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I took a measurement where a pair of speakers (about 38" from each other) is placed on a 48 inch by 28 inch desk surface and a sub-woofer (consumer brand, without high pass filters for the main speakers) is on the right side of the desk. The room has about $500 amount of bass absorption panels (5.5" thickness (by my measurement) GIK brand. One 12"X48" and one 24X48 right behind the desk, one 12X48 and one 24X48 on the opposite wall, a 12X48 at a corner, a 12X48 at another corner.).
Mic was placed at the usual listing head position.
The walls around the left and right speakers are not symmetric. The right side wall is about 42" from the center of the right speaker. About 25" left from the center of the left speaker there is opening: ways to other areas and to downstairs.
I see a nasty dip and peak at 114Hz and 125Hz, respectively,on the left channel. I moved the left speaker around within the owner's practicality limit, but could not eliminate such dip and peak. For example, moving the left speaker up made the dip and peak nastier. Is the dip and peak something audio maniacs usually accept, or is it worth trying harder to remove it?
I tried wide-overlaping the subwoofer with the speakers on the desk by making the high cut frequency for the subwoofer higher, but observed new deep dip in the overlap. It was hard to achieve shallow dip in all three cases: L, R, L+R.
One possibility is to change the system to a subwoofer and satellite system with a rather high crossover point (about 150Hz): Cambridge Audio Minx or Bose AM 5. I put the left speaker on the left side of the desk where Bose AM 5 bass module's port would be located, and could almost eliminate the dip and peak. However, I have no idea whether the new high-crossovered subwoofer and satellite system will produce new nasty dip and peak in 100Hz - 200Hz.
The frequency-amplitude graphs are 1/48 oct smoothed.
Edits: 07/16/16 07/16/16Follow Ups:
dave789-
how does your room sound?
Does your room sound good, and how does it measure?
I felt that the "room" sounds irregular in the sense that the feeling varies a lot depending on which passage of music or speech is played. This "irregular" character is from bass to treble. Sometimes it sounds acceptable, but sometimes, I feel something is severely wrong in the recording. Several times, I compared the OK passage and the problem passage on a couple of headphones, and both passages sounded OK.
By the way, let us think what you mean by "how does the room sound." In any room, I can put the speakers as close as possible to a wall and put the head as close as possible to the opposite wall to amplify the standing wave modes. It may sound "good" in short listening due to some bass boost, but it will turn out to be poor after long term listening.
The point of my question is whether the difference of about 26dB at 114Hz and 125Hz, 1/48 oct smoothing, is something audio maniacs usually accept or not, whether it is worth trying to remove the difference by relocating speakers and listening positions, etc.
Room reflections often corrupt measurements so much that its often hard to tell where the driver ends and the room effects begin.
Your best bet if you can is to take one outdoors and measure it in an open space. Even if your only 10 feet from a building it will be cleaner than indoors.
Low frequency drivers do not normally produce "sharp" features like notches or peaks. Notches are usually from cancellation (a reflected signal arriving delayed 180 degrees or N odd half wavelengths) like the typical "floor bounce" causes
It seems that the main cause is floor and ceiling reflection. As an experiment I put a 24"X48" bass absorption panel on the carpeted floor below the desk. That reduced the dip at 114Hz significantly. The effect diminishes as I lift the bass absorption panel one inch from the floor. I heard the model is 244 Bass Trap.
Previously, I could not imagine such a deep suck-out in the frequency response curve, because the listening position is what is called "near field." The pass length difference between the direct sound and any indirect sound (except the desk surface reflection) is quite big.
Rooms are funny. Make it sound good to your ears and worry a little less about the graph while still using it as a guide.
ET
"If at first you don't succeed, keep on sucking till you do suck seed" - Curly Howard 1936
Unfortunately, the bottom line is if you want perfectly flat response get headphones. I don't like using headphones all the time so this is still a valid point, but getting to perfection is a long long ride. In fact you can really only get it outside where there are no reflective surfaces to screw up the sound.
To find out if the peaks and dips are in the room or speakers, move the speakers and remeasure.
And, how are you measuring ? Are you using a swept frequency or pink noise ?
You can see measurement curves online. They are very nasty. There is no flat response headphone in the world.
...is a setting on your dryer.
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