Subwoofer crossover issue - Paradigm

Discussion in 'Speakers' started by Tom_Mack, Jun 8, 2004.

  1. Tom_Mack

    Tom_Mack Stunt Coordinator

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    I have had a Paradigm PDR-10 subwoofer for the past few years. I am using the receiver's crossover (Denon 3805) set at 80Hz. With the subs crossover was at its highest level (150Hz) low-mid bass was missing. I set the sub using an SPL meter and AVIA (even 4 dbs hot!). Now after moving the sub everywhere in the room and having the same problem, i tried lowering the crossover on the sub to around 90Hz. I checked the SPL again and the bass level was down about 15dbs! I raised the sub volume and the mid-bass and low-bass returned!

    Does this make sense? If the receivers crossover was at 80Hz, shouldn't the subs crossover be at its highest level without any adverse effects? Or could the room/sub mix be causing a peak in the >80Hz frequencies and lowering the crossover "fixed" this problem?
     
  2. Edward J M

    Edward J M Cinematographer

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    Setting the subwoofer's low pass filter to 150 Hz should have little to no effect on the sound if your 3805 is imposing a 4th order low pass filter at 80 Hz on the subwoofer via the digital bass management circuit.

    If you set the subwoofer's LPF to 90 Hz, you will in essence cascade the 3805 LPF and the subwoofer LPF. The subwoofer LPF is probably 2nd order, so the combined filter rate will be 6th order (36 dB/octave) above 90 Hz. This will simply roll the sub off more quickly above 90 Hz than the 3805 could accomplish alone.

    None of what you are describing should have really affected the low bass response of the subwoofer. Sounds like something else might be the culprit. Just double check the following:

    All speakers set to small.
    Pre/pro xo set to 80 Hz.
    Sub level to -5 in the pre/pro.
    DVD player set to bitstream.
    All dynamic range control circuits off in DVD and pre/pro.
    All bass limiters off in pre/pro.
    LFE channel level set to max (i.e., unattenuated level) in pre/pro.
    Low pass filter disabled or set to 150 with the sub.
    Sub and speaks calibrated with Avia or internal AVR tones.
     
  3. Tom_Mack

    Tom_Mack Stunt Coordinator

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    All speakers set to small.
    YES

    Pre/pro xo set to 80 Hz.
    YES

    Sub level to -5 in the pre/pro.
    -3

    DVD player set to bitstream.
    YES

    All dynamic range control circuits off in DVD and pre/pro.
    YES

    All bass limiters off in pre/pro.
    NONE

    LFE channel level set to max (i.e., unattenuated level) in pre/pro.
    NO LFE channel. Just Sub.

    Low pass filter disabled or set to 150 with the sub.
    Like I said, this causes issues whether it should or not

    Sub and speaks calibrated with Avia or internal AVR tones
    YES



    I also tried setting the sub crossover to 90Hz, calibrate using AVIA, then reset the crossover to 150Hz. SPL levels raise by around 10-15dbs. The meter is definately picking up a spike in the sub's upper frequencies. Odd.

    I'm going to try to use a tone generator and see just where the spikes are with the crossover at 150Hz and if there are any dips if I set the sub to 90Hz. From listening to the bass frequency sweeps, obviously the LFE drops from 90-120Hz, buy the other channels sound better with the lower sub crossover. Again odd.
     
  4. ScottCHI

    ScottCHI Screenwriter

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    what are you measuring exactly to come to this conclusion? an avia tone?

    is the spike just above 90Hz perhaps?

    also, the labelling of the frequencies around these crossover knobs on subs are notoriously "off" on many subs.
     
  5. Tom_Mack

    Tom_Mack Stunt Coordinator

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    I expected this. Until I can pinpoint what the problem is, I'm just setting the knob to what sounds best to my ear.
     
  6. GrahamJW

    GrahamJW Stunt Coordinator

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  7. Tom_Mack

    Tom_Mack Stunt Coordinator

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    Thanks John.

    I believe this answers my questions completely.
    There must be something wrong with the cutoff on the PDR subs. I guess I'll keep the knob at 100Hz until I get a better sub. I don't think I'll miss that 100-120Hz range on the LFE too much.
     
