Configuring and Deploying JBL PRX800 Speakers for Medium-Sized Audiences
- Height of the Speakers
- Spacing of the Main Speakers
- Reverberant Surfaces and Speaker Angles
- Spacing of the Subwoofers
Point Source portable PA systems are often an excellent choice for applications where performers and presenters need to bring their own sound systems to an event; where the need for maximum coverage with minimal loudspeakers and crew are paramount. Point source systems are also ideal in more permanent installations where budget is sensitive and the sound reinforcement needs do not require the complexity of high powered line-array type systems.
A typical medium-sized PA would consist of 2 main speakers, 2-4 subwoofers, monitors for the performers, and for exceptionally wide spaces, side- or out-fills. Such a system would be ideal for audiences of about 100-500 people and loud volume requirements. Examples include a theater or worship space where the audience is seated, bars and clubs where live music is a main focus, and of course gigging bands and DJs needing high-level sound reinforcement.
We choose certain loudspeakers because we like the way they sound – though as reality dictates, we are often required to use these sound systems in environments which are not designed to have ‘good sound.’ In the applications above, simply using the speakers “out-of-the-box” will probably achieve acceptable results. However, if the speakers are tuned to the space and to each other, you can get the most out of the system you are using. Spoken and sung vocals will be easier to understand and instruments will sound more natural. The sonic experience will be much more consistent, and the overall sonic signature will be better, leading to a higher quality experience for the audience and performers alike.
In this article, we will be discussing how to configure a medium-sized PA using JBL Professional’s PRX800 series. PRX800 speakers use a unique app called “Connected PA” that allows you to configure and control your entire system via Wi-Fi from anywhere in your venue. This includes assigning speaker function, setting levels across individual speakers, groups, and back-of-the-box functionality including EQ presets, polarity, and input sensitivity. Additionally, users have access to 8 PEQs for the system, 50 ms of delay, and real-time metering. Further, the PRX800 speakers feature a highly accurate baseline frequency response, high power handling with excellent dynamic range, and sophisticated waveguides that control the directionality of the systems down to very low frequencies.
Here, we’ll be covering basic tuning without any outside measurement equipment. This will be the sort of tuning you’d do when time is limited, like when you’re loading in equipment for a gig later that same day. For more detailed tunings and installed systems, we recommend using Smaart Di v2 from Rational Acoustics. Smaart Di v2 is a dual-channel, FFT based, real-time audio analyzer which allows users to make informed decisions about the frequency & time response of their systems. Di v2 is an excellent option for configuring a system of this size, as its basic functionality is well-matched to the level of control available within the PRX800 speakers. To get going with Smaart, in addition to the Smaart Di v2 software license, the hardware requirements are quite minimal; in fact, you likely already have everything you need. Those items being, a host computer to run Smaart, a measurement microphone (such as the DBX RTA-M), and a 2x2 audio recording interface.
STEP 1: SELECTING THE RIGHT SYSTEM
The first step to getting successfully configured is making sure that the system is well-matched to its application. The central part of your system will be the full-range main left and right speakers, or “Mains.” These speakers are doing most of the sound reinforcement work, so it’s critical to choose the right ones.
Application and loudness requirements will dictate the needs of your system, but a good way to judge the system you’ll need is the expected audience size. PRX800 speakers are best suited to applications with audience sizes between 100 and 500 people. Although there are certain variables that could make a different system the better fit, using these numbers is a good guideline to ensure what you’re getting will be powerful enough for your needs without being overly expensive. For audience sizes of fewer than 100 people, consider JBL EON600 speakers, and for audience sizes above 500, consider SRX800 or VRX900.
There are 4 choices for Mains in the PRX800 family:
- Audiences of 100-200: PRX812s or PRX815s
- Audiences of 200-300: PRX815s
- Audiences of 300-500: PRX835s or PRX825s
- PRX835 is the right solution when midrange clarity is critical, as in speech or live music applications
- PRX825 is a good choice when powerful low end is the most important factor of the show, like for EDM or for clubs. This is especially true when you can’t use subwoofers.
Generally, a single speaker for the left and right channels will provide plenty of coverage. If you are playing outdoors in a space where audience members will be listening from the side of the stage, you might consider adding an additional speaker on each side to act as an out-fill. How to place and set that speaker will be covered later on.
