To Leviathon or not?; that is the question.

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  • 4-iron
    Junior Member
    • Aug 2003
    • 13

    To Leviathon or not?; that is the question.

    Hello… I’ve been in the silent majority long enough. Over the course of several years now, you have helped me without ever knowing it. Today, I break my silence and join your group. I hope the water is warm. )

    Recently, I was fortunate enough to acquire a pair of Aurasound 1808 18” sub drivers; one of which is slated to upgrade the family’s HT. I used Kristian Ougaard’s UniBox 3 to model a vented system at 100 W which I found a 340 L cabinet tuned to 20 Hz seemed to be reasonable. Although the driver is rated at 800 watts and will be driven by a 700 watt/8 ohm Carver amp, I chose 100 watt nominal power as a more pragmatic value – the SOF -- )

    The problem is that the Aurasound’s response is only fairly ‘flat’ in the 20 to 40 Hz range, then it continues to slowly ramp up.

    20 Hz – 108.6 dB
    30 Hz – 109.5 dB
    40 Hz – 110.2 dB
    50 Hz – 111.1 dB
    60 Hz – 112.0 dB
    70 Hz – 112.8 dB
    80 Hz – 113.5 dB

    300 Hz – 117 dB

    Now, for HT that’s not all that bad of a thing, right? But for the vast majority of us, we have a one-world HT/music system. And for music, flat is where it’s at – or at least for the most part.

    Here is where the North Creek Leviathon question comes into play. The second driver is in possible need of a re-cone kit, which is available from the manufacturer for $150 or so. But, if you look at the specs for the Leviathon (customized 1808), it is clear that George has done his homework. The predicted response for a vented Leviathon for a 300 L cabinet tuned to 18 Hz is spot on -- smaller cabinet, lower tuning and response as flat as a torsion box. Even better would be 340 L at 17 Hz. I can send him my driver to have it reconditioned into Leviathon specification, but at the $400 asking price + S/H in both directions, I’m not quite ready to break out the VISA card just yet!

    So, here are my considerations:

    1). How important is maintaining a flat response when utilized in HT mode out to 80 Hz?

    2). Am I better served by spending the difference -- $250+ -- between the two available kits on a Behringer DSP1124 to EQ the sub and listening room response as well? (as suggested at http://www.theaudioworx.com/ -- Electronic Room Treatment & Loudspeaker Correction). DSP1124 info found here:

    http://www.behringer.com/02_products/prodindex.cfm?id=DSP1124P&lang=eng

    3). Can I manipulate the parameters myself starting with a standard 1808 kit?

    4). Should I simply continue with the good driver in hand going with the 340L/20Hz alignment as mentioned above?

    And finally…

    4). Is this ‘flat’ response thing just a pipe dream anyway considering room acoustics and such?

    I started a MDF prototype just to get my feet wet, but before I begin to cut any hardwood stock for the final project, I’d like to wait and see what you guys have to say. For those of you playing along at home, here are the associated T/S particulars.

    Thank you for your time and help. I appreciate it!

    Aurasound 1808
    Fs 24 Hz
    Re 5.0 ohm
    Qms 4.1
    Qes 0.20
    Vas 558 L
    Xmax 18mm
    Le 0.47 mH
    Sd 1240 cm^2
    800 W (100w)

    Aurasound NRT-18 (upgraded 1808 cone kit)
    Fs 25
    Re 5.6 ohm
    Qms 4.4
    Qes 0.28
    Vas 475 L
    Same…

    NCMS Leviathon
    Fs 14 Hz
    Re 5.0 ohm
    Qms 11.3
    Qes 0.337
    Vas 579 L
    Same…
  • ThomasW
    Moderator Emeritus
    • Aug 2000
    • 10934

    #2
    Hi, and welcome to HT-Guide......

    My understanding is that George's 'custom' driver has a second cone epoxied over the first. That stiffens the cone and adds mass = lower Fs and lower efficiency. It may look better 'bench racing' with software programs, but may be of limited benefit in real world use.

    IMO a combination of both passive room TX, combined with prudent use of active EQ, results in optimal-in room performance.

    At the usual street of $134 delivered the Behringer is the best deal in EQ out there. It's only limitation is the lowest EQ point being 20Hz.

    I think you're on the right track. Making a test box is the only way to know what's really going to happen in your room. 17-18Hz tuning is probably best. Of course you're going to use a 10" port, right?

