Too Little Power

This thread's posts have been getting absolutely facinating and quite interesting to read, but I still have no idea why nobody will even consider what I was saying...

Try it out for yourself! Use whatever sub you want and put the smallest amplifier that you can come across on the sub of your choice. (less than 80 watts for a high rms sub, and less than 50 watts for a low rms sub) You don't even have to turn up the amplifier gain if you don't want to, and you can put the subwoofer in an enclosure too. I guarantee you will come up with the same results that I did. The subwoofer will eventually be damaged if not blown with extended use at a high volume. (over 80%) By "extended" I mean 40 or more minutes of playing time. It doesn't even have to be consecutive minutes either. 5 or 10 minutes here and there.... It will eventually be damaged though! If you don't crank the volume and keep it at a reasonable level, then guess what? The subwoofer will just sound like crap. ONLY if the volume is high will the subwoofer be damaged, if not you will only hear a terrible sounding subwoofer.

That pretty much answers steven kephart's original arguement of will a subwoofer blow being underpowered. It could.... but chances are no. Depends on the volume.

Anyone reading can try it and you'll see for yourself. Keep the volume low and the subwoofer is fine. Crank the volume up and the subwoofer could possibly be damaged or blown. It's as simple as that.

The problem is, your experiment was just an observation, not a controlled test.  It's very easy to exceed the voice coil travel with uncontrolled input in an uncontrolled free air environment.  You might look into the large sealed chamber-type environments that are used by manufacturers to control the damping of the driver.  You would have to set up precise controls in every aspect of this experiment in order to arrive at some sort of a conclusion.

willdkartunes, I don't follow your "experiment."  Please describe what you did with a 60 watt amplifier and what "damage" you observed.

gbear, no one is redefining anything that I can see and your examples about outside influences (screwdriver tips?) are moot and I do not believe are at all what I or Steven are discussing.  Short of some sort of mechanical damage or manufacturing defect, the only thing that damages loudspeaker voice coils is heat.  The only thing that causes heat is power dissipation.  The only way sufficient heat can be built up to exceed the voice coil's ratings is by attempting to dissipate more heat energy than the motor system can handle.  The only way there can be excessive heat is through too much input power, OR if the heat dissipation ability of the motor assembly is compromised such as the loudspeaker is reaching Xmech, or in some cases (especially in speakers with small Xmax values) by heat build-up over time due to input signal clipping.

I used to work in a lab where one of our main functions was testing loudspeakers (and other audio and video gear.)  I have personally placed a loudspeaker in a  free-air test clamp on a square wave signal (simulating a 100% clipped signal) for extended periods of time and measured the heat build-up and can tell you with certainty that as long as the thermal and mechanical limits of the speaker are not exceeded (i.e.: as long as the power input is low enough to not deliver too much energy into the VC) the speaker will play that square wave indefinitely with no damage at all.  Turn up the power, and poof goes the VC.

Please read my comments made earlier concerning my belief for the origin of the "underpower" myth.  It actually has nothing to do with underpower, it has to do with overpower in all cases that I have ever seen scientifically discussed or illustrated.

Cheers

Read this link provided in the original thread: http://www.bcae1.com/2ltlpwr.htm

This thread was never intended to be a discussion on this topic as we have already discussed it.  Instead it was supposed to be a way for me to obtain more technical websites to use as support. 

Dyohn,

I completely agree with both you and Stephen on the issue of too much power being the cause of damage (by the definition of too much this is self validating).  But the problem is that the myth doesn't talk about the difference between rated power given by an amplifier and the actual power being delivered in a clipped environment.  WE understand how a square wave actually produces more power than a sine wave because we are informed and understand some of the more detailed aspects of amplifier and speaker operation (I'm positive I don't know as much as you two but I think i still know more than most). 

If we think about the forum this statement is usually made in the understanding of the term "power" is the rated capabilities of the amplifier.  This is because many times it is someone who understands thermal limits and clipping etc. that does not want to sit down and educate MC Dudley cool guy who just walked off the street into the stereo shop and is going to turn his gains all the way up to make his stuff louder.  Instead of presenting a argument on the defnition of "too much" pawer, us arguing that if the power supplied makes the voice coils melt it's too much becaus its exceeded the thermal limits of the speaker.  We should instead (and maybe a sticky would be really great on this topic) try to spread the understanding of how speaker damage occurs especially when clipping gets involved.  A sticky on clipping and its effects...now dyohn THAT would be a GREAT sitcky!!!

Isn't that what I said in my answer to Alpine guy?  It has nothing to do with the "rated" power on an amplifier, it has to do with actual effective output exceeding the speaker's limits.  So why the argumentative posts?  Or was I mis-reading you?

Steven, back to your original question.  Here are some resources.

This tech note from Monty Ross, an engineer and designer at Rane.  It discusses power compression in tweeters and is designed to sell one of their products, but the concepts may be helpful.

A nice technical article from Xtant on how they measure their loudspeakers and establish their ratings, with some good comments on loudspeaker failure modes.

An article focused on pro audio with good comparisons between AES, IEC and EIA test methods, and a few statements at the end concerning power effects on loudspeaker failure.

And lastly, here's a great article by Chuck McGregor about calculating sound pressure levels that has nothing to do with loudspeaker damage but is something I think should be posted on this forum! 

Dyohn,

I wasn't trying to be argumentative because I agree with the too much power thing.  But...if we are talking about the myth (too little power can destroy subs) their terms(as in the meaning of the word power when people use this statement) are that power is defined according to rated specs. 

Dyohn,

Thanks!  That is exactly what I was looking for.  I remember actually reading that Rane paper a couple years ago. 

gbear14275,

I think Xtant said it best here:

"Loudspeaker power handling ratings are one of the most commonly quoted, but most poorly understood of specifications given by loudspeaker manufacturers. It seems that every company has its own way of measuring and specifying power handling. That’s because Marketing departments are always looking for ways to be able to list higher numbers for power handling in order to impress their customers with the apparent ruggedness of their products. It is sometimes difficult for product users to understand how these specifications relate to real world amplifiers or how they relate to the way they listen to their favorite kinds of music on loudspeaker systems."

Even at work, the installers I work with think manufacturer ratings are king.  I had to prove to them that sometimes the manufacturer recommended enclosure isn't an ideal choice.  Or in another case I had to show how rated impedance is generally a made up number to closely describe the actual impedance of the driver, and are quite often rated wrong.  The reason for this is because all of these ratings, including the power handling specs of car audio equipment, come from the marketing department.  Rated specs should always be taken with a grain of salt.