Serious Issue With MM12s

scoty19

Hey guys,

I need some serious help. This sub has been nothing but trouble for me. I ordered the Polk Momo MM12 Sub from sounddomain. They shipped it to me and the driver was dead on arrival. So I returned the thing, and they replaced the driver. They sent the sub back to me, and I hooked the thing up. I am running a Kenwood KAC 7201 amp. This puts out 460 watts bridged. Should be fine for the sub. I set the gain to about 1/3 of its max power. I turned the bass almost all the way down on the head unit. I was not using any bass boost. THe head unit has a seperate volume control for the subs, and I kept that at about 50-75%. I was sitting in traffic today, and all the sudden i smelt burning. Then the subs shut off. I guess the coil burnt out. It still hits, but with barely no bass at all. Theyre going to replace the drivers again, but I dont want to go through all this again. Do you guys have any suggestion on how to set this damn thing!?!?!

Thanks!

Systems

i have two MM12s hooked up to an RF 601s, which is rated @ 150Wx2. my gain is about 2/3 of the way. i have not had any problems thus far. one of my MM12s was previously blown because of some faulty construction, but it was replaced. and before that i blew an MM10, which was smoking just like you described. these subs obviously cannot handle anywhere near its suggested power rating. if anything i would not even run it at half the RMS rating. 150-225W is plenty for an amp i would say

LittleCar_w/12s

I hate to break it to you, but Polk Subs are some of the best I've dealt with, yet one of the most picky when it comes to treatment. Aside from a short lapse in their good engineering just recently with the mm's, the main cause of the burnout and breakages are Improper break-in time. I belive that the proper time is 45 hours at a low listening level, and it should be progressively raised after that.

In short, they do handle that much, just not right away. I would suggest, as 'markyboy21' does to run them at that 150w range for a while, but only for the break in period. You may just have the bad subs, but please make sure to break-in properly, even though they will still replace it almost forever if it keeps happening.

Hopefully you have better luck so that you can come to love these subs as others have, and make good use of that 46w

-Jerry

scoty19

Oh Im definately not doubting the quality of the sub. I just really need some assistance on making sure it works well. Wouldnt turning the gain down be how you break the sub in? If not how do I go about doing that? What should I have the bass on the head unit be set at? How about the volume level on the sub control? Also Ive read about clipping burning out the coil. This sounds like it might be what it is. How do I avoid this?

bknauss

You might be sending a clipped signal to the subs. If its clipped, its going to be "on" for more time than an unclipped signal. If you keep it "on" for too long, or have an average time "on" too long, you're going to heat the coils up and burn 'em. The problem might be the amp... but I'm not going to say I'm 100% sure.

MacLeod

And yet another Polk sub kicking the bucket. This is a disturbing trend.

I just dont think its improper break in time. In the 15 years Ive been dabbling in car stereos Ive never broken in a sub and Ive never had one blown. Although Ive mainly used MTX subs and a couple JLs, Ive always bought them, installed them and then run them at or near their rated power and have never had one blow yet.

This sounds like a quality control issue on Polks behalf cause we're seeing a lot of complaints of R.I.P. Momo subs on here and theres got to be something to it.

scoty19

I guess all I can do is call Polk when i get this new one, and have them walk me through how to set this thing up so that nothing happens to it. I might even go to a local car audio shop and have them set the gains, etc. for me.

exalted512

lol
yeah...i think mm124s are some really crappy subs
lol
im sorry to say it...i really am...but ive heard of so many of these things dying it disgusts me
i dont think your problem was clipping since you had the gains really far down
and yeah...that is one way you can do it
i am on number 7 and 8 mm124s
i have blown 6...yes...6 of these subs
if it wasnt for their 3 yr warranty...id be screwed out of some $$
i dont recommend powering them over 500 watts...at all
tried it...doesnt work
i dunno what the problem is...
every amp ive gotten has been recommended by Polk...
I dunno...i love polk...but this is getting to me...
-Cody

Systems

You got the beef with madcow.....its spreading

What size box do you have them in?

