Polk MoMo (Mobile Monitor) Speakers - What's the deal? - AVS Forum
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post #1 of 11 Old 11-20-2012, 06:51 AM - Thread Starter
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Polk is trying to break a record for "The most innaccurate information about a subwoofer driver on the internet"... except (I suppose) for vaporware.

Let's start from the beginning. Some time in the past, I picked up a 10" Kicker driver from Best Buy as an emergency replacement for a failed driver in a Polk PSW-110 - It sounded really good to me, and having no knowledge that the DIY community even existed, I became excited about modular subwoofers. Back to Best Buy, where they had the Polk 12: DXi on sale, pre-mounted in a box - for car use but very attractively presented. I bought one. Powered by a Crown amp, it sounded really good.

Fast forward a few weeks and I was messing around with several Polk 12" DXi and Kicker 12" CompVR subs, thinking myself in bass heaven. After having a few QC issues with the Kickers, I decided to use Polk to build out my subs. Wanting more, I looked at Polk's website and they pitched the 15" Mobile Monitor (MoMo) as their top sub.

From Polk's own website: "Through the use of high-tech carbon composite baskets, oversized voice coils, and state-of-the-art composite cones, we offer high-end audio performance normally found only in the most expensive loudspeaker systems."

Between then and now I learned a whole lot about bass and subwoofers and drivers. Eventually I realized the MoMo is a pure case of false advertising. Examine the official line from Polk - In reality the basket is made from plastic. The 2" voice coil is decidedly small for a high-excursion 15" subwoofer. The cone is also plastic (plain old polypro as far as I can tell), and rather heavy as well. That's not all - Polk's website listed the RMS of the 15" MoMo DVC as 425 watts, yet printed on the back of the motor is a 400 watt rating, and in their manual Polk gives the MM1540 a 360 watt rating.

Adding to the confusion, the product description for the MoMo on Crutchfield says: "The MM1540D 15" dual voice coil subwoofer handles up to 425 watts RMS, using a copper voice coil and neodymium magnet motor to drive the polymer cone with exceptional efficiency"... well great because that's what convinced me to buy it! Neo motor, super-high efficiency! I dutifully entered their inflated spec for efficiency into WinISD. That's what left me feeling it was OK that the speaker had such a small magnet! I showed it off to friends and bragged about how awesome it was an American company could design something so light and powerful and economical. It makes me ill to think about it now.

So, thanks to the thread pointing to the MoMo going on sale for $89.99, I decided to take a hammer and drill to mine. It worked fine, but I was not going to listen to it anymore and besides replacements are dirt cheap, if for some reason my suspicions were not confirmed. My suspicions were more than confirmed.

In practice the Polk 12" DXi is the superior subwoofer, but Polk seems intent to set the low bar for subwoofer value. Neither sub had the sort of sharp, brutally deep bass definition that hooks fiends. In fact neither Polk is as good as a 12" Kicker CompVR eek.gif The only good thing one could say: they are totally competent budget drivers, and commendably free of QC issues... but they don't plumb the depths.

So it is with some regret I post the following observations:

The MoMo has the black spider and the darker copper voicecoil. In the pictures of the motor assembly, the DXi is on the left, the MoMo on the right.

It looks like the same magnet on both speakers, a very modest ferrite magnet, the same one you find on all the cheapest 12" subwoofers like Kenwood and Pioneer. - so much for 'Neodymium'. The MoMo actually has a smaller pole vent than the DXi. The MoMo motor assembly weighs a few more ounces than the DXi motor - I attribute that to a bit of extra metal, resulting in the smaller vent.

The MoMo's cone weighs twice as much as the DXi cone, but only because it is thicker, not because it is stiffer. The cone is actually quite floppy and is almost exactly like a Frisbee in feel/stiffness. The MoMo's basket is plastic, not 'carbon composite'. The MoMo's spider is slightly larger but it's also quite a bit stiffer, as is the rubber surround. The MoMo does get a marginally longer voice coil - 1.15" vs. 1". The net effect is that the DXi actually sounds better, and might even be more efficient than the MoMo.

