I thought I would make a thread about improving the acoustics in my 'concrete bunker' living room. I'm a total novice when it comes to room treatment, so I hope some members will chime in to guide me a bit.
Background:
We moved to this apartment, over a year ago, and the acoustics of this concrete bunker scared me, and I have been wanting to improve them, because listening in this room was no pleasure. I have tried some small mods building some really simple absorbers from some towels in a wooden frame covered with some fabric. I placed those at the front wall behind the speakers, and it did not do very much. I also filled the underside of the sofa with abt 30 IKEA pillows, and that actually seem to help a bit, it became more comfortable to sit in the 'sofa corner' watching TV and also having music on in the background. Main listening position also improved a bit, subjectively. I did not measure before/after.
I also have some thicker type of curtains in the windows behind the listening position, and also covering the terrace door (with a window in the door), thick rug on the floor etc.
There are a lot of limitations/restrictions on the layout possible, the amount of treatment that can be accepted visually, and also the space available for absorbers/traps. Basically the layout is what it is, it was the only way I could fit the stuff due to doors, effective use of the space etc.
So this is the basic layout with room dimensions:
The height of the speakers is the height of the woofers.
I did some measurements with REW today. I attached the complete set of measurements, but here is an example of the listening position with both main speakers playing.
I also took some measurements in the corners and on the side walls, where I'm thinking it would be possible to place some kind of bass traps, thinking it would show if a certain position is better for treating a specific room mode. Usable corners are RL and the front wall corners, even if there are space limitations.
Here is a panorama-shot, taken standing by the right side wall, to give a better idea of the situation.
I will leave it at that in this first post, and continue with some Ideas I have, and some material I have stocked for this.
Background:
We moved to this apartment, over a year ago, and the acoustics of this concrete bunker scared me, and I have been wanting to improve them, because listening in this room was no pleasure. I have tried some small mods building some really simple absorbers from some towels in a wooden frame covered with some fabric. I placed those at the front wall behind the speakers, and it did not do very much. I also filled the underside of the sofa with abt 30 IKEA pillows, and that actually seem to help a bit, it became more comfortable to sit in the 'sofa corner' watching TV and also having music on in the background. Main listening position also improved a bit, subjectively. I did not measure before/after.
I also have some thicker type of curtains in the windows behind the listening position, and also covering the terrace door (with a window in the door), thick rug on the floor etc.
There are a lot of limitations/restrictions on the layout possible, the amount of treatment that can be accepted visually, and also the space available for absorbers/traps. Basically the layout is what it is, it was the only way I could fit the stuff due to doors, effective use of the space etc.
So this is the basic layout with room dimensions:
The height of the speakers is the height of the woofers.
I did some measurements with REW today. I attached the complete set of measurements, but here is an example of the listening position with both main speakers playing.
I also took some measurements in the corners and on the side walls, where I'm thinking it would be possible to place some kind of bass traps, thinking it would show if a certain position is better for treating a specific room mode. Usable corners are RL and the front wall corners, even if there are space limitations.
Here is a panorama-shot, taken standing by the right side wall, to give a better idea of the situation.
I will leave it at that in this first post, and continue with some Ideas I have, and some material I have stocked for this.
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When shopping some basotect for my speaker build, I also bought some other sound treatment (/insulation) materials. They are all in the 120*60cm format (due to shipping I guess).
So, what I have at the moment is:
2x 'Recycletherm Km0' recycled textile fiber (denim) sheets 6cm thick
4x 'Naturtherm' hemp based insulation 4cm thick
2x self adhesive basotect 3cm thick
One fiber board (porous board, directly translated from Swedish https://www.beijerbygg.se/privat/sv/produkter/byggmaterial/byggskivor/board/poros-board) 120x240cm, 12mm thick. I had some fantasy that this would work for as a porous broad band absorber placed in a corner. Not sure if it would work at all, but it's relatively cheap.
All these are 'natural' materials, I don't want to bring rockwool etc into the living room. I have some allergies since I was young, and I don't want to risk it with those materials.
