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Clipping and Underpowering explained

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Old 07-02-2009, 07:41 AM   #1
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Clipping and Underpowering explained

There has recently been some discussion about clipping in the Component vs. Non component 6x9 thread and I wanted to move discussion here so we didn't further ruin that thread.


There were bits and pieces of good info in that thread but no one really put them all together. There was also some information that was flat out wrong. Let's get some facts straight before we move on.

Facts
-A speaker will fail for 2 reasons
1) Over reaching it's thermal limits
2) Over reaching it's mechanical limits
-Clipping an amp will cause it to produce maximum power in excess of it's rating
-No speaker, in history, has ever died because it was underpowered......EVER



To start off, a signal that a speaker sees is an oscillating wave. That is, one that goes up and down. The farther each wave gets from it's zero point, the base line, the higher the amplitude. Each peak of the wave is the maximum power of that signal. Let's assume that this "peak" in our case is 100watts. Our signal from the headunit is matched to the input sensitivity (gain) of the amp so even at fill tilt, the signal is clean and not clipped so we have a pure 100watts. Now, this amp we are using in this example is rated at 100watts and if that rating is correct it will only produce 100watts, no more. So there is a cap at 100watts.

Now let's get destructive and wildly turn up the gain like an idiot who thinks it's just another volume knob. Now the amp will output 100watts before the headunit reaches it's maximum volume setting. So if we keep turning up the volume on the headunit, past the point where the amp is outputting 100watts, it will "clip" the signal. The wave will no longer be smooth and sloping. The peaks will be clipped off. The first picture below is what the signal SHOULD look like. The second picture is a clipped signal.







Notice the smooth peaks of the waves are now flat.The peak still represents 100watts but the duration at which peak power is sustained has been increased. Peak power is identical but the power over time has been DRASTICALLY increased. For example, I'm a cross country runner. I can run 15mph no problem. But I can't sustain that pace for an entire mile (4min mile) because I'll burn myself out. My body can recover from a burst to that speed but it can't sustain it. The same goes for a speaker. It can sustain brief moments at peak power because it can dissipate the heat effectively over time. But when peak power is sustained for a long time the speaker can't dissipate all the heat and will thermally fail. (think smoke)

Additionally, the flat spots on the clipped wave represent pauses in the cone's movement. So during the duration of the clip the speaker is at rest and not producing sound. It should be quite evident why this is not pleasant to the ears.
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Old 07-02-2009, 09:28 AM   #2
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good explanation. i always had that tought in my mind but your illustration of running works. thanks
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Old 07-02-2009, 09:35 AM   #3
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Quote:
Originally Posted by itsmyturn View Post
good explanation. i always had that tought in my mind but your illustration of running works. thanks
You're welcome. Glad I could shed some light on it for you.
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Old 07-02-2009, 12:17 PM   #4
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and if you have an underpowered system that does not produce enough volume...what do most people do? Crank the gains WFO and same with the volume knob. Which produces what? Blown speakers with an underpowered system. Hence, the reason people waste speakers with too little power vs a properly powered system. I think some folks are just thinking a bit toooooooooo deep on this.


I can't tell you the number of systems I've had to work on due to this...very rarely do you see a system come back that was set up correctly in the first place.
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Old 07-02-2009, 02:24 PM   #5
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Quote:
Originally Posted by GoBlueFan View Post
and if you have an underpowered system that does not produce enough volume...what do most people do? Crank the gains WFO and same with the volume knob. Which produces what? Blown speakers with an underpowered system. Hence, the reason people waste speakers with too little power vs a properly powered system. I think some folks are just thinking a bit toooooooooo deep on this.


I can't tell you the number of systems I've had to work on due to this...very rarely do you see a system come back that was set up correctly in the first place.
Still no. Where have you shown any example that an amplifier that has and RMS output below a speaker's RMS rating will cause any mechanical or electrical damage to a speaker?

It does not happen this way. If you have an amp that is at or above a speaker's rated power handling, then certainly you have an answer. But the amps physical limits will not produce enough current to cause damage. There is another issue at play if the amplifier is significantly under rated. *hint hint* <---- that is the out answer that I have been goading you into posting for the last month.

If an amplifier is rated significantly lower than its theoretical maximum output, sometimes you can blow a speaker with an amp that is "under powering" a speaker. Some brands such as Kicker and JL produce amps that are rated at a given wattage, say 100 w per channel, but will actually produce at least that. They may produce 125w or more on a single channel, but are rated at 100w because the company does not want to sell things that are less than what people expect. It is a good concept and good practice on their part because they are producing high quality equipment. The issue that comes up from time to time, is someone that buys and amp that puts out 100w and a speaker that can handle 110w will turn up the gains and the volume and end up sending more current to the speaker than it can handle over a long period of time. This is my opinion on where the myth that underpowering a speaker can blow it comes from.
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Old 07-02-2009, 05:31 PM   #6
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Quote:
Originally Posted by sooner07 View Post
The issue that comes up from time to time, is someone that buys and amp that puts out 100w and a speaker that can handle 110w will turn up the gains and the volume and end up sending more current to the speaker than it can handle over a long period of time. This is my opinion on where the myth that underpowering a speaker can blow it comes from.

This is why you (the buyer) should always by a speaker at twice the RMS power handling of the amp. At least 1.5X minimum to be safe. I'm buying an amp that puts out 45 continuious watts of power RMS. The speakers I'm buying handle 70 watts RMS.

-Joe
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Old 07-02-2009, 08:05 PM   #7
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And you are certainly entitled to your opinion. And as I stated, some people are thinking WAY to deep here. The OP explained it in clear english and how it happens.
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Old 07-03-2009, 05:23 AM   #8
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Quote:
Originally Posted by GoBlueFan View Post
And you are certainly entitled to your opinion. And as I stated, some people are thinking WAY to deep here. The OP explained it in clear english and how it happens.
Hum... I didn't think my thoughts were too deep at all for my posting.

Have a great Independance Day
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Old 07-03-2009, 06:26 AM   #9
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Wink

Quote:
Originally Posted by GoBlueFan View Post
The OP explained it in clear English and how it happens.


If I read OP right it seems at odds with what your saying.

Quote:
Originally Posted by ItalynStylion View Post
-No speaker, in history, has ever died because it was underpowered......EVER


The issue is not being underpowered! This statement is absolutely false. When you have clipping in an amp matched to speakers that cant handle RMS power twice that of the amp, then clipping can blow the speaker from too much power (clipping can theoretically cause a doubling of output power hence the recommendation to always have speakers rated at least twice that of your amp.) So it would be accurate to say that having speakers that couldn't handle twice the power rating of the amp is what would blow the speaker NOT under powering them. If you could blow speakers by having an underpowered system then you would blow speakers by turning the volume down.

Think of it this way, take the exact same system that you saw blown from being "underpowered", keep everything else the same (including gain) and put in a properly powered amp in place of the underpowered one. The speakers will burn up even faster then before even though it wasn't underpowered. GoBlueFan you are right, amps that are under rated to drive a speak can blow them, but it is not from too little power! It is from too much (as contradictory as that sounds) so saying that under powering the speaker causes them to blow in the strictest sense, is false.

I am guessing that Sooner and Itylan are engineers. Don't blame them, engineers tend to be very literal . This is born out of necessity from their profession, but it is for everyone’s benefit.
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Old 07-03-2009, 06:57 AM   #10
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RckyMntns, I think we are roughly on the same page but we are using different terminology.

We both agree that no speaker will EVER be hurt by receiving insufficient power. You said....
Quote:
Originally Posted by RckyMntns View Post
If you could blow speakers by having an underpowered system then you would blow speakers by turning the volume down.
This was something my initial post eluded to but didn't outright say. Volume is a function of power. More power=louder volume. So to the people saying that underpowering a speaker kills it they are obviously dead wrong because by their theory we all would be forced to drive around with our volume at max all the time to keep from blowing our speakers

However, I don't agree with getting a speaker with double the amp's RMS rating, in fact I think the opposite might actually do better. Headroom on an amp (more power than is needed) will keep you from clipping the amp and it is clean and controlled power. So even though the peak RMS power seen by the speaker might be more than the speaker's RMS rating it is still perfectly safe because it is less power over time than a clipped signal.

If you just bought a crappy amp and selected speakers with double the amp's RMS rating you will never use them to their potential. The speakers might (if you don't mechanically fail them) be able to handle the clipped signal but it will still sound like shit. This is why you should always have more CLEAN power than you need.

I speak from not only a theoretical understanding on this topic but personal experience as well. My sub setup in my last car was a set of 4 Tang Band 6.5" subwoofers. They are rated at 75RMS power handling. I was feeding them more than double that. Yep, over 600RMS total. How did it sound? Freakin glorious! And I never had a sub fail on me. I was able to do this because the power was clean and unclipped and I had them in a properly designed enclosure.


