Subwoofer speed is in the room, not the box

A couple of experiences that I found to help.

First is to identify what is fast bass? Where does this sound live? If you're looking for for bomb explosions and car crashes then 20hz is great but there isn't much of this in music. The deeper 'punch' for music lives in the 30 to 50 range. I want the woofers of my main speakers to participate. Experiments of plugging ports on main speakers has resulted in reduced excursion (restricts speaker movement) and lowered the volume output of the speaker and a LOSS of richness in mid bass. Not good. Let them remain open as they were designed to be.

As the main speaker begins to drop off around 40 to 50hz this is the area for the 'SUB' woofer to help. Again, the main speakers will handle the upper bass no problem. My experience is that the subwoofer quickly becomes excessively 'boomy' at higher crossover settings above 60hz. (this depends on your main speaker capability)

What works for me...My main speakers are solid bass down to 50hz. I set an EQ with a 'sharp shelf filter' cut off starting at 35hz. I do NOT want the main speakers OR the subwoofer to try and reproduce lower frequencies that it doesn't need. I don't need 20hz for music. It only adds distortion. Let the sub be focused on the proper range for tight bass. 30hz IS deep bass in music! 

The subwoofer 'low pass' is set to 40hz and will seam perfectly with the main speaker drop off at 50hz. Yes.. this is a tight range but I assure you it's the proper range for a 'SUB' woofer in music. 

The key here is that, within this tight level, you can now increase the 'gain' level of the subwoofer fairly high. Both my subs have gain settings almost 3/4 of the way up so when it calls for power it's ready! Punch of a kick drum is immediate and powerful due to an unrestricted gain level.

You will never find tight punchy bass by setting a crossover high near 80hz or higher and then having to lower the volume to remove boominess. Like stepping on the brakes trying to go faster. That's completely backwards and is NOT what a subwoofer was designed to do.

Good luck!

@erik_squires  I’m not sure how much of that matters, but I can say, conclusively, that the high pass filters absolutely make the main speakers sound better.

You're right. It does on some speakers. However, let's look at a 3 way speaker. The high pass filter will only affect the woofer. The tweeter and midrange are already 'high passed' through the internal crossover. So the woofer, that is perfectly capable of producing excellent mid/lower bass, gets restricted by a high pass.

Now you'll need to push the subwoofer to a higher crossover to compensate for the loss of bass. The subwoofer is not as good at producing upper bass as the high quality woofer you restricted using high pass.

Another way to accomplish this sound improvement is by using a lower shelf filter cutoff around 35hz. Eliminating the lower frequencies that you don't need will improve the sound of BOTH your main speakers AND your subwoofer. This way you'll retain the full sound of your main speakers. It's a win/win.

My ears much prefer the richer/fuller unrestricted mid bass sound without the high pass.

@gdaddy1 I’ve had my subs tuned to produce from 16Hz to 80 Hz. It was glorious with music. There was no reason to limit the output, BUT...

the frequency response was absolutely smooth without peaks and tilted downwards. About 1.25 to 1.5 dB/octave.

Overall, I know your approach is a popular one, but I disagree with it based on experience, and talking to audiophiles who have actually made the changes.  The approach you are taking is have the sub do the least possible.  I say, have it do the most, up to 80 Hz possible, and have the mains do the least.   It's OK that we disagree, but I wanted to acknowledge your position so I could talk to it.  Thank you.

Much of the benefit of a high pass before the mains amp is the loafing it enjoys…..

The problem w servo is input signal is compared w voice coil movement, NOT cone movements which are rarely pistonic….. But y’all like those big paper woofers flapping in and out of phase….. 

Vandy powered bass: high pass the mains before amp, high level connectors to sub amp to provide identical transfer function, VERY linear pistonic drivers ( The sub 3 use 3x8”, the 7’s use a Titanium honeycomb core push pull dual voice coil driver ), 11 bands of ANALOG EQ below 120 hz to address room issues, and the 11 bands are NOT 1/3 octave for a reason…. An excellent “ learning engineer “,,,, would ponder on that seemingly unorthodox approach……

I want to highlight something I fear may be missed. I wrote this at the top of my original post:

I want to talk about the impression that subs are fast or slow compared to planar or line sources.

So this thread is about all the things that go wrong when adding a sub and how most audiophiles attribute this to the mass of the cone. That a 15" sub has too much inertia to be accurate, and is therefore slow. This thread is very much focused on what is perceived, which is poor bass, and how different that is from the actual root cause.

That is, I wanted to center listener perceptions instead of the physics, which are clear that big subwoofer drivers are the way to go, if only you didn't have a room you had to put them in.