Sub distance setting in receiver

Discussion in 'Speakers' started by Yohan Pamudji, Nov 29, 2004.

  1. Yohan Pamudji

    Yohan Pamudji Second Unit

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    I recently installed a Pioneer VSX-1014 in my system (posted a mini-review in the ongoing 1014 thread in the receiver forum) and it did something strange with the sub configuration. It has an automatic configuration system called MCACC, where you plug in a microphone and set it up at the listening position, and the receiver does the rest. Well, it decided my main speakers are 9 ft. away while it set the sub to 20 ft. away, eventhough the sub is right next to the right main speaker.

    While this isn't physically accurate, it made my system sound worlds better than before with regard to sub integration. Previously when I manually set my sub setting to the actual physical distance, the sub sounded like it was lagging behind the main speakers, so I never used it for music. Now it sounds perfect and integration is seamless, even with music.

    My questions (finally): why does the receiver have to set my sub distance as 20 ft. instead of the 10 ft. that it really is? Could there be something wrong with my Paradigm PW-2200 sub? It's been like this since I got it 5 years ago. It's like I got a brand new sub so I have no complaints, but I'm curious as to what could be causing this behavior.
     
  2. Benihana

    Benihana Stunt Coordinator

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    no it calibrated it that way based off what it was picking up through the MCACC. It made it seem that far because that was the calibration needed to make it have even response in your room, i'm sure it will be different in other setups/rooms . I will be getting mine on the 2nd, and I'll see how mine worx out. Did you find that sub positioning didn't matter when using the calibration??
     
  3. Mark Seaton

    Mark Seaton Supporting Actor

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    Hi guys,

    I've posted on this many times in the past, but most will have a hard time grasping the situation until you start looking at Energy Time Curves and real measurements beyond the Radio Shack meter. Your receiver is likely correct relative to where you located the mic. What many forget is that any low pass filter results in what is known as group delay which is frequency dependent. What this means in the real world is that if we place a common tweeter and a subwoofer at the same distance from a mic and send them the same test signal, the sound from the subwoofer will arrive at the mic later than from the tweeter.

    If we have measurement equipment capable, we can also see that group delay is rarely constant, and below some high frequency, generally increases with lowering frequency. When we design a loudspeaker or optomize a loudspeaker system, we would prefer that in the range where two drivers cross over(and are both playing), the sound arrive at nearly the same time from both drivers. The fact that this "fixed delay" changes with frequency makes this more difficult, but we generally find that as we lower the crossover frequencies, the delays grow longer. We find that we would like to delay the higher frequency sections to better match with the lower frequency sections.

    Before I go further, let me clarify that this is different than how the distance settings are used for the 5 or 7 channels in a home theater. For the main speakers we are primarily looking to equate arrival times in the interest of not skewing the image. Curiously, we find a distance setting for the subwoofer as well...

    This obviously is not to aid in directional confusion, as there is commonly only 1 subwoofer, and directional ques are dominated by higher frequencies. This delay/distance setting can only be meant to adjust the relative arrival of the subwoofer to that of the main speakers. In my own experience I have found measuring and setting this properly to have significant sonic benefits. In reality, this is somewhat like a different form of a phase control, yet the phase control on your subwoofer delays the signal further, where setting the distance longer than your mains in the processor will actually delay your mains speakers to "wait" for your subwoofer to catch up.

    Now I'm not saying your system can't sound great without carefully measuring and adjusting this parameter. There are many compounding factors which could make the real distance for the subwoofer an appropriate setting. That said, if you want to play with this as a sort of phase control and can't measure energy vs. time, you have a good bet by counting on the subwoofer being later than the mains, so start investigating by making the virtual distance of the subwoofer longer, not shorter.

    Enough for one post...

    Cheers,
     
  4. oliverLim

    oliverLim Agent

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    Thanks Mark! Another great tip from you. Will keep this this tip in my little HiFi Black Book.

    I have been playing with this same parameter in my processor and I am now at 20 feet instead of 11 feet which is the correct distance. I did not know why but I felt that anything above 15 feet gave a more coherent sound to my ears. Now I think I know better! :)

    If I have a measurement system, how do I actually measure the energy time thing you are saying? If what I understand you were saying is correct, the phase setting basically does the same thing as the delay setting? Or it is just that they are inter related? When I delay my sub settings, I need to readjust my phase in order to balance things again or I would have cancellations near my crossover.

