Technical Questions...Please Help

Discussion in 'Archived Threads 2001-2004' started by Mat_M, Jan 3, 2003.

  1. Mat_M

    Mat_M Stunt Coordinator

    Jan 3, 2003
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    The bottom line is, I need to know what kind/type of signal comes out of a receiver's "subwoofer" RCA connector. What is the frequency range (10-150Hz?)? What is the typical amount of power sent? How is the signal processed from DVD to the connector? Will a low/medium-end receiver send out a crappier signal than a high-end receiver? If so, how? Narrower range of frequencies? Noisier signal? And ultimately, how will these differences affect the subwoofer's audio output?

    If you can, be as technical as possible.

    The motivation behind this series of questions is this: I consider myself an intermediate level HT person looking to upgrade. My first upgrade picked out is an SVS 16-46-PC+ subwoofer. I want to utilize this subwoofer's frequency range as much as possible, but I'm concerned that my receiver won't be sending it a wide (and low) enough range. I currently have a Harmon Kardon AVR300.

    Thanks for the help,
  2. PaulT

    PaulT Supporting Actor

    Oct 28, 2002
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    The LFE output is a 'Line Level' signal which could be up to 1 or 2V depending on your receiver. I downloaded the manual for your AV300 and it is not listed in the spec sheet. You will have to contact HK to find out.

    The Freq Response should be on the order of 10Hz to 80 or 100 (could be as high as 150Hz), again you need to find out what the LFE Out Freq cutoff is set to on your receiver by contacting HK. Typical new receivers are set to 80 or 100Hz, with mid to higher end units having adjustable settings. I would assume your unit is fixed.

    You do not need to concern yourself with the range of Freq your receiver is sending out of the LFE channel, however, you should try and find out what the upper cut off frequency is in order to set your sub to better match your mains.

    The differences between low or high end receivers would be the ability to have better Bass Management (adjustable Cut off freq to the Sub) on the higher end units.

    Hope this helps. Others out there may be able to improve on this reply.
  3. Bob McElfresh

    Bob McElfresh Producer

    May 22, 1999
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    Hi Matt. Welcome to HTF!
    Short Answer: the quality of the sub, placement in the room has much more effect on the low frequency sounds than the low/medium/high quality of the receiver.
    Lets start with the basics...
    BASS MANAGEMENT: Your receiver lets you define if your 5 speakers are LARGE or SMALL. And it lets you tell it if you have a subwoofer.
    If you have some small speakers, and a sub, your receiver will send to the LFE port:
    - All signals from a DVD on the ".1" track
    - All signals intended for any SMALL speaker below some frequency "A"
    Inexpensive receivers have a fixed crossover "A" of about 80 hz. The more deluxe receivers let you set the crossover.
    This means the LFE port will produce a frequency range of 10 hz (pipe organ music) to about 80 hz.
    THE SIGNAL: The LFE port is considered line-level/un-amplified. It carries almost no current and you should use a coaxial-cable to carry the signals to the sub.
    Have you ever cut a piece of CATV coax? If you cut one of your interconnects (video or audio) they would look nearly identical to the CATV coax in construction. The center conductor is usually a solid wire, 18 ga, surrounded by white insulation. Around this is either a foil/braided "shield". This protects the weak signals in the middle and acts as the zero-volt reference.
    So all coaxial cables have a 'shield' and you should use one of these cables to connect between the LFE port of your receiver and your sub.
    Look at these numbers (you wanted technical):
    Subwoofer: 10-80 hz: 70 hz bandwidth
    Audio: 80-22,000 hz: 21,920 hz bandwidth
    Component Video: 500K-4Meg: 3,500,000 hz bandwidth
    HD Video: 1-35 Meg: 34,000,000 hz bandwidth
    Do you see the bandwidth for the sub? How hard do you think it is for a receiver to produce this un-amplified signal?
    Answer: it's trival.
    Your existing HK receier is more than fine for that SVS.
    Big Hint: Search this fourm for posts on how to find the optimal subwoofer placement. Then search for "BFD" and "House Curve" to learn how to measure your rooms response and compensate with a Behring Feedback Destroyer.
    This equipment will run you:
    - Test Tone CD: $15
    - Radio Shack SPL Meter: $40
    - Behring Feedback Destroyer: ~$150
    This $200 investment is cheaper than a new receiver. And to 'do it right', you would have to do all this even if you had a flagship receiver/processor.
    Hope this helps.

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