Midbass handled by subwoofer or loudspeakers?

80 hz crossover is standard. See if you have flat response with test tones and spl meter if available. If not run sweeps to tell as best by ear. If good, leave it, if not move slightly up or down as needed depending on response. Or work on better sub placement, and as much as a few inches can make a difference. If higher crossover, sub placement may be more noticable.

Few speakers have the ability to provide the midbass slam of a quality sub, it's just a physics thing. But there are a lot of elements in play. Speaker/sub integration and the effect of the room on the FR of each individual speaker/sub can have a larger impact on actual perceived bass than the individual performance capabilities taken on their own.
So the answer is that it depends on your room and the specific placement of each speaker or sub in that room. But talking in generalities, I would say that a quality sub, properly crossed over to your speakers and positioned properly in your room, will deliver better midbass slam than the vast majority of full-range speakers sans sub.

I use all of my towers on full range mode. I also use the double bass option to include my subs. The bass overlaps very well for a nice, full soundstage in my opinion.

Those Polks should be up to the task of handling a fair share of mid-bass, but much of it also come down to how much the mid-bass can tax your main amps. The Polks seem to be of about medium efficiency (89db/w). They can call for a good deal of power to crank out big volume. If you are using a receiver for power without any killer external amps, I would opt for a crossover of about 80hz to allow your receiver to have it fairly easy. The end result will be cleaner, stronger mid-bass as well cleaner mids and highs since you are unburdening your main amps.

Me too. I have 2x15's in each LCR so they can handle it. When I try an 80 hz x-over, I loose that slam.

Wow! maybe I should check to see if my processor has this option.

I have run "full-range" speakers without crossing them over at all, and I have used the same speakers with an 80 Hz crossover. My experience is that any difference was minimal. But, I don't try to achieve Reference Level as the peaks are annoying, especially special effects.

I suggest that you try it both ways if your receiver allows you to run your mains as Large Plus the subwoofer. Then try an 80 Hz crossover to the sub.

It is true that with an 80 Hz crossover, you reduce the demands on your receiver by 66%. Bass is what calls for the most power, by a wide margin. But, you have nothing to lose by trying it both ways and using whichever sounds best to you.

While most companies recommend an 80 hz crossover, you aren't getting the most from the 2 bass drivers in your speakers with an 80 Hz crossover. According to the specs, the bass drivers don't kick in until 125 hz. With an 80 Hz crossover, you aren't using these drivers much.

Back in the old days my cheap and huge speakers had much bigger drivers than the current offerings of the popular 5" - 7". Perhaps my memory is a little off, but I seem to remember having the movie theater punch with those speakers, and with no sub. In other words, I'd say it takes a main speaker with a larger driver (and sufficient power or efficiency) than most of the popular stuff today.

Most people don't run their subs over 100hz, and in my opinion this "midbass" slam that is so sought after these days is in higher frequencies than that and are going to have to be covered by left and right (or l/c/r) mains.

Room acoustics have to allow for you to turn up the volume enough to hear these frequencies, as well. Elevated LFE and high frequencies will drown out the midbass frequencies responsible for the hit you in the chest feeling.

very true...moreso LFE than high frequencies IMO. when my mains were about 6" from the front wall and subs were in the corners, the midbass punch was weaker and details in upper mids were a mixed bag...

moving the subs out of the corner and bringing mains out into the room to about 33" from the wall cleared things up considerably. "punchy" and "tight" bass is easily robbed of it's impact when overpowered by excessive LFE...

wait a minute...did i just say "excessive" LFE...?

Yep.

"Me too. I have 2x15's in each LCR so they can handle it. When I try an 80 hz x-over, I loose that slam."

1. do your subs have as strong of motor (equally well damped) as your mains?
2. are your subs in phase w/your mains?
3. what is happening to your frequency response when you make the switch?
4. are your subs equally low in power compression and have equal or more spl capability?
5. what happens in the time domain when you add subs? do you get resonances?

any number of things could create this effect.

