Speaker driver (loudspeaker transducer) for professional and commercial sound

01

Read the power rating and size the amplifier

B&C states its nominal power handling is measured to AES2-1984: the driver is run for two hours with pink noise of crest factor 2 (6 dB) filtered to its working range (B&C: "a 50-500 Hz range is typical for woofer testing"), cone drivers in free air and compression drivers on their recommended horn. Power is calculated from the RMS voltage and the minimum impedance in the working range, and the driver must still work without permanent change in performance. [1]

Because musical programs have a crest factor that B&C says "is commonly 12 dB or more", B&C specifies a continuous program power handling of double the nominal rating as a recommended amplifier power, and warns that if the amplifier is driven into frequent clipping it should be smaller than the nominal rating. [1] EAW's application note describes the AES method as one-octave pink noise with rating at two hours without more than 10% permanent change, and explains that its own test instead uses the real enclosure, full-range weighted noise and the average rather than minimum impedance, which it calls more conservative, although the same note writes the formula as P = V²RMS / ZNOMINAL; it rates power 40 to 60 W below the level that destroyed the driver or crossover parts, and it also warns that clipping raises RMS level and heating. [4]

Editorial calculation: for B&C's 15TBX100 (1,000 W nominal, 6.2 Ω minimum impedance), 1,000 W corresponds to about √(1,000 × 6.2) ≈ 79 V RMS; the same voltage into its 8 Ω nominal impedance is about 775 W, which shows why the impedance used in the calculation changes the stated watts. At 6 dB crest factor the peak voltage is twice RMS, about 157 V. [3] [1] [4] Ask suppliers which standard, bandwidth and impedance their rating uses before comparing watts.

Give the supplier the application (PA, installed sound, horn, subwoofer), nominal impedance, required power and sensitivity, frequency range, cabinet type and volume or tuning if fixed, size and mounting (cutout, bolt circle, depth), environment (outdoor, humidity), and the datasheet and power test method required.

02

Read Thiele-Small parameters and excursion limits

B&C explains that Thiele-Small parameters describe a driver in the small-signal domain but say little about its large-signal limits, which are given by Xmax, the maximum linear excursion. B&C writes that "In a typical measurement, this value corresponds to a maximum of 10% total harmonic distortion (THD) with a sinusoidal signal", and that it now provides a linear mathematical Xmax instead of a measured one; its additional Xvar is the excursion at which force factor Bl or suspension compliance Cms falls below 50% of its small-signal value. [2]

B&C's 15-inch 15TBX100 lists Fs 35 Hz, Re 5.1 Ω, Qes 0.3, Qms 5.2, Qts 0.28, Vas 113 dm³, Sd 855 cm², Mms 163 g, Bl 25.5 Tm, Xmax 9 mm, Xvar 11 mm and EBP 117 Hz, with a recommended enclosure of 114 dm³ tuned to 35 Hz, a 100 mm copper voice coil on glass fibre, a ventilated gap for reduced power compression and a waterproofed cone. [3]

Editorial calculation: EBP = Fs / Qes = 35 / 0.3 ≈ 117 Hz, and Qts = Qes × Qms / (Qes + Qms) = 0.3 × 5.2 / 5.5 ≈ 0.28, both matching the datasheet; the swept volume at Xmax is Sd × Xmax = 855 cm² × 0.9 cm ≈ 770 cm³. Taking the 96 dB sensitivity as 1 W at 1 m (the B&C page does not state the reference), 1,000 W is +30 dB, so about 126 dB at 1 m before power compression and enclosure gain. [3] Use the full parameter set in an enclosure simulation rather than a single number.

03

PA horn driver units and large-cone pro bass drivers: what Pearller and Surpass list

The two maker pages kept on this page show the split the scope covers: Pearller lists driver units for PA horn speakers, and Surpass lists subwoofer, bass, midrange, high-frequency and tweeter drivers for professional loudspeakers. Neither page carries an AES2 power test description or a full Thiele-Small set, so ask for both, with Xmax and Xvar, before comparing their units with the B&C figures above.

04

Voice coil, ferrite motor, cone and suspension of a 15-inch LF driver

Part values below are those B&C gives for the 15TBX100.

05

Impedance, sensitivity and Thiele-Small values a driver datasheet should state

The 15TBX100 values show what one complete pro-audio driver datasheet contains; rows without a value are ones the reviewed sources do not state.

06

Send the application, cabinet and datasheet needs together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Application: [PA; installed; horn; subwoofer]
Electrical: [impedance; power; sensitivity]
Acoustic: [frequency range; cabinet volume; tuning]
Mechanical: [size; cutout; bolt circle; depth]
Environment: [indoor; outdoor; humidity]
Documents: [power test method; T-S parameters; Xmax and Xvar]

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