Sounds like it was a good ol' burn down of a **** sub

scoty19

The MM12s come enclosed sealed. That shouldnt have been part of the problem?

neomagus00

no, it shouldn't be...

i have a suggestion as to why we're seeing this 'epidemic' of blown momo subs - who would bother to come here and say, "hey guys, just wanted to say that everything's goin great, have a nice life!" i think that we see all the problems and that our view of the situation is thus severely distorted. some supporting evidence: the shop i use is polk's biggest retailer in my state, and they very very rarely get a blown polk sub back (jl, yes, but not polk). just thought i'd throw that in there.

btw, i think i've mentioned this once before - breaking in a sub actually does nothing to the thing structurally, so why should it matter?

bknauss

Originally posted by MacLeod
And yet another Polk sub kicking the bucket. This is a disturbing trend.

I just dont think its improper break in time. In the 15 years Ive been dabbling in car stereos Ive never broken in a sub and Ive never had one blown. Although Ive mainly used MTX subs and a couple JLs, Ive always bought them, installed them and then run them at or near their rated power and have never had one blow yet.

This sounds like a quality control issue on Polks behalf cause we're seeing a lot of complaints of R.I.P. Momo subs on here and theres got to be something to it.

I'm thinking its a user problem. You've got Thom and Josh both using Polk subs, beating the crap out of them at competitions, and not having a problem. Thom actually blew the fuses on one of his Zapco amps, but the sub still worked like a charm (after the fuses were changed out).

My two guesses of why subs keep blowing:
-Driving the sub amp into clipping and therefore overheating the sub and blowing it
-People failing to realize that the sub doesn't handle too much power and feeding it too much power.

LittleCar_w/12s

From what I'm seeing here, the most common problem is with the coil, not the structure. Break-in is for the structure & suspension of the sub, to loosen up the moving parts... 45 hours should be an overstaement in other words.
If the coil burns at any given wattage under it's rated power, provided under rms value, and no clipping, the it is simply bad coil-wire, or maybe the resin used to set the coil (if any) is weak or not set right.
It is a quality control issue. Every one of these subs should handle 500w of continuous DC power (500w rms AC) without burning, but some do, no matter what. Perhaps Josh, Thom or Kim could tell us how they test these?
-Jerry

LittleCar_w/12s

Perhaps all these coils came off the same 10,000 m. spool of wire??

beenthere

I'm not an expert but based on what I've read clipping does sound like a lot more likely cause than defective subs? The experts claim underpowering the subs tends to cause many more failures than over-powering them.

Systems

Underpowering subs properly does NOTHING to the sub, much better than over powering them....people underpower them, and want more from the sub.....drive the amp into clipping....dead sub.

beenthere

THAT was precisely why I mentioned clipping...

bknauss

Originally posted by beenthere
I'm not an expert but based on what I've read clipping does sound like a lot more likely cause than defective subs? The experts claim underpowering the subs tends to cause many more failures than over-powering them.

Well, I've seen more than a handful of people using Momo subs with no problems. I'm not saying defects aren't possible, but if the subs are like the amps, they go through a QA process before being shipped. There are some amps that have problems, but from what I've seen a huge majority have done just fine.

beenthere

I agree, I suspect the quality on the Polk subs is just fine. Clipping will kill a sub in no time. That's why I concurred with the post above on clipping by some guy named: bknauss

MacLeod

Originally posted by bknauss
I'm thinking its a user problem. You've got Thom and Josh both using Polk subs, beating the crap out of them at competitions, and not having a problem. Thom actually blew the fuses on one of his Zapco amps, but the sub still worked like a charm (after the fuses were changed out).

My two guesses of why subs keep blowing:
-Driving the sub amp into clipping and therefore overheating the sub and blowing it
-People failing to realize that the sub doesn't handle too much power and feeding it too much power.

I hope so. Im in Polks corner big time and would like nothing better than to see them succeed.

