Check Your Speaker Distances and Polarity, OR, "A Chorus of YUMS! Ran Round the Table!"

Most Home Theater setups these days will include some variant on Surround Sound speakers.  Indeed, a major factor in the enjoyment of modern movies at home is the ability to hear an "aggressive" Surround Sound mix as it was INTENDED to be heard:  With key sounds originating from specific points all around you, and with blended sounds, such as the musical score, filling the entire sound field.

In this post I'll discuss the two most common ways people screw this up, and how to avoid doing that!

It didn't always used to be this way, of course.  Surround Sound developed gradually; via sound mixes authored for Theatrical release (i.e., in movie Theaters).  It was all part of the big effort by Studios and commercial Theater operators to attract people away from their TV sets and back into movie Theaters.  I.e., the same financial stakes which lead to the development of "widescreen" movies.

Originally, talking picture movie sound came from a monaural speaker placed behind the movie screen.  Experiments in "widescreen" movies happened surprisingly early on -- even before TV -- and required multiple speakers spread behind that wider screen; still monaural, but spreading the sound across the area the audience would be watching.  Developments in stereo audio also required multiple speakers, along with the first problems in figuring out where to PLACE sounds in these newfangled, stereo audio mixes.  Meanwhile, the Studios and Theater owners also started experimenting with specialized speakers -- still behind the screen -- intended to carry bass-heavy audio such as explosions.

Now, imagine you are making a horse opera, and your stereo audio mix is all set to carry the big gunfight scene with actors on the left and right of the screen.  Where do you put the sound of the sheriff arriving on horseback from off camera?  Or "ambient" sounds, like the angry mutterings of the townsfolk, also off camera?

The answer is you add a "surround" speaker -- say on the rear wall behind the audience!  Heck, while you are at it, you could add SEVERAL surround speakers -- some on the back wall and some on the side walls -- but all carrying that SAME, single, "ambient" sound track.

This was the first Surround Sound, and it lasted quite a while.  It was "simple" because the ambient track could be created on-the-fly, using electronics in the Theater.  It was a dispersed -- widespread -- sound, which made the electronics not even all that expensive.  Studios soon adopted audio authoring technologies which made it even EASIER for the electronics in the theater to extract the CORRECT "ambient" sound from what was still, basically, a stereo sound track.

But all those speakers on the side and back walls simply begged for more -- for DISCRETE surround audio directed to specific speakers!  And the advent of digital audio encoding (at the Studios) and decoding (in the Theaters) proved just the ticket!  Now you could mix a movie track which included audio positioned across the movie screen (Left, Right and Center) along with Surround audio distinct to each SIDE of the theater.  Speakers on the back wall could either carry the Surround audio from the closest side, or the electronics could mix the two sides and present that to the back wall speakers.  There was also, still, the extra Effects audio for those big, bass speakers behind the screen.

So now, for the first time, you could make an audio mix capable of presenting sound from any location AROUND the audience.  You could, with careful authoring, even "pan" a sound around the room -- like that "Chorus of YUMS!", mentioned in my post title!

Movie Theater audio did not stop there, of course, but now it's time to leave the Theater and head back home -- where Surround Sound audio is just starting to appear in Home Theater setups.

The folks who were in the business of selling Home Theater products couldn't WAIT to cash in on Surround Sound.  Not only could you get people to pay more for the needed electronics, you could also get them to buy a whole bunch of extra speakers!

And the advent of SD-DVD discs provided just the needed vehicle for delivering digital, multi-channel, movie audio tracks to home movie buyers!

The FIRST Home Theater Surround Sound offerings mirrored the early developments in movie Theaters.  That is, the Surround speakers would play an "ambience" audio track.  This could be created on-the-fly from a simple stereo movie track (using the fancy new electronics sold to go with the speakers), or it could be authored as a "non-aggressive" 5.1 audio track on a movie disc.

