When a channel is selected as "Large" it means the bass information for that channel, sound below 80 Hz, will be directed to that speaker along with all the other frequencies. When "Small" is selected, the bass is filtered out of that speaker and directed to either the subwoofer output jack or to the Left and Right channels (depending on whether the subwoofer is selected as "on" or "off"). For example, if you select the center channel speaker as "Large," the center channel bass will go to the center speaker. If you select "Small," the center bass will go elsewhere.
If you have connected your subwoofer to the subwoofer output jack, select subwoofer as "On." The subwoofer will now play the Low Frequency Effects bass channel and the bass of any other speakers in the system selected as "Small." If your subwoofer is connected to the system in any other way (such as L&R pre-outs or L&R speaker outputs), select subwoofer as "Off." LFE and bass from channels selected as small will now go to the Left and Right front channels.
Left and Right Front Speakers
Sometimes the choice between "Small" and "Large" is not so clear-cut. These are the tradeoffs: When the main speakers are set to "Small" you will be increasing the top volume capability of those speakers and probably lowering their distortion as well. The downside is that the more speakers you select as "Small" the greater the workload on the subwoofer, increasing the odds that you will overtax it. Also, you will probably get better blending between main speakers and subwoofer if the main floor-standing or bookshelf speakers are run as "Large." Experiment and see what works best for you. Here are some speaker set-up suggestions:
If your main front speakers are floor-standing models with good bass response, select "Large." If your subwoofer is connected to the subwoofer output jack and you wish to limit the bass response of your main speakers for the sake of higher volume, select "Small."
Choose "Small" unless you are not using a subwoofer anywhere in the system, in which case choose "Large."
Palm-sized satellite/subwoofer systems
If the subwoofer is hooked up to the front left and right speaker or preamp outputs (recommended), select "Large." If the subwoofer is hooked up to the subwoofer output jack (generally not recommended), select "Small."
Very few center channel speakers can produce as much bass as a subwoofer or most main speakers. Unless you have a truly full-range (big) center speaker, set the center speaker as "Small."
If you are using bookshelf, on-wall or in-wall speakers as surrounds, select "Small." If you have large floor-standing speakers with good bass response, or have a second subwoofer for the surround channels (a bass freak, eh?), select "Large."
Dolby Digital processors have a "set speaker distance," or time delay function, that ensures that all channel sounds reach your ears at the correct time to aid proper imaging and localization. In most units this is accomplished by simply selecting the distance from your listening position to each speaker via an on-screen display. In other units you must select the amount of delay in milliseconds. Consult your owner's manual for specific instructions. On most receivers, once this adjustment is set, you can forget about it.