Recording - June 2010 - 6

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Mics and interference Dear Paul Stamler: I have a few questions about microphones and how they interact with other devices in studios. If a dynamic mic is used to record a guitar speaker, will the proximity of the mic’s voice coil to the speaker’s magnetic field create any audible effect on the output? In crossovers, when two coils are in alignment they can couple and pass signal to each other. We also use magnetic shielding on speakers to prevent problems with older tube TVs and CRT computer monitors. So I got to wondering if that was something we needed to worry about with mics near speakers. Also, what affect does the magnetic field of a nearby speaker have on a condenser mic, if any? Thanks for any clarification you can give me.
Jerome Malsack via email

Words of encouragement Dear Eric Ferguson: I just wanted to send a quick note to thank you for the article in Recording titled, “Become a Recording Songwriter!” (March 2010). I thought your comments and advice were right on. I also found it a great encouragement to continue what I am doing. I have been a songwriter for years and just set up my DAW studio back in July. It has been a long learning process, helped by a class in Cubase from Berklee. I spent about $6000 total on the setup and a minimal conversion of my home office. I figured it is an investment, as I am working to build up a catalog that can be used in film and TV. Thanks again for the great article, I look forward to reading more from you in the future.
Raymy Krumrei via email

Paul J. Stamler replies: Jerome: Thank you for a very interesting question. Short answer first: probably there will be no audible effect at all. The field of the speaker’s permanent magnet is pretty well focused on its own voice-coil gap, and in any case doesn’t change. The changing magnetic field associated with the speaker’s coil is very localized. I won’t say there couldn’t possibly be an effect, but my educated guess is that it’d be insignificant at best and unmeasurable in all likelihood. You do raise some examples of measurable and even problematic examples of magnetic field interaction in studios, but neither of your examples apply to this case. In the case of crossovers, there’s way more interference because the magnetic fields of free-standing coils aren’t nearly as focused as those in loudspeakers. In the case of speakers near CRTs, we’re in a completely different realm; speakers are shielded so they don’t deflect the flying electrons in a picture tube and therefore distort the picture on the monitor or TV, but an electron is many orders of magnitude smaller than a microphone’s moving voice coil. As to condenser mics in magnetic fields: there should be no effect at all. The only exception might be if a transformer-coupled condenser mic’s transformer was somehow affected by the speaker magnet (e.g., the core became magnetized). But I think that’s unlikely. There is one other issue, though, which can be a real problem: an amplifier’s power transformer creates a 60 Hz hum field which extends for some distance around the amplifier. If a dynamic or ribbon mic (or the transformer of a transformer-coupled condenser mic) isn’t well-shielded or equipped with a humbucking coil, you can easily get hum induced into the microphone. I’ve had that happen, on an old Electro-Voice 666 dynamic, when trying to mic a combo amp. That’s why I always test the hum sensitivity of mics (with my trusty Wall Wart From Hell) when reviewing them. Thanks for your letter and thanks for reading. Peace—PJS

Eric Ferguson replies: Raymy: Thanks for the kind words! I’m glad to hear that my hard-earned advice is appreciated. Home recording is fun, but as you know, can also be difficult at times. You just gotta keep doing it... It sounds like the new studio (and the hard work) is paying off. Keep up the good work, and thanks for reading Recording.—EF Even absent creators have rights Hi there, I just wanted to tell you how much I enjoyed Joe Albano’s article in the latest issue (“The Evolution of a Song”, March 2010). He has a great sense of humor and had a good message—be open to other views of your songs. And it’s impressive what a good engineer/producer can do, as is the case here. Is the final product out there anywhere so that we could hear it? Thanks!
Larry Rice via email

Larry: I am sorry, but my understanding is that because the original owner of the song has vanished and is not reachable, Joe does not have the right to post it in public because he cannot obtain permission, and we would hate to hear from them in the form of a lawsuit. The audio clips on the website are designed to give a feel for how the evolution of the piece went without actually breaking any laws... they’re re-created from the originals to simulate the process. I will forward your compliments to Joe and ask him if my understanding of the legal situation surrounding the song is correct, and if there’s any more audio available for us to post. Thanks for your understanding, and thanks for reading.—MM

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RECORDING JUNE 2010

Recording - June 2010

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