Room Treatments in the Real World

[Katji]

But having played in a wind ensemble and attended lots of concerts the concert halls aren't over dampened, usually they have some dampening combined with reflection panels.

Those are diffusers, especially those with multiple various height surfaces. ...Which are usually a feature of concert hall acoustics, big and expensive.

And...too much damping tends to dampen people's appreciation of the music.

Typical situation with most audiophiles is that they don't like low RT due to impossibility to make good simulation of big embracing sound and wide soundstage in small room without reflections. So, i think they prefer slightly smeared imaging and transients over flattish, surgically disassembled sound, which sounds totally artificial after typical live gig or orchestra sound.

Definitely.
Thing is to "get the balance right"......hence diffusion combined with absorption. And bass traps.

 

[FeddyLost]

I am pretty sure the main problem audiophiles have with treatment is the wive not letting

Not only that, but most of them maybe.
I heard a lot complains like "this rockwool and foam crushes my estetic feelings" and good cosmetically acceptable treatment is not cheap at all. And sometimes design concept just don't accept cluttering with panels, resonators and even nice wooden diffusers. Also, almost any good treatment needs a lot of space.

I never understood this. you don't need reflections for this, just widen the triangle

If room is not reflecting, it's not enough. It widens scene, but layering become weird. Also, central imaging zone will suffer.
I tried this with really low RT. Something like recommended triangle still better.

From 500 Hz to 20 KHz, I am in the dark and I am sure, I am not alone and I thought, I understood the issue

If you don't want to dive deep into studio design concepts, you can make wideband absorbers from Heradesign with rockwool and air gap and treat just reflection zones.
Usually it's enough.

Thing is to "get the balance right"......hence diffusion combined with absorption. And bass traps.

There's a lot of slightly different concepts, and most of them still require experience and big room with good proportions.

 

[SimpleTheater]

I am not an expert but I understand that the use of passive room correction (Room Treatments) in the lows, involves large contraptions... Simple wall covering are not effective down there at <100 Hz . Better use multiple subs and after that, DSP and EQ to smoothen the response... From 500 Hz to 20 KHz, I am in the dark and I am sure, I am not alone and I thought, I understood the issue. Right now the room is being painted and is naked and slap echoes are easily heard, conversations are not clear. The room will of course have some furniture and drapes when finished and a lrge screen on one wall. I have now a fixed Stewart Firehawk 100 inches.

You're exactly right about <100 Hz. I think your Amazon foam panels will be very effective >500 Hz and extremely effective >1 KHz.

When I built my home theater, a simple starting point was treating about 1/3 of the walls with treatment. I bought Owens Corning Acoustic Blanket. Since it's about 3' wide, simply roll and tack/glue it to the drywall. I covered 100% of the wall behind the speakers with the stuff.

The second area to attack was the floor, so I got a 3/8" rug pad and a thick rug. I kept the ceiling live (just paint).

I picked up a sound meter with RT60 (forgot the brand, but it was about $400), and my decay was about 32 ms, so I was happy with the treatment. IMO, the room sounded great ABOVE 500 Hz.

Below 500 Hz, was a LOT of trial and error. I started with using 4" thick stiff fiberglass insulation. Didn't take long to double them up to total 8" thick. I kept them in their wrappings so I could move them around more easily and take measurements. Once I was happy with the sound, I then unwrapped them and used my extra Acoustic Blanket to give them a nice black finish.

Based on your room size, 35 Hz is going to be a problem because a 35 Hz wavelength is about 32' long, which will give you issues at half length - 16', then again at 70 Hz (quarter length is about 16') . The width of your room will give you issues around 55 Hz and 110 Hz.

Anything lower than 30 Hz will blow right through your walls, and I don't know if you'll have an issue treating them. Then again, sub placement will completely change things as well because that will change the point source of the low frequencies and when they come into contact with your walls. That's why there is going to be a lot of trial and error.