I do think that Polk should maybe rate their subs a little more conservatively. If they test one that goes **** up at 200 watts than they should rate it at around 150. That would probably keep the power hungry from destroying them!

exalted512

i do not drive my amps to clipping...my problem is i cant learn to keep the gains down because the amps are too powerful for the subs
i have killed them before by running 600 watts to them, from a bd1000
switched amps to the 550S'...had em both running at about 550 and blew 2 more
but really...i dont give a damn...550 watts on a 500 watt sub should not kill it
and thats exactly what happened to the last 2 i had
ive discussed this with vince and he too said he keeps hearing dead momo stories
if you fry a 500 watts subs VC by overpowering it by 50 watts they need to take the RMS and drop it 100 watts
i probably have 500 watts to my subs now...im being a little more conservative with the gains this time...and the damn things still smell like theyre burning up when i crank it
i dont care anymore...ill have new subs in 3 in september...the warranty for these goes out halfway in august
forgive me if im wrong...but dont Josh and Thom both have 500.1s running 2 MOMO subs each
meaning....250 watts to each sub?
maybe thats why theyre not blowing subs
-Cody

scoty19

So anyways....since i was the one that started this post, and through all of your help have decided that it was clipping. I now need suggestions on how to avoid doing it again. I have a Sony CDX-M600 HU it has 2 volt premap sub outputs. They are designated for subs, and have a built in low pass filter. Now what do I do about setting things like the low and high pass filters on the HU, the volume control on the head unit, and the bass and treble on the head unit. Then I would need to set the gain on the amp.

Airplay355

THe head unit has a seperate volume control for the subs, and I kept that at about 50-75%

that seems to be the problem...turn your volume up on the amp not on your head unit, to many diffeent volume controls can result in distortion which is the sub killer.....

and altec you are insane if you think underpowering a sub does nothing....it is much easier to blow ANY driver by underpowering it and playing it loudly then it is to overpower it and play it loudly. the power handling ratings are RMS, so you CAN power a sub with more watts then its rated at. you will fry your sub if you underpower it and turn it up loud, that pushes the amp into clipping which is distortion, which cooks ur subs.


you need to find the frequency response of your speakers in your car so you can set the high pass of the sub at the correct level, meaning if your speakers roll off at 80 hz, you dont want to high pass them at 80 hz, they wont blend very well.

exalted512

underpowering ANY speaker will NEVER harm it
any speaker will last longer if you under power it rather than over power it or play it at its RMS
it might not sound as good though
if you do not have your gains set appropiately that and only that is what will blow your speakers
not too little power--too much gain
thats what Altec was talking about
-Cody

Airplay355

too much gain with too little power will blow speakers...when u have more watts, u can turn it up louder

turn down the volume on ur headunit...if you send a distorted signal to an amplifier it amplifies the distortion, because thats its job. if you want more volume turn up your amp, not the volume on your HU

beenthere

Perhaps the obvious is being missed when several of us have posted that "under-powering" a sub can cause premature failure. What tends to happen is when someone purchases an amp that is too small for the Sub to play real LOUD, they crank up the gain to make it louder. When they crank the gain to the point of sending a distorted signal to the speaker - poof that nice Polk Sub is gone in no time. Yes over powering can also kill a sub, but the distorted signal from cranking the amp gain too high is the problem more often than over-powering the sub. I realize the pros here know this, but some times new Polk members may not have read the FAQ's or be as experienced as some of the regulars on here.


From the Polk FAQ's: (Note this is general info. on all speakers not just Subs which is what the above thread is about).

Drive To Survive. How Not To Wax Your Car Speakers
from The Speaker Specialist, Issue 2
by Paul Seredynski

---

Though many 12-volt fans might fantasize about it, you wouldn't like living in your car: It's a rough environment. Cars are full of vibration, countless road-surface impacts and temperature swings roughly equivalent to Mars. Unfortunately, even though autosound speakers are designed with this harsh climate in mind, many suffer shorter life spans than those disappearing Martian landers. Rarely, however, are the elements to blame for "blown" speakers.
Unlike a set of home speakers, in which the engineering is packaged in its own box, a car system contains many variables, including the enclosure, cross-overs, and power source. These elements are your responsibility, so avoiding major missteps in design and use can wildly extend the life of your car speakers.

