Advice on adding reflecting surfaces

[FeddyLost]

Hello to everyone

Now I've tamed LF at LP to decent RT without any equalisation and got rid from "chuffing" bass.
But still decay times from 100+ Hz are too low and I need to add some reflection, but I'm not sure WHERE exactly.
Currently the one and only big reflective surface is floor.
All other (walls and ceiling) is inner shell from Rockfon Industrial rockwool ceiling tiles with 35 cm air gap filled with tuned limp mass bass absorbers (in corners) or fluffy Knauf basalt wool in film bags (all other cavities except wall and door openings). Inner shell include doors and window blinds for better symmetry.
I'd like to get rid from this rockwool tiles and exchange them for Heradesign wood wool panels (or equivalent) and add some reflective surfaces (like 2 layers 1/2" plasterboard).
But the main question is WHERE to put plasterboard.
I think most universal solution is to cover middle 120 cm (~1/2 of height) of all walls with absorber (Heradesign) and make two "stripes" near wall and ceiling from plasterboard.
Still, I'm not sure if it will significantly rise decay times in midrange and upper , and thinking about additional middle 1/3 of front wall, which is considered as "first reflection point" but if all sides and back wall is absorbing, i'm not sure that it is true.

Maybe there are some people experienced in room acoustics who can give good advice?

 

[abdo123]

posters should reflect frequencies down to ~600Hz or so.

more information is available in this thread https://www.audiosciencereview.com/...ps-with-a-poster-am-i-doing-this-right.24783/

 

[Hipper]

Hello to everyone

Now I've tamed LF at LP to decent RT without any equalisation and got rid from "chuffing" bass.
But still decay times from 100+ Hz are too low and I need to add some reflection, but I'm not sure WHERE exactly.
Currently the one and only big reflective surface is floor.
All other (walls and ceiling) is inner shell from Rockfon Industrial rockwool ceiling tiles with 35 cm air gap filled with tuned limp mass bass absorbers (in corners) or fluffy Knauf basalt wool in film bags (all other cavities except wall and door openings). Inner shell include doors and window blinds for better symmetry.
I'd like to get rid from this rockwool tiles and exchange them for Heradesign wood wool panels (or equivalent) and add some reflective surfaces (like 2 layers 1/2" plasterboard).
But the main question is WHERE to put plasterboard.
I think most universal solution is to cover middle 120 cm (~1/2 of height) of all walls with absorber (Heradesign) and make two "stripes" near wall and ceiling from plasterboard.
Still, I'm not sure if it will significantly rise decay times in midrange and upper , and thinking about additional middle 1/3 of front wall, which is considered as "first reflection point" but if all sides and back wall is absorbing, i'm not sure that it is true.

Maybe there are some people experienced in room acoustics who can give good advice?

Have you some measurement of decay times to illustrate the problem?

 

[FeddyLost]

posters should reflect frequencies down to ~600Hz or so

I'd like to keep interior as minimalistic as possible.
And I will get rid off exposed rockwool anyway, so I can use ordinary materials.

some measurement of decay times to illustrate the problem

For sure
I can even attach mdat, but for illustrative purposes this might be enough ...

Sticking out mids around 1K may be due to leather sofa. I don't feel this range too prominent if I don't deal with surf or bass-shy metal. Need to investigate it further.

 

[Wes]

why are the walls made from ceiling tiles??

get rid of them (carefully - they may contain asbestos)

use drywall and "plaster"

you can find the 1st reflection points with a mirror and a holder for the mirror - if your gf doesn't yet think you are insane then this will likely push her over that edge...

 

[Kvalsvoll]

I just did a description of how a small room was fixed, you will find drawing of the acoustic treatment and examples for how to analyze measurements:
https://www.kvalsvoll.com/blog/forum/topic/case-fixing-room-acoustics-for-a-f205-system/

Reflection is added by mounting reflective parts (slats) over absorption, and diffusors.

When analyzing small rooms, it is not so useful to look at RT60, you should look at the decay profile, REW now has the RT60 Decay graph window which is good for this purpose, also look at spectral distribution of the decay profile using Decay and Spectrogram in addition to the RT60 Decay.

