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External crossovers for subs

This might be a stupid question but I'm asking anyway.  I have two subs connected via Speakon connectors so they get fed the same signal as my stand mounts.  I think I've gotten the subs and mains integrated very well (at least for my tastes).  I've read here, on several occasions, that sub integration cannot be done properly without an external crossover to take send only the appropriate frequencies to the mains and to the subs.  So, what is the difference between an external crossover filtering out frequencies and the internal crossover of the speaker filtering out low frequencies that the speaker cannot play?  Can't an internal speaker crossover be built to filter out frequencies below the threshold of that which is suitable for the speaker design?  Isn't that what crossovers do within the speaker by sending high frequency signals to the tweeter and low frequencies to the woofer?  Why would it not be able to filter out frequencies beyond the capability of the woofer?

128x128jastralfu
mijostyn's avatar
mijostyn
8,570 posts
 

@jastralfu  1/2 the advantage of using a subwoofer comes from filtering out the low bass from the main speaker which lowers distortion in the main speaker. This requires a complete two way crossover. The simple low pass filter that comes with most commercial subwoofers is an unsatisfactory cheap solution.

Blending a subwoofer into a system requires more than just frequency management, it also requires time and phase management. This can only done accurately in the digital realm. The best solution is a digital preamp such as made by Anthem, Trinnov, MiniDSP and DEQX. MiniDSP also makes a crossover. 

For most people an analog solution is much less expensive and more practical. The easiest thing to do is put a series capacitors on the inputs of your main amp. This requires knowing the amps input impedance. The value of the capacitor needed to roll of the amp at any given frequency at 6 dB/oct can be easily calculated, the formula is online. Then you use the low pass filter in the subwoofer. 

james633
1,026 posts
 
  • Jastraflu,

The subs internal is just a low pass. To better integrate and take full advantage of the sub a highpass is added to the speaker. The active crossovers are doing both highpass and low pass.

I have messed around with just using a low pass, thought it was pretty good then added a highpass and it was instantly better, not a little better but drastically better.

mashif
244 posts
 

I recently went that route with a HPF from Merchand Electronics. It's 24db/oct at 80hz. Its a vast improvement in bass control and essentially turns my 3 way speakers into 4 way. Once I heard the result I added a 2nd Sub. I have a small room and chose the SVS SB1000 for their size and the great phone App for setup and tuning.  

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