Room EQ Measurements - what next - Guidance needed

[JkSpinner]

Hello all

well I succumb to the pressure and did some room measurements.  Now my room is far from perfect with very few reflective walls, large glass door on one side, large opening to the entrance on the other, so no real first reflection points,  so will be interesting to see what the results give.  happy to post pictures etc.

i used the set up setting suggested by GIK on a video on you tube.

i can post the results file, or screenshots.

is there any particular screenshot to look at first.

are there any particular settings that I should use before asking for help.  The room is a Home Theatre / 2 channel music room, but I am really only concerned about 2 channel

guidance needed

i am a simple man so not looking to get into some deep technical discussion, I like simple.  I am not looking for perfect, just looking to make it better

thanks

[Keith_W]

I don't know which professional field you work in. But in mine, I don't order a test without a question which I want an answer for. Usually I already have a suspicion what the answer is going to be, so all it makes test interpretation super easy. It is the same with acoustics - which screen you look at, and how you take your measurement, depends on what question you are asking. How the test is done matters - so if you are taking audio measurements, you have to take special precautions to make sure that you are capturing data that will answer the question you are asking. 

 

In another thread on toe in, you mentioned that your speakers sound too bright and you have been experimenting to make them less bright. The answer will be found in the amplitude response curve (the first tab, "SPL & Phase"). Place your microphone in your listening position and do a sweep, then choose 1/12 or 1/24 smoothing (Graph drop down menu). Then zoom in to the measurement - first mouse wheel to zoom out, then ctrl-right click to select a box around the measurement, then click in the box to zoom. What you want to see is a falling frequency response, the bass should be about +6dB compared to the 20kHz. 

 

Here you are displaying the RT60 curve. RT60 stands for "Reverberant Time 60 dB", which is the time for sound to decay by 60dB. It is a measure of room reverberation. However, in small rooms, RT60 has no meaning because (1) long wavelengths form modes and not reverberant fields, and (2) the noise floor of a typical room is about 45dB so you have to measure at earsplitting levels (at least 105dB) to obtain an RT60. So T20/T30 is used instead - this removes the "reverberation" requirement and measures the time for sound to drop 20dB/30dB respectively. It is then extrapolated to 60dB by multiplying the time by 3 and 2. 

 

The T20/T30/RT60 target should be between 250ms (dead sounding) - 500ms (live sounding), depending on your taste. Below 250ms sounds dead and unnatural, and above 500ms sounds echo-ey and affects clarity. 

 

 

Look at the shaded area of this graph. This is the EBU 3276 target for room reverberation. You can see that it is wider below 200Hz and between 200 - 400ms above 200Hz. I could get into a long-ish discussion about different targets, and how it varies depending on rooms, and avoiding "gaps" in reverb, but ... you did say you don't want to get too technical

 

All I will say for now is that your T20/T30 is a bit too high. The easiest way to bring it down is with room treatment. 

[JkSpinner]

Thanks Keith, that RT60 graph is just one of the measurements, I did the full set for both right and left speaker, waterfall etc.  I have posted many questions in relation to treatment, but many folk respond with have you measured, cannot give advice without measuring, waste of time without measuring, etc so  I measured.  However I have no real idea of what settings to use, as there are many, and how to interpret the results.

My room is a large 7.6m x 4.4m that is offset in the middle, I have a 3m glass door on the front left, and a 2.4m open wall on the right, also some by folds on the rear left.

My listening position is 38% from the rear wall.

my opinion.

the window causes a problem, what problem, I do not know.  
the open wall and entrance /hallway are a problem.  The entrance/hallway are really part of the lounge.  When using the Dolby test tone, the pitch, reverberation in the entrance can be deafening, so I am assuming the first reflection point is really the entrance, the sound bounces around and comes back in the lounge.  I am considering installing some office divides with absorption or diffusion panels at the first reflection points, giving me some type of symmetry, keeping some of the sound in the room, so the entrance is not so much of an issue, and also installing some absorption panels in the entrance hallway.

i do not really have a bass problem, most likely because the room is a leaky room, but when walking around the room, it gets a bit brassy along the rear wall, and in the entrance.

i agree that I need treatment, but what and where is the question, like I said, I am not chasing perfect, just better.