Recent trends in acoustic treatment is to distribute both absorption and reflection/diffusion more across all room surfaces, the surgical mirror-first-reflection approach is not so popular now.

Typical failures are too little absorption below around 400hz, and not enough reflection above 1KHz.

Pictures of your room would give valuable information.

 

[FeddyLost]

why are the walls made from ceiling tiles??

It was cheap and quick solution when i thought that calculators tell truth and total absorption is OK.
I'm still fine with that, but such dry presentation is not acceptable in hi-fi for all people I know.

you can find the 1st reflection points with a mirror and a holder for the mirror

For sure.
But I'd prefer some more variability if I will add up multichannel or slightly move speakers and LP.

Reflection is added by mounting reflective parts (slats) over absorption, and diffusors.

If I plan inner shell exchange, I can make exact wall layout in advance. Clean and smooth surfaces are more preferable, than ladder-like slats.

also look at spectral distribution of the decay profile using Decay and Spectrogram in addition to the RT60 Decay

I'm not very familiar with that. As i remember, Decay is good for distinguishing modal issues and single reflections like floor bounce/ *BIR.
I'll read about that.
Spectrograms are below.

distribute both absorption and reflection/diffusion more across all room surfaces

Due to some reasons I'd prefer to exchange only walls and keep absorbing ceiling and hardwood floor...
I may add some small carpet, but nothing more.

Pictures of your room would give valuable information

Imagine ceiling and all walls fully made from black suspended ceiling for cinema. Rockfon industrial black all around.

So, we can imagine that I want to close this rockwool tiles with 1" drywall (from 16 to 25 kg per square meter, depending on type).
Where can I place these drywall zones if I have more or less perfect triangle with 3 m side where speakers and LP are close to walls?
Obviously, it can't be any 1st reflection zone.
It should not be any complete inner angular surface (otherwise midbass will not reach tuned absorbers ASAP but just partially bounce and will make situation more complicated).
With acoustical axis at ~110 cm from floor inner shell height of 240 cm all absorption might be reasonably placed at the middle of walls.
So, we have only two "stripes" of ~60 cm height near floor and ceiling and probably middle 1/3 or maybe 1/2 of front wall.
Due to ray tracing this zone will never be real first reflection for anything higher than lower midrange, and for real "on-axis responce" it will be at least 3rd reflection.
So, my main concern is - are my assumptions correct, or maybe I shall add just these "stripes" and stay at approximately 50% of reflecting surfaces in room instead 22% as I have now?
Or maybe I'm missing something else with these "carpet bombing" ideas?

Also, have to say, that idea of "active experimenting" with absorption/reflection zone is not the funniest one after my tuned absorbers' puzzle.
I'd prefer to give layout to builders and have duty done fast and solid ...

 

[Kvalsvoll]

Excellent. You killed the room.

Your graphs indicate the room is very dry, but you also seem to have good control of decay across the frequency range. I would assume this room sounds very dry and dead - too dead. From what you write, I understand that you also experience the sound to be too dry.

It is common practice to keep the floor hard/reflective - you can add a carpet, for decor or practical reasons.

Having 22% reflective (from your post above) surface area is very little, around 60% reflective will still provide plenty absorption, and preserve more energy.

I looked up Heradesign panels, I found only very thin 25mm panels, too thin to work well for broadband absorption.

You have come this far, and you are already on the correct path to fix it. Adding more reflective area will give a more balanced sound.

Using measurements to determine how it sounds can be difficult, if a graph is to make any sense, one must have a reference to compare it to. Either you know how it shold look, or you have a measurement from a room that works well to compare. But you can listen, and judge from what you hear. The differences we are dealing with here are not subtle.

 

[Kvalsvoll]

Clean and smooth surfaces are more preferable, than ladder-like slats.

All acoustic treatment can be covered with fabric, so you end up with a smooth wall visually.

 

[Kvalsvoll]

I'd prefer to give layout to builders and have duty done fast and solid ...

Absolutely. The best approach is to design the whole room first, and have someone build it if you are not a carpenter yourself. This is how they do studios - they generally do not experiment and measure and tune much, it is designed, then built, and in the end just evaluated, perhaps with measurements - but those measurements are not used to make changes, they are more like a reference.

