Subwoofer speed is in the room, not the box

@erik_squires 

@phusis 

Just for clarification, I used your suggested high pass method for several years described in the article below. I worked directly with Barry so I'm VERY familiar with it. However, as committed as I was, I never achieved what I was looking for using this method. It was good but not great.

Using my ears (crazy isn't it?) I concluded that if your main speakers produce good bass down to 50hz why restrict them? Why? Because it sounded better, fuller, more glorious. Plugging ports and making a sealed cabinet restricts cone movement. Makes the main speaker sound thin and anemic. IMO... if you want a sealed main speaker then it should be properly designed to work that way. Sealing ports and restricting quality speakers as an after thought is a mistake.

Do you want to spend thousands of dollars on a high-end brand sub just for incremental improvements or do you want the end result to be a glorious sounding system?

I want my sub to fill the void ONLY where it's needed. I want 'punch' in the area BELOW 60 hz. This is NOT an incremental improvement. This 'small zone' makes a huge difference. Subs need to "stay in there lane". Just because the sub is expensive doesn't mean it should do more than required to get your moneys worth. Upper bass is usually handled very well by the mains and the sub has ONE very important zone to fill. SUB bass, not mid bass.

FYI...I did end up using sealed subs and MORE power to drive them. Tight with no ported bloat. Music not movies.

Here's some reading you should find interesting as it outlines your method and if you're happy with it...that's great! I wasn't and found something more satisfying to my ears. 

https://www.soundoctor.com/whitepapers/subs.htm

@gdaddy1 I have to believe your experience, but I also wish you had measurements to show us what was happening at the same time.

Agree completely with @erik_squires, @audiokinesis and others regarding treating the peaks with EQ, but not trying to boost nulls. Multiple subs helps with that (not wading into the swarm debate).

One tradeoff I have not seen explicitly mentioned (although @phusis hints at it), is that setting a higher crossover point gives you more freedom in placement of the speakers vs. placement of the subs. Leaving the issues of room treatments aside, place your speakers for the best soundstage and imaging, and place your subs to minimize the problems associated with the long wavelengths of low frequencies (which create both nulls and peaks).

Most room mode problems tend to occur with sub-125 Hz frequencies, although depending on room characteristics, they can go higher. But certainly, the lower you go, the more bothersome these tend to be. Flexibility of where you can place one or more subs helps tremendously. However, if you cross over at 35 Hz, for example, then you have pretty much lost that flexibility. You really can’t just move one of your main speakers 3 to 6 feet to deal with a peak at, say, 50 Hz, because moving them will ruin your soundstage. Crossing higher provides more options for sub placement to deal with troublesome modes.

So, up to a point, the higher you can cross over, the better, up until where you can start hearing the directionality of the subs. This is room-dependent and person-dependent, but typically is around 80 Hz. I experimented with 50 Hz to 80 Hz, and for my situation, crossing at 70 Hz sounded best.

The other issue sort of mentioned so far that could be stated more explicitly is phase-matching the mains and the subs at the point of crossover. This requires two things: (1) a continuous phase adjustment on the subs (like on those by Rythmik) or digital PEQ; and (2) a very steep and symmetrical crossover, typically implying an active crossover. That means both low-passing the sub and high-passing the mains are important. Because the wavelengths change quite a bit from 20 Hz (56 feet) to 80 Hz (14 feet), the mains and subs can only be in phase at a small range of frequencies. That is why the steep crossover is needed. Otherwise, even if the mains and subs are in phase at 70 Hz, with 6 dB/octave sloped filters there will be audible overlapping of the subs and mains from the lower audible limits all the way up to ~250 Hz or so. Because all filters have a frequency-dependent phase shift, most of that overlap is out of phase and contributing to "smudging" that translates to "slow bass."

For my Dali Epicon 6’s, what has worked well for me is an active crossover (24 dB/octave) crossing at 70 Hz to a pair of Rythmik F12G-SE’s with the GR-Research drivers. Mains about 7 feet apart works well for my space; the subs are in diagonally opposite corners of the room. Since I exclusively listen to digital, I can use Roon’s PEQ on a per-channel basis to remove the peaks from the room modes (almost entirely in the range the subs operate), and then careful placement allows each sub to fill in the other’s nulls. After the digital is converted to analog, I want to retain my Denafrips’ sound signature, so I don’t use digital PEQ involving more ADC and DAC conversions. Instead, I am using a Sublime K231 active crossover; the Burr-Brown op-amps used in it don’t seem to color the sound much.

@sfgak

Without wading in too much to solutions, the THX standard of 4th order low pass, 4th order high pass at 80 Hz is really convenient.

Keep things in mind though, the goal is 4th order response includes the speaker response, and that we do in fact use assymetrical crossovers in speaker building all the time. 2nd HP and 3rd LP is very common for 2-way speakers. The point is, if all you can do is add a cap to your amp to create a 1st order HP filter, it’s worth it.

At the end of the day though, you can't get to a 4th order electro-acosutic response unless you actually measure your starting and end point. 

@avanti1960 got it right…. and building an inert cabinet for those massive low THD but high IMD woofers is not trivial…. but then cabinet movement = trash = output = “ efficiency “….. funny how systems engineering just creeps in…..