High-end audio (high-fidelity stereo sound systems)
We currently have 5 audio systems at home in various rooms. The main music system is in a 600 sq. feet dedicated acoustically treated listening room and has brands such as: Spectral, Marten Design, Berkeley, Theta, Bryston, etc. This system is described in the article: Journal of the Audio Engineering Society, Volume 69 Issue 6 pp. 398-409, June 1st 2021.
Video and Home Theater
We have 8 video setups in various rooms. The main home theater is a thoroughly darkened and blackened room (using black triple velvet and Rosco black theatrical paint). Equipment: JVC high-end projector with a 12 feet screen; Lexicon MC12 and MC8 surround sound processors; ProAc and B&W speakers driven by multiple individual amplifiers (no multi-channel receiver). Home built stereo subwoofer system.
Concerts, plays, movies, etc.
I typically attend around 20 concerts and a few plays every year. In addition, I "attend recorded concerts" through my audio system at home. My musical taste is eclectic, but I have a special appreciation of western and Indian classical music, jazz, folk, and vocals.
Guitar
Initially playing mainly with a pick/plectrum, I now focus more on finger picking. I currently own a 1962 limited-edition Gibson acoustic guitar, a Cordoba nylon-string classical guitar, and a Fender/Squier Stratocaster electric guitar.
Art photography
Flickr link to some of my pictures: https://flic.kr/s/aHBqjzBmWF
Currently owned film cameras (all Minoltas): X700, XGM, XD5, and XD11. Currently owned digital cameras (all Canons): 1D, 6D, R8, and XSI-450.
Usual assortment of flashes, bellows, and other accessories, and lenses from 10mm to 2500mm/f:10.
Videography and podcasting
I co-founded the YouTube channel "Learning and Discovery LLC" that hosts my "High-End Audio Explained" podcast, which is shot using a studio setup at home. I also have been shooting videos of my class lectures and other presentations using a Canon R8, for eventually creating online courses.
Writing and poetry
I am currently writing 2 books, one on High-End Audio and the other about Teaching. I have written poems for birthdays, anniversaries, etc., for family members and friends.
Skywatching (amateur astronomy)
5 telescopes including a 10-inch reflector.
Carpentry
Standard collection of miter (chop) saws, table saws, grinders, pneumatic tools, etc.
Mostly do miscellaneous household projects.
Investing and trading (finance)
I started trading commodity futures (mainly silver contracts) when I was a student (in fact, it was the profits from this activity that led me into high-end audio). I then progressed to algorithm-based derivatives trading of non-equity (European) index options. I now hold only passive investments: S&P 500 and other index funds!
Health and Fitness
During the COVID-19 pandemic, I transitioned from commercial gyms (YMCA, etc.) to setting up a comprehensive gym at home. I eat a relatively optimized diet and practice time restricted eating ("intermittent fasting" for~16 hours).
Sailing: American Sailing Association certified
I don't own a sailboat but mostly sail rental boats in Florida every year.
Cars (including repairs and restoration)
During the pandemic, I fully restored at home the suspension and steering of my 2000 BMW 323ci coupe: shocks, struts, control arms, stabilizer links, tie rods, steering flex coupler, sway bar bushings, engine mounts, transmission mounts, and front-end alignment.
Current cars: Mercedes S-Class (S550), Porsche (full electric Taycan), aforementioned 25 years-old BMW (naturally aspirated straight-six with manual transmission). My first car was a 1975 Dodge Charger; as I recall, it had a 6 liter V8 engine and gave 9 miles per gallon!
Motorcycling (this hobby has been dormant for some years)
Motor Cycle Safety Foundation member
The last bike I owned was a Honda VFR750F "Interceptor"
Scuba diving and other water activities (this hobby category has been kind of dormant for some years)
PADI Open Water Scuba certification
American Red Cross Lifeguard certification
Water Polo--I was on my university's water polo team a lifetime ago!
House, furniture, decoration, DIY home repairs, etc.
Plumbing, electrical, garage, HVAC, sprinkler installation, etc.