If someone can point me in the right direction of what setting best to use for what test, I can do, and in my size room for eg, what RT numbers to use etc, I can make the changes and post the results

[JkSpinner]

15 hours ago, Keith_W said:

In another thread on toe in, you mentioned that your speakers sound too bright and you have been experimenting to make them less bright

I am not to concerned about this.  I have made changes over the past two years to overcome this.  My thread was more a question of what to the specs mean, and how should I interpret this in my room, ie do the specs indicate that the speakers are designed to be towed in etc.  but I will take a look at your suggestion above to see what it tells me.  These are the types of suggestions I am looking for

Edited August 11, 2024 by JkSpinner

[JkSpinner]

15 hours ago, Keith_W said:

All I will say for now is that your T20/T30 is a bit too high. The easiest way to bring it down is with room treatment

I would not consider my room small, at 7.6 x 4.4,  should I still look at T20/T30 or just T60 in my size room.  I assume if my reverberation time is to high, absorption is what I need.  I am thinking of starting with 2 x absorption pans on the rear wall, and several in the entrance (kinda strange I know) then look at creating first reflection point, them look at the front wall, but thought I would do some suggested tests first

[Satanica]

3 hours ago, JkSpinner said:

i do not really have a bass problem, most likely because the room is a leaky room, but when walking around the room, it gets a bit brassy along the rear wall, and in the entrance.

 

I think more or less everyone has a bass problem. Can you post SPL, Waterfall, Spectrogram?

Edited August 12, 2024 by Satanica

[alex87]

3 hours ago, JkSpinner said:

I would not consider my room small, at 7.6 x 4.4,  should I still look at T20/T30 or just T60 in my size room.  I assume if my reverberation time is to high, absorption is what I need.  I am thinking of starting with 2 x absorption pans on the rear wall, and several in the entrance (kinda strange I know) then look at creating first reflection point, them look at the front wall, but thought I would do some suggested tests first

You would still look at T20/T30 in most domestic setups and measurement volumes. They’re still Rt60 figures, just calculated differently. 
 

Don’t forget the ceiling, it’s often the largest surface one can treat to bring the T20/T30 to a desired range. 

[JkSpinner]

15 minutes ago, alex87 said:

Don’t forget the ceiling, it’s often the largest surface one can treat to bring the T20/T30 to a desired range

Ceiling is not forgotten, just off limits for now.  If there is a large enough change with my other changes, who knows, maybe it may be allowed in the future

[JkSpinner]

25 minutes ago, Satanica said:

SPL, Waterfall, Spectrogram

I measured right and left separately, should I have done L+R together, I cannot seem to attach the entire REW file

[frednork]

Where was mic when you measured?  It should be where your ears are when you are sitting listening ie best listening position (LP)? Separate Left and right measurements are good. 

[Satanica]

26 minutes ago, JkSpinner said:

I measured right and left separately, should I have done L+R together, I cannot seem to attach the entire REW file

You did it right, left and right separately. I don't think this looks terrible, but there are obvious areas there that could do with improvement, especially between 100-150Hz.

Edited August 12, 2024 by Satanica

[JkSpinner]

23 minutes ago, frednork said:

Where was mic when you measured?

Ear level listening position

[JkSpinner]

1 hour ago, Satanica said:

I think more or less everyone has a bass problem

I don’t know if I do or don’t, it certainly does not sound like I do from the listening position.  My guess is if I move the speakers closer to the front wall, I may start to have more of a bass problem.  And it not to say the bass cannot be improved.  My gut feel is that I have a leaky room where much of the sound escapes, via the glass door or into the entrance.  I usually leave the bifolds open when listening to music, and closed when watching movies in the HT.

[Satanica]

1 minute ago, JkSpinner said:

I don’t know if I do or don’t, it certainly does not sound like I do from the listening position.  My guess is if I move the speakers closer to the front wall, I may start to have more of a bass problem.  And it not to say the bass cannot be improved.  My gut feel is that I have a leaky room where much of the sound escapes, via the glass door or into the entrance.  I usually leave the bifolds open when listening to music, and closed when watching movies in the HT.

 

I don't think one should think of it as black and white, I do it or I don't, but think of it as could it be improved? Every setup could be improved, even those that have already done improving. If you've done nothing to improve your in room bass which I presume, then equalisation under about 200Hz is a no-brainer. Whether to do equalisation up to the next octave (400Hz) and what to do takes more thinking (brainer).

[JkSpinner]

1 hour ago, Satanica said:

you've done nothing to improve your in room bass which I presume, then equalisation under about 200Hz is a no-brainer

You are correct Paul, I have done noting as yet, as this is the start of my journey in room correction.  I have however made lots of small changes over the last six months.

i assume from your two comments that you are suggesting that I should start with some type of bass traps

[Satanica]

Just now, JkSpinner said:

You are correct Paul, I have done noting as yet, as this is the start of my journey in room correction.  I have however made lots of small changes over the last six months.

i assume from your two comments that you are suggesting that I should start with some type of bass traps

 

No, I think you should start with digital room correction below about 200Hz. This is where your biggest issues are and that's just typical in virtually all rooms. If you want to seriously (objectively) improve your overall sound this should be the biggest focus (20Hz to 200Hz). I presume you've heard of Dirac Live, it's one of the most cost effective and easier ways to shape your bottom octaves for the better and most solutions come with the ability to have and easily switch between multiple profiles. There are other competing solutions available.

