Live next to a church, much noise including leaf blowers at 2.30 am to blow snow. Crotchety old fart here.
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Because the engines aren’t encased in the body of the vehicle and aren’t surrounded by noise dampening materials. Also they don’t have lengthy exhaust pipes and mufflers. And they rev higher.
And so on…
But I have to wonder, why is anyone doing anything around a church at 2:30 in the morning?
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On engines used for devices like that it’s hard to even call those things mufflers. They’re more like spark arrestors.
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Clearing the snow for school I assume.
I remember telling cops that 18 wheelers and Harleys were louder then my fun car, not the case anymore… lol
Run an exhaust down the shaft of a weedwhacker with a cat converter, a resonator and then a muffler close to the end and you might not hear it anymore… But it might also kill enough power that it no longer whacks the weeds…
And you might need to put it on wheels to lug it around.
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Two stroke engines tend to be a lot louder- as mentioned they have what amounts to a spark arrestor that doubles as a low restriction muffler. Some years back, I bought a 4 stroke weedwhacker. It’s very quiet in comparison and has oodles of low end power compared to a high revving two stroke.
I have a newer 24 HP lawn tractor with a 54" deck. The engine is very quiet. It’s when you engage the PTO and the mower deck runs- even I wear hearing protection on that thing, it’s very loud.
I expect if you complained to the city they’d put a stop to the 2:30 am leaf blowers. Folks in this area do a lot of complaining about leaf-blower noise, and many city councils are now responding by requiring that all older leaf blowers be replaced with new ones. You have to toss your old one, irrespective of its actual noise level. The new ones are designed to meet a more stringent noise regulation. Usually they’d require the more strict noise level only for newly purchased equipment, but leaf blower noise has become a big enough complaint to require all old leaf blowers be immediately replaced. As you might imagine this isn’t very popular among many owners having old ones.
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Sounds extreme and unenforceable to me.
Part of the issue is the frequency of 2 stroke engines which run at a higher frequency than 4 stroke motors.
Generally higher pitched, higher frequency noises are more annoying than lower frequency noises although ultra deep frequency can quickly can be even more annoying.
Clearing snow with a leaf blower?
Ya light snow her up nort, dats what dey do.
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I’m not sure that that’s true. 2 stroke engines fire twice as often, but the combustion is not as strong as a 4 stroke, so it’s a little quieter. But it does happen twices a much as you say. Also, two strokes typically have more medium speed torque. They tend to lose torque as they rev, so they are bigger to maintain that higher end torque. 4 strokes don’t lose so much torque at high speed, so they’re smaller and therefore don’t gain torque in the mid speed range. A 2 stroke boat motor will beat a 4 stroke of the same rated horsepower off the line. The 2 stroke is operating closer to its rated power at medium RPM whereas the 4 stroke is putting out less power. Both will be equal once they reach full speed.
My 2 storke generator is surprisingly quiet.
I think a lot of the noise comes from the aluminum engine block, and having the whole engine vibrate from its single unbalanced cylinder. Even if the exhaust was completely quiet there would still be a lot of noise. A cast iron engine with a water jacket around it must reduce the noise a lot more.
I’m not sure I’m following your explanation but let’s start with a simple example comparing 2 leaf blowers both with 50cc engines both, running at 5,000 rpm.
We agree that the 2 stroke will be exhausting (creating noise) once every revolution while the 4 stroke will only be exhausting once every other revolution so everything being equal, the frequency of the noise of the 2 stroke will be twice as high pitched as the 4 stroke.
An interesting thing about human evolution is that we have evolved to be more attuned to high pitched sounds like a baby’s cry than low pitched sounds. Which is why “nails scratching on a chalkboard” is so much more irritating than significantly louder fireworks explosions. Another example is high pitched emergency vehicle sirens which are designed to immediately gain our attention.
So besides 2 stroke leaf blowers, this also explains how a tiny baby’s high pitched crying on a plane can reduce everyone to complete wrecks while the equally loud but lower pitched rumble of the engines is scarcely noticable. 
Not sure where you get that from- every two stroke engine I’ve ever had has been much louder than it’s four stroke counterpart. That goes for lawn implements, motorcycles, boat engines… you name it.
Higher low end torque for a four stroke (especially compared to a two stroke) is also a given to me.
I say this is partially due to smaller mufflers. Boat engines don’t have mufflers at all! Also, and I didn’t think of this until now, but 2 strokes don’t get as quiet at reduced throttle like 4 cycles do. 2 strokes always have full cylinder pressure when the exhaust is released. At partial load 2 strokes skip a few firing cycles and then make a single lound bang. At full throttle with the same muffler, a 2 stroke should be a little quieter compared to a 4 stroke, since the cylinder pressure will be a little bit lower due to the lower efficiency of a 2 stroke.
2 strokes have maximum torque in the mid range but it drops off at high and low speed. 4 stroke maintains a more flat torque curve. On a 2 stroke with the same horsepower rating as a 4 stroke, you can get in to mid range RPM and stay in the same gear until you reach maximum RPM, because the horsepower curve is more flat. On a 4 stroke you need to downshift to keep your RPM up where peak horsepower is.
The time period between the pulsations of noise will be half. The actual frequency of the sound from gas being released out of a high pressure chamber doesn’t necessarily change.
Well right! When I’m talking about noise, I’m referring to the entire package not just the engine itself. Like I said before, most of the two strokes I have owned have essentially expansion pipes and spark arrestors because a real “muffler” would kill its power.
Sure they do, it’s the water But listen to the same sized outboard in a two stroke vs four stroke. There’s absolutely no comparison in the amount of noise they produce. I just dumped a 6hp tiller for a 4 stroke version for this exact reason. And the bigger they get, they more difference IMO. I’d love to dump the 135hp outboard on my bass boat for a 4 stroke but the engines cost more than the boat!
I spent a number of years riding motocross. The big thumpers were night and day quieter than the 2 strokes of the same displacement…
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Sound Frequency = The number of sound pulses for a given time period
Loudness = The intensity of the above pulses
So given two identical engines outputting equal high pressure gas the two stroke will “sound” louder.
On the other side of the spectrum I happened to be in a room during an experiment with a high intensity (high decibel), very low frequency, sound radiator which initially appeared to be very quiet, in fact barely audible because although it was"very loud" the frequency was below the range of human hearing,
So if someone is running a leaf blower in the forest and there’s no one there to hear it, is it still making noise?
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