parts express amp mod- random observations

Discussion in 'Archived Threads 2001-2004' started by Aaron_Smith, Feb 19, 2003.

  1. Aaron_Smith

    Aaron_Smith Stunt Coordinator

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    So I finally got around to modifying my parts express amp to the 24 db/oct. rolloff per John K.'s web site. The modification only involved the substitution of 4 components and only took me about 30 minutes- very easy job,especially for one with soldering experience. This amp is used with my sealed 122L tempest sub, and I'm about 80% music/ 20% home theater.
    The results are promising so far; I have much less mid-range bleed through than before, and the sub is more "invisible" than before; very important because it is being used in our living room, and my wife insists that the sub is hidden behind the couch (primary listening position). A few notes:
    - even with a 24 dB/oct slope and crossover set to ~70hz, male vocals come through. Much quieter now than before, but still enough to notice.
    - the only chance my sub has at being truly invisible to my ears is by positioning it very far away from the listening position. That way the relative volume of the midranges will be weighted more towards the monitors that are supposed to be playing them.

    Another thing- I've noticed that I have strong output at 40 Hz, greatly reduced at 31.5Hz, and nearly nothing at 20 Hz. Obviously no bass boost involved here. Frankly I don't really miss the low extension- but I'd be curious to know if this is consistent with the experience of other sealed tempest users in the group.

    Lastly- how do I post pictures in a message? I just finished some sound clearing house monitors that I wanted to brag about. [​IMG]
     
  2. Ronnie Ferrell

    Ronnie Ferrell Second Unit

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  3. Aaron_Smith

    Aaron_Smith Stunt Coordinator

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    I measured with rat shack SPL. I guess it really isn't down that much when the 10dB correction is applied- about 6 or 8 dB. However, as you noted, it is very hard to actually "hear" a 20Hz note.
    Thanks for the tip on picture posting. Sounds like a lot of work.[​IMG]
     
  4. Ronnie Ferrell

    Ronnie Ferrell Second Unit

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  5. Aaron_Smith

    Aaron_Smith Stunt Coordinator

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    HA! Who's that handsome devil?[​IMG]
    The fact that my web site lists performances back in August stands as testament to my strong dislike for web related stuff. Fortunately, the fact that I got married in October (and the Acoustic Cafe went out of business) has obviated the need to update the web site with new performances.[​IMG] The life of a hack musician in Austin...
     
  6. Chris Tsutsui

    Chris Tsutsui Screenwriter

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    You think your mid range bleeds, I've got a receiver crossover point at 540hz while I have to set my plate amps at 40hz. With that setup I still get a good deal of vocals and excess upper bass coming from the subs.

    Anyways, I found John K's site regarding modifications.

    So all you did was copy the diagragm at the very bottom of the page? That gets rid of the rumble filter doesn't it?

    Is there an easy way to have the rumble filter set to like 15hz along with having the crossover adjustable from 40-160hz (24db/octave)?
     
  7. Ronnie Ferrell

    Ronnie Ferrell Second Unit

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  8. Aaron_Smith

    Aaron_Smith Stunt Coordinator

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    As Ronnie said, it eliminates the rumble filter, which could potentially be problem with a vented sub. I know that people use tempests in infinite baffle applications all the time... I'm not sure how dangerous it really is if the sub goes past it's Xmax and bottoms. Seems to me that the suspension and the spider would keep everything in line... it wouldn't sound pretty though.
    This mod is probably most appropriate for sealed subs intended for music. If you are trying to wring every last bit of performance out of the driver for HT apps, this probably isn't such a good idea- but then, vocal bleed through to the sub isn't such a big issue for HT either.
     

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