    Oliver
     
  5. Yohan Pamudji

    Yohan Pamudji Second Unit

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    Mark,

    Thanks for the excellent explanation. I figured the 20 ft. setting for the sub had something to do with the sub signal reaching the listening position later than the main speaker signals in a "normal" configuration, which is why the receiver had to compensate by calibrating the sub to be further away so its signal would get sent earlier than the mains to maintain integration/coherence. I was just wondering why this is the case, and I think you explained it quite well without splitting our brains with a detailed technical explanation. I previously thought that receivers and pre/pros already compensated for group delay, so that when you set the distance of your speakers and sub in its settings to their respective physical distances it would time the signals properly with some built-in default offset where the mains get sent later than the sub. Obviously some tweaking would still be necessary in this scenario, but not a gigantic adjustment like setting the distance from its true 10 ft. to 20 ft. just to get the signals playing nicely with each other.

    How would you use the energy-time curve? Would you play a sound clip with 3 notes in the 3 crossed-over regions (or more depending on number of crossovers) and plot it over time to see when all 3 hit the listening position?

    As an aside, it's definitely not room response causing this behavior. My sub has sounded like this all 5 years that I've had it, during which it has been in 4 different rooms--it always sounded laggy when configured straight up, which now makes sense. Now it's like I have a brand new sub that's amazingly accurate and fast compared to my old one [​IMG]

    It seems to me like this should be a question for the FAQ, or at least some variation of it. A lot of audio setup is common sense once you understand the fundamental principles, but how many newbies are going to know to try and setup their receiver's sub distance setting to twice it's physical distance? Not many, I would imagine. And even when they experience the same disappointing sub performance that I did, not many would know to play with the sub distance setting. Too late for Thanksgiving, but this is why I love and am thankful for this forum [​IMG]
     
  6. Wayne A. Pflughaupt

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    Someone help me out here: The crossovers adds group delay so that “the sound from the subwoofer arrives at the mic later than the tweeter.” Yet, the MCACC system compensates for this problem by adding even more delay to the sub. And in spite of that, the sub sounds like it’s “perfectly and seamlessly integrated” with the mains, much more so than if the correct distance settings are dialed in.

    Did I miss something?

    Regards,
    Wayne A. Pflughaupt
     
  7. Yohan Pamudji

    Yohan Pamudji Second Unit

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    By setting the distance of the sub further away than it really is, it's in effect delaying the mains and making that signal wait while the sub signal gets sent first. Think about it: since the sub is further away (based on the auto calibration) the receiver will need to send the sub's signal first to get all signals to arrive at the listening position at the same time, thus compensating for the inherent group delay caused by crossover.
     
  8. ScottCHI

    ScottCHI Screenwriter

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    great thread

    [​IMG]
     
  9. Wayne A. Pflughaupt

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    Makes sense. For some reason I was assuming the receiver was setting it up as a delay for 20ft rather than compensating for the distance. Duh... [​IMG]

    Do ya get the impression that I don’t have a late-model auto-calibrating receiver? [​IMG]

    Regards,
    Wayne A. Pflughaupt
     
  10. Joe Mihok

    Joe Mihok Second Unit

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    MCACC on my 1014 TX did wonders for my sub as well. My mains and sub are 11.5 ft away from my listening position. MCACC set my sub to 15 ft and it does not sound "slow" at all any more. My previous Denon 1803 did not allow me to adjust the sub distance and I was never quite happy how it integrated with my mains. It's a blessing the Pioneer allows me to adjust the sub distance, because now it sounds wonderful.
     
  11. oliverLim

    oliverLim Agent

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    Wayne,

    It's ok! I have been using a processor for about 6 years now and it has caught me out till Mark explained it so clearly! :) I had the exact same "understanding" as you had previously.

    In fact I had been trying to reduce the distance in the settings in a effort to get the sub to sound more coherent in my system. Ha...

    Oliver
     
  12. Lewis Besze

    Lewis Besze Producer

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    I believe all this distance setting is nothing but a phase "manupilation", which is why the distance reads "wrong" The receiver trying to create a "phase coherent" set up based on actual acoustical "measurments" by the MCACC .
     