If your speakers are more than 25 feet apart, consider placing a PRX812 in monitor position to cover the first few rows of the front-and-center audience.
After you’ve selected your mains, you will need to configure subwoofers. The size and the number of subwoofers you use depends on the size of your system and how important low frequency content is. For smaller systems handling mainly speech reinforcement, no subwoofers may be required. For large systems playing bass-heavy material at high volumes, up to 6 PRX818XLFs may be used.
Here are some good guidelines:
|2 x PRX812 or PRX815||Mainly Speech
2 x PRX815XLF or 1 x PRX818XLF
2 x PRX818XLF
|2 x PRX825 or PRX835||Mainly Speech
|2 x PRX815XLF or 1 x PRX818XLF
2-4 x PRX818XLF
4-6 x PRX818XLF
|4 x PRX825 or PRX835||Mainly Speech
|2 x PRX818XLF
2-4 x PRX818XLF
4-6 x PRX818XLF
If your system is supporting a music performance, you will also need stage monitors so the performers can hear accurate sound. A good rule of thumb is to have 1 monitor for every 1-2 microphones that will be used at any one time. If your system is mainly being used for speech, you can probably get by without a stage monitor. PRX812 and PRX815 can both be used as monitors. In fact, they have special tunings that will retain natural frequency response when the speakers are placed directly on the ground or stage.
STEP 2: PLACING THE SPEAKERS
Perhaps the most significant factor in getting your system to sound good is how you arrange it in your space. Effective use of space lets you get the most out of your system and ensures that the audience experiences what you want them to. Ineffective use of space can seriously degrade the performance of the system and lead to a bad audience experience, even with the best sound system. At the end of the day, you’re at the mercy of the space you have to work with, but here are some best practices to keep in mind that will help you succeed.
Let’s start with your mains. All PRX800 speakers use a 90° Horizontal by 50° Vertical waveguide. This means that the sonic experience will be relatively consistent for anyone in that coverage pattern, ignoring other factors.
A simple way to picture the speakers’ coverage pattern
Knowing this, here is what you should keep in mind when setting up your system:
Height of the Speakers
Speaker too high; the front of the audience is outside of the coverage pattern
Speaker too low; back of the audience is blocked
Speaker at appropriate height with downtilt angle; entire audience is in the coverage pattern
In a permanent install, it is possible to suspend the speakers from the ceiling or a stage proscenium. This work will need to be done by a licensed professional, but it is an excellent way to provide even coverage throughout a space. More information on suspension of loudspeakers can be found here.
Speakers suspended. Note how the entire audience is within coverage, and that they are at a similar distance from the speaker. This will ensure that they are hearing similar volumes throughout the space.
Spacing of the Main Speakers
When using a system this size, your main speakers should generally be about 10-15 feet apart. Because of the 90° horizontal coverage of the PRX speakers, the speakers should be no further apart than twice the distance between the speakers and the first row of audience members. In other words, if the first row of the audience is 10 feet away from the speakers, the speakers should be no more than 20 feet apart. As previously mentioned, if your speakers are further than 25 feet apart, a PRX812 or PRX815 can be used in the monitor position as a center-fill if need be.
Speakers too far apart for adequate coverage
PRX812 added to the center to cover the front and center audience members; notice that the PRX812 now has 50° of horizontal coverage because it is on its side.
At the same time, placing the speakers closer than 10 feet from each other can cause severe overlap in the coverage pattern, resulting in an unpleasant phenomenon called “comb filtering.” Comb filtering is interference that results in certain frequencies being removed, meaning the audience can’t hear everything that the speakers are doing, and the sonic experience will be completely different depending on where you are standing!
Sometimes, space constraints make it impossible to adhere to speaker spacing best practices. In an environment of high volume demand and people packed very close to the stage, you will want to arrange the speakers as high as possible above the heads of the audience. Remember, the PRX812 and PRX815 have downtilt pole cups that will help your sound distribution tremendously in these situations.
If you’re playing outdoors and reflections from sidewalls are not an issue, you might want to expand your horizontal coverage with out-fills. To do this, add 1 main speaker per side. Keep in mind the 90° horizontal coverage of the PRX800 speakers; your speakers need to be facing about 70° from each other to ensure that they won’t interfere with one another. With 160° of coverage per side, you can play to a huge audience!
