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Help with strong left image but weak right
Help with strong left image but weak right
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Old 16th October 2018, 09:13 AM   #41
turk 182 is offline turk 182  Canada
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Join Date: Oct 2012
could you post the one at 5 ms?
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Old 16th October 2018, 10:20 AM   #42
mark3141 is offline mark3141  United States
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Join Date: Feb 2013
Location: Texas transplant in MD
Help with strong left image but weak right
Originally Posted by turk 182 View Post
could you post the one at 5 ms?
Let me know if you meant something else. I assume you are asking for a before/after treating the 5ms reflection. If so, the 'before' would the left_1_forward_wall and the after would be the left_2_side_wall, but I went ahead and did before/after for both walls and speakers:

For the left and right, I have an impulse response for

0 = baseline (no absorption)
1 = baseline + absorption on forward wall (calculated reflection ~10ms)
2 = 1 + absorption on side (right) wall (calculated reflection ~5ms for left speaker and ~10 ms for right speaker)
3 = 'final' is the same as 2 but a few days later
Attached Images
File Type: jpg right_3_final.jpg (148.1 KB, 14 views)
File Type: jpg right_2_side_wall.jpg (151.7 KB, 14 views)
File Type: jpg right_1_forward_wall.jpg (147.7 KB, 14 views)
File Type: jpg right_0_baseline.jpg (147.9 KB, 14 views)
File Type: jpg left_3_final.jpg (132.2 KB, 13 views)
File Type: jpg left_2_side_wall.jpg (149.9 KB, 3 views)
File Type: jpg left_1_forward_wall.jpg (148.4 KB, 1 views)
File Type: jpg left_0_baseline.jpg (158.2 KB, 2 views)
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Old 16th October 2018, 06:29 PM   #43
Pano is offline Pano  United States
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Location: SW Florida
Help with strong left image but weak right
I can't get the files to open in REW. Keeps telling me they are not valid REW files. I'm in the latest version for Mac.
EDIT: Never mind. Bad download. Now good.
Take the Speaker Voltage Test!
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Old 16th October 2018, 10:14 PM   #44
Adhoc1 is offline Adhoc1
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Join Date: Apr 2012
Hm, a bummer from me. I did read you have a port firing out from the backside of the speaker. Still, I forgot that, -sorry. The port needs some breathing space of course, a distance like the port diameter away from the wall should be OK but preferably larger. Consideration to be taken though are in what range the sub will / can play so you avoid the null you have around 50-60 Hz. That means either close to the wall behind or very far into the room. Close to the wall: If it plays up to say 80 Hz, no further than 344/80/4 = 1,09 m, so make that about 80-90 cm or closer. Out into the room and it is capable down to say 35 Hz: 344/35/4 = 2,45 from the wall behind, make that more than 2,5 m. Increased distance means a dip at lower frequency. For a sub playing 35-80 Hz the ”no go zone” would be roughly 90-250 cm from the wall behind it. If it is placed in the ”no go zone”, you can expect a more or less large dip in the frequncy curve. The same idea applies for the main speakers and the range they play. The crossover frequency determines how far away one should place the main speakers from the sub. Within 1/8 to about of the crossover wave length is OK, preferably not further away.

As for pinpointing instruments in the soundstage, if that is the important thing and increased soundstage width is less important. If the engineer in the control room has done a good job, it is there in the recording, panned between the 2 stereo speakers. In a room each speaker has several mirror images though, = reflection points in the walls, ceiling and floor. Many sound sources, around at different places, are of no help for pinpointing what is on the recording.

The Haas effect / precendence effect locks your hearing to the direction of the first arriving sound = direct sound. Delayed (reflected) sound arriving after about 5 ms has to be about 10 dB louder than the direct sound to make a change of that first heard direction. The 0-5 ms is a bit of a zone of confusion where less dB-strength is needed. If these reflection come close enough in time, are of sufficient strength and from a certain angle, you may receive double messages about the pinpointing and it is also depending on frequency.

From ”Acoustics and Psychacoustics” by David Howard and James Angus:
”Thus the interaural intensity difference is a cue for direction at high frequencies whereas the interaural time difference is a cue for direction at low frequencies. Note that the cross-over between the two techniques starts at about 700 Hz and would be complete at about four times this frequency at 2.8 kHz. In between these two frequencies the ability of our ears to resolve direction is not as good as at other frequencies.” and:

”The main compromise in stereo sound reproduction is the presence of spurious direction cues in the listening environment because the loudspeakers and environment will all contribute cues about their position in the room, which have nothing to do with the original recording.”

It is a couple of years ago since I used REW last time but I found the ETC (Energy Time Curve) to be of better help than the Impulse Response. Tick the box for Schroeder integral and you get the overall decay time in your room. If the Schroeder Integral is a more or less straight down sloping line, fine! If it is not constantly decreasing and has large bumps, it shows you have a decay that varies, modes go up and down in time. Often because of irregular L-shaped rooms or the room has some heavy rigid walls and some light weight stud walls which low frequncies passes through and gets reflected back from another room with heavier walls. -You may get a kind of pulsating sound, this can also be seen in the waterfall diagram. You can also filter the ETC to show certain frequencies so you get an idea how the decay rate is different depending on lower or higher frequencies, one can also get a better idea which frequency causes the impulse peak you see at a certain time.

Last edited by Adhoc1; 16th October 2018 at 10:22 PM.
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