single speaker cabinet, e.g., a cabinet holding eight ten-inch speakers, or 8x10". Smaller speaker cabinets with one, two, or four speakers are more commonly used, because while the 8x10" cabinet is able to produce huge volume and powerful bass tone, the cabinets are very heavy and difficult to transport. Some single cabinets use mixed speaker sizes. Examples include MESA Engineering's 1x15"/4x10" cabinet, Peavey's PVH 1516, which has 1x15" and 2x8" speakers. and Traynor's TC1510 combo, which has 1x15" and 2x10". Large cabinets with speaker sizes other than 10", 12" or 15" are less commonly used. Examples include the 6x8" and 8x8" cab configurations. One reason that some bass players choose to use a "bass stack" rather than a combo is that the separate component approach enables bassists to use different speaker cabinets for different shows or activities. For example, a bassist playing a stadium may use an 8x10" cab for this show, but then bring a 4x10" cab for a nightclub show the next day, or a 1x12" cab for a studio recording. Large speaker cabinets may have attached lifting handles and dolly wheels to facilitate transportation. Speaker cabinets with 1/4 input jacks typically have two parallel jacks, so that the amp head may be plugged into one cabinet, and then a second cabinet can be "daisy chained" by connecting it to the first cabinet. Cabinets with horn-loaded tweeters often have an attenuator knob for controlling the tweeter. Bass cabinets have thicker wood panels than electric guitar amps, and often have stronger internal bracing. This reduces the likelihood of unwanted cabinet buzzes or rattles, which are more likely with bass cabinets due to the lower sound frequencies output. "Open back" bass speaker cabinets are uncommon, because the configuration increases difficulty in clearly reproducing low-frequency tones. Heads Separate bass amplifiers which do not contain speakers, often called "heads" or "amp heads", are usually integrated units, with a preamplifier, equalizer (bass and treble controls) and a power amplifier combined in a single unit. Some bassists use separate preamplifier/power amplifier setups, where one or more preamplifiers drive one or more power amplifiers. In the latter example, a bass player can use a bass-specific power amplifier or use a sound reinforcement system power amp. Bass amp heads are available in high-wattage power ratings that are not available in combo units. For example, the Ampeg SVT8-PRO amp head puts out 2,500 watts RMS at 2