7.1 The Most Common Questions
These are the questions installers and enthusiasts ask most frequently. Answered directly, without padding.
Q: How much power do I actually need?
More than factory, less than marketing suggests. For a system that plays loud and clean without distortion:
- Small car, one subwoofer, modest volume: 300–500W RMS to the subwoofer, 50–100W RMS to each front speaker
- Mid-size system, daily driver: 500–1000W to sub, 75–150W to fronts
- Loud system, show car: 1000–2000W+ to sub, 100–200W+ to fronts
- SPL competition: 5,000–50,000W+ (a completely different discipline)
The number on the box means almost nothing without the CEA-2006 standard behind it. A credible 500W RMS amplifier beats a dishonest "2000W MAX" amplifier every time.
Q: What gauge wire do I need?
Use this rule and you won't go wrong:
| System Power (RMS) | Main Power Wire | Speaker Wire |
|---|---|---|
| Up to 500W | 8 AWG | 16 AWG |
| 500W–1000W | 4 AWG | 14 AWG |
| 1000W–2000W | 2 AWG | 12 AWG |
| 2000W–3000W | 0 AWG | 10 AWG |
| 3000W+ | 00 AWG or parallel 0 AWG | 8 AWG |
For wire runs over 20 feet, go up one gauge. For multiple amplifiers, size the main wire for the total draw and run individual branches from a distribution block.
Q: Why does my bass hit harder with the engine running?
Because the electrical system is healthier. Engine off: battery alone powers everything. Under heavy bass loads, voltage drops as battery can't supply current fast enough. With engine running: alternator maintains 13.8–14.4V, providing stable power. If you hear a dramatic difference, you need more battery capacity or a larger alternator — or both.
Q: My amplifier has a "1000W" label but it barely gets loud. Why?
Three possibilities, in order of likelihood:
- The rating is marketing fiction. "1000W MAX" often means 250–300W RMS at best. Check if the amp has a CEA-2006 certification.
- The gain is set too low. Measure the output voltage with a DMM and a test tone. Adjust gain correctly.
- The impedance is wrong. A "1000W @ 1Ω" amplifier running a 4Ω load produces 250W. Verify speaker impedance matches amp's rating.
Q: Should I use sealed or ported for my subwoofer?
Sealed: Accurate, tight, punchy. Sounds good with all music. Requires more power. Better for small spaces.
Ported: Louder and more efficient. Extended deep bass. Sounds impressive with bass-heavy music. Needs more space. More susceptible to over-excursion below tuning frequency.
General rule: If sound quality and accuracy matter most, seal it. If you want maximum output and efficiency, port it. Both are valid choices.
Q: Can I run two amplifiers from one battery without a second battery?
Yes — if your alternator can supply the total current. Calculate total average current draw, compare to alternator output. If the alternator can sustain it, one battery is fine. If average draw exceeds alternator capacity, voltage will drop slowly and battery will discharge while driving. Add a second battery in that case.
Q: What does "RMS" actually mean?
Root Mean Square — a mathematical method for expressing the equivalent DC power of an AC waveform. For a sine wave, Vrms = Vpeak / √2. For audio, it represents the continuous power level that produces equivalent heating in a resistor. It is the only power number that represents real, usable, sustained output. Ignore peak, PMPO, MAX, and other marketing terms.
Q: How do I know if my speakers are blown?
Listening test: Distorted sound at low volume, crackling, or complete silence from one channel.
Resistance test: Disconnect speaker, measure resistance with DMM. Should read close to rated impedance (a 4Ω speaker reads 3.2–3.8Ω DC). Short circuit (0Ω) = blown voice coil. Open circuit (infinite) = broken coil or connection.
Physical inspection: Remove speaker, press cone gently. Should move smoothly with no scraping. Scraping = voice coil rubbing = physically damaged.
Q: Do I need sound deadening?
If your car sounds like a tin can — doors rattle, road noise is loud, bass disappears into vibrating panels — yes. Start with doors (biggest single impact). Trunk second. Full treatment after that for diminishing returns.
If your car is already quiet and you're building a quality system: yes, treat at minimum the doors where speakers are mounted and the trunk area near the subwoofer. The difference in clarity and panel resonance control is worthwhile.
If you're building a pure SPL competition car: debatable. Added weight versus panel stiffening. Most SPL builders treat structural panels to prevent flex, not for noise reduction per se.
Q: Why does my subwoofer sound "one-note" or "boomy"?
Most likely causes:
- Wrong box size — oversized sealed or oversized ported. Driver has too much air compliance, Q is too low, resonance peaks.
- Port tuned wrong — ported box resonance frequency too high, creating peak that dominates.
- Room mode — a cabin acoustic mode amplifying a specific frequency. EQ a notch filter at the boom frequency.
- Phase issue — subwoofer partially canceling front speakers at certain frequencies. Try inverting phase.
- No subsonic filter — ported box with no subsonic filter lets the driver over-excrete below tuning, causing uneven response.