Troubleshooting Audio Systems

Troubleshooting AudioSystems

In this chapter, you will learn about the following

  • Common audio cable and system problems
  • Troubleshooting audio cable

There may be nothing worse for a homeowner than to fire up his or her distributed audio system to play a favorite recording of Mozart or the Rolling Stones and hear static, hum, or buzz drowning out their dulcet tones, or, even worse, nothing at all.

A distributed audio system typically involves more than source devices, cable, and speakers. In many systems, there can also be selectors, volume controls, and remote controls, and each can introduce problems into the system.

This chapter looks at the most common problems a distributed audio system can develop and the processes and devices used to diagnose and troubleshoot audio problems.


Diagnosing Audio System Problems

A distributed audio system is a series of audio devices that are connected to one another over structured wiring. The parts of the distributed audio system that can cause audio performance problems are all of the components (including the speakers) and the cabling that connects the speakers and controls to the source devices. So, when you get a call that there is a problem with the audio system, gather as much information as possible and be sure to listen and analyze what the homeowners are saying. For example, if they say there is no sound or an improperly functioning control device, the obvious place to start tracking down the problem is by checking the source devices. Start with checking the components, the connections, and the parts of the system related or connected to the structured wiring system—oh, and check the power too!

Review the audio system configuration and identify all equipment components and how they are connected. The line diagram completed earlier in the project is an excellent reference for this information. Use a structured step-by-step troubleshooting process that includes at least these steps:

  CROSS-REFERENCE

See Chapter 16 for information and examples of an audio system line diagram.

  1. Identify the problem
  2. Start troubleshooting at the audio source
  3. Use a methodical approach
  4. Eliminate components one at a time as the source of the problem
  5. Refer to the manufacturer’s documentation for troubleshooting suggestions specific to a particular component.

The detail steps performed within this framework should include most of these steps:

  • Ruling out the obvious
  • Checking all connecting cables
  • Checking all control devices inline with the suspected components
  • Checking that the connection is the correct type for the equipment in use

Rule Out the Obvious

As obvious as it may seem, make sure that all of the connections are secure and fit properly, including the alternating current (AC) connection on the amplifier and any other source devices related to the problem. Make sure all components have power, especially if they are powered through a surge protector.

Check the speakers to make sure that all of the connections are secure. See if only one or both of the stereo speakers are not working. If only one is not working, check the connections throughout the distributed audio system that deliver the signal to that channel. If both speakers are not working, check the connections on both channels throughout the system and look closely at the connections from the source equipment.

Also check the volume controls, both at the source and in the affected room or zone. a room or zone volume control can’t increase the volume if the source device’s volume is set low. Another quick test of the audio is to plug a portable speaker directly into the source device. If the sound is available from the portable speaker, then the problem is likely in one or more of the distributed audio cables or speakers.

Check the Cable

As is the case with all distributed cabling systems, there is a short list of cable problem causes, including:

  • A broken connector caused by someone tripping over a connector cable
  • Corroded connections caused by too much moisture in a wall or room
  • Stretched or broken conductors caused by too much pull tension during installation
  • An audio cable that was damaged during installation

Your diagnostics should be organized to identify and isolate these common problems.

In most cases, the best way to test audio or video cables is to test the input or output levels of the cable with a signal from one of the system devices on the cable. For example, to check the cable connecting a CD-player, play a CD and test the cable at the speaker terminations where it connects to a volume control or the speakers. By far the most common audio video cable problem is an open circuit, which most commonly occurs at the cable ends.

