trunk cables is a relatively easy way to make the transition and gain substantial benefits. In addition to larger pin sizes, straight-line connection forces eliminate the twisting problem associated with circular connectors.

Fig. 2. Example of a rectangular connector that is a functional replacement for a typical 48-pin circular connector used in mixer board applications.

Rectangular connectors like the one in Fig. 2 also have guide pins and connector keying that reduce the chance of misalignment and pin damage when hand mating trunk line cable segments. However, there are no threads to get bent if the cable end is dropped. Many have locking levers that assure fast positive mating of the two connector halves without a cross-threading problem.

In addition to a more reliable initial connection, the locking lever also provides higher vibration resistance than with threaded shell circular connectors. If a lever is ever damaged, it is easily replaced on the spot since it is external to the connector housing. Many of these connectors are suitable for outside use in wet and dusty conditions, meeting the requirements of a Type 4 environmental rating per UL50.

Typically, locking lever designs allow higher pin densities to conserve space. This also means that minimal hand space is needed to connect and disconnect. Another benefit is that installation and tear-down times are reduced just plug and latch to complete a connection. Some manufacturers offer an optional connector coding feature that helps prevent mismatched cable segments; only like-coded segments should be connected.

Assembly considerations

Companies that are putting together multicore cable assemblies, find that circular connector designs can be relatively expensive compared to many rectangular connectors now available. Moreover, modular rectangular connectors are easier to assemble, saving time and labor cost. This becomes increasingly important as audio, video, power, and control cables are assembled into composite trunk cable assemblies. Modularity makes field servicing much easier too. This alone may be a strong motivator to make the switch from circular connectors.

Mixed-signal applications

Rectangular connector designs lend themselves to customized mixed-signal applications. In addition to conventional wires, rectangular housings can be designed to accommodate fiber-optic strands, Ethernet, coax, RCA audio connector lines, pneumatic lines, electric power, and many other specialized connections. This flexibility makes it easier to create trunk cables that not only carry audio and video signals, but also power and control signals for rigging, lighting, and many other functions.

Fig. 3. Modular connectors can be used for mixed-signal and power cable assemblies. Male and female pins can be intermixed on each side.

The flexibility to create hybrid cable assemblies greatly simplifies the cable assembly process. With the modular connector shown in Fig. 3 , cable subassemblies for different types of signals, power, and control can be ganged together to form a trunk cable without worrying about what goes on the ends.

At the stage end of a trunk cable using this type of connector, the usual whips can be used. Different signals and power leads are fanned out to their respective instruments, control devices, etc. For maximum backward compatibility, adapter cables can be easily assembled to go from existing whip and fanout cable assemblies to the trunk cables using rectangular connectors.

Individual pins are available either silver or gold plated for 26 to 14-AWG wire sizes with ratings up to 10 A and 250 V. The modular design automatically provides an electrical safety ground without loss of contact simply by installing the module or inserting it into its housing and attaching a ground wire. Pins for fiber-optic strands are also available, and they are just as easy to insert and remove as wire pins, as are coax and other inserts.

A host of benefits

Rectangular connectors are plentiful and available in a wide range of configurations with short lead times. They offer high quality, signal integrity, reliability, and ease of installation, troubleshooting, and repair.

Moreover, they are relatively inexpensive, making them an extremely attractive value in a wide range of venues, such as live concerts, theater, sporting events, sound stages, movie sets, and permanent installations. Trunk cables are an easy way to prove out the modular concept in rectangular connector usage. ■