TECHNICAL NOTE:  Multi-channel audio tracks are frequently described with numbers like 5.1, or 7.1.  The first number is the number of speakers surrounding the listener at ear level.  A 5.1 track would have a Left Front speaker, a Center speaker, a Right Front speaker, a Right Surround speaker, and a Left Surround speaker.  A 7.1 track would add two Rear speakers as well.  The ".1" indicates the audio mix also includes LFE (Low Frequency Effects) audio -- a separate channel dedicated to carrying LOUD bass, best played in a separate Subwoofer..  A stereo track would be described as 2.0 -- Left and Right front speakers and no LFE channel.  The same sort of numbering is used to describe a user's actual speaker configuration.  So a 4.0 speaker configuration would typically mean Left Front, Right Front, Left Surround and Right Surround speakers -- no Center speaker, and no Subwoofer for playing added bass, such as from an LFE content channel.  The latest nomenclature adds a 3rd number indicating "Height speakers".  So a 7.1.4 speaker configuration would be a 7.1 normal speaker configuration with the addition of 4, new Height speakers.

By "non-aggressive", what I mean is that this ambience audio is INTENDED to sound diffuse -- dispersed in the area all around the listeners.  Indeed one of the problems with such tracks is that it was too easy for viewers to hear the audio as coming from their actual Surround speakers!  And so special speakers were invented -- called Dipole speakers -- which fired their sound to either side instead of straight ahead.  The viewers would hear the sound bounced off the walls and thus the ambience audio would naturally end up sounding more dispersed instead of localized to a given Surround speaker.

 But just as with Theatrical mixes, the next step was authoring Home Theater movie tracks with specific placement of audio elements in the Surround Sound field around the viewers.  Since most of the Theatrical Surround Sound tracks were 5.1 tracks, so were the early movie tracks on disc.  Indeed, many of the movie discs marketed as having fancy, new, 7.1 tracks early on were REALLY just Theatrical 5.1 tracks -- with some of their Surround audio steered to the Rear speakers.

Folks who had invested in Dipole surround speakers now had to consider replacing them with normal speakers so that the audio from these new, more "aggressive" Surround Sound tracks could be heard as coming from the right direction!  (The speaker makers were, of course, delighted to sell them new speakers!)

Which finally got their Home Theater setup to the point we left off above -- where they really could hear that, "Chorus of YUMS!", moving all the way around them!

Except, umm, often it DIDN'T SOUND LIKE THAT AT ALL!

And that gets us to the point of THIS post:  How can Surround Sound go wrong, and what can you do to avoid that?

First of all, the Surround Sound can go wrong in the authoring of the audio track for Home Theater release.  Let's take an example that's all too often found in movies from the 50s, when "widescreen" movie making REALLY took off.

Suppose your movie was shot in an extra-wide screen format like CinemaScope.  This is a very wide rectangle with action taking place all across it.  Your audio track is still, essentially, stereo -- with the speakers placed behind the screen to span its width.

So somebody on the left side of the screen starts talking, and the audio comes out of the speaker behind the screen on the left.  All well and good.

But now you play this movie in your Home Theater setup.  NOW the speakers are NOT behind the screen!  Indeed the Left Front and Right Front speakers are usually a significant distance beyond either side of the screen.  So if you put that dialog in the Home Theater's Left Front speaker the viewers are going to hear it as coming from a  location to the LEFT of the actor who's talking!

There are actually movie discs out there which do just that, and the resulting "off screen" audio is at least distracting, and sometimes, pretty comical!

There's nothing you can do about such a mistake in the authoring except to remind yourself not to buy poorly authored movie discs in the future!

What SHOULD have happened, of course, is the sound engineer authoring the mix for Home Theater should have produced a blended sound -- partially in the Left Front speaker and partially in the Center speaker -- which would produce a "phantom location" for the sound as coming from the right spot in between them.

Indeed, if the sound engineer wants to pan a, "Chorus of YUMS!", around the room he'll be constantly adjusting the mix so that the right amount of audio is coming from the TWO speakers on either side of the correct, current, YUM! location.

Now to do that, he can test the sound in his mixing room speaker setup.  But what if the layout of his mixing room speakers -- their positioning in the space around the listener -- is DIFFERENT from the layout of speakers in your Home Theater?  Well the audio you hear in your Home Theater won't match what he heard when building the mix.

And so there are recommended -- standardized -- speaker layouts for Home Theater, Surround Sound speaker configurations.  I won't detail those in this post, but the Manual for your Home Theater's sound processing electronics -- usually an Audio/Video Receiver (AVR) -- will undoubtedly include diagrams of suggested speaker positioning according to how many speakers you actually have.  And these recommendations SHOULD be followed, if physically possible in your room, as it will enhance the quality of your Surround Sound.

