Originally Posted by TKO1
Yeah, this is the part I get confused on as well. I have never been able to reconcile what ARC is doing with crossovers and response cut-offs with my scientific knowledge ;-) As an example of my most recent ARC Targets auto settings for response cutoffs:
L/R: 60 Hz (Revel Concerta F12 ±1.0dB from 58Hz to 18kHz)
C: 100 Hz (Revel Concerta C12 ±1.5dB from 85Hz to 15kHz)
LS/RS: 80 Hz (Revel Concerta M12 ±1.5dB from 65Hz to 15kHz )
Subwoofer: 80Hz (Revel Concerta B12a -3dB @ 28Hz ±0.5dB in the pass band)
so given that the speakers are set to small all bass frequencies below 80Hz and the LFE channel are directed to the subwoofer. The auto measurements are pretty good albeit somewhat conservative based on their -3dB frequency. The Revel specifications for In room frequency responses are noted above.
Here's the text from Anthem:
Given this text then one guesses that ARC is equalizing the front speakers down to 60Hz, the center channel down to 100Hz, the surrounds down to 80Hz and the subwoofer up to 80Hz.
But once you upload the ARC settings for Music and Movie mode what happened to the original non-ARC crossovers? If you go into setup and look at the settings for Bass Management after uploading the ARC results the only thing you see is the Movie or Music mode settings from ARC.
What is happening between 80Hz and 100Hz on my center channel?
If anyone can answer these questions please go ahead. We would all like to understand how best to maximize our listening pleasure.
First you have to look at the crossovers that get Uploaded as the crossover for the sub my be different from the "cutoff" ARC displays. As Anthem said, the two of them are different.
It may be that the sub crossover is higher than 80Hz even though ARC is putting less resource into correcting the sub above 80Hz.
You can check the impact of all this by looking at the green, Calculated curves for Center and for the Sub at and below the crossover frequency for Center. ARC is rolling off output to Center below that and steering that audio to the sub. The question is, is the sub there to catch it or is its output too weak up there?
First find the basic volume level of the ARC solution. That's the flat part of the main speaker Targets curves to the right of the crossover frequencies. Evaluate everything with respect to that basic volume level.
Now look at the green Calculated curve for Center and note how it drops off below 100Hz. The question is, where is AT 100Hz? It should be right about the basic volume level. EXCEPTION: The effect of Room Gain is to raise the output in the bass frequencies. A +3dB Room Gain gives you a shallow hump of slightly higher output in the bass that's +3dB over the basic volume level. Depending on how high the crossover is for a speaker, the "expected" Calculated result at the Crossover should be at the basic volume level OR a little bit higher due to the application of Room Gain.
Now look at 1/2 the crossover frequency for Center. The Target curve for Center should have dropped off -12dB from its volume at the Crossover. (The green, Calculated curve for Center should be close to the Target curve.) Any Center frequencies down there will have to be handled by the Sub. That's what we mean by bass steering. It's that range from the Crossover frequency to one octave down (1/2 the crossover frequency) that's important.
Now look at the green Calculated curve for the sub. At 1/2 the crossover frequency for Center the sub's response should be the basic volume level PLUS the Room Gain lift. That shows that the sub is able to handle steered bass coming in from the Center channel down there without problem.
Now shift right and look at the green Calculated curve for the sub AT the crossover frequency for Center. At that frequency, almost all the Center channel output is still being sent through the Center speaker. But you are just starting to get bass steered to the Sub. So what does the sub's response curve look like? If it is at or above Center at that frequency then you are clearly in good shape. Whatever goes to the sub from the Center channel below that, the sub is there to handle.
If it is, say, -3dB (or worse) below where Center's curve is, then you have a hole. As bass starts to get shifted to the sub from the Center channel for frequencies below that, the sub isn't there to catch them. As you go further down in frequency, the sub's response improves and the hole is gone.
Why would ARC do that? Well ARC measures what it thinks your sub and your Center are capable of doing and does the best it can to close any such hole between them without over-stressing either of them. ARC has some built in limits -- such as no more than +6dB boost to any speaker at any frequency -- to protect the amps and speakers.
If ARC finds a problem trying to match the sub with any of your speakers it gives priority to making the LF/RF/Sub combo work best.
So what to do if you have a hole? Well of course you could replace the sub with one that has better output in high bass, or the Center with one that has better bass output itself.
But before you do that, be sure to check that you are getting the best you can out of the speakers you've got.
First, play some stereo music with bass content using a Mono audio mode so all speakers get the same thing. Now go put your ear up close to the woofer in Center and make sure audio is coming from it. It is VERY common for people to have a Center speaker with a broken woofer. If there's nothing coming from the woofer then the bass your center is producing is actually coming from the low end of its mid-range cone. Fix the speaker.
Next double check to make sure you don't have an internal crossover active in your sub. An internal crossover will artificially attenuate the high bass output of the sub -- i.e., you aren't letting the sub show off its chops in high bass. Disable any such internal crossover or crank it up to the highest possible frequency to get it out of the way as much as possible.
Be aware that setting a "THX" mode in a sub may impose an 80Hz internal crossover despite whatever you've done with the sub's other crossover controls. So don't use that THX mode.
NOTE: The whole idea is to let ARC do ALL the crossover processing. That's why it is safe, and necessary, to bypass any crossover built into the sub.
Third, try repositioning the subwoofer -- watching what happens to its output using the Quick Measure tool in ARC. Quick Measure will show you a chart, updated live in real time, of the raw, uncorrected output of any single speaker. What you are looking for is a new position that gives the sub better output in the high bass without producing too many problems elsewhere. For some subs, such as the Paradigm Servo subs, the impact of the Servo correction in the sub may reduce high bass output if the sub is positioned in a corner, for example. Moving the sub to a side wall or at least different distances from the two walls making the corner can yield a big improvement in its high bass.
Any such changes will require you re-measure for ARC.