When I was a child I was told that children need to be seen and not heard. How times have changed! When it comes to using a subwoofer in a home audio system it might be said that a subwoofer needs to be heard and not seen. Well not exactly. The subwoofer should not even sound as if it is in the system. It should blend so smoothly with the main speakers that those speakers have suddenly and miraculously extended their lower end frequency response. But this should only be apparent when the source material calls for it. Otherwise, it would only be apparent that the main speakers have an improved dynamic range and better power handling.
One of the selling points of a separate subwoofer is that it can be hidden away in a corner of the room and out of the way. This is not quite accurate either. The sub may sound too boomy and detached. It may work on a home theater system for those action movies that are enhanced by the boom. But we are talking about a quality home audio system designed to transport us to the recording site. Anything that prevents that experience we would classify as distortion.
Audionengine makes a quality subwoofer but we believe it is just a little too expensive. In the case of the A2+’s, its cost is not in proportion with the price of the main speakers. Let us see if we can find a quality low cost subwoofer that will outshine Audioengine one. How do we go about doing that. We can compare the sound of various subwoofers to determine which one has the best sound, but that would not guarantee that the sub would blend with the A2+’s. We just want something to augment them and have no particular sound of their own. This is where design comes in to play.
The midrange drivers of the A2+’s are very small Kevlar cones. They are fast and articulate. They almost blend perfectly with the silk dome tweeters. Matching the Kevlar’s to a subwoofer is another matter. Subwoofer cones need to be relatively large if they are to go deep, but how large? If the cone is too large then it will most likely be too slow to get started. Its moment of inertial will be too great. In addition, a larger driver is more difficult to stop quickly. We are talking about impulse response. A sub needs to respond in sync with the midrange/bass driver. A smaller cone is, in most cases, a better match. A 10 inch or even an 8 inch driver will do if it is designed properly. It must be a long excursion drive but one that is adequately damped.
Believe it or not, there are many small and relatively inexpensive self-powered subwoofers that will matchup with the Kevlars of the A2+’s. The key is to carefully adjust the crossover point, gain, and polarity of the subwoofer. Most people will not likely have the test equipment to make precise adjustments. But to be honest, one’s ears are more than adequate to do the job. After all, the ears will always make the final assessment as to how an audio system sounds. Instruments do not listen to music.
The subwoofer setup will require some patience, trial and error, and careful listening. What we are looking for is a natural sounding frequency response from the midrange on down. We do not want the sound of the subwoofer to spill over into the midrange and muddy up the sound. The A2+’s roll around 100 Hz. For this reason the subwoofer should initially be set up to limit its frequency response above 110 Hz. This is a good general rule of thumb because it allows some overlap between the subwoofer and midrange drivers, assuring a smoother transition of the drivers. If the subwoofer is not cut off soon enough it will sound merely tacked on and not natural. The effect we are looking for is that the midrange drivers seem to have a lower extension in bass response, but otherwise they sound unchanged.
With our mystery subwoofer in place we played some source material which actually had some low end response. Organ music is good for adjusting the sound. We should hear and fell the low petals of the organ but the recording should sound essentially the same with or without the subwoofer A good piano recording might be next. We are all very familiar with the sound of a piano. If it is a grand piano it should sound full and extended, with substantial weight in the low end, but not sound over powering. Lastly, we will need some recording with string bass. We should actually hear the strings and not just a muffled low end. Our ears are perfectly capable of assessing the sound of these instruments, particularly if they are well recorded.
If the bass sounds boomy then the subwoofer has not been adjusted correctly. Try lowering the crossover point until the boom disappears. If too much of the bass is lost then increase the gain of the subwoofer. Strong bass that is tight sounding is generally achieved by increasing the gain and lowering the crossover
How does a good subwoofer improve the sound of the little Audioengines? The A2+’s become alive. They still have the same wonderful low coloration reproduction, but the added weight of the subwoofer definition and focus. The midrange drivers simply do not have to work so hard. Overall, the sound is more musical and satisfying. The A2+’s almost disappear while the music emerges with greater clarity and ease.
Which subwoofer do you buy? There are some excellent low cost subwoofers offered by MartinLogan, Pioneer, Polk, and others. We chose one that cost less than one hundred dollars. Yes, the one that gets lousy reviews from the people who don’t understand what subwoofers do or how to set them up. The joys of state of the art on a budget! Sound this good was not even available years ago at any cost.