Re: Why aren't guitar and bass speakers flush mounted on baffle
The output of Guitar and Basses is in the low to mid octaves and not the top octaves; Guitar and Bass speakers are not designed for the top ( HF ) range where flush mounting is of greater significance to reduce diffraction of the top octaves.
Tweeters are a different scenario as HF wavelengths are much shorter.
Guitar cabs and speakers often trade and compromise on issues that are important to HiFi scenarios; because they are an integral part of the sound creation - as opposed to sound reproduction without color.
Drop-in mounting driver mounting is easy to manufacture and facilitates replacing drivers from the outside.
And there would be additional fabrication cost to flush mounting; besides that drivers in guitar and bass cabs are almost always on a recessed baffle ( often behind a grill ) for protection against "road accidents"
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