Technical Articles and Editorials
- Written by Dr. David A. Rich
- Published on 20 March 2013
- Subwoofers: A Brief Look at the Effectiveness of Using a Subwoofer in a Music System
- Page 2: The Subwoofer in the Listening Room
- Page 3: How Low Do We Need to Go?
- Page 4: Issues with the Subjective Evaluation of a Subwoofer
- Page 5: The Under-reported Issue When Adding a Subwoofer
- Page 6: Conclusions
- All Pages
Introduction: Subwoofers in a Music-only Setting
Before turning to the review of the NHT subwoofer (review to be published next week) let me give you an overview of the merits of a subwoofer in a context restricted solely to music or restricted to music as part of a soundtrack.
We are faced with two questions: does the subwoofer go low enough; and, how loud must it play with inaudible distortion until it crosses-over to the main speakers.
The URL below provides an interactive presentation of the frequency range for standard acoustical instruments:
The lowest note for A concert piano is 27Hz, (nineteenth-century pipe organs went lower). An organ of Bach's time would not extend to 30Hz. Note that while it may sound very low, standard percussion instruments do not go very deep, although they are capable of producing significant sound pressure.
A floor-standing speaker (9" to 10.5" equivalent cone area) will have a -3dB anechoic response ranging from 40 - 60 Hz (add 5 -15 Hz or so for a bookshelf speaker with 6.5" woofers). The 10% distortion point in an anechoic chamber for 100dB SPL RMS (1 meter) will also occur in this frequency range.
Note that you cannot directly compare the equivalent cone area of the speakers in the passive floor stander to an active subwoofer with the same sized driver. The subwoofer is designed to provide long voice coil excursion to achieve high SPL at low frequencies. The driver is also designed to deal with heat dispersion. By virtue of its design, the driver often does not work well above 100Hz or so. The active electronics in the subwoofer allow for special protection modes to prevent the driver from becoming damaged. Overdriving a passive subwoofer below its passband can damage the driver.