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140 to 300 Hz Buildup in Room Dynamic Microphones
Old 30th December 2017
Gear Head

140 to 300 Hz Buildup in Room

I'd like to tame the 140 to 300 Hz area in my room. It is partly treated: 3 corners, ceiling reflection points, left reflection points, front wall, right half of back wall. Whats missing: left half of back wall, left back corner, right reflection points (right reflection points are a window). Most of the treatment is 150mm/5,9inch thick rigid fiberglass, a few 100mm/3,9inch exceptions. Back wall also has bit of scatter stuff.

The measurements of the room are 5.6x4x2.6m / 17.7x13.8x8.5ft. The speakers (Two18s) are as close to the front wall as possible (0.5m/1,64ft standing on the BaseOne25s on sorbothane spheres). Listening position is about 2m/6,56ft from front wall.

Is it likely that treating the missing areas would get rid of the 140-300Hz buildup? are there special tuned absorbers for this freq regions? are there any other things i could try to get rid of that buildup? Could maybe tilting the speakers inward/outward change the freq response at the listening position in the 140-300Hz region?

Thank you
Attached Thumbnails
140 to 300 Hz Buildup in Room-tame.140.300hz.jpg  
Old 30th December 2017
Gear Guru

You have a deep null around 70Hz and a peak around 140 and your room is about 2.6M high. We are almost certainly seeing the first and second height modes in action. You can see them graphically here. 70Hz has a null at half height and peaks at floor and ceiling. 140, Peak at floor, Null at 1/4, Peak at half height, Null at 3/4, Peak at ceiling. What Height are the Woofers or Subs? at?

Old 30th December 2017
Gear Head

Thank you for the math, makes sense My ceiling absorber really does only cover a small area (1,2x0,6m).

The subs are Amphion BaseOne25s which are standing on the floor. The center of their woofer is about 0.83m above floor. The center of the passive radiator is about 0,25m above floor. The woofers of the monitors (Two18s) are 1.06m and 1.40m above floor.
Old 30th December 2017
Gear Guru

Those subs could be used at different widths horizontally, passives in or out, and at different heights, e.g. 1/4, 1/3, 1/2. And at different walls. Particularly mid, but again don't forget Height. Optimum Room Locations for Subwoofers An Analysis | Audioholics
Lots of options. When Fine Tuning, the RTA/Spectrum and Pink Noise Generator in REW will give you real time feedback on location changes.
Old 2nd January 2018
Gear Head

Using them horizontally is a really neat idea. I'll try for sure - at different heights. Big thanks
Old 2nd January 2018
Gear Guru
Glenn Kuras's Avatar
You are getting some good advise. I would cover more of the ceiling area with 4" (or deeper) broadband panels. Space them off the ceiling as much as possible.
Old 14th January 2018
Gear Head

Ive put the BaseOnes25s horizontally. First screenshot is them both being horizontal. Second shot is being left one horizontal and right one standing.

Is it a good or bad idea to try to counter the peaks/nulls with a "mixed setup" like this (in the second screenshot) regarding phase/thightness?
Attached Thumbnails
140 to 300 Hz Buildup in Room-horizontal.jpg   140 to 300 Hz Buildup in Room-mix.jpg  
Old 15th January 2018
Gear Guru
Interesting Question

Hmmm, that give pause for thought. You might get a more realistic analysis if you measured at each ear position and summed or averaged the result.
My gut says make them symmetrical, and it looks like you have a strong SBIR dip at 100Hz. Something is about 0.85M a wall. Can the cones be faced up or down to get them closer to the wall?
Old 16th January 2018
Gear Head

Indeed I felt the symmetrical setup sounded tighter when listening to the setups. Its the passive radiator that is about 0.86M away from the side wall in the horizontal setup. I put them this way because it was the flattest response in RTA. when i move them closer to the side wall the 77Hz peak gets louder and the 100 Hz notch gets wider.

They are currently lying on the ground. My guess is if I lift them, the 100Hz notch should move downwards as it is at 70 Hz when the sub is standing. So - in theory - it could be possible to move it downwards to the 77 Hz peak if i put the subs on stands with the right height which should be 355 to 430mm (so the center of woofer is on 548 to 622mm). When the sub stands the woofer is on 830mm.

I tried facing the cones upwards and tried them pointing against the front wall: the response did not change very much.

Originally Posted by pentagon View Post
Distance from front wall to center of woofer? Distance from floor to center of woofer? Nearest side wall? And for the asymmetric setup, you need that info for both. Have you measured the tuned frequency of the radiator? (Easy to do, put the mic <6 inches from the radiator center and run a sweep signal.) Where are the radiators in all these measurements? (most notable if the tuned frequency is creating a problem) A lot of incomplete information. Also it’d be better to post your mdat (after labeling the measurements properly in the name/comment section with where things are) so other factors could be looked at.
Distance front wall to center of woofer: 350mm
Floor to center of woofer: 193mm
side walls: 860mm to radiator and 1690 to woofer

i added the mdat. the "MIX" is the asymmetrical setup.
Attached Files
File Type: mdat Jan left MIX horizontal.mdat (2.93 MB, 137 views) File Type: mdat Jan right HORIZONTAL.mdat (2.93 MB, 133 views) File Type: mdat Jan right MIX vertical.mdat (2.93 MB, 142 views) File Type: mdat Jan left HORIZONTAL.mdat (2.93 MB, 154 views)
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