biz77

But it does. When an amp can't produce the requested power cleanly, it clips, and provides too much instantaneous power.

 

Lots of bickering to say the same things, and going crazy over semantics... jeez

 

FALSE! When an amplifier clips it doesn't produce any additional power, it is just that the average power and peak power are about the same. This is not a failure caused by too much instantaneous power. It is a failure caused by exceeding the thermal limits of a driver - too much power over a given period of time.

Unless your clutch was slipping the whole way down the track or you are an extremely slow shifter, the only thing accounting for the ultra-low trap speeds is the car running low on power relative to the mods.

Are you sure your clutch wasn't gone before you went to the track? 2.5 60' would basically be easing off the line and rolling on the throttle. With a decent holding clutch you should easily be able to cut 2.0 or lower 60' times. My bigger concern, however is that your car is WAY down on power. 98-99mph trap speeds indicate just a little better than stock power. I would scrap that UTEC as soon as possible and go with a tuning solution that utilizes a reflash of the ECU. Piggybacks are okay when there isn't another option. That turbo should be capable of at least another 5mph at the end of the quarter mile.

^I cut 1.8 - but not in 100+ degree weather. Miss the part that I was running 91 octane? You hit 98mph? Thats like hitting the brakes at the 8th

 

My trap speed lets you know how much faster my LGT is than the driver is OBVIOUSLY A DRIVER ISSUE IN MY CASE. Maybe you DO need to go to LALGT school:p

 

...

 

Or at least come launch my car for me at Fontana in 100 degree weather!

 

 

Clearly you've forgotten what the top-end of the stock turbo is like:) Yeah, you have the heat, but my altitude doesn't help. I'll be back in OC in August for a week. I'll try to get out there, but no, I will not be launching anyones car;)

6/5/2010

60' 1.9

 

SAY WHAT???!!!

 

 

 

But you are mistaken. I know it is painful to hear. It was hard for me to process at first that a proper 60ft is 1.6 (yes at stage 1) and beyond stage 1 good is under 1.5

 

Don't get huffy and defensive, learn to launch your car better. I am sure more than one of us will bring you a 1.6 slip from this weekend. I am not sure that will be ME!

 

BTW, if you scroll back to post #20 in this thread you can see how my stock turbo, stock tire, stock suspension, stock clutch, stage I car compares. Clearly I need to attend the LALGT school of launching;)

I'm about to order a VAG-COM cable - is this one the right one?

 

http://cgi.ebay.ca/USB-OBD2-OBDII-Vag-KKL-Interface-Cable-Audi-VW-/160429348392?cmd=ViewItem&pt=Motors_Automotive_Tools&hash=item255a559628#ht_3616wt_811

 

That is the same one I've had success with.

^ Have the same cable for my Audi. My Tactrix cable recently crapped out on me and I had to try this cable for flashing. I'm happy to say, that with the FTDI drivers in place, this cable is 100% fuctional for all aspects of tuning on my 2006 LGT using Vista Home Premium.

^ This is a poor way to set-up your gains if you like to get the most from your equipment.

 

You are taking this WAAAAAAAYYYYYYY too far. If you walked into 99.97% of hi end car stereo and even home audio shops and asked this question they would give you the clipping/distortion story. Even if they understood the actual electrical and physical properties of what was happening. Why? Because it is good enough and why make someones head spin.

 

Not everyone wears a hat with a propeller like you. Not everyone needs to know the EXACT cause down to electrons. If your friend dies of an aneurysm is a clinical study and meeting held to explain exactly how it happened down to the molecular level? NO. So yeah if he says he has a headache and then he dies, I guess it hurt real friggin bad.

 

Get a life man. Its darn hard to melt a woofers voice coil from an underpowered amp anyways. Most of the real world examples of melted voice coils are from tweeters and mids. I might not have an engineering degree but I am pretty smart. I just don't feel the need to convince everyone else of it all the time. If you need this much mental stimulation join a MENSA forum.

 

I feel better now.

 

Well m sprank, I appologize for physically dragging you into this discussion and making you participate against your will.

