[Wayne A. Pflughaupt]

On the other hand, from personal experience, if you cut too much to get the majority of frequencies down to the level of a dip, then you have to turn the gain on the sub way up. When you turn the gain up, you are amplifying "noise" from the BFD to be louder.

Exactly. You have to look at the whole picture; the BFD is only one component in the signal chain. Assuming you have your BFD’s input level set just below clipping, if your output level is –10 or -15 dB (or even less) after equalization, that’s 10 or 15 dB (or more) you reduce the sub’s S/N when you turn it up to compensate. Well, a high gain/low signal scenario is a know recipe for audible noise.

Does that matter much at the end of the day? As cyberbri and PeteD have discovered, sometimes it matters a lot.

Typically a powered subwoofer is going to be the “weak link” in the signal chain. We know what the BFD’s maximum S/N ratio is, but most sub manufacturers don’t even publish them. Either they feel it doesn’t matter much, or it’s a figure too embarrassing to publish.

When I can find a noise spec for a powered subwoofer, it’s usually 90 dB or less, with no qualifier such as “unweighted between 20 Hz- 20 kHz” (to quote from the BFD’s spec). Without the qualifier, their 90-dB rating isn’t terribly meaningful.

But for the sake of this discussion, let’s pretend that it is. If our signal from the BFD is 10-15 dB lower than what came into it, we’ve sucked our sub’s (questionable) 90 dB S/N down to a (questionable) 75 or 80 dB when we increase its gain.

At that point it isn’t terribly relevant that you managed to maintain the BFD’s excellent >94 dB noise rating. Your overall S/N can never be higher than the weakest link in the signal chain anyway.

So, the best approach IMO is to try to get the BFD’s output close to its input. Most response curves have both peaks and valleys, so the most efficient equalizing (i.e., using the fewest filters) means a combination of boost and cut filters applied to them. After EQ you’ll often end up with the BFD’s output close to its input, so you don’t burden your sub with a low-level signal.

Regards,
Wayne