I have been reading a lot on the internet, and watching some youtube educational videos like this to get some basic understanding:
So, some of the ideas so far:
-Modify the sofa even more, seal the underside to the floor, to make it a porous absorber, utilizing the pillows on top +the
IKEA pillows as the porous absorber, and the floor as the sealed back.
-I also have a 'foot rest' for the sofa (not in the picture above) which is basically a large box with an open bottom, and a pillow on top. The box part could be re-purposed to make a Helmholz resonator or some other kind of absorber. But could only be placed along the left wall.
-Some absorbers in the corners of the front wall (behind speakers). I'm thinking porous absorbers making a 45deg corner, possibly a small helmholz resonator built into it using cardboard pipes (the type used to make concrete pillars') However there does not to he high pressure of the main 35Hz mode there. My understanding it that it's best to treat the modes at their pressure maximum. Seems better in the rear left corner?
-Make some kind of removable 'head rest' for the main listening position to dampen the reflection from the rear wall / windows behind the sofa.
-Make a small Helmholz resonator (or two, maybe tuned to different frequencies) to put in the corner behind the sofa. Small one will probably not do much for the overall room, but maybe it could improve the situation when sitting in the corner? If so, I could put one behind the main listening position too. I'm thinking carboard pipe with sealed ends and a single 'reflex tube' to tune it.
-Some absorbers in the ceiling to take care of the first reflection. Maybe the hemp-based insulation with some fabric around it.
-Some absorbers to take care of the side wall first and maybe second reflections.
-Possibly some better absorbers on the front wall behind speakers.
'Next level fantasies'
-Multiple subs (not so keen on it due to space restrictions and cabling needed). I have the sub for the TV, but since it's behind the right speaker, it probably would not improve things to connect it to the stereo.
-Active absorber, basically mic and sub with some filtering. Played around with this earlier, but it was hard to get right, and it would amplify at LF due to phase margins. Same applies as above when it comes to space.
Hoping for suggestions what I shod concentrate on, and if there is something I can strike off the list right away maybe?
So, what I have at the moment is:
2x 'Recycletherm Km0' recycled textile fiber (denim) sheets 6cm thick
4x 'Naturtherm' hemp based insulation 4cm thick
2x self adhesive basotect 3cm thick
One fiber board (porous board, directly translated from Swedish https://www.beijerbygg.se/privat/sv/produkter/byggmaterial/byggskivor/board/poros-board) 120x240cm, 12mm thick. I had some fantasy that this would work for as a porous broad band absorber placed in a corner. Not sure if it would work at all, but it's relatively cheap.
All these are 'natural' materials, I don't want to bring rockwool etc into the living room. I have some allergies since I was young, and I don't want to risk it with those materials.
I have been reading a lot on the internet, and watching some youtube educational videos like this to get some basic understanding:
So, some of the ideas so far:
-Modify the sofa even more, seal the underside to the floor, to make it a porous absorber, utilizing the pillows on top +the
IKEA pillows as the porous absorber, and the floor as the sealed back.
-I also have a 'foot rest' for the sofa (not in the picture above) which is basically a large box with an open bottom, and a pillow on top. The box part could be re-purposed to make a Helmholz resonator or some other kind of absorber. But could only be placed along the left wall.
-Some absorbers in the corners of the front wall (behind speakers). I'm thinking porous absorbers making a 45deg corner, possibly a small helmholz resonator built into it using cardboard pipes (the type used to make concrete pillars') However there does not to he high pressure of the main 35Hz mode there. My understanding it that it's best to treat the modes at their pressure maximum. Seems better in the rear left corner?
-Make some kind of removable 'head rest' for the main listening position to dampen the reflection from the rear wall / windows behind the sofa.
-Make a small Helmholz resonator (or two, maybe tuned to different frequencies) to put in the corner behind the sofa. Small one will probably not do much for the overall room, but maybe it could improve the situation when sitting in the corner? If so, I could put one behind the main listening position too. I'm thinking carboard pipe with sealed ends and a single 'reflex tube' to tune it.
