A 70 Volt Meter Attenuator for Sound Reinforcement
By Allen H. Burdick
It is often desirable to monitor the levels on distributed audio PA speaker lines, known as 70 volt lines. It's simple with the right tools. This app-note shows how.
Many times a sound reinforcement system that uses the industry accepted 70 volt interface system needs to be metered. Benchmark SPM-220 and SPM-320 meter systems as well as the RPM-1, VU-1 combination can easily do the job and allow the operator to see the audio levels both in VU (average) levels as well as in PPM (peak) mode. In other words by using the peak metering capability of the Benchmark meter systems, an operator can, at any place on the system, not just the amplifier room, see whether or not his amplifier hit clip.
The following is an attenuator that will do the trick.
At the 2023 AXPONA show in Chicago, I had the opportunity to see and hear the Hill Plasmatronics tweeter. I also had the great pleasure of meeting Dr. Alan Hill, the physicist who invented this unique device.
The plasma driver has no moving parts and no diaphragm. Sound is emitted directly from the thermal expansion and contraction of an electrically sustained plasma. The plasma is generated within a stream of helium gas. In the demonstration, there was a large helium tank on the floor with a sufficient supply for several hours of listening.
While a tank of helium, tubing, high voltage power supplies, and the smell of smoke may not be appropriate for every living room, this was absolutely the best thing I experienced at the show!
If an audio system is composed of multiple components, we may have detailed specifications for each component, but we will not know the performance of the combined system without doing some calculations. You may have questions such as these:
Will my audio system produce audible noise?
Will my audio system produce audible distortion?
How will my audio components work together as a system?
How loud will my audio system play?
Use Benchmark's online audio calculators to find answers!
For example, if we know the output power of an amplifier, as well as the sensitivity and impedance of our loudspeakers, we can calculate the maximum sound pressure level that our system can produce.
This application note provides interactive examples that help to answer the questions listed above.