need help with figuring out my ELC without reference grade gear

[Joe Bloggs]

I challenge you to the following experiment:

1. Find a low frequency in your speaker system with the worst null

2. Play a sine tone at the frequency and put a dB meter at your listening position

3. Now crank up the sine tone 6dB in volume (via adjustment of the signal generator itself) and note the change in the dB meter's reading.


I'm ready to eat a few unpleasant large objects if the dB meter doesn't register almost exactly 6dB change in volume.

I've done an essentially identical experiment: Pink noise, take an FR plot (using REW and a measurement mic), identify a freq with a 12dB dip, then add 12dB with a PEQ at that freq and remeasure. Result: About an 8dB dip instead of a 12dB one. To get the dip to zero couldn't be achieved with the PEQ I had as it maxed out at +18dB and even double the 12dB gain was not enough to flatten it! This is just one of easy more than 100 similar examples.

G

My guess is you are seeing the result of a smoothed FR plot in action. Please follow the exact steps I outlined and report back...

P.S. I got exactly the result I predicted, running the test myself... particularly if I eliminate the effect of background noise by looking at FFT power plots, the power at the frequency being played rises by exactly the amount I change in my tone generator, no matter whether I'm playing at a resonant peak or trough.

Would you also predict that volumes at a resonant peak increase by more than 6dB if you add 6dB to it?

 

[gregorio]

My guess is you are seeing the result of a smoothed FR plot in action.

 
Nope, I've specifically turned Smoothing off.
 

Please follow the exact steps I outlined and report back...

 
I am interested to try out your suggestion, notwithstanding the fact that I can't see how/why there should be any difference between the two methods. It's going to take a while for me to get around to it though, my calibrated mic/REW is the method I use for SPL measurements but it takes a while to set-up and my studio doesn't have a free "while" at the moment. When I've done it I'll report back.
 

Would you also predict that volumes at a resonant peak increase by more than 6dB if you add 6dB to it?

 
Don't know, never tried, I've always tried to reduce resonant peaks rather than increasing them!
 
In theory I suppose it would depend, probably on several factors. My guess is that it might, under certain fairly extreme circumstances but most probably you'd get out what you put in. Just guessing though.
 
G