Did an interesting test on my system the other day. I have Dali Mentor 8's with dual 8" woofers and a 6.5 midbass in them - and I have a SubMersive HP. My buddy and I decided to test the mid-bass out by moving the x-over up and down using Spiderman 3 as the demo (the scene where the dude turns into sandman).

We found that a 40hz x-over yielded no less than 5dB higher than the 80hz setting (with AVR at -5 we hit 111dB vs 106dB at 80hz)!!! That's a really impressive difference and really shocked us.

I don't have any way to see what exact frequencies this scene is working over, but, clearly my mains eat it uplike it!

The reason we decided to try the experiment was that a -12 on my AVR I just wasn't getting much of that "slam" mentioned above. What I realized was that I had bumped up my SubMersive gain to try to get the slam, when really I just needed to dial the sub back and increase my AVR volume to -5 or even -3, and drop my x-o down. Now, I'm really enjoying great slam!!!

Should mention that I also have decent room treatments so that the increased volume isn't loading up the room and giving ear fatigue, etc.

As usual, YMMV, but this has worked really well for me.

I was over at Elemental Designs this summer demoing subs and their mains were EL8.3s with dual 8s and I noticed that they had a lot more mid-bass slam than my Axiom M80s.

I will go out on a limb here and say it depends on what midbass is defined at? You define the region and if your mains cover that region will be with mains and if that region is below your xo then it will be handled by your subs. We already knew this so the important thing in a great HT system is to have subs and mains equally as good so you will be covered either way. I ran 4 different graphs from 5-250hz with a XO at 40hz, 60hz, 80hz, and 120hz. My graphs did not change the response just by changing the XO. In my case in does not matter.

Sub is a single DTS-10/SMS-1. Room is roughly 2500 cu ft, heavily treated.
I have a lot of vacation time over the holidays so I will get my XTZ out and do some measuring.

Doesn't Geddes suggest overlapping the sub(s) and mains?

dr. g. suggests sealed mains and 4th order bandpass subs. both of these give 2nd order rolloff (lowpass and highpass). bag end uses something of a similar approach. it is one, of many, good approaches. but like all setups, getting it tuned right is a big part of the game.

regardless, if you are losing all your "punch" when using a sub, something is very wrong. i listed a few reasons of what could be wrong, but it is hard to tell without more information.

SO, if you have JTR 12HT's or Seaton Catalyst 12C's, would it be best to let them handle the midbass, (50-100hz ish) or would the sub be better off handling those frequencies? I ask bcause both of those have dual 12" drivers, but are spec'd at 50/60 hz respectively...

He could be just creating a better "House Curve" when adding the subwoofers to the mains running full range.

We have to remember that descriptions of what is happening can mean so many things and one man's "punch" is another mains "too much boom, boom"

Im loving the double bass setup myself.

They have higher sensitivity 12" woofers so you shouldn't conclude because they are larger woofers they will do bass better. They rolloff pretty fast and are not really considered the best woofer for 50Hz to 80Hz performance. Sensitivity increase sacrifices Woofer XMax.

If you are not going to run them full range then you should XO them @ 80Hz so that you are not creating a sharp knee response curve at the XO point.

So, other that the dedicated MBM-12 from HSU, what is the next best thing as far as a sub dedicated to, (or one that just REALLY excels at) produced mid-bass?

A pair of sealed 12" woofers with some decent travel can deliver quite a bit of output above 50Hz, especially in close proximity to a back wall. When you then consider there are 3 LCRs to divide the workload between there, other than the realities of the low frequency in-room speaker response, there's no compromise in a 50-60Hz crossover vs. an 80Hz until you are into some really extreme systems that are very carefully optimized for the room.

The next best thing is to get a measurement system and see where the real limitations are and insure that you aren't setting a powerful midbass sub in a midbass black hole.

For those of the Apple persuasion there is Fuzz Measure and another setup I was recently pointed to for iPhone/iTouch & iPad use from Studio Six Digital.

The ~35-200Hz range is all about getting a good sound producer in the right location to deliver it's power to the listener.