Assuming the cabs had similar designs (speakers, materials, ported/sealed etc) it would get a bit louder, with perhaps a tiny bit more low end response.
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It depends on the 8x10" cabinet. Ampeg's classic 8x10" 'fridge was purposely loaded with low-wattage speakers so that the SVT amplifier would cause them to distort, thereby producing the "classic SVT growl." A lot of it will depend on the speakers themselves, as well as the construction of the cabinet. I don't know that you would be any louder; in fact, depending on the ohms rating of the 8x10" cabinet, your amplifier might actually put out less wattage that it did with your 4x10" cabinet. But there is no doubt that you will have more "sound." Since you will be moving more air, you will generate more sound. Whether this increase in sound is noticeable depends on a lot of things; not leat of which is just how loud the other people in your band are playing. As for "coloring" your sound; well, that will depend primarily on the speakers.

The 8x10" 'fridge is an icon among bassists, as it allowed us to compete with the amplifier stacks made famous by Marshall and Hiwatt. Our old 2x15" cabinets were easily drowned out by guitarists armed with a 100-watt Marshall and two 4x12" cabinets. The 8x10" cabinet was a real game-changer.

One peculiar thing about 8x10" cabinets for bass is that the effect of the sound increase is often heavily dependent on where the listener is positioned. I remember a few times when I could barely hear my sound coming from my 8x10" 'fridge, but people who were standing about 30 feet in front of it said that the force of the sound was so great that it felt like they were being punched. It is something to keep in mind when you play through an 8x10" cabinet.
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Last edited by FatalGear41 at May 20, 2013,
My bassist has an Ampeg 8x10 that is very nice.
My other buddy has an Aguilar 8x10 and that cab is insanely good.
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