Room correction devices are designed to at least partially mask a room's problems without actually correcting them, so the term room correction may have been invented as a distraction from that fact. Although you can help one type of room problem in a limited way by altering the signals to the speakers, it's not a good first line of attack, and this article talks about why.
For those tempted to get on my case about being oversensitive to a semantic issue, bear with me -- room correction has many drawbacks compared to addressing the actual issues with rooms and speaker setups. Furthermore, when steps are taken to improve the room itself, then a room correction device will have much less work to do, and this will minimize its drawbacks.
As a matter of definition, rooms correction comprises an automated equalizer that listens to the sound at a certain spot or range of spots in a room, and makes adjustments to the speakers’ frequency response.These adjustments mask the room’s frequency response problems for listeners that keep their heads where the microphone(s) had been placed.
Of course, one can get marked improvements in frequency response flatness from equalization (EQ), and flatness is a key element of accurate sound. On the other hand, at least for masking room or speaker problems, automated EQ systems have the following drawbacks:
That said, there is a manual, rule of thumb approach that can be helpful without being harmful. First, you'll have to acquire real time analyzer software (RTA). You'll also need a means for equalizing the signal that includes parametric filters, which could be included your music player, such as in JRiver's Media Center, or be an electronic system.
First, place the microphone at your normal head position.
Then use parametric filters to tamp down the bass peaks -- those below 400 or 500 Hz -- caused by room modes and Allison effect.
Finally, to restore the overall bass level, use a low shelf filter to raise the level of the bass range below the highest frequency hump that you’ve just leveled off. Along with that, you might want to add a high pass at 20 Hz or so to avoid overloading your speakers with subsonic signals from the low shelving boost.
It’s crucial not to fill in any troughs in the bass response (or in any other range), because this adds resonances that degrade transient response and add group delay.
Contrary to that restriction, relatively shallow rises and troughs that are broad enough to span a couple or more octaves can be equalized to beneficial effect, but it’s important to ignore those that contribute to local ambiance, and it’s pretty much impossible to tell the difference without taking the speakers outdoors to determine which wiggles are from the speaker and which from the room.
Not to go negative on room compensation without supplying an alternative, I must point out that it's possible to reduce the effect of room modes and Allison effect with strategic speaker placement. I'll write a short piece later on about how to reduce the effect of room modes by finding and avoiding them.
True room correction, that is, treatment of the underlying sicknesses, must be done with bass traps, absorbers and diffusers. You can get most of the way to a reasonable goal with just absorbers, and these can be nothing more expensive than bats of fiberglass with decorative but thin fabric hung over them, or prefabricated absorbers available from many suppliers. Of course, doing these things right requires some knowledge and strategy, but you can count on a genuine improvement in the sound and thus your experience of the music.
Drifting Off Topic
I just have to mention the simplest EQ option, namely good old fashioned bass and treble controls. These can create helpful adaptations to room sizes and conditions, not to mention imperfect9ons in recordings, and do so without problematic side effects.
Unfortunately, tone controls fell victim long ago to a strict interpretation of the simplicity doctrine. As a result, manufacturers found or maybe just decided that they should create the impression of signal path simplicity by eliminating tone controls, even those having a bypass switch for purists, and must have welcomed the side benefit of reduced costs along with the perception of higher value.
This might be a good time to introduce another audio issue that interests me, and which will be the topic of a later article. This is exemplified by a state of affairs where many reject tone controls, yet happily employ other forms of equalization. One is present in the production and playback of vinyl records. LPs are equalized during master creation to compensate for shortcomings in that medium's available frequency response and dynamic range. Equalization is again applied by the preamp or line stage during playback to more or less reverse the original equalization. The aggregate of the two equalizations is more complex than tone controls are.
Software and equipment
Parts Express sells a pre-configured room measurement system for a reasonable price. With a little more effort, if you have a PC laptop, you can get by with a lot less money by just buying a measurement mic and TrueRTA software. You'd either use the laptop's built-in sound card, or add an external one, for which I recommend the Steinberg UR22 for its resolution and ease of use. An excellent and very affordable equalizer is the high definition box from MiniDSP. I know Behringer pro market equalizers are recommended by others, but they're no picnic to understand or program.
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Every company making electrostatics has its own approach, so each design in this category is a mixed bag of attributes -- mostly positive, some negative, and rarely indifferent.
To begin with, and probably why you’re interested in electrostatics, all offer exceptional clarity, immediacy, smoothness, low distortion, and transparency, especially in the midrange and treble. Various criticisms, however, have accumulated over the decades, spread out among a number of makers, past and present.