8 x 18″ PA Subs Sound System – Help Me Pick the Right Amps
Setting up a PA system with eight 18-inch subwoofers requires careful amplifier selection to ensure optimal performance, efficiency, and longevity. A mismatched amplifier can result in distortion, power loss, or even equipment damage. Whether you’re designing a PA system for concerts, clubs, or large outdoor events, choosing the right amps is essential for achieving deep, powerful bass.
In this guide, we will explore how to select the best amplifiers for an 8 x 18″ PA system, including power requirements, impedance matching, and recommended amplifier brands. If you’re looking to build a powerful PA system with earth-shaking bass, this article will help you make the right choices.
Understanding Power Requirements for an 8 x 18″ PA System
1. Determining Power Handling for Your Subs
Each 18-inch subwoofer has a specific power rating measured in watts RMS and peak power. To properly power your PA system, consider:
RMS Power: The continuous power a subwoofer can handle.
Peak Power: The maximum power it can handle in short bursts.
For example, if each 18-inch subwoofer is rated at 1000W RMS, the total power requirement for an 8-sub PA system would be 8000W RMS.
2. Matching Amplifiers to Speaker Impedance
Speakers in a PA system typically have 4Ω or 8Ω impedance. When wiring multiple subs, you need to calculate:
Series wiring increases impedance.
Parallel wiring decreases impedance.
If your subs are 8Ω and wired in parallel (two per channel), the amplifier should support a 4Ω load. Ensuring the right impedance match prevents overloading the amp or underpowering the subs.
Choosing the Right Amps for Your PA System
1. How Much Power Do You Need?
A general rule for PA systems is to supply 1.5x to 2x the RMS rating of the speakers to avoid clipping and distortion.
For an 8 x 18″ PA system, an amp should deliver:
8000W RMS total (1000W per sub)
1.5x power headroom = 12,000W RMS recommended
Divide by 2 channels = 6000W per channel amplifier
2. Recommended Amplifier Types
There are two main types of amplifiers used in high-power PA systems:
Class D Amplifiers (Best for PA Subs)
✅ High efficiency, low heat generation
✅ Lightweight and portable
✅ Ideal for subwoofers due to power efficiency
Recommended Class D Amps for an 8 x 18″ PA System:
Powersoft X4 – 4-channel, 5200W per channel @ 4Ω
Lab Gruppen FP14000 – 2-channel, 7000W per channel @ 2Ω
Crown I-Tech 12000HD – 2-channel, 6000W per channel @ 4Ω
Class AB or Class H Amplifiers (Older but Reliable)
✅ Warmer, more dynamic sound
✅ Often heavier but rugged
✅ Used in traditional PA systems
Recommended Class H Amps:
QSC RMX5050a – 5000W bridged @ 4Ω
Behringer NX6000 – 6000W bridged @ 4Ω
3. How Many Amps Do You Need?
You can choose between:
1 high-power amplifier running all 8 subs
2 mid-power amplifiers running 4 subs each
4 smaller amplifiers running 2 subs each
Best Configurations:
✔ One Powersoft X4 (4-channel) can run 8 subs at 4Ω per channel.
✔ Two Crown I-Tech 12000HDs can run 4 subs each at 4Ω per channel.
✔ Four Behringer NX6000s can run 2 subs each at 8Ω per channel.
Wiring and Setting Up Your PA System Amps
1. Parallel vs. Series Wiring for Subs
Parallel Wiring (Lower impedance, more power)
Series Wiring (Higher impedance, less power needed)
If using 4Ω subs, connect two per channel (parallel for 2Ω load). If using 8Ω subs, wire two per channel (parallel for 4Ω load).
2. Using a DSP (Digital Signal Processor)
A DSP processor is essential for tuning a PA system. It helps:
✔ Prevent clipping & distortion
✔ Apply crossover filters for subwoofers
✔ Fine-tune EQ & compression
Recommended DSPs for an 8 x 18″ PA System:
Xilica XP4080
DBX DriveRack PA2
Powersoft Armonía DSP
3. Setting the Crossover for Subs
For an optimal bass response, set the crossover at 80Hz to 120Hz and roll off frequencies above 150Hz.
Common Mistakes to Avoid When Choosing PA System Amps
❌ Underpowering the subs – Can cause distortion and damage.
❌ Overloading the amps – Running too low of an impedance may trigger protection mode.
❌ Ignoring ventilation – High-power amps generate heat; ensure proper airflow.
❌ Skipping limiter settings – A limiter prevents speaker damage during loud peaks.
Recommendations for an 8 x 18″ PA System
If you need serious low-end power, consider this setup:
�� For a high-end system:
(1) Powersoft X4
(8) 18″ subwoofers (1000W RMS each)
Xilica XP4080 DSP
�� For a mid-range system:
(2) Crown I-Tech 12000HDs
(8) 18″ subs
DBX DriveRack PA2 DSP
�� For a budget-friendly setup:
(4) Behringer NX6000s
(8) 18″ subs
DBX 231s EQ + Crossover
Building an 8 x 18″ PA system requires matching the right amplifiers to your subwoofers for maximum efficiency, power, and sound quality. By choosing the correct power rating, impedance matching, and wiring configuration, you can create a professional sound system that delivers deep, chest-thumping bass for any event.
Investing in high-quality amps like Powersoft, Crown, or QSC ensures your PA system remains reliable and powerful. With the right setup, your subwoofers will perform at their peak, providing ground-shaking low frequencies that will impress any audience.
