How to Use a Real Time Analyzer to Set Crossover Points
A real time analyzer (RTA) can make loudspeaker crossover adjustment far more controlled than listening by ear alone. It shows the energy arriving at the microphone across the audio spectrum, helping you identify where a woofer and compression driver overlap, separate, or leave a gap. Used carefully, it is valuable for both passive crossover design and active DSP setup.
The display is not a direct instruction to move a filter to every visible peak or dip. Room reflections, microphone position, driver sensitivity, horn loading and measurement smoothing all influence the graph. The goal is to find a stable acoustic transition, then confirm it with phase, impulse and listening tests.
| Measurement approach | Best use | Main limitation |
|---|---|---|
| RTA with pink noise | Fast overview of tonal balance and overlap | Room modes and reflections can mislead |
| Swept sine or gated response | Accurate driver roll-off and crossover region | Slower and more setup-sensitive |
| Nearfield measurement | Low-frequency woofer integration | Cannot represent the listening position |
| Transfer-function measurement | Phase, delay and acoustic summation | Requires a suitable interface and software |
Prepare A Reliable Measurement Chain
Use measurement software with an RTA or spectrum display, a calibrated measurement microphone, an audio interface and a stable loudspeaker position. Place the microphone on the main listening axis, normally at the height of the compression driver, and point it according to the microphone manufacturer’s calibration file. Disable automatic room correction, tone controls and loudness processing before taking readings.
In an Australian living room, the measurement environment may be an open-plan space in Sydney, Melbourne or Brisbane, with hard floors, glass and nearby walls contributing strong reflections. Begin with the microphone about one metre from the loudspeaker for crossover work, rather than treating a sofa-position measurement as the only reference. Keep the level moderate and protect high-frequency compression drivers from excessive test noise.
Read The RTA Correctly
Pink noise is useful because it distributes equal energy per octave, but the RTA display may use different weighting or resolution settings. Use logarithmic frequency scaling, a sensible averaging time and moderate smoothing, such as one-sixth or one-twelfth octave, to reveal broad trends without erasing the crossover behaviour. Slow averaging helps stabilise the trace when the room or signal is variable.
A sharp notch is rarely a reason to redesign the crossover immediately. It may be caused by a reflection, microphone interference or a room cancellation. Look for repeatable slopes: the woofer should reduce output as frequency rises, while the horn driver should become increasingly useful above its passband. Measure each section separately at the same gain and microphone position before measuring them together.
Find The Acoustic Crossover Region
Disconnect or mute the high-frequency section and record the woofer response. Then reverse the process for the compression driver and horn. The useful crossover region lies where both drivers have adequate output, acceptable distortion and a safe operating margin. It is the acoustic overlap, not simply the nominal electrical filter frequency printed in a design document.
For example, a woofer with a 1 kHz electrical low-pass may still produce substantial output above 1 kHz, while a compression driver set to 1 kHz may have a very different acoustic slope because of the horn and diaphragm. A crossover point around 800 Hz, 1.2 kHz or 1.5 kHz should therefore be judged from the measured acoustic responses. The bi-radial horn design also affects directivity and the way energy reaches the microphone.
Set Levels And Filter Slopes
Match the output levels of the two drivers before judging the crossover shape. If the horn is several decibels more sensitive than the woofer, lower its level with an attenuator, amplifier gain adjustment or DSP output trim. A level mismatch can make an apparently smooth crossover look like a steep step, or hide an integration problem beneath excessive energy from one section.
Change one variable at a time. Try the intended filter slope, then inspect the combined response. A fourth-order acoustic transition often provides useful control, but a second-order network may be appropriate when driver roll-off, polarity and directivity already support it. A smooth amplitude trace is desirable, though a small broad rise can be preferable to a narrow cancellation that only disappears at one microphone location.
Account For Horn And Room Behaviour
Horn-loaded systems can maintain high sensitivity and controlled dispersion through the crossover region, but their response is strongly shaped by mouth size, flare profile, driver diaphragm behaviour and cabinet geometry. The microphone must be on the intended listening axis. Moving it vertically or horizontally can change the balance around the crossover as the directivity of the woofer and horn diverges.
At low frequencies, room modes dominate what an RTA shows. A measurement in a Perth apartment may produce very different bass peaks from one in a large Adelaide listening room, even with the same loudspeaker. Do not use a single room peak to choose the woofer’s electrical cutoff. Use multiple positions or a close measurement for bass, then assess the listening-area average for final equalisation.
Verify Phase And Timing
An RTA displays magnitude, but it does not reliably show whether the drivers arrive in phase. Use an impulse response or transfer-function measurement to estimate acoustic delay between the woofer and compression driver. Time alignment is especially important in a passive loudspeaker, where physical driver placement and network topology determine the relative arrival time.
Test normal and reversed polarity when the system permits it. A deep null with reversed polarity can indicate good acoustic overlap and a suitable delay relationship; a shallow change suggests that the filters, timing or measurement conditions need attention. Restore the correct polarity and choose the setting that produces strong, even summation without an artificially narrow listening window.
Apply Recommendations For Repeatable Results
Keep a written record of microphone position, amplifier gain, filter settings, polarity, smoothing and measured levels. Repeatability matters more than a spectacular single trace, particularly when comparing a custom loudspeaker system in a Berlin demonstration room with its eventual installation in an Australian home.
Use the following practices when setting crossover points:
- Calibrate the microphone and interface before measuring.
- Measure each driver separately before evaluating the combined response.
- Use moderate smoothing and average several readings.
- Set levels before changing crossover frequency or slope.
- Check phase, polarity and timing after every major filter change.
- Confirm the final setting with familiar music at a safe listening level.
Listening remains the final check. Voices should stay centred, cymbals should sound clean rather than aggressive, and bass transients should connect naturally with the lower midrange. Australian high-end buyers may compare systems at a local dealer, a Melbourne audio show or a dedicated home room, so the best crossover is the one that remains coherent across realistic positions and recordings rather than the one that produces the flattest graph at a single point.