Perhaps you are the owner of a regional production company, the sound guy for your band, or the production manager for a venue. Over the years you have purchased better microphones, switched from an analog console to a digital console, added a DSP to your system and maybe even moved to self-powered loudspeakers. Every once in a while, you’ve had a band mixer or system tech show up with SMAART, or Systune, or SpectraFoo to “tune your system.” Sometimes the results have been impressive, other times, not so much. Either way you see that said sound person has well over $1,000 invested in software, computers, microphones and interfaces to enable them to do whatever they’re doing, and you decided it is not worth the money for your business, band or venue.
In this article, I am going to talk turkey about the realities of room tuning, purchasing a measurement system and making it work for your circumstances. Measurement is close to my heart, as I have 15 years of using dual-channel FFT analyzers, going all the way back to JBL(!) SMAART. But measurement systems aren’t for everyone, and I fear that too many people have purchased the software and then been left disenfranchised as they realize that interpreting the data captured can be daunting and time consuming.
I personally believe that measurement is good for the industry, but I also know that it’s easy to make the purchase and later regret it in the process of learning to apply the tool. This article will hit your hands right before the Christmas season, probably about the time you are making sure that the year’s books are in order. My hope is that this article will help you decide whether to make the jump into a measurement system leading into 2015.
What Measurement Cannot Do
Let’s get the “negatives” out of the way first. There are a number of things that a measurement system will not be able to do for your company, band or venue:
• First and foremost, a measurement system will not be able to correct problems with evenness in the coverage of the sound system. The speaker’s directional coverage (or lack thereof) and aiming are things that a measurement system will not solve.
• Second, a measurement system will not solve problems with evenness of the low-end in a room. Bass frequencies have a spatial distribution that is a consequence of the location of the speakers and the geometry of the room. These spatial effects are not something that one can correct with measurement and equalization, as physics dictates the modal distribution in 3-D space.
• Third, measurement systems cannot preemptively help you determine how sound will change in the room once the audience arrives. It takes experience to understand how the audience will influence the sound of the system.
• Fourth, a measurement system will not enable you to magically improve the sound of a substandard sound system. That’s not to say that some improvement cannot be made, but the underlying transducers, cabinet designs and processing are going to set an upper limit to how much improvement you can see.
• Fifth, you will not be able to develop completely new presets for loudspeakers in the field. Measurements in a venue are too messy to reliably change things like crossover points while simultaneously insuring that the speaker’s polar response remains consistent. One can, however, use a measurement system to insure that the manufacturers loudspeaker presets are faithfully implemented in the system processing.
• Sixth, you will not be able to upcharge for measurement systems on a typical gig. Plenty of production companies have system techs that utilize measurement to insure a quality product, but this is part of the overall bid pricing, not a standalone line item in your quoting. Now, I have plenty of experience being hired to tune up existing systems, which is of course billable, but that is separate from the typical show bid familiar to production houses.
• Seventh, having a measurement system does not insure that you will have time to use it! Learning to take measurements quickly takes practice, and ideally a block of time (15 to 30 minutes) should be specifically carved out in the setup process to facilitate measurements.
• Eighth, owning a measurement system won’t make you a system tech. The tools only facilitate collecting data, not interpreting or acting on the data. When your company, band or venue considers purchasing a measurement system, training from the vendor should automatically be factored as part of the total cost of ownership.
• Ninth — and possibly most important — a measurement system won’t replace the meat computer in your head, nor listening with your ears. Measurement, when used properly, is a tool that helps you quickly make sense of what you are already hearing and drill down to potential problems with more subtlety and precision than your ears alone allow.
I know that both SMAART and Systune offer quality factory training, and I would consider one of their training classes as a mandatory expense as part of product ownership. Purchasing an expensive tool without learning how to use it will only result in frustration. Note that there are two parts to learning a measurement system. First is the mechanics of making the software operate how you desire, so that you can get out in the world and start measuring. Second, and more important, is learning how to understand what the software is telling you. Manufacturer training is designed to instruct on both of these fronts. After training, the best advice I can give is practice. Measure as much as you can in as many different circumstances as possible.
What Measurement Can Do
Now that we have a realistic picture of some of the problems that a measurement system will not solve, I am going to make a case for places where a measurement system adds value for audio professionals:
• You will have help finding problems precisely. Not sure if a room resonance is at 185 Hertz or 215 Hertz? A measurement system can nail that down very quickly.
• We humans are bad at hearing phase, but phase response is readily analyzed with a measurement system. Measurement opens a whole world of controlling phase-based interactions between loudspeakers to the audio professional. Owning a measurement system makes setting up multiple zones of coverage quicker and easier.
• Once you have practice at taking measurements quickly, a measurement system facilitates finishing system setup in environments where one has very little freedom to make noise before the show starts. Five minutes of strategically timed measurement can give a good picture of potential system performance issues.
