Your sub experience: Easy or hard?

I’ve run a single sub + 2 desktop main speakers for ~15 years. Until ~5 years ago the mains were powered; then I switched over to a series of passives.

For me, the hard part of subs wasn’t placement--I only had one placement option, and luckily all the subs I’ve tried sounded good in that spot. Specifically, in my nearfield setup (home office), the sub’s effect sound flattest/best in the listening seat equidistant from the speakers. So I lucked out there.

But for me, the hard part was getting a high-pass filtered signal to the mains. Some subs have built-in crossovers that can do this. Sometimes those crossovers are high quality and sound good; other times they’re trash and sound bad (I’ve had both). I solved that issue for once and for all by picking up a transparent, high-quality external electronic crossover ((Marchand XM-66 in which the high- and low-pass filter slopes 24 dB/octave).

The other hard part is matching the sub’s output level to that of speakers. I found two things that help:

• I get better results by far when using sealed/acoustic suspension speakers. They sound better here, and have the benefit of having a real drop-off out output at the resonant frequency. I count on that when setting the crossover
• And it helps to cross over to the sub at the lowest frequency (that is comfortably above the -3 dB drop-off point of the mains).

Would all this apply to a far larger, high-end system in a living room? Yes, but also no, because there the physical placement of the sub (or subs) would consume much time & effort.

@atmasphere - hi atmasphere, I was wondering, which of your two set-ups, with the DBA and the single sub, do you feel sounds better? And, of subs in general, do you believe forward-firing subs produce more accurate lows than downward-firing ones? thanks much!

in friendship - kevin

@kevn The DBA setup is more accurate. The single sub suffers a bit around the edges of the room where it gets too much reinforcement. Forward or downfiring has no effect (in practice) simply because in most rooms the bass is entirely reverberant by the time you hear it due to the wavelengths involved (at 80Hz the wavelength is 14 feet).

Thanks for your quick reply, Ralph! : ) - kevin.

@jrpnde , nice article and very correct. A sub not only has to match the mains in frequency response but also in time. This is the problem with DBA's. They do a great job of evening out the bass response throughout the room. But, they are not necessarily and probably not matched in time with the main speakers. You have to be in phase and in time with the main speakers or you have essentially an echo. Bass transients like bass drums lose their impact. The buzz in bass strings disappears. The only way you can do this easily is with digital signal processing. The Anthem system was mentioned above. MiniDSP makes the least expensive unit that I know of. There is Trinnov, DEQX and Lyngdorf. People who are digiphobes need not apply and more than likely would be better off without subwoofers. You can not recreate a live performance without subwoofers. To do it right takes much more driver surface area than you would think. Residential rooms stifle bass. Add a processor to this and you have considerable expense. If you can not do it right you are more than likely better off from a sonic perspective not to do it at all. You can kiss the live performance goodbye but this is not what most people want anyway. They want a more polite system that is very detailed. They rarely listen over 85 dB and bass loses it's energy at this volume subwoofers or no. 

Another important aspect of subs is that they take the load off the main speakers which can make serious improvements with their performance in terms of distortion and headroom. Good subs do not low pass at 40 Hz. They are used in conjunction with a high pass filter on the mains and cross between 80 and 120 Hz then time corrected usually by delaying the signal getting to the main speaker so the group delays match at the listening position. You have no idea what is happening unless you measure it. If you think you can do it by ear, good luck to you. Getting it right would be like winning the lottery. Like everything else in this life there are no cheap easy solutions only people who want to sell cheap easy solutions. 

Sorry for preaching.