Don't try to spin it so you look semi-correct. You are confusing actual cause/effect with symptoms. The only two things that kill speakers is too much power over time and too much instantaneous power. Distortion does not kill speakers. Clipping does not kill speakers and too little power does not kill speakers. I've shown how I can provide a speaker with all of those nasty things and how it will survive indefinately through all of them. It's not semantics. It's ignorance.

 

It would be like me telling you that my friend died from a headache. As it turns out he had a brain aneurysm, but he said he had a bad headache and then within a couple of hours was dead. I'm going to say that he died from a headache because it is just semantics and that's what I want to say. Do you ever get a headache? Are you dead?

NSFW, ratings are ratings, and a "200w" amp is a 200w amp at a certain frequency creating a sine wave. That does not say what the "200w" amp can do if over driven.

 

The case biz77 states is true, but that isn't what we see in practice. In practice, the underpowered sub woofer is over driven by an amp that is capable of distorted power higher than the rated power of the sub or the undistorted rated power. This is done because the user wants more volume, and just turns things up.

 

It is both true and what we see in practice. Let's go back to my example and examine why I would be less than comfortable running an amp rated for 400 watts into my 700 watt rated sub under the same conditions as the little 15wpc Panasonic shelf system.

 

Let's say our 400 watt amp is capable of producing 400 watts as a pure sine wave across it's entire bandwidth. A sinewave has a crest factor of 3db, which means that the average power is half of the peak power. Running this particular amp in this fashion should pose no problem to my speaker rated at 700 watts.

 

Now we take the same amp and run it into clipping. This produces what approaches a square wave. Unlike a sine wave, a square wave has a crest factor of 0 db, which means the average power is equal to the peak power. This 400 watt amplifier is now providing power to the speaker that is identical to that of an amp that is running a clean sine wave at 800 watts. But wait! The subwoofer was rated for only 700 watts continuous power. I'm now exceeding the thermal capabilities of the speaker by 100 watts. It probably won't last long under those conditions. So am I underpowering the speaker? Is distortion killing the speaker? Is the clipping killing the speaker?

biz77, I did notice that the link pretty much agrees with what you said...

 

This is absolutely false:

 

"5.21 What's worse for a speaker, too much or too little power? [iDB]

Problems occur (in everyday operation) when distortion is fed to a speaker. This occurs MUCH more often when you are dealing with an underpowered system -- typically the owner will turn up the volume too much or set the amplifier gains too high to try and get more volume from the system. These introduce distortion to the signal -- this will destroy *any* speaker. (See section 5.22 Why is distortion harmful to my speakers? [RK].) "

 

The explanation beyond this is okay, but the statement that distortion kills speakers is absolutely untrue:

 

I can take an old Panasonic shelf system I have sitting at home rated for ~ 15 watts per channel and hook one channel up to the subwoofer system I use in the car - a single Polk Audio SR124 subwoofer. It is rated for 700wrms and 1,400 watts peak per the manufacturer. I can then crank that 15 wpc Panasonic shelf system up so that it is clipping non-stop with very audible distortion. I will be able to do this indefinately and that speaker will not be harmed. The speaker has more than enough thermal capacity to dissipate the power that is being fed to it. Furthermore it can only reproduce the signal that it is fed. It doesn't know the difference between a clean signal, a distorted signal and a clipped signal. That right there disproves that "distortion kills speakers" and also that "clipping your amp kills speakers."

 

So now the question becomes would I be comfortable performing the same test with a decent quality 400 watt rated amplifier? No I would not. Now who knows why I wouldn't?

http://www.mobileaudio.com/rac-faq/rac-faq_5.html#SEC111

 

Just because it is written on the internet doesn't make it true;)

 

The ONLY two things that can kill a speaker are too much power over time and too much instantaneous power. Period. End of story. No further exlpanation needed.

 

It is very easy for me to disprove any of these myths in this thread with real World experiments with items I have sitting at my house or work.

Fact is, underpowering (in and of itself) isn't bad... the problem is, most people over-drive the low-powered amp, which results in distortion, which can damage the sub.

