Opinion on Sub Setup

Discussion in 'Archived Threads 2001-2004' started by John Gido, Jun 28, 2002.

  1. John Gido

    John Gido Second Unit

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    I have a Yamaha RX-V595 A/V receiver and am using a Polk PSW350 for a sub. Which configuration will produce the least amount of distortion at near reference levels, LFE level on the receiver at "0" (-20dB to 0dB) & volume on the sub amp at "9 o'clock" or running the sub amp higher and the LFE output lower.

    I would assume that the second option would be more efficient because the receiver LFE level (pre-amp) signal would be lower than the sub amp level (amp), thereby producing less distortion.
     
  2. Vince Maskeeper

    Vince Maskeeper Producer

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    John,

    Your assumption is correct, however one issue:

    People have taken to interchanging the terms "LFE" and "SUBWOOFER" as if they are identical, and they are not. Usually a receiver or preamp unit will have 2 controls, one called LFE and one master control level for the subwoofer (like the master control level for the Center, Surrounds, Etc).

    The LFE control only affects the bass content on the dedicated LFE track of a 5.1 soundtrack. The Subwoofer control affects all signal going to the sub- both the rerouted bass and the LFE.

    As a result- the ideal is to place the LFE at a fixed point and adjust the overall sub level. This will keep both the LFE and the rerouted bass from other channels at a proper calibrated level.

    99% of the time, if you have a LFE control, the "correct" setting is to place it as high as it goes. This will make it so that the intended LFE output is correctly even with the rerouted bass output- and then you can adjust the subwoofer overall (using the subwoofer speaker output control) to get the overall level correct.


    After you handle the above- then your question comes into play. Usually it is best to run the sub wide open (or close), and adjust the level using the Subwoofer control in the preamp (again, this would be different than LFE control).

    -Vince
     
  3. John Gido

    John Gido Second Unit

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    Thanks Vince. I remember reading a thread on this a while back but couldn't find it quick enough.

    I have the LFE output set as high as it will go and after calibrating w/SPL meter and disk adjusted the volume on the sub amp to its current level (approx. 9 o'clock). Was watching "True Lies" last night and during the THX intro, the sub just didn't sound right although it sounded fine during the movie.

    Being a musician I remember that signals from a pre-amp should definitely be lower than the power amp used to amplify them to make them as clean as possible. I didn't know if the receiver/sub amp combination equated to a pre-amp/power amp configuration.
     
  4. Dustin B

    Dustin B Producer

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    John, I'll just add a little about what reference level bass entails. At full reference each of your speakers needs to be capable of hitting peaks of 105dB. The sub on the other hand is asked to produce 115dB peaks. However, if you are like most of us, you have all your speakers set to small and are rerouting the bass from all your speakers to your sub. This means now at reference your sub will be asked to produce peaks as high as 121dB at the listening position.

    This is Tom Nousaines data on the PSW350. It was measured 2m from the sub in a 7500ft^3 room with a strict limit of 10% distortion. In a smaller room the number will increase a little bit.

    POLK PSW350 - 99.8 / 25hz~82

    The first number is an average of peak output between 30 and 60hz and the last is what it could do at 25hz.

    With my current amp I can't get my speakers to 105dB cleanly. With a more powerful one I could. My sub comes close, but not quite there either (if I added a second one I could). However, I generally demo at 5dB (sub a couple dB hot) and watch at 10dB under reference (sub a couple dB hot).

    Bottom line is don't attempt too close to reference with your sub. Hopefully it has protection circuitry and will either stop or just sound bad when you push it to far. But none the less I'd stay at least 10dB below reference without the sub hot maybe even closer to 15dB.
     
  5. Vince Maskeeper

    Vince Maskeeper Producer

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    John,
    Check your receiver to see if you have two controls for bass level in the receiver: one for LFE and one for Subwoofer. They should be 2 different controls in the reciever, and then the actual subwoofer's volume on the sub itself... for a total of 3 controls.
    You should be able to set the LFE control at max, set the subwoofer's volume at max, and then dial the level using the subwoofer level output in the receiver.
    hope that is more clear
    -Vince
     
  6. Dustin B

    Dustin B Producer

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  7. John Gido

    John Gido Second Unit

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    Dustin,

    Thanks for the reply. I usually don't run anywhere near reference. However, with the weather being what it is here in NJ and my system being in my living room, we have a window AC unit making an awful lot of noise and I need to boost the A/V system a little louder thatn normal, but still no where near reference.

    Vince,

    I do remember seeing 2 different settings on the Yamaha for LFE/Sub. I will look into that further. I cannot see the need for running the amp on the sub at maximum volume as the room is not that large. Would running it a 50-75% and adjusting at the receiver still be OK?
     

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