Sorry in advance for the long post…
I’ve noticed that after flying turboprops in 2024 my tinnitus is noticeably louder and I tend to get headaches shortly thereafter. I first noticed this with the Cessna 208, but it also happens with all other turboprops to varying extents.
I did a bit of digging and found that there are significant spikes in the 5kHz - 12kHz range, depending on the plane and the state of the engine (Idle, vs Max power), and comparing these same planes under the same conditions to 2020 the spikes are much less significant.
For example, here is a frequency analysis of the Cessna 208B from the cockpit with the engine at idle (full rich)
You can see there is a spike right around ~6500Hz
Replicating the same conditions with the 208B in 2024 you can see there is a similar spike at ~6500Hz but it is significantly more prominent.
This is a zoomed in view comparing the two, the green line shows where the spike tops out in 2020.
In 2020 the spike was a ~10db increase in volume while in 2024 it’s a ~21db increase! It’s generally agreed that a 10db increase is perceived by humans as roughly double the ‘loudness’ - which means a 21db spike is going to be perceived as much louder, and in this frequency range it can be quite painful (for some folks)
And here’s the same plane, interior, at Max power setting.
2020:
2024:
Detail view:
You can see the noise floor is quite a bit lower, while the spike is a bit higher in the 8kHz range.
This same pattern plays out when you look at the TBM930. Here it is in 2020, Interior, power at Max.
And here is it in 2024, same conditions.
We can see similar spikes in the 8kHz - 12kHz range here. Again the green line shows the limit of the spikes in 2020. It’s not as significant here obviously, but it’s still spiking a noticeable amount over 2020 (about 3db higher)
And unfortunately the Headphone Simulation option doesn’t eliminate the issue, you can see there are still spikes of up to 16db in these ranges with headphone simulation on here (TBM930, Interior, Max power, Headphone Simulation ON)
I’ve tried to mitigate this myself using various tools, including a static eq (Equalizer APO w/ PEACE GUI), a dynamic eq (TDR Nova), a multiband compressor (C5 w/ Voicemeeter Potato), among others, but the problem I’ve run into is that the spikes will change in frequency and intensity as the engine condition changes so I haven’t been able to completely eliminate these spikes without making the whole thing sound muffled in the high freqs. Example below:
And these spikes will change depending on the aircraft, and whether your viewing from internal (cockpit) or external view, so even using a dynamic eq is not going to solve it entirely.
I know this isn’t going to impact everyone, it’s really only going to impact some folks, such as myself, but it has made it difficult for me to fly some of my favourite aircraft unfortunately and I’m hoping that there might be a way to allow us to reduce these spikes back to the 2020 levels as I never found that I ran into this problem while flying the same aircraft in 2020. Also, I’d like to note that I’m not an audio engineer or any other kind of audio professional, just an enthusiast and a long-time tinnitus sufferer haha
The aircraft I’ve personally noticed this on so far are:
- Cessna 208
- TBM930
- PC12NGX
- Cessna 408
- Vision Jet (Not a turboprop I know, but the spikes are just as significant and noticeable)