  8. Polaris

    Polaris Auditioning

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    Hey Tom,

    I have a couple of suggestions you may wish to check out: Before I get to that, let me just say that I only know Paradigm to make good products and although the PDR-10 may not be the company's current flagship, I'm sure it's still a pretty decent unit. The same can be said for your Denon AVR. In other words, my presumption is that your challenge is NOT due to substandard audio gear!

    There is some further info that may be helpful, but in the absence of that I shall rely on mere intuition.

    If the sub has a phase/polarity adjustment, I suggest playing around with it. It may be an infinitely variable adjustment between 0 and 180 degrees say (typically a rotational knob), or some sort of 'click-stop' or toggle switch that adjusts the phase in fixed increments (like 0 OR 180 degrees). Your sub may be currently playing partially or fully out of phase with respect to your mains. If that is indeed the case, you shall surely observe attenuated mid and deep bass especially with music program material. The effect is normally more pronounced in the mid-bass but can carry over into the deep bass if your mains are capable of substantial deep (< 45 Hz) bass output and the high-pass Xover in the AVR is of low order (gentle slope). Note that when you calibrate the speaker levels of an HT system with pink noise and a sound level meter, you do so speaker by speaker which does not reveal the speaker interactions that shall occur when they all play together.

    If your sub does not feature phase/polarity tweaking capability, try reversing the polarity of your mains by swapping + for - (red for black) on the speaker connections on the rear of your AVR. Do this VERY carefully with the AVR unplugged checking over all connections before firing everything up. Ensure there are no stray wire shunting strands etc. You may also take this opportunity to ensure that all your mains are actually in phase (you may wish to verify polarities on the speaker ends of the cables as well)!

    NB: The reduction in dB when you turned the Xover on the sub down is 100% normal when calibrating a sub's level with pink noise. In turning the Xover down, one attenuates the upper part of the band and reduces the (upper) bass energy that emanates from the sub. Of course, it can also be possible that there is some gain/crossover interaction but I am assuming such is not taking place: Even so, gain/crossover interaction is typically a very minor issue and can be easily compensated for.

    One more thing: If you can defeat or bypass the crossover in the sub, do it! In addition to the excessive attenuation caused by cascading crossovers, Analog/LCR filters are notorious for the group delay they introduce. Time alignment in audio reproduction is critical in obtaining accurate sound. If you want that kick-drum to exhibit a natural attack and decay with a nice tight/snappy texture, bypass the sub's Xover. Always remember that the low frequency sounds from the sub must mate with the upper harmonics/partials/overtones from the mains for faithful recreation of musical timbre. If you cannot defeat the sub's LP Xover, turn it up to its highest pass frequency (typically fully rotated in a clockwise direction - 150 Hz in your case).

    I hope this helps. If not, we'll just have to try something else!

    Keep well and enjoy your rig!
     
  9. Robert_J

    Robert_J Lead Actor

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    Hello Dexter. Welcome to HTF. You may want to check the posting dates before you offer advice. I don't think Tom waited around for 5 years before taking action on his problem. He hasn't posted here in 4.5 years.

    -Robert
     
  10. douglas-b

    douglas-b Stunt Coordinator

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    Beter late than never, a Dexter.
     
  11. Polaris

    Polaris Auditioning

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    HAHAHAHAHAHAHA!

    Alright guys, alright! I glanced at the wrong date as the message post date! HAHAHA! How embarrassing. I really found it weird that the components were so dated (PDR-10 and 3805)!

    I'd be more careful next time!

    Cheers
     
  12. MarvinJr

    MarvinJr Stunt Coordinator

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    lol that's the 2nd post I have read like this, where the thread was years old and got a reply. i was just reading along like it was new too. I see why it's confusing.....because each post shows todays time and date too for some reason.
     
  13. Robert_J

    Robert_J Lead Actor

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    Check your profile because I see the date/time when the post was made. But then again, I've been through a few software upgrades on this site and my default settings may be different than the new members.

    -Robert
     
  14. Clinton McClure

    Clinton McClure Casual Enthusiast

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    Hey I had a PDR-10!
     
  15. Stephen Tu

    Stephen Tu Screenwriter

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    I think the problem is that the post date is this small, non-boldfaced font at the top of the post, while the "local time & date" (referencing *now*) for each poster is listed under the username and are big & bold. I think that this "local time, local date" information is not very useful & potentially confusing, and should be removed.
     

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