[Keith_W]

Gosh, SNA's editor makes me grumpy.

 

Re: "Window is causing a problem. What problem, I do not know". 

 

It helps to think of every surface or opening as an absorber with different coefficients of absorption. The industry uses "NRC" (Noise Reduction Coefficient), where NRC 0 = no absorption, perfection reflection, and NRC 1 = 100% absorption, zero reflection. The NRC varies according to frequency. 

 

So walls will have an NRC close to 0 for the entire frequency range. Foam absorbers have an NRC of 0.8 - 1 down to a lower frequency limit (depending on the thickness and density of the foam) where it starts dropping down to 0. You can think of a closed window as a kind of membrane absorber. Membrane absorbers are pressure absorbers, meaning they selectively absorb certain bass frequencies whilst reflecting everything else. When you open the window, it becomes a broadband absorber (because sound escapes outside and only some of it comes back). The easiest way to determine what your window is doing is to go outside and measure the frequency response with the window open and again when it is closed. Subtract closed from open and that should give you a rough idea what your window is doing. 

 

When you say that "reverberation at the entrance is deafening", I presume you mean this entrance? 

 

 

The reason it is deafening is because that entrance is located in a small enclave. Any sound that enters that enclave bounces between the parallel walls and concentrates in there. If you don't listen from that position, I wouldn't worry about it. 

 

 

Re: "Small room". When we talk about small room acoustics, this means that the largest dimension of the room is less than the lowest wavelength of interest. A 20Hz frequency has a wavelength of 17.15m. All our listening rooms are small. A "large room" is a concert hall, basketball stadium, cathedral, etc. 

 

Small rooms can not form reverberant fields below a certain frequency. A reverberant field is multiple overlapping room resonances. Small rooms produce room modes (standing waves) instead. 

 

 

Anyway, let's look at your FR graph. I have drawn in a typical room response target which I have aligned between the critical midrange frequencies of 100Hz - 1kHz. I have calculated your Schroder frequency for you and indicated where Schroder is (123Hz) and the transition boundary (492Hz) with T30 = 0.4s and Room Volume = 105 m^3 as inputs. You need to think of the behaviour of long wavelengths differently to short wavelengths. Below Schroder, bass frequencies form modes, the frequency response is dictated by the room. No matter what speaker you put in there, as long as it is in the same position and has the same bass output, the frequency response will look roughly the same. Above the transition boundary >552Hz, there is minimal room influence on the frequency response, what you hear is the direct sound of the speaker + reflections. 

 

Looking at the target, we can see that below 100Hz you have about 3dB less bass than you should. Above 1kHz you have up to 3dB more treble than you should. Above 12kHz the treble drops off rather abruptly. 

 

So what can you do? The first thing to point out is that the target curve I drew for you is one among at least a dozen target curves. Different people like different tonal balance. So you need to decide if you like the sound above Schroder (123Hz) or not. Does the midrange and treble sound OK to you? If not, no need to do anything. Otherwise, your options are either DSP or new speakers. 

 

Below 123Hz, you have problems, but again you should ask yourself whether you mind lacking bass and whether it sounds OK to you. Otherwise, it's going to be subwoofers and DSP. 

 

Bass treatment will help even out the bass response and paradoxically might give you a bit more bass. But bass treatment is intrusive and not an option for most people, and is often less effective than hoped unless a lot of treatment is deployed. DSP and subwoofers is the best option, but it comes with its own learning curve. Basically, you have an unfortunate choice between one option which does not work too well, is expensive, and intrusive. Or the other option which does work well, but requires a huge upgrade in knowledge. 

 

Edited August 12, 2024 by Keith_W

[Keith_W]

I realize that one question we haven't answered is whether we should treat the first reflection point. Answering this question is difficult and requires some maths. What you need to do is look at the first 50ms of the energy time curve (ETC) and look for little peaks indicating what time the reflections are arriving. You then calculate the distance from the time using the equation d = 343 * t, and then get out a tape measure and decide which wall is causing that particular reflection. Then you compare left and right. 

