Most everyone agrees that capturing a snare drum with a Shure SM57 will work nicely. And others know that adding in a small diaphragm condenser, like the AKG C451, will sound even better (with correct placement). On guitar cabinets, it’s pretty much the same effect: the SM57 captures that hi-mid presence while the C451 adds some thump and sizzle. It’s an age-old trick that has stood the test of time.
The key is coincidence (and that’s no coincidence!); to illustrate, those applying this mic technique must get the two capsules as close together as possible, thus eliminating phase distortion while capturing all frequencies without cancellation and comb-filtering. While you can always use two mic stands to position the two transducers, they will often shift out of ideal position, not to mention taking up more setup space, for example, around the snare drum. Most of us “audio vets” gaffer’s-tape the SM57 and small condenser together; it’s why used C451s so frequently have tape marks on them.
Finally, we have a modern solution: the X-Clip. Its vaguely x-shaped design grabs the SM57 on one side and a C451 (or any similarly-sized pencil mic) on the other. Simply slide the X-Clip onto the SM57 (pushed to the front of the mic, where the body is wide and non-tapering); position your SM57 as normal; and insert the C451 into the X-Clip, then slide it forward so the capsule is right next to the SM57's capsule. Voila—phase coherence via one stand in 10 seconds … and no tape!
The X-Clip now sells for $19.99 direct at theXclip.com. I paid $30 for mine; add shipping to that and you'd start to think that this a bit pricey for a little piece of plastic. Yet after your first session (or first FOH mix) with an X-Clip, I expect you'll be singing a different tune, just like I did.