REAL subwoofers!

By Stig Erik Tangen
20 Mar 1996

Drivers

For this project I bought some custom ScanSpeak drivers (25W7564) that were produced for a loudspeaker that was not too successful on the market. Therefore, ScanSpeak sold the remaining stock for next to nothing to a Norwegian speaker-component shop, where I bought four of them for use in my own subwoofers.

Since these drivers were a custom model, they will unfortunately not be made anymore. To match their quality, it is needed to look for something really special as replacement. The brand new ScanSpeak 25W8565-01 is an excellent choice. It has different parameters than the 25W7564, but in this box the differences in frequency response will be less than +/-1 dB in the whole 15-100 Hz range. Therefore it is no danger to regard the 25W8565-01 as an equivalent driver (in this system, not necessarily in other boxes). It will even have higher max. SPL than 25W7564 (with higher input, though), partly because of a longer voice coil and slightly larger cone area.

The very satisfying sound quality from my sub-woofers is to a large extend a result of the outstanding quality of these custom drivers. Special features includes very stiff and rigid carbon fiber filled paper cone, diecast magnesium chassis, double spider, low-loss rubber surround and vented magnet system. They were designed with subwoofers in mind, and are not recommended for use above 150 Hz. The same attributes are valid for the 25W8565-01, except for the double spider. The 25W8565-01's cone is even stiffer than on the 25W7564.

ScanSpeak 25W7564 driver parameters
Fs: 27 Hz
Qe: 0.32
Qm: 3.78
Qt; 0.29
Sensitivity: about 89,5 dB
Re: 6.8 ohms
Vas: 97.3 l
Sd: 298 sq. cm

ScanSpeak 25W8565-01 driver parameters
Fs: 19 Hz
Qe: 0.35
Qm: 5.91
Qt; 0.33
Sensitivity: about 88.5 dB
Re: 5.5 ohms
Vas: 222 l
Sd: 333 sq. cm

Recommended driver mods:

• Blocking the semi-resistive vents around the magnet to avoid air leakage and noise.
  
• Make the chassis stiffer by adding 'Plastic Padding' to it.

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