Good luck and let us know what you decide.

 

[kevin52]

Kieth Yates started talking about the best RT 60 for a home listening back in the 70's there an article by Kieth and a paper from Earl Geddes about multiple subs.

The procedure I would follow is:
Set up speakers/Subs to optimize LF response as per Geddes measuring the room as you go. Using a mic with you preferred DSP
software/hardware.
Install room acoustics as per Yeats article to get correct RT 60 for room with lots of diffusion.
Apply DSP as needed to get the best possible freq response.

https://keithyates.com/a-matter-of-diffusion/

http://www.gedlee.com/Papers/multiple subs.pdf

 

[dasdoing]

Simple wall covering are not effective down there at <100 Hz

they are on the backwall, but you need a lot of material down there

If room is not reflecting, it's not enough. It widens scene, but layering become weird. Also, central imaging zone will suffer.
I tried this with really low RT. Something like recommended triangle still better.

this is true. still, using reflections widening the image has the same problem (you are creating a "second speaker" and the acustical source will be somewhere in the middle of the speaker and the reflection), plus it smears the central image.
you can use a plugin to widen the center image.

btw: the regular triangle is wide enough once you start to listen to the ambience in the recording. you can't if your ambience is overpowering it

 

[FeddyLost]

they are on the backwall, but you need a lot of material down there

Not only a lot.
There's another problem: you need to gradually increase flow resisitivity from zero to some value if you want to optimize absorption, which is technologically impossible or very difficult.
Maybe some molten synthetic wool materials like hollowfiber/basotect can keep form in plates and be very flow-through-able, but with cheaper rockwool it's impossible.

still, using reflections widening the image has the same problem

It depends on reflections' strength and time delay.
But in small rooms there are no options for delays and suppressed reflections.

you can't if your ambience is overpowering it

That's why I prefer dryer room. Mine is small from the start, so there was no choice.

 

[FrantzM]

Perhaps it is time to revive this interesting subject.

Update.

I moved from the original living room and have a dedicated room 5.5 x 3.2x 2.8 meters. It is all concrete and partially treated with some fooam matterial I bought from Amazon.. I have cared to measure the room, frankly. Repeating for the 100th time my system ( I am almost proud of it). It was inspired by mostly @RayDunzl . He uses the same speaker and same subwoofers but with DRC quite often: JBL LSR308 and Dayton Audio SUB1500
I use an AVR for the system with a miniDSP 2x4 for the subwoofers...
Foam material are in the front , first reflection (meaning side) and back walls and on the ceiling. There is also a thick carpet on the floor. I used REW and the miniDSP 2x4 to linearize the subwoofers, then presented the resulting "subwoofer" to only one subwoofer input on the AVR, Integration through Audysey XT32, I use the smartphone APP, but am trying to convince myself not to splurge for the PC version of Audyssey..
Then, this discussion came up:

Quest for Real Bass Traps​

I had forgotten about this, my own thread. I would like it to be more lively , the subject is an important one and in particular, the issue of Room Treatments vs DSP/EQ in the bass. I would call bass the frequencies below 300Hz, roughly below the Schroeder frequency for a medium sized room... A rough, ballpark figure

I am very satisfied with my present system. It can improve.
The debate that came up was Room Treatment in the bass vs DSP/EQ and/or multiple subwoofers.

To not hijack the other thread, I would prefer that the discussions continue here ...

Peace

 

[abdo123]

I feel like there is two points that people often miss with EQ:

1) only when the system behaves like a minimum phase system (smooth Excess group delay) that EQ can meaningfully correct a response, otherwise the phase and group delay will not be corrected and the ringing will continue to be audible.

2) steady state (regular in-room) measurements only represents what we hear below 100Hz.

Here are some examples of my room, we can see that EQ pretty much corrected a lot of the ringing below 100Hz.

And it's even visible in the Group Delay

This is because my Excess group delay looks something like this.

