My speaker system was designed to be used with a manufacturer-supplied active crossover unit. The crossover offers several adjustments, notably:
- choice of xover at 63 or 80Hz
- independent level controls for the subs
- independent phase controls for the subs
- 0 or 180 degree phase adjustment
- 2 xover slopes (24db and 18db/octave (or maybe it's 12db - hard to tell, and I have no manual))
But when using REW with a FBQ2496, I'm wondering whether it might not make sense to try and subsume the functionality of this active crossover. It just seems better to me to eliminate components in the signal path if possible, and doing so certainly simplifies the room optimization problem (believe me - I've spent hours tweeking the knobs and switches on the front of this active xover and measuring the effects with REW, but the ability to control the frequency response of the system this way is crude at best).
To see if eliminating this xover is possible, I tried measuring the following:
a. prepro full range output -> active xover -> sub output (80hz xover)
b. prepro sub output (configured with 80hz xover)
Here's what I see (a=green, b=yellow, smoothed 1/24db/octave):
nf xover vs prepro sub output.jpg
From this graph, there are a few things that are clear. First, I've got some problem going on around 23 and 36Hz. I'm not going to worry about that here (since this is the measurement for one sub, and I actually have two... plus I probably need to reposition it to avoid this drop-out). Second, we can see that the active xover is operating with a different output level than the prepro sub output (~15db). If I adjust for this (so that we can compare similar curves) I get this graph:
nf xover vs prepro sub output2.jpg
From this graph it appears that the active xover is applying some equalization to the sub since the sub as measured directly from the prepro shows 18db or more attenuation at 20Hz. So the question is, what exactly is this equalization, and can I reproduce it with the FBQ2496...
This is where I'm venturing off into territory I'm unfamiliar with, so please bear with me, and let me know your suggestions. Taking a cue from some things I've read in this forum about designing a house curve and shelf filters, I came up with the following:
filter1.jpg
That's 3 parametric filters: -31db, 8 BW Oct @ 80Hz; -36db, 10 BW Oct @ 1400Hz; and -12db, 1.5 BW Oct @ 52Hz (seat of my pants); plus a 33db gain in the sub output level (I think my amp has the headroom, although I'm not sure what this means about noise I might be injecting into the system). To get a better idea of what these look like across the entire spectrum, here's an expanded picture:
filter2.jpg
Clearly I can apply some spot filters to smooth this out a little more, but my main question is whether this approach seems reasonable, and/or whether there's another route I should take. (I haven't yet tried this filter in my system, just with REW... so I can't tell you how I think it sounds.)
Thanks for your input...