Low RT 60 in HT. Would i need correction ? - AVS Forum
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post #1 of 7 Old 04-03-2014, 06:15 PM - Thread Starter
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I have just been measuring my system with REW and have found on the RT60 graph the following and was worried i might have inadvertently over dampened my room on the high end possibly ? Can anyone offer any insight or possible things i could do to help in some way if its needed ?

The room is a small HT i built about 5 years ago and have the entire lower half of the walls covered in 1" rigid fiberglass up to ear height. Front wall is 100% covered in 1" rigid fiberglass.Carpet on floor. And i have 2 corner bass traps made of 4" rigid fiberglass. Room dimentions are 5m x 3.5m x 2m

The is the graph in REW. Would some diffusers be needed on the walls in front of the 1" fiberglass maybe ? Something like a binary amplitude diffuser possibly ?

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post #2 of 7 Old 04-03-2014, 07:00 PM
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Yes, your room has too much absorption. You don't want to cover more than 25% of the surfaces as a general rule. I would rip out some of the 1 inch fiberglass if you can.

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post #3 of 7 Old 04-03-2014, 10:07 PM - Thread Starter
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Oh wow 25%. Thats a bit of a difference. Back when i built the room i was told 50% here at AVS.

Ok well all my walls are cloth lined so would be a big job to pull it all apart and put it all back together. Any general rules as to what walls need treatment and what dont ? Obviously i would leave the first reflection points i guess. What about the back wall ? Or the front wall for that matter ?
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post #4 of 7 Old 04-04-2014, 07:03 AM
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It depends how you go about it. 50% is a good figure if that is augmented with diffusion or scattering in front of portions of it. 1" absorbers are only going to trim the high end. Ditto for carpet. You want even absorption at frequencies down to 250hz or so, or lower if possible. This means several inches deep.

I am using 12" thick pink fluffy absorber panels through much of my room (thicker in many places) and you get a pretty even absorption coefficient down to 150hz or so.


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post #5 of 7 Old 04-04-2014, 09:54 AM
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Quote:
Originally Posted by Timoxx4 View Post

worried i might have inadvertently over dampened my room on the high end possibly ?

This is an issue where you will find broad disagreement, so be warned. biggrin.gif

I think your RT60 is fine, though it's unbalanced with that large rise below 300 Hz. One goal of acoustic treatment is for the RT60 times to be uniform versus frequency. That probably matters as much as the absolute values. So you definitely need more bass trapping. Further, RT60 values in a small room are not reliable. A room that size doesn't have reverb. It has a series of individual reflections which is similar but not the same. A small room can have reverb, but only if it's mostly empty. So the real question is how does it sound? Is music clear and tight? Does it sound full when you crank the volume? Or is the sound dull and lifeless even at loud volume? I prefer mostly dead, especially in a small room, but others may disagree.
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The room is a small HT i built about 5 years ago and have the entire lower half of the walls covered in 1" rigid fiberglass up to ear height. Front wall is 100% covered in 1" rigid fiberglass.Carpet on floor.

This is your main problem. The front wall behind the speakers is not a source of reflections unless you have dipole type speakers that send sound equally out the rear. It's much more important to treat the rear wall behind you. Further, rigid fiberglass one inch thick is too thin, and this is why your RT60 times are so unbalanced. This RT60 graph was measured in a small room very similar in size to yours, before and after adding extensive treatment (both absorption and diffusion):

dlr_rt60.gif

Even though the decay times are short, the room sounded fabulous (IMO) when we set it up.
Quote:
i have 2 corner bass traps made of 4" rigid fiberglass. Room dimentions are 5m x 3.5m x 2m

That's a start, and four inches thick is good, but you need more of those and less coverage with the one-inch stuff. If you want to add diffusers, the more usual place is the rear wall behind you rather than the front wall.

More info here:

Front Wall Absorption
All About Diffusion
Hearing is Believing

--Ethan

RealTraps - The acoustic treatment experts

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post #6 of 7 Old 04-06-2014, 06:30 PM
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At times like this I feel the ages old "Master Acoustics Thread" should be locked and re-done from scratch.
The 1" thing up to ear height has gotta caused many HT's not to be properly balanced for absorption, all that does is EQ the sound.

This graphic may make it simple to grasp, 1" at best will only absorb down to 2,400 hz.
Then you have to take into account the material you are using.
I'd rip out the 1" that is applied in all the non-needed areas, and use it appropriately at your first reflection points.
2" material + 2" air gap if that's all the real estate you want to give up.
I also have issue with any generic 25% or 50% rule, it's best to do it right, and confirm with ETC.
No need to absorb everywhere if those reflections are not causing your acoustic issues.
Acoustic+treatment+material+plus+airgap+explain.jpg

Post some ETC charts for your mains to start, the R, C, L individual at your MLP.

Mike R,P.E. clickable DIY hot links:

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post #7 of 7 Old 04-07-2014, 11:31 AM
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Quote:
I think your RT60 is fine, though it's unbalanced with that large rise below 300 Hz. One goal of acoustic treatment is for the RT60 times to be uniform versus frequency. That probably matters as much as the absolute values. So you definitely need more bass trapping. Further, RT60 values in a small room are not reliable. A room that size doesn't have reverb. It has a series of individual reflections which is similar but not the same. A small room can have reverb, but only if it's mostly empty. So the real question is how does it sound? Is music clear and tight? Does it sound full when you crank the volume? Or is the sound dull and lifeless even at loud volume? I prefer mostly dead, especially in a small room, but others may disagree.

Right which he should view the decay times to see where the problems really are. smile.gif

BTW he did post the rew file in the master thread and I believe there is a problem with the way he ran the test. Needless to say though 1" is not recommend as it will only suck up the upper energy in the room.

Glenn Kuras
GIK Acoustics


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