While i could correct for the dips in 30 to 40Hz they're very seat dependent so i left them be.

This is what the overall response looks like (1/12 oct smoothing) with EQ only below 100Hz, speakers are flat on-axis with smooth directivity. It sounded still muddy and colored, but with good sounding sub-bass.

We can see that there are still messiness below 1KHz, much of which is not very different from seat to seat. only below 300Hz where things really change dramatically between seats. Maybe we can use EQ to correct it? Lets have a look at Excess Group Delay.

Yeah looks pretty messy! It seems like there are only two regions I can use EQ on and that's 600 to 700 and 300 to 400. 600Hz to 700Hz show a more or less a linear response, but around 384Hz there is some resonances that we can EQ.

First I tried a PEQ of -2.5dB gain with Q = 2 to bring the response down.

Now you might expect that it would help with subjective sound quality but it barely did anything. We have to go back to point two that i shared, what we measure above 100Hz rarely show us what we actually hear. Above 100Hz we need to focus on Direct sound (speaker tonality) and very early reflections (less than 50ms late).

I applied Frequency dependent windowing (10 cycles) to the measurement without any PEQ at 384Hz and here is the result.

There is an early reflection that is causing 10dB peak at 384Hz! When all reflections arrive (measurement without FDW) it's only a couple of dB high because all the other late reflections are filling up the response else where.

While playing pink noise I decided that the sound was most neutral with a PEQ at 384Hz and a -7dB gain with Q of 2. This is what the regular steady state measurement looks like with that.

This is about how far you can go with regards to EQ. This is what 'Neutral' measures like in my room. There is nothing more to improve with regular IIR filters.

I'm thinking of dabbling with FIR to see if i can smooth the Excess Group delay between 100Hz and 200Hz but that's a project for another weekend. I cannot reiterate how dramatic pulling down early reflection peak was in terms of sound quality.

 

[RayDunzl]

Unsmoothed Group Delay...

JBL LSR 308 green
MartinLogan reQuest red

Opinion:

JBL sprays the room

MartinLogan doesn't

Doesn't look the same when smoothed, but I find it interesting, nonetheless.

Same thing happens with unsmoothed frequency response:

JBL red, ML black

That really shows my bass hole and the 220Hz dipole/wall cancellation.

 

[Flaesh]

Doesn't look the same when smoothed, but I find it interesting, nonetheless.

I love these pictures every time I see them. Except for the hole in bass.

 

[curiouspeter]

Unless you have a dedicated listening room, the audio system will have to co-exist with the living area. Room treatments like bass traps have no place in the living room. At best, we can do something about placements and that's about it.

Use RoomPerfect or Dirac Live to fix room issues. They are really pretty good.

 

[dasdoing]

Room treatments like bass traps have no place in the living room

I am curious...Is this Peter talking or Mrs Peter? lol

 

[Thomas_A]

As soon as you use two speakers you are leaving the idea of being truthful to the stereo recording. You can get closer by near-field listening or highly directive speakers but still being off what is on the recording. My take is instead to be closer to the event which is dependent on your model of listening. Multichannel is one solution and we all know that upmixing stereo to multichannel is not true to the recording. What should the room look like? My suggestion is a room which is pleasant to be in and have normal convesations in. Not too lively and not too dry. If anything the wall at the speaker side can be damped somewhat. The rest is thick carpets, sofas, pillows/blankets, coffe table, paintings, decoration on the wall etc. ”Normal” stuff in a room.

 

[Hexspa]

I feel like there is two points that people often miss with EQ:

1) only when the system behaves like a minimum phase system (smooth Excess group delay) that EQ can meaningfully correct a response, otherwise the phase and group delay will not be corrected and the ringing will continue to be audible.

2) steady state (regular in-room) measurements only represents what we hear below 100Hz.

Here are some examples of my room, we can see that EQ pretty much corrected a lot of the ringing below 100Hz.

