I bring this up because it has substantially improved my listening room by keeping city noise out, thus quieting the room considerably.
My home, built in 1968, is in a busy metro area, a mile or so from freeways and downtown. Turns out that 50 years ago they were using pink fiberglas insulation batts, but not much of the stuff, and the bays between the joists were hardly ever sealed.
This lets in noise (and stink-bugs) and even tiny amounts of airflow destroy the insulating capabilities of the fiberglas.
So this week I had an insulating firm come in and re-insulate my place with “firm-pack cellulose”, i.e. ground-up fireproof bugproof paper, that they blow into the walls through a hole into each bay between joists, until the space is firmly packed with the stuff. It seals off any air/bug leaks, absorbs quite a bit of city sound, and gets the walls up to R-19 insulating value.
I’d recommend this to anyone with a similar background noise issue - it really kills a lot of outside and traffic noise for around the price of yet another hardware component in the hifi stack.
That sounds like a great improvement.
Our neighborhood used to be calm and quiet until WAZE starting routing drivers through it and we have a lot of mid-life crisis loud motorcycles being purchased and driven in the area.
I have never understood how it can be legal to purchase something that, when operated, can be heard inside every home. Well, I guess airplanes and helicopters also qualify.
The exhaust noise on the typical Harley is illegal, but noise ordinances are rarely enforced.
These bikes are actually fairly quiet stock, but few Harleys leave the dealership with a stock exhaust.
Took another step toward quieting this old house over the weekend.
The issue was that now that the house lets in less city noise, the sound of the HVAC became more apparent.
I addressed this by lining the large metal intake plenum (2’x2’x18") to the furnace with dynamat to cut resonances with the fan motor, and then further used some leftover heavy floor carpets from a pervious car to cover the plenum and intake duct, for absorption. This carpet is about 3/4"thick and has a 1/8" rubber backing - it’s heavy carpet.
The result is very pleasing - I can no longer tell when fan-only circulation is running more than a couple of feet from the intake, and can barely hear the heating/AC running while in the listening room.
An excellent Saturday project.
Would you mind sharing some pictures of where did you do your improvements. I am fighting myself with a noisy HVAC that I wish will die soon for a quieter replacement.
Not to high jack this thread, but we just moved into an old house built in 1951. It’s built like a brick shipyard! LOL At some point, the windows were all replaced with nice double-hung units which keep out a lot of road noise. And the HVAC system which I was told is still using the same air handler from 1977, is super quiet. Even standing directly under it in the hallway, it’s just a faint rumble. Out in the “music room”, the only way I can tell the unit is on is when I feel the nice cool breeze blowing down on me.
So I feel that we are very fortunate for the quietness of this house. The only thing that stinks right now is that where I have the listening position, it’s right smack in a null point for the bass. If I lean forward a foot or stand back a foot from the listening position, I have really good bass. But in the hot seat, not so much… Unless the music is fairly bass heavy, then it just loads the room and you have no choice but to hear the bass. Though the bass is always felt through the floor and couch!
No HVAC system is like any other HVAC system.
Mine is like many less-expensive homes, with a single large intake covered with a slatted register, rather than several return ducts in several rooms. My intake register is 2’x18" located in the ceiling of a hall that runs the length of the house.
I’d suggest removing your intake air filter (if it has a straight-in register in front of it) and using dynamat or equivalent /and thick carpet to cover everything you can see without restricting the airflow.
If it’s not like that, cover all the outside parts of the HVAC sheet-metal ductwork that you can access without making ugly, with dynamat-like-stuff to kill resonances. In my case, the intake plenum was enough oversized that I could also carpet it on the inside for absorption without blocking the flow.
Experiment.
One can also experiment with different MERV ratings of the intake air filter. Going from MERV 8 to 11 can make a substantial reduction is noise and not place too much load on the air handler but don’t over do it or wear on the motor will increase with the restriction (and less air flow, of course)
maybe consider, that the material, in this case, carpeting will mold over the seasons…it will breed with the humidity during the hot summer…
there are many materials that are inert, as an alternative…
" carpeting will mold over the seasons… it will breed with the humidity during the hot summer…"
That’s just silly.
a) Very little carpet is not synthetic these days, and nylon with a rubber backing doesn’t “rot”
b) The carpet in the intake plenum is only exposed to the return air, i.e. same dry air as in the rest of the house.
c) Has your carpet rotted? I don’t live in a swamp, so mine hasn’t.
it will trap moisture; it’s a perfect breeding ground…that’s the rub…
and if you lift your rugs…the black areas are the same flesh eating bacteria – black mold…
doesn’t matter if carpeting is organic or not…
Complete nonsense.
If I look under a rug or carpet I see clean wood floor, not black mold. I don’t live in a swamp, so I don’t get condensation on my walls, floor, or furnace. If anything, I’d like to raise the humidity in my home most of the year.
I recently watched the removal of hundreds of square yards of ten-year-old carpet from a gym, on a plywood floor on concrete - no mold.
Synthetic carpet does not "trap moisture"or absorb it any more than fiberglas insulation - perhaps you are thinking of old-style wool carpet with jute padding, maybe on a damp bathroom floor?
Have the carpets in your car rotted? They certainly see a lot more moisture than anything in a house.
I can’t remember, are you running a sub in the system? Though the room impacts the bass response you hear in a specific spot, you should be able to manage and tweak this with speaker and sub placement. Room does have the largest impact on bass response, but moving the sub around can help dial it a lot.
jamesh - wrong thread?
Oops, sorry! 
I get a little excited when talking about bettering bass response. I’ll leave…
James, since you just got kicked out of the thread (LOL), I’ll reply to you via email about the subs and room issue. 
Just as follow-up, I made a smaller improvement today, re. noise transmitted through the windows. My living/listening room has a wall of four 30"x8’ windows behind the speakers. I have 3D-printed diffusors directly behind the speakers, but an audible amount of traffic noise was getting through the double-pane windows.
I got a 12"x12"x1/8" sorbothane sheet for each window, and plastered it to the outside of each window below vertical center. The stuff is very sticky, and seems to be durable, as I’ve had one sheet stuck on a window for a couple of years.
The theory is that the fairly-thin glass in double-pane windows is basically a large drumhead membrane held around the edges, and it resonates to low-frequency noise and creates harmonics as well. The sorbothane damps the resonances in the glass, and thus reduces the amount of outside noise that gets through to the inside.
One might think that this would be only marginally effective, but I’m pleased to report that the amount of audible traffic noise is somewhat reduced, to the point that freeway noise is really no longer audible in the room.
Here’s the stuff I used: https://www.mcmaster.com/sorbothane
Too bad it’s Black, but in my setup the squares are mostly behind a TV and the diffusors, so it’s not really visible inside the room.
In town where I live, my sense is that many of the offenders are actually police who ride bikes with straight pipes.
I’m out of the city and now that I’m in the burbs it’s the darn crickets(and other bugs/creatures)!