Cable Properties

The three properties that should be tested, usually with a good quality multimeter, on an audio cable (or any cable for that matter) are:

  • CapacitanceCable capacitance is a common problem on audio lines that are more than 100 feet or 30 meters in length. If the capacitance is too high, it may interfere with systems that have high impedance. Use a handheld multimeter or a cable test device to determine the capacitance of the cable. If the capacitance is too high for the device to which it is connected, consider replacing the cable with one that is rated at less than 100 picofarads per foot pF/ft).
  • InductanceHigh inductance can affect audio by changing the tone of the sound during transmission. Inductance can vary depending on the cables are installed and whether they are coiled or looped. A coiled up cable will typically have higher inductance than an uncoiled cable. The best way to correct inductance is to ensure that the length of the cable between two devices is appropriate and without unnecessary loops or coils. Some systems also have inductor circuits built-in to block certain frequencies in an audio signal; for example, the crossover in a woofer may “roll-off” higher frequency sounds. If the audio is distorted in this situation, the problem may be in the crossover and not the cable.
  • Resistance (impedance)Depending on the needs of a specific audio system, if the resistance is too high, the audio signal may be decreased in quality, especially at the speakers. Impedance is how much a cable impacts the flow of current through the wire and is measured in ohms. Systems are either high impedance or low impedance, but low impedance systems are typically in the range of 150-ohms to 800-ohms and high impedance is generally in the range of a few kilo-ohms to tens of kilo-ohms. Residential systems are typically low impedance devices and the rule of thumb is to assume output impedance at around 1 kilo-ohm (K-ohm). The speakers and other distributed components of an audio system should be matched for resistance and impedance.

To troubleshoot the audio visual (AV) system for resistance, perform these checks:

  • Check all connectors and connections for improper installation, loose shielding, stray strands, or damage.
  • Check the cable for continuity using a volt-ohm meter (VOM) or multimeter.
  • Check any cables that terminate at the distribution panel from the end of the cable terminated at a wall outlet. The resistance of the cable should be close to that of the terminator or the device connecting to the outlet.
  • If RG6 cable is installed, use a multimeter or VOM to check the resistance between the center conductor and the shielding in the cable. If the resistance is below 100 K-ohms, it is likely that the cable has a short in it at some point and should be replaced.

Cable Verification

If you suspect that a problem may exist in the distributed audio cabling, you should perform the same cable tests you performed to test and verify the cable during trim-out:

  • Visually inspect the terminations at the distribution panel, at the source device, and at the outlets. Depending on the type of cable in use, check to see that the connector or jack is properly attached.

    • Coaxial cablingIs the connector’s wire mesh inserted around the outer channel of the connector body? Is the center conductor wire extending the proper distance (about -inch) beyond the front of the connector? If the connector is a crimp-on type, is the connector tightly crimped to the cable? Is the screw-on collar (on an F-type connector) properly aligned and tightly connected?
    • Speaker wireAre the wire conductors in contact when they connect to the outlet jack (a condition that may exist if too much insulation was stripped from the wire)? Are the jacks securely fastened to the conductors?
    • Twisted-pair (TP) If RCA or mini-plug jacks are in use, is the wire pair insulation preventing the two conductors from touching at the jack. If a balanced interface is in use, is the connection providing a ground line?
    • Commercial audio cablingWhen using a manufactured audio cable set, are the connectors firmly attached to the cable without breaks, cracks, or splits between the connector plug or jack and the cable?
  • If the connector jacks and plugs are good, next test the cable for its transmission properties.

    • Digital versus analogVerify which interface format is in use. In most systems, the format will be either be analog or the more common standard digital signal formats used in residences, Audio Engineering Society/European Broadcast Union (AES/EBU), which recommends shielded TP cable. Verify that an analog device is not connected at the source or in a room or zone. AES/EBU does not convert digital signals back to analog.
    • Coaxial cableThe cable should carry 75-ohms of impedance, which can be verified with a multimeter. Check the cable for continuity as well.
    • Speaker wireMost speaker wire (also called zip wire) fails to meet the requirements for in-wall cabling specified in the building and electrical codes. Distributed audio wire should have a Class 2 or 3 fire insulation rating, and clear insulation speaker wire doesn’t. There are commercial audio cables that do meet the codes, but not many do. If standard two-conductor, clear-insulation speaker wire is installed in the walls of a home, your first recommendation is that it should be replaced. Secondly, it must carry 4-ohms to 8-ohms of impedance and can be verified with a multimeter.
    • TPShielded TP (STP) cable should carry from 100-ohms to 120-ohms of impedance if connected to a digital interface. TP cable used for analog audio transmission should carry 45-ohms to 70-ohms of impedance. Verify that an analog device isn’t connected to a digital device. If it is, you may have found the problem. Verify continuity, impedance, and perhaps even run a wiremap test on the cable.