  13. Mark Seaton

    Mark Seaton Supporting Actor

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    No, it is most certainly a digitally executed delay. You can plot an energy vs. time curve, or ETC and watch the impulses delay more or less. More importantly, if you were to invert the polarity of the subwoofer, you should see the same distance as this is measured by looking for the peak energy, not phase. In early days of home theater setup we did directly adjust delays, now systems wisely just ask for the distances and do the math for you. If you try and measure this you need to remember that in all cases I have seen, the speaker with the longest input distance does not change when the sound eminates.

    Let's presume the front 3 speakers are all set to the same distance, and the subwoofer is behind them in the corner. If we continue to increase the distance telling the processor that the subwoofer is further, testing will show the impulse from the subwoofer to remain the same, but ALL of the other speakers will eminate later as the subwoofer distance is entered. We should remember that the processor only looks at the difference in distance between the speakers, not the absolute distance. In really long or odd rooms, and with certain processors, this can be used to your benefit. Sometimes a processor will only allow a maximum distance. I have also seen other processors more intelligently limit you to a maximum difference in distance. A processor will have a finite amount of delay available.

    In the case where there is a maximum on the distance input and you have a very long room, you can set your closest speaker to "0" distance and subtract the distance of this speaker from the real distance of the remaining speakers. Inputting this difference yeilds the same result. This makes sense with the conceptual operation and goals of the distance settings, and I have confirmed this with many processors and receivers. Then of course there are companies like Meridian who have their own wacky ideas on such matters... Good thing they do other things very well. [​IMG]
     
  14. Jeremy_R

    Jeremy_R Stunt Coordinator

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    I have to ask a question about all of this because I'm curious. I too have noticed a slight delay in my subs response. I have my mains set to 10' and my sub set to 5'. The reason I did this is because my subwoofer is directly behind my listening position. I have the phase switch on my sub set to 180. What do you guys recommend I set my sub distance at???
     
  15. Mark Seaton

    Mark Seaton Supporting Actor

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    One thing to be cautious of is in confusing excessively long decay times in room with something that can be fixed with a delay setting. It won't fix acoustic problems. Subjectively I find the most difference in the crossover region which makes sense, as these are the only frequencies which would be affected at all by this, where the really low frequencies have a long enough period/wavelength that small delay changes are inconsequential. In short, careful measurement and setup can indeed make for a better integration with the main speakers. It won't make a bad subwoofer, or room, great.
     
  16. Jeremy Anderson

    Jeremy Anderson Screenwriter

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    Okay, I understand the concept but I haven't seen anyone address my obvious concern: Doesn't delaying the mains effectively result in sounds not syncing to the video? I mean, if putting the subwoofer distance 10 feet further than that of the mains truly delays the output of the other speakers, doesn't that put the sound 10ms behind the on-screen action?
     
  17. Mark Seaton

    Mark Seaton Supporting Actor

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    Any home theater processor I have measured already has 20-50ms of propagation delay (latency) from input to output. We need to also remember that any modern video scaling device (separate or internal to a display) will have latency on the order of 100s of milliseconds. You will notice that many newer processors actually have delay adjustments to add sufficient delay to the audio to sync with the display.

    A good confirmation of this is that your pre-processor only looks at the difference between distances, not the absolute distance. It does not compensate for sitting 20' vs. 6'.
     
  18. JohnDG

    JohnDG Stunt Coordinator

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    Can we formulate a "rule of thumb" for this without the use of measuring equipment? Is this true for all rooms?

    jdg
     
  19. Max F

    Max F Second Unit

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    Great thread! Now this is why i come to these forums.

    I wish i could change my sub distance settings on my reciever...[​IMG]

    I have some questions:
    Would changing the phase from 0 to 180 change the delay?

    How much does the filter on the reciever and/or subwoofer change the delay compared to the "slowness" of bass itself?

    If the speed of sound is constant, why is bass slow? Is it because the whole wave has to move through our ears before we hear it?

    What causes the most problems for sub integration, the delay of the subwoofer (say a ported sub with filters on the reciever, BFD, and x-over on the subwoofer) or peaks in frequency response? In other words, which is more perceivable: delay in subwoofer response or lingering room resonances?

    Why does my wife hate when i talk about speakers?
     

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