# Acoustic analysis from an aircraft engine?

I have found it surprisingly easy to find information on jet engines; however, I've been unable to find acoustic information so I can make a noise spectrum model. I'm looking for oscillations from 100Hz up to 1MHz. I could make some guesses based on the number of blades, diameter and rotation speed, but I believe this information is out there because there exists noise reduction insulation on aircraft, and environmental noise rules. In my search, I've found that NASA as analysis tools for acoustic liners, but nowhere have I found a study where these frequencies are described (I realize they will be different for different engines)

Ideally, what I'm trying to find is a decibel vs. frequency chart.

My motivation is purely academic as I have found (I think) that certain capacitors inject noise via ultrasonic oscillation into electronics, and I'm trying to find the frequencies involved. (I'm pretty sure that I'm going to have to make a blade/stage/rpm/thrust model for the noise, but I'm really hoping that the acoustic information is out there.) At this point, it's possibly down to nomenclature and that I am not looking for the correct term as aviation is full of lingo.

Has anyone ever seen acoustic data for a jet engine anywhere?

• Have you looked at fly-over spectrograms? These are available in scientific literature, but of course they include the complete aircraft. Is that maybe what you're looking for? Otherwise there are some very simple models to model the noise of the engine based on some parameters. Dec 28, 2018 at 23:56
• @Daniel No, but I'll take a look for those. The complete aircraft would be fine, and I'm just hoping to get a general feel for concentrations of noise energy. I'll dig in the library. Dec 29, 2018 at 1:32
• Is that even a thing, 1MHz acoustic noise? Jan 15, 2022 at 18:12
• @Pilothead "noise" is not an acoustic phenomenon only, any unwanted and/or random signal in acoustic or EM spectrum is noise by definition. Jan 21, 2022 at 9:10
• It strikes me that acoustical analysis of an engine like this would be something the manufacturer would do in an effort to improve noise insulation/reduction (like the saw-tooth nacelles seen on some engines), but wouldn't necessarily be made public. The public part would be mostly marketing "New! Improved! 32% quieter than our previous model!!" jargon. Jan 21, 2022 at 15:50

Found some info in a really old TU Delft uni book on aircraft sound (VTH-78 from 1973, in Dutch, paper copy only). The pics are from a French article by Y. Covillard: "Unitės de measure dans l'acoustique aéronautique", published in l'Aeronautique et l'Astronautique, no. 32, 1971. The English notes are my translations.

Max frequencies are about 16 kHz, which makes sense since most articles are interested in audible noise. Unfortunately we don't have information on which bypass turbine engine was measured.

I don't really have an example or a proper answer, but you may be able to download a decibel/noise meter on your phone (such as Spectrum on iPhone), and use it at an airport when a jet flies by. They tend to record sound levels and a frequency spectrum as well. I have used these before to get a general sense of the noise levels. As a previous commenter posted, these may focus only up to 16 kHz though. Perhaps there are also tools you can buy for cheap or rent that could measure in some of your desired range.

I'm not sure if this is what you are looking for, but here goes:

For example, Benshuai Lyu & Ann P. Dowling have studied the effects of lobed nozzles on installed jet noise. The article displays graphs plotting frequency vs. decibel of variable arrangements of jet nozzles. The graphs go up to 20kHz, which would be the upper limit of audible spectrum (*.

S. Khardi has published a study "An experimental analysis of frequency emission and noise diagnosis of commercial aircraft on approach" (link to pdf). The document contains several graphs displaying noise profiles.

*Your question does mention the upper limit of frequency range you are interested in as 1MHz, but in a later comment you mention "I'm interested in the acoustic only."

Quite frankly, if I understood your question correctly, the data/graphs you request are very easy to find with simple "jet engine acoustic spectrum" google search, so I suspect I've misunderstood something.