-Some absorbers in the ceiling to take care of the first reflection. Maybe the hemp-based insulation with some fabric around it.
-Some absorbers to take care of the side wall first and maybe second reflections.
-Possibly some better absorbers on the front wall behind speakers.
'Next level fantasies'
-Multiple subs (not so keen on it due to space restrictions and cabling needed). I have the sub for the TV, but since it's behind the right speaker, it probably would not improve things to connect it to the stereo.
-Active absorber, basically mic and sub with some filtering. Played around with this earlier, but it was hard to get right, and it would amplify at LF due to phase margins. Same applies as above when it comes to space.
Hoping for suggestions what I shod concentrate on, and if there is something I can strike off the list right away maybe?
Hi, try to put the speakers upside down, in order to make the woofer stand at equal height from ceiling to pavement.
Well, a room just for music reproduction !
Not possible to flip them around, they weigh a lot, and are divided by a 45deg slant. https://www.diyaudio.com/community/threads/full-size-3-way-project.389962/post-7140661
Even if I could, I don't think I would like having the mid and tweeter on the floor anyway
For 'next level' I still have to stick with something realistic as long as there is a woman in the household Any comments on the ideas mentioned. I think some of you experienced guys could remove and add some stuff to that list? Maybe some pointers for my specific situation?
Even if I could, I don't think I would like having the mid and tweeter on the floor anyway
For 'next level' I still have to stick with something realistic as long as there is a woman in the household
Any comments on the ideas mentioned. I think some of you experienced guys could remove and add some stuff to that list? Maybe some pointers for my specific situation?
Oh, I forgot one of the ideas, and that is to add some kind of sliding door in the opening towards the kitchen. This is not for absorption, but for blocking noise. There is normally a lot of chatter coming form the kitchen, and I guess the music that goes in the other direction is not always appreciated either..
I'm thinking there could be some leakage allowed, I'm guessing sealing it completely will make room modes worse?
I'm thinking there could be some leakage allowed, I'm guessing sealing it completely will make room modes worse?
There's somewhat of a free standing arrangement right now with the two openings by the speakers.
Try leaning a 4x8 sheet of plywood over the doorway (or even both of them) and see what you think
of the bass. It's all a compromise.
Also try to get the rug to cover more of the left side of the floor, and the area in front of the speakers.
Try leaning a 4x8 sheet of plywood over the doorway (or even both of them) and see what you think
of the bass. It's all a compromise.
Also try to get the rug to cover more of the left side of the floor, and the area in front of the speakers.
Hi, few quick thoughts: you could have couple subwoofers hidden under the sofa. Bass traps can be quite obtrusive and similarly complex/costly I think. I will start with getting rid of flutter echo in my place and it looks from the photo you probably have flutter at least between the sidewalls and perhaps front to back, unless the curtains help with it already.
On the right side, there is a door I can close, but subjectively I don't think the bass improves when I close it.
I found I did the measurements with the DSP optimized for the corner (left channel delayed), so I re-did the listening position.
It seems that looking at the FR, the nulls at 63 & 80Hz are the worst, and these are more even in the corner(with the delay active), and it sounds a bit better. I'm guessing the asymmetry and compensating delay make it more even in the corner?
Here are some screenshots of that, also showing where the nodes are:
Link: https://amcoustics.com/tools/amroc?l=543&w=382&h=258&fo=200&fu=30&r60=0.1
So, there are these nulls in the frequency response, and also the ringing from standing waves. I have a feeling these are the biggest issues in the subjective bass 'quality' when listening.
I found I did the measurements with the DSP optimized for the corner (left channel delayed), so I re-did the listening position.
It seems that looking at the FR, the nulls at 63 & 80Hz are the worst, and these are more even in the corner(with the delay active), and it sounds a bit better. I'm guessing the asymmetry and compensating delay make it more even in the corner?
Here are some screenshots of that, also showing where the nodes are:
Link: https://amcoustics.com/tools/amroc?l=543&w=382&h=258&fo=200&fu=30&r60=0.1
So, there are these nulls in the frequency response, and also the ringing from standing waves. I have a feeling these are the biggest issues in the subjective bass 'quality' when listening.