    Regarding 'flat' response, it's virtually impossible to obtain and if obtained usually results in an over-dry sound. Most people target flat response then dial in added tweaking, to create a 'house-curve' that's tailored to their taste.




    theAudioWorx
    Klone-Audio

    IB subwoofer FAQ page


    "Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-Bresson

    Comment

    • 4-iron
      Junior Member
      • Aug 2003
      • 13

      #3
      Hello...

      The Behringer EQ has always been part of the plan since I first read your ditty over at AudioWorx. I think that makes a lot of sense.

      With all the tweaking in box volume, tuning and such, the predicted response from 40 to 80 Hz remains relatively unchanged. So, I turned my focus to the 16 to 40 Hz range. I landed on 340 L tuned at 17.5 Hz. This looks like a good staring point.

      This also falls very close to what Wilson Audio does with their XS sub. I estimate that monster at about 779 L. Allowing for bracing, port volume and driver displacement, I figure Wilson tuning at or near the 350 L/driver range – this, keeping in close with where I’m at now.

      I’m opting for an 8 inch port in lieu of the 10. A 10 inch port is required only at the very highest of power levels (>700 W) and at that point, I doubt my ears would be able to pick up the port ‘chuff’ anyway. But maybe my neighbors could though!

      Thanks, 4-iron

      Comment

      • 4-iron
        Junior Member
        • Aug 2003
        • 13

        #4
        Hello…

        I made mention of a ‘possible’ need for a re-cone kit on one of the drivers. The basket, cone, surround, voice coil and spider are all in fine shape. Only the tensile leads between the cone and terminals are bad. Are any of you aware of a ‘kit’ or easy fix to repair such a problem?

        I used de-soldering wick to replace the bad section and that actually worked pretty well. But, I’d like to do the job properly if a better fix is available. It seems a shame to have to do a whole re-cone kit if that’s all that needs to be replaced.

        Thank you,
        4-iron

        Comment

        • ThomasW
          Moderator Emeritus
          • Aug 2000
          • 10934

          #5
          Paul

          I'm not aware of any aftermarket company that offers just new leads. Why not contact AuraSound and ask if they'll sell you some new leads. The only issue would be attaching them to the VC.

          BTW I think your use of solder wick is a very clever idea. :T




          theAudioWorx
          Klone-Audio

          IB subwoofer FAQ page


          "Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-Bresson

          Comment

          • Hank
            Super Senior Member
            • Jul 2002
            • 1345

            #6
            I started a MDF prototype just to get my feet wet, but before I begin to cut any hardwood stock for the final project, I’d like to wait and see what you guys have to say.
            You're not planning to make a "hardwood" cabinet are you? Just curious.

            Comment

            • 4-iron
              Junior Member
              • Aug 2003
              • 13

              #7
              Hello Hank...

              Thank you for your interest. I make my base cabinets using MDF and baltic birch plywood. The outer shell is 3/4" MDF. The base is doubled up to 1-1/2" MDF to provide support for spike hardware. The rear panel is 1-1/2" laminated MDF and baltic ply. This allows enough room to fully recess the speaker lugs/plate and provide additional back wave damping.

              The front baffle is 2 layers of MDF and 1 baltic ply for a 2-1/4" thickness. For 8" diameter drivers or less, I typically use the drill press and a large Forstner bit to cut air relief scallops. With a driver of this size (this is a VERY large driver!) I won't have to worry about the front baffle 'choking' it's air flow. All internal bracing is baltic ply set into dadoes to provide strength and accurate placement during glue-up. I also use interlocking rabbet joinery to mate the sides to the top and base which makes for an air tight fit and aids in assembly -- no glue drift.

              I use the bandsaw to resaw hardwood stock for veneer -- typically 1/8" to 3/16" thickness. Then joint and edge-glue to create veneer sheets. This allows enough 'meat' to work a soft radius on the edges if desired and there's no risk of sanding through to the MDF substrate. If I want a larger radius such as on the front baffle, I cut the quarter rounds from the same stock maintaining color and grain continuity. Also, the book-matching grain pattern has a very nice look.

              Of course, I don't go through all that trouble of joiner details and such when making a prototype. I simply oversize the basic 3/4" MDF only cabinet -- glue and screw -- then creep up on the desired volume and tuning by adding solid fillers and/or trimming the port. Once satisfied, I then go back to the workshop with a final draft plan.

              This is probably MUCH more than you wanted! ops:

              Comment

              • Hank
                Super Senior Member
                • Jul 2002
                • 1345

                #8
                No, 4-iron, that's fine, and a good cabinet construction method, ala NorthCreek (MDF outer, solid core plywood inner). I was just concened that you might be considering solid wood construction. Have fun!

                Comment

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