Live Sound Reinforcement

Name: Live Sound Reinforcement
Uploaded: 2017-08-16T14:07:07+00:00
Duration: PTM10S8
Channel: Ira Welch
Description: Live Sound Reinforcement

Live Sound Reinforcement
Live sound system wiring

We’re going to discuss the most commonly used cables and connector types used in the live sound reinforcement industry. As mentioned in a previous lesson live sound utilizes both coax and twisted pair type cables and we looked at how signals are transmitted over these cable types. Coax = unbalanced transmission Twisted pair = balanced transmission

Before we can actually hook up any equipment in our sound system we need the proper cables to interconnect it all together. The two most common connector types on the ends of our sound cables are the XLR and TRS connectors. ¼” Tip, ring and sleeve X series, latching rubber

Live sound reinforcement systems actually utilize many different cable and connector types however we will concentrate on the most commonly used. Some other cables that will be incorporated into the system are composite cables with RCA ends.

Which is the video lead and which color is the left channel and which color is the right channel? YELLOW = VIDEO WHITE = LEFT CHANNEL RED = RIGHT CHANNEL

Our sound system will also need speaker cables and connectors.

When it comes to wiring one of biggest problems that technicians face are grounding problems. Ineffective system grounding is the most commonly encountered stumbling block in eliminating system noise, notably “hum and buzz”. The ground terminal should never be removed This type of plug is considered a technical ground

Utilizing too many paths to ground will result in noise because it creates a ground loop within the building or space and acts like an antenna that will create more EMI (electro magnetic interference). This EMI will be super imposed back into the sound system. For this reason a dedicated electrical circuit is required for any permanently installed sound system.

If the sound system is a temporary set up such as night clubs or concerts or other similar events then all equipment should be plugged into the same electrical circuit. ALL OF THESE OUTLETS ARE PART OF THE SAME ELECTRICAL CIRCUIT

Even outlets on the same electrical circuit can cause ground loops so if at all possible the equipment should be plugged into a power strip. Amplifiers will amplify the noise making matters worse so it’s important to keep all amps on the same electrical outlet too.

Another way to eliminate noise in a sound system is to use only balanced wiring, which means shielded twisted pair cabling. It may also be necessary to lift the shield ground of the signal path, when this is done it should always be lifted at the beginning of the signal path.

Another way to combat noise problems is to use a direct injection (DI) box. The DI takes an unbalanced cable from a musical instrument and converts to a balanced connection.

Here is a typical set up using a DI box, the cable back to the mixer is a balanced cable.

Another type of cable that is commonly used in stage set ups is an audio snake cable. Audio snakes are used to limit the length in which microphone cables carry signals to the mixing board.

Audio snakes are long cables that run from your stage to your soundboard. They enable all of the instruments and vocals to be plugged into one signal cable and also control the amount of cables going to and from the soundboard. COMBINATION XLR AND TRS SNAKE CABLE, THE CABLE ENDS RUN BACK TO THE MIXER.

On a sound stage almost everything gets a microphone, for example a set of drums may have 5 different microphones. For this reason audio snake cables provide a very efficient solution in handling all the mic inputs back to the mixer, it also eliminates the safety hazard of too many cables on stage and the additional noise produced by cable coils.

XLR and TRS cables are fairly easy to custom make. One of the skills required to make these cables successfully is soldering, and tinning is essential to making a good cable.

Both the soldering iron and the wire to be connected should be tinned, tinning of the soldering iron prevents oxidation and helps in heat transfer. Tinning the wire allows for proper contact connection, without tinning the wire first you will more than likely make a dry solder connection which will easily break off.

Here are some wire gauges typically used in sound reinforcement: Microphone and line level cables 22 to 26AWG shielded, one pair. Speakers two conductor 16 AWG minimum, no shield required. A good rule of thumb for speaker cables is for every 100’ step up to the next gauge for optimal performance. Remember the larger the cable the lower the loss.

We’ll start with the TRS plug, usually referred to as a ¼” phone plug because of it’s long standing application in telephony. There are actually three versions of the phone plug: TS: a mono version TRS: a stereo version TRRS: a stereo version that includes a microphone connection. TRS TS TRRS

The TS plug is designed for unbalanced connections which means we wire a coax cable to the connector. The center conductor goes to the tip and the shield gets wired to the ring. Prep the coax cable as shown, the coax braid must be copper, aluminum braids will not accept solder. The braid is twisted to resemble a copper conductor & tinned.

A very important reminder here, always make sure to slide the connector boot and strain relief onto the cable before soldering the connector on. Solder your cable leads onto the connector. The connector leads should also be tinned.

Here is a TRS connector, this is a stereo connector as opposed to a mono connector, it has two ground rings. This is a balanced connection, the shield is connected to the sleeve contact.

Here are the corresponding female connectors to the TS and TRS balanced and unbalanced male connectors.

The TRRS is a mini 1/8” connector used in smart phones and doesn’t apply in our applications. This is for your information if you want to use a head set with speakers and a mic you must have a TRRS.

Here is an XLR male connector, pin 1 always goes to ground or shield, based on what you see is this photo balanced or unbalanced? These are straight thru connections, there is no crossing over of wires from end to end.

When making an XLR connector the process is similar to making a TRS: Strip a ¼” of insulation Tin the ends Slide the conductor through the hole in the contact and solder into place.

Here is the pin out for both male and female XLR mic plugs, these pin numbers appear on the front of the connectors. You may not always have black and red twisted pair just match colors to their respective pin numbers.

We can also make an XLR to TRS cable by matching the tip, ring and shield conductors to their corresponding contacts.

We can test these cables using a DMM and check for opens and shorts, pin 1 to pin 1 should show continuity, when the black lead is moved to the other two pins you should see an open.

The same test procedure can be done with TRS cables as well. The biggest challenge when making these cables is keeping the conductors separated from each other so they don’t short.

Some other XLR connectors are the: 4 pin used for headsets with a mic 5 pin lighting control 6 pin dual channel intercom and stage lighting

Banana plugs used for speakers can be a single connector or a dual plug, both speaker wires are wired into the plug regardless of the color of the plug.

It is important to maintain polarity when hooking up speakers. Speaker wire is usually bonded together with one conductor jacket having a line on it to identify left and right. Each of these speaker wires has a means of differentiating between the two

Keep the speaker wires consistent from end to end, if you decide for example that the white line on one speaker wire will be designated as the negative (black) lead then it is important that all speakers are wired the same way. Not maintaining proper polarity will result in phase distortion through the speakers, not all speakers will have the same phase design.

When an electrical signal is sent to the speaker it will push out first and then pull back, you want all your speakers to do this at the same time. If you reverse polarity on some speakers then some will push out while others will be pulling back, hence you have phase distortion.

Live Sound Reinforcement

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