Experiment III – Fishing String / X/Y H4n + 2 Piezo Microphones

Date of Experiment: September 19, 2011

Purpose + Introduction:

The purpose of this experiment is to detect the differences between the 2 different sized piezo and the X/Y H4n microphones before attempting further experiments with these microphones.

Result + Observations + Data:

I came across some difficulties when attempting my first setup.  In one instance, I thought the piezo microphone’s weight and size would be negligible to the vibration of the
string.  So I tried attaching the microphone directly to the string; the string did not resonant.  Another difficulty I found was that the piezo microphones were extremely sensitive and the X/Y H4n microphones were extremely insensitive.  The recording levels were set to 35 for the piezo microphones and 100 for the X/Y H4n microphones.  The results below will show why.

The link below is the original recording done during a regular studio session.

Notice how clear it is to hear distant footsteps and the clicking of the computer mouse.  Now compare it graphically with the spectrogram.

It is clearly shown in the spectrogram that recording at a level of 100 will pick up a lot of unwanted background noise – the mass of random blue dots.  The background noise will be more evident when it is compared to the piezo microphone recording below.

Input 1 (25/32″ diameter)

Input 2 (1 1/16″ diameter)

Notice how Input 1 (first sound) produces a higher frequency than Input 2 (second recording).  Now to compare it graphically with the spectrogram.

After analyzing the 2 different spectrograms, I noticed some obvious similarities and some shocking differences.

Similarities I found were:

  1. Resonating tones at 1k, 2k and 4k Hz.

Differences I found were:

  1. Input 1 there is a cut off at around 12k Hz, while Input 2 there is a cut off at around 7k Hz.
  2. Input 1 has another frequency at 8k Hz, but is just an overtone from the matching 1k, 2k, 4k Hz
  3. Input 2 has another set of frequencies at 2.5k Hz and 5k Hz.

Ironically, even with the extra set of frequencies, the sound output from Input 2 was more accurate to the X/Y H4n recording.

Airborne and vibration sounds are very similar in sound colour.  However, there are pros and cons to both.

X/Y H4n microphone Piezo Microphone
Pros
  • Records want humans hear
  • Records resonance from
    the aural atmosphere
  • Records just the sound
    from the string
  • More accurate to the
    resonance of just the instrument
Cons
  • Very quiet compared to piezo microphone / hard to hear
  • Picks up external noise
  • Extremely sensitive –
    picks up sound from any equipment, setup and procedure errors
  • Need to find consistency
    for recording (placement of microphone and size of microphone)

Conclusion:

In conclusion, attaching the piezo microphones to the bulldog clips rather than attaching directly to the strings was a more effective recording method.  The recording from the larger piezo microphone was also more accurate than the smaller peizo microphone.  Next, I will experiment with the piano to identify the differences in sound from the strings and the soundboard.  This should provide me with a better understanding to passive amplification and the change in sound
colour.

Leave a Reply

Your email address will not be published. Required fields are marked *

*

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>