How on earth will I be able to fix this..oh god!

[emreyazgin]

30dB valley!..Using ethan's Hz-Distance calculator I found out that the problematic frequencies I have (87hz and 125hz) are almost exactly related between the speakers' distance from the back wall. One of them is a 6/4 wavelength (so in phase with the returning wave) away from the back wall and other one again full wavelength but inverse phase.

I have played a continuous sine wave of 125 hz while moving the microphone around the room to find where it resides and I found out that its on the top, bottom and corners of the front wall behind speakers. I have also checked the back wall's middle but the 12h hz was only increasing when I was really close to the wall (within half foot or so). I already have a few broadband absorbers I made before and I am making 2 huge ones (4" thick 3 foot by 6 foot).

Any advices? Do you think it makes sense to use the smaller (100cm by 60cm 4" thick) on the front wall and use the huge ones on the back wall?

[Duke]

I don't know if this is practical for you to try, but here goes...

Imagine looking down on the triangle formed by your listening position and the two loudspeakers. Presumably this triangle is inside a rectangular room. Now imagine rotating this triangle somewhat, either clockwise or counter-clockwise, while the room stays fixed. This will stagger the distances of both speakers (as well as yourself) relative to the walls of the room. How much to rotate depends on where everything started relative to the room boundaries; eyeball it, and don't go all the way to a diagonal setup. The resulting asymmetry should help smoothe out the bass response because now each speaker's wall-bounces will be zigging and zagging at different frequencies, so they won't sum to such monstrous peaks and dips.

Duke

[emreyazgin]

Originally Posted by Duke

I don't know if this is practical for you to try, but here goes...

Imagine looking down on the triangle formed by your listening position and the two loudspeakers. Presumably this triangle is inside a rectangular room. Now imagine rotating this triangle somewhat, either clockwise or counter-clockwise, while the room stays fixed. This will stagger the distances of both speakers (as well as yourself) relative to the walls of the room. How much to rotate depends on where everything started relative to the room boundaries; eyeball it, and don't go all the way to a diagonal setup. The resulting asymmetry should help smoothe out the bass response because now each speaker's wall-bounces will be zigging and zagging at different frequencies, so they won't sum to such monstrous peaks and dips.

Duke

Firstly thank you so much for your response. I need to update you on the shape of the room, please see the attached image file. Also, I didn't considered tilting the "triangle" in order not to badly affect the stereo image, I will definitely give it a try though.

When I look at the plan of the room I always think that the speakers fire the sound to the back wall and the back wall fires the sound back and the convergent shape of the front walls focus the sound to exactly where I am and that might be the reason of the large peak and the dip. Thats the reason I am building two large absorbers and I will try them at the back wall and I will also use 3 normal sized (but again 4" thick) absorbers on the 3 walls on the front wall. Any comments on this idea?

[Glenn Kuras]

I would set up so you are facing the right wall. That itself would help out A LOT. After that just straddle as many corners as possible.

Glenn

[emreyazgin]

Originally Posted by Glenn Kuras

I would set up so you are facing the right wall. That itself would help out A LOT. After that just straddle as many corners as possible.

Glenn

Hi Glenn,

By right wall you mean the longer wall on the far right? Is that because the back of the room will act as a natural bass absorber? Diffraction?


Edit: I am moving the whole furniture to the new location, all the cables etc are tied to the desk, so its easy to do so (a bit heavy though..). I will post the new REW response curve once Im done..half way there..

Cheers,
Emre

[emreyazgin]

It actually interesting now..The dip and peak got worse..but the rest is more even...hmmm

[Weasel9992]

Originally Posted by emreyazgin

It actually interesting now..The dip and peak got worse..but the rest is more even...hmmm

No, the dip and the peak got better. Neither of them is as broad as they were before. You can deal with what you have now to a large degree with absorptive treatments in the usual places (corners, back wall, front wall, etc.). If that doesn't do it, then add trapping at the first reflection points and on the ceiling.

Frank

[Duke]

Emreyazgin, if you identify and treat the first reflection zones then a skewed triangle setup in your main room (probably oriented facing generally towards the right-hand wall as Glenn suggests) should still image well, but your bass will probably be smoother (thought it might not go as deep, as you'd be getting less boundary reinforcement).

I'm not an expert on what you can reasonable expect from absorptive room treatment devices so can't really address your question there.

Unfortuntely, I cannot be sure in comparing the two graphs because the vertical scale is different. The second graph defiintely shows an improvement in the region between 50 and 70 Hz, and it looks to me like the big dip and peak are both improved as Frank says, but I could be thrown off by the compressed vertical scale. Try this: Draw an imaginary horizontal line at the average SPL (about 74 dB in the first graph and about 66 dB in the second one) and look at the total area of the dips and peaks, rather than how deep they go (trying to make allowance for the different vertical scales). Note that the ear does not hear like the eye sees, and narrow-band peaks and dips are not nearly as audible as broad, shallow ones.

If you can do one-third-octave smoothing of the graphs, I think that would be more representative of what the ear would perceive. Any comments on that, Frank or Glenn?

Duke