Anthem AVM 20 owners with 20hz capable subwoofers...

Discussion in 'Archived Threads 2001-2004' started by Erik_C, Oct 23, 2002.

  1. Erik_C

    Erik_C Stunt Coordinator

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    My AVM 20 v. 2.0 seems to have almost a wall filter for frequencies below 20hz. I have a Velodyne 18" sub, and realized that some organ music didn't sound right. I put in a test disc, and found that 10, 12.5, and 16 hz tones were 30-40dbs lower in level than they should be. But 20hz comes in like gangbusters, at the level I expect. I reconnected an old Yamaha receiver to verify the sub's working and yep, the subbass was back. So it's the Anthem. Here's what I know:
    Anthem's boundary gain feature is set to off.
    Anthem's bass peak limiter is set at 0 db.
    Sub's at the correct volume, because 20hz + sounds great.
    Using the Anthem's internal crossover: mains crossed over at 60hz, sub crossover also at 60hz.
    Velodyne's internal xover is switched off.
    I want my 16hz back. What is wrong?
    -Erik
     
  2. Michael Mohrmann

    Michael Mohrmann Screenwriter

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    Erik,
    I am assuming you are using the same cable/connection to the AVM-20 as you did to the Yamaha receiver. If that is the case, the best I could come up with is (in descending order of severity):
    • Your AVM-20 is defective
    • Your AVM-20's hardware or software is not installed properly
    • This is a "feature" of the Motorola 56367 chipset, although the specs indicate -3 dB @ 1 Hz and -0.4 dB @ 10 Hz for a digital connection (-3 dB @ 2 Hz and -0.5 dB @ 10 Hz for an analog-DSP connection)
    • Some setting in the AVM-20 is preventing lower than 20 Hz
    Trying to be the optimist with the AVM-20 (it's getting hard these days), I will assume the last issue. The only other settings I could come up with other than what you have mentioned are:
    • Subwoofer Phase and Polarity, menu 4h, submenu f & g, page 48 AVM-20 owner's manual
    • THX Ultra2 Sub setting, menu 4i, submenu d, also page 48
    Michael
     
  3. Michael Mohrmann

    Michael Mohrmann Screenwriter

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    Erik,

    One other question I have. When you are playing the test tones, I am assuming that the signals are being sent to the sub via the subout connection. Is the listening mode set to 2 channel stereo or some other DSP mode?

    Michael
     
  4. Erik_C

    Erik_C Stunt Coordinator

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    Michael:
    You're right. Sub gets fed by sub out, and the Anthem is in 2-channel Analog-DSP mode.
    Oh, and a couple other things: I got my AVM new as v. 2.0, so I'd hope everything was installed properly at the factory. And it's not a sub phase issue: the Velodyne's speaker cone does not move under 20hz unless I crank the Anthem's volume up 30-40dbs.
    -Erik
     
  5. Michael Mohrmann

    Michael Mohrmann Screenwriter

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    Erik,

    It is starting to sound like the AVM-20 (or at least yours) does have a brick wall at around 20 Hz. I wonder if this is what the digital crossovers are doing in the Motorola chipset.

    One test you could perform is to use the analog output of your CD?/DVD? player to the AVM-20, connect only the AVM-20's main output to the subwoofer, and select analog bypass. This would at least isolate it to digital circuitry should you get some output through the mains channel less than 20 Hz (much depends on the frequency range of your analog outputs).

    Short of that, I would imagine an email to Anthem's tech support is in order here.

    Michael
     
  6. Chas_T

    Chas_T Supporting Actor

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    This may be off the wall and probably irrelevant. Are the speakers on the AVM set to small or large? Would this make a difference?
     
  7. Shawn O

    Shawn O Stunt Coordinator

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    looking forward to your findings Erik.Hopefully it's just some stupid setting.
     
  8. Michael Mohrmann

    Michael Mohrmann Screenwriter

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    Erik,
    I had another thought or two about your issue (sorry, but I have a friend who is a bass lover and your problem would bother him).
    Have your tried to play your test disc through a source (DVD or CD player) that is using a digital connection? I am mostly curious to see if this is just the AVM-20 in general that is cutting off the low bass (via its digital crossovers), or maybe the analog-to-digital converters (ADCs) that are "at fault".
    My second suggestions gets a bit more complicated. I am not sure whether the AVM-20 acts like the Lexicon MC-1 I use to own, but maybe it does. If you are using the analog connections and the analog-DSP modes, it is possible that the signal strength (gain) from the analog connection may not be enough to properly optimize the ADCs.
    Check page 44 of the AVM-20 Owner's manual. Near the top of the page is a section called Adjust Levels. This is normally used to try and balance all of the outputs from your analog sources. The paragraph right after that in the same section describes adjusting the analog-DSP levels. If this bar graph is too low or too high, it could have an impact on how the AVM-20's ADCs interpret the signals.
    Michael
     
  9. Michael Mohrmann

    Michael Mohrmann Screenwriter

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    Erik,

    Have you been able to find a solution to your low bass problem with the AVM-20? Or have you decided to try another processor?

    Michael
     
  10. Chas_T

    Chas_T Supporting Actor

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    Yes. I agree. Please share the solution as it's an integral part of any system to produce those frequencies.
     
