Rethinking "Danger: Low Power"

[Ducatista47]

Remember this old JBL Pro white paper? http://www.jblpro.com/catalog/support/getfile.aspx?docid=246&doctype=3

I always thought it flawed because it warns against, amongst other things, tweeters blowing out from clipped waveforms. Bipolar transistor amps I could see doing this, but tubes don't clip like that. So if you turn it way up and the tweeters blow anyway, what is doing it? This 1991 Rane paper wants us to believe another answer, and it makes sense to me. http://www.hotsound.com.br/clipping_effects.pdf Why would using a more powerful amp help? Because clipping is not destroying anything. Power is, through compression of the lower frequency output. It is when turning up the amp has insufficient energy to increase woofer loudness - but beau coup to feed more and more energy to the tweeters. If the amp is big enough, poof. Oddly, it means a tiny amp would lack the power to kill the tweeters, but a bigger amp could.

A properly sized amp, by JBL standards, would not because the lower frequencies, indeed all frequencies, would keep getting louder. The theory is the listener would cry Uncle before the energy was sufficient to fry the tweeters. But it has little to do with the quality of the signal, just the quantity.

Makes sense to me, how about you? Unrelated, I find this page to be very interesting. It is an almost zero BS take on amplification, listening, design and common sense sound engineering. All in the service of elucidating Gainclone amps. http://www.adx.co.nz/techinfo/audio/gainclone1.htm (http://www.adx.co.nz/techinfo/audio/gainclone1.htm)I enjoyed every word.

[Mike F]

Would`nt the capacitors in the crossovers take care of any clipped/dc signals coming from an overdriven amp?

[Ducatista47]

No doubt they would stop DC. I don't think they would stop Justin Bieber or other forms of distortion. Definitely would not stop the overpowering watts the Rane paper points to. It seems to be simple power - too much energy - that is the killer.

[Allanvh5150]

I cant say that I ever blew a high frequency driver from supplying too much power. In my experience I have found that things tend to blow when they are overdriven. Plenty of good clean power never hurt.

Allan.

[Ducatista47]

I cant say that I ever blew a high frequency driver from supplying too much power. In my experience I have found that things tend to blow when they are overdriven. Plenty of good clean power never hurt.

Allan.
Yeah, overdriving is what this is all about. When the amp is not powerful enough to keep increasing the low frequency power with increasing gain, but has enough power to keep increasing the high frequency power (what amp doesn't?), the tweeters are overdriven. A really big amp is in theory going to make your ears bleed before too much energy goes to the tweeters. But I say never underestimate the "ability" of some JBL lovers to turn it WAY up despite things like pain and heart palpitation. The JBL literature usually included a warning that the speakers were capable of damaging hearing before speaker damage occurred, if the speakers were driven with sufficient clean power.

[BMWCCA]

I blew an 075 back in 1969 or so. Back then JBL had that unconditional life-time warranty. They repaired it with a new coil and shipped it back for free with a note to check for a "high-frequency oscillation" in my amp. At that time it was a Kenwood receiver. I traded it in on a Fisher SA1000 which I played even louder with no problems, including playing my Gibson EBO bass through the system. :eek:

Next was a Crown D150 which played those same speakers all through college including many a weekend when we'd put them out on the porch and play them to the Blue Ridge mountains so loud one time the Crown went into thermal shutdown (the old D150 without the faceplate so I just stuck a pencil underneath it to increase airflow and played for several more hours without incident). I have never fried a tweeter since, and that includes many "fragile" 035Ti's.

I think I'm with JBL on this one.

[grumpy]

Interesting idea. I think things are not so simple, but I'm not selling limiters.
Key is too much HF energy will indeed fry tweeters. I prefer adequate
amplification (which IMO -can- vary by amp type) and education to limiters at home.

[Don C]

A clipped waveform has a lot of harmonics that were not in the signal at the amplifier input. These can blow your tweeters with frequencies too high to even hear. Your speakers have a high pass filter to keep the low frequencies from getting to the tweeter, but no low pass filter to block higher frequencies.

[1audiohack]

I remember reading the attached link by Charlie Hughes some time ago describing the formation of square type waves due to increasing distortion caused by lack of headroom in power amps. I don't remember if this article goes into the dramatic increase in heating the load/driver has to dissipate when driven with a clipped signal. I didn't reread it tonight but I remember having an AhHah moment near the end.

