I presume that <100hz panel traps are not uncommon anyway.
The same traps will be installed on hopefully at least one more wall before weeks end
Zaphod wrote:Wasn't the HF TL increase due to the mid/high absorber to be
After all, some of the sound is converted into heat and this will
help also TL.
If i recall, even eric always said that the worsening of TL related
to mid/high narrow band absorption was to be related to the user
cranking up the volume to compensate for the sound absorbed,
hence letting out more bass from the room.
Zaphod wrote:The TL term in the phrase you quoted is clearly out of place. :oops:
You can't use an absorber to stop sound leaving a music room.
Shaky science paragraph: Absorbtion coefficients are measured on a difuse sound field, giving an average absorbtion for that frequency for all vectors. Difuse sound comes from lots of directions, including those that go through the 2' and 4' lengths of the absorber, and not just those that go through the 2" depth. Obviously the If you have speakers on wall A, and absorbers on opposite wall B, that's sound going through the thinest direction of the absorber, and will get less absorbtion than the published absorbtion coefficient, at least in the first reflection. In other words the sound is still going to hit the wall, and probably a lot more of it than you are expecting.
An absorber will reduce the sound field within the room, effectively reducing the db volume in the room. According to "Noise control in buildings" by Cyril M. Harris, pg 4.11, the amount of noise reduction is given by level reduction in db = 10 log (A after / A before)
where A is the total absorbtion in sabins. So, if you had a room with carpet and people and cabinets with around 140 sabins, and then covered the walls with an absorber with NRC=0.70 giving new absorbtion of 789 sabins, then you'd end up with a difference of 7.9db.
This is a good thing when you are trying to silence machinery, or screaming babies, or some other reasonably constant db(C) noise source. But you are not a CONSTANT noise source. What happens when you are playing your stereo or instrument is that you turn the volume up to where it feels comfortable for you. i.e. whatever TL gains you made by adding absorbtion, are negated almost precisely by turning up the volume 7.9db. So you've spent money on absorbtion. And either you've turned up the volume to the point where your speakers are now distorting, or you spend money on new and better speakers and amplifiers to compensate. So now you've spent a lot of money, and the result is that the same amount of noise is heard outside the room, and inside the room isn't any louder either. So all you've really done is just spent money.
Instead of putting up absorbtion to get room to room TL, why not use something that's commonly used for TL, such as gypsum or concrete or decoupling.It's very important to understand what "NRC" means. It stands for "Noise Reduction Coefficient." This is a measure of how much sound is absorbed by a material inside a room. This number tells you how much quieter the room will be from sounds generated within the room.
This is completely different from the measurement called "STC", which is the "Sound Transmission Class." This number measures the ability of a material to block sound either leaving or entering a room.
generally speaking, that one layer of:
Acoustic Ceiling Tiles and Rigid Fiberglass and Rigid Rockwool have a high NRC (.5 to 1.0) and a low STC (0 to 1)
Sheetrock/Drywall/Gypsum has a high STC (28 ) and a low NRC (0.01).
My use of 'high' and 'low' are simply relative adjectives. For example there are STC 70 wall configurations that block a lot more than a single sheet of sheetrock.
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