AudiaFUSION’s amplifier modules feature a sophisticated impedance monitoring mechanism that allows you to monitor the integrity of the cabling and loudspeakers connected to that output channel. There are a few important details to note about AudiaFUSION’s impedance monitoring capabilities.
Up to four independent, user-specified frequency bands can be monitored simultaneously. Frequency bands are defined in terms of center frequency and bandwidth. The software allows you to capture the average impedance over that frequency band. If the average impedance of the band changes by an amount larger than the user-specified tolerance percentage, then either an LZ or HZ warning is activated.
Impedance can only be measured when a strong enough signal is being output. Fusion will only update the frequency bands of the impedance curve that it can reliably calculate. When no signal is being sent to a particular frequency band, Fusion will freeze the impedance curve at the last known value. Therefore, Fusion may not be aware of problems that arise when no signals are being sent to the speaker.
It is feasible to send a high frequency pilot tone (above 19kHz) at a level that is strong enough for impedance monitoring to be active, but low enough to be inaudible. This would allow Fusion to monitor the impedance constantly. Additionally, sending pink noise to the speaker will allow you to capture a full-bandwidth impedance graph, which is useful during project commissioning as well as to capture baseline impedance averages.
There are a few additional caveats to watch out for when using impedance monitoring, particularly with constant-voltage (70/100V) systems:
- In a zone of 25 speakers, cutting the cable to the last speaker in the chain only increases the impedance by 4%. However, setting your impedance tolerance to a value as low as 4% could easily result in false warnings, since the impedance of the line could change by such a small amount due to other factors, such as temperature fluctuations. Therefore, impedance monitoring of large speaker zones may not reliably indicate certain problems.
- Speaker-level volume controls also affect the overall impedance and therefore could potentially cause false warnings.
Figure 1. Fusion impedance monitoring frequency band setup window.