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Thread: measuring Thiele-Small parameters - what am I missing?

  1. #11
    Join Date: Oct 2016

    Location: Bolton, England

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    I'm Andrew.

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    Thanks for the offer Geoff - much appreciated. I have the Thiele/Small parameters for some of the drivers from manufacturer's data sheets, but I'm not looking for data for any particular drivers, I'm trying to learn how to make measurements. Simply looking up specs from data sheets or other sources won't help me learn how to make measurements, so I'll have to get stuck in and get my hands dirty - best way to learn in my opinion

    Basically, I'm intrigued to learn what makes a good speaker sound good. Is it how expensive the drivers are? Is it the complexity and sophistication of the crossover? Is it the simplicity of the crossover? Is it a "perfect" driver/cabinet/vent Thiele/Small alignment? I'd like to do some playing about and find out what I can. My opinion (prejudice?) at present is that it's quite possible for speakers to be "all wrong" in terms of flatness of frequency response etc. yet still sound very nice. Do they sound better as refinements bring them closer to being "correct"? Let the research (or playing about ) commence.

  2. #12
    Join Date: Jun 2008

    Location: N. Ireland

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    I'm Steve.

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    Very soon I will have in my possession (if the postman gets a move on) a DATS V2. I am hoping to use it to measure a pair of drivers I have recently acquired. One thing I will need to check though,
    and that is the required accuracy of the weight of the additional mass I will add. I have a roll of tape and I have weighed it on 2 different industrial machines, both giving 324 grams. Now, they cant
    measure fractions of a gram, will this be accurate enough?
    They swim... the mark of Satan is upon them. They must hang.


    FLAC / WDTV Live / Cambridge Audio / Tannoy VX12

  3. #13
    Join Date: Apr 2012

    Location: Southall, West London

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    I'm Geoff.

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    What mass are you thinking of adding and where?

  4. #14
    Join Date: Jun 2008

    Location: N. Ireland

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    Quote Originally Posted by walpurgis View Post
    What mass are you thinking of adding and where?
    Hi. Is this aimed at me? I have seen people simply lay a chunky roll of tape on the woofer cone, centrally of course before performing the sweep.
    They swim... the mark of Satan is upon them. They must hang.


    FLAC / WDTV Live / Cambridge Audio / Tannoy VX12

  5. #15
    Join Date: Apr 2012

    Location: Southall, West London

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    I'm Geoff.

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    Quote Originally Posted by aquapiranha View Post
    Hi. Is this aimed at me? I have seen people simply lay a chunky roll of tape on the woofer cone, centrally of course before performing the sweep.
    I asked because I'm not sure what you have in mind. I don't know the function of the tape.

  6. #16
    Join Date: Jun 2008

    Location: N. Ireland

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    I'm Steve.

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    Quote Originally Posted by walpurgis View Post
    I asked because I'm not sure what you have in mind. I don't know the function of the tape.
    Ah I see, sorry. I am as new to all of this as the next person! Once I have the TS parameters, I may need help with the box design...
    They swim... the mark of Satan is upon them. They must hang.


    FLAC / WDTV Live / Cambridge Audio / Tannoy VX12

  7. #17
    Join Date: Oct 2016

    Location: Bolton, England

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    I'm Andrew.

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    Quote Originally Posted by aquapiranha View Post
    Very soon I will have in my possession (if the postman gets a move on) a DATS V2. I am hoping to use it to measure a pair of drivers I have recently acquired. One thing I will need to check though,
    and that is the required accuracy of the weight of the additional mass I will add. I have a roll of tape and I have weighed it on 2 different industrial machines, both giving 324 grams. Now, they cant
    measure fractions of a gram, will this be accurate enough?
    The mass needs to be between about 5g and 15g - much less than your roll of tape!
    You can look up the weight of coins and use them as accurate weights. For example a 20p weighs 5g and a 50p coin weighs 8g.
    The problem I had was fixing them to the cone. I tried double sided sticky tape but the coins can resonate at certain frequencies (you can hear them buzzing) and the effects show up on the impedance curve. Also, the sticky tape damaged the dust cap slightly when I peeled it off. Blu Tack wouldn't stick at all. If anybody knows a better method to add mass I would love to hear about it.
    Of course, you could use the test box method instead of added mass.
    Actually, you only need to add mass to calculate Vas. You can get the other parameters without the added mass.

    BTW, as an update to my original question, I'm now using ARTA software to do measurements and I'm making some progress. I'm working on a pair of speakers using small drivers which I know won't produce earth-shattering bass but I'm using them to get some practice mainly for crossover design.

  8. #18
    Join Date: Apr 2012

    Location: Southall, West London

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    I'm Geoff.

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    Laying a driver on its back will alter the resonance anyway, as the cone weight then bears fully on the suspension. So I'm not sure how an accurate reading can be done this way.

  9. #19
    Join Date: Oct 2016

    Location: Bolton, England

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    Quote Originally Posted by walpurgis View Post
    Laying a driver on its back will alter the resonance anyway...
    Yes, I discovered that quite early in my experiments. With some drivers the shift in resonant frequency is quite considerable - with others, hardly any change.
    Yes, you couldn't just lay a driver on its back and place a weight on it anyway because the weight will bounce around.

  10. #20
    Join Date: Jun 2008

    Location: N. Ireland

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    Quote Originally Posted by RothwellAudio View Post
    The mass needs to be between about 5g and 15g - much less than your roll of tape!
    You can look up the weight of coins and use them as accurate weights. For example a 20p weighs 5g and a 50p coin weighs 8g.
    The problem I had was fixing them to the cone. I tried double sided sticky tape but the coins can resonate at certain frequencies (you can hear them buzzing) and the effects show up on the impedance curve. Also, the sticky tape damaged the dust cap slightly when I peeled it off. Blu Tack wouldn't stick at all. If anybody knows a better method to add mass I would love to hear about it.
    Of course, you could use the test box method instead of added mass.
    Actually, you only need to add mass to calculate Vas. You can get the other parameters without the added mass.
    The roll of tape was just what I had seen online. I will have a good read of the manual to see if there is any advice or hints in there, thanks

    Sent from my SM-G960F using Tapatalk
    They swim... the mark of Satan is upon them. They must hang.


    FLAC / WDTV Live / Cambridge Audio / Tannoy VX12

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