ARC sets the crossover at 150 hz. Why?

[ex audiophile]

I thought I'd share what appears to be my first serious room acoustic problem. The system noted at the bottom is located in a 15 x 20 bedroom; lots of furniture, carpet, queen bed and original shipping boxes for audio stuff. When I ran the ARC program (Genesis) I was very surprised to see how high the program had set the crossover. I repeated the sampling protocol 3 times with almost identical results each time. Be aware I am a novice at this. In reviewing the response curves I noticed that output from both speakers was markedly attenuated at around 100hz. My assumption is that the ARC wizard, after saying "shit, look at that drop around 100 hz" decided to get some help from the sub and moved the crossover up so that the sub could cover the missing frequencies.

My understanding of drops/nulls/suckouts is that they are difficult if not impossible for room correction to deal with, and in fact attempting to do so with the mains can put a dangerously high load on the amp. The sub, with its own powerful amp is better able to cover these drops. All this is supposition on my part.
Further, the downside of high crossovers is that the sub starts putting out directional frequencies and perhaps subs are not as good at reproducing these +100 hz frequencies, not sure. Obviously there are a number of good reasons why 80 is typically advised.

So, i'm prepared to have all of this shot down, mocked, and set afire but I thought it interesting and look forward to other thoughts and explanations for the crossover setting. If by any chance I am mostly correct in my interpretations I expect a few "attaboy grasshopper" comments I tried to attach the full .arc file but apparently that file type is not supported. I will be receiving the second Fathom next week and look forward to retesting. I'm thinking if this is a room acoustic problem the second sub will not solve anything but should spread out the low frequency output, making it less directional. I have to say the system sounds extremely good; I can hear the general location of the sub but i can do that with single subs running conventional crossovers as well.


Sonos Port (S2 os) - STR integrated - Revel 128be pair - single Fathom 12" sub

 

[Vasr]

ARC in the auto EQ mode selects a crossover frequency based on the characteristics of the main and sub curves it measures but it is not fool-proof.

I think in your case the steep drop-off in the mains - the red speaker may be getting affected by the room but the more even blue speaker also seems to have a steep drop-off below 200hz which might mean that your main speakers don't have a good low frequency extension. Because the sub seems happier in that range triggered a higher crossover frequency.

You can manually adjust this using ARC Genesis full software to select the crossover frequency and see what the effect is but 120hz is not necessarily bad even if at the maximum end.

So, you would have to figure out which compromise works better. A lower crossover frequency manually set but the deficiency in the mains not corrected for or higher crossover frequency with flatter response in the crossover region but the sub getting more directional.

You may also want to investigate why the red speaker is getting so disturbed below 200hz - too see if it is a room issue (which may require some repositioning to try to fix it) or an issue with the speaker itself. One way to do the latter is to swap the speakers and see if the same curve manifests in the other speaker.

 

[ex audiophile]

ARC in the auto EQ mode selects a crossover frequency based on the characteristics of the main and sub curves it measures but it is not fool-proof.

I think in your case the steep drop-off in the mains - the red speaker may be getting affected by the room but the more even blue speaker also seems to have a steep drop-off below 200hz which might mean that your main speakers don't have a good low frequency extension. Because the sub seems happier in that range triggered a higher crossover frequency.

You can manually adjust this using ARC Genesis full software to select the crossover frequency and see what the effect is but 120hz is not necessarily bad even if at the maximum end.

So, you would have to figure out which compromise works better. A lower crossover frequency manually set but the deficiency in the mains not corrected for or higher crossover frequency with flatter response in the crossover region but the sub getting more directional.

You may also want to investigate why the red speaker is getting so disturbed below 200hz - too see if it is a room issue (which may require some repositioning to try to fix it) or an issue with the speaker itself. One way to do the latter is to swap the speakers and see if the same curve manifests in the other speaker.

thanks, yes the red (right) speaker is much worse. Great idea to swap them, I'll do that in the morning and use quick measure to see if it's speaker or room. I may send the file to Revel as well, they might be able to tell if there is a speaker issue.

 

[North_Sky]

Yeah, if you want a lower crossover you need full range speakers, or ones that can extend say to 40Hz. Then a crossover @ 80Hz is perfect (double the low frequency capability of your mains).
If your mains are capable down to 60Hz then a crossover between say 90 and 110Hz is fine.
You don't want your sub(s) higher than say 110Hz or they'll be localisable.