External crossovers for subs

Whether you filter the speakers low frequency with and internal or external crossover. It is more or less the same results assuming all things are done correctly. But for proper integration you either have to high pass the mains or low pass the subs under the main.

you can add a capacitor in line with the mains inputs. Harrison makes some cheap one you could try ($30, they sound transparent). I have used them and it works fine. It is more messing around than using an active crossover.

I have tried all the methods. Blending with no highpass with a low low pass, using capacitors to roll off the mains, an active digital solution and ended up using an active analogue solution. The integration can be fine without it but it is very doubtful it will be as good as an active system.

A couple worth trying IMO.

Sublime Acoustics K235 is a $1200 analogue solution. It has a 60 day trial period. They also have a $600 model that is about the same.

Minidsp SHD is another one that is super flexible digital option. It requires a bit of computer skills.

@james633 the subs have an adjustable low pass filter/crossover so it seems like all the filters needed are already there and using an external crossover isn’t necessary for proper integration.  Unless I misunderstood your post.

One benefit of an external crossover is that the high pass filtering is done before the signal enters the power amp. Removing low frequencies from the signal sent to the power amp results in less amp distortion, and more power for the speakers.

By the way, the problem with the Harrison filters is that to achieve the crossover frequency you want, the input impedance of the power amp must be figured into the equation that determines the capacitor value required to achieve that crossover frequency.

What make/model is your sub? Many active subs have all the active crossovers you need built in. There are pros and cons with every type of crossover filter, whether active, passive, internal, or external. There’s not a set of absolutes that apply to all situations. Proper sub integration is a variable that’s unique to each situation - the room is significant factor, as are all the settings of the low pass frequency, gain settings, any high pass settings that might be applied to your mains, along with how all that works with the rest of the system in your room. Overcoming the particulars of your room with proper adjustments is more important than the type of filter or it’s proximity to the sub. There are DIY programs that can be used to help make adjustments, or you can do it by ear to suit your tastes. There’s really no wrong way to do it if you’re happy, and aren’t damaging anything.

My view is that a "sub" woofer should simply be reinforcement of the lowest frequencies that the main speakers might struggle with in a given room. Many, many subs are setup poorly IMO, and treated as a featured component with the gain set too high relative to the output of the mains, and low pass frequencies set too high where they affect the vocal range (above 70hz), and the subs end up dominating everything else in the blend. I prefer to set the low pass filter in the 40-50hz range so that the sub only augments the bass my main speakers produce, set the gain level so that it’s barely noticeable except for on bass heavy passages, and I run the main speakers full range because I prefer not to send the signal that goes to my main speakers through the filters of the sub, but that’s a matter preference based on the specifics of my situation.

Some speakers may respond well to having the low bass filtered from the mains via a high pass crossover filter (whether active or passive, or internal or external), and handled solely by the sub, but that’s also a variable, and there’s potential for degrading the main signal depending on how that filtering is done, quality of parts, etc. Many variables, many matters of preference, YMMV..

@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.