A few questions after first measurement

[nixoblivion]

Hi.
So i measured my room yesterday with my new ecm8000 just to demo and see how things work out!
So now i know, my room kinda sux :P but thats not a problem, i guess.

I was surprised to see some differences after measuring my room several times in a row, with no changes (mic pos, volume etc) at all! Everything under 40hz-50hz was just random it seemed! I had some differences at 50 and 70hz as well. Mostly those were at max at 2db, so nothing big. Im just curious.

My tascam vl a-5 apparently go down to 38hz and the ecm8000 should be able to cope with that too, so not sure why its just random and the changes at 50 and 70hz.
I measured with very long sweeps (10s) with start silence (5s) and end silence (1s) and an averaging of 8 sweeps, per meassurement.

Im also very surprised, my left and right speaker have huge differences in the low end! at around 75hz (which is a general problem in my room it seems) it adds up to 15db difference between L and R channel!!! This seems weird to me, since i have tried to build up as symmetrical as possible, so the back wall is the same distance from both speakers, im pretty much in the middle of the room (though the right wall is 1.6m and the left wall is 2.1m away). But can that make such a huge difference?

Last but not least, im quite surprised by the fall of the top end. after 6khz the graph just falls down quite strongly, a total of -17 from 6-20khz. I had the ecm8000 pointing upwards, heard that this was the better way to measure. This does surprise me a little since our ear has the least absorbion in front, so i would think pointing the mic that way would be the most logical...

I will make more meassurements in the next days and find out the problems better, just want to make sure im doin things right :P

[Weasel9992]

Differences between the left and right are actually really common. As far as placement goes, you should have the mic at ear level (seated, so about 45" or so), right in between the speakers. What preamp are you using?

Frank

[Ethan Winer]

Originally Posted by nixoblivion

Everything under 40hz-50hz was just random it seemed!

What software did you use to measure? Regardless, that's a clear tip-off that you have truck traffic or other such LF noise leaking into the room. If you play the test tones 10 dB louder is there less randomness? If so, that proves it's noise.

--Ethan

[nixoblivion]

Thx for the replies.
yes. i had the mic at ear level, so right between speakers at hear height, pointing upwards.
im using an mbox2 as preamp. i use fuzzmeasure as software.

i actually have no road outside, so it cant be that. but maybe there was some other low frequency noise around. i will test again tomorrow or so, and then ill see.

what was also a little weird, was that the waterfall only showed ringing over 100hz. my graph shows quite a fall under 100hz, so maybe its that. still i was surprised since in most waterfall diagrams their are problems at lower frequencies (50, 70 or something the like)

[ciro]

Originally Posted by nixoblivion

Im also very surprised, my left and right speaker have huge differences in the low end... This seems weird to me, since i have tried to build up as symmetrical as possible, so the back wall is the same distance from both speakers, im pretty much in the middle of the room (though the right wall is 1.6m and the left wall is 2.1m away). But can that make such a huge difference?

You need symetry in the front wall.
Anyway,this 50 cm difference will give you different L/R low response.

My (bad) experience with my old position in the room:
*different distance monitors/adjacent walls (not 50cm, but near) + a door in the front (right)side of the room = -5 or 6 dbs in the lows of "R" speaker and very different individual L/R measured/audible response.
And poor stereo image.

I swapped it 180° (and added more 9 or 10 traps)
and now it´s ok

Thanks - Ethan Winer/Real Traps and GIK site for the valuable information and Bryan Pape for all the great advices.

Ciro