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I've been thinking about making some soundhole style magnetic pickups for acoustic guitar. I have some questions about that and I can't think of anyone that I would rather ask than Rick, so I hope you'll catch this and give me your thoughts, please!
Acoustic guitars present some challenges for magnetic pickups. I like the Sunrise pickup...But it is awful large, the Fishman is quite a bit smaller, and a more modern design.
I imagine, from what I already know, that I'd want a lower winding count, with a fine wire and a resistance around 5-6K. A proper preamp would be a great help and a requirement if you want to go direct into a PA...But magnet type is a big question for me. I've made pickups with alnico, ceramic and rare earth (neodimium) magnets. Would I want a very strong magnet for this? What would I need to do to give me a good string balance? This part seems like the biggest problem for me.
Thanks in advance!

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Mark Swanson
Swanson Guitars
http://www.MarkSwansonMusic.com

I use the LR Baggs M1 and really like it. Most natural sounding soundhole pickup I've heard. I used the Sunrise in the past but prefer the natural sound of the Baggs. Can't help with design, I have a hard enough time just installing pickups.

The problem with small strong magnet structure is false nodes impressed upon the strings.

I'm curious about why you have a particular DC resistance in mind.    It doesn't tell you very much about a pickup.   I know everyone thinks it's an impedance measurement, but it's just DC resistance. For instance, I've found that you can tame the harshness of ceramic magnet pickups by winding them way, way up in DCR, and then preamping to preserve frequency response close to the pickup.   Completely counter-intuitive, completely against the grain of what everybody else does.   But it works.   

String balance with bronze wound strings is a real issue.   I'd suggest a different magnet structure under the wound and unwound strings.   Even something like Alnico 2 for the unwounds, and Alnico 5 for the wounds might be interesting.   

There's a real balance of science and art in pickup design.   So far few of the scientific measurements really tells you what a pickup sounds like.   There are too many factors in the magnetic interface realm that have nothing to do with coil frequency response.   It's a dark art, one of the closest things to alchemy that I get involved with these days... It's also fun!

Thanks for your thoughts, Rick.
I think I know how to wind a clear pickup, I don't think it would benefit an acoustic guitar to have a really hot pickup. I'd rather depend upon a preamp for gain and I like the high end of a lower output pickup.
I guess I'll just have to make a few and see which magnet type is the best. I've used the neodimium magnets in solidbodies and had good luck, the key is as you say not to use too much magnet. For those I like a metal core and the magnet on the bottom. But in the case of bronze wound strings, it is obvious that you need to tame the plain strings to get the balance even...it'll take some playing around I guess!

_________________
Mark Swanson
Swanson Guitars
http://www.MarkSwansonMusic.com