Help!! No High Pass Control on Many Subs. Why Doesn't This Make Sense to Me?

Discussion in 'Speakers & Subwoofers' started by Arthur S, May 11, 2004.

  1. Arthur S

    Arthur S Cinematographer

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    I thought I knew a fair amount about powered subs. Now it seems that I am just finding out that while virtually all powered subs have a low-pass crossover control, many powered subs have no high-pass crossover control.

    Is it because the pre-amp or receiver is supposed to handle high-pass, or what?

    Thanks

    Artie
     
  2. Wayne A. Pflughaupt

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    Yes, the pre-amp/receiver typically handles the high pass.

    Regards,
    Wayne
     
  3. John Garcia

    John Garcia Executive Producer

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    Otherwise known as bass management, you receiver can, and in most cases should, handle BOTH high- and low- pass.
     
  4. ScottCHI

    ScottCHI Screenwriter

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    well, no control, but there is a high-pass crossover. it's fixed, typically around 80-100Hz, for the speaker-level connections.
     
  5. Kevin C Brown

    Kevin C Brown Producer

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    I thought that any sub with speaker level inputs has this. The "crossover" freq knob is combined low pass (to the sub) high pass (to the speaker level *outputs*). ??
     
  6. Edward J M

    Edward J M Cinematographer

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    No, I also thought the same at one time, and DustinB clarified this. The high pass is almost always fixed - usually at 100 Hz. Only the low pass is variable.

    Yes, it doesn't make much sense. He says it's largely a cost issue. One would expect both the high pass and the low pass xo to be varied when the user tweaks the low pass filter, but that is not the case.

    Also keep in mind the subwoofer plate amp fixed high pass is typically 1st order (6 dB/octave), and the low pass is typically 2nd order (12 dB/octave). This compared to the typical AVR at 12/24 for the same.

    Also, don't confuse the high pass at 100 Hz with the infrasonic high pass designed to protect the woofer from overexcursion below the tune point. Most plate amps actually have TWO high pass filters.

    Regards,

    Ed
     
  7. Arthur S

    Arthur S Cinematographer

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    Thanks Edward

    My receiver is a couple years old and does not have variable high pass. As best as I can determine, the high pass xo is at 100Hz. Many receivers a couple years old or older had no adjustable high pass, and some were reported to have xo at 120 Hz.

    My receiver has a lot of the newer upgrades, i.e. DPL II, Circle Surround, 6 powered channels (tested to put out 92 watts per channel with all 6 channels driven simultaneously). In short, it meets most of my needs most of the time.

    I was counting on the sub high pass to overcome the 100Hz fixed high pass on the receiver. I don't feel the need for new electronics now, but I do want a new sub. I have my eye on the HSU dual 1220's and the HSU 500 watt amp. The standard high and low xo modules in the amp are at 51 Hz. What is also good is that you can buy plug in xo modules at any of these frequencies: 28;34;43;51;62;75;91;109;131, and 131 Hz.

    Some subs, for instance, Velodynes, come with a fixed high pass at 80 Hz. That is not too bad but if you have full range mains, 80 may be too high.

    Your recent tests of $600 subs was quite something. Thanks for all the time and effort you put into that project.

    Artie
     
  8. Edward J M

    Edward J M Cinematographer

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    Hi Artie:

    80 Hz works very well for most HT applications where the AVR is doing the digital BM.

    Even 100 Hz is OK most of the time, but it can sometimes result in localization of the subwoofer depending on its location in the room with respect to the other speakers.

    Even if the AVR has an adjustable xo, you wouldn't want to set it much lower than 80 Hz for HT, because the LFE (".1") channel is only low passed, and you risk lopping off content otherwise.

    In the case of the TN1220 set-up you described, the user would need to set the L/R mains to large, the other speakers to small, and the sub to off/no. The output from the L/R mains is sent to the 500W amp, and the user selects the desired xo frequency module based on the bass capabilities of the L/R mains.

    The only reason I generally would shy away from a speaker level connection like described above is that it still requires the AVR amp stage to deliver a full range, full power signal into the 500 watt amp.

    If your AVR has pre-outs for the L/R channels, and the 500W amp can accept those, that would be much easier on the AVR amp stage.

    Of course, the 500 watt amp probably has an LFE (unfiltered) low level input too, if the user wants to let the AVR do the digital BM.

    Depending on the flexibility of the AVR and the 500W amp input array, you have a few options here.
     
  9. MikeNg

    MikeNg Second Unit

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    FWIW,

    Low Pass = High Cut
    High Pass = Low Cut

    People often get confused as to which portion of the bandwidth is getting lopped off.
     
  10. Mike SJ

    Mike SJ Supporting Actor

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    ...
     
  11. Edward J M

    Edward J M Cinematographer

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    A properly configured BM circuit can/will send "all" (i.e., redirected bass and the LFE .1 channel) the bass to the subwoofer via the sub pre-out.

    And this is indeed the most popular connection method. It's not perfect because the final roll-off slope of the speakers and the subwoofer are often disparate, but it is still the most popular method nonetheless.

    But for someone like Artie who owns an AVR with a fixed 100 Hz xo for digital BM, he needs to look at other connection options if he wants to use a lower xo.
     
  12. Kevin C Brown

    Kevin C Brown Producer

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    Ed- Thanks for the info. Now it makes more sense when it's suggested to twiddle the "low pass" freq knob for the smoothest transition between lows and highs. Not only a function of the low freq capability of the mains, but *also* how the low freq knob plus mains' response overlaps with the high pass in the sub.
     
  13. ScottCHI

    ScottCHI Screenwriter

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    is that really suggested?

    many subwoofers have a xover bypass switch or an "unfiltered" input. if they don't, it's usually recommended that the xover be set to it's maximum value, if a "filtered" output, such as the LFE channel, is being fed to the sub from the receiver.
     
  14. JohnnyG

    JohnnyG Screenwriter

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    What bugs me about most subs is that they call their variable low-pass filter a "crossover", which it isn't. There's no such thing as a low-pass crossover or a high-pass crossover, since neither are actually crossing anything over anything! They are low-pass filters and high-pass filters.

    Some subs have true crossovers, some have fixed high-pass and variable low-pass filters, and some have only a variable low-pass filter. Have fun finding out which is in a particular sub!
     
  15. Wayne A. Pflughaupt

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    I imagine they call it a “crossover” because most people aren’t familiar with the term “filter.”

    Regards,
    Wayne A. Pflughaupt
     
  16. Kevin C Brown

    Kevin C Brown Producer

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    I always thought: crossover = high pass + low pass

    Scott- "Twiddling" for using the speaker level inputs, not the RCA connection. For the RCA, I agree, either set the low pass as high as possible, or turn it off.
     

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