Need some tips on cheap acoustic treatment

[Tupisac]

Experiment with two mattresses, one each from behind the speaker to cover about 40-50 cm against center of the middle and a bit up on the wall. Then get or build "real" damping panels behind. 10 cm deep frame with rock-wool covered with perforated board, and covered with 6 cm well-formed acoustic foam.

Basically behind the speakers?

Yeah, this might be hard with my existing mounts. They don't allow for enough distance to fit mattress there, especially when speakers are toed in.

 

[Tupisac]

I *think* that's how it works but I am somewhat overstating my knowledge here as I haven't done it that way myself. In theory, all of the nodes need to be 1/4WL away from the wall, or more - (which is partly why the treatment needs to be so thick) but in practice walls are not perfect reflectors, and you have more imperfect reflectors beyond the wall, so it can vary.

One way to find out. I'll whip out my mic once again and do some experiments

What would be the best quick analogue for an absorbing material that I can stick to a box without getting into messy rokwool or expensive foams? Bunch of clothes? Blankets? Towels? Pillows?

 

[Thomas_A]

Basically behind the speakers?

Yeah, this might be hard with my existing mounts. They don't allow for enough distance to fit mattress there, especially when speakers are toed in.

You can custombuild the frame on the wall have mounts on part of a frame. The rest can be covered with rock wool, perforated board and foam. You loose 10 cm wall space.

 

[Thomas_A]

One way to find out. I'll whip out my mic once again and do some experiments

What would be the best quick analogue for an absorbing material that I can stick to a box without getting into messy rokwool or expensive foams? Bunch of clothes? Blankets? Towels? Pillows?

Pillows, thick and cozy. Lots of them, Try.

 

[Tupisac]

I did a test with pillows behind the speakers:

Here is the result:

Here is the earlier spectrogram without pillows:

It definitely fixes a big chunk of the problem around 200 Hz.

I also did the experiment with 150-200 Hz pink noise. I played it at around 80 dB level at listening position.
The highest measurements in potential treatment positions were:
- 85 dB in the SW corner (between Kallax and curtain) near the floor and 86 dB near the ceiling.
- 84 dB in the space over the wardrobe
- 84 dB inside the Kallax spaces near the floor.


Here is the plan from previous page for reference:

I've also played with MMM and went through a small chunk of the forum. I've seen people asking for clarity plots, so here it is:

Also, some graphs taken with MMM method (without pillows, using RTA averaging):

Before EQ:

After EQ:

 

[Thomas_A]

Suprised to see such effect with just a few pillows. I would suggest filling the wall with them to test (i.e. below and above the current pillows, and a bit against the center beting the screen, and also on the other wall when the speaker is in the corner. Just arrange them to be "stable" so they do not fall over and damage anything.

Not suggesting to be permanent, but investigate the impact of them on sound.

 

[Tupisac]

I've filled my room with massive amounts of pillows, did lots of sweeps and mmms and at the end lost track which was which.
But the differences were minor. It just slightly moved the offensive region back and forth. I guess I'll have to wait until the bookshelf is ready as I expect it to have a big impact on overall sound.


Meanwhile, I've started seeing funny shapes, like with Rorschach test. For example, this one is very bird oriented, with a swallow shaped hole and a massive cock: