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How to Train Your PM180-8

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  • czag
    replied
    Re: How to Train Your PM180-8

    You could be right. Still, adding that step to the process would just drive costs up for limited benefit. Yeah, it looks better above 2KHz, but you wouldn't use it up there anyway.
    True, but what I find most beneficial is the complete annihilation of the distortion peak at 3.5Khz, although its' audibility is VERY debatable.

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  • dcibel
    replied
    Re: How to Train Your PM180-8

    Originally posted by Jeff B. View Post
    The PM220, on the other hand, I did not like at all. The frequency response was really problematic and made the driver almost unusable for me. I think it needed a bit more attention in the driver design stage. The Eminence Beta-8A, while not having as low of nonlinear distortion, has a frequency response that is much easier to work with and really sounds good as a midrange / midbass driver for a lot less money.
    Jeff, I am wondering if you could explain a bit more about what was wrong with the PM220 for your use? Comparing the datasheets, the breakup looks actually a bit more benign in the PM220, however starting a bit lower in frequency than the PM180 which is to be expected. Thanks.

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  • DoubleTap
    replied
    Re: How to Train Your PM180-8

    We've been pretty happy with the PM-180, but do think it has a bit of a hard/brittle character to it. Many probably wouldn't even notice, it's just in comparison to the AudioTech drivers it lacks refinement. Could it be partially from out of pass-band breakup trickling down into the more audible range, possibly. I can say we'd love to try an 'enhanced' pair of PM-180s in the Derecho without any crossover changes and see how they compare.

    jbruner, contact me if you want to take this experiment to the next step. We'll try them in the Derecho and give thorough listening impressions.

    Leave a comment:


  • jbruner
    replied
    Re: How to Train Your PM180-8

    Originally posted by Face View Post
    How did you install the phase plug?

    I drilled the plug to accept a dowel pin which slides into the thru-hole. I also used some glue.

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  • Pete Schumacher
    replied
    Re: How to Train Your PM180-8

    Originally posted by Pete Basel View Post
    I have said this before, that in non-linear systems such as speakers the order of
    transfer functions matters, it does not in linear systems - which is an incorrect assumption
    being made by claiming that it can be "fixed" in the crossover.
    Filtering in the crossover might help but it does not correct for amplification of the
    motor distortion by the breakup peaks. Reducing/eliminating the breakup peaks does.

    Perhaps one of our theoretical brains could put this into language that people can understand.
    andy_c, jcandy?

    In fact, cone breakup peaks in speakers are an excellent real world example of this concept.
    In the case of this driver, the motor distortion is already very low and the breakup modes are not that severe. Crossing this driver at 2KHz with a 2nd order filter (LR4 acoustic) will keep distortion levels well below 1% even in the breakup region which is below the threshold of audibility.

    Jeff's data doesn't show any inordinate amplification of distortion by the cone breakup modes that can't be addressed in the crossover.



    By contrast, you can see such amplification in the SEAS W18EX001 distortion spectrum.

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  • Wolf
    replied
    Re: How to Train Your PM180-8

    Good Q! I was wondering that myself....
    Later,
    Wolf

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  • Wolf
    replied
    Re: How to Train Your PM180-8

    Originally posted by Rory Buszka View Post
    There are actually two layers of paper on the cone, and they are glued together with a rubber-type adhesive (the same stuff often used for attaching dust caps; it's a solvent-borne rubber cement that dries black.) The slits in the lower paper cone run the opposite direction from the slits in the upper cone.
    There may be 2 layers, as I cannot confirm that. But- the slits appear to be In the same place on the front and rear of the cone on my pair. I have the 15W/8530K-00.
    Later,
    Wolf

    Leave a comment:


  • Pete Basel
    replied
    Re: How to Train Your PM180-8

    I have said this before, that in non-linear systems such as speakers the order of
    transfer functions matters, it does not in linear systems - which is an incorrect assumption
    being made by claiming that it can be "fixed" in the crossover.
    Filtering in the crossover might help but it does not correct for amplification of the
    motor distortion by the breakup peaks. Reducing/eliminating the breakup peaks does.

    Perhaps one of our theoretical brains could put this into language that people can understand.
    andy_c, jcandy?

    In fact, cone breakup peaks in speakers are an excellent real world example of this concept.

    Leave a comment:


  • Rory Buszka
    replied
    Re: How to Train Your PM180-8

    Originally posted by [email protected] View Post
    If the pm180 is the same as the ps180, its one hell of a driver. Perhaps someone that attended DakotaDIY can confirm how good it performs with a North Creek D25-06.
    PM180 and PS180 use identical cone, motor, suspension, and frame. PM180 has no whizzer or phase plug. Someone called the phase plug a "pole piece extension", but it is made from aluminum and isn't part of the magnetic circuit. Both the PM180 and PS180 have an extended pole piece with copper pole cap.

    For another driver with a large, lightweight, hard, and less-damped paper cone, look at the SEAS Exotic 8" woofer, and I have seen that driver used by Salk, Trenner & Friedl, and Tonian Labs with good results. Either you need to design around the breakup by crossing over low, or you need to control it in the crossover with a contour filter. No real scandal here.

    Leave a comment:


  • arlis_1957@yahoo.com
    replied
    Re: How to Train Your PM180-8

    If the pm180 is the same as the ps180, its one hell of a driver. Perhaps someone that attended DakotaDIY can confirm how good it performs with a North Creek D25-06.

    Leave a comment:


  • Jeff B.
    replied
    Re: How to Train Your PM180-8

    Originally posted by caleb View Post
    Do you have the cojones to modify it?
    I wouldn't worry about modifying the 180, as I made it work to my satisfaction the way it was. And I wouldn't mess with trying to fix the 220. However, Josh can modify all he wants, as this is heart of DIY, isn't it? More power to him.

    Leave a comment:


  • caleb
    replied
    Re: How to Train Your PM180-8

    Originally posted by Jeff B. View Post
    I posted measurements of the PM180 a few months ago. It is really a pretty decent higher sensitivity midrange drivers when used between 200 - 2 khz, which is how I used it in a design. The Neo magnet and the shorting ring give it excellent nonlinear distortion measurements and it can easily be made to operate with very flat response in this midrange window. I wouldn't use it full-range though. Within the limitations of the driver I would consider it excellent and worth the money as well as any other driver in this same cost range.

    The PM220, on the other hand, I did not like at all. The frequency response was really problematic and made the driver almost unusable for me. I think it needed a bit more attention in the driver design stage. The Eminence Beta-8A, while not having as low of nonlinear distortion, has a frequency response that is much easier to work with and really sounds good as a midrange / midbass driver for a lot less money.
    Do you have the cojones to modify it?

    Leave a comment:


  • Jeff B.
    replied
    Re: How to Train Your PM180-8

    Originally posted by caleb View Post
    These drivers seem really overpriced at this point. I wonder if the performance before modification justifies the asking price. At this point would you even consider owning these if you were somehow prevented from modifying them?
    I posted measurements of the PM180 a few months ago. It is really a pretty decent higher sensitivity midrange drivers when used between 200 - 2 khz, which is how I used it in a design. The Neo magnet and the shorting ring give it excellent nonlinear distortion measurements and it can easily be made to operate with very flat response in this midrange window. I wouldn't use it full-range though. Within the limitations of the driver I would consider it excellent and worth the money as well as any other driver in this same cost range.

    The PM220, on the other hand, I did not like at all. The frequency response was really problematic and made the driver almost unusable for me. I think it needed a bit more attention in the driver design stage. The Eminence Beta-8A, while not having as low of nonlinear distortion, has a frequency response that is much easier to work with and really sounds good as a midrange / midbass driver for a lot less money.

    Leave a comment:


  • Pete Basel
    replied
    Re: How to Train Your PM180-8

    Originally posted by jbruner View Post
    Tough question. I do think they are overpriced, especially since the driver's design is incomplete. It looks like they just removed the pole extension from the PS180 and slapped on a dustcap. The resulting pole cavity is a glaring problem visually and acoustically. I hate it when pricing is based on market positioning rather than value.

    I would not have tried them, but, a) They were on sale, b) Ryan and Jeff both thought they were good, and, most importantly, c) I knew I could fix them if I needed to.

    I really wanted to design a high-output speaker that could deliver realistic dynamics with high fidelity. I concurred with most of the design choices in Vapor's Derecho, and even used the same B&C woofers.
    Where did you cross to the tweeter and which tweeter did you use if you don't mind my asking?

    Leave a comment:


  • Face
    replied
    Re: How to Train Your PM180-8

    How did you install the phase plug?

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