This of course possible because the design is based on known and predictable solutions.

 

[FeddyLost]

too dead

It's too dry even for studio purposes if I understand RT from REW correctly. Or maybe at the edge.
Really great for movies with moving virtual sound sources, but for hi-fi it's barely exciting.

around 60% reflective will still provide plenty absorption

Ok, I assume this as support for idea of "reflecting stripes" and will not risk with middle of front wall.
"Still not live enough" is better than unexpected strong reflections in low mids.

I looked up Heradesign panels, I found only very thin 25mm panels, too thin to work well for broadband absorption.

With existing airgap I think they will work as good as current tiles. Their LF performanse depends on airgap and filling as for any velocity-based absorbers.

is to design the whole room first, and have someone build it

For this approach my room is too small. It would not allow anything but small nearfields in 1m triangle if I'd follow standard quidelines.
With architectural 4,3x4,7 m and some doors and windows 3 m triangle is just impossible without heavy damping. Maybe too heavy...

 

[Hipper]

They are very low decay times from my limited experience and what I've read. Mine are around 200ms which is still too dry for many. Having decay times of 50-60ms must sound - well it would be interesting to hear! I note that in Kvalsvoll's link the decay times are around 70ms.

Is it possible that you just need to spend a bit of time listening to get used to this new sound and perhaps learn to enjoy it?

My room is 4.2m x 3.86m and a a conventional build (for the UK) - wooden floor with carpet, brick walls with wall paper and a concrete ceiling.

I've added copious amounts of bass traps, attempted to reduce side wall reflections, and used EQ. As a result I get quite an even frequency response in the low frequencies with decay times over the whole range generally around 200ms which has produced a sound I like. I particularly find that reducing reflections gives a crisper more detailed sound. I can post my results if you want to compare.

I tried carefully placed ceiling panels but could hear no difference - room is 2.4m high and I listen quite close - about 1.5m to each speaker.

Unfortunately I can't advise on building a room!

 

[FeddyLost]

Is it possible that you just need to spend a bit of time listening to get used to this new sound and perhaps learn to enjoy it?

No, I'm very familiar with dry sound, that's why I really was ready for total absorption.
My hi-fi started from headphones and IEMs and I almost never go to live concerts (except some chamber music with velvet cello) so I'm not a fan of "enveloping sound".
All untreated rooms are too boomy for me now.

Currently I'm almost OK with sound, but if it's too dry even by studio standards, not all tracks will sound right.
Also, maybe some interference notches and comb filtering are not masked properly in my auditory system with decaying reflected sound, I don't know for sure. At least MyRoom concept from GS with diffusion being reported as more clear than simple absorption.

My room is 4.2m x 3.86m and a a conventional build (for the UK) - wooden floor with carpet, brick walls with wall paper and a concrete ceiling

I've lived in such apartment and it's almost impossible to get decent LF without aggressive EQ with placement, acceptable for ordinary life.
My current room is initially concrete and aerated concrete brick walls with 2500 msec RT without any absorption...

I tried carefully placed ceiling panels but could hear no difference

They start to work decently with airgap from 6" and more, and have some logarithmic benefits curve: after getting some decent RT at LP, any improvement requires more and more, and still in modal region you'll need tuned bass traps or really thick superchunks ...
With 2,4 m starting height there's also no room for big ceiling superchunk.

 

[abdo123]

if you're thinking about redesigning the entire room from scratch, then try to have:

1) 30% of surfaces covered with absorption ( Full range, as thick / as low as you can)

2) 20% of surfaces covered with diffusion (also as long / as low as you can)

3) manage frequencies below 100Hz with multi-subs.

btw these percentages are for each surface, for the floor you can create hollow 'tile-less' space in the floor, fill the space with absorption material cover the the absorption material with thin carpet or acoustically transparent fabric.

 

[Kvalsvoll]

Ok, I assume this as support for idea of "reflecting stripes" and will not risk with middle of front wall.
"Still not live enough" is better than unexpected strong reflections in low mids.

The idea is to add reflective - HARD - surfaces, either on top of absorption, or replace some of the panels, as you have suggested. Exactly how you do it, must be for you to decide.

