Help with room 250Hz - 500Hz build up

[blayz2002]

I've done some DIY treatment in my room, but after reading this months "Room For Improvement" article in SOS thought I'd run some test (noting too techy as 1 I'm not and 2 I don't have the kit). Anyway I found I still have a build up around 250Hz - 500Hz, how can I tame that?

Here's the details

Room L= 13.5 x W= 9 x H= 7.5,

I have the monitors set up along the width facing away from window that runs the full width and roughly half the height of the wall.

I have managed to get a 2x4 ft 6inch Rockwool (RW3 covered with Ready Trap bags) trap in each of the front corners, also one in the right rear corner , cannot do the left rear corner as that where the door is, so I just leave the door open.

So I have another 2 traps (all 2x3.4" covered with Calico) 1 6inch on the rear left wall to ceiling corner and 1 4inch on the rear wall to ceiling corner.

I've then got a 2 inch cloud (2 inches of the ceiling) above the mixing position.

I then also have some cheap (2 inch eggshell type) foam at the left and right mixing positions.

I'm using a Blue Sky Media Desk monitors.

Using RealTraps - ModeCalc my room mode shows there would be build up around that frequency, and running the test MP3 from: Room For Improvement: Audio file
The notes do indeed get increasingly louder around those frequencies. Other than that those bass frequencies the rest are ok.

[jwl]

250Hz has a wavelength of 4.5 feet, which is an even multiple of 9 feet (2x) and 13.5 feet (3x). 500Hz is obviously an octave from 250Hz. So that's why you have that buildup, these are room mode harmonics in action.

The solution is probably more absorbers, maybe try putting some in the wall/ceiling corners?

Alternatively, you could build a tuned resonator to those frequencies.

Personally, I'd start with more broadband traps in more corners....

[blayz2002]

Cheers J, makes sense.

So just more traps, I was also thinking about stuffing the cavity behind the existing corner traps as supposedly that should help with even broader frequency absorption,

Anyone have any more info on that?

I will probably get a couple more 6 inch traps in the wall ceiling corners though.

[andrebrito]

One option is to use wood slat/perforated or micro perforated panels tuned to the region of your interest that you wish to absorb (250-500 Hz might be hard to find in your area). Check who sells these kind of panels near your zone.

I can give you an example but using gypsumboard - document is in spanish/portuguese but scroll to page 7 for the chart absorption

http://www.uralita.com/NR/rdonlyres/...oPLADURFON.pdf

[John Suitcase]

I might try moving back from the window a bit, or hanging some treatment over it. Windows do weird things, they reflect high freq stuff, and at louder volumes can resonate and rattle.

[jwl]

blayz, I think putting more material behind the 6" panels won't hurt, as more mass (all else being equal) = more absorption. Though, I'm not sure but I think the biggest effect is that it will lower the frequencies that will be absorbed. I'm sure what you have already goes well below 250Hz. So as I say it won't hurt, but I'm not sure how much it will help from 250-500Hz.

I'm not sure the window will help that frequency range either.

I'd still recommend more traps in more corners, I think more coverage area will help you more than more mass behind the coverage area you already have.

Also, if you do decide to build a tuned Helmholtz resonator, there are some excel spreadsheets that contain the corrected formulas on how to tune it (to 250-500Hz in your case). Be careful when you calculate this, many of the formulas floating around contain an error and will give imprecise results.

[andrebrito]

This kind of corner traps absorbers with air cavity behind them have not yet being studied in detailed. Since the air in the cavity creates a kind of ressonance effect on these panels then placing more material in that cavity will deslocate the ressonance point to an higher frequency (since you are decreasing the air cavity).

You said everything was OK below 250-500, have you tried to move the speakers and the listening position and see what happens ? What mic are you using ? Did you test your speakers in another room and obtain the 250-500 bump ?Could you use something like Room EQ Wizard Home Page to make measurements ?

So just more traps, I was also thinking about stuffing the cavity behind the existing corner traps as supposedly that should help with even broader frequency absorption,

Just looking at your photo, you workstation and especially your speakers are much too close to the wall and window.

Move at least 1-1.25 meter from the front wall, and widen your speaker distance (larger stereo image) -- this should make a big difference.

Having around your speakers at least 0.6m clearance from any workstation or racks (which inside air cavity prone to resonate in that range) is recommended.

Low frequency absorption should be located usually more in rear of room than in front.

Alternatively considering to update speakers to a larger size with 6.5" to 8" woofer such as Tannoy System 6/8 DMTII (passive) or Dynaudio Audience 52 (passive) or Genelec 1030A/1031A or Dynaudio BM5A/BM6A ... would provide low frequency down to 50-60Hz and much cleaner bass or low mid.

Good luck!

[blayz2002]

Originally Posted by andrebrito

One option is to use wood slat/perforated or micro perforated panels tuned to the region of your interest that you wish to absorb (250-500 Hz might be hard to find in your area). Check who sells these kind of panels near your zone.

I can give you an example but using gypsumboard - document is in spanish/portuguese but scroll to page 7 for the chart absorption

http://www.uralita.com/NR/rdonlyres/...oPLADURFON.pdf

I'll take a look into this.

Originally Posted by John Suitcase

I might try moving back from the window a bit, or hanging some treatment over it. Windows do weird things, they reflect high freq stuff, and at louder volumes can resonate and rattle.

The monitors are actually 2.5 ft from the window, which makes my monitoring position roughly 4.5-5ft. So don't think I need to be further away. I should really get heavier curtains I guess but that's more affecting the highs I would have thought?

Originally Posted by andrebrito

This kind of corner traps absorbers with air cavity behind them have not yet being studied in detailed. Since the air in the cavity creates a kind of ressonance effect on these panels then placing more material in that cavity will deslocate the ressonance point to an higher frequency (since you are decreasing the air cavity).

You said everything was OK below 250-500, have you tried to move the speakers and the listening position and see what happens ? What mic are you using ? Did you test your speakers in another room and obtain the 250-500 bump ?Could you use something like Room EQ Wizard Home Page to make measurements ?

I used the staircase bass file, to test low end response, and up to approx 200Hz the notes are very even, but there's a tiny dip just before 250Hz then it gets increasingly louder. I imported that file into Harbal to check the frequency plot.

I did download Room Eq wizard but haven't done any tests with it yet, I'll see if I can get my head around it.

Originally Posted by High Fidelity

Just looking at your photo, you workstation and especially your speakers are much too close to the wall and window.

Move at least 1-1.25 meter from the front wall, and widen your speaker distance (larger stereo image) -- this should make a big difference.

Having around your speakers at least 0.6m clearance from any workstation or racks (which inside air cavity prone to resonate in that range) is recommended.

Low frequency absorption should be located usually more in rear of room than in front.

Alternatively considering to update speakers to a larger size with 6.5" to 8" woofer such as Tannoy System 6/8 DMTII (passive) or Dynaudio Audience 52 (passive) or Genelec 1030A/1031A or Dynaudio BM5A/BM6A ... would provide low frequency down to 50-60Hz and much cleaner bass or low mid.

Good luck!

As above I'm already far enough away from the windows (it doesn't look like that in the pics though). If I move further back I'll be smack in the middle of the room which would be worse (as that's where any nulls will be), and it's difficult to move the room around as it's so small.

I'll mess with the width of the monitors and see if that helps at all. And I'm aiming on getting a second set of monitors and some of those are considered.