Extraction fans ?

I use ac infinity quiet as a 🐁

The quietest fan on the market is the S&P inline, Solar and Pilar I think they're called. Iv used them for several yrs now and the next accoustic box fan at the time was twice as loud.The home grow size are mostly less than 50db.Your hoover is around 100db.You can also make your own box out of anything from wood to cardboard.You'd be suprised how much effect a cardboard box has. Some fans have come close in recent yrs but I haven't seen 1 which a such a low DB rating.Reduce more noise by buying a bigger one than you need.The CFM which is the cubic meter of the air. Length x width x height.4ft length by 4ft width by 8ft height is 1mt x 1mt x 2mt is 400cfm which is around 4inch,I guess but you'd want a 6inch then reduce the speed by a separate controller but make sure its a variac controller as the cheap ones make the motor hum.

as people said, buy 2x bigger than you need and run it on half speed. i tried infinity line, very quite, was researching few british made ones, but really good rewievs having models will cost you 400£ plus controller, so i bought cheaper alternative 6 inch fan with 69pro controler from infinity. was doing grows in shared house, so basically renting hotel room and growing there, managed to pull 3 or 4 grows without anynone in house or neighbours realising what i was doing.

Terrabloom and ac infinity (puked in my mouth a bit) among others make good fans. an "EC motor" i think is what you want. This allows 0-100% control or at least 10-100% in some cases. Buy larger than you need and run at 50% or less. All duct fants are fairly loud when amped up. bigger sizes are obviously louder, but a 6" at 50% is probably quieter than a 4" at 90-100%. Having both an active intake and an exhaust can help, but i wouldn't bother on anything smaller than a 5x5 or 4x8 for that. A 6" should be fine for a 4x4 or 3x3. I recently used 2 at 25%,give or take, in a 4x4. That's only becaue i had extra lying around. i normally have them hooked up to a 10x10 - 2 6" intakes and 1 8" exhaust. 50-60% power does well. If you buy a duct silencer, that significantly increases CFM/power needs, so buy even bigger if you do that. You could also use insulated ducts that will cut down on some noise too. If you live in the same room you grow, this might be woth it, but otherwise just running a good quality fan at 50% or below will be fine if it is behind a closed door in a room you mostly stay out of. "they" say you want to have cfm rating (after you account for silencers, filters, duct length and number of 90-degree bends which all deduct from the fan's potential CFM) that is at least 1/3-1/2 of your tent volume. I'd wager this safely errs on the high side of "enough". I mostly adjust this so that my RH isn't much different than outside the tent. If i recall the recommendations for greenhouses is lower, so the greenhouse recommendation, if you can find a reputable source, is probably a more accurate guideline.

I find running a larger fan on low is quieter than running a smaller fan on high to get the same amount of air movement. I run AC Infinity cloudline t-8 And it’s pretty quiet on low. I have a 12 inch AC Infinityfan in my house and it’s super quiet on low. Some fans come fans come with a silencer. You may want to check that out. The carbon filters seem to reduce the sound a little bit, but the silencers make a big difference.

AC Infinity with silencer