Sunship Audio

Measuring Loudspeaker Response at One Metre and Two Metres

Frequency-response measurements are strongly influenced by microphone distance. Moving from one metre to two metres may appear to be a minor change, yet it alters the balance between direct sound, room reflections, driver integration and measurement noise. The result can be a different-looking graph from the same loudspeaker in the same room.

For horn-loaded loudspeakers, measurement distance deserves particular care. A compression driver, wooden horn and woofer may have different acoustic centres and radiation patterns, while a passive crossover is designed to combine them correctly at a listening position. Understanding what changes with distance helps separate the loudspeaker’s behaviour from the room and the measurement method.

What Distance Changes In The Sound Field

In an ideal free-field measurement, doubling the distance reduces sound pressure by approximately 6 dB. A tone measured at one metre will therefore be considerably louder than the same tone measured at two metres, unless the measurement system compensates for level. This inverse-square relationship applies most clearly when the source radiates into open space and the microphone remains within the loudspeaker’s intended coverage angle.

Distance also changes how the microphone sees multiple drivers. At one metre, the woofer and compression driver are observed from a relatively close position, so small differences in acoustic path length can affect the response around the crossover region. At two metres, those path-length differences represent a smaller proportion of the total distance, and the summed response may appear smoother if the system has been time-aligned correctly.

The effect is particularly relevant to large bi-radial horns. Their controlled directivity can maintain a consistent tonal balance over distance, but the microphone must be placed on the acoustic axis. A small vertical or horizontal movement may expose the edge of the coverage pattern, changing the treble response more than the extra metre itself.

Nearfield Detail And Farther-Field Context

A one-metre measurement is useful when the goal is to inspect the loudspeaker as a device. It reduces the proportion of reflected sound arriving at the microphone and produces a stronger direct signal relative to the room. This is convenient in a domestic listening room in Sydney or Melbourne, where ceiling, floor and sidewall reflections can arrive only a few milliseconds after the direct sound.

At two metres, the test begins to resemble normal listening more closely. The microphone captures a more integrated wavefront and gives the crossover, horn and woofer greater distance to combine acoustically. This can be valuable for a system with a first-order passive network, where driver overlap and phase behaviour contribute strongly to the measured result. The explanation of crossover slopes provides useful context for interpreting that region.

A longer distance does not automatically produce a more truthful graph. In a typical Australian home, the microphone may be closer to a rear wall, timber floor or low ceiling than the loudspeaker’s designer intended. The measurement then contains both direct sound and early reflections, which can create comb filtering: a series of peaks and dips caused by the two paths arriving out of phase.

Preparing A Reliable Measurement

The measurement position should be defined precisely. Place the microphone on the central listening axis at the chosen height, use a calibrated microphone file, and keep the loudspeaker and stand in the same position for every comparison. Record the sound-pressure level as well as frequency response, because a two-metre trace displayed at the same vertical scale may otherwise be mistaken for a tonal change.

A time-windowed or gated measurement can suppress later room reflections, although the lower frequency limit becomes less useful as the window shortens. A 5-millisecond window may provide meaningful information only above roughly 200 Hz, depending on the software and room. Bass response below that region should generally be assessed with nearfield techniques, ground-plane measurements or carefully interpreted in-room sweeps.

Useful controls before comparing distances include:

Outdoor measurements are attractive in parts of Australia because of large blocks and quieter surroundings, but wind, heat and nearby hard surfaces can still affect the result. In Perth or regional areas, a paved driveway may behave as a strong acoustic reflector; in Brisbane, ventilation noise and open windows can add low-level broadband sound. Controlled indoor work is often more repeatable than an improvised outdoor test.

Horns, Directivity And Listening Distance

A conventional small loudspeaker may broaden its radiation at low frequencies and narrow it at high frequencies. A horn-loaded system is deliberately more controlled through much of the midrange and treble. This means the response at one metre can remain closer to the response at two metres than it would with a wide-dispersion design, provided both measurements stay inside the horn’s coverage pattern.

The listening room still matters. At one metre, direct sound dominates, making it easier to examine compression-driver smoothness, horn resonances and crossover handover. At two metres, the room contributes more energy, while the loudspeaker’s directivity determines how much of that energy reaches the walls. A well-designed horn can reduce the difference between direct and reflected tonal balance, which is valuable in large rooms in Adelaide or open-plan spaces common in newer Australian houses.

Dynamic material can expose another distinction. A frequency sweep is continuous and relatively predictable, while music contains changing peaks and averages. Orchestral recordings, for example, can show how headroom and radiation pattern interact during quiet strings and powerful brass; orchestral dynamics offers a practical listening perspective that a static graph cannot provide.

Choosing A Useful Measurement Distance

Neither distance should be treated as a universal industry standard. One metre is often the clearest option for engineering checks, product development and comparing individual drivers. Two metres can provide a better view of system integration, particularly when the loudspeaker is physically large or designed to be heard several metres away.

For custom loudspeakers built around compression drivers and woofers, it is sensible to keep both distances in the test record. Differences between the curves may reveal directivity changes, room influence, microphone alignment or phase interaction rather than a fault. The most informative report identifies the windowing method, smoothing, microphone position and whether the trace represents one speaker or a stereo pair.

Measurement factor One metre Two metres
Direct-to-room ratio Usually higher Usually lower
Overall sound-pressure level Higher before compensation Lower before compensation
Driver integration Useful for close inspection Often more representative of combined output
Room-reflection influence Lower, especially in a gated sweep Greater in ordinary indoor testing
Bass interpretation Still affected by room and boundaries Strongly affected by room and placement
Best use Engineering checks and direct comparison Listening-position and system-integration assessment

A practical Australian listening-room routine is to begin at one metre, then repeat at two metres on the same axis and with matched playback levels. If the curves differ substantially above the room’s modal region, investigate angle, coverage and crossover integration before changing components. If the largest differences occur below about 200 Hz, examine placement, boundaries and room modes first.

For a demonstration room such as Sunship Audio’s Berlin facility, controlled spacing helps visitors understand what belongs to the loudspeaker and what belongs to the room. The same discipline benefits a customer in Canberra, Hobart or the Gold Coast: a response graph becomes far more meaningful when its distance, timing window and acoustic conditions are clearly stated.