Multimeter suggestions

Discussion in 'Archived Threads 2001-2004' started by Joel Grice, Feb 24, 2002.

  1. Joel Grice

    Joel Grice Extra

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    Can anyone suggest what to look for in a multimeter for measureing T/S parameters? I know I need to look for one that measures frequency, but what else is good?

    Also, if anyone has any specific make and model suggestions, it would be greatly appreciated.

    Thanks,

    Joel
     
  2. Patrick Sun

    Patrick Sun Moderator
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    I would think for T/S parameters you need a Woofer Tester, which you can get from Parts Express pretty easily, but thay are not cheap ($200 I think).
    No multimeter is going to measure frequencies, per se, w/r/t speaker driver testing. You'll need a frequency generator source, and a calibrated microphone device, and some software to record the frequecy/SPL readings. I suggest you mosey over to WayneJ's Speaker Builder site for information on that topic.
     
  3. Marv

    Marv Stunt Coordinator

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    Joel, "The Woofer Tester" from Parts Express would be the easiest. But a multimeter can come in real handy anyway. I suggest a meter that measures in "True RMS" they seem to provide (for the most part) more accurate readings as the freq changes. Some cheapo meters don't read any AC voltage with any accuracy unless it's 50~60hz. I've got 3 meters and I can get 3 different readings on the same AC source as frequencey changes. Here is a link to some meters with great specs Extech and some very cool SPL and Data Logging meters. Radio Shack did/does carry some of them on their website. Praxis from Liberty Instruments is some free software that will measure T/S parameters. I just use my PC and some FreeWare tone generating software and this MS Excel spread sheet T/S Calc to get my own measurements with my multimeter.
    I can provide some more links to some freeware if you need them.
    -Marv G
     
  4. Bob Hill

    Bob Hill Stunt Coordinator

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    Not to get too far off topic but why aren't more of the DIYers using an oscillioscope for measurement and calibration of their respective home theaters? I am new to the home theater thing and I was just curious about this.
     
  5. Joel Grice

    Joel Grice Extra

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    Thank to all for the help and info.

    The PE woofer tester is price prohibitive.

    First, I will try the Praxis route. Marv, if I use Praxis, do I still need a multimeter? Any links to any info or software that will help me make my measurements will be appreciated.

    Bob, I thought about this but I know nothing about oscilliscopes and all of the buttons, dials, etc look very daunting. I checked eBay and found some but they were somewhat expensive. What are your thoughts?

    Joel
     
  6. Marv

    Marv Stunt Coordinator

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    Excellent point Bob. I wish I had one. Here is a link to a free software oscillocsope True Audio .
     
  7. Bob Hill

    Bob Hill Stunt Coordinator

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    I was thinking that a good O-scope would handle most all of the testing applications that you would come accross in a home theater enviornment. I currently don't have one but I do plan on getting a good rack mount one within a few months to calibrate virtually everything in my home theater and home recording enviornments.
     
  8. jeff lam

    jeff lam Screenwriter

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    O-scopes are great. They can measure just about anything including frequencies. Although I wouldn't spend money on one. Most reliable ones are in the $2000 range, with some getting up into the $12000 range.

    I believe the digital HP ones I used in school were $4500 each.
     
  9. Mark Krawiec

    Mark Krawiec Agent

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    if all you want to do is measure TS, then i think, the praxxis (without the $800 breakout box!) is the way to go.

    you also get an rta which would be what you'd want to measure room response, all for free. of course, you need a mic and maybe a preamp (not sure if the praxis setup requires this) which will cost you- but calibrated diy mikes can be had for 30 bucks or so.

    whether or not to get a scope is a more complicated question. by itself, a scope really isn't that useful to measure speaker parameters or room responses. you'd need to add some form of signal generation, as well as a mic/preamp, all of which would need to be calibrated. the kind of data you'd generate wouldn't be in the form typically used. and you'd end up spending as much as you would have for something like a complete praxxis setup (or clio, or any of the other measurement setups)
     
  10. NikhilC

    NikhilC Auditioning

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    If you're looking for a multimeter just for T/S measurements, try out Speaker Workshop. It's currently free software that uses your soundcard for impedance measurements to derive T/S parameters (among other things). Accurate and excellent. If you spend around $60, you can put together a rather nice speaker design/measurement setup with a jig to interface with and a calibrated mic with pre-amp. For more information on Speaker Workshop and extras, check out Eric Wallin's Audio DIY Projects.
    Good luck,
    Nikhil
     
