30Hz - 20kHz test tone result (please help me test)

Started by remo on 27 October 2004. 2 replies.

Originally posted at johnlsayers.com, topic 2559.

I just did a pretty unscientific test of my room at mix position. I played a 30sec 30Hz - 20kHz sine wave (download here http://www.nixonaudio.com/room/30Hz-20kHz.wav) ...into my mike (Studio Projects C1 into Amek CIB (all EQ off)) and here are the results with the main peaks labeled.
External image, not preserved — original: http://www.nixonaudio.com/room/testtone.jpg
is this a good way to see where my problems are? I didn't include the dB levels but trust me they are quite large as I can easily hear where the peaks are. here is the result for a similar test with 10 seconds of pink noise recorded at mix position.
External image, not preserved — original: http://www.nixonaudio.com/room/pink.jpg
Seeing as there is a distinct similarity between the two is it fair to say I can target the problem freqs? What can anyone else tell me about my room from these results? Is there another test I should do? Is there something fundamentally wrong with my test/results? here is the dimentions of my room
External image, not preserved — original: http://www.nixonaudio.com/room/1.jpg
External image, not preserved — original: http://www.nixonaudio.com/room/5.jpg
In honesty.. I usually find my self cutting a lot of 110 out of my mixed because it sounds boxy with it in... looks like I'm cutting out meat that I need... My mixes usually translate a little on the "light" side with no chunky in your chest bass. I can NEVER get the "meat" I want into my tracks.... any suggestion welcomed! And I would like to se other people's results from this test.. :D
Information that's missing - ceiling height, whether one or both speakers driven, exact distances from center of woofers to front, back, sides, as well as vertical placement relative to floor and ceiling; same with mic position during the tests. Also, any mic that isn't omnidirectional will get different results depending on direction it's aimed; all mics will exhibit boundary effects relative to all boundaries in the room. Directional mics have a larger response variation with on-axis vs. off-axis placement (whether they are pointed at the source or not) In addition to this, the specific speaker used will change the results; basically, any and all dimensions from anything to anything can/will skew the results of the test. A basic start on tracking down where your problem(s) come from would be to download this spreadsheet from Harmon http://www.harman.com/wp/index.jsp?articleId=131 Enter your room dimensions into the sheet, it will graph the peaks and nulls for each axial mode of your room in all three dimensions for the first 4 harmonics - for a basic starting point which doesn't take tangential or oblique modes into account, you can make sure neither the speakers or your head/mic are at either peak or (especially) null positions in any of the three axes; in smaller rooms (most of us) as little as 2-3 inches can change results, especially for nulls. One method I use that works fairly well; I copy the graph area of this sheet to the clipboard, dump it into Paint (open 3 or 4 instances of paint) - then select each axis separately, copy into another instance of paint, re-size to match your room plan, rotate as necessary, and paste beside that wall; draw RED lines straight across the plan starting at all peak and null points on the graph, and GREEN lines in between; do the same with an elevation view of the room for vertical placement; then, make sure everything (woofers, head, mic, instrument) are in a "green" area. I'm out of here for now, but will try to remember to post some examples when I can; if I don't get back, "bump" this to remind me... Steve
Remo, > here are the results with the main peaks labeled < Just as important as those peaks are all the nulls. --Ethan