View attachment 229509

And it's even visible in the Group Delay
View attachment 229510


This is because my Excess group delay looks something like this.

View attachment 229499

While i could correct for the dips in 30 to 40Hz they're very seat dependent so i left them be.

This is what the overall response looks like (1/12 oct smoothing) with EQ only below 100Hz, speakers are flat on-axis with smooth directivity. It sounded still muddy and colored, but with good sounding sub-bass.

View attachment 229500

We can see that there are still messiness below 1KHz, much of which is not very different from seat to seat. only below 300Hz where things really change dramatically between seats. Maybe we can use EQ to correct it? Lets have a look at Excess Group Delay.

View attachment 229503

Yeah looks pretty messy! It seems like there are only two regions I can use EQ on and that's 600 to 700 and 300 to 400. 600Hz to 700Hz show a more or less a linear response, but around 384Hz there is some resonances that we can EQ.

First I tried a PEQ of -2.5dB gain with Q = 2 to bring the response down.

View attachment 229504

Now you might expect that it would help with subjective sound quality but it barely did anything. We have to go back to point two that i shared, what we measure above 100Hz rarely show us what we actually hear. Above 100Hz we need to focus on Direct sound (speaker tonality) and very early reflections (less than 50ms late).

I applied Frequency dependent windowing (10 cycles) to the measurement without any PEQ at 384Hz and here is the result.

View attachment 229506


There is an early reflection that is causing 10dB peak at 384Hz! When all reflections arrive (measurement without FDW) it's only a couple of dB high because all the other late reflections are filling up the response else where.

While playing pink noise I decided that the sound was most neutral with a PEQ at 384Hz and a -7dB gain with Q of 2. This is what the regular steady state measurement looks like with that.

View attachment 229507

This is about how far you can go with regards to EQ. This is what 'Neutral' measures like in my room. There is nothing more to improve with regular IIR filters.

I'm thinking of dabbling with FIR to see if i can smooth the Excess Group delay between 100Hz and 200Hz but that's a project for another weekend. I cannot reiterate how dramatic pulling down early reflection peak was in terms of sound quality.

Do you have any links so that I can understand the concept and applications of Frequency Dependent Windowing better? What I gather is it limits the time domain of the impulse from which it FFTs the SPL response. You seem to be using it to apply corrective EQ in order to counter the effect of specific reflections. Is this because the initial reflections have a greater impact on perceived tonality than late? You appear to say as much in your post (…steady FR doesn’t represent what we hear above ~100Hz…).

I read the REW help but it seems like you understand the topic with enough clarity to take action so I’ll appreciate any help. Also, the idea that one can manipulate excess group delay with FIR filters seems juicy so I’ll humbly accept a bone on this topic also. Thanks.

 

[JHC]

Just shared the below in another thread, never try room treatment before (vs. MiniDSP), this type of service might come free from solution vendor, something to consider and might save some time...

 

[FrantzM]

Do you have any links so that I can understand the concept and applications of Frequency Dependent Windowing better? What I gather is it limits the time domain of the impulse from which it FFTs the SPL response. You seem to be using it to apply corrective EQ in order to counter the effect of specific reflections. Is this because the initial reflections have a greater impact on perceived tonality than late? You appear to say as much in your post (…steady FR doesn’t represent what we hear above ~100Hz…).

I read the REW help but it seems like you understand the topic with enough clarity to take action so I’ll appreciate any help. Also, the idea that one can manipulate excess group delay with FIR filters seems juicy so I’ll humbly accept a bone on this topic also. Thanks.

+1

Peace.

 

[MarnixM]

For my own living room two years ago I did an ARTA measurement. I add the text for the results:

ARTA User Manual
To be able to judge a room on acoustic behaviour the International Organization for Standardization developed a standard for measuring. This is the ISO-3382 standard with three sub standards 1,2 and 3. Number two (ISO 3382-2) in meant for small rooms like our living room. The standard describes exactly what, how and with what the measurement has to be done.

