A question about sound.

[The-Borg]

Hi.

I hope this is in the correct section.

We have a club limit of 81 decibels which is enforced on all IC motors..
Electric has be exempt form this as normally there is no noise what so ever but with the new generation of EDF's.
The noise these make is becoming an issue.

The question is - "Is measuring 81 decibels from an IC's the same as 81 decibels on a Electric" This may sounds a dumb question but the frequency/pitch of an IC is different than that of a Electric and it's the perceived level of noise/nuisance that we are interested in and how to measure it.

Thanks

Stuart.

[vintage1]

Well...its a long answer to be complete. BUT the simple answer is that your noise meters will have a built in ferquency filter that 'weights' the noise against a curve that has been generated by statistical analysis of 'how loud' people find certain frequencies.

So at e.g. 1 meter, or wahtever yiour standard distance is, yes the meter will reflect the annoyance level *at one meter*. Or rather the 'perceived loudness'. Irritation level is quite another tghing. I was woken by a 40B sound last night. The sound of The Puppy widdling on the bloody carpet. THAT'S annoyance level.


What is an issue though as many have discovered, is that models with very high frequency noise - proper jets are the most obvious - read high on the ground, but at distance the high frequencies get knocked out. AND they sound quiet. Which is why a full size jet at ground level is a blast of roaring white noise, but 3 miles overhead, its just a rumble of thunder.


I certainly have at least one electric model - foamie jet - that puts out more like 100dB, and another on a 17K DD prop that is pretty loud too.

You should be checking Electric model noise allright. But make a test not just at a short distance, but also at longer range. You may well find that the wlelectrics carry less - or indeed MORE- than the glos.


Strangely I haven't noticed EDF's being noisy though.

[slipstick]

Most of the noise from both IC and electrics is generated by the prop....so they're not a different as you might at first think.

The standard DEFRA/BMFA test is 82dB(A) at 7 meters and it would be reasonable to expect any plane to pass it. After all electrics are often classed as "silent flight"....it's pushing your luck claiming it's silent flight if it can't even meet the sound levels designed for IC motors ;).

Steve

[The-Borg]

Thanks for you help.

Stuart.