Understanding REW measurement

[ccs777]

Hello,

I am working on a home studio project having two pair of studio monitors one of them is KH 310 A which I used for testing. I have done measurements as per REW guidance I obtain from here and there.
I want someone to validate my acoustical solution for this room by checking my data of REW. I would be able to pay for the charges if any. I am doing this job as a hobbyist and want to learn more in the field of acoustics.

Tools used:

ECM 8000 without any calibration file.
Audient Evo 4(calibrated as per REW)
Nuemann KH310 A

measurements done on listening position. One with mic facing the speaker and other towards ceiling.

 

[simplex]

Hi,

I also started just several weeks ago using REW to implement digital correction to my stereo equipment. I'm definitely no expert and far from the idea from charging a fee for what I have to say here .

My room is basically also L-shaped, similar to yours, but it's a living room, not a dedicated studio. So your goals may be different, I'm trying to achieve a clear and enjoyable (very subjective!) stereo soundstage that takes care of the acoustic disbalances of my room.

I took several measurements in a fully furnished room at different microphone positions around the main listening spot, left and right channel separately. So there are a sofa, armchairs, a certain amount of bookshelves, small tables and dressers, and a woolen carpet, which are supposed to stay where they are now - more or less. No bass traps, absorbers, or diffusors were installed.

This way I got measurements of my room that were taken under 'live' conditions. Averaging and smoothing left and right SPL curves showed clear differences between the channels, and keying in the basic measurements of my room (wall to wall, floor to ceiling) showed the room modes that had most impact regarding to peaks and troughs. Generating and implementing FIR filters based on these measurements clearly had a positive effect on my stereo image.

In a next step I'm planning to apply absorbers to the pair of walls that show the highest impact room modes, this is clearly behind the speakers and behind my listening spot. After that, new measurements will be necessary. Possibly you will apply more physical treatment to your room.

My question to you now: wouldn't it make sense to carry out your measurements after the furniture is in place? I would assume that your measurements in a 'naked' room might be interesting to work out basic room modes more clearly, but in the end you'll probably need measurements in the fully furnished room to see the need for or the effect of physical room treatment.

 

[ccs777]

Hi,

I also started just several weeks ago using REW to implement digital correction to my stereo equipment. I'm definitely no expert and far from the idea from charging a fee for what I have to say here .

My room is basically also L-shaped, similar to yours, but it's a living room, not a dedicated studio. So your goals may be different, I'm trying to achieve a clear and enjoyable (very subjective!) stereo soundstage that takes care of the acoustic disbalances of my room.

I took several measurements in a fully furnished room at different microphone positions around the main listening spot, left and right channel separately. So there are a sofa, armchairs, a certain amount of bookshelves, small tables and dressers, and a woolen carpet, which are supposed to stay where they are now - more or less. No bass traps, absorbers, or diffusors were installed.

This way I got measurements of my room that were taken under 'live' conditions. Averaging and smoothing left and right SPL curves showed clear differences between the channels, and keying in the basic measurements of my room (wall to wall, floor to ceiling) showed the room modes that had most impact regarding to peaks and troughs. Generating and implementing FIR filters based on these measurements clearly had a positive effect on my stereo image.

In a next step I'm planning to apply absorbers to the pair of walls that show the highest impact room modes, this is clearly behind the speakers and behind my listening spot. After that, new measurements will be necessary. Possibly you will apply more physical treatment to your room.

My question to you now: wouldn't it make sense to carry out your measurements after the furniture is in place? I would assume that your measurements in a 'naked' room might be interesting to work out basic room modes more clearly, but in the end you'll probably need measurements in the fully furnished room to see the need for or the effect of physical room treatment.

Hello,

Thanks for writing, I would first answer your question: I have taken measurement to understand impulse and decay at very early stage and before going into treatment. Attached is what I have planned for this area. Just to identify the room reflections below 500 hz and identify targets I have conducted these tests. Once that is evaluated we will proceed with room treatment and conduct further tests and check response.

First 8 measurements are taken for right speaker and next eight with left one for 34 Hz to 500 Hz with sweep of 256k. I am not able to understand how my Impulse graph is starting from negative value(attached). What I was expecting was an Impulse response for one single frequency and reflections to follow. So here I am confused what next should I do or how to derive results to determine my next step of acoustical panel design.

Ok Now you need to share me your setup for my own happiness

 

[simplex]

Being an REW noob myself, I never used the impulse graphs. Just averaged SPL curves based on full range sweeps.
But I'm curious and eager to learn: so could you just lead me to the point where to find these impulse measurements in REW? Just need an entry point to discuss that topic further.

 

[ccs777]

Being an REW noob myself, I never used the impulse graphs. Just averaged SPL curves based on full range sweeps.
But I'm curious and eager to learn: so could you just lead me to the point where to find these impulse measurements in REW? Just need an entry point to discuss that topic further.

I believe it is a tab next to Distortion tab. For smaller room reverberation measurement is difficult such as RT 60 will not give accurate results thus impulse and decay becomes useful that is what I have understood.

