Posted by Nando Dalva on January 29, 2013 at 4:58pm
Im planning on making a 3 string bass and have built guitars before, I was wondering if you needed a bigger box to get the right pitch. If so, how big and what shape gets the right acoustics?
THANKS
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Any of the phosphor-bronze acoustic bass string sets sold out there should work well. I'd probably go with a light gauge set if I were building it. The only problem with using commercial bass strings is that they come in two scale lengths - 34" and 30" so using those will semi force you into using either scale length.
You might try the bottom 4 strings in a baritone guitar set. That uses a 27-28" scale length.
Some folks on CBN have experimented with weed whacker filament for strings. Can't say much about that having never tried it.
Generally, the bigger the box, the more "woof" you'll tend to hear - and the greater the likelihood of feeding back when amplified. Putting a center block down the middle (like Gibson does with their semi-hollow ES series guitars) - or just extending the neck all the way through to the tail will go a long way towards cleaning up the sound and giving you better sustain. (The big selling point of neck-thru basses is their generally longer sustain times.)
If I could suggest: go with a bigger box to get some of that woody tone you're probably after, but don't let the box get too deep. That will only make it more boomy and muddy sounding. Unless that's the sound you're after, I'd trim the box height down to around two inches maximum give or take. Think along the lines of the Höfner 500/1 (i.e. Beatle Bass) for inspiration and ideas. It has a relatively small body like a CBB would. And the total height of the sides is about 2" including the thickness of the top and bottom. So figure the inside dimension is about a half inch less assuming the top and bottom are approximately 1/4" each. Get some more ideas from violin shaped basses here.
As far as shape goes, sound waves generally don't like hard angles. The waves get trapped or ricochet back and forth across hard angles and you get oddball cancellations and interference. Like when you toss a rock in a pond and you see clean radiating circles- until they hit the shore and start bouncing back. Then you'll see turbulence where the incoming waves collide with the outgoing waves. That's "phase cancellation" and "distortion" you're seeing. Same thing happens with sound. And parallel surfaces (like a...um...cigar box?) tend to maximize that effect. Something that's a large part of what gives them their unique sound. They're all wrong - but in a musically pleasing way. That's also why most guitars have rounded shapes.
If you were to do a box from scratch, the closer you got to an oval the less of an effect the box shape would have on the sound. A balalaikas triangular shape was selected because i was the easiest shape to build that had no parallel surfaces inside it. Much easier than steaming and trying to bend the wood sides for a guitar. The sound waves would still reflect in a triangular body cavity - but not directly back at themselves, thereby reducing the possibilities for unpleasant sounding wave interactions. The only problem with the triangular shape is that when you build a three string instrument with a triangular body - you've built a balalaika - not a CBG! :-)) And they do sound different than CBGs so the square shape of the standard CBG is not something you'll just want to walk away from.
Replies
What about strings... its gunna be fully acoustic.
Any of the phosphor-bronze acoustic bass string sets sold out there should work well. I'd probably go with a light gauge set if I were building it. The only problem with using commercial bass strings is that they come in two scale lengths - 34" and 30" so using those will semi force you into using either scale length.
You might try the bottom 4 strings in a baritone guitar set. That uses a 27-28" scale length.
Some folks on CBN have experimented with weed whacker filament for strings. Can't say much about that having never tried it.
Generally, the bigger the box, the more "woof" you'll tend to hear - and the greater the likelihood of feeding back when amplified. Putting a center block down the middle (like Gibson does with their semi-hollow ES series guitars) - or just extending the neck all the way through to the tail will go a long way towards cleaning up the sound and giving you better sustain. (The big selling point of neck-thru basses is their generally longer sustain times.)
If I could suggest: go with a bigger box to get some of that woody tone you're probably after, but don't let the box get too deep. That will only make it more boomy and muddy sounding. Unless that's the sound you're after, I'd trim the box height down to around two inches maximum give or take. Think along the lines of the Höfner 500/1 (i.e. Beatle Bass) for inspiration and ideas. It has a relatively small body like a CBB would. And the total height of the sides is about 2" including the thickness of the top and bottom. So figure the inside dimension is about a half inch less assuming the top and bottom are approximately 1/4" each. Get some more ideas from violin shaped basses here.
As far as shape goes, sound waves generally don't like hard angles. The waves get trapped or ricochet back and forth across hard angles and you get oddball cancellations and interference. Like when you toss a rock in a pond and you see clean radiating circles- until they hit the shore and start bouncing back. Then you'll see turbulence where the incoming waves collide with the outgoing waves. That's "phase cancellation" and "distortion" you're seeing. Same thing happens with sound. And parallel surfaces (like a...um...cigar box?) tend to maximize that effect. Something that's a large part of what gives them their unique sound. They're all wrong - but in a musically pleasing way. That's also why most guitars have rounded shapes.
If you were to do a box from scratch, the closer you got to an oval the less of an effect the box shape would have on the sound. A balalaikas triangular shape was selected because i was the easiest shape to build that had no parallel surfaces inside it. Much easier than steaming and trying to bend the wood sides for a guitar. The sound waves would still reflect in a triangular body cavity - but not directly back at themselves, thereby reducing the possibilities for unpleasant sounding wave interactions. The only problem with the triangular shape is that when you build a three string instrument with a triangular body - you've built a balalaika - not a CBG! :-)) And they do sound different than CBGs so the square shape of the standard CBG is not something you'll just want to walk away from.
Anyway, hope some of the above was of interest.
Cheers!
Bass wavelengths are LONG and have shallow ampitude ratio. Bigger box? Of course, for unampified sounds...
I found a BIG box, for Cuesta Rey cigars. It's 17x9x3 inches. You might use a paintbox, or a good sized cutlery box. Maybe a wooden backgammon?
Thanks, I'm ordering a huge one on ebay, like 17.5x8.5x4 so that should work.
Thanks for the quick reply