Question 1

How do I use a spectrum analyzer to find the source of a hum or buzz?

Accepted Answer

Electrical hum shows as a sharp peak at the mains frequency (50 Hz in most of the world, 60 Hz in the Americas) and its harmonics. A pure 50/60 Hz fundamental with weak harmonics suggests magnetic interference (transformer coupling). Strong even harmonics (100/120, 200/240 Hz) indicate a ground loop. Odd harmonics suggest rectifier noise from a power supply. A buzz (rich in harmonics up to 1 kHz or higher) usually points to a lighting dimmer or LED driver. To locate the source: check if the hum changes when you disconnect audio cables one by one, switch off circuits one at a time, or move cables away from power lines. SonaVyx hum detector automatically identifies 50/60 Hz harmonics and analyzes the harmonic pattern to suggest whether the cause is a ground loop, magnetic pickup, or power supply issue.

Question 2

Can I use a spectrum analyzer for HVAC noise assessment?

Accepted Answer

Yes, spectrum analysis is the standard method for HVAC noise assessment. HVAC noise has characteristic spectral shapes: broadband rushing noise from air velocity over diffusers, low-frequency rumble from fan motors and duct resonance, tonal noise from fan blade pass frequency (BPF = RPM/60 × number of blades), and duct breakout noise. Measure the octave-band spectrum (63 Hz to 8 kHz) with no other noise sources active and compare against the NC (Noise Criteria) or RC (Room Criteria) curve specified for the space. The octave band where the measurement first exceeds the NC curve identifies the dominant frequency range to treat. SonaVyx RTA mode with 1/1 octave display and NC curve overlay directly shows compliance or identifies the problem bands.

Question 3

How do I use spectrum analysis to optimize equalization?

Accepted Answer

Play pink noise through the system and capture the spectrum at the listening position using RTA mode with 1/3 octave resolution. Pink noise has equal energy per octave, so the RTA display directly shows the system frequency response. Compare the measured response against your target curve (flat, house curve, or other). Identify bands that deviate by more than ±3 dB from the target. Apply EQ cuts for bands above the target and gentle boosts for bands below. Re-measure after each adjustment. Focus on the 200 Hz to 8 kHz range first. For more precise EQ, switch to transfer function mode with the console output as the reference, which gives a cleaner measurement immune to ambient noise. SonaVyx crosshair readout shows exact frequency and level values for precise EQ setting.

Question 4

How do I use a spectrum analyzer for machinery noise diagnostics?

Accepted Answer

Machinery noise has predictable spectral signatures tied to rotational speed. The fundamental frequency equals RPM/60. Harmonics indicate: 1× (unbalance or misalignment), 2× (misalignment, looseness), blade pass frequency (number of blades × RPM/60), gear mesh frequency (number of teeth × RPM/60), and bearing defect frequencies (specific to bearing geometry). Use a high-resolution FFT (16384 or 32768) to resolve individual harmonics. Track the spectrum over time to detect degradation (a bearing developing a fault shows increasing energy at its characteristic frequency). SonaVyx order analysis feature maps the spectrum to multiples of a reference frequency, making it easy to identify which harmonics are present and whether they correspond to specific mechanical faults.

Question 5

Can spectrum analysis help identify rattles and resonances?

Accepted Answer

Yes. Rattles appear in the spectrum as broadband burst energy at specific frequencies where the exciting vibration exceeds the mechanical threshold of a loose component. Play a slow sine sweep while watching the spectrum: a rattle will produce broadband noise (harmonics and sub-harmonics) that appears suddenly at the resonant frequency and disappears as the sweep moves past. Structural resonances show as sharp peaks at the natural frequency of a panel, fixture, or component. To identify the source, touch suspect surfaces while monitoring the spectrum — if a peak diminishes when you dampen a surface, you have found the resonating element. SonaVyx spectrograph view is particularly useful for this because it shows the time history, making it easy to correlate rattle onset with the sweep frequency.

Question 6

How do I measure background noise spectrum for acoustic design?

Accepted Answer

Measure with all intended noise sources active (HVAC, equipment) and no transient sources (speech, closing doors). Use the SPL meter with octave band analysis and slow time weighting. Measure for at least 30 seconds to get a stable Leq per band. Record the 1/1 or 1/3 octave band levels from 63 Hz to 8 kHz. Compare against the appropriate criterion: NC curves for commercial spaces, RC curves for thermal comfort zones, or NR curves for European standards. Measure at 3 or more positions at seated ear height, 1 m from walls. Report the arithmetic average of the positions. If the HVAC system cycles, measure during the loudest phase. SonaVyx RTA with NC curve overlay provides instant visual comparison, and the SPL mode logs the data for export and reporting.

Question 7

How do I use spectrum analysis to check for electrical interference?

Accepted Answer

Electrical interference appears as discrete tones or modulated noise at specific frequencies. Common signatures: 50/60 Hz mains hum and harmonics, GSM mobile phone interference (217 Hz buzz from TDMA), Wi-Fi router noise (spikes at varying frequencies), switching power supply whine (typically 20-50 kHz, often audible as intermodulation products), LED dimmer buzz (harmonics of mains × dimmer frequency), and USB bus noise (1 kHz and harmonics). To isolate the source: disconnect equipment one at a time while monitoring the spectrum. Use SonaVyx with the microphone directly monitoring the audio chain (via a DI box or line input) rather than acoustically, to hear what is in the electrical signal before it reaches the speakers. The hum and problem detectors flag common interference patterns automatically.

Question 8

Can I use a spectrum analyzer to verify speaker crossover behavior?

Accepted Answer

Yes. Measure each driver individually (cover or disconnect the other drivers) and compare the spectra. Each driver should roll off at the crossover frequency according to the crossover filter slope. Typical slopes: 12 dB/octave (2nd order), 18 dB/octave (3rd order), 24 dB/octave (4th order). The acoustic rolloff includes both the electrical filter and the driver natural rolloff, so the actual slope may differ from the electrical crossover setting. Compare the low-pass and high-pass responses: they should cross at the -6 dB point for a maximally flat summation (assuming in-phase, same polarity). If the crossover frequency is incorrect, the crossover region will show a dip or peak when both drivers play together. SonaVyx multi-trace overlay lets you view each driver individually and the combined response simultaneously.

Spectrum Analyzer Applications: Noise Diagnostics, HVAC, Machinery, and System Tuning

Frequently Asked Questions