REW measurements - discussion
- Thread starter insider9
- Start date
- Sep 20, 2016
- 1,182
- 646
- 12,070
I've managed to get some room treatment in. Not DIY and not yet sure about placement nor performance. So I've looked at the impulse response graphs to better understand where the treatment would do the most.
Here's some graphs before:
Right speaker - here
Left speaker - here
Here's after:
Right speaker - here
Left speaker - here
I'm mostly interested in understanding how to work out points of reflections based on these graphs. Time delay = distance? Right?
The most curious fact is the after treatment right speaker graph shows reflection after 18ms that wasn't there before. That's sound traveling 6.2 meters. Indicating the only (at present) not treated wall. How can it be that this was not the issue before treatment?
Here's some graphs before:
Right speaker - here
Left speaker - here
Here's after:
Right speaker - here
Left speaker - here
I'm mostly interested in understanding how to work out points of reflections based on these graphs. Time delay = distance? Right?
The most curious fact is the after treatment right speaker graph shows reflection after 18ms that wasn't there before. That's sound traveling 6.2 meters. Indicating the only (at present) not treated wall. How can it be that this was not the issue before treatment?
sadly I won't be able to contribute anything but I imagine there'll be quite a lot of informative posts by others especially Ellisdj.
Would be great to see some pictures of the treated room when you get a chance.
Would be great to see some pictures of the treated room when you get a chance.
I find analysing the impulse response very difficult - you need to look at the graphs in certain ways.
Matt Khan on AVF is the man to ask this to
Matt Khan on AVF is the man to ask this to
- Sep 20, 2016
- 1,182
- 646
- 12,070
Thanks Ellisdj
I think I'm getting the hang of it in fairness. I find it very interesting to look at. Will post some thoughts later.
EDIT
So far managed to figure out which are floor and ceiling reflections. Contemplating the others at the minute.
I think I'm getting the hang of it in fairness. I find it very interesting to look at. Will post some thoughts later.
EDIT
So far managed to figure out which are floor and ceiling reflections. Contemplating the others at the minute.
- Sep 20, 2016
- 1,182
- 646
- 12,070
For the time being lets look at one speaker only (left) in my setup.
Looking at the impulse response before treatment with comments - here
This is with treatment how it's currently placed - here
And that's how it was when I just placed it by hunch (already linked before) - here
Sadly no way to overlay these in REW. I've managed to get get rid of the reflection at 3.74ms by sliding the treatment about 12 inches to the right. Between the last two grahs already treated room.
I'll explain how I've managed to figure out which reflections are which in the next post.
Looking at the impulse response before treatment with comments - here
This is with treatment how it's currently placed - here
And that's how it was when I just placed it by hunch (already linked before) - here
Sadly no way to overlay these in REW. I've managed to get get rid of the reflection at 3.74ms by sliding the treatment about 12 inches to the right. Between the last two grahs already treated room.
I'll explain how I've managed to figure out which reflections are which in the next post.
- Sep 20, 2016
- 1,182
- 646
- 12,070
So just looking at this graph - here and how I got the comments.
I took notes of time delay of the reflections. The four annotated ones are as follows:
1.74 ms / 3.76 ms / 5.10 ms / 13.51 ms
I have converted these into distance
0.6 m / 1.28 m / 1.74 m / 4.6 m
These distances are where the sound has to travel further than the direct (non-reflected) impulse.
I then measured the distance from speakers to the mic and added it to the above distances. Getting these values
2.33 m / 3.01 m / 3.47 m / 6.33 m
That's the distance the sound traveled from the speakers to the mic reflected of a surface.
I've also compared the pre/post measurement and reaslised that the two reflections on both speakers remain. Also both speakers had reflections in mostly same places. That indicated that these are front to back and not so much sides.
The two reflections that remain are floor and ceiling. To check which is which I measure the distance from the speaker to the ceiling and ceiling to the mic.
Continued...
I took notes of time delay of the reflections. The four annotated ones are as follows:
1.74 ms / 3.76 ms / 5.10 ms / 13.51 ms
I have converted these into distance
0.6 m / 1.28 m / 1.74 m / 4.6 m
These distances are where the sound has to travel further than the direct (non-reflected) impulse.
I then measured the distance from speakers to the mic and added it to the above distances. Getting these values
2.33 m / 3.01 m / 3.47 m / 6.33 m
That's the distance the sound traveled from the speakers to the mic reflected of a surface.
I've also compared the pre/post measurement and reaslised that the two reflections on both speakers remain. Also both speakers had reflections in mostly same places. That indicated that these are front to back and not so much sides.
The two reflections that remain are floor and ceiling. To check which is which I measure the distance from the speaker to the ceiling and ceiling to the mic.
Continued...
