Systems List › DIY › B&C 21SW152-4 25Hz Ported
The response has a roughly 3db peak at the vent tuning at 25hz but this is flattened out with the addition of a 25Hz high pass filter. At high output levels vent compression also reduces this peak, despite using a 10" diameter pipe wih a 1" round over on both ends. A 25hz steep high pass filter was engaged to prevent excessive cone excursion below the tuning and also flattens out the peak at tuning.
The maximum long term and short term output both are very high at 25hz and above. There is even a large amount of output at 20hz still which is below tune substantially. There was a slight tapping or over excursion sound that developed near 30-35hz at the loudest levels. There was some grill buzz evident but no noticeable vent noise at the highest output levels achieved. The compression performance for this system is also quite good even at the highest power levels used. Notable vent compression is in evidence though, plus this is an area of high power and low excursion for the driver so it is usually a double whammy for reflex systems. The distortion performance is also very good up until the final nominally 127db output sweep where the driver seemed to hit over excursion briefly near 32hz. Even at the 125db nominal sweep level the THD was below 10% everywhere above 18Hz! The THD skyrockets below the tuning which is typical of resonant systems.
A great all around performance in the 20-120hz range. If the tuning had come in closer to 30hz as was intended the output and efficiency would have been even higher but 20 to 25hz output and extension would have been sacrificed in the process. Overall this system measured remarkably well for a standard bass reflex design and had superb output from 20Hz on up. The compression performance was also good considering that one driver was absorbing power levels in excess of 5,000 watts at some points.