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Post by howardmil on Aug 30, 2019 15:53:09 GMT
   Hi Ethan: Would you have some ideas on 2 issues? My 24 by 14 by 8 listening carpeted room has 2 monster bass traps (gik limiters) straddling front ceiling corners. 2- thicker 48 inch high absorption panels at first reflection points. And 2 - 244 ceiling clouds half way between me and speakers. Speakers are 4 feet from front (14 ‘) wall and I’m 11 feet back centered listening position. Rest of room is bare, ( lots of unpacked boxes behind me with 11 feet to back wall. I have 3 Alpha absorption/diffusion panels not yet installed for BACK WALL ( approximately 11 feet behind me. Problem: some “ shrill” flutter on female operatic voices and such with large transient vocals- ! Would the Alphas fix this on wall behind me? The GIK ceiling 244’s seem to have small effect on the flutter or echo— or might I need alphas in back and possibly more absorption on ceiling or at left or right of my listening position?? By the way— my speakers are accurately measured to cm from each wall position and toe in. I play Chesky test for stereo and is ‘just about perfect’ for center image. However , some program sources drift a touch to the LEFT.... Importantly- there is a small 4 foot wide by 1 foot deep (8’ to ceiling) ‘Opening ‘ or alcove mid way between the cabinet of left speaker to front left wall. (The right side speaker is on straight drywall to front right wall). Could this small opening affect image and if so, how could it possibly be fixed? I know these are 2 long questions but I greatly appreciate your help. Thanks |
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Post by Hexspa on Aug 30, 2019 18:12:56 GMT
Not totally following but, if you're hearing flutter echo from your listening position then you need to work on your RFZ. If your image is drifting then check your symmetry, speaker volume and distance to listening position. Also, once your system is highly accurate, you will actually hear whatever non-centered image that's in the recording. You can use a stereo scope to monitor the signal. www.meldaproduction.com/MStereoScope |
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Post by howardmil on Aug 31, 2019 14:57:52 GMT
Indeed- 4 by 8 by 12 inch deep alcove ( leading to boiler room door) exists adjacent to 1/2 of left speaker cabinet. Other side is full drywall to front wall.
Can’t find a way to fill this space with drywall divider or anything that wouldn’t require professional installation ( $!)
Don’t know what type of divider might work? Presumably should be of similar material as drywall??
Any ideas?
Thanks
Howard
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Post by rock on Aug 31, 2019 16:43:45 GMT
In my experience flutter echoes are usually easy to hear what surfaces are causing the echo by turning your head to listen for the direction. As Hexspa says, you need to cover your reflection areas and after that, you might need to treat your side walls with alternating absorbers on each side. It's good to treat your back wall too but use thicker for more LF absorption there.
Your "alcove" may not be a cause of problems but if it is, you can cover that space with absorption and do the same on the opposing side for symmetry. Pictures may help.
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Post by howardmil on Aug 31, 2019 21:11:03 GMT
It appears that you are on the right track! I have posted 3 pictures above and here on first question for your inspection. It appears that as to the flutter echo it surely could be tamed somehow, as I am putting up behind me on 14 foot wide long 3 GIK alpha 5 absorbers/diffusors to see what happens. As to the somewhat shifting STEREO IMAGE to the left, this is truly bothersome and ironically, became more of a problem since treating the room with Monster traps with range limiters up front as well as the ceiling absorbers, (which does not SEEM to be of that much influence). On the other hand, the room does sound overall BETTER.....with the treatment so far. (excluding the above Alphas for back wall). One picture has the left side alcove half way back from left speaker cabinet. The right side of room as you see has the opposing first reflection point absorber, but a somewhat heavy moving blanket behind it covering a 5 foot by 4 foot window on the right. The left opposing side just has the left first reflection point absorber against the drywall. Hope this helps alot and can get this straigntened out. Regards Howard    |
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Post by Hexspa on Aug 31, 2019 21:17:09 GMT
You're sitting really far back. That gives the room more opportunity to exert influence on what you hear. Try sitting closer.
