I went to a local Bed Bath and Beyond to find silent or near silent humidifier. Salesman introduced this Air-O-Swiss Ultrasonic Humidifier as the best machine on market. He added Venta-Sonic does the same job but costs $50 less, and all other brands can't compare. I bought both units to compare. Air-O-Swiss is a clear winner, hands down.The two machines sat side-by-side. It's clear immediately to everyone that Air-O-Swiss is quieter. Even at highest setting, Air-O-Swiss Ultrasonic Humidifier ' noise level and frequency are lower than Venta-Sonic's, and they blend nicely into background. They don't give me headaches as Venta-Sonic. At lower settings, Air-O-Swiss Ultrasonic Humidifier can be virtually silent. With Air-O-Swiss Ultrasonic Humidifier on, I slept very well. The next night was Venta night. Unfortunately, the base machine noise was just as bad as the first unit that I returned earlier for noise problems. I tried to go to sleep with it on but after a few hours, headaches and agitation from the noise made me shut it off and switch on Air-O-Swiss and slept through afterwards.
I kept on alternating units days and nights to observe results from continued operation. After three days, Venta-Sonic unit began to add that strange squeeking noise. Air-O-Swiss gave consistent good near silent performance...and going strong still. Just based on noise-level alone, I had to return Venta-Sonic even though Air-O-Swiss Ultrasonic Humidifier costs $50 more. But that extra costs are further justified by the following:
1. Consistent Performance - I can put Air-O-Swiss Ultrasonic Humidifier on automatic mode with preset humidity level before I go to sleep, when I wake up, my bedside humidity reader (far away from the machine) has within 1% margin of error to the preset desired level.
Venta-Sonic however, I can put it to MAX settings, and I get only around 32% sometimes and other times anywhere below 50%.
2. Greater Output Capacity - My bedroom is 300 square feet+, half of 600 both machines claim can cover. Air-O-Swiss comfortably reaches my desired level (b/w 40% and 50%) with lower settings (It can go as high as 75%, I only set it up to 50%). Venta-Sonic labors over 8 hours at MAX settings and gets me LESS humidity! It won't get me above 50%.
3. Ease of Use with Digital Control - I like Air-O-Swiss Ultrasonic Humidifier
' Auto Mode with Desired Humidity Setting. The machine adjusts output automatically. Venta-Sonic only has two dials, you'll have to experiment for a while to find the optimal settings. As soon as atmospheric humidity changes, which can be daily or a few hours, you'd have to re-adjust again...that's like shooting darts in the dark all the time, you can get close if lucky but never on target.4. Better Mist Venting Notch Design - I put both machines on 3-feet-tall dresser. Air-O-Swiss Ultrasonic Humidifier notch is tilted higher than Venta's. This means when operating cold mist, Air-O-Swiss Ultrasonic Humidifier 's disappears into air vs. some Venta's still hit the floor - not enough to form condensation but less efficient in humidifying - perhaps that contributes to Venta's lower output previously mentioned.
5. Better Craftsmanship - Venta-Sonic is a notch below Air-O-Swiss Ultrasonic Humidifier , appears to be made simpler and CHEAPER.
Filter changes and clean up are similar. Venta needs to change filter cup. Air-O-Swiss Ultrasonic Humidifier needs filter cup and once-a-year silver stick change. Both are fool proof. Venta filters are more expensive but Air-O-Swill has extra silver stick. Cost-wise it's similar. I like Air-O-Swiss Ultrasonic Humidifier 's option of replacing resins - just dump old resin in filter cup and put new packet in and you get a NEW filter - this cuts cost by almost 65% and less trash for the environment.
Water tank design is similar. Both fills water upside down. I still prefer Air-O-Swiss because the top is more leveled, easier to sit in sink or bath tub than Venta's tilted top. When moving Venta-Sonic, water spilled between base and tank. I had no problem with Air-O-Swiss.
Anything Air-O-Swiss Ultrasonic Humidifier can improve? Sure! The humidity reader on the machine is adjusted about 13% lower than actual average room humidity. They probably did it to ensure average humidity far away from the unit reaches target, but I think they can do so internally without having to show it. It would be a mistake to read the room humidity off that machine.
After I got the machines, I googled on both. There was one review elsewhere saying that Venta-Sonic broke after a month and half, out of store 30-day warranty and owner took a loss. Air-O-Swiss has 3 year warranty, if I remember correctly, Venta 1 year.
The trouble I went through is worth the finding of the right humidifier for me. Hope this helps those with similar concerns!
I first purchased a tear drop shaped Humidifier (made by the same company) for my bedroom. I loved it so much, I wanted to have another one for my home office, so purchased this 
We live in an arid conditions in Las Vegas, the winters here are pretty hard system (low humidity, dust devils, hard water, etc.) DH and I developed a dry skin after a few winters, so we bought humidifer of well-known pharmacist in desperation, poor train, we should have learned it! No filter, noisy, well-known left white mineral powder size of furniture (including distilled water), not to mention it also left us with a terrible smell and taste of our mouths in the morning ... Yuck!