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Flat Frequency Response

In our line of work, we get asked about ‘flat’ audio responses all the time: What is flat audio response? Is flat response good? Why is flat good? We also run into: “When I hear a system that has a supposedly flat response, I think it sounds stale,” or the more general comment, “I don’t like the way flat sounds!” We get these questions and comments all the time. As time and technology move forward, and culturally more and more people are listening to recorded audio through all sorts of devices, curiosity about technical, audio performance terms is increasing in our culture. In this article, we will uncover some of the mysteries about what flat audio response means (1), why it is important (2), and how you can use this knowledge to seek out equipment that suits your listening tastes or have really good arguments with your friends (3).

First off, if you are not familiar with the term frequency response, please refer to the article "Frequency Response in a nutshell,” before continuing.

Flat Frequency Response Graph1. To begin, let us pretend that we have a theoretically, perfectly, flat responding speaker in front of us and it is playing all the frequencies that we can hear at the same time. Now we are also going to pretend that we have an output device (amplifier) that is sending the speaker all the frequencies that we can hear at the exact same level. Barring any environmental effects, our pretend speakers will be voicing (playing/sounding) all the frequencies at the exact same level/volume; this is what flat response means in regards to speakers. If the speaker has a flat response, it will stay true to the variations in level differences from the amplifier; i.e. the speaker does not alter the sound coming from the source; it is flat (accurate). So why is this important?

2. Flat audio response is used as a reference in many different fields in the manufacturing industry. In regards to an audio product, the flatter the audio response is, the more accurate it reproduces the sound from an input source. Manufacturing audio gear that can closely achieve flat response can be expensive; a lot of math and technology goes into audio products with this property. In marketing, accuracy is promoted as a good thing and yes, to a certain degree, accuracy in audio products is good thing. However, accuracy is not always interpreted as “sounding good.” Because each person’s hearing is not the same as anyone else’s, and there are some cultural aspects that play a part as well, what sounds good to one person may sound awful to another.

If someone, let’s say, has a hearing deficiency in the upper frequency range (treble/highs), a speaker system with a flat audio response might sound slightly muffled; a criticism this person might give could be “the highs aren’t clear or the bass and mids are over powering.” This scenario is completely normal and very common*. It is for this reason that most good, quality sound systems allow the user(s) to make adjustments to the sound output by increasing/decreasing certain frequency areas. Our high frequency, deficient friend would take advantage of the “treble’ adjustment by turning it up so he/she could hear the high frequencies to their liking.

Flat Frequency Response Graph

The above is a rough example of what our friend’s hearing response might look like. The red line indicates the high frequency deficiency.

Flat Frequency Response Graph

This graph represents the areas of the audio spectrum that our friend might boost in order to percieve all the frequencies as being the same level.

Note: The music in our culture and what we commonly listen to plays a large role in how we like our music/audio to sound. Please see the article "Music and You,” for more details.

3. Listening to a flat response system can further your knowledge about what qualities you like in a sound system. If you are able to listen to music that you commonly enjoy on a flat system, you can pick out the areas of sound that you want more or less of. It would be even better if you are able to make adjustments to the sound (an equalizer) as you are listening so you can play around with it. You need no technical background in science or audio engineering to do this; turn the knobs or move the sliders but be careful with the volume control; we don’t want you to hurt your ears. The results from this exercise can give you an idea of what audio properties you prefer your sound systems to have. For instance, when using a flat response system as a reference, I prefer a little boost of bass, a slight decrease in mids, and a pinch of extra treble to put it simply.

Flat Frequency Response Graph

Sound systems come in all shapes and sizes. Each system has its own unique sound signature. If you find a sound system that you like, look into its properties (frequency response) and see what it is that you like. Remember, although ‘flat’ means accurate reproduction, it does not necessarily mean that you will like how it sounds when listening to music/audio that you are familiar with.

* “Facts about Hearing Loss”, Center for Hearing and Communication, web. 2012

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C. Crane
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