Automatic Room Correction has won the Subwoofer Wars

Dannad wrote: " ARC can detect accurately speaker distance based on first time of arrival and based on timing could differentiate between direct and reflected."

It depends on the wavelengths and reflection path lengths. In order to get good direct-sound data at a given frequency the time window has to be open and reflection-free for at least one wavelength, and possibly more. If the wavelengths are long relative to the reflection path lengths, the reflections start to arrive before the first wavelength is even finished. Now factor in the time-delay-induced phase rotation of that arriving reflection and we have bad data, because the microphone can ONLY sense the combined net pressure at its location - it CANNOT tell how long a path some or all of that pressure (or lack thereof) travelled before arriving.

I use time-gated measurements regularly, and in a "normal" room there will be a lower limit, typically in the several hundred hertz region, below which we simply cannot get good first-arrival-sound data. We can get good in-room data all the way down, but we can usually only get good first-arrival sound data down to several hundred hertz.

" However, from a perception standpoint, correcting on total volume is not a bad idea as you will have both speaker irregularities and room peaks and valleys that are not in the recording so removing them, on balance is better."

Imo the first-arrival sound is what matters most north of the Schroeder frequency region (yeah I know that term is debatable within the context of a small room). If the off-axis response (which dominates the "room response") has not been addressed by the loudspeaker design, then address it with acoustic treatment if we can. And if we can’t THEN imo it might well make sense to compromise the first-arrival sound for the sake of the overall tonal balance, but I’m not sure I’d trust an algorithm to make those decisions - I’d want to make the adjustments by hand.

Imo what we definitely DO NOT want is that a DIFFERENT "room EQ" be applied to the left and right channels (north of the Schroeder frequency), as despite the term what we’re REALLY doing is EQing the first-arrival sound, and we don’t want to introduce a channel mis-match into the all-important first-arrival sound. (Just to be clear imo the in-room sound matters a LOT, but the most effective place to address it is at the loudspeaker design stage, followed by room treatments.)

" I can’t see latency being an issue as it would be consistent across channels by design (or intentionally different)."

If we run everything through the DSP unit, that is true. If we only run the subwoofer’s signal through the DSP unit, then latency could be an issue. And not everyone wants to run the signal going to their mains through a DSP unit. So, imo, whether or not latency is an issue "depends on the specifics".

Duke

Dannad wrote: " Does ARC do this? I don’t know, but it is certainly possible. "

I would be surprised if automated room correction algorithms are that sophisticated. But perhaps they are... I must admit that my knowledge of the topic is apparently outdated.

" If we are talking low bass, then the latency can be minimal."

I recall seeing where latency on the order of 16 or 18 milliseconds was a bragging point for a subwoofer-specific DSP system. That corresponds a one wavelength delay at ballpark 60 Hz, relative to the mains (and more than one wavelength north of 60 Hz). Maybe that 16 milliseconds figure was on the high side relative to what’s being done today?

"you either have timing information that is created by two speakers... On the other hand, a lot of spatial cues are volume based... "

My understanding is that localization cues (sound image locations including soundstage width) are primarily conveyed by the first-arrival sound, influenced somewhat by early lateral reflections. And that good ambience (soundstage depth, envelopment, spaciousness, immersion, "you are there") without degradation of clarity calls for a very clean first-arrival sound, followed my minimal early reflections, which in turn are followed by a fair amount of relatively late spectrally-correct reflections, which hopefully then decay neither too quickly nor too slowly fairly uniformly across the spectrum.  (These aren't the only things that matter, but are among them.)  

Duke

TBC: By ARC I mean the acronym generically, not a particular brand. There are at least 4 brands of automatic room correct systems which include subwoofer integration.

Adjusting the arrival time and levels of a sub to match the main speakers is trivial for these systems to do but in addition to that what they do far far better than your average audiophile is the crossover slope /phase matching and bass EQ. It is that most audiphiles have no idea what this is, that it matters, that they’ll have to learn and adjust for it that makes a new sub hit or miss.

This just does not happen with most modern ARC (generic) systems.

I’ve been using a TacT RCS 2.2Xaaa, in my system, since the 90’s.    Not much has changed, since then.     FFT is called that, because it is and can discern between direct and reflected sounds.      Read the ’How REW makes it’s measurements’ section (page 5), here:   https://www.roomeqwizard.com/REWhelp.pdf        Especially, the fifth paragraph, of that treatise