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Objective Benchmarks: Frequency Response

Premium Two-Channel PC Speaker Roundup

We’re going to start with the objective benchmarks, and since Tom’s Hardware isn’t an audiophile-centric publication, we offer some background information to help our readers make sense of frequency response charts.

Perhaps the best way to understand speaker frequency response is to learn how it is measured. A special audio signal is played over the speakers, which equally covers the entire audio spectrum at the same level. The speaker output is then measured across the part of the spectrum that humans can hear, from 20 Hz to 20 kHz, and the resulting data is the frequency response. A perfect speaker in ideal conditions would produce a completely flat response, the same as the test signal. Peaks and valleys in the response graph mean that the speaker isn’t playing back all portions of the audio spectrum equally.

Testing speaker frequency response is best performed in ideal acoustic conditions, such as a lab equipped with an anechoic chamber, and that is something rarely found anywhere except at a high-end studio facility. We’ve done the best we can, but in less-than-ideal conditions, we’re going to see a lot of bumps in the frequency response due to phase cancellation (sound waves from the satellites canceling each other out) or comb filtering (frequency response errors caused when sound interferes with the room it’s measured in or objects in that room). Readers need to keep in mind that our frequency-response measurements are most useful as a comparison tool between the speakers we’re testing, not as absolute representations of reference response.

Before we discuss the results, here’s a quick legend of the audio spectrum:

  • The sub-bass range is from 20 Hz to 60 Hz, and it isn’t heard so much as felt. Sound in this range provides a sense of power.
  • The bass range is from 60 Hz to 250 Hz. This is where you can hear the bass rhythm, especially in the 90 Hz to 200 Hz area.
  • The lower mid-range is from 250 Hz to 500 Hz. It’s also called the bass presence range.
  • The mid-range is from 500 Hz to 2 kHz. This is where you can hear instruments and vocals.
  • The upper mid-range is from 2 kHz to 4 kHz. Higher instruments and most vocals are heard here, and the human ear is very sensitive to changes in this range.
  • The presence range is from 4 kHz to 6 kHz. Too little sound in this range will make the audio seem like it’s coming from farther away.
  • The brilliance range is 6 kHz to 20 kHz. This is where you hear harmonics and clarity, and accented sound in this range will make it seem crisper and clearer with higher fidelity.

Here are the frequency responses of all four speakers superimposed. Generally, all four of these 20 speaker systems follow a similar line, but there are some notable differences:

The green result indicates that the Altec Lansing Expressionist Bass FX3022 is relatively flat overall. It starts with a relatively sharp curve to about 75 Hz, so there’s not a lot of powerful sub-bass, but that’s to be expected without a sizable subwoofer. There’s a small dip in the bass range at about 100 Hz, which might be a concern, but we’ll need to listen to draw any conclusions and we’ll get to that in the subjective tests. The midrange is fairly flat considering the less-than-ideal test conditions, but there’s a sharp peak at about 13 kHz and then the sound drops off sharply to the 20 kHz limit. Chances are that the peak will add brilliance to the sound, and we might not notice the sharper 15 kHz drop-off compared to the competition.

The purple line represents the Bowers & Wilkins MM-1 results. These speakers have the strongest sub-bass presence in our test group, but unfortunately that's accompanied by a very big drop in the audible bass range at 100 Hz. This is a disconcertingly deep valley in an important range that can make the difference between deep or shallow bass tones. Once again, we’ll have to pay attention during subjective testing to see if this manifests itself under real-world listening conditions. Aside from this, the MM-1 results are exemplary, with strong results all the way to 20 kHz.

The Creative Gigaworks T40 Series II result is represented by the blue line. These numbers were achieved with the bass and treble adjustments set to maximum. We delve into the differences we saw between settings on the next page. These speakers appear weak in the sub-bass range, which is no surprise when you consider that they make do with the smallest drivers in the group. But the actual audible bass range is exemplary, and because of this, we expect the Creative offering to sound bass-heavy at the expense of some low-end presence and power. The rest of the spectrum is fine relative to the competition.

Finally, the orange line represents the M-Audio Studiophile AV 40s results, which probably indicate the flattest response in the group. The worst thing we can say about the AV 40s is that they lack a little sub-bass presence below 40 Hz, but without a subwoofer this is to be expected. These results are taken with bass boost enabled, and as mentioned previously, we will have a look at the effect of audio settings on the next page.

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