Adjusting Subwoofer Phase <-- Awesome Bass, Part Deux!

In my prior post on Choosing a Crossover Frequency, I discussed the fundamental role played by a Subwoofer in any good, Home Theater system, and the equally important choice of allowing that Subwoofer to handle the lowest bass frequencies which would otherwise be played through the Main speakers.  This task of "steering" bass from the various Main speaker channels to the Subwoofer is the job of the Crossover processor -- part of the "Bass Management" system in your Audio Video Receiver (AVR).

The Crossover does not act like a switch, with bass suddenly cut off to each Main speaker and sent instead to the Sub.  Rather, the Crossover rolls into effect over a range of frequencies -- typically one Octave (factor of 2 in frequency).  So for example, an 80 Hz Crossover -- the most common choice -- actually rolls into effect from 80 Hz down to 40 Hz.  At 80 Hz, all the audio in the Main speaker channel is still coming out of the Main speaker.  At 40 Hz, all the audio is being sent to the Subwoofer.  And IN BETWEEN, the Main speaker and the Subwoofer SHARE the job of producing the audio output!

So in that critical range of in-between frequencies, a given Main speaker and the Sub are playing the SAME audio at the SAME time.  But the Main and Sub are not located at the same spots in your room, and the differing designs of the Main and Sub undoubtedly introduce different delays in how the electrical input signal to each turns into motion of their speaker cones -- creating the audio you hear.  The upshot is the audio waves arriving from the Main and Sub may very well NOT reach your ears at precisely the same instant of time!  The sound which SHOULD have blended perfectly from the two of them will not do so.

Technically, this timing mismatch is called Phase error, and it can be a real problem!  If the two wavefronts are a full 180 degrees out of Phase, for example, they'll CANCEL each other out!  That is, the result of improper Phase matching is anemic sounding bass.

In this post, we'll talk about how to get your Subwoofer(s) into proper Phase with your Main speakers.

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Lip Sync, OR Why Are Her Lips Still Moving After She's Stopped Talking?

Certain flaws in your Home Theater viewing are bound to take you out of the moment -- flaws just too annoying to ignore.  And Audio out of sync with Video is certainly one of them!

We've all seen examples of poorly "dubbed" movies, where the lip-sync error is so humongous it's comical.  But errors even more subtle will still leave you with the irritating feeling that something is just, OFF.  And once that sync error is corrected, there's that Ahhh! moment as you settle in and realize this is finally RIGHT!

In this post we will talk about Lip Sync errors -- where they come from, and what you can do about them.

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Calibration Discs <-- You NEED These!

EVERYONE interested in Home Theater should have a few Calibration Discs in their collection. This is true even if you intend to hire a professional to come in and set up your system for you. Professionals will bring tools and computer programs which are both expensive to buy and daunting to learn. But even though you can't fully match their professional results, you should STILL have calibration discs handy to confirm there are no silly setup errors in your system, and to check whether any problems you spot while playing real content are due to oddities in that content, as opposed to something you've overlooked in your system setup. Calibration Discs provide you with content of known "correctness" which you can use for this.

There are LOTS of different calibration discs out there at this point, and more likely to come out over the next year or so as UHD (4K) video becomes more mainstream. Some of them are pretty specialized. Some require you also have those professional tools mentioned above. Some are hard to find, or even out of print. The most sensitive test I know of to confirm that Speaker Distance Correction is happening properly, is found in the Avia Pro SD-DVD multi-disc set, which is long out of print. And even in that case, this particular test was included in an add-on disc to that set, which only appeared several years after the set first shipped! Try getting your hands on THAT one!

In this post I'm going to discuss two, generally useful Calibration Blu-ray Discs. And also, one specialized disc -- in this case an SACD disc -- to give you a flavor of what's out there if you go looking for such specialized, test content.

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