In it I will answer the following questions:
By far the most popular posts on Sound Design Live are about sound system design and speaker coverage. Let’s look at the five most common questions that sound engineers like you and I come across in our work. Many of these answers will leave you with more questions, but don’t get overwhelmed! This only a survey course. If you’d like to read further on any subject, there is a list of helpful articles at the bottom of the page.
#1 – Why is sound so difficult?
- It’s invisible.
- It’s incredibly specific. You can only experience it at the location you are at in any given moment, unlike light which can be seen at many different locations at once.
- We experience it logarithmically, but talk about it linearly. We say that sound is loud or soft, for example, but those words have no meaning on their own. They demand comparison. To actually measure sound you use objective criteria like units of sound pressure. Sound is both a science and an art, and you cannot ignore either component.
- Sound reinforcement is far from perfect. Air is the medium we use to deliver waveforms from speakers to ears. With constant changes in temperature, humidity, and wind there is nothing constant we can rely on. Our ears are amazing devices. From the thresholds of hearing to pain is an increase of 32 trillion in the power level. The lowest to the highest frequency we can hear is a ratio of 1000:1. Comparatively, our equipment is quite limited. Speakers are “mechanical devices attempting to produce wavelengths that vary in size by a factor of over 600:1.”² Our technology is advanced, but it’s far from perfect.
#2 – How do I tune a sound system using a graphic EQ and an RTA?
The short answer is that you don’t. Pulling half the bands down on a graphic EQ is like removing a tumor with a wiffle ball bat. This is because graphic EQs and real time analyzers both have fixed frequency bands and fixed bandwidths. They are really only appropriate for ear training, and possibly the war zone that is monitor world.
Testing the system with your favorite CD is also a bad idea. First of all, because your emotional connection to the music will influence you. Secondly, it’s slow. You’ll have to wait for a certain part of the music and rewind and restart.
Once I tweeted out, “Testing your sound system with Aerosmith is like testing projectors with Star Wars.” It’s true. Do you ever see the video crew put up a projector and start watching movies? No, because the first thing you need to do is see damn thing is aligned to the screen.
In an interview withe ProSoundNews, John Meyer said, “When technicians install a new projector, the first thing they do is put up a resolution chart to make sure everything is working properly and in focus. We need to apply the best practices in articulation tests, along with other measurements for the coherence and intelligibility of systems.”
For EQ, parametric EQs are much more powerful and now commonly available. For measurement, a dual channel analyzer like SIM, Smaart, or SATLive will give you much more detailed information and the ability to measure with whatever source you choose. For test signals, use pink noise. If people complain, layer in some classic rock. Everyone likes classic rock. Especially the Spanish.
#3 – How do I tune a sound system, really?
Universal Rule Number One: If we verify every element of the sound system, nothing will go wrong, but if we skip any one part then the entire system will fail & mass hysteria will ensue.
Many people still think that sound system tuning is all about taking some random measurements, averaging them together, and setting an EQ. It’s actually a lot more interesting and complicated than that. Here is a simplified list of the necessary steps.
- Driver functionality and polarity: Do you think a lighting technician starts running a show without making sure that all of their instruments work? No! Better make sure all of your speakers are playing what they are supposed to play.
- Speaker aim and splay: As Steve Bush from Meyer Sound likes to say, “Put sound where there are people.”
- Speaker level and crossover: Compare the on-axis and acoustic crossover position for every source.
- Phase/delay: Match the phase response of all sources at the spectral crossover frequency by adjusting delay as necessary.
- Filter/EQ: Set a gold standard and use it as comparison for all on-axis and crossover measurements.
#4 – How do I fight microphone feedback with a graphic EQ and an RTA?
I set you up for this one. Guess what? Controlling microphone feedback is all about stage layout and mixing. Simply getting to know your gear (instruments, microphones, speakers) and the optimum placement of each part on stage is more powerful than anything you can do with a graphic EQ.
The five points you want to focus on are:
- Microphone Placement: For loud stages and busy rooms, close miking with directional microphones is generally the best way to go.
- Speaker Placement: Floor wedges should be placed off-axis to microphones and as close to each performer’s head as possible. Make sure your FOH speakers cover the house and not the stage.
- Instrument/Source Placement: Your goal is to balance every source input for the performers and audience. Avoid placing guitar amps and drummers directly behind vocal mics. Switch to all eDrums and synths if possible. 😉
- Mix: In small to medium venues, you aren’t “mixing” in the classical sense, you are providing sound reinforcement. Only add to the stage what the performers need to play well. Only add to the house what the audience needs to dance well and buy more drinks.
- EQ: Use narrow-band filters on a parametric EQ to surgically remove problem frequencies when you’ve exhausted other options.
#5 – How do I find speaker coverage and aim angle without reading all 535 pages of Bob McCarthy’s treatise?
I made it real easy for you to get started. Just use this speaker coverage calculator.