February 20, 2013, by Mark Frink
Touring as a monitor engineer has taught me many tricks over the years. Here are some of my favorite pieces of advice for those who may be just starting out…
Like Groundhog Day (or a symphony pops tour), I keep repeating the following: the best loudspeaker accessory is the simplest and cheapest.
If you have nothing better to do one day, find an hour to cut some 2 x 4 lumber into one-foot lengths and paint them black.
Alternatively, covering them with black gaffe tape, affectionately called “paint on a roll,” helps by providing a better grip with cabinet surfaces and smooth stage floors.
Clair’s 12AM is only one example of a floor monitor that often requires a block of wood to correct the angle at which it addresses a performer. A dozen should be included in every loudspeaker cable trunk.
The CSM Series (shown right) of low-profile floor monitors from QSC include integral rear legs that provide up to 15 degrees of additional angle (in one-degree increments) to provide additional coverage upstage.
Fifteens or Twelves?
More than ever, the choice between 12- and 15-inch woofers presents a dilemma to sound companies and monitor engineers.
QSC CSM monitors with integral rear legs for up to 15 degrees more angle
These days, with so many using in-ear monitors and carrying their own system, there’s a great chance that locally-provided or house wedges won’t even be needed for many shows, making it hard to pick one model of “rider friendly” wedge that will be used infrequently or simply for support acts.
Single 12-inch floor monitors have gained in popularity due to their smaller size, smoother transition to the horn in the vocal range, and some also prefer dual 12-inch designs for greater “punch” at higher volumes. On the other hand, 15-inch monitors, although larger, provide more lows.
Usually the most important rider requirement after “bi-amped,” is that all wedges in a system are matched, allowing the engineer the false security of copying one monitor mix EQ to all of the other mixes.
Bi-amplified or Passive?
Most loudspeakers originally included built-in passive, high-power crossover networks to split the amplified signal and send lows to the woofer and the highs to the horn.
Today, most two-way loudspeakers can be bi-amped, powering woofer and horn with their own amp channels, with each amp channel filtered for the frequencies its driver reproduces with an active or line-level crossover. Not only are HF horns several times more efficient than LF cones, they also require less energy due to their portion of the frequency spectrum.
The advantage of bi-amped floor monitors is that when they’re pounded with kick drum or bass, the LF amplifier can peak without distorting or clipping the HF amp and its horn.
If you never need loud wedges in your venue or for your band, passive wedges can save money by both halving the number of amp channels and eliminating active crossovers.
A hybrid approach would be to use a number of passive wedges, while also supplying a couple of beefier bi-amped wedges for the drummer and bass player, as well as for the side-fills. There are many wedges that sound very good run passively on a single amp channel.
My favorite is the EAW SM200, which can also be switched to bi-amp operation, and is a staple of many performing arts centers. Another favorite is the Turbosound TXD-12M passive-only floor monitor.
Like all self-powered loudspeakers, self-powered floor monitors provide advantages and challenges. After the missing amplifier rack, the great advantage is that, as a closed system, the combination of drivers, processing and power in a single product provides extremely consistent results.
The Meyer Sound MJF-212 offers the option of a VEAM multi-pin that puts AC power, audio and RMS data into a single connection
The accompanying challenge is that instead of a loudspeaker cable, each wedge must be supplied with its own signal from the monitor console and its own AC from a power distro. Solutions involving Edison-to-PowerCon cables with XLR stingers taped onto them, distributed from AC quad-boxes and male XLR fan-outs or sub-snakes are a common solution.
Meyer Sound provides a VEAM multi-pin option for most of their self-powered products that puts AC power, audio and RMS data into a single connection, and the company’s recent self-powered MJF-212 employs dual 12-inch woofers and a 40-degree conical horn to minimize interaction with adjacent monitor mixes.
In our modern world of digital consoles, it’s common for monitor engineers to build output EQ libraries for specific models of wedges.
By eliminating variances between amp channels used for woofers and horns, both passive and self-powered floor monitors provide a level of consistency, allowing EQ presets created on one rig to work on another system in the next city or country.
Bi-amplified wedges that use specific or proprietary processed amplifiers, such as those from L-Acoustics, d&b audiotechnik and Nexo provide a similar level of consistency.
Modern amplifiers that incorporate DSP, such as more recent Crown, Lab.gruppen and Yamaha models, allow manufacturers and vendors with proprietary loudspeakers to achieve a similar level of consistency.
