Subwoofer using Twin Colossus 18XBs

Discussion in 'Home Theater Projects' started by johnBell, Apr 23, 2006.

  1. johnBell

    johnBell Auditioning

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    [​IMG] I'm in process of trying to construct a subwoofer using two Fane Colossus 18XBs which will be good enough to provide quality low bass for my excellent hifi setup, but also have the muscle to provide decent performance with my home theatre kit. I've got access to good facilities and materials for making the cabinet, but I have had conflicting advice about the best way to proceed, so I was wondering if there was anyone out there who could answer these questions for me:

    1. [​IMG] Should I go for a vented box? If so, should it be about 200 litres?
    2. [​IMG] The three different software programs I have conflict about what size to make the ports, and indeed therefore what to make the resonance of the enclosure - I want the beast to go down reasonably to about 20hz if possible because I listen a lot to organ music.
    3. [​IMG] Instinct tells me that I should make the drivers downward firing, but am I barking up the wrong tree to think this?
    4. [​IMG] I'm going to need a really powerful sub plate amp to drive two Collossus 18XBs in parallel - about 600watts RMS+ into 4 ohms. Does anyone know of such an amp, which can operate at 240v? (I'm in the UK)
    5. [​IMG] I already have the two new Fanes, so I really can't afford to replace them, but are they up to the job, [​IMG] or was I badly advised even about them? I don't doubt their ability to produce the SPL required, but can they go down low enough for what I want? [​IMG] [​IMG]

    I've got lots of other questions, but I would appreciate someone giving their learned opinion about the above. Cheers - JB[​IMG]
     
  2. BlakeN

    BlakeN Stunt Coordinator

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    You are going to have to use a vented box to get any kind of low end. You are going to need to do some heavy eq cutting to get 20Hz flat with those. With the high FS this speaker just isn't designed to go down that low. With the low xmax anything below 25hz and your speaker is going to bottom out. I would say build 2 boxes 112l and tune the boxes to 40Hz and see if you like it. Most of your music will sound great but you won't be getting anything in the 20Hz range.

    I would say sell them both for as much as you can get and buy a tumult http://www.adireaudio.com/Home/TumultSeries.htm , an aresenal http://www.ascendantaudio.com/arsenal15specs.html or even a maelstrom http://www.adireaudio.com/Home/MaelstromSeries.htm
     
  3. johnBell

    johnBell Auditioning

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    Many thanks for your reply, Blake. Much of what you say I have taken on board[​IMG] , but I bought the XB version of the Colossus because it has an xmax of over 7mm, which seems impressive for an 18 incher. Fane themselves suggest that the speaker can be persuaded down to at least 25hz with a low tuned box, but I completely take your point that overuse of equalisation will result in possible damage to the speaker at very low frequencies[​IMG] .
    Is it impossible then to have a box tuned really low, say 22hz, to enhance performance of sub-bass? I'm not really looking for thunderous performance down there for big films, but rather a clean sound for my music.
    Anyway, many thanks again for your advice[​IMG] , and I'm off to look at the other drivers you suggest. I suspect they are out of my price bracket, but I'm always willing to look and learn. Cheers, John[​IMG]
     
  4. SteveCallas

    SteveCallas Second Unit

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    Yep, my sub is tuned to ~14.7hz - it works because even before the output of the port comes into play, the driver is very capable to pretty low frequencies. With a ported design, a lower tune will give you cleaner bass in the musical range. The lower tune pushes the port output - and accompanying effects like increased group delay and increased port velocity - into frequencies where they will should no longer be audible (a good design should eliminate any chance of port noise being audible to begin with though). Essentially it behaves like a sealed design in the musical range yet still gets free output down low.

    From the sound of it though, that driver isn't up to the task. Can you share the TS parameters?
     
  5. johnBell

    johnBell Auditioning

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    Hi Steve,
    TS Parameters of Colossus 18XB as follows:

    Resonant Frequency (fs) 32 Hz [​IMG]
    Impedance (Re) 6.0 ohms
    Electromagnetic Q (Qes) .34
    Mechanical Q (Qms) 6.58
    Total Q (Qts) .323
    Voice Coil Overhang (Xmax) 7.2mm
    Surface Area of Cone (Sd) 1.12m2
    BL Product (BL) 25T-M
    Peak Dia. Displacement Vol. (Vd) 1.61cc
    Compliance Equivalent Vol. (Vas) 246 liters / 8.69 cu.ft.

    It's clearly the fs that is the main concern, as well I suppose as the Xmax problem that you identify, but the drivers do have appreciable output below free air resonance, and they will handle power well (but that doesn't save the speaker if cone excursion is too high, I know)

    Your further comments would be greatly appreciated.
    With thanks, John [​IMG]
     
  6. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    "The lower tune pushes the port output - and accompanying effects like increased group delay and increased port velocity - into frequencies where they will should no longer be audible"

    I would think that if the peak port speeds occur when the fundamental output is subsonic then it would actually be easier to hear chuffing - there's no audible fundamental to mask the chuffing noises.

    Just food for thought and like you said, good design prevents this in the first place.
     
  7. SteveCallas

    SteveCallas Second Unit

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    Correct, the port velocity should be kept in check to begin with by using a large enough port. The increased group delay won't be audible and the actual port output - depending on the tune - barely will if at all. Some sealed fans claim proclaim port output doesn't sound as clean as driver output - I won't argue that, instead, I'll push the port output down low enough where it will be felt instead of heard anyway.

    john, you honestly can't do too much with that driver for subwoofer use. I'd second the suggestion to sell them and I'd either get a SoundSplinter RLp15, or, if you really want to use an 18" driver, wait a bit longer until Ascendant Audio starts selling the Alliance 18. Either choice would make for a much better performing subwoofer.

    I didn't catch the Le parameter, but if I had to guess, I'd imagine it's pretty low, and thus, this driver is better suited for use as a woofer in a speaker design or possibly a superwoofer.
     

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