Quick Answer / Summary: Low-Z PA: 4-8 ohm loads, heavy gauge (12-14 AWG), short runs (under 30 m), speakON connectors, current up to 15 A. 100 V line: transformer taps at each speaker, thin cable (16-18 AWG) over hundreds of metres, because current is low at high voltage. Never mix the two: a 100 V line into a low-Z speaker destroys it, and a low-Z amplifier into a tapped line presents the wrong load.
PA amplifiers run either low-impedance (4-16 ohm) or high-voltage distributed lines (70/100 V). The two topologies want different cable, different connectors and different loss math. Choosing the wrong one wastes copper or loses power.
Low-Impedance Runs
Low-Z is the studio and club topology: one amplifier channel per speaker or pair, 4-8 ohm loads, current in the amps. Cable is heavy because current is high: 12-14 AWG for runs of 20-30 m, speakON connectors rated for the current. Loss math follows the 5% rule – loop resistance under 5% of the load. The advantage is fidelity and damping; the limitation is distance, since resistance and damping loss grow with length and low impedance.
Where Low-Z Wins
Short runs, high power, critical monitoring: clubs, studios, stages. The amplifier sees the real load and damping stays high.
The Distance Wall
Beyond about 30 m at 4 ohm, cable losses and damping become the limiting factor. That is where distributed lines take over.
70/100 V Distributed Lines
A 100 V line steps the amplifier output up through a transformer, so the same power travels at high voltage and low current: a 100 W system at 100 V draws 1 A, not 11 A. Cable can be thin (16-18 AWG) over hundreds of metres, and each speaker has a line transformer with power taps (100 W, 50 W, 25 W settings). The trade: transformer bandwidth and insertion loss, and a low-impedance speaker connected directly to a 100 V line will be destroyed. Label the topology at every connection point.
Tap Arithmetic
A 100 W amplifier feeds ten 10 W taps, or twenty 5 W taps. Total tap power must not exceed the amplifier’s rated line power.
Why Thin Cable Works
At 100 V, 100 W is 1 A. The same 100 W at 8 ohm is 3.5 A, and at 4 ohm 5 A – the transformer trades current for voltage.
Connectors, Labelling and Safety
Low-Z: speakON for anything above 100 W, binding posts for installs. 100 V line: terminal blocks or euroblock connectors on the amplifier and each speaker’s transformer, with the line treated as a power circuit – insulated, labelled, and never patched while live. Safety: 100 V can deliver a shock; the line is not touch-safe like a low-Z output. Labelling: mark every cable ‘100 V LINE’ at both ends, and keep line and low-Z cable in separate stock.
Treat the Line as Power
100 V lines carry hazardous voltage. Isolate before patching, and never assume a speaker cable is low-voltage.
Separate Stock
Different gauge, different connectors, different labels. Shared cable stock is how a low-Z speaker meets a 100 V line.
Topology Comparison
| Factor | Low-Z | 100 V Line |
|---|---|---|
| Load | 4-16 ohm | Transformer taps |
| Current (100 W) | 3.5 A at 8 ohm | 1 A at 100 V |
| Cable | 12-14 AWG | 16-18 AWG |
| Distance | Under 30 m | Hundreds of metres |
| Connector | speakON | Terminal block |
| Safety | Touch-safe | Hazardous voltage |
Real-World Application Scenarios
A club’s main PA runs low-Z: 12 AWG to 8 ohm tops at 20 m, speakON throughout. A supermarket’s ceiling system runs 100 V line: 18 AWG over 150 m, 20 speakers at 5 W taps, terminal blocks at every ceiling tile. A church hybrid uses low-Z for the main hang and a 100 V line for the lobby and corridors.
Recommended Internal Resources
(1) Product cluster – https://zh-zong.com/productlist/ (anchor: PA speaker cable, low-Z and line); (2) FAQ – https://zh-zong.com/faq/ (anchor: topology and tap questions); (3) Contact – https://zh-zong.com/contact/ (anchor: request line-system cable).
Related Reading in This Series
- Amplifier and Speakers: Planning the Run Before the Purchase
- Speaker Amplifier for PC: Short Runs, Noise and the Right Cable
- Home Amplifier and Speakers: In-Wall Cable Done Once
Frequently Asked Questions (FAQ)
Q: Can I connect a normal 8 ohm speaker to a 100 V line?
A: No – it will be destroyed. A 100 V line needs a speaker with a line transformer and the correct tap.
Q: Why is 100 V line cable so thin?
A: At 100 V the current is low: 100 W draws 1 A, versus 3.5 A at 8 ohm. Thin cable carries it over long distances.
Q: How much tap power can one line take?
A: The sum of all taps must not exceed the amplifier’s rated line power. Ten 10 W taps on a 100 W amplifier is the limit.