[Wayne A. Pflughaupt]

HClarkx wrote:

I've seen your thoughts on this but haven't seen anything proving that the room decay is fully offset by the filter time response (i.e., that the two match).
Also, can you refer me to tests that confirm the time components added by the filters correct room decay characteristics?

I haven’t seen any comprehensive in-room testing, other than Ethan Winer’s EQ vs. Bass Traps extravaganza. The test has some problems, though, mainly that the sheer number of measurements presented is mind numbing, and the guy who set up the equalizer did a really bad job of it.

Ethan also did a simple evaluation of the effectiveness of the Audyssey MultEQ, which claims to reduce ringing. His conclusion was that it was a mixed bag as far as dealing with extended low frequency signal decay, aka “ringing” or “modal ringing.”

Since there seems to be a dearth of in-room time domain testing, other than these two, I’ve done some of my own (although I haven’t posted any results). After studying waterfalls ’til I’m bleary-eyed, I’ve found pretty much the same thing as Ethan, that actual in-room measurements show that it’s a mixed bag using an equalizer as a fix for extended low frequency decay issues.

I compared multiple waterfalls (as alluded to here, you won’t get a true picture from a single sweep) of equalized response using what I’ll call “modal filters,” that REW recommended to improve ringing (which is what REW does when you run the “Find Peaks” routine), to the “smoothing filters” I like to use (i.e., simply EQing out peaks and nulls with no regard for any effect on ringing). What was apparent was that the modal filters improved ringing for some peaks REW had identified, but for others there was no improvement at all.

Even then, the improvement waterfalls did show for modal filters was only apparent in the short-duration 300 ms window. When the window was lengthened to 600 or 1000 ms, any advantage modal filters showed over smoothed fully vanished. The overall trend was that modal filters had the effect of quickly attenuating decay in the short term (compared to smoothing filters), but only down to a certain level. In the long term, both sets of filters were showing comparable results (this despite the fact that most of the smoothing filters were set for boost!). Which is to say, there was no reduction in ringing.

That’s one thing I have noticed here at the Shack where people (including myself) have posted graphs showing that an EQ filter improved ringing: They’ve all been short-duration 300 ms windows, not long-duration.

You can clearly see this “fast attenuation but only to a certain level” effect with the first set of comparison graphs from Ethan’s Audyssey evaluation - note the region between 56 and 20 Hz.

Ethan and John both maintain that narrow filters have the greatest effect on time domain. That’s one thing I have yet to evaluate at length, but intend to.

Regards,
Wayne