@chungjh
While not exactly what you inquired about, here is my experience with subwoofers and EQ:
I was told that getting the subwoofers would be the easiest part, but that integrating them with the ESL’s with proper high-pass filters (HPF) and low-pass filters (LPF) would be more challenging. There were all sorts of recommendations about HPF’s, including passive vs active vs analog vs digital. The LPF was easier, as it’s integrated into the subwoofer itself.
It seemed that integrating a HPF would be most challenging, and all methodologies would change the sound quality (SQ), and since my system was very transparent, detailed, and musical, I didn’t want to interfere with the superb SQ, whether that be integrating a capacitor into the interconnect feeding my amplifiers, or changing a pre-amplifier to some sort of DEQ device with unlimited fiddling with orders of filters, etc.
Ultimately, I decided not to even bother with using a HPF, and, as you can determine from my description below, I am very content with the SQ and musical presentation without any HPF.
Before the purchase of my subwoofers, I was told that the subwoofers and electrostatic speakers are poor matches, and I was prepared to follow through with complex HPF, etc, if necessary, but either I’m just lucky with my placement, and set up, or the Martin Logan Balanced Force subwoofers just match perfectly with my Sound Lab electrostatic speakers, with simply placing the subs in a standard stereo position. Consequently, I’m reluctant to start with endless fiddling when it’s perfect now, with only a slight stagger to the subs. (I did note that if the subs were placed symmetrically, that there was a band of low frequency sound that got cancelled out between the two subs.)
After a couple of months of listening, I got the Martin Logan Perfect Bass Kit (PBK), which is room EQ software that can either be automated or manually set up using a microphone measuring from 5 different points in the room.
Firstly, l have really been appreciating the marked improvement in texture that the subwoofers give to all musical instruments with just the standard operation using the LPF set at 55 Hz in conjunction with my Sound Lab electrostatic speakers. Regardless, I followed through with proper room EQ set up using the PBK, and at first I was rather pleased: the bass sound did sound more refined, slightly more precise, and not quite as thick at the lowest register.
Without any EQ, my room has an increased signal from 20-40 Hz, and then dramatically drops between 40-50Hz, before slightly rising back up to ideal flat signal after 60 Hz or so. After the PBK, the Room EQ flattened out the signal rather markedly, to make it appear almost ideal.
When I first listen with the Room EQ, as I mentioned, the bass sounds more refined, and perhaps slightly more precise, but it does seem to detract from some of that more visceral component of the lower frequencies. If I only listen for an hour or less, then I am content with the Room EQ; however, I noticed that if I have a longer listening session for a few hours or more, that I get rather significant ear (listening) fatigue, which has never before been a problem with my system. So I turn the Room EQ off, and listen to the standard subwoofers without any EQ, and the fatigue immediately disappears…so I’ve reverted to listening to the subwoofers without any EQ, and I think that it sounds superior, although it measures worse!
So, that somewhat supports my opinion that audio measurements are an idealized representation of what some people think music should sound like but they are mostly wrong…