In 2006 I built a full iso box for a new rig.
5/8" particle board, 3/4" plywood base, sealed door with glass, carpet lined…it even had wheels.
It took a lot a work and even looked fairly snazzy…but it was a colossal failure.
Firstly, instead of suppressing the computer noise into blissful silence, it actually converted it to a strange low frequency rumble emitted out the (necessary) rear thermal openings.
It actually took the acoustic energy generated by the computer, and made it effectively louder by condensing it and altering it’s frequency like a megaphone.
Secondly, it made any maintenance and port/cable access to the machine an absolute feggin nightmare.
I lived with it for about a month, trying various linings, portings etc, but just gave up and took it apart to use for shelving.
It was far more effective to get higher quality fans, high efficiency power supply and aftermarket CPU cooler, and hook all that up to the Zalman multi-fan speed controller I already had.
On my newer quad core build, components had advanced by miles to make them many times quieter than my previous machine. Hard drives, PSU’s and tower cases have come a long way. (Even the stock Intel CPU cooler was quiet enough to not require me to get an aftermarket one.)
On this machine, the BIOS also has fan settings for silent to high performance mode. Add to that my old Zalman fan controller and all I hear is a bit of fan noise.
Note: One component that has gone the other direction with regards to noise, is video cards. They come with small, high RPM fans that output only slightly less noise than a canister vacuum cleaner with dry bearings.
I replaced that nonsense with a Scythe heatpipe cooler and now my NVidia is essentially inaudible, and it doesn’t turn into a space heater when doing HD video transcoding or playback. (The heavy stock cooler was slapped on with a giant gob of thermal paste, and some of the peripheral chips weren’t even in contact with the cooler. Unbelievably shoddy assembly. Hardly a wonder the fan never spun down.)
You can get a proper iso box, but they are fairly big with usually sophisticated cooling systems, and cost a fortune. Fine for a big production studio.
But, for a project studio modern comps are fairly quiet and can be made near silent with quality aftermarket components like fanless PSU’s, SSD’s and coolers.