- Sep 20, 2016
- 1,182
- 646
- 12,070
The other two reflections were not easy to determine. The front wall reflection could've been the back wall as the distances are very similar. With the back wall mostly covered they would disappear completely though. They've not on one side slightly remaining.
This way I knew it's likely to have been the front wall (behind speakers) I have moved one of the panels to confirm this and the reflection was pretty much gone.
The last reflection was a nightmare to determine and I asked my son for that as measuring wasn't the easiest by myself. But we finally got to grips with it and given the symetric nature of it we concluded it's the only plausible explanation. Sound bounicing of back wall then to fron wall and back to the mic.
EDIT
I hope it makes sense. All you need is a measuring tape and a calculator (as long as you rememeber the speed of sound 🙂 )
This way I knew it's likely to have been the front wall (behind speakers) I have moved one of the panels to confirm this and the reflection was pretty much gone.
The last reflection was a nightmare to determine and I asked my son for that as measuring wasn't the easiest by myself. But we finally got to grips with it and given the symetric nature of it we concluded it's the only plausible explanation. Sound bounicing of back wall then to fron wall and back to the mic.
EDIT
I hope it makes sense. All you need is a measuring tape and a calculator (as long as you rememeber the speed of sound 🙂 )
- Sep 20, 2016
- 1,182
- 646
- 12,070
Also for the eagle eyed you may have noticed the first "spike" is at 0.2 ms super close to original impulse. That's mightily close and accounts for 7cm distance and is a direct reflection from the mic stand. Yes I have moved the mic in it's stand forward (moved the stand back the same amount) and re-took the measurements. It pretty much removed that spike :biggrin:
How did you determine the time delays?
Also the spikes on the graph you feel are the distances from the mic?
Also the spikes on the graph you feel are the distances from the mic?
- Sep 20, 2016
- 1,182
- 646
- 12,070
The X axis on the impulse response graph is in miliseconds. The main impulse is at 0 ms (X axis) 100% (Y axis). In an ideal world it should be just that and nothing else. All else is reflections, diffractions, etc.
From there you can convert the time delay from original impulse into distance. Then you just need to unleash your inner Sherlock to figure out which is which. Tape measure helps a lot but also differences between measurements when you move panels around.
From there you can convert the time delay from original impulse into distance. Then you just need to unleash your inner Sherlock to figure out which is which. Tape measure helps a lot but also differences between measurements when you move panels around.
- Sep 20, 2016
- 1,182
- 646
- 12,070
Here's the newest measurement with one panel on the floor. Treating the first reflection. If only I knew the ceiling could handle the weight.
Also notice much smaller notch at 0.2 ms from moving the mic forward in it's stand.
And that's before and after
Also notice much smaller notch at 0.2 ms from moving the mic forward in it's stand.
And that's before and after
Time in milseconds converted to seconds x 343 = distance in cm.
Then add the distance to the mic to get the reflection distance.
Then work out what it is and try and cover it
Then add the distance to the mic to get the reflection distance.
Then work out what it is and try and cover it
- Sep 20, 2016
- 1,182
- 646
- 12,070
I thought I already posted this. It's likely that not all panels are necessary. Picture link here in case it doesn't show up.
As to your question regarding frequencies you can't get that info from impulse response graph. That's purely to establish where the reflections points are. I've not yet managed to get the treatment to target specific frequencies, only reflections.
Yes, distance you will get distance in meters though but the therory is sound (s x m/s = m)
Then add the distance speaker to mic. This is the distance the sound has to travel. Which is the distance you measure
speaker > reflection point > mic
and it's for you to figure out where the reflection takes place. Fun, fun, fun 🙂
As to your question regarding frequencies you can't get that info from impulse response graph. That's purely to establish where the reflections points are. I've not yet managed to get the treatment to target specific frequencies, only reflections.
ellisdj said:
Yes, distance you will get distance in meters though but the therory is sound (s x m/s = m)
Then add the distance speaker to mic. This is the distance the sound has to travel. Which is the distance you measure
speaker > reflection point > mic
and it's for you to figure out where the reflection takes place. Fun, fun, fun 🙂
- Sep 20, 2016
- 1,182
- 646
- 12,070
From speaker to reflection point and from reflection point to mic. I guess measuring other way round will give the same result. Total distance has to be what you got from converting time delay in impulse response graph.
EDIT
That's for first reflections. You may have a couple reflections that will make it even more interesting. Got one on right speaker i still cannot figure out (18 ms)
EDIT
That's for first reflections. You may have a couple reflections that will make it even more interesting. Got one on right speaker i still cannot figure out (18 ms)
Similar threads
TRENDING THREADS
-
-
-
-
Question Audio system for a small (5mx5.5m) living room in a Central London flat
- Started by rs_ldn
- Replies: 20
-
-
-
Facebook
Twitter
Instagram