HELP - How Hard is to Blow a Bass Driver

As I came home I see my little brother and his friend BLASTING a Prodigy song in my listening room. I don't know the song but it was about 1 MIN. of just full loud annoying bass only (the kind you hear in Honda Civics while the liscense plate is rattling). As I ran into the room to lower the volume I saw the Driver shaking like CRAZY. Not "in and out" motion but more like shaking erratically all over the place.
Amp is the Exposure 18(70 watts rms)
Speakers are the PMC Fb1
Volume at 12 o-clock

I'm concerned that there might be damage to the Drivers. I can't hear any damage but could there be internal damage (coils)that might show up later on? Any way to test for damage?

Thanks for your help as I am stil in a cringing state
Dr. balance,

With a 70 watt amp - it's more likely that the upper frequency
drivers could be damaged if they overdrove the Exposure 18
into "clipping".

If the amp is driven into overload, and can't supply enough
voltage so that the peak voltage equals the peak input voltage
times the amp's gain - it will clip off the top of the wave
at its maximum voltage.

Because this means a sharp kink in the wave - that results
in a lot of high frequency distortion products which get
routed to the tweeters and high frequency drivers by the
crossover - resulting in fried tweeters.

Listen to your tweeters - if you can hear them OK - then
you are probably fine. Tweeters don't stand for abuse
very long - they just go "phht"

Sounds like you dodged the bullet.

Dr. Gregory Greenman
Thanks guy for the input. I was very concerned because I heard distortion. The song consisted of EXTREMELY LOW BASS only. The bass that was comming out of the Bass driver was driven into distortion, however for a short period of time only 30 seconds (my guess) whould that be enough time to cause any damage to either the bass driver or tweeter. I gently pushed the driver in listening for scraping sounds and it moves freely. There also doens't seem to be any damage when listening at normal levels. My question, however is, is it possible for there to be unheard damage that will show up later (ie, stress) or would I know right away if there was damage?
Hi All,

Here is a discussion about how to avoid damaging speakers. I hope you find it helpful.

UNDERPOWER – Your speakers have a “recommended” power rating as stated in the literature. These figures are only guidelines for matching to your amplifier or receiver. The speakers can actually accept much more peak power than the specification indicates as long as the power (wattage) is undistorted or “unclipped”. IT IS EASIER TO DAMAGE THE SPEAKER WITH TOO LITTLE POWER RATHER THAN TOO MUCH!

The music that your system plays normally requires very little power to provide a reasonable volume level. The rest of the amplifier power waits in reserve to allow for dynamic peaks in the music – the crescendo of an orchestra or the impact of a drum or bass guitar. These types of passages cause the amplifier to put out many times the amount of power it does during the softer sections.

If the amplifier does not have sufficient “dynamic power reserves” or “current capability” (the muscle behind the amp’s power rating) the amplifier can go into a condition called “clipping” where the power becomes distorted. This clipping distortion is seen by the speaker as heat and can damage the fragile wires in the voice coil sections of the speaker elements. With severe clipping these wires can separate from each other or literally burn and char. If this occurs, the sound will become distorted or you will hear a scraping noise. In some cases a damaged driver will not make any sound at all. If you are concerned about your amplifier’s current capability, please contact your dealer for advice.

TOO MUCH BASS – speakers have a specific low frequency capability but as with all things they have a limit. Some modern music contains an extreme amount of bass energy (Rap, synthesizer music, etc). These types of music can tax the ability of any loudspeaker if played at a high volume (remember clipping).

The “loudness” control in your system is designed to compensate for the human ear’s inefficiency to low frequencies at low volumes. Only use this control when listening at low background volume levels. Never use it high volumes!

Equalizers are like elaborate tone controls. They can boost or cut the signal at a number of points along the bass, midrange or treble sections. If they are used improperly, a large boost in the bass or midrange can easily cause the amplifier to try and put out up to ten times its available clean power. This can cause severe amplifier clipping and quickly damage all connected speakers.

An addition to clipping, too much bass boost can cause the woofer to pump in and out excessively. At high volumes the “former” (around which the voice coil is wrapped) can slap against the back plate of the magnet assembly. It will be heard as a popping sound. This action can dent or bend the edges of the former, which may cause scraping or can stop it from moving entirely and no sound will come out of that driver.

OTHER METHODS OF ABUSE INCLUDE (but are not limited to):

Turning on the system with the volume set to a high level.

Changing radio stations with the volume set to a high level.

Lowering the needle on to a record with the volume set to a high level.

Forwarding or rewinding tapes with the volume set to a high level.

Plugging or unplugging ANY wires with the power on.

Trying to play a musical instrument or microphone through your system.

Playing video games through your system.

Playing high energy, high volume soundtracks through your system.

Best Regards,

Barry Kohan
Hey Barry;

I would like to offer another way to really--aw shucks I really want to use the F*-word--up your speakers, and that is with one of those 'test CDs' that push the speakers to the limit. I blew out my cute little horns sitting on top of my very expensive speakers when I used one of these CDs and paid no attention to the small print warnings about turning down the volumn when running this so-called "test".

Dr balance,

The fact that you heard distortion with deep bass only is what
you would expect if the amps were driven into clipping.

It takes a lot of power to do the deep bass notes - so they
are the most taxing for the amplifiers.

The distortion - which is often described as a "cracking"
sound is what you expect to hear from an amp that is clipping.

If that's what you heard - then the tweeters could have
been under some stress - but if they are still working -
then you probably corrected the problem in time.

The problem is basically too much power and hence energy
going to the tweeter which heats them up. The coils can
get so hot that they melt - and that ruins the tweeter.

However, if you correct the situation quickly, which is
what sounds like you did - then the coils just got hot
but didn't melt. So they'll be fine.

If they are damaged - you'll know it - the tweeters won't

But if you don't notice a problem - then your speakers are
OK - and I wouldn't worry that there's some "hidden" damage.

Go back to enjoying your stereo system.

Dr. Gregory Greenman