Thank you for chiming in here too
I thought about subs under the sofa for sound effects in movies, but I don't think I want my butt shaking when I listen to music.. Then there is the cabling for subs. That's the reason I'm not using surround speakers any more (and space). Now I only have a center + fronts with a sub for the TV. I would like to avoid the subs, even if I know it's advised... When I played around with DSP, active speakers, multiple subs etc before, I got so tired of all the cables, amps, a billion DSP-settings and crap, that I threw everything out and built a pair of passive speakers instead
I'm already down that DSP and active speakers road again, and I would like to avoid going all the way, and repeating the same mistake,.. It's a confusing hobby this..I definitely have plans to put something on the side walls, and in the roof for the first reflection. Flutter, I'm not sure how I can measure that? My ears are not trained to hear it I think.. Ok, if the room was empty, I sure I could, but now I'm not so sure. I have seen it mentioned, and I think I get the concept. It would be mostly higher frequencies, right? Some thin absorbers should be enough to reduce it?
If you can do loud handclap you should be able to identify it, its kind of robot sound, can be quite long tail behind the hand clap. Even if hanclaps won't tell if its a problem or not for your stereo setup clarity you can evaluate rooms in few secpnds, kind of gauge how bad it is. Its long duration repetitive echoes between two parallel walls and reduces intelligibility. I'm not sure what is its rank between acoustic issues but surely flutter echo is quite distinct sound to identify so its just feels logical thing to check it first.
Here is some samples http://research.spa.aalto.fi/publications/papers/dafx22-flutter-echo/
See also attached PDF
So yeah I think almost anything on the bare walls helps but you probably find suitable acoustic products and information yourself, I'm not too deep into this. I would imagine bare walls make sure not just first order reflections arrive but many orders. Sidewall reflections might help with envelopment if late enough but I would guess anything bouncing between front and back wall is really bad.
Messing around with handclaps, for example sitting on the floor on a rug gives almost no flutter so it seems rugs help already for floor / ceiling flutter. Standing up on the same spot clapping around above furniture level gives much much more. Even if rugs weren't very effective for "floorbounce", a singular first reflection, they would help for the 9th order reflection for example, as it would have met the rug many times, reducing flutter.
You dont need to rely on hand laps, measure Early Decay Time with ARTA or any other measurements you find relevant
Here is some samples http://research.spa.aalto.fi/publications/papers/dafx22-flutter-echo/
See also attached PDF
So yeah I think almost anything on the bare walls helps but you probably find suitable acoustic products and information yourself, I'm not too deep into this. I would imagine bare walls make sure not just first order reflections arrive but many orders. Sidewall reflections might help with envelopment if late enough but I would guess anything bouncing between front and back wall is really bad.
Messing around with handclaps, for example sitting on the floor on a rug gives almost no flutter so it seems rugs help already for floor / ceiling flutter. Standing up on the same spot clapping around above furniture level gives much much more. Even if rugs weren't very effective for "floorbounce", a singular first reflection, they would help for the 9th order reflection for example, as it would have met the rug many times, reducing flutter.
You dont need to rely on hand laps, measure Early Decay Time with ARTA or any other measurements you find relevant
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Get some 12” Sonotube and cut a 90 degree wedge out lengthwise. Fill the tube with foam damping or similar. Place the tubes standing in the corners about a foot from the walls. Cover the outside with damping of your choice. It will help tremendously! The longer the tube the better and floor to ceiling is great. It breaks up standing waves very effectively and looks ok uF the use matching fabric on the outside. Try it, it’s cheap. Forgot to say put 5he opening toward the corner!
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Edit time over. Dont take my words if you are targetting some specific performance. My thoughts are for quick and relatively easy/cheap/unobtrusive treatments that would give big benefit, although not studio grade but already much better than bare cpncrete bunker would
Following what you come up with, my progress is slow
Following what you come up with, my progress is slow
I think I won't be able to fit that 12" + distance to the wall in any corner... That's abt 60cm in total.
