I've used a number of Shure SM7 microphones in various facilities and it's not uncommon to hear a slight hum or buzz in the background. The hum can always be varied by rotating or moving the microphone. Sometimes it is related to a nearby CRT, sometimes it's from an unidentifiable source. Sometimes it sounds like a ground loop. In some facilities, there is no hum. Unplugging the mic from the cord always stops the hum. That makes me believe that the SM7 is not particularly resistant to magnetic fields, RF, etc. Anyone else had this problem and if so, what did you do to solve it? Has anyone had this issue and went to a different microphone, such as an RE20 or RE27?
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Microphone Hum/Buzz
- Thread starter BobOnTheJob
- Start date
According to the specs, this Mic is highly shielded, so that seems rather odd.
R
R
No experience with this particlar mic, but in general, many dynamic mics have a tiny transformer inside, which should be wrapped in foil
to prevent hum pickup. This foil is sometimes connected to the shield, sometimes not. I had this exact problem with
a desk mike I put together out of parts, and had to put back the foil shield I had not replaced.
It may be possible to wrap the xfmr, but I can't imagine Shure Bros wouldn''t already have this shielded.
It could be that the coil on the diaphragm sits out high enough ( not in the gap) with this model to be susceptible to picking up
hum fields.. If rotating the mic changes it, It's definitely a field. Do the offending facilities have flourescent lights?
Ballasts for flourescent lights throw quite a field.
Does this mike have a metal grille? It may need such shielding.
to prevent hum pickup. This foil is sometimes connected to the shield, sometimes not. I had this exact problem with
a desk mike I put together out of parts, and had to put back the foil shield I had not replaced.
It may be possible to wrap the xfmr, but I can't imagine Shure Bros wouldn''t already have this shielded.
It could be that the coil on the diaphragm sits out high enough ( not in the gap) with this model to be susceptible to picking up
hum fields.. If rotating the mic changes it, It's definitely a field. Do the offending facilities have flourescent lights?
Ballasts for flourescent lights throw quite a field.
Does this mike have a metal grille? It may need such shielding.
I have always loved the way an SM7 sounds but use the RE20's because announcers beat the crap out of mics.
I like the guys who after they are "on the air" slap the mic and boom to the side.
With the SM7 I have replaced and replaced the shielded wire from the element to the transformer a bunch. Announcers keep fiddlin with the mic (up down up down) as most are compulsive obsessive. Remember the days when the old AM announcers turned the rotary pots on the RCA console up and down while they were talking?
This many times can't be seen until you have it all apart. The shield is the first to go.
Even with this the mics will pickup crt if close. (LCD screens don't have the magnetic field.)
Let me know if your shied is broken.
I like the guys who after they are "on the air" slap the mic and boom to the side.
With the SM7 I have replaced and replaced the shielded wire from the element to the transformer a bunch. Announcers keep fiddlin with the mic (up down up down) as most are compulsive obsessive. Remember the days when the old AM announcers turned the rotary pots on the RCA console up and down while they were talking?
This many times can't be seen until you have it all apart. The shield is the first to go.
Even with this the mics will pickup crt if close. (LCD screens don't have the magnetic field.)
Let me know if your shied is broken.
It could be that there is something amiss in the power wiring of some of these facilities. I once tracked down hum field interference which was blurring an electron microscope picture. It was caused by improper wiring in a sub panel where the neutral was miswired. Inside the conduit, which was in the wall about 10 feet from the scope, the current going up the line was not equal to the current coming down the neutral so the fields did not cancel. Fixed the wiring and the problem.
I am not suggesting that you tear into power wiring, rather I am just offering a possible cause for strong ac magnetic fields.
Neil
I am not suggesting that you tear into power wiring, rather I am just offering a possible cause for strong ac magnetic fields.
Neil
BobOnTheJob said:I've used a number of Shure SM7 microphones in various facilities and it's not uncommon to hear a slight hum or buzz in the background. The hum can always be varied by rotating or moving the microphone. Sometimes it is related to a nearby CRT, sometimes it's from an unidentifiable source. Sometimes it sounds like a ground loop. In some facilities, there is no hum. Unplugging the mic from the cord always stops the hum. That makes me believe that the SM7 is not particularly resistant to magnetic fields, RF, etc. Anyone else had this problem and if so, what did you do to solve it? Has anyone had this issue and went to a different microphone, such as an RE20 or RE27?
overall, this seems pretty abnormal...
what is your application... are you in a studio, or auditorium, and are you interfacing to a PA system....
The Shure SM-7 and SM-5B do not work well with a CRT monitor nearby. Perhaps it is the brand of monitor. Same studio with an EV and no buzz.
Lane
Lane
On air or production studios in all cases with variable results. Some have no buzz, other have it.knowbetter said:BobOnTheJob said:I've used a number of Shure SM7 microphones in various facilities and it's not uncommon to hear a slight hum or buzz in the background. The hum can always be varied by rotating or moving the microphone. Sometimes it is related to a nearby CRT, sometimes it's from an unidentifiable source. Sometimes it sounds like a ground loop. In some facilities, there is no hum. Unplugging the mic from the cord always stops the hum. That makes me believe that the SM7 is not particularly resistant to magnetic fields, RF, etc. Anyone else had this problem and if so, what did you do to solve it? Has anyone had this issue and went to a different microphone, such as an RE20 or RE27?
overall, this seems pretty abnormal...
what is your application... are you in a studio, or auditorium, and are you interfacing to a PA system....
Thanks Lane...In the future, I may move in the RE27 direction based on it's better hum rejection.Lane Lindstrom said:The Shure SM-7 and SM-5B do not work well with a CRT monitor nearby. Perhaps it is the brand of monitor. Same studio with an EV and no buzz.
Lane
Two things to look at on both the -7 and the -5:
First, go get some LCD monitors and throw the CRT ones to the sales and office staff.
Second, look at the cable which runs from the XLR socket on the side of the yoke into the mic body. It should have a ferrule where it goes into the mic body which is clamped with a setscrew. That ferrule is bonded to the shield of the cable, and they're notorious for breaking loose, or having the setscrew loosen or get dirty. Either will result in a buzz on the mic audio.
First, go get some LCD monitors and throw the CRT ones to the sales and office staff.
Second, look at the cable which runs from the XLR socket on the side of the yoke into the mic body. It should have a ferrule where it goes into the mic body which is clamped with a setscrew. That ferrule is bonded to the shield of the cable, and they're notorious for breaking loose, or having the setscrew loosen or get dirty. Either will result in a buzz on the mic audio.
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