Understanding Frequency Response

Both headphones and speakers can be described in terms of their frequency response characteristics. Suppose you've produced or obtained a precise recording of a series of tones, covering the entire range of normal adult human hearing (20Hz-20,000Hz). If you play this series of recordings over an average speaker, chances are you'll perceive differences in the loudness of the different tones, although they were recorded at the same level. Switch speakers, and the pattern of differences can change. Recording the results with precision laboratory instruments can produce graphs similar to Figure 11.6. This graph is known as a frequency response curve —or rather, it's a pair of frequency response curves for two different products. On the whole, Product A is more accurate than Product B, because the bulk of Product A's curve lies close to the 100% line—the point at which the product produces precisely the output it should, given its input. To the extent that a speaker's frequency response curve lies close to the 100% point, it's considered to have a flat frequency response.

You'll sometimes see frequency response curves similar to those in Figure 11.6 in test reports of speakers in consumer and audiophile magazines. Most manufacturers don't make such graphs readily available. Instead, they report a frequency response range. This is the range of frequencies between which sound reproduction is at 50% or greater what it should be. For instance, one speaker might have a frequency response range of 30Hz-10,000Hz, and another might have a range of 20Hz-25,000Hz. The second is probably a better speaker, particularly at reproducing high notes, but the range alone doesn't tell you how the products performed in the wide middle ground. If the second speaker's reproduction fluctuates wildly, you might actually prefer the first speaker, especially if you seldom listen to music that pushes far beyond 10,000Hz.

The environment in which a speaker exists affects its frequency response curve. Furniture, wall hangings, carpets, floors, and so on can all affect a speaker's frequency response curve.

Chapter 11

Similarly, the precise shape of your ear and skull can affect a headphone's frequency response curve. Indeed, part of our subjective experience of sound comes from the way sounds interact with the bones and tissues of our bodies on the way to our ears, so when measured apart from a human body, or a good simulation thereof, a good pair of headphones exhibits a frequency response curve that would be considered quite poor for speakers.

20 200 2,000 20,000 Frequency (Hz)

20 200 2,000 20,000 Frequency (Hz)

Figure 11.6

A frequency response curve lets you compare the quality of sound reproduction of two or more speakers or headphones.

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