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.
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:
See Chapter 16 for information and examples of an audio system line diagram.
The detail steps performed within this framework should include most of these steps:
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.
As is the case with all distributed cabling systems, there is a short list of cable problem causes, including:
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.
The three properties that should be tested, usually with a good quality multimeter, on an audio cable (or any cable for that matter) are:
To troubleshoot the audio visual (AV) system for resistance, perform these checks:
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:
Chapter 9 provides information on how to perform the cable tests referenced in this section.
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.
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.
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.
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.
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.
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.
Part I - Home Technology Installation Basics
Part II - Structured Wiring
Part III - Home Computer Networks
Part IV - Audio/Video Systems
Part V. Home Lighting Management Systems
Part VI - Telecommunications
Part VII - HVAC and Water Management
Part VIII - Security System Basics
Part IX - Home Technology Integration
Part X - Appendices