Myth Busted! Underpowering

For giggles I wanted to see if it was possible or even plausable to blow a sub using a "small" amp. (or as I would have "mis"stated in the past...underpowering it).

I was convinced by some very well informed and knowlegeble people on this forum that it was not possible to blow a sub by "underpowering" it. I was stubborn at first to understand this as it was something I was told would happen often throughout my years in the industry, even though it really didn't make any sense.

Regardless of believing this shouldn't be possible, I decided to attempt to destroy a sub using an amp with a 10x less power rating then the subs power rating, crank it up, and see what happens.

First, here's the specs on the components used for the "experiment".

AMPLIFIER SPECIFICATIONS:                                                                                   Max Power output: 30W + 30W, RMS Power output: 15W + 15W (4ohm, 30Hz-20kHz, less than 1% THD)                                                                                                    Frequency Response (-3dB) 10Hz - 45 kHz                                                             Damping factor (100 Hz) “More than 100”

SUBWOOFER SPECIFICATIONS                                                         HighEndurance  Multi-Layer Voice Coil                                                                       Deep Bumped Back Plate for Extreme Excursion                                                         Max. Power Handling: 300W, RMS Power Handling:150W                                    Sensitivity (In Car): 90 dB SPL.                                                                                Usable Freq. Response (In Car): ±5dB 45Hz-1500Hz                                               Nominal Impedance: 4 Ohms
Terminal Connector: Screw (gold plated, quality)                                                        Kapton Voice Coil                                                                                                   Rubber Surround            

(I measured an Re of 3.8 ohms)

For the headunit I used an older JVC KDS580, preouts, with a 20a power supply.

For the amp I used a 150a power supply. This amp is really small, about the physical size of 2 cigarette packs. I only used 1 channel of it @ 4 ohm to the sub so the output should be 15watts rms, 30 watts max. I used a "y" adaptor to both RCA's to form a mono input or "mixed stereo" if you wish.

The sub was installed into an "optimized" vented 8'' enclosure.

What I did first was break out the old "My Disc", The Sheffield/Autosound 2000 test disc (yes I know it's ancient).

I set the volume on the deck to 50 (maxed out), loudness on, Bass and treble full up, and turned the gain all the way up on the amp.

For hours on end I ran sweeps (low and high distortion), square waves,bursts, correlated pink noise (20 to 20), warbles, individual 5 second frequencys from 10hz to 99hz and various dynamic music.

Not only did the sub handle it fine, it sounded pretty good on certain tracks...actually shaking things in the "lab" as it hit resonances. The sub was moving quite a bit at times, but nothing too excessive. I heard no bottoming out and smelled no voice coil. The amp however was getting warm/hot to the touch.

Once I got tired of all the "noise" I figured I would just let it play heavy bass music for the rest of the day or until something gave.

Something did. The amp basically took a dump. (please no "I told you so's", this is what I predicted and expected before I started the experiment, my hypothesis based on info I received from this forum)

The amp still operated but only at 3/4 to full volume...once you turned the volume down to a "comfortable" listening level, you could hear it breaking up pretty bad, at lower volume levels no audible info at all would come out of the amp. So I tossed it in the garbage.

Anyhow, aside from the physics and common sense standpoint, it appears conclusive to me that the amp did not have enough power to damage the sub no matter how hard I tried, in any way shape or form. The amp gave up way before this sub ever would have. The sub is still in perfect shape and always remained cool as a cucumber throughout the test, so to speak.

After that I Bridged the sub to the deck power (don't think that's a good idea, but I did it) and ran it the rest of the day along with 2- 6.5's at moderate levels. The deck, speakers and sub are all still fine, it actually sounded pretty good but I am about 100% sure if I cranked it up for any length of time, the decks outputs would have became toast.

Keep in mind this was not the most "scientific" of tests and I haven't verified personally if this also holds true for other types of transducers. But I believe it confirmed that what I have been told about using a low powered amp on a sub in the past is untrue. I was going to take other measurments and scope it but I saw no point. The sub was not doing anything acoustically or physically unusual or unexpected. (occasional audible distortion not too pleasing to the ear was about the worst scenerio)

What I also can conclude from this is when I witnessed first hand in the past subs being damaged by amplifiers I believed were too "underpowered", the opposite would seem logical. Those amps were too powerful, and probably rated unreliably.

So, this myth is busted. I also have an 8'' sub for sale...barely used. Any takers?

Steven, I want to read the story but I can't seem to find it. I have not become familiar yet on how to fully navigate my way around here.

I entered "too little power" on topics and 682 came up. Perhaps you can guide me to a shortcut?

Thanks

Don't ask me killer. I argued this topic until everyone was about to reach through the screen and strangle me.

Most every reply made sense but the "kicker" was a link to a discussion on this topic. Some of the "posters" were people I know for a fact are tops in the field.

