SPS Blog Post #2 - Proper Loudspeaker Placement: How To Avoid Lobes and Nulls

In an effort to almost continue what I was talking about last week,  I have opted to further research how to properly set up a loudspeaker array for the maximum amount of even coverage as well as reducing phase issues and as much as possible.  For this, It is necessary to know how to reduce the amount of lobes and nulls within a loudspeaker system.

The word lobe, when used in the context of audio, is often defined as a maximum of sound pressure that occurs within a sound field caused by the loudspeaker array.  The author of the article, Pat Brown, describes them as "'fingers' of sound pressure 'maximums' in the three-dimensional space..."(Brown 3)  Lobes can be problematic as most microphones set within a lobe will almost undoubtedly feedback.  Nulls, on the other hand are the exact opposite.  Nulls could be thought of as sound pressure minimums within a speaker array, which can cause a lose of speech intelligibility within the audience.

As Pat Brown has detailed in the article, There are many possible "solutions" one can take to combat these problems, such as comb filtering, with some being much better ideas than others.  One could use an analyzer resolution to reduce the comb filtering and adjust the equalizer.  Though this may seem like a quick fix, them problem has been temporarily masked and has not truly been fixed.  Another option would be to notch out certain problem frequencies, although this could be detrimental to the sound quality because you are removing necessary frequencies.  One could simply be to conclude that the audience won't even notice the filtering and do nothing, but that truly doesn't solve anything.  The only real way to solve the problem is to address the spacing of the loudspeaker array.

Comb filtering and phasing is a timing issue, so by spacing two loudspeakers that are close together further apart, the amount of lobes and nulls created will be reduced.

Take note that it is also possible to reduce these lobes and nulls by using quality loudspeakers.  Some loudspeakers are built to have features, such as horn-loaded components and aggressive pattern control, that help reduce interaction with other loudspeakers, which will reduce a lot of comb filtering and phasing issues.  Though larger speakers seem to be better, if size is an issue in a particular venue, one can use smaller speakers in greater number set up closer to the audience, such as an exploded array (Brown 3).

To fully understand this, I had to further research what an exploded array is.  Though I wasn't able to find an exact definition of explanation  from many images I could find I gather that it involves separating the components in a loudspeaker from each other so that the highs and the mids are not coming from the same speaker enclosure.

Works Cited

Brown, Pat. "Proper Loudspeaker Placement: How To Avoid Lobes and Nulls." ProSoundWeb. 13   Jun 2012: 3. Web. 17 Jan. 2013. <http://www.prosoundweb.com/article/lobes_and_nulls/>.

SPS Blog Post #1 - Optimizing The Low End: Run & Gun Subwoofer Arraying Techniques

First off, I would simply like to state that this was one of the most informative and easily comprehendible articles pertaining to this issue I have read.  Bennett Prescott really knows his stuff but also has a way of explaining sometimes complex concepts in an easy to understand way.

Now to the nitty gritty.  This topic has been one that has always intrigued me.  Low end sound is crucial to any mix and getting it to sound its absolute best is often difficult and tedious.  Luckily Bennett Prescott was kind enough to list off a few techniques and information that can help every system tech have their low end sounding its very best.

Prescott shows how a "small sound source", being an acoustic sound source where no dimension of the source is larger than one-quarter wavelength at the frequency of interest, demonstrates near perfect omnidirectional response in the free field he is testing.  But when one subwoofer is set up next other subwoofers, the omnidirectional response demonstrated by the single sub has now been altered and begins to demonstrate what is called pattern narrowing, which occurs due to phasing.  Prescott defines phase as, "the offset between two waves, measured in degrees".    When two waves are perfectly in phase with one another, meaning a difference of 0 degrees, there is a boost in gain of 6 dB.  However, two wave out of phase by 180 degrees will cancel each other out perfectly.  Any other kind of phase relation will contribute anywhere between 6 dB gain or wave cancellation.  Any sound sources outputting waves that are between 120 to 180 degrees out of phase with each other will begin resulting in sound reduction, which is what we as system techs do not want.

From there, Prescott demonstrates different arrays of subwoofers and the effects each one has on the sound they output by diagramming the noise boosting and canceling caused by phasing.  Some of the most intriguing diagrams were the ones demonstrating a left and right stereo array causing what is called a "Power alley", where the sound from both subwoofers arrives at the center of where an audience would be located and would be boosted in gain, where as about a third of the sound that would reach the audience, roughly the far left and far right of the audience, is reduced or cancelled out.

