Are you saying it didn't have enough true low end, or just that the additional strings gave it so much more up top that it didn't really sound like a bass?
It had a pretty good low end but if you want to get the most out of the guitar strings , you have to keep the treble and brightness cranked up. This is going to give you some bottom but it's going to be bright . It was a powerful,wall shaking sound of an identical guitar and bass part being played together. Absolutely great for certain pieces
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The biggest drawback is that you really can't play most traditional type bass parts with any authority. For example, you can take a stadard three chord rock and roll piece and play some 8 string power chords that will rattle the rafters like no other single instrument I've ever heard. Open E and A chords in particular take on a pianolike sound in addittion to the guitar and bass sound it's designed to produce. It makes for an incredibly full and powerful sound. But, you're missing the walking bass line
You have a huge sound that fills the room, and for some things it works really great. But you tend to miss the dark sounding walking line on the majority of things you play. If you try to play a darker and more traditional bass line on an 8 string, it just doesn't work right for the most part. For starters, you have an identical guitar note for every bass note you play wether you want it there or not and the second thing is, it just doesn't feel like a bass and when you get one in your hands you aren't going to play it like a bass. The neck feels more like a Gibson 335 than a bass and that tends to be the way you respond to it as a player.
Don't get me wrong, it's a great and very unique instrument and I've had the pleasure to Wow some pretty good crowds , including a couple standing ovation solos that I will remember till the day I die, but it's an odd duck and it doesn't fit in most places.
Rick