Reverberant Surfaces and Speaker Angles
The final major factor to consider with your main speakers is how they might interact with reflective surfaces in the venue.
Reverberant surfaces can cause two significant problems:
- Loss of intelligibility: Loss of intelligibility occurs when there is excessive interaction between the reflected sound and the direct sound. When this happens, vocals become hard to understand and distinct sounds within the mix become difficult to pick out. Side walls, ceilings and back walls are common causes of loss of intelligibility
- Slapback: “Slapback” is when the sound reflects off a solid surface and comes back to the audience with a significant delay. This affects high frequencies the most, and can be incredibly distracting.
Loss of intelligibility will generally occur when sound is bouncing off of side walls, ceilings, or a back wall that is too close. Slapback will occur when sound is bouncing off a solid back wall that is further away.
Both of these problems can occur both indoors and outdoors, although they will be more prominent indoors. Outdoors, surfaces like exterior walls and automobiles are common causes. Materials like solid wood, metal, concrete, stone, and glass are all highly reflective. When possible, acoustical treatments like diffusers or thick curtains will go a long way towards eliminating these problems.
To keep sound from bouncing off of the ceiling and back wall, keep the vertical coverage pattern of the PRX800 speakers in mind, place the speakers at an appropriate height, and utilize the downtilt angle. In most cases, you don’t need to worry about sound reflecting off of the floor or the ground, as the audience will absorb that sound. Human beings are excellent at absorbing and diffusing sound; keep this in mind if you are tuning the system without people there!
To keep sound from reflecting off of side walls, you can either arrange the speakers closer together, or angle them inward towards the audience. When the speakers are angled inwards, a toe-in angle of about 20° is ideal.
Speakers too close to side walls; reflections can cause problems
A better utilization in a tight space
Spacing of the Subwoofers
Whenever possible, subwoofers should be clustered in the center of the plane of the main speakers, and on the floor or the ground instead of on stage. This optimal placement will result in the best possible low frequency coverage. For live music or club settings when exceptional low frequency response is required, a line of 4-6 PRX818XLFs will provide incredible punch and bass clarity.
If the subwoofers must go on stage instead of on the ground, it is still a good idea to keep them center clustered. Splitting the subwoofers apart will result in highly irregular low frequency response throughout the entire space and should be avoided whenever possible.
STEP 3: TUNING THE SYSTEM
Once you have your speakers placed, you are ready to tune! Tuning can take anywhere from about an hour to a full day, and you can use measurement equipment ranging in sophistication from your own ears to a $10,000 measurement rig. If you’re using PRX800 speakers in a mobile application, you’ll probably be able to get your process down to an hour or so. As mentioned above, a quick tuning can be done based on what you hear, but for more detailed tuning, JBL recommends using Smaart Di V2 from Rational Acoustics.
Once you have your speakers placed, verify that the systems are working as expected (Left is Left, Right is Right, etc.) and that the console and previous output settings are cleared – that you are starting without the last gig’s settings already applied. There is nothing quite as frustrating as going through a whole alignment session only to realize that you forgot to clear a buried EQ from the previous system deployment. If you hear anything that sounds totally wrong, it’s probably a good idea to confirm that the equipment is in working order. After all, EQ or Delay cannot fix a malfunctioning XLR cable or unplugged power cord, and your ears should always be the first analysis tool you reach for.
In a quick tuning with a mobile rig, the easiest thing to get right (or wrong!) is the polarity and level of the subwoofers. PRX800 subwoofers and mains are crossed over at 80Hz; the subwoofers have an 80 Hz low-Pass filter, which matches the selectable 80Hz high pass on their output. This makes for easy sub deployment when you’re using a PRX system.
Using Smaart, it is possible to precisely align the polarity and timing of the subwoofers for ideal phase response. Without Smaart, turn on one subwoofer, and experiment with turning the polarity between normal and flipped. Use whichever position yields the best bass response. Load this position into the rest of the subwoofers, turn them on, and make sure that you’re getting the bass you expect.
Changing subwoofer polarity
Afterward, set the level across the entire subwoofer group so that the volume of the subwoofers matches the volume of the tops and gives you the amount of bass that you want for your application. Make sure to listen from various points in your audience area to ensure even coverage.
