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Thread: Low pass filter

  1. #1

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    Question Low pass filter

    This may be a stupid question, but here it is anyway. If I set my receiver's low pass filter at 100hz, does that mean that only frequencies less than 100hz will go to my subwoofer? Does it also mean that my other speakers will only play frequencies above 100hz or does the receivers low pass filter only affect the sub? Also, if the sub's high is 120hz is there anything wrong with setting the receivers filter at 150hz (assuming that it doesn't affect the other speakers)?

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    Bell, the filters in the receiver are both a low pass to the sub and a high pass to the speakers, at least theoretically at the same selected frequency. These filters don't suddenly cut off all response above or below that frequency, but roll it off at about 12-24 dB per octave, depending on the design. So, there's some blending of the sub above the crossover frequency and the speakers below it.

    The most commonly suggested crossover frequency is 80Hz(if the speakers have good response that low)which has been found to be a good compromise, being high enough to take some of the low bass load off the speakers and the receiver amps and low enough so that the location of the sub isn't easy to detect(you shouldn't be aware of the sub as a separate sound source). So no, you shouldn't set the crossover at 150Hz except with very small speakers that don't have much response below that point. Set 80Hz, or 100Hz if that's the lowest setting that the receiver has.

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    There are no stupid questions. Look at your speakers freq. and set the sub to that, the smaller the speakers the higher the freq. will be. Then you need to use the sub to make up the differance that is where having full range speakers comes in and the sound is much better. Just listen to the Bose systems at CC and unplug the sub, some of the mids dissapear, having a fuller range speaker the mids and highs are played through the speakers and only the lows are comming through the sub.

    Dave

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    That is a good explaination. Belling does have small speakers so to avoid a dip in the frequency response it may be better to experiment with the higher filter settings.

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    Default Re: Low pass filter

    Originally posted by Belling
    ...if the sub's high is 120hz is there anything wrong with setting the receivers filter at 150hz (assuming that it doesn't affect the other speakers)?
    Actually this would leave a gap in the combined response in the 120 to 150 Hz range. You either want to set your sub freq to its highest setting (or use its LFE input) and do the bass management at the AVR. This avoids both any double filtering of the sub's signal and gaps.

    As to where to set the AVR, as JK said, 80 Hz is pretty standard. It's low enouigh that localization of the bass becomes difficult, but high enough to unburden the mains, which often results in better bloom to the midrange. Even bookselves should be strong to and somewhat below this frequency.

    Slight exception to what I think dave posted. You want to be far enough above your mains' -3 dB lower limit that you're solidly into their "flat" responce region. If you select an AVR cross-over point that is too low, then a different double filter emerges, the AVR x-over and the natural roll-off of the response of the bass driver(s).
    More later,
    Tour...
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    Default Re: Re: Low pass filter

    Originally posted by Tour2ma


    As to where to set the AVR, as JK said, 80 Hz is pretty standard. It's low enouigh that localization of the bass becomes difficult, but high enough to unburden the mains, which often results in better bloom to the midrange. Even bookselves should be strong to and somewhat below this frequency.

    Tour, I agree with that even for bookselves, but he is running the RM6700 speaker set, does that still hold as a good setting for them given they are an even smaller speaker? I was thinking he would probaly end up in the 110-120HZ area when done, does that sound right for those?

    Dave

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    Question

    Dave Shepard is right. I have rm6700 speakers which are very small and have an advertised low of 95hz. If I base manage from my receiver my choices are 100, 150 or 200hz. I am thinking of getting an SVS sub (it's in a big room) but other suggestions are welcome (see my previous main post). The SVS 's high is 120hz. I suppose that I could mannage base at the sub by turning off the sub at the receiver. What should I do?? (I plan to buy a new sub but buying other new speakers is not an option at this point.) Thanks for all of your help.

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    The SVS will do 150 Hz, as will any other decent 10" or 12".

    Just select 150 Hz in the AVR, disable the low pass filter at the SVS, set all the speaks to small, and set the sub to on/yes.

    Your only other choice is speaker level, and using the low pass filter at the subwoofer. Most sub amps have a 1st order fixed high pass at 100 Hz, and a 2nd order variable low pass. It would probably work with your rig, but its a PITA.

    If you go speaker level, set all speaks to small except the L/R mains. Set the L/R mains to large, and set the sub to off/no. Run the speaker level output from the AVR to the sub, set the low pass on the sub at around 100-110 Hz, and then run the speaker level out back to the L/R mains.

    Due to the high xo, the sub will be easy to localize (this is a problem with any tiny sats that require a high xo).

    No matter which brand sub you buy or which connection method you select, I advise keeping it somewhere near the front stage preferably in between the L/R mains and close to the center channel. That will minimize localization.

    Doc
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    Default Re: Re: Re: Low pass filter

    Originally posted by dave shepard
    Tour, I agree with that even for bookselves, but he is running the RM6700 speaker set...
    Yup, that's different... NEVERMIND...

    Doc's got him...
    More later,
    Tour...
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    Better to remain silent and be thought a fool, than to open your mouth and remove all doubt. - Old English Proverb

    "It's easy to get lost in price vs performance vs ego vs illusion." - doro
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    Rebuilding Maggie 2-ch & Amazing 2-ch... Building 2-ch "wall"... Figuring out the HT

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    Thumbs up

    Thanks Doc, and thanks again to everyone who responded. A couple more questions: 1) If the SVS subs will do 150hz, why does their web site state 120hz? 2) Would it be better to set the AVR at 100 0r 150hz? Polk claims that the rm6700 speakers have a low of 95hz. Thanks again.

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    It will start to roll-off and get a bit of a ragged FR in the 120-150 Hz region. I think it will handle 150, but it won't be optimum, and most subs are happier below 100 Hz.

    If you set the AVR to 100 Hz, you might see a shallow depression below the xo, but it shouldn't be severe. Try both settings and see which sounds best. I wouldn't go below 100 Hz until you get larger speakers, though.
    "What we do in life echoes in eternity"

    Ed Mullen (emullen@svsound.com)
    Director - Technology and Customer Relations
    Specialty Technologies
    SVSound

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    As far as a sub recomendation mine is still the same as I stated in your other post. The room size dictates it and you will have the sub for furure speaker upgrades when you are ready, the sub needing upgraded will not be required and will give you an ass beating in the mean time :D . SVS is the only sub Co. one needs to coincider (IMO), I've auditioned many before making pulling the trigger and am sooo glade I went with them and so will you I promess.

    Dave

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