How to Train Your PM180-8

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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.

[Rory Buszka]

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.

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.

[Pete Basel]

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.

[Wolf]

Re: How to Train Your PM180-8

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

[Wolf]

Re: How to Train Your PM180-8

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

[Pete Schumacher]

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.

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.

[jbruner]

Re: How to Train Your PM180-8

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.

[DoubleTap]

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.

[dcibel]

Re: How to Train Your PM180-8

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.

[czag]

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.

[johnnyrichards]

Re: How to Train Your PM180-8

True, but what I find most beneficial is the complete annihilation of the distortion peak at 3.5Khz, although its' audibility is VERY debatable.

It isn't debatable, if it were - we would all be using cheaper drivers.

[dcibel]

Re: How to Train Your PM180-8

It isn't debatable, if it were - we would all be using cheaper drivers.

Ya! Debate time! Let's argue over the merits and audibility of decreasing distortion at 3.5kHz on a driver that will in most cases be low-passed at 2kHz.

[johnnyrichards]

Re: How to Train Your PM180-8

Let's do it

Why wasn't this driver more popular with high end commercial and DIY guys? As a midrange, it easily exceeds the -40db threshold of so-called "inaudibility". It offers superb linear response, excellent build quality etc... Remove the excursion demands of the bottom two octaves from the driver, what makes a Revelator a better choice?

[Pete Schumacher]

Re: How to Train Your PM180-8

Let's do it

Why wasn't this driver more popular with high end commercial and DIY guys? As a midrange, it easily exceeds the -40db threshold of so-called "inaudibility". It offers superb linear response, excellent build quality etc... Remove the excursion demands of the bottom two octaves from the driver, what makes a Revelator a better choice?

[ATTACH=CONFIG]58029[/ATTACH]

1. For a Dayton driver, it's expensive. That's one strike against it with the DIY crowd.
2. For commercial guys, it's a Dayton driver which is associated with the DIY crowd. Strike 2.
3. Revelator has a pedigree. Most DIY builds don't need high sensitivity, so the pedigree wins. Strike 3.

It really is a nice sounding driver and there aren't many high sensitivity mids out there to choose from with performance like this for this price. That's one reason we went with it in our higher sensitivity design. Can't use a Revelator if you want better than 90dB sensitivity. And most commercial designs don't even try to leave the 80s/2.83V, so why use the PM180?

Just some observations as to why it doesn't show up in more builds.

If a DIY guy is going to do a high sensitivity 3-way, it should be high on the list as the mid over a number of other "pro" models.

[DoubleTap]

Re: How to Train Your PM180-8

It isn't debatable, if it were - we would all be using cheaper drivers.

Totally untrue, of course it's very debatable. Otherwise nobody would dare use an Accuton for a midrange.