What Frequency Band are the LFE in...

Discussion in 'Archived Threads 2001-2004' started by Richard_s, Apr 16, 2002.

  1. Richard_s

    Richard_s Second Unit

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    Sorry All I know I read this in a post here just can't seem to find it.
    I have the SA-wm40, Polyfilled (approx 18 oz - port left unobstructed), Placed on top of Oak platform with spikes, 40# barbell weight with felt pads on it place on top of case.
    I am interested in if even with these mods the subwoofer is going low enough to use for the LFE/Bass for HT. Not the "feel" but for the sound (loud explosions, gunfire etc). I never felt the Sa-wm40 was capable of "shaking the room".
    Right now as best I can tell using the AVIA sweep test I am -3db at 28hz-29hz definitely no booming. Maybe with some placement I can get it lower but given my room this may not be possible. Is this low enough for the frequency band used for the LFE/Bass effects.
    I also set my system at reference level and put on some music with heavy base and cranked up the subwoofer until my radioshack SPL meter read 110db (seemed boomy but I guess in this kind of test this is expected) and it appeared to handle this just fine (did not go to 121db just too loud OK for quick peaks maybe). I also left my Subwoofer set properly and cranked up the amplifier to 100db stereo only mode(JBL n26 + Sa-wm40) seemed clear and crisp was not aware of any distortion or booming.
    Can't find the Newbie thread/manual that was being worked on is that still around I wanted to read it through again
     
  2. Phil Iturralde

    Phil Iturralde Screenwriter

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  3. Harold_C

    Harold_C Stunt Coordinator

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    -3 dB at 30 Hz would provide very good performance in a home theater system. Doing better than that requires spending a lot of money on a sub/amp combination.

    I doubt that the Sony subwoofer will actually do that. I don't know the Thiel-Small parameters for that driver, but the cabinet size looks a bit small for a typical 12 inch driver to get that low in a vented enclosure. It's probably tuned with a peak at 50 or 60 Hz for efficiency, which is not the end of the world.

    The sub is almost certainly underpowered for full Dolby reference level output. However, room gain and other factors probably make it fine for volume settings say 3 to 6 dB below Dolby Reference Level.

    I would just calibrate the sub to the same SPL as your other speakers on the Radio Shack SPL meter -- perhaps set the sub a few dB lower to compensate for the inaccuracies of the meter.

    It should sound fine up fairly close to Dolby Reference levels. My guess is that Sony follows standard Japanese design practice and builds so much current limiting and protection circuitry into the sub amp that it would be difficult to damage the subwoofer no matter what you do.
     
  4. Richard_s

    Richard_s Second Unit

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    Phil: Thanks I will read all the references.

    Harold:

    Glad to hear if I can get to 30Hz then this should do quite well for HT.

    When I run the AVIA sweep test from 200 down to 20 there are peaks and valleys (some +6 db some -6db but they are narrow bands). In general it holds +/-3 db over this band. The warble test also holds quite level and seems very uniform throuought the test to my ears.

    The Sony holds (with the mods described) from 65 down to 30 (definitely) within a band of +/- 3db so I guess that seems quite good for a subwoofer of this size. Not sure what is meant by a "tuned peak" and what that means to subwoofer performance, I am still learning. I set the power level of the sub to match the mains in the AVIA setup. After doing the crossover adjust I go back and tweak the level a tad (they seem to interact). In the AVIA front speaker set-up I can run the main adjusted to 85db and by cranking the volume all the way up on the subwoofer keeping the receiver set for the 85db I can get to approx 112db from the subwoofer seems quite good but can not tell if distorted.
     
  5. Harold_C

    Harold_C Stunt Coordinator

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  6. Richard_s

    Richard_s Second Unit

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    Phil:
    In reading the links you supplied it raised a question. I am leaning towards getting the Denon 1602. This has a subwoofer output that according to what I can find out is not affected by the "small" speaker setting (80hz) rather one has to use the subwoofer crossover to balance. In the links it talks about the receiver needing to MIX the LFE and the redirected bass to the subwoofer output. Does the Denon unit do this? I was planning to set up the system making all the JBL's "small".
    Harold:
    Yes I am sure room gain has alot to do with it. With the modifications I was able to eliminate the "boom" and allowed for me to move the Subwoofer into positions in the corner it is in to bring up the base while not having the subwoofer boom. I do not have a great room to deal with so I am happy with the results. the room is 16x24 with a cathedral 14 foot peak in the middle right were the TV and the listening positions are.
    Have to go rent "phantom menace" and see how the system sounds the ultimate test.
    I assume an "anechoic chamber" is one devoid of acoustic gains.
    Thanks for you input.
     

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