Originally Posted by blueman335
You've got a concoction of things creating a guitar's tone, the main ones being the wood, guitar design, PU, and amp. Bridge PU's are usually overwound to some degree to add output & warmth, and make up for the sharp, bright sound from that position. Try the same PU in neck & bridge, and it will seem darker & more powerful in the neck, and brighter and weaker in the bridge, due to vibration & string energy. Since each position has a totally different EQ, there is no reason that the same magnet type has to be used in both PU's. Which magnet is best depends on how the variables all come together. Never assume that the manufacturer knows best which magnet will sound best in your guitar thru your amp for your style of music.
Alnico magnets give more color & character to the tone, which is great with clean to moderate amounts of overdrive. To me, ceramics are bright, sterile, and harsh clean, a problem with blues and classic rock, but ideal for metal. While most big manufacturers use A5's, A2's, and ceramics, there are other alnicos that deserve more use (and thanks to this forum, they're starting to).
Common alnicos:
A2 - Rounded highs & lots of mids. Good harmonics. Loose low end. Low output. If a HB is wound to be bright, an A2 works in the neck slot. In a hot neck PU, an A2 will most likely make it muddy with flabby lows. In a bridge it has more virtues, & provides needed warmth and the low end isn't so noticeable. Some players call it's tones rude (in a good way).
A3 - Like a A2 but with a little more treble. Low output. Good substitute for an A2 PU when more treble is needed; can be used for bridge or neck. Since I like bright neck HB's, I think an A3 makes a better neck magnet than an A2.
A4 - Balanced EQ. Good replacement for an A5 when more mid & less treble is needed. Medium output. I use these mostly for warming bridge HB's that have stock A5's, but they can also be good in the neck in some guitars.
A5 - Scooped EQ; lots of treble & low end. The treble gives good definition and cut. Can be a little bassy in the neck position of some HB's (i.e. '59N in a LP). Very popular stock magnet in both neck and bridge HB's. High output.
A8 - Warm and smooth with lots of mids but the high end isn't as rounded as an A2, so there's more bite. Tighter low end. High output, which can be used to balance volumes with a neck PU. For most music styles, suitable for the bridge position only. Players are finding more uses for these, in high output HB's (Custom, JB, etc) and low output bridge PAF's. Interesting substitute for the A2 in a PGB or the A5 in a '59B.
That's the basics. If you have some HB's and the tones aren't quite what you want, get an assortment of replacement magnets and take a few minutes and swap some out.
