1. The Rules have been updated regarding posting as a business on TGP. Thread with details here: Thread Here
    Dismiss Notice

Cutting cone from speaker to use as a dummy load possible?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by cap'n'crunch, Feb 15, 2009.

  1. cap'n'crunch

    cap'n'crunch Member

    Messages:
    1,405
    Joined:
    Dec 27, 2004
    Location:
    NH
    Would a speaker with a removed cone still handle the rated wattage? I've got some old audio speakers that are relatively high wattage lying around wasting space. Can a guy cut the cones out and place a speaker in a box to use as a dummy load. I've got a 10" that is 150 watt RMS rated and want to use it as a dummy load for a 50 watt tube amp.
     
  2. thilton59

    thilton59 Member

    Messages:
    80
    Joined:
    Jan 22, 2009
    Location:
    CA
    I've never heard of doing that, but you would have to make sure that the ohm values match(from amp to speaker). Or you could save the speaker and get a resistor and a piece of sheet metal...
     
  3. hasserl

    hasserl Member

    Messages:
    4,734
    Joined:
    Oct 24, 2004
    Location:
    So Cal
    Yes you could, but how would you keep the whole assembly together with no cone to hold it? Solve that and you could have something like Weber's MASS.
     
  4. cap'n'crunch

    cap'n'crunch Member

    Messages:
    1,405
    Joined:
    Dec 27, 2004
    Location:
    NH
    Well, I would only be cutting the cone about halfway or so so that the coil wires are still attached to the cone. Next I would mount the speaker face first to a piece of plywood with some foam rubber pressed up against the coil to keep it from moving and perhaps popping out. Then simply build a case around it with a jack mounted in the case. I suppose a guy could even mount the modified speaker to the back panel of a closed back cab with an added jack to plug into it. The 150 watt audio speaker that will be the subject already has some cone damage anyway so, its basically trash anyway. I've been using it as a load mounted in a sealed box already but, just wanted to keep it from vibrating across the floor while in use.

    Thanks for your replies...
     
  5. gtrnstuff

    gtrnstuff Member

    Messages:
    2,263
    Joined:
    Oct 19, 2005
    Location:
    Middle TN
    Sounds like you've got a plan. What's the worst that could happen? Voice coil rubs and shorts out? I'm into the DIY experimental head space sometimes, but if you really need reliability, I'd recommend the Weber MASS also.
     
  6. hasserl

    hasserl Member

    Messages:
    4,734
    Joined:
    Oct 24, 2004
    Location:
    So Cal
    But you need the movement of the voice coil to get the reactive load. I don't think holding the VC stationary is a good idea. It'd be simpler and better to just buy a large power resistor, they aren't very expensive.
     
  7. Trout

    Trout Member

    Messages:
    7,576
    Joined:
    Jun 23, 2006
    Location:
    Illinois/Far West Burbia
    Get yourself a piece of bicycle inner tube, use it to make a dummy cone/load. Glue the coil to it and mount it frame .

    I would use some crappy 100W 5 inch car speaker to keep the size down.
     
  8. phsyconoodler

    phsyconoodler Member

    Messages:
    4,351
    Joined:
    Jul 11, 2005
    Location:
    calgary canada
    Or just order a big resistor from your local electronics store.

    Or read Gerald Weber's book about usiing an old speaker to make a headphone amp.
     
  9. ntasher

    ntasher Member

    Messages:
    36
    Joined:
    Jan 18, 2009
    I think you are heading for trouble... First off, the actual load would be lower than the speaker rated 8ohms - it will be just the DC resistance - somewhere between 3-5 ohms. The actual load has a reactive part that is the result of cone movement in the magnetic field.
    Second - you will generate substential heat that will probably exceed the design margins of the speaker. The coil movement allows for heat to dissipate into the air. The result would be premature failure of the load that can take away your OT and power tubes in a heartbeat. Now THAT is going to hurt. Please use power resistors to make a dummy load.
     
  10. donnyjaguar

    donnyjaguar Member

    Messages:
    4,242
    Joined:
    Nov 4, 2005
    Location:
    Canada
    Hasserl is right. The impedance of the speaker is determined by the resistance of the suspension on the cone, and of course the air it is moving. If you remove the cone and just leave the spider in place, it'll bottom out at very low power and the impedance that it will present to the amplifier will be much higher than normal. Use a power resistor and be done with it.
     

Share This Page