The reason the absorption seemed to make things worse is because it made things better. Your room was so reflective before that directionality and image was a non-issue - it was just too much of a wash to pinpoint the problems. It's just like mixing a record - perhaps there are other analogies - in that the first listen doesn't sound too bad. It's only after you say, "I'll have a bit of compression over here..." that other problems start revealing themselves.
I think this is a common problem whenever someone tries to fix something. It seems like they, or things, get worse before they get better. This is no different than the flu where, when you're actually sick, you don't feel it as much. Only when you begin the healing process do the symptoms really become obvious.
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Post by howardmil on Sept 1, 2019 0:41:45 GMT
It’s actually the photo, for some reason. The speakers are 4 feet from back wall, 3.25 from sides and I sit 11 feet from the loudspeakers ( almost 8 feet between speakers.)
I tried removing that blanket covering window on right but wasn’t happy overall with sound so I put it back up.
I must kill more reverberated sound I noticed today. If the Alpha traps on back wall is not enough, I’ll have to ask for further advice. I could put my chair closer, but I don’t care for near field listening so I sit a few feet further than the distance between speakers.
Howard
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Post by Hexspa on Sept 1, 2019 9:35:59 GMT
You can always try compensating with speaker toe-in. That's if the image shift is static. If the image is fluctuating laterally then you probably have a bass problem from about 120Hz to maybe 300Hz or so.
I'm guessing that since sub bass isn't easy to localize and your image should be stationary above the Schroeder Frequency since the modes are tight enough there to support that range. The bass, but not sub, range is still vulnerable to modes and is able to be localized. Hence, when your bass notes change, some frequencies will be louder and others quieter in your room and at the listening position. This will happen even if the stereo information in the audio file is identical in both channels because you have SBIR - your speakers are probably not sitting in identical modal copies - to consider as well.
If I'm right then more bass traps is the answer - as usual - or even trying to reposition your speakers to balance the SPL response. You can confirm the difference between them by taking individual acoustic measurements of each speaker and trying to correlate image shift with mono sine waves tuned to where you have the most discrepancy. Or you could just run a looping sweep - I believe Ethan has one for download somewhere on his site - in the bass range and listen for any change in image. You can also try sweeping above 300Hz to hear whether that stays centered or not.
Failing all else, judicious corrective EQ can also be applied here. However, based on what I'm seeing, you're far from exhausting the option of more trapping.
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Post by howardmil on Sept 2, 2019 19:21:49 GMT
 Hi Im currently investigating your proposed ideas. In the meantime,,, would any of these in the above image have an effect on the problem or any other sound problems in the room.>? As you can see, I have 2 1 foot wall inlays on the sides of my listenng chair going to back of the room. I have just installed Diffusor/absorber panels as seen. ALSO...having just recently moved in ,,,do these boxes behind me make any difference one way or the other on my listening room? Thanks |
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Post by Hexspa on Sept 3, 2019 2:13:26 GMT
Everything makes a difference - and very often an audible one. I've never heard or seen perfection but most of us have an idea of how it would appear. With that goal in mind, either move toward it or be content with what you care to achieve.
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Post by howardmil on Sept 6, 2019 13:39:14 GMT
What about this 6 by 4 window on right reflection point with a 48 tall inch full range absorption panel standing in front ( but slightly below) half the window... Should window be covered, light material shades, or half open as in attachment picture? Would this be balanced with left wall panel and dry wall and have influence on image shift to left ?  |
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Post by Hexspa on Sept 7, 2019 2:53:41 GMT
Like I said, everything matters. The best way to calibrate your speakers is to run pink noise through each of them. You can filter it above your Schroeder Frequency to minimize the influence of modes on the result. Set them to the same level C-weighted, slow response at your listening position. Also make sure they are positioned in your standard equilateral triangle with the tweeters pointing at your ears.
Barring that, it's probably a modal issue or something to do with your perimeter or other obstacle.
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