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Low End Rumble Coming from Bluebird Mic
Old 22nd May 2019
  #1
Gear Head
Low End Rumble Coming from Bluebird Mic

Blue Bluebird mic circa 2010.

After about 10 minutes of being plugged in and receiving phantom I am getting a huge sub low rumble with intermittent bursts of energy in the same range.
(photo attached)

The problem seems contained to that region and is somewhat transparent with a steep HPF around 100 Hz

It may be one of 50 different things, but I'm not much of an electronics wiz, so before paying to repair or replace I just wanted to make sure it's not a common and simple issue resolved with a soldering iron or xlr swap etc.

The answer to my question may be "just get a new one" or "take it to a repair shop", but I was wondering if there's an easy answer I'm just not aware of.

The attached image is basically just ambient room noise with the preamp cranked to demonstrate the issue clearly. No "musical" signal

Thanks in advance.
Attached Thumbnails
Low End Rumble Coming from Bluebird Mic-bluebird.jpg  
Old 22nd May 2019
  #2
Lives for gear
 
thismercifulfate's Avatar
It’s probably just picking up your HVAC system. Very common when recording outside of a professional recording facility. Do the same test with another condenser mic.

Last edited by thismercifulfate; 23rd May 2019 at 01:59 AM.. Reason: Typo
Old 22nd May 2019
  #3
Gear Addict
 
Murky Waters's Avatar
 

Suggest checking the phantom power on the mic pre. Swapping devices (mics/preamps) may help identify the source (process of elimination).
Old 24th May 2019
  #4
Gear Head
Quote:
Originally Posted by Murky Waters View Post
Suggest checking the phantom power on the mic pre. Swapping devices (mics/preamps) may help identify the source (process of elimination).
Thanks for the tips.

I've done that all already, to no avail.
Old 24th May 2019
  #5
Gear Addict
 
Murky Waters's Avatar
 

Quote:
Originally Posted by coreycoleman View Post
Thanks for the tips.

I've done that all already, to no avail.
Well, what did the swapping tell you? Did the noise follow the mic or the pre-amp? Or did the noise exist regardless of which mic and pre combination you used?
Old 24th May 2019
  #6
Lives for gear
 

If the phantom power is clean it shouldn't do anything to the audio quality.
Preamps on the other hand can have self noise, typically high frequency hiss.
Low frequency may occur too but its typically a matter of AC EMF, Shielding, cable, or ground loops.

If your monitors are on when testing it can cause a feedback loop and given the fact the mic has a broad frequency response it could feed back in the low frequencies long before the highs. If the mic is on a stand, you can even have low frequency vibrations coming up through the stand which are being heard.
The easiest way to know is put on headphones and lift the stand off the floor and see if the response changes.

Given you say this happens when you crank the preamp all the way up, you can simply unplug the mic and see if you still have any background noise. This could be preamp noise and disconnecting the mic rules it out. I do suspect, as others said, you are dealing with ambient room noise. This is one reason room treatment to flatten the room response is so important.

What the real question is however, what is the background noise level with the mic set to normal operating levels. Cranking the preamp is going to reveal the flaws in your setup. Noise is cumulative in a signal chain. There may not be one source, there can be dozens of individual components which all add up to what is commonly referred to as the noise floor. The goal when purchasing or upgrading is to buy the best quality gear you can afford so self noise and distortion are minimized. That quest is like a Pyramid, the closer you get to the apex the more expensive beating back flaws becomes.

What you have to determine is if you can get by using gear that contains 10 cent resistors and $.50 op amps, or whether $10 hand made military precision resistors and $80 op amps make a big enough difference for you to spend what it costs to get the best. no man made electronic components are flawless, they have inherent flaws which are part of their design and the impurities added to make the components work properly are the same elements that cause noise.

The difference in high quality gear is first, great circuit designs. Second well built components using the best raw materials available.
Third and by far the most important is screening components. In mass produced gear, there is very little quality screening. Its cheaper for them to make a thousand boards and get a pass or fail with the board or components running under normal operating conditions.

High quality gear will have every component tested and only the best components cherry picked from a batch of parts. I used to do this all the time building and repairing gear. Back before amps had modular amplifying devices, we used to take a hand full of transistors and stick them in a tool called a load line analyzer. You'd pass different voltages through the transistors and you'd get different variances. If two transistors were off too much your stereo sound could wind up being unbalanced. You'd go through a batch to find the closest matches so your amps would push pull evenly or stereo channels had the same frequency responses.

