Reading Loudspeaker Frequency Response Curves: What to Check Before Comparing
Check frequency range definitions, test conditions, smoothing and windowing before using loudspeaker response curves to compare system proposals.
Before comparing two loudspeaker frequency response curves, check how both were measured and displayed. A smooth line or a wide frequency range is not enough to establish that one system is the better choice for your venue. Ask for the measurement context, then connect the evidence to your application.
1. Read the definition behind the frequency range
A frequency range needs a level criterion. Is the quoted endpoint a cut-off below a reference level, or is the specification describing variation within a stated band? Genelec's glossary, for example, distinguishes cut-off points from passband response tolerances and describes its frequency response measurements on the acoustic axis in free-field conditions. This is a manufacturer's documented approach, not an assumed definition for every supplier. Source: Genelec Technical Glossary.
For a quotation comparison, ask each supplier to state the reference level, tolerance and applicable frequency band. Leave an unclear field marked “not specified” until it is explained. Do not silently treat different definitions as equivalent.
2. Identify the system and measurement conditions
The public description of IEC 60268-21:2018 concerns acoustic output measurements of electroacoustic systems, including passive and active systems with processing. It separates physical measurement from evaluation of perceived sound quality. A response chart should therefore be treated as one part of the evidence, rather than a complete listening verdict. Source: IEC 60268-21:2018 public description.
Ask what was actually measured: a single cabinet, several cabinets, or a complete system with subwoofers. Request the microphone distance and angle, measurement environment, input level, amplifier and DSP preset. If two charts describe different configurations, first decide whether either configuration matches the proposed installation.
3. Check smoothing and graph scales
Rational Acoustics distinguishes spectrum banding from transfer-function smoothing: they process different kinds of measurement data differently. Its explanation also shows how smoothing can suppress narrow response features and make broad trends easier to see. Two traces displayed with different smoothing settings may therefore look more different, or more similar, than a fair comparison would suggest. Source: Rational Acoustics, Banding Vs. Smoothing.
Request the measurement type, smoothing setting and labelled horizontal and vertical scales. Use matching scales when reviewing charts side by side. This makes the display easier to interpret, but does not make different measurement conditions equivalent.
4. Ask what the measurement window excludes
Time-window choices matter when separating direct sound from later arrivals. Rational Acoustics explains that its FTW smoothing emulates time-windowing and can exclude reflections, while a shorter effective window limits low-frequency resolution. Ask which windowing method was used and where the resulting trace is considered valid. Do not assume that a visually clean trace provides equally reliable information across its entire displayed range. Source: Rational Acoustics, What is FTW Smoothing?.
5. Request a comparison record
The following is a practical purchasing checklist, not a substitute for a test standard. Send the same questions to each supplier and keep the answers beside the charts.
| Record | Ask the supplier to identify |
|---|---|
| Product and configuration | Model, cabinet count, subwoofers and the system represented by the trace. |
| Range definition | Reference level, tolerance, cut-off criterion and frequency band. |
| Measurement conditions | Environment, microphone distance, acoustic axis or off-axis angle, and input level. |
| Signal chain | Amplifier, processing, preset version and enabled filters. |
| Chart processing | Measurement type, smoothing, windowing, valid frequency limits and graph scales. |
| Further evidence | Available output-level, distortion and coverage information, with their own test conditions. |
Use the evidence to develop a system proposal
For a house of worship or a live event, start with the audience layout, programme material and operating requirements. Use our sound system brief checklist to organise these details before narrowing the product selection.
When approaching YASHWEI, include the proposed application and the evidence you need to evaluate it. Discuss your system requirements. Model-specific data and available documentation should be confirmed for the proposed configuration.