The definition of “pro audio” in the future includes tight integration of loudspeakers, amps and DSP that allows precise and predictable results in a wide range of applications.
One, Two, Three
Intuition invites the age-old rock wedge approach that two are better than one, but there’s a case where it doesn’t necessarily apply. Dual high-frequency sources firing at a microphone will cause comb filtering unless the mic is exactly equidistant from both.
The Crown I-Tech Series of power amplifiers are outfitted with DSP, which can help with consistency
A difference of an inch introduces a deep cancellation notch at 6,000 Hz, or at 3,000 Hz at two inches. Moving a vocal mic, or one of a pair of wedges a small distance can therefore change the HF gain-before-feedback. This comb-filtering scenario can be avoided by using a single wedge for vocals in a monitor mix.
On the other hand, presenting that performer’s instrument through double wedges gives it added presence, due to the arrival at both ears from dual sources. Stereo floor monitors allow for panning of other performer’s signals in perspective on stage, making them easier to discern.
When a performer needs the ultimate in monitoring – lots of their vocal and their instrument, plus everything else – a time-tested approach is to use three wedges on three mixes. The center wedge carries the vocal, while the outside stereo pair provides the performer’s instrument, along with any reverb in stereo and the rest of the band’s instruments and vocals panned in perspective.
If you’ve ever had the experience of working with a rap act (or other very loud concert) with performers running around with wireless mics, you’re familiar with the frustration of trying to get the wedges loud enough.
The usual stage monitor setup has pairs of wedges across the front of the stage, supplemented by enormous side-fills. If the wedges are rearranged in symmetrical pairs so that they’re equidistant from the center of the stage, then it becomes relatively easy to apply minor timing delays into each mix to synchronize them with the side-fill’s arrival at that position.
The secret to making this work is to place the side-fills low and angle them up, or even better, to fly the side fills, so that each fill mainly covers its own side of the stage.
With the introduction in the ’80s of coaxial drivers in studio monitors, the road was paved for development of more accurate-sounding wedges. Two-way loudspeakers can employ time-offset correction using modern DSP, but that only works for a single on-axis point, except for coaxial drivers where minor delay synchronizes both transducers throughout their entire coverage pattern.
Coaxial floor monitors are naturally smaller, because the horn exists within the woofer, and they also solve the age-old problem of book-matching left and right low profile versions for double-wedge positions.
A prototype of the EAW MicroWedge, which offers a coaxial design
PAS was an early innovator due to their involvement with the UREI 813B, and their 15-inch SW coaxial wedges are still tops in the category. L-Acoustics’ 115XT HiQ is a modern example of a coaxial loudspeaker enclosure with floor monitor angles that also incorporates a pole-mount cup and rigging points, to provide extra functionality as a distributed zone or fill loudspeaker. The EAW MicroWedge has a built-in angle to help build multiple cabinet wedges into an arc.
Input Channel EQ
Most manufactured professional monitors exhibit fairly smooth, flat frequency response. It’s common for monitor engineers to take the vocal microphone du jour and repeat the mantra of “Test: one, two” while exercising the graphic EQ, whether out-board of an analog desk or inside a digital console. This results in some predictable results.
The mic’s proximity effect, in combination with the enclosure’s half-space coupling with the floor persuades the operator to cut 160 Hz. The mic’s presence peak, combined with compression driver’s efficiency below its mass break point convince us to cut 2,500 or 3,000 Hz. With two wedges angled inwards, frequencies just below the crossover point must be tamed with a cut around 1,000 Hz.
When a wedge sounds “boxy” it’s often blamed on “room modes,” though it usually comes from a response peak around 300 Hz, where the woofer becomes directional and enjoys the extra gain of baffle loading.
After you’ve carved up your wedge for the vocal application, how will the instruments sound? What if you took the four-band input EQ and used it to make the vocal sound natural instead? While you’re at it, roll the high-pass up to 150 Hz. There, that’s better.
Using channel EQ runs counter to the common wisdom of “tuning” the loudspeaker and the vocal mic with output EQ, but there are several practical applications. A simple lack of output EQ, a support act using spare inputs on a headliner’s monitor console, using a single console for both FOH and monitors by splitting inputs to double channels, and finally splitting monitor desk inputs to double channels for both wedges and IEM.
Mark Frink is a long-time live sound mix engineer and writer/editor on pro audio topics.