        CROSS-REFERENCE

      Chapter 9 provides information on how to perform the cable tests referenced in this section.

Ground Loops

Another common problem that is typically attributed to cabling is a ground loop that can create a humming noise in the audio playback. A ground loop is caused when two or more AC powered devices that are connected to the electrical system on two different outlets in two different rooms are linked to one another with an audio cable and part of the AC power flows over the cable.

Solving ground loops is not an easy task because there are no absolute grounding systems. Solving this problem may require assistance from an electrician to balance the grounding of the outlets in use or, if an unbalanced line is in use, the installation of a balanced audio interface.

Check the Controls

Distributed volume controls and selector controls can and do go bad, but not often. In most cases, if a volume control is not properly responding to changes in its setting, the problem is either the connection or the volume control itself.

Remove the control from its outlet, assuming it is not a remote control, and check its connections carefully. Also check the wiring where it comes into the outlet box or structured wiring bracket. If the wire is bent or kinked that could very well be the issue. If the connections appear to be proper, replace the control with a new one. If this solves the problem, then the control was bad. However, if the problem persists, then you should check the cabling both before and after the control.

Balanced Versus Unbalanced

Beyond the obvious, such as the source device being unplugged, AC power can cause audio problems, especially if the speaker interface is unbalanced. There are two types of audio interfaces used in audio systems: unbalanced and balanced.

Unbalanced Interface

An unbalanced interface is typically installed on a single conductor shielded wire, such as a solid core conductor cable like coaxial cable. The shielding around the wire serves to ground not only the cable, but also the two devices connected to it, typically an amplifier and a speaker, but could also include a microphone or other audio source device. Unbalanced cabling is typically terminated with RCA or mini-plug connectors.

The problem with an unbalanced interface, especially one of some run length, is that it is very susceptible to picking up what is called ground loop interference that can add hum or buzz to the audio playback by a speaker.

Ground loop interference is a common characteristic of shielded copper wire. Removing the cause, the cable’s shielding, isn’t the way to solve it. However, it can be removed with an isolation transformer. While all systems that use an unbalanced interface are likely to have ground loop interference problems, on smaller systems, it’s typically not much of a problem. However, in a high-end system that includes some professional level audio or video equipment, either the cabling should be replaced or an isolation transformer installed.

Balanced Interface

Professional and better audio devices are connected using balanced cabling, constructed to minimize the amount of interference they pick up. A balanced cable has the built-in capability to pass along the audio signal and filter out interference.

A balanced cable includes two 24-gauge conductors to carry signals plus a grounding wire. Several manufacturers produce a variety of balanced cabling. Balanced cabling is typically terminated with an XLR connector. The balance in this type of audio cable is achieved by maintaining the impedance of the two signal lines equal to that of the ground. However, balanced audio also works on ungrounded cabling as well with the right equipment.


Review

The obvious place to begin diagnosing distributed audio problems is checking the source devices. Make sure that all of the connections are secure and fit properly, including the AC connection on the amplifier and any other source devices related to the problem. Check the volume controls, both at the source and in the affected room or zone. If sound is available from a portable speaker connected to the source device, the problem is likely in one or more of the distributed audio cables.

There is a short list of cable problem causes, including: a broken connector, corroded connections, stretched or broken conductors or damaged cable. Your diagnostics should be organized to identify and isolate these common problems.

The three properties that should be tested on an audio cable (or any cable for that matter) are: capacitance, inductance, and resistance (impedance). To determine if a problem may exist in the distributed audio cabling, test and verify the cable using the same tests used during trim-out. Visually inspect the terminations at the distribution panel, at the source device, and at the outlets. Test the cable for its transmission properties.

