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I am trying to figure out what to do with my basement walls. Attached is a picture of the [outside] walls (other side of [outside] wall is vinyl siding).


What I would like to do is this: build a 2x4 stud wall [inside] in front these walls with one layer of 5/8 inch type-X drywall.


Questions:


1) How much of a gap between the stud wall and the concrete should I have? I know I can do a range of gaps my recollection is that more than 6 inches is unnecessary. I would like to make as small a gap as possible (more SQFT inside room). Thoughts on gap size?


2) Should I add mass to the framed portion of the [outside] wall? The yellow and white material in the picture is a very lightweight thermal material (dont recall the name) and I am guessing that the absorption of that material is low to zero at

3) what kind of STC can I expect from this wall construction? All the STC numbers for different types of walls all assume the same materials on both sides but I will have two very different materials on each side.


4) To drilock the concrete or not? The concrete table in the Master handbook of acoustics shows between .3 and .4 in most of the frequency ranges for untreated concrete block walls BUT if it is painted those numbers drop to zero. Drilock would (I assume) be the same as painting? Am I correct in that assumption? Also - I have poured concrete not block are the acoustical properties of poured concrete radically different from concrete block?


5) insulation of gap what type? I have heard Thicker beats denser how about both thicker and denser? Fill the entire gap?


Any and all suggestions are welcome! Thank you!
 

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Quote:
Originally Posted by usualsuspects
I am trying to figure out what to do with my basement walls. Attached is a picture of the [outside] walls (other side of [outside] wall is vinyl siding).


What I would like to do is this: build a 2x4 stud wall [inside] in front these walls with one layer of 5/8 inch type-X drywall.


Questions:


1) How much of a gap between the stud wall and the concrete should I have? I know I can do a range of gaps – my recollection is that more than 6 inches is unnecessary. I would like to make as small a gap as possible (more SQFT inside room). Thoughts on gap size?
the bigger the better from a sound isolation standpoint. But you should REALLY consider adding a second layer of 5/8" drywall.

Quote:
2) Should I add mass to the framed portion of the [outside] wall? The yellow and white material in the picture is a very lightweight thermal material (don’t recall the name) and I am guessing that the absorption of that material is low to zero at
i don't know anything about moisture and construction and so forth, just sound isolation. if one side of the wall is currently a low mass thing (like 3/8" OSB or this yellow stuff, etc.). If your goal is high performance, then without a doubt you should add mass here.

Quote:
3) what kind of STC can I expect from this wall construction? All the STC numbers for different types of walls all assume the same materials on both sides but I will have two very different materials on each side.
STC is totally meaningless, totally. indeed, higher STC DOES NOT MEAN a better wall for theater. The reason is that STC ignores all frequencies below 125hz, even in the relevant ASTM standard it warns to not consider this applicable to music and so forth.

Quote:
4) To drilock the concrete or not? The concrete table in the Master handbook of acoustics shows between .3 and .4 in most of the frequency ranges for untreated concrete block walls – BUT if it is painted those numbers drop to zero. Drilock would (I assume) be the same as painting? Am I correct in that assumption? Also - I have poured concrete – not block – are the acoustical properties of poured concrete radically different from concrete block?


5) insulation of gap – what type? I have heard “Thicker beats denser” – how about both thicker and denser? Fill the entire gap?


Any and all suggestions are welcome! Thank you!
for insulation there is NOTHING AT ALL wrong with nromal cheap fiberglass.



good luck!
 

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Quote:
Originally Posted by usualsuspects
What I would like to do is this: build a 2x4 stud wall [inside] in front these walls with one layer of 5/8 inch type-X drywall.
In order to even out the room to get a perfect square, you may be better off using 2x3 and leaving a slight gap. You will also save a very minor amount on wood.

Quote:
Originally Posted by usualsuspects
4) To drilock the concrete or not? The concrete table in the Master handbook of acoustics shows between .3 and .4 in most of the frequency ranges for untreated concrete block walls – BUT if it is painted those numbers drop to zero. Drilock would (I assume) be the same as painting? Am I correct in that assumption? Also - I have poured concrete – not block – are the acoustical properties of poured concrete radically different from concrete block?
Blocks are hollow and will have different characteristics than poured. Drilocking walls shouldn't be done strictly for soundproofing but should be done because you will be framing over them and defintely do not want a water problem after construction. It helps keep down moisture.

Quote:
Originally Posted by usualsuspects
5) insulation of gap – what type? I have heard “Thicker beats denser†– how about both thicker and denser? Fill the entire gap?
Insulating for sound purposes requires more density than insulating for energy purposes.
 

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Quote:
Originally Posted by chiltown
Insulating for sound purposes requires more density than insulating for energy purposes.
that is not correct. hundreds of historical lab tests point to these basic rules


1. thicker beats denser

2. excessively dense is bad

3. for mid/high frequencies, without a doubt, denser is better

4. there is no reason to nbelieve that at the all-important low frequencies density can be correlated with superior performance, there might be reason to believe the opposite
 
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