# Listening room: Problems/Solutions Acoustics



## Metallising (Oct 22, 2009)

Hi,

I use my bedroom as listening room. The first time I instaled my speakers and played some music I found some problems.
- Weak and distorted stereo image.
- Painful medium high and high response.
- Huge modal problems.
- Flutter echo between rear and front wall.
- Hard comb-filtering.

So, I measured it.
I found peaks at 55hz, 93hz, 137hz and dips at 82hz and 210hz.

Once I don't have much practical experience in acoustic treatment I'm going to need your help to solve this problems.

When listening to music the worst and more notable problem is the 55hz peak. So I'm thinking to invest or to try building something like those RPG Modex tuned bass traps, they have a really high Q and are very effective dumping the frequency they are designed for. I don't know if it is the best solution, but I know it works.
However, I can't build a tuned bass trap for every problematic frequency. So I need a acoustic solution to smooth all the bass reponse, it's impossible to get it flat, but at least smooth all those dips and peaks. 

All the others problems I think it's possible to solve using aborption on the walls. Medium and high problems destroy my stereo image so maybe some rockwool panels in walls and roof may solve it. Some people advised me to use diffusers on the speakers axis which make sense for me.

Two graphs in attachments 

Hope to get some help!

Thanks in advace
(Sorry for my english :neener


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## Mika75 (Feb 5, 2009)

....and what speakers are u using ?


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## Metallising (Oct 22, 2009)

Nearfield studio monitors. KRK RP6 (6,5 woofer). No use of subwoofer.

Room: 12x10x9

I was using BW 805 before, the problem was the same.


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## Mika75 (Feb 5, 2009)

..is there any bass/treble adjustment available on the KRK ? If u sit closer do u still have the issues?


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## bpape (Sep 14, 2006)

A sketch/pics of your room so we know dimensions, locations, etc. would be a huge help.

Bryan


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## Metallising (Oct 22, 2009)

Yes, KRK have bass adjustment -4dB, -2dB, flat or +2dB. However there isn't any electronic adjustment that can solve my acoustic problems without causing even more severe problems. No matter how bass adjustment is made, the modal problems will always be there.
When I sit closer there isn't any bass at all, if I sit further then the bass is so boomy that I can't stay there for too long without going mad. So I placed my chair between those two extremes.

An important thing I forgot to say is that the walls of my room are made of drywall, then it comes the brick. I'm affraid that the hard null at 82Hz is being caused by the drywalls, it may be a resonant frequency at which the drywall is vibrating sympathetically, acting as a diafragm, causing a huge dumping effect at a very high Q frequency. Do you think is this probable?

I attached a sketch of my room, it looks really bad but it's sufficient to get an ideia.
I'm european so I'm more confortable with meters instead of feets. The measurements in meters are more accurate than in feets.

My room is empty, just have a bad and a chair (and alot of free space to fill with lots of bass traps ahah) 

Final note about speakers placement: Some experts in the field say that is better to have a room with more width than depth, so I placed the speakers like its shown on the sketchs 


Thanks in advance


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## bpape (Sep 14, 2006)

Looks (not sure how to scale things are) like you're sitting centered in the room length which will maximize modal issues. While sitting back farther may be boomy without treatment, it's likely smoother overall and we can treat the rear wall.

Bryan


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## Metallising (Oct 22, 2009)

Yes, that's true, I'm seated centered in the room length and width. You are totally right about it, in theory it makes sense to have more severe modal issues in this position. I haven't thinked about it.

I ill measure the room response in a farther position and post the graphs. Hope you can help me to take conclusions about it.

Once again, thanks in advance.


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## Mika75 (Feb 5, 2009)

Heres some suggestions. :sneeky:

-Having equal distance from the side walls will enhance those bass frequency's, try moving the speakers closer together & or change the distances so they are not symmetrical. 

-Sit closer and have no bass? ...then use the +2 bass boost!

-Sitting closer just like ur at the pc will almost remove the room from ur direct sound, except for some reinforcement from behind them (a broadband absorber will work well on the wall behind the KRK)









-or use them on the left side wall firing towards the bed


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## Metallising (Oct 22, 2009)

I placed both speakers with equal distance from the side walls to get a balanced stereo image and equal diffusion of first reflections. If I place speakers in a non-symmetrical way there is going to be more energy in one side than another.
It may solve some modal problems, but destroy stereo image that isn't less important than bass response. 

