Big car driver needs HT amp...

Discussion in 'Archived Threads 2001-2004' started by Peter Bourgon, Mar 22, 2002.

  1. Peter Bourgon

    Peter Bourgon Auditioning

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    I found a steal on Infinity Reference 12" woofers, and am interested in building my own single-driver subwoofer for my home theater. The driver is a a massive beast, intended originally to be used in a car audio application. It takes 300W RMS, 1200W peak and has a 4 ohm impedance (which may cause problems).

    My original thought was to use a car amp to power it, and using an old PC PSU to get the 12VDC to the amp, but I quickly realized that adequate ampres would not be fed to it in this manner. Further, professional DJs I know assure me that trying to convert power to feed into an amp is just a Bad Idea(tm) to begin with - out goes the idea of using a bridge rectifier to get 120VDC and stepping it down massively!

    So, understanding that the concept behind this project is cost-effectiveness, can anyone suggest to me a realistic way to power this woofer in a home theater setup? Be it a particularly cheap amplifier that has gained a reputation for being halfway decent, or some homebrewed scheme for driving big woofers like this one, I'd like to hear everything you guys can throw at me. Bear in mind the impedance will likely cause some problems... alternative suggestions welcomed. I really want to make a DIY-project out of this one.

    Regards,

    Peter Bourgon
     
  2. Dustin B

    Dustin B Producer

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    Power handling is just about meaningless when it comes to sub design. Can you find us the rest of the T/S specs. Then we can help you out some more.

    It doesn't matter if you goose a driver with 1400W, if in the allignment you've choosen 1400W will get the driver to three times Xmax. As an example for this, a Tempest has a Pmax of 700W RMS. But in an EBS ported enclosure it only takes about 250W to get it to Xmax.

    As for amps there are several that are quite cost effective. As an example the QSC RMX 850 can be had for $299 new, less used and can put out 850W into 4ohms when bridged.
     
  3. Kyle Richardson

    Kyle Richardson Screenwriter

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    No problem with it being a "car" subwoofer....just hook it up to an inexpensive plate amplifier like the Adire AVA250 or the Parts Express #300-794. Both of those amps will handle 4 ohm loads and put out 250 watts.

    Kyle Richardson

    Acoustic Visions
     
  4. eric nyhof

    eric nyhof Stunt Coordinator

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    For $135 you can get a plate amp from parts express that puts out 272 watts into a 4 ohm load. I don't know how good it will sound though because car audio drivers are usually lower quality that home audio drivers. Theya re usually designed for small enclosures and small volumes. Then agian it might sound great.

    But back to the amp, I baught one a few weeks ago to power a shiva sub in a 5 ft^3 box. I'm still waiting on the sub and for right now i have a 12" orion from a car. Its not designed for such a big box but it still manages to shake the cabinets all over the house,
     
  5. Peter Bourgon

    Peter Bourgon Auditioning

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    Certainly. The T/S specs are below, or alternately in a much easier to read PDF at: http://manuals.harman.com/INF/CAR/Bo...s/REF1220w.pdf
    VOICE COIL DC RESISTANCE: Revc - 3.43 ohm
    VOICE COIL INDUCTANCE @ 1 KHZ: Levc - 1.16 mH
    DRIVER RADIATING AREA: Sd - 82.15 in^2
    MOTOR FORCE FACTOR: BL - 10.86 Tm
    COMPLIANCE VOLUME: Vas - 4.55 cubic feet
    SUSPENSION COMPLIANCE: Cms - 320.47 ┬ÁM/N
    MOVING MASS, AIR LOAD: Mms - 137.20 grams
    MOVING MASS, DIAPHRAGM: Mmd - 130.14 grams
    FREE-AIR RESONANCE: Fs - 24.00 Hz
    MECHANICAL Q: Qms - 8.21
    ELECTRICAL Q: Qes - 0.60
    TOTAL Q: Qts - 0.56
    MAGNETIC-GAP HEIGHT: Hag - 0.31 in
    VOICE-COIL HEIGHT: Hvc - 1.25 in
    MAXIMUM EXCURSION: X-max - 0.47 in or 11.91 mm
    Also, I noticed several people pointing me to plate amps that put out less than 300W RMS. I'm not looking for the highest fidelity, clarity or power in this sub - just a little more 'feel the music' power at lower volumes. That said, will these plate amps be powerful enough to put out that kind of juice? What sort of corrolation should I be making between the driver's rated nominal and peak wattage and the type of amp I'll have to put into it?
    Thank you so much for your help,
    Peter Bourgon
     