  11. Blake R

    Blake R Stunt Coordinator

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    If you?re examining video, or something like radar or television frequencies sure get a scope, but to calibrate a home theater system? A scope is essentially a wide band amplifier/active filter. Why analyze in-room audio bandwidth limited signals with a scope? Have you ever tried to design a 20 MHz class ?A? amplifier? Even a modest bench scope like a dual trace, 20 or 30 MHZ(video bandwidths) is pretty expensive. But what?s the point? Compared to video, audio spectrum bandwidth is within epsilon of zero. Forget it. Go on down to Rat Shack, get the SPL meter, take some room measurements using intelligent parameters like ?sweet spot sub only?, ?sweet spot mains only?, ?sweet spot mains+sub?, etc. etc. Have fun with it. Find the audio hole or the room cavity resonance. Mine is 64Hz. Run some test tones in octave or decade steps, get your log paper out (or PC) and plot a room response curve. Or just get the PC based audio analysis tools. Don?t go broke getting lab gear unless you?ve got some serious AF/RF design to do.

    RBR
     
  12. BruceD

    BruceD Screenwriter

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    Bob and Blake,
    Here is a very effective HT calibration tool. It uses MLS signals and FFT to perform extensive acoustic measurements of your speaker/room interface. Even shows you where that SPL meter can be responding to room modes in the
     
  13. Rich Kraus

    Rich Kraus Stunt Coordinator

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    "Also, if anyone has any specific make and model suggestions, it would be greatly appreciated."

    though it has been made clear that a multimeter aint the way to go for testing speakers- they are really handy to have around anyway. its like carying a decent folding knife, you never knew how handy it was to have around, until you had it around.

    bummer is they aint cheap either. figure $200-300 for a mid range fluke or beckman. im a fluke fan myself, currently using a fluke 79III for my "round the house" testing, twiddling, and tweaking. might want to look at the new(ish) fluke 100 series meters. IIRRC, they are nifty little meters and they are a good bit cheaper than the 70 and 80 series meters.
     
  14. Joel Grice

    Joel Grice Extra

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    Everyone keeps stating that I can't use a multimeter to measure T/S parameters. I beg to differ. Again, I've never done this yet but I've done a lot of research so far.

    From what I've read, you only need a tone generator, a multimeter, an amp and some resistors. By measuring different voltages and resistances, you could calculate the T/S parameters.

    Yes, it's a lot of math but that's the fun part.

    Am I wrong? Is this a bad way of doing it?

    Please let me know,

    Joel
     
  15. Mark Krawiec

    Mark Krawiec Agent

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    joel, of course you can.

    if the DMM doesn't have a freq counter you will also need one. otherwise you're quite right and the basic procedures are in LDC or in Testing Loudspeakers

    good for theory but in practice very tedious.
     
  16. Marv

    Marv Stunt Coordinator

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    Joel, here is an easy to use tone generator that's popular around here. NCH Tone
    And that True Audio link to "TrueRTA" is a very good tone generator. The meter I use for measurements is the Radio Shack 22-174 ($89.99) True RMS. It's a little slow but works very well. You will not need a freq counter when using tone generating software because you already know the freq. ----Also that "TrueRTA" has a true rms meter function which I have not tried yet. You could get all your testing done with very little investment. It does not take much of an amp to do the testing either (2-10watt should be fine)as long as you calibrate the level often. I already done the math for you if you can use that MS Excel link I gave earlier, but if the math is fun for you then go for it, it's a great way to learn.
    -Marv
     
  17. Marv

    Marv Stunt Coordinator

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    Oops almost forgot to mention that when using your PC or amp for that matter make sure that there is no eq being used, eg- equalizer.
     
  18. Joel Grice

    Joel Grice Extra

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    Thanks Marv,

    That Radio Shack MM is the exact one I've been loooking at.

    The tone generator that you mentioned is also the one I have been playing with.

    I do love the math and for me the whole point of the DIY is for me to learn. I designed my box on paper and then checked myself using Unibox.

    I think I'll try it with the MM.

    Thanks,

    Joel
     
  19. Patrick Sun

    Patrick Sun Moderator
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    Joel, if you have the time, energy and enthusiasm for doing the measurements in this manner, more power to you. Just remember, some of us are sorely lacking in most of those areas at their current stage of life. [​IMG]
     

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