Some (mostly stereo) preamplifiers, integrated amplifiers, and receivers offer a subwoofer output, but these jacks often are just a summed preamp output without any low or high pass filtering. In other words, a full-range signal, from the lowest bass to the highest treble is present on the subwoofer jack. The user is expected to use the low-pass filter on the subwoofer’s plate amplifier to blend the sound of the subwoofer with the sounds of the main speakers. Obviously, opportunities for error abound with this setup, and few users get it right.
Another mistake that can be made on the way to subwoofer use is availing oneself of the speaker level inputs and outputs on the subwoofer’s plate amplifier. The crossover frequency, even when disclosed, can vary significantly depending on the impedance of the main speakers. If anything, using the speaker level inputs and outputs on the subwoofer is often worse than having no crossover at all.
Now the good news is that Audio-Video Receivers (AVRs) and Surround Sound Processors normally DO have high and low pass filters to the satellite speakers and the subwoofer, respectively. And in all but the most inexpensive of AVRs, the crossover frequency can be set by the user.
This ensures that several things are working properly:
- The slopes of the low-pass roll-off and the high-pass roll-off are symmetrical.
- The relative volumes of the high-pass to the low-pass are often adjustable.
- The AVR’s power amplifiers (often weak little things) are spared the burden of having to supply excessive bass current into the satellite speakers.
- Relieved of the necessity of having to produce excessive excursions (a chore now routed to the subwoofer), the bass drivers of the main speaker exhibit less distortion and can play somewhat more loudly.
- Often, due to the reduced intermodulation distortion of the main speakers (no longer having to produce bass), the speakers can sound cleaner and more open.
But these benefits can rarely occur when the main speakers are being fed a full-range signal. For stereo systems, there are a few preamplifiers that offer actual bass management; Parasound, Anthem, and Emotiva come to mind. But otherwise, one must use an aftermarket “electronic crossover” to split the frequency range. Most electronic crossovers available are intended for pro audio or live audio use. Their sound quality can vary extensively, and few will sound good in a home environment.
The JL Audio company does make a high-quality electronic crossover, the CR-1, but the going price is in the neighborhood of $3,000! Marchand Electronics is another company that specializes in making electronic crossovers for various applications.
But, in fact, there IS a way to get stereo bass management without having to pay such a premium! Common music streaming programs such as JRiver Media Center and Roon offer digital signal processing (DSP). If you’re willing to dig deeply into the DSP controls, you can create digital high-pass filters for your main speakers without degrading the sound quality. You can further customize the slope of the high-pass filters to perfectly mirror the low-pass filters on your subwoofer plate amplifier. This DSP option can provide true stereo bass management without the necessity of dedicated electronic crossovers.
But for most consumers, application of the AVR or surround processor’s bass management will suffice, allowing you both the benefits of the subwoofer and the greater openness of the main speakers. And in most cases, you don’t need to buy anything extra!
If I absolutely had to criticize the AV model of bass management, the only negative thing I could say would be that virtually all AVRs and surround processors offer monophonic bass only. I generally find that having true right and left bass subwoofers offers a more realistic presentation of the recording. Detractors claim that since bass is non-directional below about 80 Hz., one should hear no difference between a mono and a stereo bass setup. In some rooms, that might be true. But in my room, and to my ears, independent channels of stereo bass sound better.