 

 

Here is an example. The time lag between the main signal (the big spike) and the reflection is 11.4ms. So (11.4/1000 *343) = 3.91m. I then look around my listening room to see what is 3.91m. Answer: floor bounce. 

Edited August 12, 2024 by Keith_W

[frednork]

5 hours ago, JkSpinner said:

Ear level listening position

Great! so all your measurements should be useful then.  Your amplitude plots (SPL) are surprisingly flattish which is why I asked about measuring position.  But perhaps a bit too flat.  Looking at your SPL I would say the overall sound in that room would be a bit lean and whilst would expect flat in an anechoic chamber, when we use a normal domestic room we expect the bass to be plotting higher than the treble depending on preference to some extent. Likely reasons for this are that indeed your bass is leaking out so not building up as much as some rooms but also on the other side it looks like from the RT60 you posted that there is very little absorption in the room. The ideal would be to have fairly flat RT60 from high frequencies down to around 100hz or so and then can increase a bit.  RT60 around 600ms is too high for me and likely also the reason for the SPL graphs showing higher values  as you go up in frequency than expected/probably desirable.  Even 500ms is a bit high for my taste but this is something you can suck and see to some extent. Placing absorption around the room anywhere (except first and second reflection points) will help enormously.  Broadband absorbers  will work well to start to bring your RT 600 down in the areas you need it most and begin to even things out.  If you look at my thread mentioned in your other thread which also includes a prediction tool on how absorption will impact RT60's for your room you can figure out whats needed. Maybe aim for 450-500 to begin and see how that looks and post back .  The variation in the bass is not terrible compared to many rooms so may be best to leave that for now and see how reducing RT60's impacts on that and then revisit the bass  later once you know what you are really dealing with.  Remember the impact of panels on my setup , its not that dissimilar to yours. Most rooms arent.

 

Regarding reflection points just dont use absorption there (for now at least) and am not sure if the panel next to the couch is a recent addition to act as a mirror reflection point for the glass side but it looks like it is a bit too far back to do that. Assuming you know how to determine where the reflection point is but if not just yell out. Here is the link to my thread for reference 

 

Edited August 12, 2024 by frednork

[Satanica]

I agree with the above advice that the sound appears to be to lean, not enough bass overall fro about 100Hz down.
Room correction (EQ) could help, at the expense of the overall headroom of your system.
Multiple subwoofers, crossed over at 80-100Hz (in conjunction with room correction) would also be a solution.

Edited August 12, 2024 by Satanica

[JkSpinner]

2 hours ago, Satanica said:

sound appears to be to lean, not enough bass overall fro about 100Hz down.

Would moving the speaker back closer to the front wall, or closer to the side wall help, or  increasing bass on the tone controls?

[JkSpinner]

5 hours ago, Satanica said:

start with digital room correction

I thought, (through my research that Dirac is what I would look at after room treatment, like the final step.  And as far as I know, I would need a new amp, and I am not sure that is on the cards at this stage, but who knows what the future holds

[JkSpinner]

4 hours ago, Keith_W said:

first reflection point.

I will read this again, and have a further look at my charts.  My idea around the first reflection point is to Create them - which will prevent some of the sound from leaving the room,  might help with the leaky room, and also create some symmetry, as my speakers are different distance from each side wall.  Using diffusion may also help with the dead or flat room.  Just a guess here.

[Satanica]

17 minutes ago, JkSpinner said:

Would moving the speaker back closer to the front wall, or closer to the side wall help, or  increasing bass on the tone controls?

 

It will definitely change the measured reponse, that's for sure. Unfortunately, like many things, it will probably become a trade off, improving in some areas and reducing in others. 

 

But I like that you are thinking about the idea. I think that's it's worth exploring. I wouldn't sacrifice your preferences for imaging and soundstage width. So I don't think you should change the speaker width to improve bass if it reduces your enjoyment of the mids and highs. If you feel like you have the freedom, then moving the speakers back could overall be very worthwhile. If do, I'm sure there are those of us here who would like to see the measured change. 

Edited August 12, 2024 by Satanica

[JkSpinner]

3 hours ago, frednork said:

Placing absorption around the room anywhere

I am thinking (gut feeling) that some diffusion on the back wall either side of the back surround speakers, as a start, maybe the corner as well, then on the brick wall, maybe on the privacy screen, maybe beside the speakers.  But Diffusion on the front wall, maybe diffusion beside the speakers as well, I am not sure, hence the measuring and questions.  And I still think some absorption in the entrance, if the noise is that deafening in the entrance, then I can most likely hear that in the listening position, I don’t think it will hurt.  Either way, most absorption panels come in packs of four or six so one pack should be enough to start.