In my earlier article, I promised to return to the subject of room correction and so I am. Some Acousticians will tell you that you need to spend thousands of dollars having an expert come in, measure your sound room (using mics, spectrum analyzers, and other arcane devices, not measuring tapes, well, probably that too), and apply thousands of dollars worth of room treatment (some of dubious providence) and that anything short of that is pointless. And, to a certain extent, they are correct, of course, it is also how they earn their living, so they are not exactly unbiased. There is no question that acoustical testing, analysis, and treatment performed by a reputable expert can effect major improvement in a listening room. Of course, if you want to spend the money, you can also build a proper sound room using basic fundamentals, like minimum 35’ wall lengths, no parallel surfaces, right/left symmetry, and dampened surfaces. In the case of multi-channel audio that means an anechoic chamber, and for two-channel a live-end and a dead-end. On the other hand, most of us are stuck with the rooms we have available, and audible improvement is audible improvement, and the most readably audible audible-improvement is room EQ (Equalization).
First I would like to specify that I only recommend electronic room correction for digital systems, the reason for this is that analog equalizers introduce significant phase shift to the signal, and before you start espousing about how somebody told you phase shift is a good thing, we are talking about phase shift between frequencies, so the physical distance between you and the musicians changes as they play different notes, completely collapsing the soundstage we are trying to build. The second thing you need to know about room EQ is that it requires massive amounts of power. A 3dB boost doubles your power requirement, so if you are not well over-amped, stick to drops and avoid boosts (though if the system you are using is automated you may not have control over this so figure on at least a 5% drop in overall available volume before speaker damage becomes a factor).
About twenty years ago I worked for TAG McLaren Audio (yes, the watch and Formula 1 guys who broke up over irreconcilable differences in management, I could tell you stories), who as far as I know was the first to build a digital surround processor with built-in room EQ. The system consisted of a multi-band parametric EQ that operated between 0Hz and 200Hz (I believe it was eight for the main speakers and five for the surrounds, but I was not able to find the parameters in a quick search of the internet and it was twenty years ago) and a stepped tone sweep that let you set up each channel using an SPL meter (I found I could set it up by ear in about five minutes), there were also instructions on how to use a computer and spectrum analyzer software to set it up, and John Mulcahy (the primary architect of TMREQ) eventually wrote some software to do it automatically. The effect was stunning, the soundstage became significantly more solid and clarity was vastly improved.
I can hear you ask, “Why to only 200 Hz?”, and the answer is directionality. Low frequencies have marginal directionality because the waveforms are so long and signals below 80Hz are mostly felt (or heard by your skeleton) rather than heard by your ears. I have heard systems that use full-range room correction, and despite more advanced features like phase correction, though the tonal balance is improved the image wanders all over the place, so it is my recommendation to stick to the low frequencies and use room treatment to deal with midrange and highs.
While built-in room correction is, for the most part, the province of multi-channel systems, two-channel lovers need not be left out in the cold if your digital source is computer-based as there are many cost-effective software solutions available, though admittedly, I haven’t personally researched them because as I pointed out in my first article, I have taken a rather old school approach to setting up my sound room, and such an approach would color the results of my listening tests as well.
So, what are the benefits? It is my experience that oddly enough most rooms cause strange peaks in the lower frequencies which appear to be more audible than the dips and seem to mask midrange detail in one channel or the other (it could be a harmonics thing). Mostly it is a clarity issue, not only does the bass become tighter and more accurate, it actually becomes more palpable, and as mentioned above, the image becomes more solid. Of course, not all rooms are the same, and all of the rooms I tested it in were very bad rooms (hotel rooms, offices) acoustically, so your results may differ. All I can say is in my experience the difference has been profound.
In conclusion, I heartily recommend experimenting with electronic room correction in your quest for a better HiFi experience if the opportunity presents itself. As long as you have the option to return the necessary hardware or the costs of doing so will not be too onerous, I believe most will experience positive improvement and that is a good thing.