First a thanks. I wrote you a few months back about a good "all-around" mic. Among many suggestions, you mentioned that AT4050. I did some additional research and decided to try that mic. I really like it -sweet tone, easy to use, somewhat affordable.
Next a question about micing a guitar amp. Do you have any general guideline for doing so? it seems that one of the most difficult things to do for me, so far, is get a good "metal" sound. It seems to require mic placement (I see that the engineer for the latest Evanessence album uses an SM 57 at the middle of the cone and another mic around the edge) and some judicious EQing. Do you have any tips?
Thanks for all your help.
Amongst many other uses, the very affordable Shure SM57 is somewhat of a "standard" for micing guitar cabinets.
If you want to keep things simple, use one SM57 placed almost right up against the grill, and move it around until you get the sound you are looking for. If you point it right at the center of the cone, you will get the brightest sound. The more you move it off to the side, the less bright it will be... it's kind of like EQing with the microphone.
The next step would be to use two Shure SM57 microphones, with one pointed right at the center of the cone, and another off to the side a bit, or even placed on another speaker in the cabinet. It's important to try to keep them the same distance from the speaker to minimize phase differences. But, then you'll have two different tones that you can blend to taste. You can either blend them up front and record the results to one track, or keep them separated on two different tracks to give you more control of the blend when mixing. Not too long ago I read about some other engineer who uses two SM57 microphones right next to each other, with the capsules aligned, but with one pointed straight at the center, and then the one on the side of that angled in towards the center or edge (depending on what works best). I tried that on some recent heavy guitars, and it worked well since they were both very much in phase with each other and I could blend them depending on the type of tone I needed.
Another thing I've done many times, and that many other engineers also do, is use an SM57 combined with a Sennheiser MD421. Sometimes on the same speaker, sometimes on different speakers. The MD421 gives you a different kind of tone than the SM57 and the combination can make a good blend when it comes to mixing time.
In addition, I'll many times add a third microphone when tracking. The third microphone will usually be a large diaphragm condenser microphone. Your AT4050 might be a good choice here. I've used many different ones. Sometimes I'll put it right up close like the dynamics, which will give a really bright cutting sound from the condenser, but many times I'll back it off of the cabinet a couple feet or so to capture the whole cabinet sound plus just a bit of room tone... moving it back also keeps it from getting too bright or harsh. Here, especially, you'll need to play around with the position to find a spot where it not only sounds good, but doesn't cause weird phase nastiness when blended in with the close dynamic microphones.
Ribbon microphones are also popular on guitar cabinets these days, especially the Royer microphones. I don't have a Royer, so I haven't personally tried it out. However, I did try out my AEA R84 microphone on guitar cabinets several times, and usually didn't like it. Maybe I just never found the right spot... but, mostly it just wasn't the sound I was looking for. The one time I really liked the ribbon a lot was when I was recording a soft bluesy/jazzy guitar sound for a very sparse lullaby type song... in that case I was looking for a really warm and full tone, and the R84 got that for me. Not my first choice for heavy rock/metal stuff, though.
Basically, experiment with the above and see what sounds best to you. A lot of it is going to depend on the guitar, the guitar player, the amp/cabinet, and the room. The remaining part is microphone choice and placement. If you are unsure, you can also use a DI box to split the signal off of the guitar before going to the amp, and record the clean DI signal as well. Then you have the choice of using amp simulator plug-ins, or using a re-amp device to record through a different amp/cabinet in the future if the original tone you recorded is not working. Most plug-in simulators still don't sound as good as a great amp/cabinet recorded well with microphones, but they can still be pretty good.