Sub-sonic filter for standmounts?

Discussion in 'Speakers' started by JohnSmith, Mar 5, 2004.

  1. JohnSmith

    JohnSmith Supporting Actor

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    I have a pair of ported standmounts in my Hi-Fi system, biamped with four 60W channels (50Hz - 22KHz +/- 3dB (free space conditions) not using a subwoofer.

    Because frequencies below the port could produce noise is it worthwhile using a sub sonic filter on the LF terminals?
     
  2. Edward J M

    Edward J M Cinematographer

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    A ported speaker will typically exhibit a 4th order roll-off (in an anechoic or quasi-anechoic environment) below the tune point; that's pretty steep.

    Port noise will be more of an issue at/near the tune point than anywhere else in the bandwidth. I think excessive cone excursion below the tune point is more what you should be concerned with.

    Excessive cone excursion could bottom the driver, and also will modulate the midrange frequencies (this phenomenon is called intermodulation distortion) since the mid-bass driver is probably crossed over to the tweeter at around 2000-2500 Hz.

    It couldn't hurt to add a 2nd order (or higher, maybe even 3rd or 4th order) high pass filter at maybe 45 Hz to protect the drivers from excessive low frequency energy if they are being driven on full range and you really drive them hard. The midrange should clean up a bit too.


    [​IMG]
     
  3. JohnSmith

    JohnSmith Supporting Actor

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    Thanks for the info. These are the speakers.
    http://www.ruark.net/products/Contemporary/etude.shtml

    How much would a high quality, high pass filter cost? Would I connect it to the speaker cable to between the LF terminals and poweramp? Why's it called it a high pass filter- I would think calling it a Low Pass filter would make more sense?

    I'm sending the speakers full-range (stereo integrated amp) passively bi-amped.

    I assume if you use ported standmount/bookshelf speakers at normal listening levels then you wouldn't need one of these?- you would only need one of you notice parping/distortion/port noise.
     
  4. Edward J M

    Edward J M Cinematographer

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    I would tend to agree. These speakers are not appropriate for reproducing really deep/powerful bass, so you shouldn't be sending them that kind of source material at high volumes.

    These kinds of things tend to be self limiting. If the speaker starts to sound crappy, turn it down - simple.

    Another way to skin this cat is to buy an A/V receiver or pre/pro that has a decent on-board bass management circuit. You could set the speakers to small (which imposes a digital high pass filter at the pre-amp stage), and set the crossover to say 40 or 50 Hz.

    The nice thing is that this method will conserve amp power since you will be sending the amp stage an already filtered signal. In comparison, imposing a high pass filter after the amp stage (like you are considering) still requires the amp to deliver a full-power, full-range signal, obviously.

    Regards,

    Ed
     
  5. JohnSmith

    JohnSmith Supporting Actor

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    Thanks for the info again- but no way I would replace the integrated/poweramp system with a AV amp or av pre-amp- even my £5500 Lexicon MC-1 doesn't close to the sound quality offered to me by my stereo integrated amp, considering the MC-1 is about 6x the cost- it's worse for 2ch, and inferior DAC's to my off-board DAC.

    I guess if I really wanted to do it propely I should think about active bi-amping, which I'm not willing to do (requires new speakers, Linn for example)
     
  6. JohnSmith

    JohnSmith Supporting Actor

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    What about something likes this?


    CD-->DAC-->SS Filter-->Integrated-->Poweramp-->Speakers

    Placing a line-level sub sonic filter at the DAC RCA outputs- therefore the stereo integrated amp plus the 2 channel poweramp won't be getting ~40hz and below.

    I don't wish to replace the DAC, integrated or poweramp.
     
  7. Edward J M

    Edward J M Cinematographer

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    Yes, I think that will work. It won't be an infrasonic filter, per se, since you are looking at around 40-45 Hz.

    There are some real filter eggheads (and I mean that in a good way) running around this forum (Dave Alan being one IIRC). Seek them out for specifics. I would imagine filter quality varies (like anything else in this world), so a crapola filter might indeed do its job, but SQ might suffer too if you aren't careful.
     

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