It's been a while since I first brought this question and the progress has been slow for a number of reasons. First was actually getting hands on a generator that I wanted as they have been caught up in the supply train shortage and none were on hand for a while and then there was just a lack of motivation to get on it as the supplies I first wanted were not in stock.
As a result it has taken way too long for a small project but on the good side, I was given plenty of time to look over and sort through tons of options for materials to use and came up with lots of alternates which seem to work fine and I was able to get for very little other than using up lots of the "handy" stuff stacked around in the garage.
My wife thinks that may be one of the best things about the project as I did clean up/ use up a number of things that have been hanging around too long!
But I'm now down to calling it nearly done and wanted to let you folks know what I have done to get a generator that is big enough to do all the household items I consider necessary and some which I call just nice. As mentioned, being quiet was also a big priority as well as keeping it portable so that it is not out in the weather full time but can be rolled out and put together as needed.
For the portable part, I went with a Champion 4000 surge/3500 run watt dual fuel inverter hybrid generator so that I can store several 20 pound bottles of propane without worry about it going bad, then added the wheel set for portable and a DIY cover to control the noise as the larger size generator is somewhat more noise than some of the smaller that would not have done some of the items I wanted to run.
For materials, I had most of it on hand but wasted some effort and money trying to glue up sheets of a plastic foam type material but gave up on it and used simple layered sandwiches of cardboard, compressed fabric shipping padding in a lightweight wooden frame and pink foamboard as the outside layer.
The study I did says there are tons of ways to go with materials but one thing to keep in mind is that each type has advantages as well as disadvantage and we need to also keep in mind that each type does different things for the sound we want to control.
My first step was to make slanted walls to deflect the sound toward the ground, where I DID NOT want a solid surface like concrete which would reflect the noise but I used the ground as a second soft area to absorb the sound waves. A 2X4 frame laid on the ground with cardboard to deflect down into the ground.
Then the second space was filled with 2" thick compressed fabric that was used shipping materials which I picked off Craigslist. It is easy to work, reasonably lightweight , cheap/free and does a good job of absorbing the sound. Not hard to work, once I got around to trying the radial arm saw to cut it! A dust mask was needed but it was quick and easy!
Then as a semi- weather resistant outside, I used scrap 3/4 inch foam as another layer to both deflect a bit but also absorb the vibrations that reach it.
I have found that the exhaust is not really a big problem after getting to this point as I simply let it out inside the cover and use more venting air to carry the heat out. I had thought to add a muffler on a 1/2 inch pipe but find it not needed. The venting is critical for this to work but turned out to be quite simple as I had things on hand. A meat thermometer shows the exhaust air as just short of 120 degrees, which isn't bad when we have 94 ambient today!
For venting, I knew I wanted plenty of air and one of the things that worked really well for that was a surplus fan from an old microwave! They move a lot of air and the 110ACV worked out handy due to having plugs on the generator face for easy access. I had to design a box of plywood on the side for pushing air in so that it did not leave the motor in the hot air coming out, then also a vent on top set up to allow for air to come out but not in a direct line so that sound waves would follow. Air easily flows around corners but sound doesn't!
So the result is one 2X4 frame laid on the ground, four side sections leaning in and one top laid on it all. Somewhat weird looking pink that will eventually get painted but it all lays down flat in storage and the generator rolls inside very nice. One of the hangups on the progress was getting the interlock switch for the outside breaker panel as they seemed to be extinct for some time!
It fits what I wanted at just under $600 with sound readings that I love!
Nearest property line, which is also one of the neighbors most likely to tie on if we need it is 52 DB, at the sidewalk in front 40 DB and in the house, nearest bedroom, around 10-15db but hard to measure as my breathing is picked up too well at that low level!
Less noise than the average lawnmower!
I'm happy and I'm done!!!