All the best.


http://www.excelsior-audio.com/Publications/Square_Waves_&_DC_Content.pdf

[yggdrasil]

A clipped waveform has a lot of harmonics that were not in the signal at the amplifier input. These can blow your tweeters with frequencies too high to even hear. Your speakers have a high pass filter to keep the low frequencies from getting to the tweeter, but no low pass filter to block higher frequencies.
+1

The effect of clipping is the creation of high frequency harmonics, hence more energy to the tweeter.

[Hoerninger]

.. but no low pass filter to block higher frequencies.
Sometime somewhere I read that it is wise to include a series coil with a guitar speaker to acoid damage when clipping - but that is not a tweter.
____________
Peter

[rdgrimes]

http://www.lansingheritage.org/html/jbl/reference/notes/power-req.htm

[DavidF]

"...don't think they would stop Justin Bieber or other forms of distortion...."

Jeez, you caught me off guard with that one. That would a bring a harsh resonance to the ear, indeed. Easy enough to remedy, thankfully.:D

[Mike F]

A clipped waveform has a lot of harmonics that were not in the signal at the amplifier input. These can blow your tweeters with frequencies too high to even hear. Your speakers have a high pass filter to keep the low frequencies from getting to the tweeter, but no low pass filter to block higher frequencies.

That makes sense. A steep low pass filter ought to help in filtering out inaudible ultrasonics.

[Mr. Widget]

A clipped waveform has a lot of harmonics that were not in the signal at the amplifier input. These can blow your tweeters with frequencies too high to even hear. Your speakers have a high pass filter to keep the low frequencies from getting to the tweeter, but no low pass filter to block higher frequencies.Sure all of us know this... the point that Clark and the Rane Note is making, beyond possibly Rane's desire of selling limiters, is that this "fact" about clipping that we all ascribe to is really a theory and the fine people at Rane are proposing an alternative theory.

That said, theory or not and clipping or compression aside, the fact is enough people have fried expensive tweeters with under powered amps that simply using a bigger amp if you must play it louder is the safest way to go. I'd suggest the point Rane is making is almost more of a semantic argument than a practical one.

I fried my first set of LE85s back in the '70s with a 40wpc integrated amp... bought a Marantz 510 with over 300wpc and then proceeded to scare many a roommate and undoubtedly didn't do my ears any favors but never blew another tweeter.


Widget

[Titanium Dome]

I've blown up, burned up, and/or fried at least one of about everything (woofer, midbass, mid, tweeter). In the case of the woofer, it was too much power; in the case of the others, it was too little power played too loud. Most (or all) of this occurred in the mid-sixties to early seventies and was accompanied by heavy partying and stupid ideas.

The JBL 123-A I ruined was replaced by JBL for free after I sent the original to CA. Somewhere I still have the original "don't do-that" letter admonishing me for "applying too much power for too long, thus exceeding the driver's ability to dissipate heat."

[edgewound]

Clipping from a tube amp and solid state amp is totally different.

The output transformer in the tube amp is sort of a buffer of protection that gives a ceiling to how much power the amp will deliver from the output tubes. No matter how distorted it gets, once it runs out of juice, it won't go any higher in output.

Not so with a solid state amp. The drivers are Directly Coupled to the amp's output devices and are at the mercy of the input voltage. Keep adding more input signal/voltage and the amp will still try to make more power until the severly clipped wave form "looks like" DC current.

Tube guitar amps are a perfect example of this. A 50 watt tube guitar amp can wail away into a true 200 watt speaker(s) all day long with no problem.

Put a tube 100 watter driven hard through a 50-100 watt speaker and it will fail.

[Rolf]

I remember being told for many years ago that if you use a small amp, overdriving it, it will send out very high UHF to the tweeter, and that is what can kill them. Whit a high power amp you will hear that the woofer getting in trouble long before the above situation occur.

[louped garouv]

Clipping from a tube amp and solid state amp is totally different.

The output transformer in the tube amp is sort of a buffer of protection that gives a ceiling to how much power the amp will deliver from the output tubes. No matter how distorted it gets, once it runs out of juice, it won't go any higher in output.


do you have any experience with OTL style tube amps?

[Mr. Widget]

do you have any experience with OTL style tube amps?I do... the ones I had were far from linear devices... they made some speakers sound better than anything else and they made my 1400 Arrays sound flabby and painfully bass heavy.

As far as their performance during clipping? I try avoid clipping amps these days!


Widget

[louped garouv]

I do... the ones I had were far from linear devices... they made some speakers sound better than anything else and they made my 1400 Arrays sound flabby and painfully bass heavy.

As far as their performance during clipping? I try avoid clipping amps these days!


Widget

Thanks for your thoughts... it's interesting to hear what
different folks have to say about these things....

and the range of perspectives you can see/hear is quite large/diverse....