Baement Ceiling

[gtrguru]

My question wasn't answered by searching the web, but I knew you slutz would know.

Basement studio, empty 8" floor joists as a ceiling. Looking for good acoustics first, sound deadening second.

• Option 1 Fill with 6.5" fluffy fiberglass and cover with fabric.
• Option 2 Fill with 8" of Rockwool/Mineral Wool and cover with fabric.
• Option 3 Option 1 or 2, but drywall instead of fabric.

[lakeshorephatty]

Fabric will be better than drywall for acoustics, but worse for isolation likely. other than that i want to know answers too. I'm going to be doing something similar too.

I think if 6" or greater the density of the material isn't as crucial and sometimes less dense is better but I'm no expert.

Actually what i was curious about is which of these options is better, both covered with fabric:

- 6 inch of roxul
- 4 inch of roxul with 2 inch air gap above.

I've read that having the air gap actually can increase the bass trapping but I'm not really sure. I'm going to keep searching...

Russell

[gtrguru]

I've read the same about the air gap. I was thinking mineral wool, space, mineral wool.

[SAC]

Thus far there are elements of isolation, LF bass trapping, and mid/high broadband absorption characteristics being mingled together.

Not knowing the intended use of the room, dimensionless, orientation of joists, etc....I will assume a general use as a critical listening/control space.

My first suggestion is to obtain a measurement package like RommEQWizard or FuzzMeasure or ARTA in order to make LF modal waterfall plots as well as ETC responses to identify the specular reflections in order to determine what exactly is actually going on in the space that needs to be treated.

No sense chasing snipe that are simply assumed to be there.

If all you need is the control of first order specular reflections, a 4 inch panel suspended from the joists (optimally with a gap up to 4") will work fine.

On the other hand, you can fill the space between the joists and cover the material/space with a form of orchard netting or chicken wire to provide support and cover that with a stretched flame proof cloth covering. I am not as keen on this solution as the joists will act as reflective barriers of which we do not know exactly how they will influence the behavior based upon their orientation, spacing, etc. Measurements would address this.

If you require more LF modal control, you will need to utilize other/additional methodologies - as what has been proposed will do little for that.

But I hope that gives you a bit of a direction regarding the use of a cloud to mitigate first order reflections.

[Ethan Winer]

Originally Posted by gtrguru

• Option 1 Fill with 6.5" fluffy fiberglass and cover with fabric.
• Option 2 Fill with 8" of Rockwool/Mineral Wool and cover with fabric.

Either material is fine, but fill the entire 8 inches. No sheet rock unless isolation matters more than acoustics inside the room.

--Ethan

________________
The Acoustic Treatment Experts

[gtrguru]

Thanks Ethan! I was talking to a gentleman at my work who is LEED certified and he suggested that leaving an air gap between 2 pieces of the rock wool might be the best way. 2" of rockwool, 2-3" air gap, 2" rock wool, sub floor.

Any thoughts?

[dainja]

Short note: building code is not respected if fibreglass is used between floors where I live, because the R value can cause moisture problems (the two floors will not have the same temperature...).

For this reason I used roxul safe n sound in my studio ceiling and Walls. Passed inspection and seems to work well.

[Glenn Kuras]

Originally Posted by gtrguru

Thanks Ethan! I was talking to a gentleman at my work who is LEED certified and he suggested that leaving an air gap between 2 pieces of the rock wool might be the best way. 2" of rockwool, 2-3" air gap, 2" rock wool, sub floor.

Any thoughts?

The air gap is like a free lunch if you can not afford to fill the full area. Filling the full area will absorb a bit more low end.

[Smithcok]

The air gap (much discussed in other threads - I'd search around) comes into play when you are spacing an absorber off of a reflecting surface. However, assuming you aren't at the point where you are worrying about over damping the high end in the room (among other concerns), I'd just get the full 8" of glass fiber up there.

[Ethan Winer]

Originally Posted by Smithcok

I'd just get the full 8" of glass fiber up there.

Exactly, as I said.

Plus, an air gap between layers of insulation as described is not so useful.

--Ethan

________________
The Acoustic Treatment Experts

[jhbrandt]

Originally Posted by gtrguru

Basement studio, empty 8" floor joists as a ceiling. Looking for good acoustics first, sound deadening second.

Just a point; Do you know why you want sound deadening if you are looking for good acoustics? They are not the same and can often be contrary to each other. - Just something to think about.

If an absorptive ceiling is what you are after, I agree with the posts above. Fill the joist cavities with attic blanket (fiberglass) and cover with fabric. Then attach finished wood lath strips to cove the fabric joints and staples.

Cheers,
John

[gtrguru]

Originally Posted by jhbrandt

Just a point; Do you know why you want sound deadening if you are looking for good acoustics? They are not the same and can often be contrary to each other. - Just something to think about.

You mean I can't have my cake and eat it too? I'm looking more for good acoustics. I can live with some sound bleed I just hope my wife can. Anyone have a spare couch just in case?

[jhbrandt]

Absorptive ceilings are the norm, especially if they are low.

What is your overall design? How are you treating the rest of your room? (Walls & floor)
Can you post a drawing?

Cheers,
John