Silencer box measurments

Hello everyone, I am about to get into the phase of my build where i need to make my silencer boxes for the HVAC. I am planning on using 8'' flex duct up in the ceiling joist which is 11.5'' deep after the beef up with 2 layers of 5/8'' gypboard. I am planing on building one supply and one return for each room ,but i don't know what is the measurements for each side of the board used for the silent box? I know it has to has to have a few turns but how do you come up with the measurement of how big the box should be?

Rivernile wrote:

Hello everyone, I am about to get into the phase of my build where i need to make my silencer boxes for the HVAC. I am planning on using 8'' flex duct up in the ceiling joist which is 11.5'' deep after the beef up with 2 layers of 5/8'' gypboard. I am planing on building one supply and one return for each room ,but i don't know what is the measurements for each side of the board used for the silent box? I know it has to has to have a few turns but how do you come up with the measurement of how big the box should be?

it depends - what are the velocities in the 8" round (or how many CFM's are you going to be moving?) Rod

Rob , Its a three ton unit with a Air Handler ,i got it from a friend.

Rivernile wrote:

Rob , Its a three ton unit with a Air Handler ,i got it from a friend.

Wow - how the heck big is your studio? The tonnage of the unit tells me nothing about the air movement.......... However - there is one thing I know - and that is that the air handler for a 3 ton unit is going to need a heck of a lot larger duct size than 8" flex duct............ Something is very strange with this picture........... please provide more information.......... Rod

Hi Rob The my whole entire basement is 1400sft,but i am usining about 600sft of that for the studio area. Control room =12'-2.5'' X 17'-6'',Live room - 14'X17'-8'' aprox. The rest of the space is aloted for bedroom ,workout room,video editing suite and chill area. So i think the 3 ton unit could run the whole space.I will get the blueprint and email it or post it.

Can you build a soffit inside the room to run your flex duct through?

Hi Ted I have space in the ceiling/floor joist,like 11'' i could use to run the duct. My problem is the silent box itself.

The image above would represent a "silent box". Maybe a Silent Box is a specific design someone created? If you're going to remove a great deal of sound travelling through a duct, you'll need a significant structure. The soffit pictured above is easy to incorporate in many rooms, is inexpensive and very effective.

Some threads on silencer boxes that you might find interesting: viewtopic.php?p=70959#p70959 viewtopic.php?f=1&t=11542&start=5 viewtopic.php?f=2&t=9761&start=0 http://www.electricsuppliesonline.com/6siforroduld.html viewtopic.php?f=2&t=11485&p=89855&hilit=silencer#p89855 viewtopic.php?f=2&t=11508&p=96578&hilit=silencer#p96578 viewtopic.php?f=2&t=13821&p=97928&hilit=+silencer+ducts+might+look+#p97928 viewtopic.php?f=2&t=14136&p=100059&hilit=silencer#p100059 - Stuart -

Thanks Stuart I'll go thru them

Ok Guys im back with another dellema. So i figured out the silent boxes and my mesurements came to where it tightly fit between the existing cieling joist nicely and cleared my new ceiling also. But after i read through the threads i noticed that the silentcers are usually connected to the inner joist right where the out register would meet the inner ceiling. Now look at my picture and tell me how can i do this ,because my inner ceiling joist are 16'' o/c i can't fit the silencers in there. What do i do to not compromise my isolation ?How do i build the registers? Would building a box like the two bottom pictures cover for any sound isolation loss?

Hi there! got no experience at all in building it (yet) From reading articles and picture posts from other dreamers i sorted out that silencer should alow wider air flux even after the damping instalation inside to lower air speed; lets say 10% minimum (gess) ; damping angles should not alow a straigth path to view and sound...

Hi there, One should take in account that air speed inside the duct is critical to inside noise floor, the slower the flux the silenter it will be. the path inside the silencer at low speed will be less "whistled" To renew all m3 air in room flowing in a 8" pipe how long it would take? see engine specifications. dont ever use lower diameter diameter ducts than engine's hope i could help!