Mavic Air - Noise levels

[JDawg]

Sorry, got to disagree. All being equal, smaller drone, lighter drone, smaller props, less noise

My M2P is much quieter than my smaller Mavic Air, no competition.

 

[FoxhallGH]

Lots of YouTube videos measure it and everyone does it slightly different because there is no set standard for how far away to hold the dB meter.

The tests that you see on YouTube are all 'comparitive' - so you are correct, in that it doesn't give an exact noise dB figure (there's no ... "A Mavic hovering at 27 ft outputs xdB of noise" statement), but what these tests do quite accurately show is a 'comparison' between one drone and another, or one prop' type and another - as long as the same measuring equipment and distances are maintained for the entire test.

 

[FoxhallGH]

Sorry, got to disagree. All being equal, smaller drone, lighter drone, smaller props, less noise

Smaller drone can also mean smaller motors. Smaller motors need to swing lesser pitched prop's faster to get the lift, and also to get the stability from the gyro effect of the spinning prop's - which are on shorter arms than the e.g. Mavic Pro or Phantom ... If you do some rpm tests with different prop types, you do see (and hear) that the quieter prop's spin at a lower rpm (well on the Mavic Pro's anyway).

 

[Bwoody321]

I'm curious about the Mavic Air noise levels but I don't see any reference to this on the official Specs page.

On the Casey N You Tube video he seems impressed by how quiet it is when it starts and takes off.

Anyone know what the noise level actually is? Oddly enough the noise levels of the Mavic aren't on the Mavic specs page anymore. Possibly I'm looking for the wrong words.

Roughly 100db I’m fairly certain

 

[maverickheir]

I'm curious about the Mavic Air noise levels but I don't see any reference to this on the official Specs page.

On the Casey N You Tube video he seems impressed by how quiet it is when it starts and takes off.

Anyone know what the noise level actually is? Oddly enough the noise levels of the Mavic aren't on the Mavic specs page anymore. Possibly I'm looking for the wrong words.

Expressing sound level is tricky because it requires some kind of standardization in the reporting.

Firstly, loudness perception is frequency dependent. The same sound pressure level expressed in dB at different frequencies will not yield the same 'loudness' to the human ear. Human hearing has a dynamic range of 20Hz to 20kHz depending on age, genetics and health. But the response curve is not flat. The 'peak sensitivity' of human hearing is often between 2kHz - 5kHz (i.e. "equal loudness contour" for a typical response curve of human hearing). The "dBA" weighting can be applied to standard sound pressure level measurements to mimic human loudness perception when expressing sound levels, but then you still have a problem. Depending on whether the drone is hovering or flying, the frequency changes as the motors spin at different frequencies. There are also different aerodynamic effects at different rotor frequencies that are generating the noise so the sound spectra changes depending on what the drone is doing. So it gets pretty tricky really fast with so many changing conditions. It's entirely possible for the drone to be 'loud' while hovering, but be 'quiet' when flying fast (or vice versa) as it's frequencies shift higher when the rotors spin faster outside of human peak hearing sensitivities. So do you quote hovering loudness or flying loudness?

Also, even for omnidirectional noise sources in ideal environments, it follows the inverse square law of propagation which means it's dependent on distance from source. How far do you place the audio measurements from the drone to report dBA levels? But real drones actually produce directional noise, further complicating the problem. I guess reporting the noise level close to the source at it's loudest level is useful, but I still see it plagued by directionality and the fact frequency and noise spectra changes when the drone is in operation versus hovering. Perhaps they can represent the absolute loudest noise level under all conditions. I guess that might be useful as it represents a worst case.

Also, what's most important for the drone is how 'incognito' the drone is to the public. Low frequency sound actually travel further than higher frequency sound due to losses and noise attenuation in the air. So even if two noise sources produce 100dBA noise, but one at a high frequency while another at a low frequency, in the real world you'd probably hear the lower frequency at a far distance due to noise attenuation in the air. So even source noise reporting is dubious.

