HD audio formats have been gaining ground for a number of years, and they have allowed digital audio tracks to sound more spacious, precise and natural than ever before. One of the more technical explanations for this is that covering very high (albeit inaudible) harmonic frequencies preserves the authenticity of each instrument’s timbre. It is also true that speakers and headphones capable of delivering very high frequencies (at least 30 kHz) generally provide a very pleasurable listening experience. High definition digital audio is precisely this… but it’s also something more.
The crucial importance of low frequencies
With so much focus on delivering ultrasonic frequencies, the importance of very low frequencies can be overlooked. A piano, for example, can produce frequencies below 30 Hz. While we don’t hear these frequencies, we do feel them. This holds true for an upright bass, drums, an organ… Low frequencies add a physical dimension to sound, without necessarily making your couch tremble.
The height of the soundstage produced by two (hi-fi) or seven (home theater) speakers greatly depends on their ability to deliver lows. In fact, lows significantly change our perception of mids and highs.
That being said, many listeners are happy with a pair of floorstanding speakers, thinking that their coverage of low frequencies is sufficient. This is completely false, even if specs published by manufacturers can imply otherwise. Delivering low frequencies is either a matter of using an emissive surface and trapped air, or relying on the principle of resonance (bass-reflex). And yet, the drivers equipping most floorstanding speakers and nearly all compact speakers are less than 6.3” (16 cm) in diameter. What’s more, these drivers also deliver mids, making their delivery of lows less efficient.
Apart from a few, very large speakers which are mechanically amplified by certain rooms, virtually no speaker is able to deliver substantial lows on its own.
Balanced sound: impressions vs. reality
It is important to understand that a speaker with a linear frequency response will not necessarily offer well-balanced sound. Our ears are particularly sensitive to mids, and this hypersensitivity is accentuated as the volume is turned up.
In practice, 6 or even 10 additional dB are necessary to make lows (drums, bass, etc.) seem balanced with mids (vocals, percussion instruments).
However, speakers capable of producing an extra 6 or 10 dB in the lows simply don’t exist. Some listeners nevertheless have the impression that their speakers provide balanced sound. The simple explanation for this is that these speakers have been installed in a room that either amplifies lows or attenuates mids and highs.
The miracle of subwoofers
In movie theaters, the challenge of speaker sensitivity is met with a number of solutions: active equalization of multichannel audio recordings, Dolby’s renowned LFE channel (.1), and the use of subwoofers, which are specially designed to exclusively deliver low frequencies. To this end, subwoofers are equipped with one or more specific drivers. Even if only a 6.3” (16 cm) driver is used, it benefits from a heavier cone and a large copper coil capable of handling more power than a wideband driver. Additionally, the driver can withstand greater excursions, a necessary trait for a rigorous exploration of low frequencies.
Adding a subwoofer to your stereo system will substantially enhance overall performance while improving the balance of the main speakers. Consequently, the sound will be richer and more detailed than ever before.
Although subwoofers aren’t always the most elegant speakers, they make such a large contribution to the overall performance that it would be a shame to forego adding one. The good news is that subwoofers cost quite a bit less than a pair of speakers, and adding one could allow you to enjoy your current speakers a lot more.This post is also available in: French