• Measurement helps repeatability. If you regularly have gigs in the same venues, the software can help make sure that this month’s show sounds the same as last month’s.
• Auditory memory is very short. It is difficult to compare sounds only a few seconds apart, let alone hours apart over course of an event. Storing and comparing response curves gives concrete insights to keep the system performing for the entire duration of an event.
• Having a measurement system enables quality checking of gear for broken drivers, mis-wired/damaged cables or other anomalies. Traces can be quickly measured and stored at the shop, and then later compared against during times of maintenance.
• For those whose companies also perform installations, a measurement system gives a quantified deliverable to sell to clients. In my personal experience, reports built around measurements are powerful tool to demonstrate the value you add to the project.
• Measurement is incredibly valuable for getting multiple zones of an audio system to play together. Front fills, delay lines, downfills, subwoofers, foldback, etc. all benefit from being integrated together with a measurement system.
While the list above is not exhaustive, it should provide a range of insights as you consider this fairly sizable investment. For some readers, owning a measurement system is mandatory, and for others it may never make sense. I personally consider having a measurement system at my side a mandatory tool when working as a system tech. When I am working as a mixer, however, the measurement system may be used, or may be left in the case.
Tips After Making The Leap
Hopefully, this article makes you want to purchase a measurement system, or perhaps dust off one purchased previously. To this end, I’d like to give some practical tips to the new, or newly invigorated, measurement system user:
You don’t need expensive measurement mics. Yes, super high-end microphones are nice, but the reality is that inexpensive mics work quite well. I don’t have a measurement microphone over $200 that I use regularly in the field.
Have multiple measurement microphones. The saying goes, “if you don’t like the measurement trace, move two feet.” Because of local room effects, measurements even a few feet apart can vary wildly.
Trace averaging is your friend. Building on multiple measurement microphones, averaging a number of traces in area of the audience is the best way to get a clear picture of response anomalies that are not localized to one very specific spot in space. Having several microphones set up facilitates capturing traces for averaging in parallel.
Make peace with the floor bounce. A response anomaly that contaminates most measurements is called the “floor bounce.” Sound from the P.A. will hit the floor and reflect back into the measurement microphone, slightly delayed in time. The result is a dip in the measurement, typically somewhere between 100 Hz and 250 Hz. This dip isn’t a real problem with the sound system and it obscures useful data in these frequencies. Avoid the rookie mistake of trying to fix frequencies that appear to be missing in the floor bounce.
Learn to use the ground plane. Ground plane measurements are measurements made with the microphone immediately adjacent to a reflective boundary, so that any “floor bounce” occurs at a much higher frequency. The ground plane is useful for measuring subwoofers, and the midrange frequencies obscured in measurements with conventionally placed microphones. Anyone who has used a PZM microphone has already used the ground plane unknowingly. I carry a Crown PZM as one of my measurement microphones, and use it all the time for measurements below 1 kHz.
Don’t equalize to the trace. Measurement systems have lots of flexibility in how the data they collect is displayed, and this can lead to make equalization judgments based on a display view that doesn’t correlate well with how we hear. As you learn how to measure, the measuring system can help you with the frequency and width of equalization applied, but the amount of boost or cut should be chosen by ear.
Be careful with boosts. As is typical for learning to work with any equalization tool, be careful with boosting frequencies.
Most of the work is in the midrange. At high frequencies, the sound system will be directional, so the measured response will be fairly similar to what the manufacturer designed, minus high-frequency absorption. The range of frequencies where the sound system and the room interact most strongly is in the midrange. From approximately 200 Hz to 2 kHz is where most of the venue specific tuning work is to be done.
A “flat” line isn’t necessarily the goal. Experience has taught me that an overall response curve that has a slight upward tilt in the low mid frequencies (<250 Hz), and slightly downward tilt at high frequencies (>10 kHz) is generally perceived as pleasing by a broad range of people. But this guideline is far from universal, and there is plenty of room for artistic interpretation. Don’t automatically aim for a flat line if your hearing doesn’t support the outcome on your screen.
Scratching the Surface
These tips barely scratch the surface of measurement techniques, but a number of them are things that I wished I learned earlier. For instance, I wish I started carrying a PZM microphone for ground plane measurements much sooner. And some things — like the ability to quickly take and average a number of measurements together — wasn’t technically feasible when I first started taking measurements, but now is standard procedure.
As a final admonition, let me reiterate that purchasing training should be considered part of having a seat at the measurement table. The hardware surrounding measurement has become so much more powerful and affordable, that it may be tempting to skip the training. The ultimate power of measurement lies in using the meat computer in your head to recognize useful data and learn how to act on it, and training is the fastest, most pain-free way to get grounded in the principles to make successful measurements.
