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Have I used too many bass traps ? 100-400Hz decays faster than 500+Hz!

TangoDJ

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Recently I have upgraded the HT/listening room with acoustic treatments. Now, the REW measurements show 100-400Hz region decays faster than the 500+Hz region. Also something strange is happening around 50Hz and 85Hz.

The REW experts here - would you mind having a look at the REW measurements and offer suggestions what can be improved. This Google Drive Link has:
  1. The picture of the room and 3D rendering with measurements.
  2. The processor (AVM 70 ARC Genesis) calibration details. I ran the REW measurements WITH ARC calibration ON.
  3. The "House Curve" settings. I have two rows of seats. The main listening position is in the Front.
  4. Raw REW measurements for both Front and Back seats.
  5. Few spectrogram and decay pictures

Equipments​

Processor: Anthem AVM70
Amps and Speakers:
McIntosh MC 462 (450W/ch) - for Fronts (Paradigm Founder 100F).
McIntosh MC 255 (250W/ch - for Center (Paradigm Founder 90C) & Surrounds (Paradigm Studio 100 v2)
Two Monolith 5X (200W/ch) - for Wides (Paradigm Studio 40 v2), Backs (Paradigm Studio 20 v2) and Heights (6 Paradigm CI Pro P80-R)
Subs: Two JTR RS2
TV: LG C1 83in OLED
Rest: Panasonic DP-UB820 4KPlayer, AppleTV (dedicated Streamer and PreAmp upgrade plan for future)

Room​

18 feet wide x 22 feet long x 10 feet high. Open to the hallway and stairs at the back.
Rendering in 3D with initial GIK suggestions.
https://gikacoustics.roomle.com/t/planner?mode=3D&id=n1m3jdtyodje51hd8ed26nh0sjwqoh6&shared=1

Room Acoustic Treatments​

DIY 18”x18” Bass Traps, GIK Monster and 244 Panels, GIK 6A Alpha Pro Diffusor/Absorbers
 

sam_adams

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Your measurements have no timing reference so it's very difficult to reach a conclusion about how well the room correction is working.

tref.png
 

Hipper

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I tried to download the .mdat files but my REW says they are not mdat so I can't open them.

Generally lots of bass traps will smooth matters, particularly at the lower frequencies, and certainly the decay times, but they won't necessarily iron out everything. Look at the results I posted here (post 60) for my stereo set up.

Often if the dips are very narrow you may not hear them. The way to check this is to use this free test tone CD:

https://realtraps.com/test-cd.htm

If you can hear them then there are a few possible solutions: move speakers, subwoofer(s), an equaliser or DSP, or tuned bass traps. GIK make 'Scopus Tuned Bass Traps':

https://gikacoustics.co.uk/product/gik-acoustics-scopus-tuned-bass-trap-t70/

I looked into these tuned traps but the problem was that I needed to find where the troublesome frequency was in my room so I could place the traps there but despite using test tones and a sound pressure level meter high and low, left and right in my room I could not find anything so I didn't buy any. Eventually I tried and succeeded with EQ even though we are told it won't work and not to do this. That's probably good advice though as I've still no idea why EQ worked.

As for decay times the most important range is 0-500Hz. Bass traps are mostly broadband so reduce the whole frequency range. Also bass behaves differently up to around 300Hz (the Schroeder Frequency of a room). Above that you should consider the frequencies as rays reflecting off walls etc.. Some like reflections. I don't! For stereo, stopping these reflections tightens up the sound (for multi-channel I've no experience).

I would question whether the panels on your ceiling make any difference and could be better employed elsewhere. It depends on your speaker dispersion patterns - does it send sound to your ceiling that ends up at your ears?

One point I would add concerns leather sofas. I've only used fabric seats but read that leather reflects sound, notably the higher frequencies. How that impacts you I can't guess but you might experiment with duvets, blankets etc to hear if anything changes. Likewise reflections off the screen and gear near the speakers, certainly for stereo music only listening.
 
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TangoDJ

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I tried to download the .mdat files but my REW says they are not mdat so I can't open them.

Generally lots of bass traps will smooth matters, particularly at the lower frequencies, and certainly the decay times, but they won't necessarily iron out everything. Look at the results I posted here (post 60) for my stereo set up.

Often if the dips are very narrow you may not hear them. The way to check this is to use this free test tone CD:

https://realtraps.com/test-cd.htm

If you can hear them then there are a few possible solutions: move speakers, subwoofer(s), an equaliser or DSP, or tuned bass traps. GIK make 'Scopus Tuned Bass Traps':

https://gikacoustics.co.uk/product/gik-acoustics-scopus-tuned-bass-trap-t70/

I looked into these tuned traps but the problem was that I needed to find where the troublesome frequency was in my room so I could place the traps there but despite using test tones and a sound pressure level meter high and low, left and right in my room I could not find anything so I didn't buy any. Eventually I tried and succeeded with EQ even though we are told it won't work and not to do this. That's probably good advice though as I've still no idea why EQ worked.

As for decay times the most important range is 0-500Hz. Bass traps are mostly broadband so reduce the whole frequency range. Also bass behaves differently up to around 300Hz (the Schroeder Frequency of a room). Above that you should consider the frequencies as rays reflecting off walls etc.. Some like reflections. I don't! For stereo, stopping these reflections tightens up the sound (for multi-channel I've no experience).

I would question whether the panels on your ceiling make any difference and could be better employed elsewhere. It depends on your speaker dispersion patterns - does it send sound to your ceiling that ends up at your ears?

