Room correction, DSP for dummies.

I used to be a "purist" but....
I got religion with a modest home theatre system that was in my front parlor-- nothing especially WOW, an older Meridian pre-pro that was a cast-off from the bigger projection system, a McI multichannel amp and a small array of Mirage speakers. Like I said, nothing special, perhaps a little better than a ’box store’ system.
I finally discarded the Meridian b/c it was long past its sell-by date, and bought a mid-range Marantz AV pre-pro. It came with a very basic form of Audyssey. The degree to which that tightened up a fairly small powered woofer in this modest HT system was surprising, at least to me. Most evident playing the music from a soundtrack on a Blu-Ray disc.
I now use a very modest DSP (DSpeaker 8033II or whatever the latest model is) to control a pair of 15" sealed subs in my main two channel audio system.

They are powered from a separate line out on my line stage so the main speaker system, with its integrated woofers, runs full range and the DSP unit is not in their signal path; it only affects the subwoofers, which are, after the test signals were run, set to roll off at 55hz on a steep (-24db/octave) slope. It’s a fairly big room, and I’ve managed to get these subs to cohere nicely with the main speakers, which are Avant-garde Duos, a hybrid horn-dynamic woofer design.

I’ve very sensitive to discontinuity-- having lived with electrostats for decades and never satisfactorily blended dynamic woofers with those, this works. Not a huge investment in wooferdom, or in the DSP unit. I gather than these units work by lopping off peaks, not adjusting for dips in frequency response.

The result is not an audible deadening of the music- perhaps because I’m rolling off pretty low and keeping the DSP unit out of the main channel signal path.
Certainly cheap enough to experiment with----

@david_ten - I’m sure someone could speak with more knowledge, but the ones i’ve used have a mic that comes with the unit, you put it into test mode and it sends a sweep frequency through the system, starting at very low frequencies, runs the range, then repeats. You can reposition the mic in some cases to try to even out the response in more places in the room, but my Fred Flintstone version is, the little microprocessor reads these sweeps, sometimes a 1/2 hour worth of them, and creates a number of filter sets. When the thing is done with this process, something signifies that (an LED or simply the beauty of silence) and you are in business. It essentially reads the room and creates a filter or set of filters to compensate for the peaks.
I’m using this at a crossover of 55 hz with a very steep slope, so it doesn’t mess with the midrange phase or introduce as many electronic anomalies as it might for a cheap plastic device. (I use a linear PS for it, not the supplied wall wart). I think what it does, sonically, is remove some peaks so the response is flatter. The bass sounds more contained, less amorphous, tighter. I’m reluctant to have such processing in the higher frequencies but I gather that can be done with better units, setting phase, crossover points, an altogether more elaborate device that goes beyond the simple task of smoothing out the bass response in a given room. I think the device is agnostic in the sense that it doesn’t care what the room or speakers are-- it just reads the sweep frequencies it generates and creates a filter set to compensate for them based on some algorithm or set of machine instructions. That’s probably the limit of my technical understanding.
NB> David, I don’t know if you addressed your follow up to Grannyring (whose real name is apparently "Bill" or both of us, since I’m also a "Bill) but you got my response FWIW.

@erik_squires - agree not a substitute for some treatment, including bass traps.

I guess I walked into a debate between David and Bill (the ’other Bill) unwittingly. My concerns with whole system DSP (and I’ve never heard the Lyngdorf ) if that’s what’s being discussed are:

settings and adjustments- is this done entirely through electronic measurement by the device itself or do you, as the user/listener, tweak the settings to taste?
to what extent does digitizing the signal (including of an otherwise all analog source) compromise the sound?
are you limited by being unable to substitute key components if you adopt a solution that integrates processing and amplifier(s)?

Does an "add on" DSP device that allows you to integrate DSP into an otherwise conventional system fall short of the best that DSP can do, so that you cannot retain an ’unprocessed’ system if you choose to?

I was curious about the MiniDSP products a few years ago, but they seemed to involve more than I needed for simple bass management and I was reluctant to introduce anything between my line stage and main amps that could affect the sound in a negative way. I guess I’m not entirely out of the "purist" camp, though I recognize that at some level, all of this is "processed" to a degree, even in the analog domain....