Bottom Line
A speaker will always fail becuase of excess power over time. It will never fail because of insufficicient power. And I mean power SEEN by the speaker.

The most important thing is setting your gains correctly so you don't over reach the limits of the amp and send a clipped signal to the speaker.
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Old 07-03-2009, 07:43 AM   #11
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A couple of you are completely missing the point. If some dude builds a system and it's not loud enough for him (underpowered) what will he do?

Like I said, you are thinking WAAAAAAAAAAAAAAY too deep here. You are completely forgetting the USER in this whole equation. Some of you have gone completely off the deep end on the techy side of it...the OP has clearly stated how it happens. No need to continue to beat the dead horse.

If you take into account of how a system is built, and how it's being used you might start getting the idea of where I am coming from. The average joe off the street usually don't have a clue how to put a system together. What usually happens is that they buy the wrong speakers, wrong amp and end up with a system that is not loud enough. SOOOOOOOOOOO...they end up cranking the gains WFO and every other device that will allow them to make it "louder". Then on top of it, they bust out the volume knob to WFO distortion and all. The end result of this ends up being a toasted speaker or two. One underpowered system with blown speakers. Have you ever seen a stock speaker wasted by the stock head unit? Underpowered and the user running WFO attempting to get decent volume out of it.

Had they done their homework and put a sufficiently sized amp with appropriately rated speakers they would have had the volume they were looking for the entire time (system design). And in the process, the gains are not WFO, they don't have a need to twist the volume knob off the radio to get the volume they need.
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Old 07-03-2009, 07:45 AM   #12
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[quote=JoeSchmuck;734030]Hum... I didn't think my thoughts were too deep at all for my posting./quote]



That was not directed at you...you just happened to post inbetween the post I was referring to.
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Old 07-03-2009, 08:06 AM   #13
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GoBlueFan, you're right. That's why I stated in my bottom line that it's all about setting the gains properly and not overreaching the amp's potential. If both of those things are done correctly you wont ever blow speakers.

I also want to point out that I think you coined the correct difference in your second to last post. It's not the speakers being underpowered that causes problems but the SYSTEM being underpowered. This is the key verbal difference; but it makes ALL the difference.
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Old 07-03-2009, 08:13 AM   #14
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So my original statement of underpowering a speaker is more dangerous than overpower it...stands. Just have to step back and look at the ENTIRE picture to understand it.
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Old 07-03-2009, 09:19 AM   #15
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Quote:
Originally Posted by GoBlueFan View Post
So my original statement of underpowering a speaker is more dangerous than overpower it...stands. Just have to step back and look at the ENTIRE picture to understand it.
No, you're mixing this up again.

Underpowering a speaker---->Normal, you'll do this 99% of the time in normal listening.
Powering a speaker with a clipping amp---->Bad, sends a shit ton of dirty power at the speaker
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Old 07-03-2009, 09:57 AM   #17
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Sorry I didn';t have time to read the whole thread however I explained this in the GENERAL CAR AUDIO FAQ'S at the top of the page and I'll just paste it here. I also included commentary from numerous engineers.

Q: Will I blow my speakers if I "under" power them?

A: Another one of those myths I keep seeing repeated all the time but I believe it is just because some have not actually had this explained before. This one came from people blowing speakers while using amps that were rated less than what the speaker(s) could handle and blaming it on "under" powering. A very simple answer that dispels this myth is "if that were the case, every time you turned the volume down you would blow the speakers"! Let's say you had a speaker rated at 200 watts rms and your amp produced 100 watts rms. When an amp goes into "heavy" clipping it can "theoretically" produce twice its rated power so you could "theoretically" send 200 watts to that speaker when clipping the amp. This will NOT blow the speaker (sans a defective speaker or inaccurate rating) since the speaker is capable of handling that amount of power and it doesn't "know" if that power is from a "clipped" source. Now let's say you have a 200 watt rms speaker and a 150 watt rms amp. Under heavy clipping this amp could "theoretically" produce 300 watts which can blow a speaker rated at 200 watts rms since that is more power than the speaker is rated to handle. In these cases people would state "I blew the speaker because I was under powering it when in fact as you can see by the example they actually overpowered it.

