Impedance and mic performance!

[SHIBbYinc]

Hey there,
I am fairly new to the recording aspect of music so please excuse newbie-like ignorance where found. Anyways it has come to my attention that my good ol' trusty SM57 apparently is designed for low impedance, however my 003+ rack has an impedance of 2K (Sm57 is designed for 300 ohms). I would like to know if and how this will affect that microphone's performance, and if this is true (I am not 100% on this information) is there anyways asides from getting a new rack in order to remedy this?

 

[Trevoire520]

In a low impedance pre the 57 tend's to get a bit less boxy, the high end comes across as a little less harsh. It's a subtle difference, but can make a difference when stacking up several guitar tracks. You will get a bit less level out of the mic at low impedance though.

If you don't want to buy a low impedance pre then you can make up a mic cable that will change the impedance the mic see's (instructions here: http://www.recordingmag.com/resources/resourceDetail/330.html)

 

[TheWinterSnow]

depending on how the impedance from the 003 is being achieved can make a difference. If it is purely resistive then the microphone will have a longer time constant and in an LC circuit of that nature will result in a lowpass. There are mods that people have done with making their own cables (with resisters in them) to decrease the impedance of their 57. In the end the difference it will only slightly reduce your extreme highs and what should be left will be a lot more musical especially for guitars. If you are really worried about high end and you have done recordings and don't have enough, you can pickup a mic preamp that has the correct input impedance.

In a low impedance pre the 57 tend's to get a bit less boxy, the high end comes across as a little less harsh. It's a subtle difference, but can make a difference when stacking up several guitar tracks. You will get a bit less level out of the mic at low impedance though.

If you don't want to buy a low impedance pre then you can make up a mic cable that will change the impedance the mic see's (instructions here: http://www.recordingmag.com/resources/resourceDetail/330.html)

the guy is a bit backwards but the idea is correct I guess. Jumping pins 2 and 3 on the cable will bring the impedance of the gain stage in parallel with the mic's resistor, lowering impedance, increasing output current and loosening up on the lowpass filtering which would actually allow the coil to move more freely (not less like mentioned). Either way the mic should be loaded with an impedance that it was designed for to sound the best. The frequency response designed by Shure is only obtained if it is loaded at the impedance they designed the mic to work with.

The mod should open up the sound of the mic, making it brighter, more open and natural sounding. make sure that you know the actual load if the preamp's impedance and be sure to use the adding resistors in parallel to calculate the correct total resistance. If you pre's impedance is really 2K and the 57 should be loaded near 300, a 330 resistor will get you to about 280 ohms impedance which is the closest value in the standard available resistor, the next closet impedance is 380 ohms with a 470 ohm resistor (280 is closer to 300 than 380).