Technical Articles and Editorials

Subwoofers: A Brief Look at the Effectiveness of Using a Subwoofer in a Music System


Issues with the Subjective Evaluation of a Subwoofer

In my opinion, everything that affects the sound of a subwoofer is fully characterized by its measurements. To paraphrase Peter Aczel a fast woofer is an oxymoron. If the subwoofer is not flat in the near-field you will hear it (see measurements section of the NHT B10d at SECRETS for more details). If they do not go as low as the material you want to play, you will hear it. If the woofer cannot achieve the SPL you want to reproduce at inaudible distortion levels, you will hear it.

Room effects are the most significant factor to impact the sound, not the subwoofer. This depends on the placement of the subwoofer and your seat (Toole Sound Reproduction Loudspeakers and Room Focal Press, 2008; chapters 12 and 13). For those with the Toole text, it is best to carefully review the sections on waterfall and other time-domain graphics. The text clearly indicates the parameters required to produce a plot with usable data is often not well understood (Section 13.5). Proper setup and interpretation of waterfall and similar plots are especially difficult to set up and interpret. Some measurement tools designed for consumer use make very nice looking plots but do not provide the user with the ability to set up the measurement correctly. When using such tools it is possible to convince oneself that large changes in the time domain can occur with no visible change in a properly setup frequency domain plot.

Frequency and time-domain response issues can be resolved at one's seat optimally or several seats sub-optimally with precise room EQ, provided the subwoofer is relatively flat and the deployment in the room is done thoughtfully. Room EQs that provide frequency plots on a PC come in handy to ensure the subwoofer is properly placed before the electronic correction is applied.

In difficult rooms, multiple subwoofers may be needed. Passive room absorbers can also assist, but these are large and expensive if they are to have any effect below 100Hz. Multiple subwoofers are especially useful when a flat frequency response over multiple seats is desired (Chapter 13.3 of the Toole text).