Placement and dimensions of those surfaces will affect sound, but the most important difference will be a different decay profile with more energy at higher frequencies.

If you add diffusion, that will also affect sound, and will not preserve energy like a flat reflective surface, because diffusion will also absorb.

 

[Kvalsvoll]

At least MyRoom concept from GS with diffusion

Great concept, unfortunately not practically posiible to do in most of our small home rooms - we simply do not have enough space.

 

[Kvalsvoll]

I note that in Kvalsvoll's link the decay times are around 70ms.

If you look at the slope of the decay, it ends up somewhere around 150-200ms, the slope in the RT60 Decay fixed 2KHz is around 40dB/100ms.

RT60 is not very usable for evaluation of those small rooms, but one can look at the slope of the decay. The smaller the room is, the steeper/shorter the decay will be.

 

[FeddyLost]

you're thinking about redesigning the entire room from scratch, then try to have

Good idea, but practically it's impossible.
In fact, only exchange of inner shell walls is planned with existing openings for windows and doors.
And one of the reasons was to make pure stereo wihout any processing.

but the most important difference will be a different decay profile with more energy at higher frequencies.

In fact, I'm not sure anymore ... found out that datasheet for current rockfon says it have around 0,7 absorption in mids and highs ( it's really not much and maybe not enough), while Heradesign superfine with porous lining may have up to 0,95 ...
So, with such solution I can totally kill lateral reflections at the acoustical axis level, but have strong reflections from other directions, except ceiling.
It will be not random at all.
Looks like I need to estimate directions and places. Most troublesome is transition zone, where I have 8" woofer working up to 500 Hz ...

 

[Kvalsvoll]

In fact, I'm not sure anymore ... found out that datasheet for current rockfon says it have around 0,7 absorption in mids and highs ( it's really not much and maybe not enough), while Heradesign superfine with porous lining may have up to 0,95 ...

Absorption data may not be comparable, and also depends on area and angle of incident. Now that you have the panels in place, you evaluate from what is actually observed in the room - by listening, measuring. If there is too much absorption, adjust accordingly by reducing absorption and adding reflection. If the data sheet indicates there may not be sufficient absorption, and in-room analysis tells you otherwise, then it is of course the actual situation on the room that guides further adjustments.

The Rockfon panels I have used all had very good absorption, down to the frequency range where they are no longer efficient due to limited thickness. But panels such as these will always reflect some sound as well, but that is not a problem except from 1. reflection points and speakers with low directivity.

Absorption panels are designed so that chosen density gives the best absorption for the chosen thickness of the panel. So a thin panel is made of more dense material than a thicker one. This means there is limited performance increase achieved by mounting with air gap behind, compared to using the same total thickness with appropriate less dense material.

 

[FeddyLost]

Absorption data may not be comparable, and also depends on area and angle of incident

That's main problem. Without known directivity of sources and absorption quotients for different angles it's unpredictable.
But i suppose that wood wool panels will be better for 1st reflections than Rockfon panels with low angles of incidence.

there is too much absorption, adjust accordingly by reducing absorption and adding reflection

It's kind of puzzle assembly "in vivo" that i'd like to avoid.
Too much hassle with all that building job in living apartment.

I can imagine only one decent solution - put some extra absorption (wood wool panels with some hollowfiber mats lining instead Rockfon) and then adjust it by some thick wallpapers and maybe even make some improvised binary amplitude diffusers from wallpaper strips. Final combination will be glued (still don't know how) and painted.
All other ideas looks not very realistic.

The Rockfon panels I have used all had very good absorption, down to the frequency range where they are no longer efficient due to limited

For sure if we talk about big room where sabins matter more than exact placement of speakers and listener. Like factory or at least cinema.
My room (inner shell) is 3,6x4 m and I have no ITD gap with all reflections blending with direct sound.

panels such as these will always reflect some sound as well, but that is not a problem except from 1. reflection points and speakers with low directivity.

Exactly. I tried to hang Knauf fluffy rockwool on walls and it was very useful. But totally not acceptable for normal life, of course.
My 1st reflection on one wall is door and window blinds, so I need to use something rigid in their frames.