How do I set the crossover for 2 channel listening on my HT system?

Your head unit is sending a low level signal @ what ever you set it at and normally that roll off is the same as the roll on of the next crossover point. No different than any crossover. IF they lap at the same frequency and have a vey gradual slope there can be all kinds of bloating. 

If you set your sub to a lower point the sub plate (whatever you have) will play lower but your signal is limited by how you're set up. If you would have set the subs in the head unit to "Large Speakers" the subs will be controlled just by the plate.

My subs are set at 4th order 24db but the slope from the mid bass coupler columns is at 48db. A VERY steep slope. Because of that alone there is little bloat and almost no combing or suck-out.

That is what you want to try to do, but remember 50% of great sound is the room, know your room. Ground up approach. Room, Bass, then all the rest, not the other way around. With todays systems you have to work to get bad sound to tell the truth.

Regards

I understand a subwoofer crossover should roughly match a speaker’s low frequency capability,

You want it to blend in with the low pass of the speaker in the room, which could be a lot lower than 49 Hz.  As I've written elsewhere, that's a complicated place and measurement is essential.  In addition, if you can use a high pass filter to reduce the bass to your speakers you will get lower distortion and higher dynamic range, and that means raising up the crossover point to 80 Hz or so. 

You do not say which Denon receiver you have but I would think that the crossover function in the Denon would contain both low and high filter capabilities so both your mains and sub will be crossing over at the same frequency. The low pass filter on your sub is not needed with type of set-up.

I would set the crossover frequency in the Denon somewhere between 60 and 80 hz and set the low pass filter on the sub at the highest frequency the filter allows.

Thanks to all. To oldhvymec4: The front speakers are indeed set to Large in the speaker set up of the Denon AVR-2807. I thus understand the crossover setting on the Denon is irrelevant and the low pass filter setting in the M&K will control. On the other hand audiorusty appears to say the low pass filter on the M&K is irrelevant-- yet it is suggested I set the low pass on the M&K to its highest available, which in this case is 100Hz.  These seem contradictory.

Eric_squires: The 49Hz figure cited is the manufacturers spec for the 805S. I haven't any instrumentation to determine precisely. As indicated that figure is ±3dB and the M&K rating is ±6dB so there is a fractional difference where the blended frequency should be which I also cannot calculate and thus have used the speakers 49Hz as a "compromize". 

Thanks to all. To oldhvymec4: The front speakers are indeed set to Large in the speaker set up of the Denon AVR-2807. I thus understand the crossover setting on the Denon is irrelevant and the low pass filter setting in the M&K will control. On the other hand audiorusty appears to say the low pass filter on the M&K is irrelevant-- yet it is suggested I set the low pass on the M&K to its highest available, which in this case is 100Hz. These seem contradictory.

The large/small setting in the Denon will control whether or not any bass is routed out the subwoofer output. The crossover setting in the Denon is irrelevant for the FL/FR speakers set to Large, but still relevant for any other speaker set to Small -- center, surrounds, etc.  Note that crossover settings do not apply to the LFE channel as that typically covers a frequency range of 3Hz to 120Hz based on the source mix.  Since you are using bass management in the Denon, you should set the low pass on the M&K to the highest setting, essentially disabling it. You don’t want to use both.

I like simple. Set your 805s to large and just adjust the sub until it sounds right. It would be tricky if your loudspeakers were full range but they cut off pretty high. 

To bjp9738: Thank you for the clarification that the Denon crossover settings fo not apply to the LFE channel. I was concerned I was mutiplying or contradicting the settings if both the Denon's and M&K's were in play.

Based on what you said, if I am only listening to 2-channel stereo (thus only employing the FL/FR speakers and subwoofer and not the remaining surround sound speakers) there  apparently is no base management being used in the Denon. Under this circumstance I assume I should NOT set the low pass on the M&K to its highest setting but instead find an appropriate setting sounding best with the front speakers. Do I have this right?

(Also presumably when reverting to HT and using all speakers your advice to set the M&K high would then apply.)

@dsands You didn’t say which model you have, but in most Denon AVR’s, if you have your Fronts set to Large, bass will never be sent to the subwoofer unless you set the subwoofer mode to LFE+Main, or you set the Fronts to Small. I do not believe there is any way to engage the subwoofer in the Denon and NOT use the Denon’s crossover settings.

So I think your best approach might be to set Fronts to Large, set sub mode to LFE+Main, and then set a crossover point of either 40Hz or 60Hz in the Denon for your Fronts and leave the M&K’s low pass at its max.

bjp9738:

Thanks for beng so generous with your time and information. The fronts are set to large and I'll follow your guidance regarding the settings on the receiver and sub and--to take a line  from russ69 above--set the sub to its max and then make any slight  adjustment until it sounds right.

I appreciate everyone's input. 

No matter how large my speakers are (cruelty my mains have two 8” drivers) I always crossover (highpass) at 60hz or more. I have found subs to be much better than anything short of super speakers below 60hz. 70-80hz will depend on the speakers/room as at 70hz and above tone of the sub comes more into play as it need to match the speakers. For small speakers like the 805 I feel 70hz is a good place to start but for most speakes 60hz is the magic number with a 24db slope.

trying to come in under you speakers without a highpass from the receiver will not be optimal. Also keep in mind the port is out of phase with the drivers so as you crossover higher the phase could change a bit.