Even if you have a well authored audio mix, and the best possible placement of your speakers, the  YUMS! may *STILL* not sound well matched as they pan around you.  For example, if you've not properly balanced your speakers for matching Volume, you will definitely hear the differences as those YUMS! circle the room.  See my post on Balancing Speaker Volumes with an SPL Meter.

Even then, you may hear the YUMS! change as they circle the room.  For cost considerations, or due to physical constraints, you may very well not be using the same model of speaker for all your speakers.  Different speakers exhibit different sound "Timbre".  This is the colorization of the sound -- distinct from volume and pitch -- due to the specific design of the speaker, its enclosure, and how its placement causes its audio output to "couple" with the geometry and reflections of your viewing room.  This can be a tough problem to eliminate entirely, but you can usually come close by selecting speakers made by the same company -- even though they are different models.  Companies tend to produce speakers with a "house sound" -- a Timbre that's somewhat common across their models.

And yet, even if *ALL* that is matched, the YUMS! still may sound wrong -- may sound as if they are simply not coming from the right direction!

And THAT's likely due to one of a pair of common mistakes which are EASY to fix!

It all comes down to the idea, mentioned above, that the location of the sound in the Surround Sound field is usually a "phantom" location -- between two speakers -- created by properly blending the sound sent to those two speakers.  You might think the ear hears this by volume difference -- i.e., the placement ought to appear closer to the speaker which is louder.

But in reality the ear hears it by TIMING difference.  And that means the precise timing relationship between the sounds coming from those two speakers is crucial.

In your electronics, there will be a speaker configuration setting with a name like Speaker Distance or Listener Position, and it's astounding how often people simply ignore that!

Speaker distance adjustment is done by delaying the audio sent to the "closer" speaker to match the timing of the audio from the "farther" speaker.  And it's this adjusted, timing match which enables the ear to correctly position "phantom" sounds between the two speakers.  Of course if all your speakers are equidistant from your listening position, no such adjustment is needed!  But this is seldom the case.

Take the simple case of stereo speakers -- Left and Right -- which are equally distant from your center seating position.  No distance adjustment is needed in that case.  But suppose your seating is a typical, three-cushion sofa set about 10 feet from the speakers.  If you shift yourself to the right side of that sofa, you are actually closer to the Right speaker and farther from the Left speaker.  Without a compensating distance adjustment this will make the sound field appear to shift to the Right.  That is, a sound which SHOULD be located precisely in the middle between those two speakers will now appear to be shifted more towards the Right speaker.

Now with multiple seating positions you can't, of course, have one set of speaker distances which are perfect for EVERY seat.  But if you know ahead of time that your preferred seating is going to be at the Right side of that sofa, then you SHOULD adjust your speaker distance settings to reflect that location!

You'll need a friend to help you measure your speaker distances.  Use a steel tape measure (to avoid stretching) and hold it taught enough to minimize its natural sag in the middle.  Measure from the front grill of each speaker in turn to your seated ear location, at your primary listening position.  Keep in mind that if you normally recline a recliner seat, your measurements should reflect that reclined position.

Having entered the correct speaker distances, also make sure your sound processor is configured to actually USE them.  Speaker distance adjustment is a type of digital audio processing, so if there's a setting in your sound processor to bypass audio processing you must re-enable processing for the speaker distances to have any effect.

TECHNICAL NOTE:  That latest thing in Home Theater audio these days is "immersive" audio tracks which add content intended for Height speakers.  The two popular formats are Dolby Atmos and DTS:X.  These allow your YUMS! to leap OVER the table instead of simply circling around it.  Normally, you enter speaker distances for your Height speakers the way you do for all your other speakers (and your Subwoofer).  But the Dolby Atmos system adds a new TYPE of speaker which may sound rather like 2nd cousin to the Dipole speakers I mentioned above.  These are called, simply, Dolby Atmos speakers, or, more descriptively, "Up-firing" speakers.  The can be found built into otherwise "normal" speakers, as extra speaker elements on top -- pointing up towards the ceiling.  Or they can be sold as standalone boxes intended to be stacked ON TOP of your normal speakers -- and again pointing up at the ceiling.  They work by firing their "Height" audio towards the ceiling, where it is then reflected back DOWN to your listening position.  And the question is, what DISTANCE should you enter for these?  Technically the correct answer is you should measure the distance from the speaker up to the point on the ceiling halfway between the speaker and your seating position, and then add the distance from that point on the ceiling back down to your seating position.   But most AVRS equipped to handle Dolby Atmos audio tracks try to simplify this for you.  They expect you to enter just the distance from the Up-firing Atmos speaker to the ceiling above it.  The AVR then kinda-sorta doubles that to calculate the correct amount of audio delay.  You'll need to check the Manual for your AVR to find out what distance it wants you to enter.

