Subwoofer speed is in the room, not the box

agreed that measurements and acoustic panels and traps are critical to a near perfect integration.  

i do believe that some subs give the impression of being faster than others in the same room.  

i tried several subs and came to the following conclusions-

subwoofers need to have low audible enclosure resonance above your crossover region or they can blur the midrange clarity of the mains. 

subwoofers with parametric eq are excellent for taming peaks and to even the response between left and right subs, especially when one is near a corner. 

deep flat response down to 20hz makes a huge difference and makes them worth the effort. 

sealed subs are less efficient but have lower distortion in critical frequencies.  

some overlap between subs and mains is ok but not much. 

putting the subs inside the main speakers makes integration much easier.  spread your mains wide if you have to!

I agree with @avanti1960 except in one technical nitpick:

The efficiency of a driver in a cabinet is determined by the driver, not the box. Sealed and ported cabinets will have the exact same efficiency if they use the same driver. The difference is the -3 dB location will shift down for a ported cabinet. Also, the optimally flat solution for a sealed cabinet can be much smaller than for the optimally flat ported solution.

I recently made a sealed center channel, and using sealed cabinets reduced the volume by about half, and raised the -3 dB point a little, but since I was going to crossover at 80 Hz, the -3 dB point of 45 vs. 60 Hz was moot.

@gdaddy1 wrote:

After many, many tests...I respectfully disagree. So does REL.

From REL..."Almost 100% of the time, newcomers will set the crossover too high and the gain (volume level) too low. This will result in a sound that is fatter, boomier and improperly integrated with the main speakers. The secret is to realize the crossover needs to be lower than the main speaker’s output at which point the gain can be significantly higher resulting in very flat, natural and extended deep bass."

This is a very revealing quote that only exposes a misunderstanding: it states that "newcomers" sets the low-pass frequency of the sub(s) too high while - as we can deduce - running the mains full-range, in which case of course there'll be an overlap, with all that implies when too severe.

From that I take it REL is really only considering the scenario where the mains are run full-range with the subs then "added" on, and thus the only variable here is centered on the subs and their low-pass frequency that will be dictated by the bass extension and overall character of the mains; all things being equal, the lower they reach, the lower the low-pass, and that explains REL's position of a highly set low-pass as generally bad because of the resultant overlap with the bass performance of the mains (when run full-range). 

Except some of us here are advocating high-passing the main speakers, and this changes everything with two variables to consider - that is, both a low-pass and a high-pass frequency. This being the case a, say, 90Hz subs low-pass can be a perfectly sound choice when the mains are high-passed accordingly. Some overlapping between the subs and mains, which is inevitable, isn't necessarily a bad thing, but obviously when taken to the extreme can be detrimental. 

I'm not saying REL's approach with the mains run full-range and the subs fittingly (low) low-passed is a bad choice (albeit, to my mind, a lesser one compared to high-passing the mains), only that making a blanket statement on the deficiency of a higher crossover point between the subs and mains is downright incorrect, and taken out of context with your quote above. 

Almost 100% of the time, newcomers will set the crossover too high and the gain (volume level) too low. This will result in a sound that is fatter, boomier and improperly integrated with the main speakers. The secret is to realize the [subwoofer] crossover needs to be lower than the main speaker’s output [emphasis added] at which point the gain can be significantly higher resulting in very flat, natural and extended deep bass.

@gdaddy1 That’s correct, but there is a key phrase here which is not in any conflict with what I’m saying:

The secret is to realize the [subwoofer] crossover needs to be lower than the main speaker’s output

Yes, exactly. And at no point am I advocating otherwise. This is why I’m consistently advocating for a high pass filter. If you are using a subwoofer strictly to fill below the main speaker output, then that’s as high as you can go. I’ve also suggested plugging ported speakers for the same reason. It raises the -3dB frequency allowing the sub to do more work while meshing smoothly with the mains.

What I thought I was pretty clear about is that raising the -3dB point of the main speakers to ~ 80Hz and using the subwoofer to take over at least 2 octaves at the bottom is a lot better than leaving the main speakers alone, and using the subwoofer only between 20 and 30-40 Hz.

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? That’s the difference and why I advocate the way I do.

​​​​​I can't speak to my speakers IM or doppler distortion. I can say when I first heard my current speakers I was underwhelmed by their sizzle and boom dynamics and beguiled by their cohesively musical rightness at any volume while forbidden by their cost of ownership for almost a decade.

It may very well be using the subs high pass circuit is suspect, the difference is clearly noticeable. Could you describe your experience using the Velodyne Digital Drive Plus high pass?