Atlantic Technology 272 PBM THX instruction manual How Much is Enough?, Dual Subwoofer Placement

Model 272 PBM THX Atlantic Technology®

Figure 5: Assymmetrical arrangement for 2 subwoofers in a home theater, for example, one closer to a corner than the other

How Much is Enough?

Sometimes people prefer more bass impact for movies than sounds natural when reproducing music. You may wish to determine both a video level and an audio level if you find yourself falling into this camp. Remember however, the most common error people make when setting up their system is to play the subwoofer (and surrounds) too loudly. Of course, the Home Theater Police will not arrest you for this act. But should you desire the most accurate overall reproduction, a well balanced sound from bass to highest treble is the best way to get it. Have fun. Experiment. Enjoy.

Dual Subwoofer Placement

When two subwoofers are used you may wish to place them asymmetrically; that is, in slightly different positions in the room (Figure 5). This will reduce common mode room resonances that occur with symmetrically positioned sub- woofers. You can also try placing the subwoofers in the same corner, if you wish. Experiments have shown this to be a viable means of produ- cing smooth bass response in many rooms.

Using the Subwoofer Lo-Pass Control

When used with the complete System 270 THX, the 272 PBM THX Lo-pass control should be set at 80Hz unless you are using a processor with its own built-in crossover. The goal is to optimize the performance of the system by ensuring that the subwoofer and satellites produce a cohesive and well integrated sound “picture.” The low frequency response of the System 270 THX satellites has been optimized to work with approximately an 80Hz crossover point.

Higher crossover frequencies pass more bass but can sound boomy and may be more easily localized to the subwoofer. Higher crossover frequencies may be suitable, however, when using very small satellites that have no real low frequency performance. Settings lower than 80Hz should be employed if you are using larger speakers that have extended bass response. This way, the subwoofer will only reproduce the very lowest bass frequencies that are in the range where the large main speakers begin to roll off. It’s generally undesirable to have the main speakers and the subwoofer overlap too much. Larger speakers means a lower Lo-pass crossover frequency, smaller speakers means a higher Lo-pass crossover frequency. Consult the manufacturer’s specified low frequency response for your main speakers to determine the appropriate Lo-pass setting on your subwoofer. In the end, however, a little time spent experimenting will generally result in dramatically better bass response.

The Phase Invert Control

A subwoofer operating out of phase with the rest of the system won’t provide optimum low frequency performance. Also, the correct subwoofer phase can enhance room acoustics. Since there is so much variation in the industry regarding phase, and no standards have been established, a switch that will reverse the phase of the subwoofer is provided on the amplifier panel. Listen to a monaural musical source with strong bass content. (For example, you can use the mono switch on an FM tuner or preamp, or use a Y-connector on the outputs of one of your source components to get a mono signal.) Experiment with the position of the phase switch to get the most extended bass. It should be obvious which is the correct setting. In particular, there will be a smoother more integrated transition between the satellites and the subwoofer when they are properly phased.

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