Support with interpretation measurement and room treatment

[JDortmans]

Hello all,

I am new to this forum and I want to thank you in advance for your support.
Last year I did build a new house which has a basement underneath of 12 meter x 8 meter size.
One of the rooms in this basement is my new music listening room.
The inner dimensions of the room is 5 meter x 7,2 meter and 2,5 meter high.
The sealing is treated with acoustic spray (black paper glue mixture, Acosorb.com/acoustic-spraying) of 25 mm thick.
At the moment I am only using my 2 front speakers to listen in stereo.
Front speakers are Magnepan 20.1 in combination with a special Magnepan active filter for bi-amping them.
The power amps I use are a Krell KSA 300S for the low frequencies and a Audio Research VS 115 for mid and high frequencies.

I did some measurements with REW v5.19 using a Behringer ecm 8000 and Behringer U-Phoria UM2 USB audio interface.
Attached one of the mdat measurement files I created.

My question:
Although I only treated the sealing of the room the sound is already much better than expected in this concrete box.
The main problem is that in the low frequencies I miss some detail and at some frequencies the bass gets very loud for an moment.
I did some experiments with the position of the speakers (at the moment 2 meters from the back and 60 cm from the side).
I also changed my listening position by moving my couch backward towards about 1 meter from the back wall.
This resulted in a big improvement in resolution, detail and level of bass.
But still at some frequencies the bass is to loud and I miss detail.
Based on the measurement I done can you advise me how to improve the acoustics of my listening room?

 

[linearphase]

Can you give us a better idea how this room is laid out. A sketch, even hand draw can be very helpful.

 

[JDortmans]

Hello, thx for your replay!
I attached an image of my room with dimensions in meter and centimeter.
In the meanwhile I found out more about the behavior of my room.
The website of amcoustics was very helpfull for this. amcoustics.com/tools/amroc?l=720&w=500&h=250&r60=0.6
I also attached a image generated by this website which shows the frequencies which I also measured with REW.
I am studying more and more about the treatment of this.
I hope you can help with this.

 

[linearphase]

Thanks good info. Amroc is good, I use it all the time but it is hard to beat good measurements. I will try to look at your REW tonight. In the meantime I have several questions and comments.

1. How much flexibility do you have in moving things in the room?
2. How about room treatments do you have flexibility?
3 With solid concrete you have essentially have 100% reflections off the walls.
4 It takes a LOT of absorption to tame a room like that -10’s of square meters and the material is going to be thick.
5. To get started I would move the couch at least 2 meters from the back wall.

You mention bass clarity but how is imaging? With dipoles there is a lot on information radiating out of the back. That will have to be partially absorbed and likely also diffused.

If you want to experiment- quilts, moving blankets, duvets and similar material hanging over ladders or other fixed supports work well to absorb midrange but will have NO effect below 100 HZ. Membrane type absorbers such as limp mass absorbers are most effective at low frequencies.traditional bass traps can handle for 100- 1KHz

 

[linearphase]

Two things I forgot. Initially the side walls and back walls will need treatment. A thick rug on the floor can also help a lot.
The general order of solution.

1 Speaker and listening position placement
2. Room treatment
3 Assuming you will accept it room Equalization.

Each of these is equally important. I find most people who do not believe in any of these have systems that sound only a fraction as good as they could. I have helped at least ten people set their systems up using this process. In every case significant improvements were observed.

 

[linearphase]

After looking at the REW data it shows you have thug amount of reflections so you should do the following things.

1. move the couch 2 meters away from the back wall
2. add a large area or wall to wall carpeting
3. if possible as a test hang large quilts, duvets, or other large absorptive blankets on both side walls at the points of first reflection. Google if you do not know where this is. These absorbers are more effective if they are at least 12cm from the side walls.
4. Toe in the mains so that a line that passes through the plane of the front speaker panel intersects this same point of first reflection.

These bumps in the bass response are the nasties you are hearing. To absorb them will be tough. Low frequency absorbers will be necessary and they will be big. You could try bass traps but they are not very effective at very low frequencies.
What you really need are limp mass membrane absorbers. They can be DIY if you are handy or can be bought. You will need about 100 sq ft of surface area for them to work fully.

Note that equalization can tame most of the peaks you have but it will not fix the dips you have. The respose above 200 Hz is Ok but not optimized.

Sorry for dumping all this on you at once. the key is to tackle one issue at a time. Listen, and if you want to learn, measure after each step. keep good records. it may take a while but you will get better at this.

good luck!


MORE DETAILS BELOW FROM YOUR DATA

The ETC under impulse response reveals just how many reflections you have.

The ETC found under the impulse response shows how energy arrives asa function of time. any energy after 0 sec will have deleterious effects on sound, though as long as it is below 10% the effects are mostly inaudible. As you can see you have energy arriving at 5 and 14mS (.005 and .014 seconds) that is 75% as strong as the main arrival from the speakers. This will have significant negative effects on the sound clarity and imaging. The area circled with green shows where the later reflecting are coming from these are also not good but not as important as those before about 6mS.
To learn how to find where all these reflections may be coming from Google calibrated acoustic string. You can easily make yourself one. it use mine all the time. the trick is to systematically find and place absorbers at the points where you find the reflections. Note that they can be anywhere including on tables and furniture in your room.

 

[linearphase]

BTW REW has a very useful Room acoustics calculator built in. It is in the top menu and is called Roomsim.
Pretty good instruction on using it are in the help files of REW. It not only models the room but where you have placed the speakers and listening position, so you can drag the speakers and LP around and see what effect they will have on the response. For your room as is I would set the absortion coefficient to .4 for the ceiling and zero for all areas that are bare concrete.
By increase the absorbtion coefficient you can roughly simulate the effects on the frequency response.

 

[JDortmans]

Thanks a lot for the info.
Let me first answer your question's.
1. This is my dedicated listening room in the basement of the house. So I am pretty flexible in moving things.
2. I am aware I need more room treatment so also flexible here.
3. The walls are solid concrete and all plastered except the ceiling because the sealing is treated with acoustic spray (25 mm).
4. Like mentioned the whole sealing is covered with acoustic spray. I am aware more absorption is required.
5. I started with the couch approximately 1,5 meter from the back wall. Moving the speakers from 1,6m from the front wall to 2m and moving the coach more to the back wall from 1,45m to 1,2m.
This was a big improvement compared to the initial situation.
The house was newly build in 2019 and I entered the house in December. So until now I had limited time experimenting because a lot of things have to be finished in the house.
I am also learning a lot from the information and provided by Acoustic fields.
I am thinking in building my own diaphragmatic absorbers and I am also thinking of using diffusers on the back wall.
The front wall is also used as a projection wall. It is painted with special paint for that.
I the corners of the front wall (behind the speakers) I have room for treatment.
I was thinking of putting a diaphragmatic absorber behind each speaker in the corner so area of the front wall I use for my beamer (3,5 m) is still available.
I have a background in engineering (automotive and now robotics software engineering) and I like doing these improvements my self if realistic.
I have done some experiments with putting big boxes the amplifiers came in on top of each other in the 2 corners behind the speakers.
A very small improvement although I could not measure the difference with REW.

I hope this information helps and I am looking forward in receiving the required help and discussing the required treatments!