Ran REW, now what?

[saikatbiswas82]

I repeat, am a novice with room measurements & treatments..

You had mentioned this in your post..

I was trying to interpret it..1/4th thickness of the frequency..The OP measurements had a peak at 37hz.. So was doing the math (37/4= 9.25) and seeking clarity if the thickness of the bass traps should be 9.25 inches.. If my interpretation is wrong, help me correct it..



Agreed.. Since you have microphone to take measurements, was requesting you to share room response before Dirac correction, to see untouched bass response only as information..

Share, only if you like to, else please disregard my request..

The idea to trap a particular frequency,:

1. Calculate the wavelength
2. Divide that number by 4
3. Install bass trap of that resultant thickness.

In free air if we consider the speed of sound as 343.2m/s, the wavelength of 37 hz would be 365.18 inch. 1/4 wavelength would be 91.295 inch

In theory we may need approx 7.5 ft thick acoustic absorption material to trap 37 hz. Which is ideally impossible.

 

[elangoas]

Can't say if it can be tamed unless tried. But the entire wall needs this treatment as the peak at 35 Hz is too high compared to the higher harmonics. If there is a window at the other end, it will be wiser to open them only for measuring.

Taming 35Hz room mode with absorption will need several feet of thickness.. We have discussed this in the other thread.. (Thickness of the trap should be 1/4th wave length of that freq)..

Since the 35Hz room mode is in the sub-woofer range (below 80Hz), if he moves the sub location, then the peak will defnetly reduce (or) become nil.. I have tried positioning the subs in my room and it works..

 

[sud98]

The idea to trap a particular frequency,:

1. Calculate the wavelength
2. Divide that number by 4
3. Install bass trap of that resultant thickness.

In free air if we consider the speed of sound as 343.2m/s, the wavelength of 37 hz would be 365.18 inch. 1/4 wavelength would be 91.295 inch

In theory we may need approx 7.5 ft thick acoustic absorption material to trap 37 hz. Which is ideally impossible.

Which is true for absorbent type traps, but resonators are different, as they will resonate at that frequency at a different phase to cancel it. Just too scared to build one

 

[elangoas]

The idea to trap a particular frequency,:

1. Calculate the wavelength
2. Divide that number by 4
3. Install bass trap of that resultant thickness.

In free air if we consider the speed of sound as 343.2m/s, the wavelength of 37 hz would be 365.18 inch. 1/4 wavelength would be 91.295 inch

In theory we may need approx 7.5 ft thick acoustic absorption material to trap 37 hz. Which is ideally impossible.

Right.. Thank you.. Wasn't aware of that calc, when i posted this.. But yeah, fairly understood this now..

 

[sud98]

Taming 35Hz room mode with absorption will need several feet of thickness.. We have discussed this in the other thread.. (Thickness of the trap should be 1/4th wave length of that freq)..

Since the 35Hz room mode is in the sub-woofer range (below 80Hz), if he moves the sub location, then the peak will defnetly reduce (or) become nil.. I have tried positioning the subs in my room and it works..

For one, the response you are seeing is of the speaker and not the sub. If I use multiple subs, yes, they will also do what the resonator does by cancelling the modes. For movies, I understand, I can push all lower frequencies to the sub, hence its placement becomes useful. For music, I ideally like to listen in direct mode with the speakers, wherein the placement is more difficult.

 

[elangoas]

Just too scared to build one

Get an other sub and kill the 37Hz mode & the multiple's , by placing it ideally in the room & using miniDSP..

 

[elangoas]

For movies, I understand, I can push all lower frequencies to the sub, hence its placement becomes useful. For music, I ideally like to listen in direct mode with the speakers, wherein the placement is more difficult.

If you can actually benefit from dual subs & mini DSP to get smoother response below 80Hz and if it works for movies, it should also help for low freq in music..

Why overlook the benefit of subs for music and reproduce from Floorstander which will induce peak because of placement.. You don't like subs for music?..

 

[sud98]

Get an other sub and kill the 37Hz mode & the multiple's , by placing it ideally in the room & using miniDSP..

But keeping in the middle of the room is a no go. like 3.5feet from front wall (which is possible) but 3.5 feet from back wall is not possible as I have recliners there.

 

[elangoas]

But keeping in the middle of the room is a no go. like 3.5feet from front wall (which is possible) but 3.5 feet from back wall is not possible as I have recliners there.

