TECH2

The review I just wrote of the Sonos Play:3 streaming music system, and another I recently finished of several small Bluetooth speaker systems (you’ll see the full results soon in the print edition of Sound+Vision) reminded me of just how important listening is in audio product design.

Most of us know that speakers are supposed to have a flat frequency response, reproducing all frequencies at the same volume given the same input voltage. That rule emerged after years of experiments at the Canadian National Research Council in Ottawa, comparing results of blind listening tests with lab measurements to see what type of frequency response most listeners prefer. The details of these tests have filled several white papers, but the upshot is that a speaker should have a flat frequency response on-axis, with an off-axis response that’s as smooth as possible.

However, these tests were done mostly with relatively large, relatively full-range speakers of relatively good quality. That’s great if you do all your listening on the living-room couch. But what if, like most of us, you do much of your listening elsewhere, on small, low-cost speaker systems with limited bass response?

My Bluetooth speaker test suggests that the rules are different for products that lack bass. Here, a not-well-enough-known psychoacoustic principle comes into play: A lack of bass can make a speaker sound as if its treble is boosted, even if its frequency response is flat.

For instance, the Monster iClarity HD produced the best frequency response measurements of all the Bluetooth speakers I tested, but because it has no bass, it sounds bright. In contrast, the Jawbone Jambox delivered less impressive frequency response measurements, but its sound was subjectively more balanced because it has more bass and a rolled-off treble.

I noticed this same psychoacoustic principle at work when I reviewed the Sonos Play:3 and the Veho 360BT Bluetooth speaker. If you roll off the treble to counteract a lack of bass, you get what seems to be a more balanced sound.

To my knowledge, there are no hard-and-fast rules regarding this practice, i.e., “roll off the treble at -6 dB/octave above 12 kHz if the bass response decreases by 24 dB/octave below 120 Hz.” Because there are no firm guidelines, the cheaper the audio product, the greater the need for the designers to fine-tune the sound according to the tastes of a panel of experienced listeners.

My guess is that more manufacturers are going to do this as products like the Play:3 and the Jambox prove it’s possible to get satisfying sound from small, low-cost audio products.