The Importance of Loudspeaker's Frequency Response

If you're going to understand anything about audio-how speakers work, the effect of room acoustics, how to set your subwoofer's level, the concept of bass management/low-pass filters, anything about audio-you have to understand frequency response. This is the cornerstone of everything in audio. It all starts and stops with frequency response. Amplifiers, receivers, speakers, CD and DVD players, they all have to have as close to perfect frequency response as possible, or else they just won`t sound right. Nothing else matters if the frequency response is no good. Can't make it any clearer than that.

An audio device with good frequency response is able to play all the low, middle, and treble tones correctly-and in the proper proportion to each other-and that's what tells our ears whether or not this is a high-fidelity unit with rich, vibrant, lifelike sound.

To understand frequency response, remember this: the loudness of sound is expressed in a unit of measure called the decibel, or dB. To define frequency response, we specify a range of frequencies, and then we state by how many decibels (dB) the equipment varies from perfect. For example, a speaker may be said to have a frequency response of 40 Hz-20 kHz (that's the range), ± 3dB (that's the variation).

Now it's time for another hard part: Frequency responses are almost always shown as a graph. This graph is known as the [Frequency Response Graph." (Clever, no?) You have to know how to read a graph, no excuses. If you paid attention in Mr. Kelleher's 6th grade class, great. If not, you'll be sorry now.

Now look at figure 2. The black line is a speaker with excellent frequency response. The frequency response curve (so-called because a speaker's frequency response curves, or drops off, in the low bass and high treble) is pretty flat ("flat" is good, because it means the device is accurate with very little up or down variation), with no serious peaks or dips. For speakers, ± 2 or 3 dB is considered very good. Electronic equipment (receivers, CD players, etc.) should be within ± .5 dB.

The red line in Figure 2 shows a speaker's frequency response with a big 7 dB peak (so-called because the graph looks like a mountain's peak) in the upper midrange around 6 kHz, which will make it sound harsh and irritating.

Figure 2-Speaker frequency response curves-Good and Peaked

Figure 3 shows what speaker frequency response curves look like that correspond to various subjective descriptions.

Learn these terms and learn how they look as frequency response graphs, and you'll be on your way to a meaningful understanding of loudspeaker sound.

Figure 3-Subjective descriptions shown as frequency response curves

Try to listen in an environment similar to your home listening space because room acoustics have a tremendous influence-good and bad-on how a speaker sounds. Some rooms are too [live", with lots of hard, reflective surfaces, which can make a speaker sound too bright and shrill. Conversely, rooms can be [dead," or overly absorptive, like a room with thick carpeting, heavy drapes and overstuffed furniture. Speakers in a room like this can sound dull and lifeless. So bear in mind that a crowded, noisy open showroom floor or a small sound room filled to the gills with speakers and other equipment will sound nothing like your 12 x 15-foot den or your 17 x 27-foot living room with vaulted ceilings.

One advantage of buying from an Internet Direct company with a home trial arrangement is being able to listen to speakers in the actual location where they'll be used. Many ID companies have a trial period where you can live with the speakers for a week or more and return them if you don't like how they sound in your home. This is actually a major improvement over the way speakers were typically purchased in years gone by, when customers would listen to several models in a retailer's sound room. The problem with that, of course, is that a dealer's sound room bore almost no acoustic resemblance to a consumer's actual listening room, so people often got an unpleasant surprise when they got their new speakers home and discovered that they sounded quite different than they did at the store.