Audio System EQ: The single most misunderstood concept in the live sound community.

Is the mystery of how to set the equalizers in your live sound system driving you crazy? Don’t feel bad. It’s no wonder you’re having trouble finding the truth, the internet is full conflicting opinions on the subject. With so much false information out there, it’s hard to find the truth.

I have viewed videos online on “how to set your equalizer” where someone literally shows you the worst possible method imaginable. I have followed discussion groups on Facebook hashing it out and offering mostly incorrect advice with a hair of truth here and there to make it seem logical. The scariest thing of all of is that some of these people are professionals. They are getting paid to run sound and still don’t understand the job of the system equalizer.

The sad part is that it’s not really a mystery. Let me lay some truth on you, there is no debate amongst equipment manufacturers on how to set an equalizer. There is no argument between audio consultants and contractors on what the purpose of the equalizer is. How can this be? Well, there are no arguments because the procedure for equalizing a live sound system is both scientific and logical and leaves no room at all for individual interpretation. The only people unsure about setting an equalizer are those that do not have a proper grasp on sound. I want to give a very basic explanation of what an equalizer is actually for and how we adjust it. For more information on the subject, please check out a professional training course on live sound from BH Protech or a professional in your area.

So, you go purchase a couple of loudspeakers for your venue. You have paid a pretty penny for these things because you wanted fidelity. Fidelity is the degree of exactness with which something is copied or reproduced. But, when you hook them up, they don’t sound accurate at all, in fact, they sound bad. They didn’t sound this way on the sales floor. What’s up?

Acoustics, that’s what’s up. Acoustics are the properties or qualities of a room or building that determine how sound is transmitted in it. Many people think that reverberation is the only acoustic phenomenon that exists. “Wow, this room is a lot more bouncy than the last one we played.“ In reality, reverberation is only one of the acoustical properties of a room. There is also absorption, reflection and resonance or standing wave. In other words, even though you might start with a flat response, absorption changes that response by soaking up the higher frequencies. Reflection can cause lower frequencies to bounce back and add all kinds of clutter to your previously flat speakers. Resonance or standing wave occurs when the wavelength of a frequency matches the dimension of a wall or ceiling surface. The result is that these frequencies actually get louder in the room. Resonance usually shows itself as feedback. In the end, acoustics have wrecked your flat response.

It is vitally important to understand the significance of acoustics. This is the difference between live sound and recording. In live sound, the room is half the battle.  Every room is fundamentally different in sound. Wall dimensions, floor coverings, seating, ceiling height and even the fluffiness of the audience profoundly change sound from room to room. This is why most manufacturers do not offer presets for system eq. It is impossible to predict what the acoustics of your room will be if they don’t know where you will be performing. We need a way to adjust the sound so we can achieve that flat response we paid so much for and we need to be able to have that fidelity in any room we may encounter. They are all different. This is why we need an equalizer.

First and foremost, it’s called an “Equalizer” for a reason. You will notice it doesn’t say “DBX System Tone Control” or “Ashly Curve Generator” or even “Yamaha Manual Feedback Remover”, It is called an “Equalizer”. It is called so because it serves the purpose of making the levels of the frequencies in the room equal. An equalizer is never intended to be the “tone control” of your system. That is what the mixer is for. Qualities such as punch, sizzle or bottom happen at the channel EQ of the mixer, not the system EQ. If you are trying to spruce up your system by adding lows at the system EQ, you need to realize that you are adding lows to every live microphone in the system: overhead drum mics, choir mics, vocal mics, etc. None of these mics need more low end. If you want to make things more crispy in the highs, you would never add it to the system EQ unless you want your bass player to sound more crispy (yuck) or the kick drum to be more crispy, (please no). Please understand, I’m not saying your mix should sound flat and lifeless, I’m saying your speaker system should be accurate. What you put in should come out sounding the same, only louder. If you want to make it kick, do that with the mixer channel strip.

I will point out again, this is not up for debate. If someone is telling you something different, they are misinformed. Any tech working at any pro audio equipment manufacturer will say the same. Any competent pro audio contractor or system designer will say the same. We in the industry just shake our heads and chuckle at the discussion groups and videos out there. It’s unbelievable that so many sound techs have totally skipped formal training and are out there making up procedures and theories as they go.

The actual use of the system equalizer is to calibrate the system. With an equalizer, we can turn up the frequencies being absorbed in the room and turn down the frequencies that are too loud due to reflection and resonance. In the end, we should be able to overcome the acoustics of the room and have a flat or “equal” response again. The room may still have reverberation but the system will be tonally true.

So, now that we know what the EQ is for, how do we adjust it? The common method is to do it by ear. In fact, this is the only method most people use. Too bad this method can easily be proven to be unreliable. Putting on your favorite jam and tweaking the EQ to suit your ear would be great, if your ear didn’t change from day to day. That’s right, your ear can change significantly from day to day. How much loud music have you listened to in the car or in your earbuds? Do you have allergies or sinus problems? The fact is, there are all kinds of circumstances that can and do affect your hearing on a daily basis. You may have a great ear today, but what about last week or next month. Your ears change, period. Again, this is common knowledge.

The other issue with tuning by ear is that most people don’t hear the absorbed frequencies as well as they hear the ones that are too loud. This is a fact of our human hearing. Oh sure, you can tell that 1 KHz is about to feed back, but you probably don’t have a clue that 4 KHz needs to be boosted by 3 dB. You hear the loud spots because they stick out but you don’t recognize the weak spots. Yes, there are a few out there with an ear good enough to hear both but those operators are still subject to the day to day changes in hearing.

So, how do the pros do it then? We all use an RTA to tune a system. An RTA or Real Time Analyzer is a device that precisely measures the frequencies throughout the audio range. The RTA displays each frequency band (usually 31 bands) and with the use of a flat response reference microphone, shows how loud each individual band is in the room. We run pink noise through the speaker system and the RTA tells us what is actually happening in the venue. As you may know, pink noise is made up of the frequencies in the audio range all being produced at the same time. So, if pink noise is a flat signal source, the RTA should give a reading of all frequencies being equal. If it doesn’t your system is not calibrated correctly. At this point, we simply boost the bands that the RTA shows as weak, and cut the bands that the RTA shows as too loud. In the end, we can achieve true fidelity because our system is accurate. What we put in comes back out exactly the same, only louder.

Now that your system is calibrated and you are working with a clean slate, you can tweak those channel inputs to your heart’s content. Boost those lows where they are needed, in the bass and kick drum. Go ahead and make it sizzle a bit more, by adding highs to the overhead mics and choir mics. Trust me. Try it and see. Your system will be clearer. Your mix will be cleaner. You will get more punch than you used to. You’ll get less feedback. You can even run louder if you want.

Go get yourself an RTA. In the old days an RTA was just too expensive for most of us but technology has changed all of that. Now you can get an RTA for your smartphone for free. These may not be of the quality that we professionals use, but they will work fine for most end users. If you don’t trust yourself, hire a professional audio consultant or contractor such as BH Protech.

I hope I have cleared up the misunderstanding about system equalizers. Please check out our other blogs on audio system operation and watch for a training seminar in your area.

Dave Barnes
System Design and Implementation
BH Protech LLC


One Response to Audio System EQ: The single most misunderstood concept in the live sound community.

  1. A round of applause for your article post.Much thanks again.