Those magical days when the HVAC is off

@ostemo8- your original post and the comments it has generated have raised a number of different issues relating to different kinds of "noise." When I was doing the whole house generator, I was looking at the current draw of air conditioners- some of the older type units pulled a huge amount of current on start-up- in the neighborhood of 100 amps! Newer units are not only far more efficient but depending on the type of compressor for the air con, can vary significantly in start up power and running power draw.

You have gotten some good input on noise reduction within the listening room relating to HVAC and overall noise reduction in the listening room. You may not have the luxury of starting from scratch in terms of construction--my room was done within an existing 1880s house that had been completely restored to high preservation standards circa 2004. Some of the things--insulation for example- were done by the previous owner, but the air conditioning units (and furnaces, along with electrical work) were all done by us after we purchased the home in 2017.

One thing I suggest before people get spendy on power accessories for hi-fi is to have an electrical system "audit" done, preferably by a commercial level electrician. I have had the meter pulled by the utility to check the meter block (corrosion can be an issue), and to go over the main service panel, both for integrity and wiring. When I did the electrical "subsystem" for the hi-fi, I specified a sub panel with copper buss bars. That is what feeds the big iso transformer, via 4 gauge wire, which can help with some electrical "noise."  This additional service is then fed from the output of the iso transformer to the listening room in 4 gauge to another service panel adjacent to the listening room, where the dedicated lines (10 gauge) are fed.

It is certainly possible that the HVAC system is contributing to electrical "noise" on your hi-fi but it probably depends on the particulars of the HVAC units, their age and how they are wired, all in relation to how the hi-fi electrical is wired. Most modern houses are 200 amp service, but the reason I like an "audit" is that a lot of problems start with corrosion, bad wiring, deteriorating service panels (in Texas, it is not uncommon for the service equipment to be outside, not in a basement), placing further demands on your electrical system given the elements.

When I had the back up generator installed, I also consulted Rex, one of the guys who helped Fremer sort out the electrical system nasties in his system. Rex can do this remotely, for a modest fee, using photos, drawings and phone calls.

Otherwise, I think you’ve gotten some good input here, including from the contractor @rock-on for all the different factors that go into new construction.

I’m no guru, I’ve done a number of dedicated rooms over the years and learned from each experience. A lot of this is know how, rather than just buying a black box. Because my house is old, and the floors are all longleaf pine (stuff that is now quite costly to find and replace), I also stiffened joists and added a subfloor where my turntable and front end is located. I still needed better isolation for a very high mass turntable (245 lbs), so had to resort to a big Minus K isolation system, which sits under an HRS platform. That does not seem to be an issue for you, so it is irrelevant but it does show the lengths to which you might need to go in some existing situations where you don’t have the luxury of starting from scratch.

Bill Hart

I use an oversized iso transformer (10kVa) for my main system, which draws very little current. The AC system also has variable speed compressors, not just variable speed fans, so once set temperature is reached, the compressors wind down and function as dehumidifiers. I’m in Central Texas, where air conditioning runs pretty much constantly. Until the building boom here, the grid was not only more stable, but very quiet. It is still quiet compared to where I lived in the lower Hudson Valley (old infrastructure) but much more "iffy" with the demands now being placed on it. FWIW, the outdoor air compressor units are at the opposite corner of the house from the listening room. 

We just finished installing a large 26kVA back up generator, and I had the contractors wire it in such a way that the electrical subsystem for the main hi-fi is not connected to the ATS for the generator (in other words, the system will not be powered by the generator if the utility power goes out). None of this came cheaply, but was worth it in my estimation for peace of mind. Given that my speaker system is 104db sensitive, I can hear any power or grounding anomalies and it is dead quiet.

The other aspect is ambient noise in the listening area. I measure around 32 db C weighed during the day. I can do more to quiet the room by using soundproofing, not just acoustic blinds, on the dormer windows facing the street, but usually don’t bother. I do not use "power conditioners" or noise trapper type tweaks, as such. The house is also very well constructed, old, longleaf pine and when it was restored, the insulation used (shredded denim in netting) was installed. Room to room dialog is almost impossible because of the construction/insulation methods. (Walls are shiplap, not just drywall).

PS: AC Infinity makes duct fan silencers if you hear air rush through your vents. I first got onto that company when I had a silencer box built for the air compressor that drives my tone arm. I was able to put together a relatively inexpensive fan cooling system with central panel and sensor for inflow and exhaust fans for the silencer box. Now, it appears that they are big on leaf growing equipment. Go figure, as they say in Jersey.