Ventilation grilles/registers

#1

Hi all,

Long time reader/first time poster.

I'm in the process of building a multi-purpose mixing/recording room in my garage and I'm looking for some advice regarding supply and return grille/registers.

I'll level with you here, I put very little consideration into the registers themselves during planning and it wasn't until I added a cheap domestic grill to the return duct and switched the fan on, that I realised this was a factor I'd missed.

I'm struggling to find a supplier here in Australia that provides technical data on these products (in the way Nailor or Titan do in the U.S).

I suppose my questions are what should I be looking for? Are there certain designs/products that are more conducive to acoustic applications?

Please feel free to merge the thread if there are others discussing the same. I couldn't see any and I'm at my wit's end trying to find a solution!

Thanks in advance.

#2

most low noise registers also need low noise air movement - so if your air velocity out of the register is still "fast", then step one would be to reduce the speed - expansion of the air volume is one way to do it after reducing the fan propulsion at the air handler. in general, you need large openings and preferable some meaasure of directing the air so it goes where it is effective.
sometimes this is simply a drop on a large mix console (=heat) and the cool air dropping and the warm air rising mix and form a stable temperature which is comfortable. in other cases, you need to get the air past the equipment, etc into the wider space to ensure a good flow and mix.

#3

gullfo wrote:Source of the post most low noise registers also need low noise air movement - so if your air velocity out of the register is still "fast", then step one would be to reduce the speed - expansion of the air volume is one way to do it after reducing the fan propulsion at the air handler. in general, you need large openings and preferable some measure of directing the air so it goes where it is effective.
sometimes this is simply a drop on a large mix console (=heat) and the cool air dropping and the warm air rising mix and form a stable temperature which is comfortable. in other cases, you need to get the air past the equipment, etc into the wider space to ensure a good flow and mix.

Thanks Gullfo - appreciate the reply.

I'm about to switch out the inline fan for a lower-powered one as I miscalculated - by a long way - the required airflow when converting from m3/h to cf/m.

Hopefully, this goes some way to improving the situation.

For context, my design is very basic. Two baffle boxes - one pulling air via an inline fan, the other pushing air in passively (no fan).

Even with the overpowered fan, the airflow noise is almost nonexistent without a grille but is incredibly loud with the grille on - supporting your point above - so I'm looking for some ideas on the best way forward. What types of grilles are best supply/return? Diffusers, egg crate style etc.

Am I overthinking this part? I'd love to see/hear what others use as registers and any thoughts on how crucial this component of the design is once a suitable air speed has been implemented.

#4

i would consider using 2 low speed fans one on intake and one on exhaust. filtering on intake (as a general rule i recommend using HRV/ERV product for energy, long term reliability and filtering vs diy fan assemblies). the use of the two fans will help balance the air flow and can also help reduce noise (although in your case it seem like the vents are the real issue here)

most studios i design - i use a number large slot diffuser types - 4+ 1" slots x 36-48" - this may be overkill for your project.
e.g. https://www.hvacquick.com/products/resi ... -Diffusers

so something like this may be more correct:
https://www.hvacquick.com/products/resi ... ar-Grilles

#5

Thanks Glenn - this is good info and much appreciated.

#6

Jumping in on this older post because I’m curious how others handled noise control with their grilles. I’ve been testing a few low‑resistance models, and the airflow is great, but some still add a bit of hiss once the system ramps up. Has anyone found a type or placement trick that keeps things quiet without choking the air?

#7

Hi there, And welcome to the forum!

Sorry about the delay approving your post and responding: I had a major crash on my main notebook on Christmas day(!), where I had all my e-mail accounts, and it took a while to get it up and running again, and recover the backups... Technology is wonderful until it fails... sigh!

Regarding low-nise HVAC grills: more important than the grill ("register") is the airflow velocity going through it. Try to keep it below about 300 fpm, and you should be OK with noise. If it is still an issue at 300 fpm, then lower the velocity even more. Under 200 fpm shouldn't give you any hassle.

Have you measured or calculated the speed through yours? If it is under 300 fpm and the noise is significant, then it might not be caused by the register at all, but rather by something upstream, inside the HVAC duct itself. If you take out the register completely, leaving just an empty hole, and you still hear noise, then it isn't the register.

If the flow is slow, and it IS the register causing it, then the noise might also be caused by a sudden change in flow direction: is the HVAC duct leading into your register relatively straight for a few feet, directly into the register? Or does the flow direction change close to the register?

Hopefully one of the above suggestions will get you on the right track to fix it.

- Stuart -

Soundman2020 - Studio Design Forum