Systems ListDIYB&C 21-IPAL Dual Opposed Sealed

System typeSealed
DriverB&C Speakers 21-IPAL
Driver Size21 "
Number of drivers2
Internal volume5.5 ft3
External volume8 ft3
Dimentions (Width Height Depth)24 " 24 " 24 "
Weight180 lbs


This system is comprised of a pair of B&C 21-Ipal drivers, mounted dual opposed, in a 24" cube. This cab was originally tested with a pair of B&C 21SW152-4 drivers with decent results. The reason this cabinet was used to test the 21-Ipal drivers is mostly due to issues with getting enough amplifier on them to reach their limits. The drivers present a very low impedance, dipping below 1ohm in some parts of the frequency bandwidth. It is very difficult to find an amplifier capable of producing enough power into such an impedance. In this case two drivers are wired in series to present a 2ohm load, which is a bit better fit for the K20 amplifier used, but it really isn't designed to produce optimum results into an impedance that low when bridged. Regardless, what data was collected confirms that, while the amplifier still fell a bit short of reaching clear limits of the 21-Ipal drivers, it seems to have gotten close for the most part and has provided enough data to make some conclusions about the drivers finally. Based on the data from B&C the 21-Ipal drivers should be capable of 3 to 4dB more deep bass output. This appears to be confirmed with this test. The distortion performance is excellent considering the tiny air volume and the driver excursion levels. The compression performance was also exemplary based on the data prior to the amplifier running out of juice. The sensitivity and overall response shape was as expected given the driver design and the small sealed cab. Overall headroom capabilities, based on the burst output and max long term output, are very strong especially considering the size of the system. It is a very power dense 24" cube. The output above 40Hz is among the top systems that have been tested. 4 of these drivers could be wired in series and put on a large bridged amplifier but only the biggest touring grade amplifiers will have enough power to make use of 4 of these drivers full capabilities.  If only these drivers were available in a 2ohm or 4ohm configuration it would be much easier to power 1 or 2 of them properly.