 The effects that physical and/or digital delay have on subwoofer arrays was very eye opening, in that simply moving one or two subwoofers a foot behind the others can have a dramatic effect on the way the sound is heard within the audience.  I never thought about how a physical delay focuses sound back onto the stage while a digital delay affects the sound on both sides of the array equally.

One of the best tidbits of information I gained from this article is the mixing of both center subwoofer arrays and stereo loudspeakers to create the most even sound coverage possible. Prescott states that he uses the technique of using a left right center sub array in tandem with the stereo loudspeakers most often than any other, which is something I'll take with me and try applying when and where I can.

Journal Entry - Friday, November 16, 2012

As a drummer, I constantly geek out over drums and drum hardware and gear.  One of my biggest obsessions is Ludwig Vistalite drums.  You know, the acrylic drums John Bonham used to play.  It is my dream to own a set of Vistalites.  So needless to say, when I saw Russian Circles perform at Will's Pub, I had to take a picture of drummer Dave Turncrantz's kit.  I love the way way shines through the translucent shells, especially when colored lights shines through Dave's red drum shells, creating new colors.  I wish this picture really did the kit justice.

Journal Entry - Friday, November 16, 2012

This is a bit of a mystery.  This picture was taken around 1 am after a lab, just as I got home and got out of my car.  While walking to my front door, I saw this in the sky.  I assumed it was a plane, but it did not have any flashing lights and it didn't appear to be moving.  I only saw three stationary lights: 2 green lights and a brighter red light.  My money is on UFO.  I want to believe.....

Journal Entry - Thursday, November 15, 2012 post 2

I was sitting below this light during a Vectorworks lab and simply thought this looked really cool.  Each fluorescent light was a different color and thought it looked bizarre. It was completely unintentional that I left the flash on, causing the ceiling to be completely blacked out when in fact the room this picture was taken in was very well lit.  the low level lighting give the pic kind of an eerie feeling, but more than anything, I just love the contrast between the three colors and the black background.

Journal Entry - Thursday, November 15, 2012

This is a picture from the first live lab I participated in.  I was able to see how a live lab runs, what my job was, and who does what.  This picture is of the band in the middle of their set.  I took this picture because I wanted to showcase the way the light beams are visible with the help of the hazer.  I also wanted to show something which, in my opinion, I would have changed for this performance.  I feel that the moving lights could have been a little more exciting, rather than just moving spots back and forth.

Journal Entry - Wednesday, November 14, 2012 post 2

It was a bit risky, but I was able to catch this picture on my drive to Celebration, FL to visit my girlfriend.  I wish I was able to get a better quality picture; one that captured the vividness of the colors in the sky.  My favorite part of this picture is the red and pink clouds caused by the angle of the sunlight passing through them.  It almost reminds me of amber shift that happens when you dim a white light.

Journal Entry - Wednesday, November 14, 2012

I wish that people would stop using those obnoxiously bright headlights on their cars.  I nearly killed myself today because of them.  While driving home from getting groceries, a car that was equipped with said headlights tailgated me down University Blvd. The reflection of the cars headlights were reflected from my side and rear view mirrors directly into my eyes and because those headlights were so bright, I was temporarily blinded and nearly popped the median and almost hit a man trying to cross the road.  Needless to say, I now hate those super bright, blue headlights.

Journal Entry - Wednesday, October 24, 2012

There always seems to be a plane going over my house every 45 minutes or so.  Now, I've never actually timed this occurrence, but I'm sure I'm in the ballpark with my estimate.  As I stated in my past entry, I'm a fan of low lighting, so I usually have little to no light in my room and my window's blinds all the way up, and when night falls, I constantly see the little white light blip across the sky.  Not sure why but I really enjoy watching it go by.  Perhaps its the contrast of  the one solitary light moving across black sky.  Like a blinking shooting star.  I would include a photo, but each one came out looking awful so I won't subject you to it.

Journal Entry - Tuesday, October 23, 2012

I'm not a fan of fluorescent lighting.  I have a tendency to develop headaches if I am in a room with fluorescent for too long.  It's too just too harsh on my eyes.  When exposed to it for too long, it sort of starts to look like strobe light cranked up to maximum pulse.  Instead, I am more of a fan of soft, low lighting.  Mood lighting, if you will.  I like the shadows and the contrast of light and dark found within low lighting.  The above picture is as bright as my room will ever get.  I refuse to use the fluorescent light.  Such....... pain......