A ground loop can create a humming noise in the audio playback. A ground loop is caused when two or more AC powered devices that are connected to the electrical system on two different outlets in two different rooms are linked to one another with an audio cable and part of the AC power flows over the cable.

If a volume control is not properly responding, the problem is either the connection or the volume control itself. Remove the control from its outlet and check its connections carefully. Check the wiring where it enters the outlet box for bends and kinks. If the connections are proper, replace the control with a new one. If the problem persists, check the cabling both before and after the control.

There are two types of audio interfaces used in audio systems: unbalanced and balanced. An unbalanced interface is typically installed on a single conductor shielded wire, such as a solid core conductor cable like coaxial cable. An unbalanced interface is very susceptible to ground loop interference and can add hum or buzz to the audio playback by a speaker.

A balanced cable has the built-in capability to pass along the audio signal and filter out interference. A balanced cable includes two conductors and a grounding line.

Questions

  1. When diagnosing an audio system problem, what should be the first area to check?

    1. Structured wiring
    2. Volume controls
    3. Connections
    4. Source devices
  2. Which of the following is not a common cable problem?

    1. Broken connector
    2. Corroded connection
    3. Cable quality too high
    4. Stretched or broken conductors
  3. Which of the following can impact the performance of an audio system?

    1. Capacitance
    2. Inductance
    3. Resistance
    4. Cable length
    5. All of the above
  4. What is the rule of thumb for residential audio system impedance (resistance)?

    1. 4-ohms
    2. 20-ohms
    3. 1 kilo-ohm
    4. 20 kilo-ohms
  5. Which of the following can cause audio cable problems at the connector?

    1. Insulation material
    2. Stranded versus solid wire conductors
    3. Conductor wires in contact
    4. Ground loop
  6. Which of the following is a digital audio standard?

    1. AES/EBU
    2. IEEE
    3. NEC
    4. S/PDIF
  7. What impedance should a coaxial cable used in a distributed audio system carry?

    1. 15-ohms
    2. 50-ohms
    3. 75-ohms
    4. 100-ohms
  8. Which of the following cable types is least likely to meet the building and electrical codes for fire safety?

    1. STP
    2. Coaxial
    3. Speaker wire (zip wire)
    4. UTP
  9. Two AC power devices that are connected to AC power in two different rooms and are linked by an audio cable are likely to cause what audio system problem?

    1. Feedback
    2. White noise
    3. Ground loop
    4. Clipping
  10. An unbalanced audio interface is typically installed on what type of cable?

    1. Solid core, single conductor cable
    2. Stranded speaker wire
    3. UTP
    4. STP

Answers

  1. D. If a source device is not connected, powered, or has improper settings, it is likely the cause of at least one audio system problem.
  2. C. I’m not sure if this is entirely possible, but about the only problem it can cause is cost. The other issues listed are all common cable problems.
  3. E. Actually, just about anything at all relating to an audio system can, if only in a small way, can cause some problem. But these choices are the causes, either alone or in combination, of many audio system problems.
  4. C. Most systems will range a bit lower than 1 kilo-ohm, but that is the standard rule of thumb.
  5. C. If the insulation has been stripped too far back on the conductors so that they make contact at the connector, the audio signals are being shorted out.
  6. A. This standard does not convert digital audio signals back to analog and, as a result, the standard is not compatible with standard analog audio devices.
  7. C. Coaxial cabling is commonly used in unbalanced audio that has longer run lengths.
  8. C. Commonly available speaker wire typically has transparent insulation doesn’t carry the NEC/UL fire safety ratings for in-wall installation.
  9. C. A ground loop condition can add buzz to the audio signal.
  10. A. The lack of a grounding conductor is the key characteristic of an unbalanced cable.






HTI+ Home Technology Integrator & CEDIA Installer I All-In-One Exam Guide
HTI+ Home Technology Integrator & CEDIA Installer I All-In-One Exam Guide
ISBN: 72231327
EAN: N/A
Year: 2003
Pages: 300
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