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Discussion Starter · #1 ·
Hi all! i am just moved in to a much smaller room.. and i do work as an engineer... BIG CHANGE FOR MY EARS... i took care of first reflections on the sides 4 broad band corner traps 3", 2 3" panels behind speakers 6"from the walls.. but i have a enormous peak at exactly 131 hz... and i really can't work with this peak...
there is a null about 20 inches above my head.. room is really too small to move the set up entirely...
i have some very generic graphs here.
i'm thinking of either trying to move the speakers closer to the null which means higher.. and tilt them downwards ( then what about reflections from desk?) this does get the peak smoother but causes 2 more dips in critical low mid frequencies...
Or should i build a perforated panel to target the 131 hz and keep the speakers where they are?

Thank you so much!

Alessio
 

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Discussion Starter · #2 ·
First graph shows listening position... measured with room eq wizard ( radioshack spl meter, that's why highs ar funny)
second graph is the mic 20 inch higher closer to the null

the 3rd and 4th graphs are taken with another software "fuzz-measure" and zoomed in a bit more

i 've only used one speaker for the test.
 

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A little too much at a time , with mixed issues... it seems we are mixing modal issues with specular behavior...
But the measurements show good agreement - they are just not windowed usefully nor a waterfall generated and windowed usefully.

Also, it would help greatly if you post the original mdat files on the forum so that they can be opened in REW (or a wav file, allowing it-to be opened on other platforms).

For modal analysis you will want to generate a waterfall and window the x axis from 0-~250 Hz and open the time (z axis) WIDE and then scale down as necessary.

As far as specular reflections, you generate an impulse response and then convolve the ETC from the impulse.

If you are still locating the speakers, you have gotten ahead of yourself in placing early reflection panels...
And are you addressing SBIR?

...Too many issues at once!

BTW, all measurements made at the listening position must be made with the mic capsule at the EXACT same point in space!!! If you want to explore multiple positions I would suggest exploring various positions forward or behind on a symmetrical centerline between the speakers in the same vertical plane. (I am not sure why you are exploring higher positions unless you are considering changing your listening height or repeatedly standing up and down as you watch/listen....)


Do you have a sub? What is the configuration we are dealing with??????? Speakers, room, speaker mounts (and you mention a desk???)

There are so many variables at play without us knowing any of them.

And you drive each speaker individually for specular issues and the ETC. Running them both at once for anything other than modes is simply conducting a comb filtering lab.
For specular issues, you will generate a left speaker and a left speaker response.

As far as SBIR, there are calculations designed upon the speaker topology. There are also wall bounce calculators available on line (Thomas Barefoot's is one that comes to mind).

So first you want to determine the modes that the room supports. This can be done with a speaker placed in the front tight floor corner and the mic positioned in the rear diagonally ceiling corner.

Also, you can measure the bass response and generate a waterfall windowed from 0-~250 Hz at the listening position to get an idea of the local behavior. This will be done with the mic in the listening position where your head will be. Unless you will be standing up and down while listening, we do not care what is happening above or below.

You can determine if SBIR is an issue by repeating a full range sweep and moving the speaker towards the side wall and seeing if the frequency changes, Likewise you can repeat it and this time move the speaker closer to the wall.

If you have the speakers currently placed equidistant from both the side and front walls, this is a mistake. These distances should not be equal of even multiples of one another.
If there is a change in the null frequency, SBIR is an issue.

You then deal with mapping the modal response in the vicinity of the listening position, with the listening position placed symmetrically between the left and right boundaries. You then make several repeat waterfall measurements taken over small intervals in front and in back of the proposed listening positions to see modal distribution. As moving the listening forward or back a bit is the easiest way to minimize its being located in a peak or a null.

Then one applies bass trapping with a minimum facing of at least 6 mil thick plastic or a solid panel reflective covering in order to retain the mid-high energy in the room. Corner taps should not be oriented so as the redirect the energy back at the listening position. This is most easily accomplished by making the traps lightly asymmetrical with the out side wall face shorter than the front wall face, thus redirecting incident high gain reflections to the back of the rum and not at the listening position.

Thus, you deal with SBIR and with modal issues first.

THEN you deal with specular energy and absorbers!

Lots of unknown variables to be addressed one at ta time in an isolating manner. So you need to take it slowly and systematically. Jumping around will not help and will only cause more work, as if you change speaker positions, that will invalidate the previous measurements - especially the ETC and the determination of any early reflections and specular wall treatments.

More details of the speakers and room will help.....
 

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Discussion Starter · #4 ·
Ok you re right little info...

i did the test using only one speaker.. the measurement 20inch higher is there because of the null that helps the huge 131hz peak im experiencing...

I do have a big mixing type desk ( no console ) but i'm sure it is reflecting sound. there is really no potion for me to move in the room.. i am not experienced at all with room eq and its been such a pain to make it work... i will post the rew files right away! so that if you can take a look at them it would be a blessing...
Option one.. move the speakers into the null ( not completely) and tilt them down...
add a cloud above me, and a perforated panel to target the 131 hz mode. After all this.. i would have to check on highs's make sure the room is not to dead...


here the room size with the relative modes

10.3ft - 54hz-108hz-163hz-217hz

8.3ft - 67hz-135hz-202hz-270hz

Cieling - 8ft 70-140-210-281


thank you so much!
 

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Discussion Starter · #5 ·
speakers are not equidistant from walls. speakers are mackie MR8 active.
i really do rely on my ears mostly,, and if needed i look for measurments to pinpoint the smaller problems.. but i feel i first want to get the best fix i can to this 131 peak that really bothers me and i really can;t work with...

Thanks!
 
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