70 V and 100 V Speaker Transformer Tap Reference
Read distributed-speaker transformer tap labels, distinguish line-voltage and low-impedance modes, and record the exact tap before calculating amplifier loading.
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Read the selector in context
A transformer tap label states a nominal power selection at a specified distributed-line voltage. It is not an acoustic output level or the measured speech power at that moment. Read the column for the actual system voltage and the exact speaker model.
| Marking | Meaning | Check against the product |
|---|---|---|
| 70 V / 70.7 V column | Tap powers for the designated constant-voltage system. | The documented system nominal voltage and selector position. |
| 100 V column | A separate power mapping for the same transformer positions. | Do not carry the 70 V watt value across to the 100 V column. |
| Low-impedance / bypass mode | Connection intended for the specified low-impedance amplifier arrangement. | Do not select bypass for a distributed-line output. |
| Unavailable position | A position may have no permitted value in one voltage column. | A blank or prohibited setting is not permission to use the adjacent value. |
| Tap wattage | Nominal transformer loading at the stated voltage. | Amplifier loading and required design margin are separate system checks. |
Read a named manufacturer example
JBL Control 25-1 documentation supplies a transformer selector and a separate low-impedance mode. Read its actual 70 V and 100 V tap table; the two columns do not assign the same power to every selector position. Do not transfer that mapping to another Control model or a visually similar loudspeaker.
For that exact Control 25-1 model, the published transformer taps are 30, 15, 7.5 and 3.7 W at 70 V; the 100 V set is 30, 15 and 7.5 W. The separate low-impedance mode is 8 Ω. Read the actual selector mapping in the product instructions before recording a position.
- Identify amplifier output mode and nominal line voltage.
- Record exact speaker model and transformer option.
- Transcribe selector position and its permitted power for that voltage.
- Link each speaker ID to its branch and endpoint record.
Keep the loading input traceable
Record speaker ID, quantity, line voltage, tap position, rated tap watts and manufacturer document revision. Preserve mixed tap settings as separate rows so a load worksheet can use the real inventory. Changing taps changes the system load.
This page interprets labels and supplies no amplifier capacity verdict or acoustic coverage design. Use cable endpoints for branches and test records for commissioned settings and observations.
For the separate numerical task, use distributed speaker loading. Use the equipment data identified above as inputs within each tool’s stated scope.