It is important that a (calibrated) measurement microphone is omni-directional (fi. the EMM6) and is positioned at least on a distance of 1 meter free from all room walls. Instead of an omni-directional speaker indicated in the standard we mostly have to stick to our two speakers.

By ARTA, the program for impulse response measurement and real time analysis of spectrum and frequency response, it is possible to measure the most parameters as describe in the ISO 3382 standard. ARTA even measures in eights octaves bands from 63 – 8000Hz, while the standard recommends that measurements be taken in the six octave bands from 125–4000 Hz.

ARTA User Manual

Quantity Symbol ​	Subjective Aspect ​	Optimum value living room​
Reverberation time T30, T20 and interpolated T60 (s)​	reverberance, loudness, involvement​	T60 around 0.500 mS​
Early decay time EDT (s)​	reverberance, clarity​	Equals T60​
Center time Ts (s) (“Schwerpunkts Zeit”)​	clarity​	Proportional to T60​
Clarity C80 (dB) (“Klarheit”)​	clarity​	-3 dB or higher​
Clarity C 50 (dB)​	clarity​	-2 dB or higher​
Definition D50 (%) (“Deutlichkeit”)​	speech definition​	>50%; the higher, the better​
Bass Ratio (BR)​	reverberance, loudness​	Music: 1.0 -1.3​
Strength G (dB)​	relative sound level, intimacy​	​

Table 1: ISO3382 parameters provided by ARTA, their subjective sound aspect and optimum values​

In ARTA for a living room the so called swept-sine method is the most optimal way for a impulse measurement. It gives a better estimation than other excitation signals (periodic noise and MLS) in acoustical time-variant environments and slightly non-linear systems as our living room is.

Figure 1: Energy decay curve of a swept sine excitation in ARTA on a measuring position 1 meter height and on 5 meter distance from the speakers​

After enabling the T60 toggle and logging all filter bands (63 – 8000Hz) a table can be generated with all the parameters over all the bands.

Table 2: Measured results in ARTA for the ISO 3382 acoustic room parameters for my living room.

 

[FeddyLost]

this type of service might come free from solution vendor, something to consider and might save some time...

This prediction comes with some project of acoustic treatment.
Project is more interesting than such prediction itself.

Do you have some empty drywall room or a lot of windows? RT @ 125 before treatment is much less than RT @ 4000 which is unusual for an ordinary living room with furniture.

 

[abdo123]

Do you have any links so that I can understand the concept and applications of Frequency Dependent Windowing better? What I gather is it limits the time domain of the impulse from which it FFTs the SPL response. You seem to be using it to apply corrective EQ in order to counter the effect of specific reflections. Is this because the initial reflections have a greater impact on perceived tonality than late? You appear to say as much in your post (…steady FR doesn’t represent what we hear above ~100Hz…).

I read the REW help but it seems like you understand the topic with enough clarity to take action so I’ll appreciate any help. Also, the idea that one can manipulate excess group delay with FIR filters seems juicy so I’ll humbly accept a bone on this topic also. Thanks.

you seem to have perfectly understood everything.

Unfortunately REW doesn't offer any sort of frequency specific cycles so I can't pick one cycle for 20KHz but 10 for 100Hz so you kind of have to experiment a bit with your room and your hearing and trial and error what works (pink noise is incredibly discerning).

However a cycle is one frequency length so in that way it's frequency specific, but 10 cycles for 20Khz for a space as big as a room is way too much.

 

[JHC]

This prediction comes with some project of acoustic treatment.
Project is more interesting than such prediction itself.

Do you have some empty drywall room or a lot of windows? RT @ 125 before treatment is much less than RT @ 4000 which is unusual for an ordinary living room with furniture.

Yeah.. it's a den/listening room under construction, nothing but concrete and dry wall when finished. Instead of covering the surfaces with soft material, I am considering just apply treatment as is.