  6. Dustin B

    Dustin B Producer

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    Remember it takes a doubling of input power to get a 3dB increase in output from a driver. So the difference between 250W and 500W will only be 3dB. And 3dB is not a great difference. Unless it is a really low efficiency design 250 watts will be oodles of power.

    Out of curiosity, how much of a steal is this driver? Because a Dayton DVC12" will easily outperform it for $105USD.

    Throw the Dayton in a 120L enclosure with a 4" flared port tuning it to 20hz with 160-250W power applied and you will have a very nice sub for very little money.
     
  7. Rudy H

    Rudy H Stunt Coordinator

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    Exactly what Dustin said, the 12inch Dayton DVC will beat it performance wise, for music and moreso in HT, and will probably cost less. And it has a 5 year warranty.

    Plus the Infinity wouldn't be suitable for a vented box where as the Dayton would be fine in one.

    I use a 15inch Dayton DVC with the Parts Express 300-794 plate amp, and it really does put out a ton of power.
     
  8. Pat K

    Pat K Stunt Coordinator

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    Basically, Infinity Reference series sucks.. I was thinking you had an Infinity Perfect..thatd be a different story.
     
  9. Peter Bourgon

    Peter Bourgon Auditioning

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    I'm getting the Infinity reference driver for $60 shipped. Actually, it's two drivers for $120 - a buddy of mine is going to be building an identical woofer, except to put in his car.

    I just stepped out of the garage after finishing the enclosure, more or less. It's a completely sealed design, which may or may not be ideal for the application but was an order of magnitude easier to put together for my first DIY sub. It's also considerably smaller than a ported design would have been, and since portability is somewhat of an issue a smaller design would be better. I made it out of 3/4" MDF, used silicone sealant on all of the joints, and will be padding the inside and perhaps staining the outside to match the rest of my setup. Who knows.

    I will pick up that 300-794 plate amp from Parts Express - or rather, place an order - this afternoon. If there is anything else someone might think I'm overlooking, please chime in; I really appreciate all of the help I've received here.

    Regards,

    Peter Bourgon
     
  10. Jack Gilvey

    Jack Gilvey Producer

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  11. Peter Bourgon

    Peter Bourgon Auditioning

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    The specifications on the driver stated that 1.25 cubic feet of internal air would be optimal for a sealed enclosure. I clocked in just above this, allowing a threshold for the volume the cone itself takes up as well as any braces or supports. Turns out that the box was sturdy enough without any internal bracing, so no volume was taken up by that - but I hadn't originally planned on using a plate amp, so I think that should cover that volume.

    So, yes, slightly more than 1.25 cubic feet. Just around 35L, actually, which is a lot less than the 120L you listed above. Does this seem odd?

    Regards,

    Peter Bourgon
     
  12. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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  13. Jack Gilvey

    Jack Gilvey Producer

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    I'd agree on the Dayton, I think (know) it would be a much better mate to your box. Modeling that Infinity in 35L shows a Qtc of ~1.0 even heavily stuffed, so it'll be pretty boomy, and curtailed deep bass, with a resonance of ~50Hz. That recommendation must be for a car, where boominess is a virtue and cabin gain can make up for anemic lower response. Even in that box with "only" 250 watts, it's reaching its excursion limits below 35Hz.

    Looking closely at that .pdf file, you can see the same response I described in the "out-of-car" graph, the hump @ 70Hz and the deep drop.
     

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