BTW, clipping is murder on tweeters due to the increase in high frequency content (this is what happens during clipping and not that myth you may have heard about "DC current" or the speaker "stopping" due to the wave being cut off etc ) so the above does not apply! (part of this was based on info I received from several audio engineers as well as testing I did on my own after learning about it and if you'd like more detailed info I have it ).

Quote:
Originally posted by msmith:
The only thing that thermally damages speakers is power... more specifically: average power over time.

I'll explain...

If you take a given amplifier, let's say 100 watts and operate it just below clipping with music material, the "Crest Factor" of the amplifier's output is equivalent to the "Crest Factor" of the program material.

"Crest Factor" is the difference between the average level of the signal and its peak level. For example, a pure sine wave has a "crest factor" of 3dB, meaning that it's peak level is 3dB higher than its average level. We all know that 3dB represents a power factor of 2, so another way to look at it is that the peak power of the signal is twice that of its average level. So, if we play a sine wave on our 100 watt amplifier, just below its clipping level, the average power (over time) the speaker is needing to dissipate is 50 watts.

A true square wave, by comparison, has a crest factor of 0db, so it has equal average and peak power. Our 100 watt amplifier, playing a square wave, unclipped, into our speaker requires that the speaker dissipates 100 watts of power (twice the heat as a sine wave).

Music has a significantly higher crest factor than sine waves or square waves. A highly dynamic recording (Sheffield Lab, Chesky, etc.) typically has a crest factor of 20dB or more, meaning that its average power is 100 times lower than its peak power. So, if we play our 100 watt amplifier just below clipping with the typical audiophile recording our speaker is only needing to dissipate 1 watt of average power over time.

Modern commercial recordings typically exhibit crest factors of around 10dB, meaning that the average power is 10 times lower than the peak power. So, our 100 watt amp just below clipping would deliver an average power over time of 10 watts that the speaker has to dissipate.

Okay, so what happens when we clip the amplifier (which we all do at times). When the amplifier enters into clipping, the peak power no longer increases, but here's the KEY... THE AVERAGE POWER CONTINUES TO INCREASE. We can often tolerate a fair amount of clipping... as much as 10 dB or more above clipping with a reasonably dynamic recording... a bit less with a compressed commercial recording.

So, if we turn the volume up 10dB higher than the clipping level with our Sheffield Lab recording, we have now reduced the crest factor of the signal reaching the speakers by 10dB... so instead of needing to dissipate 1 watt average, we are asking the speaker to dissipate 10 watts average, and we're probably ok.

If we turn up the volume 6dB past clipping on a compressed commercial recording (or bass music recording), we have taken the crest factor of the signal from a starting point of 10dB to only 4dB, asking the speaker to dissipate an average power of 40 watts instead of 10 watts... that's FOUR TIMES the average power, which generates four times the heat.

SO, in most cases, the reason clipping can damage a speaker really has nothing to do with anything other than an increase in average power over time. It's really not the shape of the wave or distortion... it's simply more power over time.

When someone plays Bass Mekanik clean (unclipped) on a 1000 watt amplifier the average power is 100 watts (10dB crest factor). You can also make 100 watts average with Bass Mekanik by heavily clipping a 200 watt amplifier.

If someone is blowing a woofer with 200 watts of power due to a lack of restraint with the volume control... they will blow it even faster with a 1000 watt amplifier because they will probably turn it up even more and now they have more power to play with... this is the recipe for aroma of voice coil.

When woofers are rated for power, an unclipped signal is assumed. We use test signal with a crest factor of 6dB for power testing and can run a speaker at its rated power for hours and hours on end without thermal or mechanical failure. For example, a W1v2 can dissipate 150 watts average power for eight hours or more with signal peaks of 600 watts. So, we rate the speaker for 150W continuous power. This way, when a customer needs to choose an amp for it, they will hopefully choose one that can make about 150 W clean power... Even if they clip the bejeezus out of that amplifier, it is unlikely that the speaker will fail thermally. This is a conservative method, but it needs to account for the high cabin temperatures in a car (think Arizona in the summer) which significantly impacts heat dissipation in the speaker. A top plate that starts at 150 degrees F is not as effective at removing heat as one that starts at 72 degrees F in the lab... and this affects the ramp up of heat in the coil.

DISCLAIMER: The frequency components of clipping can affect tweeters due to their low inductance and lack of low-pass filtering. Clipping essentially raises the average power of high frequencies to a point that can damage tweeters... Woofers and midranges couldn't care less about these high frequency components because their filtering and/or inherent inductance knocks that stuff out of the picture.

