Microphone Impedance Matching - Using an SM58 on iPhone 4 [UPDATED]
⚠️ Warning This post is more than 10 years old. I do not delete posts, because even old information is still useful, but please know that some material on this page may be outdated or incorrect. Thanks!
8/25/12 Update: The Tascam iXZ is another good alternative to the KVConnection cable, and is more flexible than the VeriCorder or KVConnection adapters, though it's a little more cumbersome. It's also only $30 on Amazon.
1/6/11 Update: The VeriCorder XLR Adapter Cable includes +6.1dB attenuation so you can have a slightly amplified XLR input on your iPhone 4, and is a slightly better solution than the KVConnection cables (in my experience).
Update 2: KVConnection's latest revision to their XLR adapters (here and here) add in impedance matching! Rejoice, for you shall no longer need any extra adapters/transformers - check out my video sample with the new adapter :)
Update 1: I have finally gotten ahold of the RadioShack transformer, and it works beautifully! Below is a sample recording with the SM58 and my iPhone 4 (no intermediary devices besides the KVConnection adapter and the line-matching transformer):
Here's an image of the setup for this connection (in its most basic form):
From KVConnection: We are working on a iphone adapters with built-in impedance
matching transformers
for the low impedance microphones like your Shure SM58 which has an output impedance of 150 ohms. The iphone needs to see 800 ohms or more of impedance to recognize that an external mic is plugged in.
Since I have a pretty good single-person interview solution for audio and video on my iPhone 4 (I'm almost finished crafting a nice tripod adapter as well, so I can grab my mini-tripod and iPhone, and have a stable platform), I am now working on finding a solution to the problem of recording interviews where one person would interview another, with a handheld mic.
There are a few battery-powered handheld condenser mics that would work out of the box (like the Nady SPC-25), but I would like to use some of the nicer dynamic mics I have on-hand with my iPhone, like the Shure SM58.
It seems that I might be able to do this with an impedance transformer—if I can get the 'low impedance' (~150 Ω) microphone output level of the Shure SM58 transformed into the required 'high impedance' (800 Ω +, according to KVConnection) of the iPhone's input, I should be able to use the SM58, or any other so-called 'Lo-Z' microphone with ease. And they'd look a lot nicer, too.
I'm considering the following adapters (and might be able to pick up the RadioShack adapter tonight):
The advantage of the second transformer is that it should work great with most other consumer recording devices (cameras, DV cams, other portable recorders, etc.), without needing yet another adapter to get to the final plug. I'm not a huge fan of the 1/4" TRS connector—I figure, if you need a plug that big, stick with XLR (even if it's not balanced) - it locks in, and looks nicer :-)
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