I know that in small rooms we have to get a compromise between all acoustic problems, however I believe that is possible to get a closer solution to ideal acoustics.

Like you suggested, I can try sit closer and use +2dB, listen and measure it. The bass response there is really unbalanced but I ill try anyway. I post the graphs latter.
We cannot forget that sitting close to speakers will change the stereo balance, so, to maintain it I have to get the speakers closer together, which means tinnier stereo image and more phase related problems.


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## bpape (Sep 14, 2006)

If you stay with the orientation you have, you can still shift things to one side a bit. You'll still have some modal issues until you get past 60% but they'll be better. It's not that much difference in energy. We'd just need to hit the side wall reflections for sure. Either way, the back wall still needs to be done.

Now, if you were to change to the rotated orientation, your distance off center would have to be much less and you'd not be sitting in the center of the room, would have more space behind you, etc. You would in fact lose space to the side of the speakers but a panel directly to each side will help with the boundary effects. 

Bryan


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## Mika75 (Feb 5, 2009)

After I found the best position I stumbled upon this speaker placement calculator which was very close to what I already had.. 

Setting Up Speakers In A Rectangular Room by George Cardas

You may find it hopeless with ur room though :dontknow:


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## Metallising (Oct 22, 2009)

When you say "get past 60%", you mean moving speakers and listening position to 60% or more of the total width of the room? 

Rotated orientation, means something like this? :










Maybe I can try some measurements at this configuration too: 










It solve the question of being in the center and the balance of stereo image. I have to measure and listen in those positions.
For now all room sound bad and very "live", but at least changing the position I can solve some modal problems before adding absorption.
If changing speakers placement smooth that 55hz, 82hz and 93hz dips and nulls, then it's much easier to flat all bass response using bass traps with a larger Q.


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## bpape (Sep 14, 2006)

I meant facing the long way in the room though you may find corner orientation to work OK.

Past 60% is your seated ear position from the wall in front of you or the wall behind you (nearfield listening)

Bryan


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## Metallising (Oct 22, 2009)

Hi again,

After thousands of measurements this is the best graph I can get. 
Do you think this graphs is better than the first one? Or at least, is easiest to treat?

In both positions (both graphs) it doesn't sound good, however, while listening music I found that 2º position have a larger sweet spot, it's possible to move a little and don't ear a huge diference.

Mika75, thanks for the link. I tried in that way, but bass gone! It was a useful test anyway.

Graph/Plot


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## bpape (Sep 14, 2006)

What specifically are the problems you hear?

The room is very small, will require a proportionately larger amount of treatment to get things smoothed which will end up being deader than you're used to but will be more tonally accurate.

Bryan


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## Metallising (Oct 22, 2009)

I belive is possible to treat bass using helmhotz principle and keep the room "alive". It's possible to tune the treatment for low frequencies only. The room also needs some mid/high treatment, but I don't want it too "dead". 

I'm hearing unbalanced bass response and not tight as it was supposed to be. Also, some bass notes don't have discernibility. 
For exemple, some cello notes (100hz-150hz) sound boomy, a kick drum (80hz) sounds really weak, an electronic kick (50hz) sounds good in some positions but if I move 30cm it ill disappear or get boomy. The electric bass is the best example to understand how unbalanced is my room, depending on the note sometimes I can hear, don't hear, hear it boomy or weak, and rarely hear it coming from one specific direction.
Obvious I used well recorded instruments on testing.


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## bpape (Sep 14, 2006)

What you describe as your issues are a function of a total lack of BROADBAND bass control and very excessive decay times. 

The measurement you have now is certainly a big improvement over the original one. Now we just have to deal with the time aspect of the room as well as trying to fix the last couple of stragglers.

2-3" thick panels directly behind the monitors will address SBIR problems.

Corner bass absorbers will work for general decay time control and sit at the end of 2 dimensional boundaries

A thick panel behind you will help with peaks/nulls off the rear wall.

A thick panel over your head will help with height related modal issues.

Bryan


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