Speakers: types, sensitivity, impedance

A sealed box extends less deeply for a given volume but rolls off gently (12 dB/octave) with a dry, small-room-friendly bass. A ported design typically buys 5 to 10 Hz of extension and 3 dB of bass efficiency, at the cost of a steeper 24 dB/octave slope and a port resonance that can excite room modes.

Practical rule: below 20 m², a sealed box or a ported design tuned high (port around 45-55 Hz) avoids bloated bass. Above 30 m², a low-tuned port becomes genuinely useful or the bass sounds thin.

Transmission lines and horns work, but demand serious placement freedom: pick them only if you are willing to optimise the room around them.

Sensitivity (dB/2.83 V/1 m) tells you the level produced for a given voltage. Every 3 dB lost doubles the power needed for the same level, so an 85 dB speaker asks roughly four times the power of a 91 dB one.

Useful figure: for 95 dB peaks at 3 m, an 88 dB speaker wants about 50 to 100 W per channel with headroom to spare. Below 86 dB, look for current delivery rather than paper watts.

Beware sensitivity quoted at 1 W/1 m into 4 ohms: it looks 3 dB better than the same speaker measured at 2.83 V.

Nominal impedance (4, 6 or 8 ohms) says little about difficulty. What matters is the minimum impedance, the frequency where it happens, and the electrical phase. A 3 ohm dip around 100 Hz hammers the amplifier's power supply.

Tube amps and low-current class A or D designs prefer a load staying above 6 ohms. An amplifier that nearly doubles its power from 8 to 4 ohms has the current reserve demanding loads require.

An amp running unusually hot, tripping protection, or hardening the upper midrange at volume almost always signals a load mismatch, not a speaker fault.

Rule of thumb: a single 17-18 cm woofer per side covers up to 20-22 m². Between 22 and 35 m², aim for twin 16-17 cm woofers or one 20-22 cm. Beyond that, real 35 Hz capability without compression becomes legitimate.

A speaker too large for the room cannot be fixed downstream: modes excite the bass and the only cure is distance from the walls, often impossible. A well-placed bookshelf on a rigid stand routinely beats a floorstander jammed into a corner.

The stand is part of the speaker: enough mass, decoupling from the floor, and the tweeter at seated ear height (85-100 cm) are non-negotiable for a bookshelf.

Allow 30 to 60 hours for new suspensions to settle: bass loosens and the upper midrange relaxes. Do not pass final judgement on the first evening.

Verify absolute phase on both speakers: one inverted channel literally hollows out the stereo centre. A mono signal must produce a perfectly centred, compact voice.

Torque the binding posts, re-check driver screws after a few weeks, and remove the grilles for critical listening — they usually cost 1 to 2 dB in the treble.