Home Theaters

It is important to the fullness of music. Many people quibble about the amount needed. It all comes down to individual taste, for which there is no accounting.

What am I talking about? Low notes in the music we listen to, of course. And for home theater, not just music, but all sounds in general. Low frequencies are a part of everything, and when gone, the quality of reality is missing. From the most early music, it was known that the lower octaves make the sound ‘right’, and natural. If we remove the bass, we remove musical reality, for it is not very often that we listen to any instrument that cannot reach into the low end of the spectrum. There just aren’t that many pieces of music written for D-flat piccolo as a solo instrument.

true bass fanatics start salivating when they hear this baby, a JBL B460 subwoofer, complete with 8 cubic foot enclosure and 18" driver, a legendary 2245H.

It used to be that most people used  what were known as full range speakers, so that the rolloff of the very bottom octave in music was not that noticeable. The trend of the last 15 or so years is to have smaller speakers, known as satellites, to produce much of the audio spectrum, with a subwoofer for the lowest notes. Care must be taken here to be specific, as what most people refer to as a subwoofer is, in reality, a woofer, with no means of reproducing what a true subwoofer would be producing. In truth, a subwoofer, by definition, reproduces below what a woofer does, and by convention, that is any frequencies below 40Hz. Because the satellites in use today have woofers that are 6.5" in diameter, or less, and they are housed in enclosures that are quite small, they have little hope of reproducing  bass frequencies down to 40Hz - at realistic levels. What does this mean? Many speakers of that ilk will reproduce a 40Hz tone with no problem at 75db, but when the music is being played at 85-90db, that woofer is being asked to double the apparent acoustic output (an increase of 10db is equated by human ears as twice as loud, although the actual power is much more, the ear is not very linear in its response to sound pressure). The woofer struggles to do this, and all frequencies it reproduces are adversely affected.  All of that to say this, no one would truly be happy with a subwoofer when used with current satellite speakers, as there would be a huge hole in the bass, and this would be very unnatural. What happens, in most cases, is that the ’subwoofer’ is being asked to provide the musical content to around 125Hz, and sometimes higher. (Remember that crossovers are not brick walls, and that both the higher and lower drivers are still reproducing frequencies on the far side of their crossover points.) So the subwoofer that most speak of today is, in fact, a woofer, but I won’t try to change the world, it can be much like trying to teach pigs to sing.

a Sumo Samson subwoofer, with an active crossover, the Delilah, which made integrating the Samson into any room sonically much easier. It has provisions for stereo or mono output, and continuously variable output levels, along with several fixed crossover points.

What we must realize, now, that we have accepted the fact that most will be using a ’subwoofer’ to reproduce the first 2.5 octaves of music, is that the ear will be able to localize the woofer, and if the placement is not correct, the sound will be off. Some will not notice, but it can be very apparent under the right circumstances.

So - one of the first rules, whether listening to music, or watching movies, should be that the subwoofer should be in the middle of the room, or under the screen, or between the satellites. This will prevent sonic anomalies most of the time.

What is better, although more expensive, is the use of a pair of subwoofers. This will make placement easier, and also allow for a stereo amplifier to drive them. (Because of the way the market is, it is much easier to get a good, inexpensive 200wpc stereo amplifier, rather than a good, inexpensive 400wpc mono amplifier.  This allows the bass to have more of the characteristics it should, as explosions originating on the left of the screen will be reproduced there, and not out of phase from the middle. It is a factor that once heard, will annoy the listener when only one sub is used.

Smaller subwoofers, like this Velodyne Acoustics model, are easier for smaller installations, and can be easily used in pairs. Although powered, these units are ruggedized to withstand the pounding, and the amplifiers fare well.

This leads to the next point. Using a non-powered subwoofer is usually preferable to a powered one in that the amplifier can usually be of higher quality, and is also not taking a pounding - most subwoofer failures today are electronic in nature, as the pounding of the air mass moves or breaks a circuit component.

More specifics about woofers in our next installment, including output levels, acceptable distortion, and crossover points. Also covered will be active versus passive crossovers, and the benefits and problems with each type.

-