Using a professional electrinic solution
I would recommend using a high quality electronic crossover with active subs if you play music with extreme low frequency content.
Originally Posted by garmtz
a) you can select crossover frequency and slope to suit the room and your main speaker placement and the capabilities of your main speakers.
b) by removing the heavier bass component from the main loudspeakers with a good high slope crossover at greater than 6dB/8ve you significantly reduce the power demand on both the main speaker and it's amplifier, allowing higher playing volumes before distortion. This has the additional advantage of reducing intermodulation distortions.
I have B&W 12" subs which have their own electronic (low level) crossover built in. I discovered that my Monitor 30s sounded worse with the B&W crossover in circuit than when they were fed directly. So I installed a quality electronic crossover.
My crossover is to my ears acoustically transparent both to the filtered (75Hz @18dB/8ve*) music minus low bass fed to the M30s, and to the (75Hz@12dB/8ve*) bass fed to the subs which, whilst sounding impressive on thunderously huge orchestral works never impinge on the enjoyment of a string quartet or piano solo, or voice. They did take a little setting up though but it's worth the time and effort as they integrate really quite well!
*The crossover slopes are different for the HF and LF as the B&W has a low pass filter built-in.
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