You'd have different tests for most components and if you put the time into it you can get excellent fidelity from relatively inexpensive components.
Thing is its the manpower, not the components that make the gear expensive. A robotically board made in a batch of a thousand may only cost $10 to manufacture. The same circuit built by hand with all the testing to get the best possible results might cost a grand in comparison.

Again it comes down to how much noise there is when the mic is set to "Normal" operating conditions.
Most preamps will have the noise levels increase exponentially once pushed past 3/4 of max. If you're having to run it over 2/3 I'd say you likely have noise from poorly matched gear.
Old 25th May 2019
  #7
Gear Head
Quote:
Originally Posted by Murky Waters View Post
Well, what did the swapping tell you? Did the noise follow the mic or the pre-amp? Or did the noise exist regardless of which mic and pre combination you used?
The noise is specific to that mic, regardless of preamp. I have many other mics and pre's.
Old 25th May 2019
  #8
Gear Head
Quote:
Originally Posted by wrgkmc View Post
If the phantom power is clean it shouldn't do anything to the audio quality.
Preamps on the other hand can have self noise, typically high frequency hiss.
Low frequency may occur too but its typically a matter of AC EMF, Shielding, cable, or ground loops.

If your monitors are on when testing it can cause a feedback loop and given the fact the mic has a broad frequency response it could feed back in the low frequencies long before the highs. If the mic is on a stand, you can even have low frequency vibrations coming up through the stand which are being heard.
The easiest way to know is put on headphones and lift the stand off the floor and see if the response changes.

Given you say this happens when you crank the preamp all the way up, you can simply unplug the mic and see if you still have any background noise. This could be preamp noise and disconnecting the mic rules it out. I do suspect, as others said, you are dealing with ambient room noise. This is one reason room treatment to flatten the room response is so important.

What the real question is however, what is the background noise level with the mic set to normal operating levels. Cranking the preamp is going to reveal the flaws in your setup. Noise is cumulative in a signal chain. There may not be one source, there can be dozens of individual components which all add up to what is commonly referred to as the noise floor. The goal when purchasing or upgrading is to buy the best quality gear you can afford so self noise and distortion are minimized. That quest is like a Pyramid, the closer you get to the apex the more expensive beating back flaws becomes.

What you have to determine is if you can get by using gear that contains 10 cent resistors and $.50 op amps, or whether $10 hand made military precision resistors and $80 op amps make a big enough difference for you to spend what it costs to get the best. no man made electronic components are flawless, they have inherent flaws which are part of their design and the impurities added to make the components work properly are the same elements that cause noise.

The difference in high quality gear is first, great circuit designs. Second well built components using the best raw materials available.
Third and by far the most important is screening components. In mass produced gear, there is very little quality screening. Its cheaper for them to make a thousand boards and get a pass or fail with the board or components running under normal operating conditions.

High quality gear will have every component tested and only the best components cherry picked from a batch of parts. I used to do this all the time building and repairing gear. Back before amps had modular amplifying devices, we used to take a hand full of transistors and stick them in a tool called a load line analyzer. You'd pass different voltages through the transistors and you'd get different variances. If two transistors were off too much your stereo sound could wind up being unbalanced. You'd go through a batch to find the closest matches so your amps would push pull evenly or stereo channels had the same frequency responses.

You'd have different tests for most components and if you put the time into it you can get excellent fidelity from relatively inexpensive components.
Thing is its the manpower, not the components that make the gear expensive. A robotically board made in a batch of a thousand may only cost $10 to manufacture. The same circuit built by hand with all the testing to get the best possible results might cost a grand in comparison.

Again it comes down to how much noise there is when the mic is set to "Normal" operating conditions.
Most preamps will have the noise levels increase exponentially once pushed past 3/4 of max. If you're having to run it over 2/3 I'd say you likely have noise from poorly matched gear.
Thanks for the reply.

I have many other mics and pre's and the problem is specific to the mic.

The problem persists at lower input levels. I gained up the pre to demonstrate the problem visually in a clear way in the spectrum analyzer.
Old 25th May 2019
  #9
Gear Addict
 
Murky Waters's Avatar
 

Quote:
Originally Posted by coreycoleman View Post
The noise is specific to that mic, regardless of preamp. I have many other mics and pre's.
Microphone requires service.
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