Acoustic Stub Microphone Specifications - SM5

Song Meter SM5 User Guide
Core Product
SM5
Accessory

Sensitivity, noise, signal-to-noise ratio and directionality measurements for the SM5's acoustic stub microphones.

Settings Used During Measurement

Unless otherwise specified, the following settings were used.

Sample rate
48 kHz
Preamplifier
Enabled
Gain
16.0 dB
High-pass filter
Disabled

Sensitivity and Noise

Sensitivity is measured in dBFS re: 1 Pa, or the theoretical digital signal level, measured in decibels full-scale, produced in response to an input sound with 1 pascal of sound pressure. In a real-world scenario, positive dBFS readings mean the recording would clip in response to a 1-Pa sound with a given configuration of settings.

Noise floor characteristics are measured in dBFS / √Hz. This indicates the amplitude of noise that will be measured, in decibels full-scale, based on the square root of the bandwidth over which the noise is measured.

The microphone was placed orthogonal to the sound source, so these charts represent the sensitivity and SNR at 90 degrees off-axis.

Figure 1. SM5 Acoustic Stub Microphone Sensitivity and Noise, Linear Frequency Scale
The sensitivity starts at 11 dBFS re: 1 Pa at 100 Hz, then increases to 20 dB at 6 kHz. From 10 kHz to 16.5 kHz, it decreases linearly to -4 dB, then settles back to 0 dB for 18–20 kHz. The noise floor decreases from -91 dBFS per square-root-hertz to -100 dB at 1 kHz. From 7 kHz to 20 kHz, the noise decreases linearly to -108 dB.
Figure 2. SM5 Acoustic Stub Microphone Sensitivity and Noise, Logarithmic Frequency Scale
The sensitivity appears relatively flat at +12 dBFS re: 1 Pa between 100 Hz and 4 kHz. It increase to +20 dB, where it stays for 6–10 kHz. It then decreases to -4 dB at 16.5 kHz and settles back to 0 dB. The noise deccreases gradually from -91 dBFS per square-root-hertz to -108 dB from 100 Hz to 20 kHz.
Table 1. SM5 Acoustic Stub Microphone Sensitivity at 1 kHz with and without Preamplifier
Sensitivity w/o Preamp at 1 kHz -28 ± 3 dBFS re: 1 Pa
Sensitivity w/ Preamp at 1 kHz -2 ± 3 dBFS re: 1 Pa

Signal-to-Noise Ratio

Signal-to-noise ratio (SNR) is measured as the difference between the sensitivity, in dBFS re: 1 Pa, and the noise floor, in dBFS / √Hz. The resulting unit of SNR is dBFS re: 1 Pa / √Hz.

Figure 3. SM5 Acoustic Stub Microphone Signal-to-Noise Ratio, Linear Frequency Scale
Between 100 Hz and 1.5 kHz, the SNR increases from 103 to 115 dBFS re: 1 Pa per square-root-hertz. From 4 kHz to 6 kHz, it increases to 120 dB. From 10 kHz to 16.5 kHz, it decreases to 104 dB. It then increases to 107 dB by 20 kHz.
Figure 4. SM5 Acoustic Stub Microphone Signal-to-Noise Ratio, Logarithmic Frequency Scale
In the logarithmic view, the overall shape is a steady ramp between 100 Hz and 10 kHz from 103 to 122 dBFS re: 1 Pa per square-root-hertz. It then falls off to 104 dB at 16.5 kHz, then increases to 107 dB.
A-Weighted SNR at 1 kHz 78 ± 3 dBA re: 1 Pa

Maximum Sound Pressure Level

The maximum sound pressure level (max SPL) represents the loudest sound a given recorder and microphone can record without clipping. This measurement is typically provided at 1 kHz, but it will vary across the frequency spectrum based on the microphone sensitivity. If a microphone is more sensitive at 2 kHz than at 1 kHz, then the max SPL will be lower at 2 kHz than at 1 kHz.

Table 2. SM5 Acoustic Stub Microphone Max SPL at 1 kHz with and without Preamplifier
Max SPL at 1 kHz, Preamp Disabled, 0 dB Gain 122 ± 3 dB SPL
Max SPL at 1 kHz, Preamp Enabled, 0 dB Gain 96 ± 3 dB SPL

Directionality

Directionality indicates how the sensitivity of the microphone changes depending on the incoming angle of the sound. Directionality depends on frequency, so it is measured at multiple different test frequencies. The resulting plot is normalized so that 0 dB corresponds to the on-axis sensitivity of a microphone at any given frequency.

Terms like omnidirectional and cardioid refer to broad categorizations of microphone directionality, but measurements of real microphones may fall in between standard categories.

Figure 5. SM5 Left Acoustic Stub Microphone Directional Response
The directional response is generally omnidirectional, with a slight increase in directionality in higher frequencies. At 90 degrees off-axis, the 1 kHz response is down by 2 dB, and the 16 kHz response is down by 5–6 dB. The angle of lowest sensitivity is 165 degrees off-axis in the frontwards direction. At this angle, the 1 kHz response is down by 4 dB, and the 16 kHz response is down by 20–25 dB.
Figure 6. SM5 Right Acoustic Stub Microphone Directional Response
The directional response is generally omnidirectional, with a slight increase in directionality in higher frequencies. At 90 degrees off-axis, the 1 kHz response is down by 2 dB, and the 16 kHz response is down by 5–6 dB. The angle of lowest sensitivity is 165 degrees off-axis in the frontwards direction. At this angle, the 1 kHz response is down by 4 dB, and the 16 kHz response is down by 20–25 dB.