Mt - Vs - Mtm

Discussion in 'Archived Threads 2001-2004' started by Clif Forsyth, Dec 5, 2002.

  1. Clif Forsyth

    Clif Forsyth Extra

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    I have seen quite a few speakers that come in either a MT or MTM arangement. They add a second driver to the MTM. The second driver a mid/base is the same as the one in the MT. So essentially you have 2 mid/base drivers(of the same type) and 1 tweeter. The crossover is the same it's still a 2 way. What benefit can be derived from this that you can't get from the MT with just the 1 mid/base and the tweeter?
     
  2. Patrick Sun

    Patrick Sun Moderator
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    You get a speaker with a higher efficiency (but you have to take into account the polar radiation response of a MTM in the vertical orientation, and this usually means using 3rd order or higher crossover slopes to help in that aspect).

    Most of the time, it's the midwoofer that limits the level of overall efficiency for the speaker. By adding the 2nd midwoofer, you get a boost in efficiency (3db - 6db), even after accounting for baffle step loss. But MTM almost always produced a speaker that would be rated for 4 ohm load (requiring an amp that could handle a low impedance speaker load) if 8 ohm nominally rated midwoofers are used.
     
  3. Clif Forsyth

    Clif Forsyth Extra

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    So, really what you are gaining is effeciency which means a higher spl which means a speaker that is louder at a given power input. And most amps put out more power at 4 ohms than 8 ohms theorectically if the speaker can handle the power then it can be driven louder. But as far quality goes there is really no difference unless you use a 3 way crossover. Am I on the right path here?
     
  4. You gain efficiency. will usually require 4ohms. Will tend to have better imaging. Will have a much smaller sweets spot (vertical dispersion).
     
  5. Patrick Sun

    Patrick Sun Moderator
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    The crossover will still be a 2-way crossover, but with 3rd order slopes (or higher) to handle the vertical dispersion issues.
     
  6. Mark Fitzsimmons

    Mark Fitzsimmons Supporting Actor

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    Some MTM's use a 2.5 way crossover design. This is where the speaker works basically like a 2 way but the second M is low passed at say 800hz or so. So the second woofer is used only for these lower notes where the extra displacement is going to be most advantagous. Polk LSi9's work like this.
     
  7. Mark, AFAIK, the 2.5 way is usually arranged as an TMM not an MTM.
     
  8. Brian Bunge

    Brian Bunge Producer

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    Tony,

    Check out the PSB Stratus Bronze and Stratus Silvers. They're both MTM's and both 2.5-way speakers.

    P.S. Did you get to check out your cap/resistor stash over the Thanksgiving Holidays?
     
  9. [​IMG] ...I must admit that I forgot until after it was too late. My fiance is coming up here tomorrow for my B-day and I had her brother set the parts aside for her to take with her. If you click on my link below, you can see my list of caps and resistors PRIOR to the HTF LT project. While the larger values are mainly used up, I am pretty sure that the low value cap supply is still good. On the resistors, ALMOST all of the ones listed are valid to a reasonable quantity. I will update it right when she gets here.
    (again, sorry)
     
  10. Brian Bunge

    Brian Bunge Producer

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    Tony,
    That's OK. If I'd waited another day to ask you could've faked it![​IMG] I need an exact copy of the LT you built me so if you wouldn't mind checking your stash when she brings it I'd appreciate it. That's assuming you still have the numbers for my specific LT.
     
  11. Brian, I have records of EVERYTHING from that project [​IMG] ...well..almost.
    Here are the numbers for your project
    Actual
    Qtc=0.707
    Fb=33.99hz
    Wanted
    Qtc=.6
    Fb=18hz
    Theor.
    R133.640
    R273.630
    R3119.960
    C10.412
    C20.047
    C30.116
    Actual
    R133.000
    R275.000
    R3120.000
    C10.420
    C20.047
    C30.115
    % diff
    R1-1.9%
    R21.8%
    R30.0%
    C11.9%
    C20.0%
    C3-0.9%
    make-up
    R133
    R275
    R3120
    C10.22, 0.20
    C20.047
    C30.1, 0.015
    oh..and sorry for hijacking the thread:b
     
  12. Clif Forsyth

    Clif Forsyth Extra

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    No problem this leads into another question I have about exactly this subject. I am going to start a speaker building project for a 2 way mini monitor. The design and specs I found on the internet. The crossover used is a 2 way 4th order L-R. The author is very specific about the crossover components. One of the things he mentioned was measuring his capacitors to 1% of the design values. This leads to my question. can I measure capacitance with a standard multi meter or do I need something specific.
     
  13. Patrick Sun

    Patrick Sun Moderator
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    You'll need access to a LCR meter, not a conventional multi-meter.
     
  14. Aaron_Smith

    Aaron_Smith Stunt Coordinator

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    I would be pretty thorough about checking out your amp/reciever's specs for a 4 ohm load. Many of the ones that are "safe" for 4 ohms have much higher distortion at that load. Most home theater recievers have pretty wimpy power supplies compared to true hi-fi amplification and have a tougher time providing enough current to drive a 4 ohm load effectively. To correct it, they simply put a 4 ohm resistor in series with the speaker terminals that is added to the circuit with a switch on the back panel (8 ohm/ 4 ohm). If you find one of these switches, I'd avoid 4 ohm speakers.
    The sound quality would in fact be different with an MT vs. an MTM. The MTM will have a smoother polar frequency response in the vertical plane.
     

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