John Sayers' Recording Studio Design Forum Archive

Let me ask one more thing.
what if the duct just before the register is bigger than the supposed 0.9 ft2 (that is calculated for the 270CFM)?
Then there is no need for a register at all, I can just use the rigid duct as is, right?

Soundman2020 wrote:That would work, but it doesn't need to be that thick. You can use 2.5cm thick insulation on each side. That allows you to get more hangers into the same space. On the other hand, given the expense of your core material, I can understand you wanting to make your hangers thicker! It will work OK as you are planning, so if the cost would be too high doing a larger number of thinner hangers, then it's fine to do fewer hangers with thicker insulation.

And I can now go with 3cm and 20kg/m3 dense material for each side of the homasote board instead of the 4cm 40kg/m3 and that will leave me space for more hangers.

What do you think, is that a better option?

Gregwor wrote:20 kg/m3 of fiberglass?

I know where I live Homasote is worth more than gold so I am using 2" insulation in my design to save thousands of dollars.

I found the 2.44m x 1.22m Homasote board that is 10mm thick around 10euros each, so is not cheap but it's ok.

Soundman2020 wrote: Therefore, the current best control room designs do return that diffuse field after about 20ms, or maybe 30 ms, or maybe even 50 ms in a large room, and that gives your brain all the clues it needs to figure out the room that it is in, and correctly interpret the acoustic "signature". As long as the "gap" is at least 20ms long, and up to about 50ms, your brain is happy: the room sounds natural, neutral, open, neither too dead nor too live, and you get to hear only the pure, clean, unmodified sound exactly as it came out the speakers, not colored in any way by the room, or by these subtle psych-acoustic effects.

[...]

So, the sound field that comes back at you from behind 20ms (or more) after the direct sound, also has to be at least 20 dB lower than than the direct sound, and it has to be diffuse, not specular. In most control rooms, that is achieved with a combination of acoustically absorptive surfaces (to reduce the level by 20 dB), acoustically reflective surfaces (to send a little bit of the sound directly back, but not much) and acoustically diffusive surfaces, to break up the sound into a diffuse field.

[...]

Now, if your room is bigger, then the ITDG can be longer: 30ms is good too! And you can also have a slightly lower level, such as maybe 25 dB down, especially if he room is large, ... as long as you still have an overall decay time that isn't too short for the size of the room.-