Sound(s) from Multiple Running Generators

[zzvyb6]

Our part of min-Michigan has a huge number of electric power districts out. Ice and falling trees is taking down poles, and causing transformer burnouts. We have power, but about a 1/8 mile away is a high-end subdivision/neighborhood, each with it's now running standby generator. You can easily pick up the drone sound from the common rpm between all these units. I could sleep thru this, but frequently there are loud thumping noises coming from there. I'm guessing that this is 'FM-ing' (Frequency Modulation) cause by individual generators catching up on a load from motors starting, wells running, etc. It's currently 21 deg F here, so furnaces are definitely running. What do you think is going on? Otherwise it sounds like the 'katerpillar drive' going bad on the Red October.

 

[Rustyiron]

I think that power companies can easily get complacent with tree trimming then you have a storm, nothing special just the right combination of snow, ice with a little wind and thousands of homes are out of power. The media blows this out of proportion and of course the residents are not used to this either and the frenzy grows. Urban areas are the worst, their idea of being prepared is to have their "devices" charged!

 

[Hay Dude]

I think that power companies can easily get complacent with tree trimming then you have a storm, nothing special just the right combination of snow, ice with a little wind and thousands of homes are out of power. The media blows this out of proportion and of course the residents are not used to this either and the frenzy grows. Urban areas are the worst, their idea of being prepared is to have their "devices" charged!

It’ll be interesting to see when some of these state bans on ICE engines under 25HP start taking affect in cold climates. That covers about 95% of every backup generator in the country.

I’m thinkin there’ll be a new thing called “people popsicles”

 

[turbo36]

Our part of min-Michigan has a huge number of electric power districts out. Ice and falling trees is taking down poles, and causing transformer burnouts. We have power, but about a 1/8 mile away is a high-end subdivision/neighborhood, each with it's now running standby generator. You can easily pick up the drone sound from the common rpm between all these units. I could sleep thru this, but frequently there are loud thumping noises coming from there. I'm guessing that this is 'FM-ing' (Frequency Modulation) cause by individual generators catching up on a load from motors starting, wells running, etc. It's currently 21 deg F here, so furnaces are definitely running. What do you think is going on? Otherwise it sounds like the 'katerpillar drive' going bad on the Red October.

 

[Rustyiron]

I very recently saw a tv show, "engineering disaster" iirc and that footbridge story was covered.

 

[orezok]

When the military marches across a bridge, they are instructed to break cadence as it can cause vibrations in the bridge that can cause failure.

 

[John_Mc]

Our part of min-Michigan has a huge number of electric power districts out. Ice and falling trees is taking down poles, and causing transformer burnouts. We have power, but about a 1/8 mile away is a high-end subdivision/neighborhood, each with it's now running standby generator. You can easily pick up the drone sound from the common rpm between all these units. I could sleep thru this, but frequently there are loud thumping noises coming from there. I'm guessing that this is 'FM-ing' (Frequency Modulation) cause by individual generators catching up on a load from motors starting, wells running, etc. It's currently 21 deg F here, so furnaces are definitely running. What do you think is going on? Otherwise it sounds like the 'katerpillar drive' going bad on the Red October.

I wonder if what you are hearing is the "beat frequency" caused by slight differences in the frequency at which the generators are running. They are supposed to run at 60 Hz. Most common generators (other than inverter generators) do this by running at 3600 RPM. If one generator is running at exactly 3600 and another is running at 3599 rpm. The sound of the exhaust pulses will sometime reinforce each other and sometimes interfere. This creates a "beat" at a frequency equal to the difference - in this example, that would be 1 Hz which humans can hear as a "thumping". With multiple generators running, I imagine you can get some rather complex sound dynamics going.

Without hearing the noise myself, I can't say that is what is going on, but it's a possibility.

Musicians sometime use beat frequencies to tune different instruments into sync with each other: rather than comparing one note to another, you can listen for the beat frequency. The slower the beat, the closer they are to matching. When the beat disappears, they are hitting the same note.

 

[zzvyb6]

I wonder if what you are hearing is the "beat frequency" caused by slight differences in the frequency at which the generators are running. They are supposed to run at 60 Hz. Most common generators (other than inverter generators) do this by running at 3600 RPM. If one generator is running at exactly 3600 and another is running at 3599 rpm. The sound of the exhaust pulses will sometime reinforce each other and sometimes interfere. This creates a "beat" at a frequency equal to the difference - in this example, that would be 1 Hz which humans can hear as a "thumping". With multiple generators running, I imagine you can get some rather complex sound dynamics going.

Without hearing the noise myself, I can't say that is what is going on, but it's a possibility.

Musicians sometime use beat frequencies to tune different instruments into sync with each other: rather than comparing one note to another, you can listen for the beat frequency. The slower the beat, the closer they are to matching. When the beat disappears, they are hitting the same note.

Yep. That's what I figured it is.

 

[diesel85]

I have very sensitive hearing, and I noticed this too.

One thing I have noticed is that I can hear most diesel engines running from a long ways away. They have a very low frequency that I can pickup.

What is really interesting is that my tractor (a BX2200) parked about 1000ft+ away will subsonically rattle my plates in my cupboard at certain engine RPMs. I can barely make the low frequency noise out.

I notice only diesel engines do this phenomenon.

 

[grsthegreat]

When power is out, the only time im upset is when i cant hear my generator running.