These headphones were disappointing. I bought them to use in a computer room that has a refrigerator size disk drive and an even bigger AC unit. These headphones do a good job of reducing the low-frequency noise but most of the high frequency stuff comes right through. As a result the noise reduction for me was about 20 - 30% of the total. I also tried them with a leaf blower and had the same results. They do seem to work well at taking out low rumbling humming noises like you would find in air travel but not for anything that has high pitched fan noise like AC units or vacuums.