SPL Measurement Guide

Installation Guide & Technical Information Database

SPL/Clamped Power Measurements

Pre-Testing Setup

  1. Cabin Configuration:
    • Ensure the cabin remains consistent for every test (e.g., passenger door shut, driver door open, windows closed, seats leaned forward, etc.). This consistency is essential for accurate results.
  2. Meter Location:
    • Decide on a fixed SPL meter position (e.g., kick panel, headrest, or windshield). Keep the SPL meter in this position for all tests.
  3. System Settings:
    • Be sure to use the same settings throughout testing:
      • Radio volume
      • EQ settings
      • Crossover settings
      • The same sine wave tracks
    • Any changes should be done one at a time and re-tested (See Advanced Cabin Testing section below).

Step-by-Step Testing Process

  1. Determine Testing Power Level:
    • Conduct a full-power test burp to find the maximum SPL/clamp power output.
    • Divide by four to get the testing power level, usually around 25% of the max. This will minimize coil heating and impedance shifts while providing sufficient pressure to generate meaningful data.
  2. Measurement Routine:
    • Measure Each Frequency Individually:
      • Start from 10 Hz below your current peak to 10 Hz above your current peak.
      • Example: If your peak is at 40 Hz, measure frequencies from 30 Hz to 50 Hz, one at a time.
    • For each frequency:
      • Record SPL (using an SPL meter).
      • Measure and log AC voltage, AC current, and clamped power.
    • The output must be loud enough to pressurize the cabin effectively but not so high that the coils begin to heat up. Heating causes impedance changes, leading to errors in the data.
  3. Data Logging and Analysis:
    • Log All Measurements into the efficiency calculator:
      • Track values for SPL, AC voltage, AC current, and clamped power.
      • The calculator will highlight the most efficient frequency in green and the highest power frequency in red.
      • Export this data to save for future testing use.
      • Email data to info@bassahaulic.com for additional help/analysis.

Advanced Cabin Testing

  • Make ONE Change to the cabin configuration or enclosure at a time.
  • Test using a narrower frequency range (e.g., 5 Hz above and below your new peak).
  • Log the data and compare results to identify positive or negative effects on efficiency, bandwidth, or output.
  • Make ONE More Change to the cabin configuration or enclosure.
  • Re-test the narrower frequency range, and repeat the process.

Tools Required

  • SPL Meter: Examples include Term Lab, SPL Labs, SSA APMX, etc. (Term Lab or SPL Labs are preferred).
  • AC Current Clamp: (Add-ons available for Term Lab and SPL Labs).
  • AC Voltage Meter: (Add-ons available for Term Lab and SPL Labs).
  • Bassahaulic SPL Efficiency Calculator.

Key Considerations When Clamping

  • For a single non-strapped amp, connect the DMM probes to the corresponding positive/negative speaker wires.
  • Place the AC clamp around either the positive or negative speaker wire.
  • For two strapped amps, connect the negative DMM probe to the (+) output of the [slave] amp and the positive DMM probe to the (+) output of the [master] amp.
  • Place the AC Clamp around the positive wire(s) leaving the [master] amp.
  • (If there are two positives and two negatives, use only one set—either positive or negative). It is crucial to measure all current leaving the amplifier.

Notes on Testing Levels

  • Avoid high power levels (to prevent coil heating and impedance shifts that make the data unreliable).
  • Avoid power levels that are too low (as they won't pressurize the cabin sufficiently).
  • Ensure the power level is sufficient to pressurize the cabin but not so high that it results in significant coil heating.

Summary

This process will help you determine your efficiency peak and power peaks to better understand your car audio system's performance. With consistent setup and careful logging, you can identify the changes that improve overall system efficiency and output, leading to noticeable gains over time.