PRX800 speakers come pre-tuned with a very neutral frequency response, meaning that they will sound accurate right out of the box without applying EQ. However, depending on your space and your source material, you might want to tweak this a little bit. Keep in mind that you’re not mixing the show using the PA system; the PA should be a neutral conduit that allows you to shape the sound how you want it.
A good way to set a system EQ before soundcheck is to play some pre-recorded music through it that matches the material you will be playing. In order to make informed decisions, you’ll want to use high-quality sound files of material that you are very familiar with. Play some songs through the system at the level that you’ll be using for the performance, and walk around the space to make sure that you get a complete picture of what you’re hearing. You want to make sure that you’re hearing the sound you’re used to; everything that ought to be present in the mix should be well represented.
There are two main concerns that are easy to address when doing an EQ using our ears with a system like this:
- If the audience is going to be close to the speakers in a loud space, listen for harshness. If the system sounds harsh, a hi-shelf filter can be applied, or a PEQ can be applied if there is one specific frequency that sticks out.
- Often, certain low frequencies will build up as a result of room geometry. This is a fairly common problem. If the low frequency sounds overly resonant or “boomy” in various places throughout the room, try applying a filter to reduce the response of the problematic frequency.
Less is More: Don’t try to EQ every single frequency to perfection. A few subtle filters are almost always a better choice than a slew of extreme bumps and notches. After you apply your EQ, use the bypass button so that you can compare your EQ to what the system sounds like without EQ.
Adjusting frequencies in Connected PA
After we’re happy with the frequency response from the mains, we are going to set gain levels across the system. In a roughly symmetrical space, the level on the left and the right will be the same. If the space is asymmetrical and one side needs to be louder or quieter relative to the other, you can adjust individual speaker gain directly from Connected PA!
There are three main goals when setting system gain:
- The system should be set loud enough for whatever it’s being used for.
- The system should not be so loud that audience members are going to be uncomfortable or have their hearing damaged.
- When playing at levels you’ll be playing at for the whole performance, your system should not be in limit. When you set your speakers, turn the gain knob all the way up. This way, you’re using its full dynamic range when making adjustments in the app. Here’s how to get set up:
- Pass music through the system and turn it up to where it will be for the performance. If the speakers’ meters are showing green and the music is loud enough, you’re done!
- If the speakers’ meters are showing red, that means that they are in limit. PRX800 speakers will not let voltage go through the system that would harm it, but running the speakers in limit will cause compression and the sound quality will suffer. Pull the gain meter down a bit until they are showing green again.
- If the speakers’ meters are showing green but the system is not loud enough, check to make sure your gain is set appropriately at your source, the preamp, the mixer, and the app.
In some cases, someone else will be running the mixer and using your speakers. In this case, set the gain in Connected PA at such a level that they can play at the volumes they need, but not turned up so much that they will drive the system into limit.
System is too hot, all speakers are in limit.
System at a reasonable volume with plenty of headroom left
SUMMARY AFTER TUNING
Now that the system is tuned, give it a listen and make sure you like the work that you did! In our system, We should now notice a few things:
- Plenty of high frequency presence without harshness.
- The low frequency is punchy and resonant without being “boomy.”
- We can play at concert volumes without pushing the speakers too hard.
- The subs and the mains are working well together.
All of the work that we did tuning will help make sure that we’re getting the desired output from our system across most of the venue. This will yield excellent results for the gig, and it allows us to tackle many different applications and spaces with the same rig. The adjustments that we can make in Connected PA ensure great sound every time.
MORE DETAILED TUNING: SMAART DI V2
Smaart, developed by Rational Acoustics, is the industry leader in real-time dual-channel FFT based audio analysis. Now in its second generation, Smaart Di provides a nimble and quickly adaptable measurement environment with all critical configuration and control parameters accessible from a single intuitive user interface. As you would expect, Smaart Di’s Spectrum and Transfer Function engines have all the same power and capabilities as those in the flagship version of Smaart (v8). Though, in the spirit of simplicity, Di does not include a separate Impulse Response Mode. Di is perfect for quick and precise measurements without the demands of Smaart v8’s multi-measurement, multi-mode, and multi-window complexity. Besides developing the Smaart brand, Rational Acoustics also offers training on the software and system alignment tasks - in many languages and all over the world. Those interested in attending a Smaart Operator Fundamentals course should sign up for the Rational Acoustics newsletter – the “Rational Report,” and check in on the Rational Acoustics training schedule for upcoming courses.