So as if that wasn't enough, I did that experiment, although I mention it was not very scientific.

These "5 different occasions" in the past...can you be more specific on the circumstances and honest component specs, as well as the "condition" of the components?

Thanks.

In my case the amp never "overpowered" the sub.  I was simply over working the amp  (beat the tar out of it for hours) until it gave up. Most probably heat related.

I am still interested in the specs on killer sonatas equipment to find out how subs could have blown from doing this 5 times.

If anyone's curious the amp I used was a Kenwood KDC-322 (discontinued) and the sub was a DHD 6080 SVC 4ohm.  The amazing thing was that at certain frequencies, it was impressivly loud.

who woulda thunk?

master5 wrote:

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Steven, I want to read the story but I can't seem to find it. I have not become familiar yet on how to fully navigate my way around here.

I entered "too little power" on topics and 682 came up. Perhaps you can guide me to a shortcut?

Thanks

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for 3 of the 5 occasions (kept having to warantee the subs) it was a single type S 12" sub (could handle 300RMS) powered by a jbl bp300.1 running at 4ohms. in these cases, the sub was underpowered by 150rms. I went through 3 different subs. They were in a sealed box built to alpine specs.  the other 2 involved a JL 6W0 SVC 4 ohm powered off a MTX 202 at 4ohms. in these cases, the sub could handle 75RMS but were only receiving 35RMS. in all 5 instances, the gains were not maxed out but set to the best of the installers ability without test equipment (by ear). There might be some hidden variables that I dont know about but the common factor in all 5, is that all the speakers were underpowered.

Thanks nouse, I told you not to tell me so !

I actually had fun doing it but really wanted to see that sub explode or burn up. But it just wasn't gonna happen, period. Someone was in the "lab" with me building a custom overhead console and I was deriving particular pleasure in annoying the crap out of him. (As I stated this 15 watts of "raw" power was playing the sub quite a bit louder then expected). But since he required my help he was more or less forced to put up with it. And I was explicit that the experiment was not going to end until something gave, even if it meant running it for weeks at full tilt..lol

Anyhow, additional thanks for the "backup" on tips at work, that was much awaited as I knew you would be familiar with what I was talking about, and you exceeded my expectations. Similar to your signature, we should never under estimate the power of human stupidity.

Have a good one.

Thanks Steven, that was interesting reading. Brought back some recent memories, am I right? No wonder so many of you seemed a bit "perturbed" back during our little "debate". I can see you have been there before.

As far as what Killer experienced, in his defense I also have had "strange" experiences with Alpine subs, but I sell the type R's. They do seem to blow often, even in sealed enclosures, and I can smell the voice coil burn.(I love the smell of resin and gasoline but voice coils STINK). I basically stopped promoting them. The subs are rated pretty high in power handling and I believe the amps I use have fair ratings. I don't know what happened to Alpine but "back in the day" I was doing very well in competitions using thier 8'' subs, they were incredible and indestructable.

I will need to do a little research unless someone knows why these Alpines are toasting so easily. I know some are mentioning JL audio, but I once recieved a free 10w6 and it took me 10 years to destroy it. Those are good subs, I can't see anything but age or extreme overpowering ever damaging one of those.

Good report.  Thanks

Killer, if your speakers blew they were not underpowered.  If you used a 150 watt rated amplifier and drove it into full clipping, it simply put out enough energy to fry the voice coil on the sub.  Simple.  A 150 watt amp could produce as much as 450 or so watts peak in full clip mode.

It is always too much power that kills speakers.  The listed ratings on a particular piece of gear have nothing to do with it.  Proper setup is the key, and/or proper power measurements using an oscilloscope.

Steven Kephart wrote:

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"the best of the installers abilities" does not mean that it was set properly. My guess is that your head unit has high voltage outputs, right? Well the JBL BP series amplifiers weren't designed for those types of outputs and would start to clip as soon as you turned up the gain any. They were also notoriously under-rated.

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Steven, you may have found the hidden factor. Atleast it explains the JBL amp, not the MTX. The deck has 8V pre-outs. if the JBLs couldnt handle that, then that might have been the problem.

I want to thank everyone again. Your patience and knowlegde is what encouraged me to find out for myself, otherwise I would have never given second thought to what I used to believe was fact.

I feel alot more confident now to help others who have the same misconceptions about this topic, as well as debate with plenty of backup. I also feel I can do a better job setting up a system. I was always telling people that they shouldn't use a particular sub because they don't have an amp with enough power. I was fearful it would cause damage and now I know the facts about how to set it up correctly without worrying about "underpowering". I have been converted thanks to many of you.

I think my sub and amp sales/installs will increase as well once I share this knowledge. Just about everyone I work with was convinced that we didn't have amps powerful enough for our subs. I know for a fact that is not the case thanks to everyones input here.