I wanted to satisfy myself regarding this, so I ran my Rode NT4
through a series of tests (quiet room, ticking clock) to determine
whether there is any difference in the noise floor, or the signal/
noise ratio, using the internal 9v battery or P48. The results are a
little inconclusive, but my general impression from A-B listening
tests is that the noise level is slightly better using the battery
than using the phantom power. But the differences are minor.
I do not own a separate 48v phantom power supply, but I do own
several devices that provide 48v phantom, so I was able to test the
Rode through each of these devices. I did not change any settings
other than turning on or off the phantom power and waiting several
minutes for the voltage to stabilize.
I used the following devices to supply 48v: Marantz PMD670, Art
USBDualPre, MBox (original) audio interface, Alto analog mixer.
Samples were recorded using the PMD670 (line inputs when not using
the 670's phantom power) or a Powerbook running Amadeus Pro 1.5 (in
the case of the MBox). I used Amadeus to analyze all the recordings,
and I used Quicktime to do A-B listening comparisons.
Numbers indicated slight differences (<=3D 1dB) in noise, but in every
listening test the noise was slightly more prominent when using
phantom power. In one case (MBox) the noise using phantom power was
of a slightly higher frequency, and the overall noise level was 1.1
dB louder, and this difference was clearly audible.
In the case of the PMD670, using phantom power introduced a 150 hz
hum (very objectionable), which increased the overall noise level by
about 1.2 dB. But the higher frequency hiss showed no audible
difference.
One other oddity is that the MBox delivered a 3.8 dB higher signal
level using phantom power than it did using battery power. This gave
the MBox a better s/n ratio using phantom power (2.7dB better), which
was audible when the two tracks were normalized to match the peak
signal levels. All of the other devices showed signal levels within <
1dB of each other.
I don't know if this is of any use to anyone but myself, but based on
these results, I wouldn't purchase a phantom power supply just to
power the NT4 for recording low source levels. Depending on the
phantom power supply, the battery may be a slightly quieter source of
power for the NT4 - at least the one I own. And there may be other
factors that I do not have a handle on (like the quality of the 48v
power supply).
John
On Jan 21, 2012, at 3:51 AM, wrote:
> Ben wrote:
>
>> I've owned two NT4s and noticed an increase
>> in noise (~4-5dB from memory) when I used
>> 9v battery power on them. It's a shame.
>
> Thanks for the correction. I have not used the NT4. Specs for mics
> I have used have not indicated this pattern, but then again specs
> are often simplified to the point of being misleading.
>
> I have noticed no difference with my Sennheiser ME66 + K6, but then
> again I don't use it in a low-noise studio environment. I would not
> be surprised if the "no difference" was in fact around 3dB.
>
> -- robinparmar.com
John Crockett
Let us live in harmony with the Earth
And all creatures
That our lives may be a blessing
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