One point I would add concerns leather sofas. I've only used fabric seats but read that leather reflects sound, notably the higher frequencies. How that impacts you I can't guess but you might experiment with duvets, blankets etc to hear if anything changes. Likewise reflections off the screen and gear near the speakers, certainly for stereo music only listening.

Thanks a lot @Hipper for your insights and suggestions. I have put both REW measurements in a zip file in the google drive - hopefully you can read it now.

I was asked to look at the "Spectrogram with wavelets" for the LFE and apparently it shows a room mode at 52 Hz.

REW Pic MLP LFE Spectogram with wavelet.png


Don't have much room to move the furnitures or subs. Contemplating options ...
GIK makes tuned traps at 40Hz, 70Hz & 100Hz - not sure if they will help.
 
Last edited:
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TangoDJ

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How many traps do you have going exactly?
Front:
Two DIY 18" x18" x 10' high in front corners,
Two GIK Monster ( 2'x4'x7" deep) behind the subs,
1 GIK 244 (1'x4'x5"deep) behind the Center

Right:
One DIY 18" x18" x 10' high (effectively) next to bookshelf,
Three DIY 18"x12"x 26" high on top the bookshelves
One GIK 244 (1'x4'x5"deep) on top of the right surround speaker

Left:
One GIK AlphaPro (2'x4'x6") Diffuser/Absorber on the door
Two DIY 10"x6"x8' panels in the corner
Two GIK 244 (1'x4'x 5" deep) stacked

Back:
Multiple GIK AlphaPro (2'x4'x6") Diffuser/Absorbers to cover most of the wall

Ceiling
Three GIK 244 (2'x4'x5"deep) with range limiters

You can see the Room pictures and REW measurements in here.

E.g. MLP L+R RT60 looks like
REW Pic MLP LR TR60.png
 
Last edited:

FeddyLost

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GIK makes tuned traps at 40Hz, 70Hz & 100Hz - not sure if they will help.
As far as i see, you have completely nice HT room with decent measurement.
Also, for small rooms it's useful to look at EDT instead of Topt, and there we see something different.
If you need measurements much better, you'll have to hire some acoustician and rebuild the whole room from the ground. Don't forget that you have a lot of house structures behind your bass traps, and they also define room-to-sound interactions.
It looks like it's not an option now.

So, IMO - if you are subjectively satisfied with sound, stop to worry about measurements.
It's not a mastering studio, where you need some parameters just to earn your living.
 
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TangoDJ

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As far as i see, you have completely nice HT room with decent measurement.
Also, for small rooms it's useful to look at EDT instead of Topt, and there we see something different.
If you need measurements much better, you'll have to hire some acoustician and rebuild the whole room from the ground. Don't forget that you have a lot of house structures behind your bass traps, and they also define room-to-sound interactions.
It looks like it's not an option now.

So, IMO - if you are subjectively satisfied with sound, stop to worry about measurements.
It's not a mastering studio, where you need some parameters just to earn your living.

Thank you @FeddyLost for your insightful comments. My current system is much better than what I used to have and when I am listening to music - I am NOT thinking at all about the 50Hz dip etc. :) And I will have to question myself if I can even hear the difference of what measurements are suggesting to improve!

Having said, if there are some simple tweaks (e.g. rearrange to position of the subs, or bring the bass panel down etc as some have suggested) - I will try them :)
 

abdo123

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I don't think ''too much absorbed bass" is a negative quality. We're talking about values generally below 300ms, so nothing is bad here.

Maybe a slightly reverberate mid-range might be better than overly absorbed. 200ms is at the edge of what people find comfortable in rooms, staying slightly above that might be a good thing.
 

Mykola

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Front:
Two DIY 18" x18" x 10' high in front corners,
Two GIK Monster ( 2'x4'x7" deep) behind the subs,
1 GIK 244 (1'x4'x5"deep) behind the Center

Right:
One DIY 18" x18" x 10' high (effectively) next to bookshelf,
Three DIY 18"x12"x 26" high on top the bookshelves
One GIK 244 (1'x4'x5"deep) on top of the right surround speaker

Left:
One GIK AlphaPro (2'x4'x6") Diffuser/Absorber on the door
Two DIY 10"x6"x8' panels in the corner
Two GIK 244 (1'x4'x 5" deep) stacked

Back:
Multiple GIK AlphaPro (2'x4'x6") Diffuser/Absorbers to cover most of the wall

Ceiling
Three GIK 244 (2'x4'x5"deep) with range limiters

You can see the Room pictures and REW measurements in here.

E.g. MLP L+R RT60 looks like
View attachment 227325
I have ordered two GIK soffit traps for test . But wonder how exactly you constructed your DIY ones ? And I am also getting advice from GIK.
 

dasdoing

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there is a decay spike in the midrange actualy. most probably caused by this huge reflection which has a 1,7m longer path:

ref.jpg


it's stronger on the right side btw


the 52Hz issue you can try two things:

- moving the subs up
- turn the subs around (yes, woofers facing the walls)
 

ernestcarl

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there is a decay spike in the midrange actualy. most probably caused by this huge reflection which has a 1,7m longer path:

View attachment 235327

it's stronger on the right side btw


the 52Hz issue you can try two things:

- moving the subs up
- turn the subs around (yes, woofers facing the walls)

I was trying to figure out how to get the distance calculation show up in the impulse plots, but can’t figure it out. I would appreciate it if you could tell us how it’s actually done in REW! A simple mouse and key hold combination?
 
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