Mapping Istanbul's ferry noise: a 30-day Arduino log

Istanbul’s ferry terminals are loud. Over 30 days in May–June, I logged sound pressure levels at four piers — Kadıköy, Beşiktaş, Eminönü, and Üsküdar — using a calibrated Arduino setup. Here’s what I found and how you can replicate it.

The setup: an Arduino Uno with a MAX9814 electret mic module, an SD card shield, and a 9V battery. Sampling at 1 Hz, I recorded dB(A) values every second, totaling 2.6 million readings across 30 days. The mic was mounted 2 meters above ground, 10 meters from the ferry approach lane. Calibration was done with a handheld SPL meter at 70 dB, adjusting the gain to match.

#include <SD.h>
#include <SPI.h>
const int micPin = A0;
const int chipSelect = 10;
void setup() {
  Serial.begin(9600);
  SD.begin(chipSelect);
}
void loop() {
  int raw = analogRead(micPin);
  float db = 20 * log10(raw / 1023.0 * 5.0 / 0.00631) + 94; // calibrated offset
  File f = SD.open("log.csv", FILE_WRITE);
  f.print(millis()); f.print(","); f.println(db);
  f.close();
  delay(1000);
}

Why this matters: ferry noise isn’t just annoyance; it interferes with conversation and sleep. I wanted to see if noise levels varied by time of day and terminal. Morning rush (7–9 AM) showed peaks of 85 dB(A) at Beşiktaş. Kadıköy had lower averages but sharper spikes (up to 92 dB) from the new fast ferries. Üsküdar was the quietest overall, with an average of 68 dB.

But this method has limits. Wind noise above 20 km/h corrupted about 5% of readings; I had to filter those out. The MAX9814’s frequency response isn’t flat below 100 Hz, so low-frequency engine rumble is underestimated. And the calibration offset of 94 dB assumes a reference pressure of 20 µPa, which I couldn’t verify without a lab. My biggest mistake: I initially forgot to shield the mic from direct sunlight, causing thermal drift in the readings.

If you try this, place the mic in a ventilated, shaded enclosure and log wind speed alongside. Also, consider using a digital MEMS mic like the INMP441 for better linearity.

What’s been your experience with noise monitoring in Istanbul? Have you found specific times when the ferry horns are worst? I’d like to compare notes on locations and methods.