@tmuikku Thank you for the info and suggestions! I did actually find that angling the TV a bit sounded better in the last apartment, so I have been doing that since. That must be due to some flutter between rear wall and TV I'm guessing, and the slight angle breaks it up a bit.
Specific performance.. Well, I specifically want improvement!
Bass is not good, so I would like to improve bass in the listening position. I don't care much about even bass in the whole room though, like with home cinema with a lot of seats etc. I would also like to improve clarity in the midrange, and for that I was thinking something for the walls and the ceiling to take care of some reflections (and flutter). I think the bass is the biggest problem both sound quality-wise, but also the most difficult to solve.
Looking at my example in post 10 above, I think I have identified two serious nulls at 63 & 80Hz in the listening position. Looking at the room mode sim, it looks like the 63Hz is a multiple of the standing wave between the front and back wall in the room, and pressure maximums should then be at the back and front wall. To my understanding, the treatment should be put in those positions to be effective? So I'm thinking some tuned resonator could do some good if placed close to the wall, and possibly close to listening position too (since listening position is close to the back wall).
The 80Hz seems to be a diagonal wave between left upper and right lower corners along the room, so the most effective places to put some treatment would be somewhere along those corners? I'm thinking maybe try a resonator in the rear left corner for that?
When I'm talking resonators, I primarily think of a small Helmholz, in principle a 'reflex box without a woofer' placed somewhere were the SPL for the problem frequency is relatively high, what I would call a high pressure node(?). Using some smaller 'sonotube' and some pipe, I should be able to make some resonators pretty easily to test out. I also simulated the placement of the damping in the resonator, and that seems to have an effect on the Q, and also some on the tuning frequency, so I'm thinking of attaching some damping to a stick poking out of the reflex pipe, so I can slide the damping back and forth to vary the resonator tuning a bit.
I have no idea what a small Helmholz resonator can achieve, maybe it has to be enormous, but I don't have the space for that.. I guess I would just have to try and see if it makes things better.
I know I can't aim for perfection, only improvement.
Specific performance.. Well, I specifically want improvement!
Bass is not good, so I would like to improve bass in the listening position. I don't care much about even bass in the whole room though, like with home cinema with a lot of seats etc. I would also like to improve clarity in the midrange, and for that I was thinking something for the walls and the ceiling to take care of some reflections (and flutter). I think the bass is the biggest problem both sound quality-wise, but also the most difficult to solve.
Looking at my example in post 10 above, I think I have identified two serious nulls at 63 & 80Hz in the listening position. Looking at the room mode sim, it looks like the 63Hz is a multiple of the standing wave between the front and back wall in the room, and pressure maximums should then be at the back and front wall. To my understanding, the treatment should be put in those positions to be effective? So I'm thinking some tuned resonator could do some good if placed close to the wall, and possibly close to listening position too (since listening position is close to the back wall).
The 80Hz seems to be a diagonal wave between left upper and right lower corners along the room, so the most effective places to put some treatment would be somewhere along those corners? I'm thinking maybe try a resonator in the rear left corner for that?
When I'm talking resonators, I primarily think of a small Helmholz, in principle a 'reflex box without a woofer' placed somewhere were the SPL for the problem frequency is relatively high, what I would call a high pressure node(?). Using some smaller 'sonotube' and some pipe, I should be able to make some resonators pretty easily to test out. I also simulated the placement of the damping in the resonator, and that seems to have an effect on the Q, and also some on the tuning frequency, so I'm thinking of attaching some damping to a stick poking out of the reflex pipe, so I can slide the damping back and forth to vary the resonator tuning a bit.
I have no idea what a small Helmholz resonator can achieve, maybe it has to be enormous, but I don't have the space for that.. I guess I would just have to try and see if it makes things better.
I know I can't aim for perfection, only improvement.
Yeah if I had some acoustic panels and would need throw them quickly somewhere I'd put those on the back wall behind listening spot, kind of "between speakers", ear/speaker height. Also some to first reflection points on side walls, again at ear/speaker height, basically from your doors towards listening position as many as you have. Ceiling if there is more.