The three most common killers of speakers are excessive power, way-ward frequencies and an overstressed power supply.

Much like your car itself, car speakers tend to perform best when properly driven. The likeliest culprit in speaker-cide is too much power. Overdriving a speaker means sending it more signal than it can physically produce. If force-fed via a ham-fisted volume control, any speaker will give its life trying to produce sound levels beyond its capabilities.

Simply because of the size of its components-which are less able to dissipate heat and offer less "suspension" to handle sudden power peaks-tweeters are usually the first to go. Also, unlike other drivers (which might produce a rapping or slapping sound if overdriven), tweeters may not give an audible sign of distress before checking out. "Edgy" and "harsh" are usually their last reported descriptions, and then they blip off the radar.

Overdriven is not to be confused with "loud." A properly installed audio system can render you near deaf without harming the drivers at all. "Properly installed" means amplifier levels are calibrated so speakers are not overdriven at normal volume settings, and each driver in a component setup (via the crossovers) only receives its appropriate frequencies.

Though it applies to all speakers, tweeters are also normally the first casualty in a system where frequencies are misrouted (1-inch dome tweeters were never intended to handle 50Hz drum kicks). Sub-woofers can easily suffer the same fate at the other end of the audio spectrum. Pumping up the bass (especially with an equalizer), in search of frequencies outside the realm of your sub's driver/ enclosure/amp will have the woofer's cone flopping back and forth worse than a cornered politician.

The search for subsonic bliss can also shorten your speakers' life span. Looking for bass beyond your woofer's setup design can put exponential loads on an amplifier, causing it to choke, or "clip," sending potentially harmful signals to your speakers. Amplifiers also tend to clip during periods of high demand due to an inadequate power supply (which includes everything from the car's alternator to your amp's internal power source).

If your car is not properly wired, when asked for some serious grunt, entire system voltage can drop, greatly lowering an amplifier's output capability. An amp starved for voltage can give up the ghost early, clip and take speakers down with it.

To avoid all these pitfalls, proper setup is key. If you are popping speakers like aspirin, common solutions are a lower amplifier level (so that normal volume settings are not lethal), a re-tuned crossover frequency (giving the speaker a narrower range of sound to reproduce), or a steeper crossover slope (which rolls off more difficult frequencies more rapidly). Properly tuning your subs' crossovers and enclosures to provide sufficient bass for your musical tastes can also mean far less stress on your amps, extending the life of all your drivers. Find the balance between levels, crossovers and a stable power supply, and your speakers will live as long and loud as you like.

Paul Seredynski is a freelance writer and autosound sage based in San Diego.

LittleCar_w/12s

Ok, I'll try to do some math for you:

If a 250w RMS amp will put out 500 peak, what it is saying is that the amp is stable to run putting out 250w RMS. or the equivalent of outputting a DC power of 500w continuously.
Given that the RMS value of a unclipped sine wave is 70.7% of the peak value, this is saying also that the amp is not using all available voltage if it can peak at 500w. The amp is effectively rated with the gains lower tham highest possible.
If you perfectly tuned a 500w peak amp, and never clipped it, you will get 353.5w RMS amd 500w peak amp. So if we have a 250wrms speaker, and a 250wrms/500wp amp, we could possibly eat the speaker without ever clipping. you see that there is over 100 w that can be squeezed there?

Also if you run a 500wP amp at full clipping, you are effectively giving it the same as a 707w sine wave, as well as feeding a square waveform to the voice-coils which cause excessive internal vibration caused by very high voltage slew.

So if I full-clipped my 150wP amp to my 400wRMS DB12's, they could handle the 212w equivalent power, but the voltage slew would eat the coils.