 

[maverickheir]

This video is good as it was measured indoors with low background noise and compares the Mavic Air (MA) to the Mavic 2 (M2). Since I only have the MA myself, I used the audio in this video to do some quick comparisons between the two drones while they are in the hovering state.

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The noise spectra of these quadcopters is interesting when you run the sound through a spectrum analyzer. You have the motor shaft spectra, which reflects the RPM of the motor. Then you have the 'blade passing frequency' that is often number of blade multiples of the motor shaft frequency, which in the case of a 2 blade propeller used in the DJI drones, is 2X motor shaft frequency. Then you will also see higher harmonics of the blade passing frequency and other broadband frequencies due to aerodynamic inefficiencies with the rotor. Typically noises are generated by blade-vortex generation, blade wake interactions, etc.

From the spectra taken from the above video comparing the drones while hovering, I can deduce the MA motors spin at a higher frequency than the M2 when hovering steady. The blade passing frequency of the MA was measured to be 377Hz (motors ~11,000 RPM). The blade passing frequency of the M2 was measured to be 189Hz (motors ~5700 RPM). If someone knows the actual hovering RPM of the MA or M2 and the above is in an incorrect range (since I couldn't find a source), please let me know but that is what I gathered from the FFT.

Also worth mentioning is that the noise amplitude of the blade passing frequency and all higher harmonics is much higher with the MA than the M2, suggesting much better aerodynamic efficiency of the M2 compared to the MA even from the get go before you look at spectral details. Perhaps the rotor design of the MA is less efficient, such as the fact it lacks any wingtip devices on the rotor and has a simple flat rotor tip. Or perhaps due to rotor wake interactions with the 4 rotors being in such close vicinity to each other in this small quadcopter due to it's small compact size compared with the M2. Surely they can at least improve on the design of MA's rotor though by adding wingtip devices like they did with the M2 with the raked wingtip to further reduce noise by a bit.

Then you also get to the higher harmonics of the blade passing frequency in multiples. This is another important detail because it shows where the noise spectra is in the frequency range and why it's so audible since human peak hearing perception is generally in the 2kHz to 5kHz range and noise in this range is more sensitive. The MA with 377Hz (1f) blade passing frequency has measurable and significant higher harmonics spectras of 754Hz (2f), 1.1kHz (3f), 1.5kHz (4f), etc. Much of the dominant higher spectral peaks can be measured between 377Hz-3kHz, which has spectra well represented within peak human hearing range.

The M2 on the other hand with it's 189Hz blade passing frequency (1f) produces major measurable harmonic spectral peaks within 189Hz to 1.5kHz. Much of the major spectral peaks occur below 1.5kHz thus just outside of peak human hearing sensitivity.

In conclusion, the MA produces higher amplitude of all harmonics when hovering, plus higher noise harmonics occur within peak human hearing range. This is probably why the MA overall sounds louder than the M2 while hovering. Interesting to note this spectra occurs while hovering. When the drone is flying at speed, the motors will spin faster and some motors spin a different frequencies to each other too, therefore the noise spectra will be completely different than hovering. However, since the MA produces louder spectra than the M2 at hover, I still expect it to be louder than the M2 under flying conditions, despite the M2 possibly having higher harmonics start to enter the peak hearing range of the human ear when it is flying harder. The M2 just seems like a more aerodynamically efficient beast.

 

[FoxhallGH]

Wow @maverickheir - excellent analysis work and a reference for all time ... Thanks

 

[hiflyer201]

The Spark is so small most people think of it as a toy, not nearly as threatening as a bigger drone like the Mavic. Hopefully the Air will be the same.

That's my feeling too, The Air seems noisier than hell compared to the spark even though I'm sure on any kind of meter there would probably not be that much difference. Staying out of sport mode around non-interested people would be a good idea too. The Spark is scary fast and the Air is scary fast and loud.
Like others have said..that loud noise has been very reassuring at times when I've let the drone get out of sight and the battery life is ticking away.

 

[Topo]

Are the motors, alone, different in sound levels? Or is this all about the noise of props? I wonder if anyone has fired up their Air, or MP without props attached. I realize that might dangerous for the motors, running without a load, tho.