Matching an Amplifier to Your Subs
Matching an amplifier to your subs comes down to voltage. The amp sets the maximum voltage across the coil; the driver's continuous rating sets how much it can take for long periods. Size the amp for clean headroom above that rating, then let a limiter, not a small amp, decide what the driver actually gets.
Work in volts
P = V² / R, so a rating converts directly to a voltage at the nominal load. For an 1800 W, 8 Ω driver such as the WM1850/8:
| Amp power at 8 Ω | Ratio to 1800 W | Max output (V RMS) | Headroom |
|---|---|---|---|
| 1800 W | 1× | 120 V | 0 dB |
| 2700 W | 1.5× | 147 V | +1.8 dB |
| 3600 W | 2× | 170 V | +3 dB |
An amp with headroom reproduces transients above the average level cleanly. Music has a crest factor, so a channel sitting at the driver's continuous rating on average needs a few dB of extra voltage on peaks. The extra watts on the amp's spec sheet are only safe if the limiter holds the long-term level down.
Why clipping heats coils
A clipped amp holds the output at its rail voltage for part of each cycle. In the limit a sine clips into a square wave at the same peak voltage, which carries twice the power: +3 dB of heat into the coil with no increase in peak level. Clipping also adds odd harmonics, which in a passive system land on the HF drivers. A small amp run into clipping can deliver more heat to a coil than a large amp run clean.
Read the amp spec properly
- Use the figure at your actual load (8, 4 or 2 Ω), per channel, both channels driven.
- Check bridged ratings separately: the minimum load is usually doubled.
- Ignore "peak" or "max" headline figures; compare continuous ratings at a stated distortion.
- Count total load per channel before you link cabs. See 4 ohm vs 8 ohm and amp channels for a stack.
Set the limiter in volts
Set the DSP's RMS limiter threshold to the voltage of the driver's continuous rating (120 V for 1800 W at 8 Ω), converted to the DSP output level using the amp's gain. Put a high-pass filter in front so the cone is not driven below the box's working range, where excursion rises steeply. A peak limiter set to the amp's maximum output stops it clipping. See limiter settings for subs.
Wavemark drivers
The WM1850/8 is rated 1800 W AES / 3600 W peak at 8 Ω; the WM18X451 1800 W RMS / 3600 W max, 8 Ω or 4 Ω. Both take the same 120 V RMS continuous at 8 Ω, so one amp platform and one limiter setting covers either.
More on ratings: RMS vs program vs peak power.
Sources: P = V²/R; RMS of a square wave equals its peak, RMS of a sine is peak/√2. Wavemark WM1850/8 spec sheet and WM18X451 product data. Calculated values rounded.
Questions
How powerful should my amp be for an 1800 W sub?
Enough to deliver at least the driver's continuous rating cleanly at your load, with headroom for peaks: 1800 W at 8 ohms is 120 V RMS, 3600 W is 170 V and about 3 dB more. Use a limiter to keep the long-term level at the driver's rating.
Can an underpowered amp damage a speaker?
Yes, if it is driven into clipping. A hard-clipped sine approaches a square wave carrying up to twice the power at the same peak voltage, so the coil heats faster than the level suggests.
Where should I set my sub limiter?
Set the RMS limiter to the voltage of the driver's continuous rating at its load, for example 120 V RMS for 1800 W at 8 ohms, with a high-pass filter ahead of it.