 

On the other side, over powering a sub continuously can also damage the sub, if it's done continously. Of course, the specs on the sub are provided with a margin of safety, so 500W to a 400W sub may be ok... then again, it may not.

 

So, simplistically, "underpowering a sub is bad"... but the real reason is because of amplifier distortion when the amp is driven too hard.

 

The bottom line is, don't distort... you should be able to hear what distortion sounds like, and then make sure you're below that level, for a given amp. Beyond that, you can overpower the subwoofer's rating a bit... but I still prefer to stay at or below it - because I can hear when I'm distorting, and have the sense to turn it down before it damages the speaker.

 

 

Totally wrong. Distortion doesn't kill speakers. The only two things that can destroy a speaker is too much instantaneous power or too much power over time. If distortion kills speakers, how do guitar amps survive? They are full of distortion.

So by what you've said, I can't hurt a sub rated at 400w RMS with an amp that's rated at 200w rms

 

Yes, entirely possible, but it wouldn't be from underpowering the speaker. It would be from overpowering it. Perhaps if you removed your head from where you have it placed most of the time you could see why that is the case.

post #34 was you showing off your internets skillz

 

 

Post #34 includes an excerpt from Manville Smith of JL Audio. Should we listen to him or you?

I've always heard under-powering did more damage when driven hard....

Did I miss the answer somewhere in the last 3 pages...?

 

 

Yes. Post #34 is your answer.

After reading some of the other posts I think I may have dove into shark invested waters. Maybe Ill slowly back out of this one before I start a shit storm all over again lol....

 

Nope, no reason to repost accurate and factual information all over again. If you want to believe the BS shoveled your way by your local "professionals" which uses metaphors that don't even apply instead of trying to understand the actual physics of it, then be my guest. As they say, ignorance is bliss and by my estimation there is an abundance of people living in their own utopia.

 

I think we're debating semantics here...

 

Fine by me. I want it to be perfectly clear, since there is SO much confusion on the subject.

You are clueless.

Distortion can cause mechanical failure. What we hear as distortion is the speaker hitting the end of it's travel.

 

 

The amp has enough peak power to move the speaker one direction, but then doesn't have enough power to stop it moving and reverse direction. The momentum of the speaker carries it to the end of it's travel and can cause mechanical failure.

 

Utter BS.

 

THE ONLY THING THAT DESTROYS A SPEAKER IS TOO MUCH POWER!!!!

 

You are describing a speaker that has surpassed its mechanical limits from (drum roll)... too much power.

 

In a sense all speakers introduce distortion when reporducing sound as they are far from perfect in converting the eletrical energy from an amplifier into mechanical energy, but what you describe above regarding momentum, blah, blah BS, blah is completely false.

 

 

Perhaps you should have looked into some of the links I poseted. From QSC "Truths and myths about clipping":

 

Clipping is bad for loudspeakers because it really heats up the voice coils.

Myth. Dynamic loudspeakers are notoriously inefficient; they turn well over 90% of the audio power put into them into waste heat instead of acoustical energy. A clipped signal does produce heat in the voice coil, but so does an unclipped signal, too.

 

A variation of this myth is that extra heating occurs because the voice coil and cone stop moving during the clipped portion of the audio waveform. This also is untrue; even if the instantaneous signal voltage stays the same for some short period of time, like a millisecond or so, the cone stays in motion because at frequencies above the loudspeaker’s resonance the voltage is an accelerative force.

 

Clipping at any power level is capable of damaging your loudspeakers.

Myth. Some may tell you that a clipped signal from even a very low-power amp will blow out a high-power loudspeaker driver, but that’s untrue. Picture a 50-watt amp driving a 500-watt (continuous) loudspeaker driver. Even if the amp is driven into very severe clipping, it will still put out less than 100 watts, and therefore will not be a threat to the loudspeaker (it probably will not sound good, though).