Best regards,

Manville Smith
JL Audio, Inc.
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Old 07-03-2009, 09:58 AM   #18
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here's more...

Quote:
taken from www.caraudioforum.com

clipping is not the key to anything-----speakers don't know the difference between a unclipped or clipped waveform----the only thing that they respond to is power----and power is converted to either movement or heat and the spape of the waveform means nothing----it looks like you believe the same misconception as the rest of the world-----so what is the solution to keep that 600 watt sub from blowing??? i hope you don't believe that a 600 watt amp would have saved that 600 watt sub----- cause when the customer clips that 600 watt amp the sub will get 1200 watts and it will blow even faster..........RC

Richard Clark, Technical Editor Carsound Magazine

Hi all,
Power is power. The speaker doesn't know if it's clipped, clean, or what. It knows there is power. And power is what kills speakers.

One thing to correct - a clipped signal does NOT create DC; this is an oft-repeated myth that should be eliminated. When you clip a signal, you actually INCREASE the HIGH frequency content! DC would be the opposite - removal of high frequency signal content.

In fact, the ultimate clipped signal would be strikingly similar to a square wave. A square wave is nothing more than a set of harmonically related sine waves - there is no DC component present. It is all AC.

This is, in fact, why clipped amps are literally murder on tweeters. Clipped signals contain much more high frequency energy than unclipped signals. This is readily passed by the high pass filter of the tweeter, and means the tweeter can receive 2-10X as much power as anticipated, and quickly blows out.

Anyway, too much power - clipped or unclipped - is what kills speakers. You can toast an speaker with clean or clipped signals. Just give it too much power.

To answer the original question, you can push the driver to its full limits with that amp, so I'd recommend running the gains down a bit, and if you hear nasty bumps/distortion from the sub, turn it down even more.

Note that you won't get more SPL from ANY driver once you're at its limits, regardless of how much more power you pour on. The nice thing about larger boxes is that you need less power to reach the limits. Would you rather hit full output with 100W or 1000W? Personally, I'll take the 100W, since it's less thermal strain on the driver and amp, and less draw on the alternator.

Once you're at the limit, you're there. More power won't help.

Dan Wiggins
Adire Audio



Dan Wiggins, CEO Adire Audio

suggest that everyone download and read the following paper, from the excellent Rane website.... this is as close to the truth on the "power or distortion blows speakers" discussion as you will get...

http://www.rane.com/pdf/note128.pdf

Regards,

Manville Smith
JL Audio, Inc.


Manville Smith, JL Audio

Wow. Doesn't anyone here recall that the recommended gain structure for 99% of all car audio system calls for a 3:1 voltage overload at the amp - speaker? This means that if the amp clips at 2 volts, we recommend feeding it 6 volts at the wide open, full pop level. Not only do we recommend "clipping" the amp, we recommend that it be super clipped.
Clipping doesn't damage speakers. A speaker is just a piece of paper driven by a coil of wire suspended in a permanent magnet. How could a speaker ever know the difference between a clipped signal and an unclipped signal? It's just a speaker.



David Navone. Carsound Magazine
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Old 07-03-2009, 04:07 PM   #19
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Manville's explanation is gold. He's a great guy too!

Dan is also the man. I recently did a test for some XBL tweeters for him against a barrage of other tweeters. They were really something special. I'd love to get my hands on a set.
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Old 07-03-2009, 05:07 PM   #20
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Quote:
Originally Posted by GoBlueFan View Post
There ya go again...thinking too deep.
You know, I think you're doing this just to stir the pot, not because you actually believe a low power amp will blow a speaker (in the way you described). It's almost comical.

But, if you are serious and don't follow, no biggie because you probably only care if you're going to damage your speakers or not. The golden rule of thumb is to buy a speaker rated for twice the power of the amp. That rule has been around for as long as I can remember (and that's a long time). This is not only for Auto but very true in Home Audio.

I once had a pair of Polk speakers (about 26 years ago) rated at 75 watts RMS and my amp was rated at 25 watts and probably weighed in at 30 LBS (not the speakers, those easily could have been 40+ LBS each or at least felt like it). That may not sound like a lot for a home system but it was a true 25 watts, not the pieces of crap you see these days rated at over 100 watts per channel and weigh 5 LBS. That's plainly a lie and probably a rated value with gross distortion. All I can say is I never blew the speakers and you could hear it outside the house just fine, it was loud!

Okay, Sea Story time is over.

-Joe
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