 

[ccs777]

Being an REW noob myself, I never used the impulse graphs. Just averaged SPL curves based on full range sweeps.
But I'm curious and eager to learn: so could you just lead me to the point where to find these impulse measurements in REW? Just need an entry point to discuss that topic further.

I have learnt to use impulse graph, first we need to set IR window, 125ms to 300 m and 15 cycles for 1Khz, next you have to check your SPL, this is a smartest thing I have seen in REW. What it does is use one frequency impulse to get a range of frequency and show you the SPL curve how sound is behaving in your room. It avoids distortion and reflections which affects your normal frequency response.

This way I have derived attached frequency response. It is an average of 5 different measurements after applying IR range to 125 to 300 ms at 15 cycles. Second image shows actual measurement and than widowed response up to 300 ms. Dark graph is actual impulse having long decay and reflections as peaks light red is what we have taken as a sample. An idea small reverberant room will have decay below 300 ms. That is why we target the behavior of one impulse below 300ms despite my room has 1.8 second of delay I can still identify the performance avoiding reflections with help of IR windows.

My next step is to work on room treatment targeting the response I have received.

 

[Lesmor]

I think your first step is to download and read Austin Jerrys REW guide

REW 101 HTS Current Version.pdf

Shared with Dropbox

www.dropbox.com

 

[pklose]

Hello ccs777,

starting out with REW is quite complicated. It has taken me a week or so to understand the user interface.

Before we get started: You have built a audio workplace and you have already installed acoustic treatment. Right? You are not sure about the performance and need some advice if you are on the right path or are already on the finish line.

Btw: The Neumann KH310 are great. I am using them too.

 

[ccs777]

Hello ccs777,

starting out with REW is quite complicated. It has taken me a week or so to understand the user interface.

Before we get started: You have built a audio workplace and you have already installed acoustic treatment. Right? You are not sure about the performance and need some advice if you are on the right path or are already on the finish line.

Btw: The Neumann KH310 are great. I am using them too.

True, I have managed to installed wall panels prepared on helmholtz resonator theory. Three feet tall from floor. I want to improve the room condition by getting sure what I have planned will work.

 

[pklose]

Hello ccs777,

ok, thanks for the clarification. If you want to investigate on the system room plus speakers, I recommend to use the analysis tool SPL and RT60.

The impulse response is not helpful in that regard. The windowed impulse response is a tool take the room out of the equation, e.g. when you are interested in the performance of a speaker and do not have an anechoic chamber at hand.

 

[ccs777]

Hello ccs777,

ok, thanks for the clarification. If you want to investigate on the system room plus speakers, I recommend to use the analysis tool SPL and RT60.

The impulse response is not helpful in that regard. The windowed impulse response is a tool take the room out of the equation, e.g. when you are interested in the performance of a speaker and do not have an anechoic chamber at hand.

thats my updated plan attached.

 

[ola1]

Hello,

I am working on a home studio project having two pair of studio monitors one of them is KH 310 A which I used for testing. I have done measurements as per REW guidance I obtain from here and there.
I want someone to validate my acoustical solution for this room by checking my data of REW. I would be able to pay for the charges if any. I am doing this job as a hobbyist and want to learn more in the field of acoustics.

Tools used:

ECM 8000 without any calibration file.
Audient Evo 4(calibrated as per REW)
Nuemann KH310 A

measurements done on listening position. One with mic facing the speaker and other towards ceiling.

-Considering you have done a pretty decent job to acquire what can be considered pretty good gear, your weak point is the use of a measurement microphone which has NO correction curves for the specific mic you are measuring with.

In other words, all your measurements are completely useless cos you are unable to apply the "correction" data specific to your own mic, which would make the measurements in REW more accurate.

For very little money - less than $80 you can get a Dayton Audio measurement microphone which has its own measurement correction data, which you can uniquely download from the Internet, using its serial number.. But be careful though, I find that the serial number on the microphone is written on plastic that easily rubs off, so when you get your Dayton Audio mic, make a not of storing this serial number safely, in a number of different places, cos overtime the serial number written on the mic will no longer be legible.

What I use is the Dayton Audio EMM-6, which is a standard XLR mic, which will need phantom power from your mic-preamp.

Dayton Audio - EMM-6 Electret Measurement Microphone

EMM-6 Electret Measurement Microphone

www.daytonaudio.com

And the measurements (calibration) for each mic can be downloaded from here :

Support | Microphone Calibration Tool

Dayton Audio’s line of home A/V, loudspeaker design and test & measurement products are compared to similar items costing far more. Your path to great sound.

support.daytonaudio.com

There are minor edits which you need to do to the calibration file so that REW can read the file properly, i.e make a copy of the original file and edit this copy to make it compatible with REW's expectations. (it is possible that more recent versions of REW may be able to read the original file, cos they now have greater compatibility with the original file from Dayton Audio) . In my time when I set up my speakers a while ago, I did have to modify the original calibration file - minor edits.

It will ideally require you get as SPL meter also, if you wish to be exact when making measurements with REW. Not expensive I think a decent one can be had for $40. check Hugh Robjohn's recommendations on Sound on Sound magazine's website/forum for options.