Originally Posted by dave.king1
Not entirely true Doc there are plenty of ported boxes, particularly bass boxes ( Markbass & Hartke ) and I think you'll find very few Fender and Vox combos that aren't open backed, even their big bass bins were ported a lot of rich stuff comes off the back of the speaker. Just read the rest of your post
Roy Buchanan used to face his twin away towards the back of the stage in most instances, mic at the front and sound off the rear of the speakers radiating out to the band and audience.
The Marshall box is very directional and if you're off centre they are just loud but get right in front of a fully cranked one and it's like a wall fell on you.
It's all good mate, I think there's a few factors working together which explain why Marshall amps are so loud, there's the directional beaming of the sound caused by the sealed back stopping the sound escaping, so it can only propagate from the front, there's also the harmonics generated by the Marshall amp when it gets pushed into overdrive, the interesting thing is that the human ear perceives the extra harmonics generated by the amp as a kind of loudness, what's even more interesting is that brass instruments, like the trumpet, Saxophone, Tuba, Trombone, etc, tend to behave in a similar way too, and as it just so happens, the human ear is very sensitive to midrange frequencies, and the human ear perceives midrange frequency harmonics as a feeling of loudness too, I think perhaps when Jim Marshall was working with Ken Bran and Dudley Craven to create what would become the first Marshall amps (the JTM 45s) he might have purposefully chosen to go with a closed back speaker design in order to create the sound that guitarists were describing to him, they wanted an amp that would be loud enough to be heard along with the drummer etc, the JTM45 was actually based on the Tweed Fender Bassman, which was originally intended as a bass amp for the Fender P-Bass, but, guitarists found that it made a great guitar amp.
And you are right too, I have seen a Hartke Bass amp where the speaker box actually did have Bass ports as well as a sealed back.
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