### Overview and Test Facility

Accurate measurement of arrow fly-by noise requires strict control of
environmental variables. Testing was conducted in the Arrow Sound Testing
Chamber (ASTC), a custom shoot-through facility designed to isolate the
arrow's in-flight noise from external sounds (wind, wildlife, traffic,
aircraft) and from noises generated by the bow or arrow impact.

The ASTC achieves an average noise floor of 22 dB(Z) across 500 Hz–31,500 Hz,
with validated free-field acoustic conditions down to 250 Hz (per <span class="font-mono">ISO 26101:2017</span>).
Reverberation times are low (0.03 s RT60, T20) from 500 Hz to 8 kHz
(<span class="font-mono">ISO 3382-1</span>).

To confirm the chamber does not affect measurement accuracy, a control test
was run both outdoors and within the ASTC. After adjusting for ground
reflections, measurements matched within ±0.5 dB, confirming the reliability
of the facility.

### Arrow Fly-By Measurement Setup

Arrows were shot through the ASTC so they passed a calibrated measurement
microphone at a fixed distance of 1 meter. Stringlines, forming a 50 mm-wide
window, ensured a consistent flight path. Any contact with the stringlines
was visually detected and that shot was repeated, resulting in all valid
measurements occurring between 975 mm and 1025 mm from the microphone. This
constrains theoretical sound level variation to ±0.2 dB (inverse-square law).

### Equipment

- Microphone: Earthworks M30 Measurement Microphone (Class 1)
- Audio Interface: RME Babyface Pro FS
- Software: Audio and Acoustical Response Analysis Environment (AARAE) in
  MATLAB
- Calibration: ¼″ microphone calibrator (94 dB @ 1 kHz)
- Velocity: Garmin C1 Pro Chronograph

### Arrow Testing Procedure

- 38 arrow configurations tested over three days
- Each configuration shot repeatedly until two valid, stringline-cleared
  measurements were obtained
- All arrows initially shot from a Hoyt Nitrum (74 lbs, 28.5″ draw)
- Average test velocity: 280.0 fps across all configs
- Additional velocities gathered using 60 lb Elite Ritual 35 and 80 lb Hoyt
  Alpha (all at 28.5″ draw)
- Each bow tuned to produce a bullet hole through paper with standard
  reference arrow

### Audio Processing and Loudness Calculation

1. Calibrate microphone input using the ¼″ calibrator
2. Trim audio to a 0.2 second window to exclude bow noise and target impact
3. Apply a Tukey window (tapered cosine, ratio 0.2) for smooth fade-in and
   fade-out
4. Screen each recording by ear and omit any with audible background noise
5. Apply 1/3-octave band FFT with IEC Class 0 filter slopes
6. Compute <span class="font-mono">L(Z)max</span> values (Fast, 125 ms time
   weighting) from 500 Hz–31,500 Hz
7. Log-average valid shots per arrow configuration in each 1/3-octave band
8. Apply Deer-Weighting and Human-Weighting: Each band adjusted per
   white-tailed deer auditory threshold (Heffner, 2010) to reflect perceived
   “loudness” for deer, whose hearing is centered one octave higher than
   humans. In addition, A-Weighting was applied to each band to reflect
   perceived loudness for humans.
9. 95% confidence intervals were calculated for each band's SPL for each
   arrow configuration using the t-distribution with degrees of freedom
   equal to the sample size minus one, to appropriately reflect the
   increased uncertainty associated with small sample sizes.
10. For bands where the lower 95% confidence interval was not defined (i.e.,
    negative in the linear domain), a value of –120 dB SPL was substituted
    for the purposes of weighted summation. These cases are marked as 'N/A'
    in band-specific CI reporting.
11. Sum the weighted bands logarithmically to yield a single-number
    perceived loudness metric