Email I got from JBL (1 Viewer)

[Mike_Ped]

I had been having a "crackle" sound coming from both my S38s, which as I use as my mains, so I emailed JBL to try and find out what the problem was. Here's what they said:

I'm sorry to hear of the problem with your speakers. Usually when drivers (meaning woofers, midranges and tweeters) are damaged in pairs, this is the result of receiving a signal that they should not have received.
There are two ways to blow speakers. The first is the one we all know and understand. If you pump 500 watts into a speaker that is only rated at a 100 watts, kaboom, it blows up. As a result, very few of us do this. So
then why are all of these speakers blowing up? Because of the second reason, "under-powering". It's really a misleading term, but let's try to explain. First let's take it to the extreme. Example: You have a 1000 watt speaker and a 100 watt amplifier. The way you like to listen to music requires 300 watts. Typically, you will ask your amp to put out that 300 watts that you want to hear. The amp will do it, but it will "clip" and "distort". Unfortunately, the human ear can't hear distortion until it reaches almost 10%. By that time it's usually too late. The speaker keeps trying to
reproduce this distortion that it's not capable or reproducing and eventually, it blows (usually the tweeter fails first). There is a very easy way to determine if you are asking too much of your amplifier. Follow
these directions to perform this test.

* Set the Bass and Treble knobs in the middle (flat).

* Make sure all Equalization buttons are turned off (loudness, EQ, contour,
etc.)

* Put on a CD

* Turn the volume half way up (electronic volume controls, display would
read 0 dB).

If you normally listen louder than this, chances are you are pushing your amp too far, causing it to clip, and blowing speakers. Generally speaking, when listening to CD, VCR, DVD, or Laser-disc, you are at maximum clean listening volume when you reach the half-way point on your volume control. The reason is very simply. These sources have a very "hot" output. In the old days when we were all using turntables, you would hit maximum volume at the 3/4 mark. This is because the output of a turntable
is considerably lower than any of the new sources. The reason this standard has not changed is because of versatility. You may be trying to watch a home-recorded VHS or Cassette, and it may not have been recorded very loud. So you need the extra volume control to make up for the difference in a situation like that.
Please keep in mind, if you normally listen with your bass and treble knobs boosted and/or the loudness button etc. pushed in, it is possible to push the amp too far with your volume knob as low as 1/3 volume. If you are pushing your receiver too hard, it is suggested that you
realize your systems limitations or recommend that you get a more powerful amplifier. Please realize, if you only buy speakers that will handle more power and not a more powerful amplifier, you won't solve the problem. The
speakers will still blow, because it is distortion that is blowing them, not too much power.
If you are handy with a screwdriver, I can send you a pair of tweeters. Please email back with your shipping address and I will send them to you. If you would rather have an authorized service center take care of this for you, then please click on Product Support on the JBL Home website link of www.jbl.com . Enter in the model # and click Submit. Then click on Service Station Locator to find an authorized service center near you. The speakers have a five year warranty. Just show them a copy of your purchase receipt for warranty service.



Now, I was amazed when all he asked for was my shipping address to send the new tweeters, and so I did give it to him and he is sending me new tweeters.

My question is, how do I avoid this problem in teh future? I use a 100 watt per channel Yamaha receiver to power the speakers and I NEVER listen to anything above reference volume. So, what can I do to avoiding blowing the tweeters in the future? Would getting a voltage stabilizer or something like that help the problem?

 

[Brett DiMichele]

Mike,

The only real cure for the power is a real amp... The
Recievers 100 Wattage rating is most likely not with all
channels driven. When listening to movies or multichannel
music all channels ARE being driven and this can tax the
weak power supplies in *most* recievers. What happens is
that you wind up sending 40 maybe 50 watts to each speaker
when it needs much more than it's getting. So you clip the
amps.. You may not hear it (with good S.S stuff these days
sometimes Clipping isn't audible) but the tweeters WILL
suffer the ill effects.

Tweeters have the smallest guage wire in thier voice coils
and Clipping generates mucho heat that the VC can not vent
fast enough and pretty soon the VC breaks down and shorts
out and you have dead tweeters.

Put the new tweeters in.. And just moderate the levels at
which you listen. Or buy a good seperate amplifier and use
the Pre Out's of your reciever to feed the seperate amp.

 

[Mark Hedges]

That clipping test seems like total BS to me. It all depends on the volume of the source or the type of volume controls. For example, if I am listening to the digital cable music channels on my DA4ES I often have the volume set above 50%, but I know damn well I am in no danger of clipping.

Many cheap mini-systems and such have very sensitive volume controls and start clipping with the volume at less than 1/3 (for a CD source). They are designed this way so that people think their system is powerfull.

Mark

 

[Michael R Price]

I think the real way to damage tweeters is not just the distortion caused by clipping, but "amplitude compression." When an amplifier clips, it does not stop amplifying the entire signal, only the part outside its maximum voltage or current under load. This is usually some bass signal. The rest of the signal is amplified as usual albeit really distorted. Say you have a big 50Hz bass signal (95%) and a little 5KHz treble signal (5%) and a 100 watt amp. If you drive the amp 6db into clipping, the amp won't produce much more than 100 watts yet the treble component of the signal will still be 20 watts, significantly distorted. Now that can kill almost any standard 1" tweeter.