I do not recommend either speaker, however I cannot think of any other driver that so misrepresents it's specs as the Polk MoMo 15" - or the rest of the MoMo series. I still maintain it's 'built like a tank' in the sense that it'll take a beating and sounds decent... I'm just not under any illusions anymore. It was designed for yachts, and it was designed to be as cheap as possible to manufacture, The ferrite magnet is so disappointingly small for a 15", for a while I literally thought maybe it really is a Neo woofer but now I feel dumb for having been so naive. Thank you to the members here who threw their healthy skepticism my way a few months back when I was talking silly:mad:

Even the stated resistance is suspect, every other driver I've configured for 2 ohm operation worked fine with my Crown XTi amps, but the MoMo (and only the MoMo) would cause my amp to become unstable and clip in the most unpleasant manner. A thorough disaster and good riddance.

Polk's words - "The MM1540 15" 4-ohm subwoofer handles up to 425 watts RMS, using a copper voice coil and neodymium magnet motor to drive the polymer cone with exceptional efficiency" Yeah right!rolleyes.gif















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post #2 of 11 Old 11-20-2012, 08:04 AM
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frown.gif

I was always skeptical about the claimed XMax...but I heard enough from others that it appeared to be legit. I guess not. There was a good reason why these were never 'discovered' to be a killer deal. I guess those that really know their subwoofer tech could see through the misleading stats all along. Just glad I never bought one now.

bg
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post #3 of 11 Old 11-20-2012, 11:04 AM - Thread Starter
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Their claimed xmax is impossible to achieve. It is in fact the xmech of the driver - for a very simple reason you see in this picture - the spider is so close to the cone and the cone is so shallow that after 25mm of movement, the cone itself bottoms out against the part of the basket where the spider is attached. Definitely a result of the low-profile design, and definitely a performance-killer.

MoMo on the right.



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Originally Posted by garciab View Post

frown.gif
I was always skeptical about the claimed XMax...but I heard enough from others that it appeared to be legit. I guess not. There was a good reason why these were never 'discovered' to be a killer deal. I guess those that really know their subwoofer tech could see through the misleading stats all along. Just glad I never bought one now.

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post #4 of 11 Old 11-20-2012, 12:15 PM
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excellent post imagic, on many levels. [thumbs up]

Listen. It's All Good.
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post #5 of 11 Old 12-17-2012, 11:53 AM
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Did you manage to build a box and listen to it? Never mind the specs for a moment.

I built one of the SVC in a 3.8l sealed cabinet powered by a Crown 1500.
I will take measurements soon, but I can tell you it outdid my sealed Tempest build by a far margin.

It will shake every door in the house and bring down every picture on the wall and beyond that it sounds incredible.
I don't run it that hot as I usually listen to music, but its nice to know it can be called upon if watching a movie.

So the specs may not match, but I can tell you it is one hell of a sub for the price.

My friend decided to do the PE 15 in ~3l sealed enclosure. He brought his over to compare and we both enjoyed the Polk much more.

So you can list all the reasons you think it isn't good, but until you build the correct box and calibrate it (I use a minidsp) then I wouldn't say its a poor performer.
Especially considering all the high praises for the PE subwoofers that are recommended all the time.
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post #6 of 11 Old 12-17-2012, 01:34 PM
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Thanks for the work tearing those apart. Interesting stuff indeed and a shame about all the false marketing.

As a side I've got a kicker comp 12 that does pretty good. Not a bad driver for $50 on sale, but I think the Infinity Ref & JBL equivalent spec out better.
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post #7 of 11 Old 12-17-2012, 01:53 PM - Thread Starter
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Dustin,

I definitely gave that driver a thorough workout in multiple configurations. I ran it ported, 2 cubic foot sealed, 4 cubic foot sealed and as a dipole subwoofer. The best performance came from the ported sub design which is no surprise - the motor is too weak for small sealed but definitely thrives in larger boxes. I fully credit it with being well-made and performing in real-life installations. It moves a lot of air, weighs very little and is cheap. I would never say it is a poor performer, I have defended that subwoofer based on my purely subjective experiences listening to it. I would say that other subs, even around that price point - do sound tighter, are easier to drive with a 2 ohm load, offer greater power handling. But as a package the Polk is worth the Money.

I have not taken the plunge with PE subs. I personally like Sony's 12" XPLOD so I'm not exactly on the PE bandwagon either. People just need to be realistic about what the MoMo will and will not do. Aside from the inaccurate specs and descriptions, the main issue appears to be that the cone is too heavy and too flat... probably because it is too flat it has to compensate with thickness. The same motor structure would do better in the 12" configuration IMO, and indeed Polk keeps selling the 12" MoMo for more than the 15" which I think is a tacit admission that the 15" tries too hard.
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Originally Posted by DustinF View Post

Did you manage to build a box and listen to it? Never mind the specs for a moment.
I built one of the SVC in a 3.8l sealed cabinet powered by a Crown 1500.
I will take measurements soon, but I can tell you it outdid my sealed Tempest build by a far margin.
It will shake every door in the house and bring down every picture on the wall and beyond that it sounds incredible.
I don't run it that hot as I usually listen to music, but its nice to know it can be called upon if watching a movie.
So the specs may not match, but I can tell you it is one hell of a sub for the price.
My friend decided to do the PE 15 in ~3l sealed enclosure. He brought his over to compare and we both enjoyed the Polk much more.
So you can list all the reasons you think it isn't good, but until you build the correct box and calibrate it (I use a minidsp) then I wouldn't say its a poor performer.
Especially considering all the high praises for the PE subwoofers that are recommended all the time.

Find out more about Mark Henninger at www.imagicdigital.com
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post #8 of 11 Old 12-17-2012, 04:45 PM
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Funny, I've tried the 12" Sony too in a small sealed cabinet. I like that one too.
If you find a 15" that you think is a big step up, let me know and I'll try it out.

I've spent a bit on subs in the last 2 years trying to see if I can find big differences, and I've personally not found any big gains in higher priced subwoofers. I just end up selling them after trying them out.
I know subs are built for different purposes, and I know a lot of people are looking for high dbl, but in my case I'm not listening at those levels, so I find 3 inexpensive subs a perfect match.
I'm sure there is a big difference if you really crank it, but I just can't listen at those levels. I do know that 1 Polk 15" can feel like its pressurizing my whole room 24x13, so that's why I asked if you tried it.

So you may ask, why do I keep trying new subs? Well I'm under the impression there's a magical sub somewhere that's going to make me change my mind. That and I love tinkering with sound.
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post #9 of 11 Old 12-17-2012, 05:45 PM
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I can't speak for anyone else's experiences, but I put some Polk MoMo 6.5" 2 ways in my truck a few years ago and they were pretty craptastic. Definitely a case of bare-faced marketing. Other people's experiences may vary.

"Still, a man hears what he wants to hear and disregards the rest." --Paul Simon The Boxer
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post #10 of 11 Old 12-17-2012, 08:26 PM
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Quote:
Originally Posted by PassingInterest View Post

I can't speak for anyone else's experiences, but I put some Polk MoMo 6.5" 2 ways in my truck a few years ago and they were pretty craptastic. Definitely a case of bare-faced marketing. Other people's experiences may vary.

Car audio is all about the install. The best drivers can sound like crap and crappy drives can sound good depending on the install.
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post #11 of 11 Old 12-17-2012, 08:49 PM
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Measure the top plate and winding length to find out the "mathematical" Xmax. Obviously not 70% Bl/Linear/Klippel verified, but they may quote just the the winding height. There are a couple of different ways this is calculated:


(Winding depth - magnetic gap depth)/2

or

[(winding depth - magnetic gap depth)/2] + (magnetic gap depth/3)


I'm curious to see how close the quoted spec in the literature, and the measured figures based on the actual motor parts, actually are. Too bad there is no industry consistent measure of Xmax.

 

Originally Posted by Bill Fitzmaurice:
It's also the very sort of Voodoo Engineering that should never be done.

 

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