NE Acoustic Sound

The Speaker Part 3: Monitors

June 12, 2020
 
 
Monitors are for the performers, not the audience.  They come in many flavors: headphones, in-ear, personal stage monitors, studio monitors, and floor wedges. 

As a sound engineer, I would love it if all monitors were headphones or in-ear … my feedback concerns would be mostly gone.  If I had no feedback concerns, then I would be free to give each performer their own mini mixer.  I am not a performer, and even if I was, I would only be able to guess what mix and volume a given performer would want in their monitor.  I do understand when a performer stops a performance to request a change to the mix or the volume of their monitor, but I also think the audience came for the performance, and not to be party to a discussion about monitors.

In-Ear Monitors

Having said I love the idea of in-ear monitors, I don't even own a set.  Why not?  In reality, in-ear, at least wired in-ear monitors, are no more expensive than stage speaker monitors, however for a number of reasons, few performers I work with want to, or in some cases, even can, use in-ear monitors … cannot because they also have hearing-aids.  I figure a set of four, OK quality, wired, in-ear monitors with individual performer controls, would cost about $1,000.  My small live sound business cannot afford having a set of in-ear monitors that will seldom get used.

Studio Monitors
 
As for studio monitors, my expertise is not in the studio, so all I can say is they should be very high fidelity, relatively small, and do not need to produce high levels of sound pressure.  Then again, when used with post production mixing, the studio speaker might be best if its fidelity is not so high but more representative of what a typical listener will own.
 

Stage Monitors

This note is mostly about stage monitors of the speaker variety: personal monitors and floor “wedges”.
 
The problem with these monitors is two fold:  As they are speakers that are near to microphones, they represent a huge feedback potential.  The other issue is, in live sound you have two sound stages:  one for the audience (FOH), and one the performers.  These two sound stages are not isolated from each other.  FOH sound does bleed into the stage area, but more importantly, particularly in a small house, the sound from the stage monitors does bleed into the FOH.  If the sound mix going to the stage monitors was the same mix as the FOH mix, then this would not be as big a problem.  

Speaker based monitors come in two varieties:  personal, and floor wedges.  
 
Personal monitors are small speakers on a stand.  Normally they are placed in front of the performer.  There are two issues:  First: this more or less one foot square box is not very visually attractive. The other issue is, since the entire point of a personal monitor is to be very close to the performer, the performer should not move around.
 
There is an alternative, at least for performers who stand, and are careful.  The speaker is behind them and pointed about mid upper back.  It is the performer’s body that cloaks the speaker from the mic, and so the performer really needs to stand still.  Failure to do so will cause feedback.
 
Floor wedges are the other type of speaker based monitors.  Now the performer can stand or sit, and within limits, move around the stage.  Unfortunately these monitors tend to be big and therefore take up a lot of stage floor space, and are heavy to lug around.  They also visually clutter the stage.
 
The problem with monitors is, in general, they need to be loud.  To the performers ears, they need to be louder than the ambient sound that includes their instrument and their fellow performer’s instruments (including vocals), and all the other monitors.  The farther the monitor is from the performers ears, the louder it needs to be.  Floor monitors are farther away from the performer’s ears than personal monitors, so they need to be louder than personal monitors.
 
You can soon get into the loudness war, that only ends when the monitors approach the feedback limit.  
 
While to the performers ears, everything is well and good, the shear volume of sound coming out of the monitors is bleeding into the FOH in a big way.  Let us not forget, the particular mix a performer may want in their monitor is often rather different than what you want for the FOH sound.
 
There is one more issue with floor monitors.  Consider a 8” bass driver, a horn for the mid range and a tweeter … three separate drivers.  To keep the volume down you want the monitor to be as close as possible to the performer.  For a sitting performer this could be only 3 ft.  All the sound is not coming from the same point but, in our case, 3 different locations with the location dependent on the frequency.  At this short range, the sound is spatially incoherent.
 
To overcome this issue of spatial incoherence, the co-axial speaker was developed.  Originally such speakers were for HiFi.  There are technical issues with coaxial speakers, particularly over a wide dynamic range.  Nevertheless some speaker manufacturers do make coaxial speakers and through careful design and some DSP have (mostly) solved the technical issues.

In-ear Monitors part 2

Before I leave the subject of monitors let me say another word about in-ear monitors. Most in-ear monitors (real monitors, and not earbuds designed to be used while jogging or biking or whatever) seal to the ear and give about 25 dB of sound isolation.  This allows the volume in the in-ear monitor to be 25 dB less than if you used floor monitors.  (Note:  for the 25 dB isolation to do any good, in-ear monitors need to be used in both ears.)  Great!  One problem:  now the performer has trouble hearing the other performers.  So some in-ear monitors don’t quite seal and give only about 15 dB of isolation.  Wonderful!  But there is the Catch 22.  The drivers in an in-ear monitor need to be tiny. With a small leak in the system, the bass is diminished.  The bass driver simply does not have the power.  Some in-ear monitor manufacturer's claim to have solved this technical problem.  I have no first hand experience, and the reviews are mixed.
 
There is no perfect way to give performer’s the monitors they want and so once again we find, live sound is a compromise, and a good sound engineer needs to strive to make the very best compromise.