Bombardier CRJ-200 Acoustics

American-Airlines-CRJ-200

Figure 1. Typical Bombardier CRJ-200 Aircraft

ceng

Figure 2. General Electric CF34-3B1 Turbofan Engine

Figure 3.  Fourier Magnitude with Note Peak Frequencies (Hz)

Figure 3. Fourier Magnitude with Noted Peak Frequencies (Hz)

I recently flew as a passenger in a CRJ-200 (aka CL-65) jet similar to the one shown in Figure 1.

This aircraft has two General Electric CF34-3B1 turbofan engines, as shown in Figure 2.

Here are the rotational speeds for each rotor.

N1 Fan Speed       7300 RPM   (122 Hz)
N2 Core Speed   17710 RPM   (295 Hz)

I made an audio recording from within the aircraft cabin nearing the end of climb-out, after hearing some distinct sine tones against the background random noise. The audio file is: CRJ200.wav

A Fourier transform of the sound file is shown in Figure 3.

A spectral peak occurs at 113 Hz, which is 93% of the N1 Fan speed.

A pair of spectral peaks occur at 277 and 278 Hz.  These are about 93% of the N2 Core speed.  The 1 Hz difference could be due to the N2 rotors of each engine being slightly out-of-sync with one another.

The other peaks remain unidentified.

Again, this recording was made from inside the cabin. So the fuselage walls would have attenuated some of the engine-generated acoustic energy, particularly at higher frequencies.

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See also: Bombardier

– Tom Irvine

One thought on “Bombardier CRJ-200 Acoustics

  1. Tom,

    The N1 and N2 speeds you noted are 100% speeds, which would be equivalent to maximum thrust. In climb power, the engines are throttled back somewhat, and this would explain why the peaks are at slightly lower frequencies that 100%. Normally, the two engines are synced based on fan speed, since that rotor has the highest vibration and if not synced would cause beating complaints. With the fan rotors synced, the gas generator rotors float, so that’s why you see a slight difference in the two peaks.

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