# Help understanding the REW results and how to improve



## katylied (Feb 24, 2012)

I have taken several measurements with REW in different rooms/speakers combinations and found that I'm always getting similar data regarding the RT60 below 200 Hz. Since I've not yet understood how to read the results of the waterfall and spectrogram, I would like to ask some suggestion and how to eventually proceed in order to improve the sound quality. Here is one example (room size is 523x430x297 cm):

























Thanks in advance!


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## protone (Apr 8, 2013)

Hi 
I have also taken a lot of RT60 measurement with REW. I am more lucky than you with my results. All values are below 0.4s. Why? This is because the walls of my room are made of wood, and they are not fixed to any stone walls. So the wood can vibrate freely, and absorb the enegrgie in the low frequency range. Your diagram shows typical values for this problem. I guess if you measure the SPL frequency from 20 to 200 Hz you will see very high peaks and valleys. And if you change the position of the microphone the position of this peaks and valleys will also change their positions. 
I have had this problem for many years. I have solved it at that time with bass absorbes. I build them myself with the help of an acoustics engineer. This has improved the situation a lot. Maybe you can find something on the market. But you must make shure they are really absobing down to 30-40Hz.
The biggest effect you can get when you place them in the corners of the room. If you canot find anything I can send you the drawings of the absorbers. But it is a lot of work to do this. 

Regards
protone


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## jim1961 (Apr 8, 2011)

The long decays in the lower bass are indicative of a need for more bass trapping.

An ETC would be helpful to see to get an idea about your reflections.


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## katylied (Feb 24, 2012)

Thanks for your comments.
Protone: you are correct as all the walls, ceiling and floor are concrete made. Only one side wall is made in drywall (gypsum board on wood stud). There is a wall to wall carpet and 10 DIY bass traps (8 pcs 1200x60x10 cm and 2 pcs 60x60x10 cm) made with locally made acoustic panels (should be made with OC703) with an added plastic foil to the front (in the 4 corners, 3 along the front wall with a 10 cm gap behind and 1 between front wall and ceiling), plus 4 absorption panels (60x60x5 cm).
Jim1961: here are the full set of measurement from the same session results taken with my all Behringer set EMC8000/MIC100 pre/UCA202. The speakers used are Martin Logan ElectroMotion (that should explain the early roll off of the frequency response). Note: the RT60 posted before was from another session.
View attachment 41502


View attachment 41503


View attachment 41504


View attachment 41505


View attachment 41506


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## jim1961 (Apr 8, 2011)

Need to see the ETC only to 50ms. Its the early reflections that need to be seen.


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## katylied (Feb 24, 2012)

I will really appreciate any help on understanding the rise of the RT60 at the low frequency or any other explanation in a better understanding of the measurements. Thanks in advance!:help:


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## jim1961 (Apr 8, 2011)

katylied said:


> I will really appreciate any help on understanding the rise of the RT60 at the low frequency or any other explanation in a better understanding of the measurements. Thanks in advance!:help:


Decay in the bass region is always longer, and thus the higher rt60. This is normal.


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## katylied (Feb 24, 2012)

Thanks Jim.
How can I limit the ETC to 50 m? I can't find any way to do it!


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## jim1961 (Apr 8, 2011)

katylied said:


> Thanks Jim.
> How can I limit the ETC to 50 m? I can't find any way to do it!


Under impulse, hit the "limits" box.


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## katylied (Feb 24, 2012)

Here we are and thanks Jim!


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## protone (Apr 8, 2013)

Hi 
Here you can see the RT 60 and the frequency response in my room. As I said befor I am very lucky to have all wooden walls and and additionaly a sloping roof. The bass is extremly dry and precise under these conditions. I dont understnd exactly how your bass traps are made, but OC 703 is not really absobing low frequency except you have a thicknes of more than 1 meter. You need a surface aible to absorb the energy. Do you have more details about your absorbers?
Frauenhofer has developped a system with steel plates and foam rubber to build a wide range absorber for low frequency. When I say wide range it means approx. 30-200Hz. Many absorbers work only in a narrow range like Helmoltz resonators, thats why you have to combine several resonators, and adjust them to differnt frequncies.
Here are my results without any equalizing.


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## katylied (Feb 24, 2012)

Thanks Protone.
I know the plate absorber are you talking about but I have some difficulties in found the materials needed where I live and work now (China). It's also quite complicated and expensive to get branded products as GIK or RealTraps here and that's why I have to mostly rely on what I can find here easily. The panels I'm using are composed by a thin alluminium frame filled by a "non fluffy" fiberglass (4"/10 cm thick) that should be of quite high density and made by Owen Cornings (I don't remeber if is 703 or 705) covered by a custom fabric that should prevent any particle output and increase the absorbtion at the low frequency (manufacturer claim). I should have the test reports somewhere but an't find it at the moment. I then added a 6 mil plastic film on the front in order to prevent the absorbtion at the mid and high frequency and covered all with a fabric of similar properties of the one usually applied to the acoustic panels (air can pass through). I can hear big improvements in the sound when the panels are installed but I'm puzzled by the long decay time of the frequency below 200 HZ. Probably increase the number of the "DIY bass traps" will help onder:......
Here is a picture where you can see the panels positioning


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## protone (Apr 8, 2013)

Hi
To know if more absorbers will help, it is important to see the exact absortion curve of the absorbers.
What i can see in your picture is that you should completely cover all corners fist. But dont do anything before you have exact data of the absorbers. Do you have a measurement without the absorbers?
This could be a helb to get an idea of the absorbers range.


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## jim1961 (Apr 8, 2011)

katylied said:


> Here we are and thanks Jim!
> 
> View attachment 41512
> 
> ...


If it were me, I would work on getting those early reflections (<20ms) under -20db.


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## katylied (Feb 24, 2012)

Hi Protone: I will try to found out the absorbtion data of the panels. I can also add more trapping as I have some more panels that I can put between the floor and the walls easily and then run another set of measurements.



jim1961 said:


> If it were me, I would work on getting those early reflections (<20ms) under -20db.


Thanks Jim. My problem is that I don't know how to read and the meaning of those graphics and much less what to do to improve the result :huh:.
I'm an absolute beginner as regarding the acoustic and if you can give me more help it will be really appreciated :help:.


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## jim1961 (Apr 8, 2011)

katylied said:


> Hi Protone: I will try to found out the absorbtion data of the panels. I can also add more trapping as I have some more panels that I can put between the floor and the walls easily and then run another set of measurements.
> 
> 
> 
> ...


Here are some links that help explain whats up:

http://www.ethanwiner.com/acoustics.html
http://www.linkwitzlab.com/rooms.htm


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