6" vs 8" fan noise difference?

[Oxygen_Man]

Im just wondering what the decibel level or noise difference is between a 6" and a 8" inline fan. All the videos online are showing the same decibel levels for 8" and 6" fans, some 6" have even higher db levels but to me, that dosent make any sense. so, from you guys that have used both 6" and 8" is there a difference in the noise produced? there would be insulated ducting on both intake and exhaust.

 

[Coconutz]

If you need a 6" get an 8" vortex and reduce the speed. You wont hear the thing.
I just keep my duct runs clean and run them full speed. I barely hear my 6" or 8" vortex fans.
Not much of a difference when they are connected to a duct besides the rush of air.

 

[Mate Dave]

It would depend on the make and model of fan, acoustic fans are quiet but all fans cause vibrations. I can't tell the difference between a 6" High powered RVK fan and a 8" Airforce acoustic when filtered and ducted, A silencer will stop any volatile air before it is expelled from your growroom. Fans are noisy period! It is of my opinion that ventilation should be adequate and working at full capacity all day and night.

Box fans or acoustic fans can be trickier to mount in some situations so see what you have to work with. I have never used a 8" RVK but I suspect without a box of acoustic ducting attached to its out air it will sound like a afterburner on a combat aircraft and if not screwed down will move around the floor by itself!

 

[Oxygen_Man]

i was looking at the s-line vortex ones. but yea, Im def wondering if 8" is louder than a 6" all variables the same(as in both had silencers or no silencers and both had insualted ducting or not. the other thing is, It will have carbon scrubber on one end and duct insulated on other, so that will slow air speed also. Is a 6" vx 8" going to have more of a "sucking sound" with a carbons scrubber on its end than a 6" also? I also do not want to dial fan speed down. i want to buy either 6 or 8" but not use fan speed controller.

 

[Harry Gypsna]

I have a 6 inch high power, and it is actually louder than the 8 inch. It uses the same motor as the 8, but in a 6 inch housing, so it is noisier.
It depends if the 6 inch is high power or not.

 

[Coconutz]

The reason some smaller fans make more noise is because they use smaller blades with higher rpms.
I havent used the S-Line, but Im sure they are killer. Vortex makes great fans, but without reducing the motor they are going to make noise.
The 8" moves twice as much air so the turbulence is a lot louder.
As long as the duct run is clean and there are no bends you shouldnt notice much of a difference in the fans when dimmed. Most of the sound you hear will be rushing air. If you reduce the speed of the 8" it will be the same wooshing sound as the 6" moving the same amount of air, with less motor noise.
What you have to watch out for are bends in the duct. That will increase the noise of turbulence and create some back pressure that will make the motor make strange noises.
The scrubber wont making any noticeable sucking sound. If there is any sound near the scrubber its washed out by the oscillating fans. It seems like the air going through the filter is deadened.
If you want to go without reducing the speed you might have to try out a few fans before you find what works best for you. Youd need to match the fan perfectly to balance the cfm vs motor noise. The old Vortex wouldnt be your best choice if thats what youre looking for.

 

[Oxygen_Man]

thanks coconutz. There has to be bends in the ducting in my case, alot of bends, atleast 4 bends 90 degree. would a 6 or 8" be quieter with motor noise and wind turbulence with all these bends, duct length equal length on both....?

 

[Coconutz]

The more air you push, the louder it will be.
With 4 bends the turbulence should be louder than the motor noise anyway.
Use the duct elbows for you bends and try to keep the duct straight and level from point to point without any sagging. Use the rigid stuff instead of the flex wherever you can.
If you use a silencer near the exit point you can cut down on turbulence noise at the exit if you need to, but it wont make it silent.
Try to keep the bends as far from the exit as possible if you need to reduce sound there.

 

[Oxygen_Man]

I looked at the hyper phresh fans and the 720 cfm 8" has a cfm drop from 710cfm down to 360 with a massive 8"x30" filter. If I get a 6" s-line, the cfm is only 327. Will a giant carbon scrubber on the 6" still lower the cfm that drastically. A huge carbon filter on the 8" hyper fan lowers cfm by 50%, and in the monster garden videos it voer powerd the s-line, Im im wondering if the 6" cfm will drop to 150cfm with a carbon scrubber, and even less with teh bends I need....maybe 8" s-line is the way to go? also will using 8" ducting on a 6" blower help reduce noise from the exit?