[warrensomebody]

Wayne A. Pflughaupt wrote:

I’m by no means an expert in this, but I’m not sure how much stock you can take in near-field response, especially one that’s not taken in a highly controlled environment with precision measuring instruments and protocol. No matter what you do or how you do it at home, you can’t fully remove the room’s influence on the reading, because low bass is omnidirectional. IMO, listening-position readings are what matter most. Of course, if you sit a foot away from your subs when you’re listening to music...

Hi Wayne - I guess I was taking cues from a brief foray into speaker design I did a few years ago, where measuring the characteristics of the drivers up close and individually was a way of eliminating the effects of the room, etc. But you do have a point -- there's no way to really eliminate the room from by doing this, especially for bass response, and the response at the listening position is what really matters.

Wayne A. Pflughaupt wrote:

Practically speaking (i.e. in everyday use), “headroom” is the difference between your normal system demands and your maximum available output. Reserve output, if you will. So “diminished headroom” would be anything that would consistently demand more output, thus narrowing the gap to maximum available output.

SNR (signal to noise ratio) is typically a noise-floor rating – i.e., how quiet your equipment is at idle.

Nope – doubling available power typically gets you about 3 dB of headroom. To put it another way, raising SPL by 3 dB requires a doubling of amplifier power.

I get your point, but it sounds like maybe we're saying the same thing here. Talking about headroom in terms of dB is really just talking about power using a particular measurement system (a logarithmic one). As I recall, 3dB is not only a doubling of power, but a doubling of perceived loudness.

Wayne A. Pflughaupt wrote:

Okay, so the mains are bi-amped. Not sure I would replace the stock crossover with the Lexicon. In addition to the slopes possibly not being the same, it’s possible the Pipedreams crossover employs some corrective equalization and/or level-matching. Many passive crossovers do this, as do active speakers, so it’s not unreasonable to expect that a dedicated electronic crossover might, too.

Good point. It hadn't crossed my mind that the Pipedreams active xover might do something beyond simply controlling the bass cutoffs and slopes, i.e. have some pre-set EQ built in. My main reason for trying to eliminate it have been (a) quest for system simplification (yes, I know I have a digital preamp, but if I can reduce 2 boxes down to one...), and (b) the thing is completely undocumented (switches on the front labeled A, B, C, D; 2 slope settings but no description of what the db-per-octave numbers actually are, etc, etc). I've tried taking measurements while adjusting all these things, but there are literally so many combinations, and my graphs are so bumpy (as you can see), that it's really hard to tell exactly what all these things do. (And the manufacturer only seems to want to sell me a newer xover!)

Wayne A. Pflughaupt wrote:

...
Here we have a plateau in response that falls off very sharply on the left, and gradually on the right. Problems like this are virtually unequalizable with symmetrical filters. You can see with the green line what an EQ attempt looks like: it didn’t eliminate the plateau – it just notched a hole in the middle of it. Which would sound better there, EQ or no EQ? Who knows? You’d have to listen and see.

Aah... but that's the real trick -- to know what to listen for when you're not an experienced sound engineer. It's one thing to think you have a good sense for whether music played over a system sounds good or not, but completely another to judge system anomolies from test tones and pink noise. Of course, the music is ultimately what we're after... but I guess I just can't help myself when it comes to getting things "right". :-)

I read a great suggestion from one of the users on this forum -- set the sweep time to fairly long, so that it goes slowly enough to audibly hear where the peaks and valleys are. I'm going to try that when I get back, and see if there's any obvious adjustments needed in the mains range (e.g. that curious bump from 3-4khz). I think it might be cool if REW had a mode that let you control the sweep frequency manually (kind of like turning the dial on an FM tuner) so that you could really get a subjective impression of what's a problem and what's not. But a slow sweep might be good enough -- certainly a huge improvement over the test tones on that old Stephen Court and Alan Parson's Sound Check CD I used to use!

Wayne A. Pflughaupt wrote:

Look again at the green (after EQ) line, and imagine what would have happened if the filter had been spread wider, to cut down more of the plateau: In trying to achieve our objective, it would have also deepened the low points on either side of it.

That’s a prime example of what can happen with willy-nilly equalizing of the mains: Causing as many new problems as you solve. That’s why you keep things general, addressing mainly broad trends, and perhaps a few egregious dips or peaks. Most importantly, you have to be able to look at a graph and recognize what you can deal with, and what is better left alone. It’s no wonder mains equalization has such a bad reputation: I’d venture that most of the people who have attempted it and badmouth it afterwards are rank amateurs who have no idea what they’re doing.

On top of everything else, much of the raggedness you see with full-range readings is the result of room reflections, and the resulting phase shift (i.e., identical signals reaching the evaluating mic at slightly different times). This is why your speakers always sound much better than they look on “paper.”

Ok - I'm getting a better idea of the problems and diminishing returns from attempting to EQ the mains. I'll be very interested to get back to some measurements with an ECM8000, etc, soon, but given that I think they sound good, I'm going to be very disinclined to put an EQ in there. Thanks again for all your input.

Warren