Interpreting the Loxjie P20 Volume Display - Predicting Settings on other Headphones
Following some questions in the HE-560 thread, I completed some simple math to interpret what the Loxjie P20 is showing with this -60 through 0 digital volume display.
Recap of Data Collection Process (from the HE-560 thread)
Equipment: FiiO Q5 DAC line out to Loxjie P20 (balanced out)
- Selected a musical track with little variation in volume (dynamically compressed). Used Sleigh Bells A/B Machines, as the 2nd half of the Treats album has extreme compression and distortion.
- Used iPhone decibel meter software as the track played, with the phone mic in the headphone ear cup
- Adjusted the Loxjie volume control during the first 45 seconds of the song to 75 decibels.
- Repeated test with six sets of headphones (listed below); recorded the volume setting
Summary of Data and Findings
| Headphone Model | Published Resistance (Ohms) | Published Sensitivity dB/mW | Loxjie P20 Setting Required for 75dB | Percent of Loxjie Display Range (-60 to 0) | Conversion Factor (Rated Sensitivity/Loxjie Display Value) |
|---|---|---|---|---|---|
| Audeze LCD-2C | 70 | 101 | -42 | 30.00% | -2.4048 |
| AQ NightHawk Carbon | 25 | 99 | -40 | 33.33% | -2.4750 |
| Focal Elex | 80 | 104 | -40 | 33.33% | -2.6000 |
| HiFiMan HE-560 | 45 | 90 | -32 | 46.67% | -2.8125 |
| MrSpeakers AEON Flow Closed | 13 | 92 | -32 | 46.67% | -2.8750 |
| Sennheiser HD-600 | 300 | 97 | -38 | 36.67% | -2.5526 |
| Published | Published | Estimate | Estimate | HE-560 Value | |
| HiFiMan HE-6se | 50 | 83 | -29.5 | 50.81% | -2.8125 |
Simple Correlations
I ran simple correlations in a spreadsheet between the variables, and found that headphone sensitivity ratings were an extremely strong predictor of the display setting:
Correlations:
Headphone Rated Sensitivity X Loxjie Scale = -0.9238 [VERY HIGH]
Headphone Rated Resistance (Ohms) X Loxjie Scale = -0.2161 [LOW]
For comparison – Headphone Rated Sensitivity X Headphone Resistance = 0.1479 [MINIMAL]
Predicting Volume Settings for other Headphones
The final column of the table is a simple ratio of Headphone Sensitivity divided by the Loxjie display setting. This follows from the high correlation. For example, the Focal Elex is: 104 / -40 = -2.6000.
Regarding the question from @rrwwss52 on the HiFiMan HE-6se, I used the conversion factor for the HE-560 (as the closest technological match). The estimate is shown in the bottom row: to reach 75 decibels would likely require a volume setting between -30 and -29.
Math: 83 / -2.8125 = -29.5
Summary
The Loxjie P20 volume display largely follows from rated headphone sensitivity. The resistance (ohm) ratings have little to do with the volume setting required.
And finally, this proves I have too much time on my hands.