 

Try that with an amp rated at, say, 400 watts or higher, though, and the results may be very different. This is because an amp, when it clips, can usually put out much more power than it is rated for. Prolonged, sustained clipping may cause that amp to put more than 500 watts into the loudspeaker for some significant time and cause a thermal failure (melting) in the voice coil. On the other hand, in a system where the amplifier and loudspeaker are well matched (i.e., amplifier power is roughly equal to the loudspeaker's program power rating), very brief and occasional clipped peaks are generally harmless.

You're all stuck on this whole electrical side of the speaker.

 

If you have a sub rated at 100w and you turn your 35w amp 'up to 11' and it distorts really badly, you can actually physically damage the cone, the surround, the voice coil, etc. Paper rips, wires break, the speaker smashes through the grill.

 

Distortion doesn't kill speakers. Too much power does. What you are describing is mechanical failure from over powering.

And the fact still remains, there is only two ways to kill a speaker. Too much power applied over time or too much instantaneous power.

Biz77, looking over how I went through that, I think we're saying the same thing. The point of bringing up the voltage rail was exactly that point, which is simply pointing out how a small "underpowered" amp can still damage a speaker. The reason is still overheating/overpowering the voice coil, but the point is that you can blow up a 75w speaker with a "50w" amp.

 

 

You made it sound like that theoretical amplifier would deliver a maximum of 400 watts while unclipped, but once you start clipping the amp it becomes an 800+ watt amp, which isn't how it works. That amp is always capable of delivering that 800 watts. How the power is applied over time is what matters.

Ean611, you are running off onto so many tangents here.

 

Let's address them one-by-one.

 

roosien092, to be clear, you are not describing "underpowering" a sub, you're describing running DC voltage through the voice coil (distortion).

 

Running less power than a sub is rated for will not damage it. Overheating the voice coil due to short term DC voltages can.

 

From "Truths and myths about clipping" by QSC, who builds professional sound reinforcement amplifiers and related equipment found in stadiums, theaters, at concerts etc:

 

http://media.qscaudio.com/forum/viewtopic.php?f=29&t=2736

 

"Clipping is bad for loudspeakers because it is DC.

Myth. A clipped signal is not DC. Even if the clipping is so severe that the waveform shape approaches that of a square wave, it’s still AC.

 

Even so, DC by itself is not necessarily dangerous for loudspeakers. In fact, a good way to check polarity of a woofer driver is to connect a small battery across it and see which way the cone moves for a given DC polarity; the amount of power dissipated is minuscule. However, a significant DC offset on an amplifier output is undesirable for several reasons: because it will dissipate power in the voice coil without producing any acoustical output; because it may cause the voice coil to travel out of the magnet gap, which would reduce the cooling; and because it shifts the driver’s at-rest position and thus makes the available excursion asymmetrical, reducing the overall safe excursion limits of the driver."

 

Example for above:

http://legacygt.com/forums/images/editor/separator.gif

Amp has voltage rails at +42V and -42V (This is Class A, rather than class AB)

 

Amp could be rated at 400w RMS at 4Ohms. (leaving small margin over rating). Peak power of amp while distorted would be significantly higher, approaching a theoretical limit 882w at 100% duty cycle. If one were to add more margin, bringing the voltage bias significantly higher for the same rating, let's say +60V/-60V, the RMS power rating could be unchanged, but the max distorted output of the amp has increased significantly.

 

Bottom line, power output can increase beyond rating, and will only stop at electrical limits.

 

Your point is moot. Your theoretical 882 watt amplifer could have been touted as a 100watt amplifer, or a 400 watt amplifier, or as an 800 watt amplifier depending on the rating method and how unscrupulous the manufacturer is. Your theoretical amplifier is capable of producing 882 watts, whether that is into an unclipped sine wave or if it is driven into complete distortion (square wave.) Here is the difference: Driven into a sine wave there is 3db of crest factor, which means the average of the musical signal is 3db down from the peak. Driven into a square wave there is 0db of crest factor. The amplifier did not magically become able to deliver twice as much power.

 

No one seems to be better at explaining this than our own msmith, so no reason for me to try any different twist on it:

 

"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."