I hope I've been informative, and not rambled................
-Jerry

beenthere

This FAQ from Crutchfield's may also be of interest:


How is it possible to blow a woofer rated for 300 watts when I'm only using a 100 watt amp to push it?


Underpowering a speaker is likely to damage the voice coil due to the excess heat created by distortion. This distortion, called clipping, is created when the amp is not able to supply the power demand when the volume is turned up. If you turn the volume up very high without the power to back it up, you'll end up clipping the signal coming out of the amp. The speaker will try to reproduce this clipped signal, and if played under these circumstances for any length of time, the speaker will not last very long.

There is a mis-conception that if you're not giving the speaker as much power as it can handle you won't blow it, but that simply is not the case. The only way to really address this problem is to replace your speaker for one with a lower power rating, and a higher SPL rating, or replace your amp with one that better matches the speaker's power handling capability. An alternative to replacing the equipment is to simply keep your volume turned down!

Make certain that power and ground wiring for the amplifier is sufficient to deliver adequate current to the amp. Proper wire gauge and clean connections are critical for strong performance.


Article #148 - Last updated 06/20/2004

exalted512

i dont care if the inventor of the original speaker came on here and said underpowering a speaker will damage it
theyre wrong
underpowering a speaker WILL NOT KILL IT
not only will it not kill it, chances are IT WILL LAST LONGER
the only thing that will kill it is feeding it power that is distorted
but for sake of argument, lets say we had two speakers
both rated at 50 watts rms
ok lets say one of them is running off an amp that is putting 25 watts to it, half of its rated power, and the other speaker is from an amp rated at 75 watts, one and a half of its rated power
from the way of thinking "underpowering will kill a speaker", you are taking in that the amp will be distorted
so im going to have the same way of thinking of over powering a speaker...im going to push that amp to distortion as well
so we have a 50 watt speaker that is getting 25 watts of distorted power and a 50 watt speaker that is getting 75 watts of distorted power
if let run like this, more than likely both speakers will fry
but i guarantee you if the speakers and amps are EXACTLY the same(which will never happen...theres always something different...no two speakers can be made exactly alike...un-noticeably close, but not ever exactly alike), then the speaker getting 75 watts will blow faster

its not that hard to understand guys...
underpowering will not kill a speaker
DISTORTION WILL
-Cody

beenthere

What part of "clipping and distortion" don't you understand???



The "under-power" conversation SPECIFICALLY refers to sending a distorted, i.e. clipped, signal to the speakers. It's stating in words what "LittleCar" illustrated via math. This isn't like some new phenomena...

You seem to be missing the point that the FAQs and other posters have made. The point is when people under-power the speaker and CRANK THE GAIN up and send a distorted signal to the speakers, it will fry. You admit this then you state under-powering won't fry the speakers. Under-powering WITHOUT SENDING A DISTORTED SIGNAL to the speakers will NOT fry a speaker, but that's not how most people operate their system. They crank the volume and distort the signal and fry the speaker, as the FAQs and other folks have posted. If the gain on an amp is properly set so it does not send a distorted signal, then under-powering is fine. There is a difference! And the reason why a higher output amp doesn't cause a speaker to blow sooner is because you don't NEED to operate the amp in distortion to get the sound VOLUME. So the higher output amp runs without distortion to generate the same LOUNDNESS as an under-powered amp that MUST be run into clipping to make the volume LOUD.

The subject is really NOT that complicated, but I think you're hung up on the phrase "under-powering will fry your speakers", which is true if by under-powering you crank the gain and send a distorted signal to the speakers to achieve the volume desired.

Glad we got this all cleared up...

Airplay355

distortion comes from turning it up too loud when there isnt enough power, the amp can't finish the sine wav so the peaks are clipped off and flattened....waves aren't supposed to be flat.

you push an amp into clipping when you drive it too hard, you are more likely to drive a smaller amp into clipping because you will need to turn the gain higher to get the volume you want.

i thought u knew this ****?