TECHNICAL NOTE 2:  Some AVRs include Room Correction processing which listens to sample output from your speakers and attempts to correct for the effects your listening room is having on that sound.  Some such systems ALSO include automatic speaker distance determination as part of this process.  HOWEVER, determining actual speaker distances this way is fraught with difficulty.  I.e., the distances determined automatically in this fashion may be wrong!  At the very least, try to check what distances the automatic system has entered for you.  You may find it easier to get accurate distances if you enter them manually.

TECHNICAL NOTE 3:  People often ask whether they need to include the length of their speaker wires in their speaker distance settings.  Or whether they need to take extra care that their speakers are all wired using wires of the exact same length.  The answer is, you don't have to worry about either of these.  Why?  Because the electric signals on the speaker wires travel at the speed of light.  Essentially the electric signal crosses that wire in no time at all -- certainly an insignificant amount of time compared to the time it takes the real, audio waves to travel from the speakers to your ears.

I mentioned above there were a PAIR of common setup mistakes which screw up Surround Sound audio.  The one left to discuss is Speaker Polarity!

You've probably noticed that it takes a pair of wires to get audio to each speaker.  The paired output jacks of your speaker power amp will include a "+" and "-" jack for each speaker, or perhaps "Red" and "White" or "Red" and "Black".  Similarly, the input pair at each speaker will be labeled in such fashion.

Speaker Polarity simply means you have to check -- and DOUBLE-check -- each speaker in your system is wired the SAME WAY.  That is, if you wire "+" at the power amp to "Red" at one speaker, you must also do that for all your OTHER speakers.

Screwing this up -- wiring a speaker in reversed Polarity compared to the other speakers -- means  its speaker cones -- the moving elements which actually produce the audio output -- will be traveling in the opposite direction to your other speakers.  And THAT means the timing of the audio is screwed up compared to the other speakers.

The technical term for this is "Phase".  If the speakers are "In Phase" -- and with proper distance adjustment applied -- then the "phantom sound" locations between each pair of speakers will be correct.  If a pair of speakers is "Out of Phase" then the sound field between them will be completely confusing to the ear.

Even if you are trying to be careful in your wiring, it is easy to mess this up -- usually because the speaker wires you are using are not sufficiently distinct as to which wire is which.  It is also possible, although pretty rare, that there's a wiring error INSIDE one of your speakers.  I.e., it's "Red" jack really should have been labeled its "White" jack.

And so it is wise to check your Speaker Polarities using actual audio.  And the best way to do THAT is with a calibration disc.  For example, in my prior post on Calibration Discs I recommended "AIX Audio Calibration", Blu-ray.  One of the test tracks on this allows you to go around the room checking adjacent pairs of speakers (in a 5.1 or 7.1 configuration) to confirm each successive pair is In Phase.  Of course if each successive pair is In Phase as you complete the tour around the room, then ALL the speakers share the same Phase.

TECHNICAL NOTE:  I don't currently know of a good calibration disc for checking the Phase of Height speakers, so you will just have to be extra careful checking your actual wiring for those.

For each pair of speakers, the test track plays audio which is In Phase followed by audio which is Out of Phase.  The video on your TV screen will identify each as they go back and forth.  While doing the test, turn your head to face the center point between the given pair of speakers.  This will give your ears the best chance to hear what's going on.

If a given pair of speakers is wired CORRECTLY, then the In Phase portion of the test track will sound like a "focussed ball" of sound positioned roughly between the two speakers.

Meanwhile the Out of Phase portion of the test track will sound diffuse -- spread out with no evident center to the sound.

If you hear the reverse, then the wiring Polarity to one of those two speakers is incorrect.

In real listening, the effects of incorrect Polarity will be much the same, although real-world audio tracks will make it less obvious what's going on.  Sounds that should be located between a pair of speakers will be diffuse -- unfocussed.

Hopefully the above has given you enough insight to see what you need to check to get the best out of your Surround Sound speaker setup.

You'll know it's right when you play a quality surround sound track and feel like exclaiming that Chorus of YUMS! round all YOUR speakers!