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Old 18th December 2010
  #29
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Graphic Language Part II

Hello All,

First off, thank you to Lupo and DanDan for the pointers and references.

After 3 days of reading hundreds of posts and using REW, i think i finally got over the first foothill. (only 10,000 more feet to go)

The room dimensions are as followed: 24' x 20'. Although this a basement room, the walls are covered in raw ceder planks. the floor has one small area rug at the listening position while the rest of the floor is concrete. the ceiling is a standard grid style drop ceiling. No acoustic treatment has been employed.

The mix desk is centered along the 20' front wall. The monitors sit about a 1' off the wall. The listening position is 5' from the wall

The graphs included in this post were all done with one channel (left). The SPL "c weighting" box was un-ticked. and the loop correction for the sound card calibration was completed.

I did not calibrate the CAD e70 mic that i used because i had no .cal file. from what i have read, calibration is an insignificant gesture, when compared to the modal and spectral anomalies of the room.

I will now make a feeble attempt to extrapolate data from these graphs. i did the best i could to massage the "windowing" to meet the requests of so many senior posters.

THE FREQUENCY DOMAIN

The Frequency Response graph and Waterfall graph are telling me that there is a huge peak in the room at 60hz and 160hz. Looking further into the waterfall i can see that the modal ringing at 60hz is lasting for about 1 second. I think this is a significant finding. The numbers tell me to start adding bass traps to the corners. (everywhere???)

The second really obvious assessment, is the null at ~105hz and 120hz. From most of what i am reading, except for Ethan's posts, I can do nothing about this except move the listening position forward or backward, an inch or two, and try again.

THE TIME DOMAIN

The ETC graph is telling me, via the measuring tool, that the first significant reflection had to travel 2.7 additional feet in order to reach the microphone. This means that a reflection point 1.35ft away from the microphone, is causing this reflection.

Well i got out the trusty measuring tape, and the closest surface i could find at 1.35ft was the desk the monitors are perched on. (it was actually 2 feet away)

The 7ft ceiling was three feet away. I am assuming that the ceiling is the cause for the next reflection seen at about 3.75msec. (going by the math i would expect the ceiling to be ~2 feet away if the total extra distance traveled for the second reflection was 4.21ft.)

Questions:

Is there any ideas on on my modal issues? Peaks and Nulls.

Am i approaching the ETC interpretation correctly?

Am i in the ballpark for locating reflection points or is my math and logic wrong?

Thank you,
-Nick
Attached Thumbnails
Measuring Room Acoustics-freq-resp-sat-18th-2010.jpg   Measuring Room Acoustics-waterfall-sat-18th-2010.jpg   Measuring Room Acoustics-etc-graph-measure-sat-18th-2010.jpg