What is it that makes Honda (and similar) "suitcase" portable generators so quiet? 1

[LMF5000]

I have a very inexpensive 1000W 4-stroke inverter generator (Zipper ZI-STE1200IV) that's not quiet, but not noisy either. It's quieter than the normal generators that run at 3600rpm, but it standing next to it requires raising your voice a little to hold a conversation. Having gotten used to its level of noise, today I was blown away after encountering a Honda EU2000i powering a mobile fridge in a local market. First time hearing one in person. It was literally quieter than the sounds of people's voices nearby!

So, my question is, what are the factors that make the Honda so much quieter than mine?

Thus far I've concluded that it's probably not the "inverter" aspect. Mine is an inverter unit too, and it idles at 4000rpm. The Honda also idles at 4000rpm (3000rpm with eco throttle on).

The differences I've uncovered so far are:
- Mine is 54cc, the Honda is 98.5cc
- In mine the engine is only lightly covered by some plastic and an open frame, in the Honda most of the engine is covered by the dense red plastic panels
- Mine uses an overhead valve (OHV) engine, with a gear-driven camshaft near the crank, and pushrods to drive the valves. The Honda is an overhead valve engine with a camshaft in the cylinder head driven by an oil-immersed rubber timing belt.
- Different exhaust design? (perhaps someone can enlighten me here)

Anything else I'm missing?

 

[SwinnyGG]

- Mine is 54cc, the Honda is 98.5cc
- In mine the engine is only lightly covered by some plastic and an open frame, in the Honda most of the engine is covered by the dense red plastic panels
- Mine uses an overhead valve (OHV) engine, with a gear-driven camshaft near the crank, and pushrods to drive the valves. The Honda is an overhead valve engine with a camshaft in the cylinder head driven by an oil-immersed rubber timing belt.
- Different exhaust design? (perhaps someone can enlighten me here)]

You just explained all the reasons why the Honda is quieter.

In general terms with any engine noise produced above the idle level is a function of load. So you can't necessarily compare your generator to any other generator unless the loads are known to be the same.

 

[Tmoose]

Once the exhaust is silenced quite a bit, Intake silencing becomes necessary.

189 Euros ( $205) vs 1000 US dollars. Some of that probably went legitimately towards Honda engineering's sound reducing efforts.

 

[LMF5000]

I can distinguish which component of the noise is there due to load - essentially the fuel/air charge is larger, the pulse of sound from combustion events is stronger, so the exhaust sound is "deeper", more full-bodied, and more forceful. I learnt the difference from listening to a regular generator under varying load, where the rpm stays fixed at 3600 (so pitch stays constant) while the sound gets stronger as power output increases.

My question is more to do with the baseline noise at idle with no load. Granted the loads may have been different, but assuming the fridge the Honda was powering was maybe 200W (just an estimate based on its size) it is still much, much quieter than mine. Still not satisfied I've uncovered all the engineering secrets.

 

[IRstuff]

It's supposed to be about 20 dB quieter, as specified, so it's designed and built to meet a tighter requirement. This may involve everything, from the innards of the cylinders to the actual sound insulation material.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[GregLocock]

Clever people spent a lot of time making it quieter, and put expensive solutions together. "Still not satisfied I've uncovered all the engineering secrets." correct. First you need a good knowledge of acoustics and vibration, then a good understanding of structures, and engines, and then you'd find there aren't secrets so much as application of known techniques and design details.

One obvious point is that the engine may be mounted on rubber bushes to the frame. The stiffness of those bushes can be optimised to minimise the transmissibility of vibration.

The Zipper appears to be open underneath, the Honda is fully enclosed. That's probably 5 dBA without even breaking a sweat. If you fully enclose the Zipper then it will overheat.

Cheers

Greg Locock


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[SwinnyGG]

My question is more to do with the baseline noise at idle with no load. Granted the loads may have been different, but assuming the fridge the Honda was powering was maybe 200W (just an estimate based on its size) it is still much, much quieter than mine. Still not satisfied I've uncovered all the engineering secrets.

My first reply was a bit on the snarky side.. but still.

Your list of differences (full enclosure with robust materials, exhaust design details, differences in internal engine design) ARE the 'engineering secrets' which make one generator quieter than another.

Greg's points about isolation of the power unit and sound reflection off of the ground are valid as well.

In short, little generators are not terribly complicated machines. Honda certainly has a lot of experience designing good ones, but their nice little gensets aren't jam packed full of secretive skunkworks technology.

 

[Tmoose]

Back in 1973 the US Gummint felt then current street, dual purpose, off road and mini-bike motorcycles' noise production was reasonably well described thusly.
"With the reduction of exhaust noise over the past few years, noise radiated through the intake system is nearly equal to the noise radiated through
the exhaust system for all motorcycle sizes. They both correspond to throttle opening, engine speed, number of cylinders, engine displacement and engine
load, and are the two predominant noise sources for most modes of operation."

https://www.gpo.gov/fdsys/pkg/GOVPU...VPUB-C13-6027aa0c351dace7992ac3b748fc0b1a.pdf

Anyone who in their mis-spent youth had a car with a V8 and a 4 bbl carb likely ran with an unsilenced air cleaner at some time, and remembers the intake moan fondly.

https://www.youtube.com/watch?v=21NRsuVPrqQ

 

[LMF5000]

jgKRI - so why are the manufacturers of cheap generators (aka "Chinese knockoffs") not implementing those features as standard to tap into the silent generator market dominated by Honda?

Greg - well-spotted! Makes sense too. Do you really think it will overheat? The cooling air intake is the grille around the recoil starter and the outlet of said air is around the muffler through the grille on the exhaust side (opposite side to recoil starter). Flow is left-to-right if you're looking at the side with the electrical outlet. Plastic channels direct air around the cylinder head - there doesn't seem to be significant flow around the crankcase, in fact the ground clearance is only around 5mm. I'm actually tempted to cut a piece of sound-absorbing mat so size and press it into the space underneath the engine as an experiment!

Tmoose - I love induction roar. For many months, I put up with the increased fuel consumption and poor low-speed torque (mushy throttle response) of a K&N cone filter just so my car would make that roar and I could hear the "psssht" of the stock recirculating blow-off valve. Eventually went back to the stock panel filter to get back the crisp throttle response, but here's what my car sounded like when I still had the K&N:

https://youtu.be/XoZFnDGy4pk?t=29s

 

[SwinnyGG]

That's a question I can't answer from personal experience, but I would be that A) a lot of their solutions are covered by patents, and Honda is a company that can afford to defend its IP with veracity; B) Honda's solutions are all cost adders. Manufacturers of cheap generators almost certainly want their products to be as cheap as possible.

 

[IRstuff]

You answered your question with "cheap." Japanese cars in the 1980s were typified with tight tolerances, quality materials, and extremely good process control.

TTFN (ta ta for now)
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[hydtools]

See also Champion, Generac, Yamaha, Briggs&Stratton for lower cost Honda competition.

Ted

 

[Tmoose]

"tight tolerances, quality materials, and extremely good process control" can only improve a mediocre or flawed design so much.

The reverse is also true.