  11. Michael Mohrmann

    Michael Mohrmann Screenwriter

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    I just popped a CD with test tones into my CD player. The disc has both 20 Hz and 16 Hz tones (the lowest). With it, I ran two stereo tests, the first test using the analog bypass mode with a subwoofer connected to the AVM-20's main output by itself, and the second test using a digital connection with a subwoofer connected to the AVM-20's subwoofer output. The subwoofer is an ACI Titan II LE, rated 20-250 Hz +/- 3 dB

    Both tests produced the same result. At 20 Hz, I am getting pretty good output at what I feel is a -3 dB point of the Titan II LE. Actually, it feels like I am getting more output at 20 Hz than before. I will probably need to retest once I am done recalibrating our system with the replacement AVM-20.

    At 16 Hz, surprisingly I am not dropping too many dBs (about 4-5) for a subwoofer I don't think is capable of much below 20 Hz. I can feel significant cone movement at 16 Hz, enough that it scared me despite knowing that the Titan II LE has protection circuitry.

    So, at least for a digital connection and analog bypass mode the AVM-20 appears to have no problem with 16 Hz signals. I think I will attempt to run one more test, the analog-DSP stereo mode that Erik is testing his system with.

    Michael
     
  12. RobertR

    RobertR Lead Actor

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    Whew, that's a relief, Michael.
     
  13. Michael Mohrmann

    Michael Mohrmann Screenwriter

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    Robert,
     
  14. Guy Usher

    Guy Usher Supporting Actor

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    If you were at 69 db at 16 what were you at 50. I will say this I really like low base and the Anthem Pre-Pro is in my future (don't tell my wife) but if I can stay flat to 25 with no bump at 50-60 I will be in "Disneyland"
     
  15. Michael Mohrmann

    Michael Mohrmann Screenwriter

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    Guy,

    I am not sure what it will be @ 50 Hz. I was mostly just trying to confirm that the AVM-20 wasn't completely cutting off signals below 20 Hz. Even if my test was a bit flawed and rushed, it did not produce close to the 30-40 dB drop that Erik experienced.

    I also repeated my test using the analog connection and the analog-DSP (A/D) mode for stereo. The 16 Hz test gave a reading that was a few dBs lower than with my other tests, but this may be because I have not adjusted the AVM-20 for the CDP's gain. I also have to take into account that my ACI Titan II LE will produce less @ 16 Hz than Erik's 18" Velodyne, which makes Erik's results even more mysterious.

    Michael
     
  16. Doug_B

    Doug_B Screenwriter

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    With an AVM 20 containing the old board (and v1.12 software, I believe), I have performed low freq measurements in the past using both a digital connection from a DVD player and an analog connection set to bypass from a CDP (for the latter case, a downstream ICBM derived a sub out channel). I measured no peculiarities for < 20 Hz signals produced by my SVS CS_Ultra, which is more than capable of going into this region without undue loss.

     
  17. Guy Usher

    Guy Usher Supporting Actor

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    I would like to know what CD player you use to even produce anything under 20 hz. It has been my understanding that CD players do use "Brick Wall" filters for anything under 20 and above 20k.
    Your AV20 is good from DC to light so that shouldn't be the problem.
    Whose "chamber" are you using to get these tones? Also it takes a real good Mike to accuratly pick up these ultra low tones.
    My experience says you need a good signal generater and some other "pricey" equipment. I don't think I would put much stock in what you are measuring in those regions if the source is a CD.
    I have "chased" these low notes for over 25 years and you will know when you really get down there, your bowels will move at about 8 to 10 hz literaly.
    I gave up on trying to go so low not that you can't, it's just that there is really nothing there, more important to me is keeping the freq response as flat as possible down to 20-25 hz and accurate, as said before distortion is distortion reguardless of what you are listening to.
    My Subs consist of 2 boxes (1.5cuft) with 2 12 inch Dyna Audio compound loaded drivers in each. 1600 dollars in drivers alone and they roll off around 24 hz but their sound quality is outstanding. I have owned bigger boxes with bigger drivers (at one point I had one with a 22in) that went lower and loader but I have yet to hear anything that sounds as good and that's what it is all about. I have a signal generator and CDs with warble tones but put them up long ago and trust my ears, if I like it then it is great.
     
  18. Erik_C

    Erik_C Stunt Coordinator

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    Hi. I'm the one who had the problem. I was out of town over the weekend, and when I got home Sunday night and turned on my amp and the Anthem, everything was better. I now get the subsonics I was missing last week. Who knows why it's working now, but it is, and I'm happy. Everything sounds great.
    -Erik
    ps: mine's the black one, not the silver one :^)
     
  19. Michael Mohrmann

    Michael Mohrmann Screenwriter

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    Erik,

    "Hi. I'm the one who had the problem."

    True, but as is the case any time someone posts a problem about the AVM-20, we all assume that we might be having the problem, and in this case not even know it. For myself, I had to perform the tests just for peace of mind.

    "I now get the subsonics I was missing last week. Who knows why it's working now, but it is, and I'm happy. Everything sounds great."

    That's weird, but great!

    Michael
     
  20. Jay Sylvester

    Jay Sylvester Supporting Actor

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    What test disc are you using? None of the stuff I have provides tones that go below 20Hz, and I'd like to verify that I'm not experiencing the same problem.

    Thanks,
    Jay
     

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