Testing a New Speaker Cabinet

Testing a new speaker cabinet takes six checks, in order: DC resistance, impedance sweep, polarity, low-level listening, leaks and buzzes, then a staged level increase behind a high-pass filter. Each one catches a fault the others miss, and every one is cheaper in the workshop than at a dance.

Kit

• Multimeter with a resistance range
• Test tones: signal generator, tone app or sweep files
• Optional: impedance measurement software and a suitable interface
• A small amplifier you can run at low level, and a DSP or processor with a high-pass filter
• Ear protection

1. DC resistance

Disconnect the cab from any amplifier and meter across pins 1+ and 1− of the input. A multimeter reads the coil's DC resistance (Re), not its impedance, so an 8 Ω driver reads below 8 Ω, typically 5 to 7 Ω. Two 8 Ω drivers in parallel should read half that. Near zero means a short; open circuit means a broken joint or a failed coil. Check the link socket too. More in testing a driver with a multimeter.

2. Impedance sweep and tuning check

Impedance against frequency is the most useful single measurement on a new box: it shows whether the cab is tuned where the design says.

• Reflex: two peaks with a minimum between them. That minimum sits close to the box tuning, Fb.
• Sealed: one peak, above the driver's free-air Fs, because the enclosed air adds stiffness.
• Scoops and horns: a more complex curve. Compare with a known good cab of the same design, or the plan's published curve.

Extra small peaks or a smeared curve point to air leaks, panel resonances or loose parts. Cabs built to the same plan with the same driver should overlay closely. Background: cabinet tuning and Thiele/Small parameters.

No measurement kit? A slow sine sweep at low level still finds Fb on a reflex box: cone movement drops to a minimum and port air velocity peaks at the tuning frequency.

3. Polarity

Every cab must move air the same way for the same signal, or adjacent boxes cancel. See phase and polarity.

Battery test (bass drivers only)

Cab disconnected from the amp, touch a 1.5 V or 9 V battery across the input briefly: positive to 1+, negative to 1−. The cone should move out. If it moves in, the wiring is reversed. Momentary contact only, and never on tweeters or compression drivers.

Pulse polarity checker

A sender plays a pulse through the system and a receiver reads each box. It works on any driver type and on a full rig. If pins need correcting, see Speakon wiring.

4. Listen at low level

Amp gain right down, music and tones quiet. Listen for:

• scraping or rubbing: a damaged driver or uneven mounting;
• rattles: loose screws, grilles, handles, or wiring slapping a panel;
• one cab sounding different from its twins.

5. Leaks and buzzes

Step a sine tone slowly through the bass range at moderate level. Run a hand along every joint, round the driver, input plate and handles. A leak feels like a draught and sounds like a hiss or chuff. Seal, tighten, repeat. To trace a buzz, press on panels and fittings while the tone plays; when it stops, you have found it. Fixes: bracing and sealing cabinets.

6. Bring the level up in steps

Only after every check passes. Set a high-pass filter to suit the cab first: below a reflex box's tuning the cone is unloaded and excursion rises fast for little output. Watch and listen for bottoming or distortion and stop at the first sign. Ear protection on, and warn anyone nearby.