Yes resonator would work at pressure node and absorber would be most effective at velocity node.
You can probably find all kinds of info on the web if you look for home studio acoustics. While some of it is pure marketing (selling products) there also seems to be some stuff that works. For example this one seems legit https://www.acousticsinsider.com/
Yes resonator would work at pressure node and absorber would be most effective at velocity node.
You can probably find all kinds of info on the web if you look for home studio acoustics. While some of it is pure marketing (selling products) there also seems to be some stuff that works. For example this one seems legit https://www.acousticsinsider.com/
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If your speaker tops are detachable you can do quick test for free: drop them below furniture level, like on the floor, so that furniture works as acoustic treatment to stop any flutter between walls. Or go listening near floor, even easier, or both. Its a quick way to kind of have an idea how much clarity changes, intelligibility. To reduce "mölinä" in Finnish But yeah, perhaps concentrate on the bass for now if thats the biggest issue. Have fun and I hope you get nice improvement what ever is that you endup with, will follow how it goes!
ps. you could probably swap speakers and television on the long wall, between bedroom and terrace doors.
But yeah, perhaps concentrate on the bass for now if thats the biggest issue. Have fun and I hope you get nice improvement what ever is that you endup with, will follow how it goes!ps. you could probably swap speakers and television on the long wall, between bedroom and terrace doors.
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Acoustic basics ... we should write a sticky post about this
*) First of all ... you need surface area to make a significant change in acoustics! Normally you say you START 10-20% of absorptive area ... that's quite a lot.
*) Rule of thumb - absorption for music STARTS at 10cm depht. When you want to absorb low frequencies get 30-50cm. Don't waste money on these nice looking foam things ... they are not good enough.
*) 2nd rule of thumb - to get an EVEN t60 ALL your absorption must be >10cm. This means no 5cm foam panel. But also no carpet. No curtons. Cause they make a muffled sound but not a controlled sound (people confuse these often). This rule is more important in a recording room - I would not want a living room without curtains
*) WHERE to put absorption? Start with 1st reflection points. Get your mirror out is the easiest way to define them. Don't forget your ceiling!!!
*) Most effective for absorption are corners - you have 8 of them. Also edges of the room ... there are also plenty of them ;-) You can put absorption at the edges of the ceiling to your walls, don't loose ANY space in the room and probably even make it look cool. (with some lights etc).
To make a SIGNIFICANT change in a room think in surfaces, not in panels. In your case - your front wall screams to be treated as a whole. Put stuff on the ceiling if you want to seriously listen to music - it makes a big difference. Make a sliding door so you don't need to hear the late echoes you would otherwise get from the other room.
Don't think about diffusion until you don't have control at low frequencies, even t60 and your first reflection points solved.
*) First of all ... you need surface area to make a significant change in acoustics! Normally you say you START 10-20% of absorptive area ... that's quite a lot.
*) Rule of thumb - absorption for music STARTS at 10cm depht. When you want to absorb low frequencies get 30-50cm. Don't waste money on these nice looking foam things ... they are not good enough.
*) 2nd rule of thumb - to get an EVEN t60 ALL your absorption must be >10cm. This means no 5cm foam panel. But also no carpet. No curtons. Cause they make a muffled sound but not a controlled sound (people confuse these often). This rule is more important in a recording room - I would not want a living room without curtains
*) WHERE to put absorption? Start with 1st reflection points. Get your mirror out is the easiest way to define them. Don't forget your ceiling!!!
*) Most effective for absorption are corners - you have 8 of them. Also edges of the room ... there are also plenty of them ;-) You can put absorption at the edges of the ceiling to your walls, don't loose ANY space in the room and probably even make it look cool. (with some lights etc).
To make a SIGNIFICANT change in a room think in surfaces, not in panels. In your case - your front wall screams to be treated as a whole. Put stuff on the ceiling if you want to seriously listen to music - it makes a big difference. Make a sliding door so you don't need to hear the late echoes you would otherwise get from the other room.
Don't think about diffusion until you don't have control at low frequencies, even t60 and your first reflection points solved.