L/r + Lfe

Discussion in 'Speakers' started by GregBe, Jun 17, 2004.

  1. GregBe

    GregBe Second Unit

    Jul 9, 2003
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    Tell me if this is reasonable. I have Cambridge Soundworks MC300 main speakers that have two 4"woofers and one 1"tweeter. I have received help before regarding crossover settings, but I have a new receiver, so I am back at it. I am trying to figure out crossovers on my H/K DPR-1001 which allows for separate crossovers for each channel. My speakers supposedly go down to 80Hz, but they really only are solid down to about 100-110 before they start to taper off. I have been messing with my crossovers and decided that 80 was too low, and have been undecided between 100 and 120. 120 has more umph and presence, but 100 seems to have more detail in things such as acoustic guitar.

    I noticed that my new receiver has a L/R + LFE setting which will play the front channel sound info below the crossover in BOTH the front channel speakers and the sub. In my MC300 owners manual, it says that the speakers should be used with a sub and driven full range. They have an internal crossover that will not let them play info they can't handle. I recognize that normally you want to cut off the signal at some point above the F3 so as to not distort the sats with something they can't handle.

    Is this internal crossover/cutoff in my speakers something that all speakers do anyway? Or is this a design characteristic of CSW? To my ears and to my warped line of reasoning, I can get the best of both worlds. If I set the receiver to L/R + LFE and the crossover on the receiver for the mains at 120, I get detail in my mains to down to 80 Hz (even though some of it is at minimal dB's), and get the impact of the sub up to 120 to fill in the limitations that all sats have in the midrange. I obviously don't want to do this if my sats are distorting, but to my untrained ear, I am not noticing this.

    Sorry for being so long winded. I could have written a few more paragraphs describing my situation, but hopefully this is enough to get some help.

  2. Aaron Gilbert

    Aaron Gilbert Second Unit

    Sep 17, 2003
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    I think the best way to find out the answer to you questions is simply to experiment. I can address a couple though. I'm not familiar with the MC300 speakers, so I cannot speak to what possible high-pass crossover they may have built in. However, just knowing that they are 4" woofers, I would say that even without a high pass crossover inside, they are going to inherently roll off at about 12dB/octave below 100Hz or so, as you have witnessed. This is true of all speakers. They have what's termed an F3 point, at which the output level is down 3dB from the midband. For sealed speakers, below F3 response rolls off at 12dB/octave, and for vented, response rolls off at 24dB octave. All that said, there is still an advantage to filtering the low frequencies at the receiver before sending them to the speakers. If you send full range to the MC300's, they will still be trying to reproduce all the frequencies below 100Hz, which will add distortion to the higher frequencies, and reduce the power handling at those frequencies.

    I do prefer to run my front L/R full range and set my subwoofer to L/R + LFE, as in my system this sounds the smoothest. However, I've got two 7" woofers in each front speaker, with clean extension down to 30Hz, so power handling and distortion are not issues.

    Aaron Gilbert

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