From my understanding, the middle of the room is the intersection of the width & length null.. So if you were to place it there, it will reduce the length mode freq (37Hz) and the associated width mode freq.. Hence the suggestion..

But, understand the placement limitations in a room.. Same in my room too, hence i put them on ceiling, but DIY passive ones (as an experiment) and it worked for me..

 

[Hari Iyer]

Taming 35Hz room mode with absorption will need several feet of thickness.. We have discussed this in the other thread.. (Thickness of the trap should be 1/4th wave length of that freq)..

Since the 35Hz room mode is in the sub-woofer range (below 80Hz), if he moves the sub location, then the peak will defnetly reduce (or) become nil.. I have tried positioning the subs in my room and it works..

How does wave length get affected by room position, the wavelength still remains the same in the room unless you alter it by some other means.

 

[elangoas]

How does wave length get affected by room position, the wavelength still remains the same in the room unless you alter it by some other means.

Am not very sure, but the wavelength should still remain the same in the room.. But change of speaker, sub position will reduce the peak of that freq in the room..

In his scenario, he has a 37Hz peak.. Which is caused by the floor stander reproducing that in the front room corner's.. If he uses a crossover and send that signal to the sub, which in turn can be positioned in the middle of the room (where the 37hz room null is), then that peak will be reduced in the freq resp chart..

 

[sud98]

After running PEQ

Waterfall

Spectrogram

I am sure I can play around the filters and get some better data but this was a first attempt.

 

[Hari Iyer]

EQ won't help if there is a peak in the minimum phase group delay at the target frequency. Check out that curve.

 

[sud98]

EQ won't help if there is a peak in the minimum phase group delay at the target frequency. Check out that curve.

English please

 

[Hari Iyer]

English please

1.Generate the minimum phase from your FR curve.
2. Check the group delay curve.
3. Check the minimum phase group delay.. if in this curve there is a peak at 35 Hz, then you will not be able to EQ that and will have to do room treatment only.

 

[sud98]

Finally, added few more treatments to my room.

1. Two Triangular traps in the back wall. Once I get a carpenter will get them installed at the top corner. As of now, resting on the floor. These are 1 feet by 1 feet by 7 feet. Filled with rockwool slabs and covered with bedsheets and finished with spandex on a wooden fram

2. Built four panels of 1 metre by 2 feet with two having 4 inch depth and two with 6 inch depth. Keeping them flexibly for now to place them either in pairs or individually depending upon which gives the best results. Ideally will fix them to the walls once the position is decided. One of them is finished with a 'TDK' poster printed online. Will get three or one more posters depending on how I position them. These were built using very thin ply (6mm) and rockwool inside with a small air gap.

 

[elangoas]

Finally, added few more treatments to my room.

1. Two Triangular traps in the back wall. Once I get a carpenter will get them installed at the top corner. As of now, resting on the floor. These are 1 feet by 1 feet by 7 feet. Filled with rockwool slabs and covered with bedsheets and finished with spandex on a wooden fram

2. Built four panels of 1 metre by 2 feet with two having 4 inch depth and two with 6 inch depth. Keeping them flexibly for now to place them either in pairs or individually depending upon which gives the best results. Ideally will fix them to the walls once the position is decided. One of them is finished with a 'TDK' poster printed online. Will get three or one more posters depending on how I position them. These were built using very thin ply (6mm) and rockwool inside with a small air gap.

I like the poster on the panel.. It looks very nice.. Were you able to take measurements?.. Do you notice an improvement after adding the traps and the panels?..

 

[sud98]

I like the poster on the panel.. It looks very nice.. Were you able to take measurements?.. Do you notice an improvement after adding the traps and the panels?..

Thanks. The posters are courtesy the bluray forum thread on wordles posters at super high resolution.
https://forum.blu-ray.com/showthread.php?s=9096919c5b0ce2b078987622e427bcee&t=176706

For the measurements, I did run one sweep and then my laptop conked, so will run them again and post. I still find a lot of modulations in my frequency graph, which I dont see in graphs posted by others. NEed to check if its related to some interference.

 

[sud98]

The Measurements

All Freq spectrum

Waterfall of left speaker

Waterfall of sub

EVerything below 120 has issues, rest seem ok

 

[elangoas]

The Measurements. EVerything below 120 has issues, rest seem ok

Length mode peak between 30 - 40Hz seems huge.. Exceeds 110dB.. What have you planned to reduce this peak?.