Tweeters blow from too little power? - AVS Forum
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post #1 of 39 Old 05-29-2013, 12:58 AM - Thread Starter
 
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I've never understood this one. People have told me in the past that you can damage a speaker with too little power. That the tweeter is likely the first to go when using an underpowered amp. But why would this be? Surely if the tweeter isn't being fed loads of power it won't get too hot?

So speakers that are used with a power in excess will be less likely to fry than one with little power? Please explain.
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post #2 of 39 Old 05-29-2013, 01:57 AM
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tweeters can blow from a clipped signal coming from the amp. Clipping the amp signal is easier to do when insufficient power is available for desired spl levels.

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post #3 of 39 Old 05-29-2013, 05:29 AM
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As you can see, with inadequate power, and too much volume knob, the signal tops get clipped off.

Typically, a driver will be more tolerant of a large signal as long as it's clean and clipping free. Once clipping is encountered, the DC signal (straight line) is very detrimental as is the accompanying high freq spikes that often occur.



A by product of the current flow through the driver's voice coil is heat. Drivers have their inherent limits thermally, but typically these high levels are very short in duration, so the heat can be dissipated between the big, high power transients. As long as the signal is clean, and the driver is moving, it can handle quite high levels of power. Once the signal becomes distorted with clipping, the driver's ability to shed the heat changes, and unless the drive level is backed off, the end is near.

Hope this helps.

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post #4 of 39 Old 05-29-2013, 05:58 AM
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tehnically it is always too much power that causes damage to speakers. But it is true that amps that are distorting put out more power than they are rated for. It is also true that a distorting amp's output starts to look more and more like a square wave as distortion increases. A square wave is, by definition, the fundamental plus all the odd harmonics in descending amounts. Thats's why if you look at amp tests, amps with limited high frequency bandwidth don't have a sharp corner where the wave goes "square." The high frequencies needed to replicate that aren't there. It's also necessary for the harmonics to be in a specific phase relationship for the wave to look square, and speakers can't actually make a swuare wave output, as I understand it. NO matter, because all the frequencies are still there, and the sound of a square wave is not detectably different to my ears than the sound of a phase shifted )no longer square) wave.

ANYWAY, it is possible for amp distortion, which is adding high frequencies, to increase the high frequency energy to the point where it will damage a tweeter, in large part because a tweeter "expects" to se no more than around 25 percent of the total power, so the tweeter in a 100 watt speaker is unlikely to be able to handle long term inputs at 50 watts. It'll overheat and die.

You can also accomplish the same thing with perfectly clean power. It's just a matter of getting the amount of power in the tweeter's frequency range to kill it.

Of course I'd have to sell all my guitar amps if they didn't distort quite a bit (I've read that guitar players will call 10 percent THD "clean"). Neither my guitar amp speakers nor any PA speaker into which I've ever run either a direct out from my speaker attenuator or a mic feed has ever been damaged by the significant levels of distortion I like. Although the direct out from my attenuator doesn't sound quite as good. It seems to have too much (ugly) high end. I assume that's because it's not passing through a voice coil that acts as a high frequency blocker (low pass filter) at around 3K or 4K Hz.
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post #5 of 39 Old 05-29-2013, 10:10 AM
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Quote:
Originally Posted by JHAz View Post

It's just a matter of getting the amount of power in the tweeter's frequency range to kill it.

This.

One of these days I'll buy some tweeters to sacrifice and test this theory. I'm skeptical that "too little" power kills tweeters. How much too little is needed? The theory sounds plausible, but so do most audio myths such as the importance of skin effect, vibration control, "clean" AC power, and oxygen free copper. biggrin.gif

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post #6 of 39 Old 05-29-2013, 11:34 AM
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Say you have a tweeter rated at 100 watts (with the proper crossover), I would say that is more likely to blow with 75 watts of distorted input than 125 watts of clean input.

In other words, a distorted input LESS than a tweeters rating can blow it up. Obviously, how much less and how distorted will tell how long the tweeter will last under such conditions.

So, IMO, if you have a speaker rated at 100 watts, your better off with a 100 watt amp than a 50 watt one, unless of course you drive the 100 watt amp into distortion.

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post #7 of 39 Old 05-29-2013, 12:41 PM
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Quote:
Originally Posted by jim19611961 View Post

Say you have a tweeter rated at 100 watts (with the proper crossover), I would say that is more likely to blow with 75 watts of distorted input than 125 watts of clean input.

In other words, a distorted input LESS than a tweeters rating can blow it up. Obviously, how much less and how distorted will tell how long the tweeter will last under such conditions.

So, IMO, if you have a speaker rated at 100 watts, your better off with a 100 watt amp than a 50 watt one, unless of course you drive the 100 watt amp into distortion.

No. MIstates even the old wives tale that's not right. A clean 75 watt amp going into a tweeter in a 500 watt speaker (so it has a reason to be a 100 watt tweeter) won't get hurt. If you push the amp so hard that it puts more than 100 watts into the tweeter, trouble could come. Can a 75 watt amp put out 100 watts? Possibly. Look at a Stereophile amp review, specifically at the measurements. Evey amp sees its distortion take off, rising quickly above some knee. Not unusual for power to be rated well past the "knee" at 1% THD. Very common to see where a 75 watt rated amp is with respect to distortion at 100 watts. Just read the curve. IF the 75 watt amp puts out enough power over 75 watts consistently enough for long enough it can damage the tweeter.

But it won't be 75 watts that does it. It MIGHT be a 75 watt-rated amp, but it'll be significantly distorted so that its total output exceeds 100 watts (assuming it's just driving the tweeter*).

If the amp is conncted to the whole speaker, not just the tweeter, then until things start distorting, you can assume that at 75 watts output, the MOST the tweeter sees is around 1/4 or about 14 watts. The rest goes to the woofer. Now, can you push a 75 watt amp hard enough to blow a 100 watt tweeter? My guess is no. But, as I said, for the tweeter to be rated at 100 watts, you have to be looking at a 500 watt speaker (ie at pro stuff). ANd my guess is that wit a well designed 500 watt speaker you'd be at as much risk of blowing something with a 75 watt amp as if I directly conected my little-used guitar distortion pedal, which runs on 9 volts and can clip like the devil but just can't put out much in the way of power..
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post #8 of 39 Old 05-29-2013, 12:45 PM
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Quote:
Originally Posted by Ethan Winer View Post

This.

One of these days I'll buy some tweeters to sacrifice and test this theory. I'm skeptical that "too little" power kills tweeters. How much too little is needed? The theory sounds plausible, but so do most audio myths such as the importance of skin effect, vibration control, "clean" AC power, and oxygen free copper. biggrin.gif

--Ethan

I think you have to have enough too little to get seriously into clipping, but not so much too little that even the high frequency energy in the clipped signal is well within the tweeter's comfort zone.

Be sure to video your tests if you do them. They could (if they come out, uh, disastrous) rank right up there with people plugging woofers into wall power to watch thm throw their cones. WHEE!

And if they don't result in flying speaker parts, they'll be actual visible evidence of the reality of the thing . . .
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post #9 of 39 Old 05-29-2013, 12:47 PM
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Quote:
Originally Posted by FOH View Post





Typically, a driver will be more tolerant of a large signal as long as it's clean and clipping free. Once clipping is encountered, the DC signal (straight line) is very detrimental as is the accompanying high freq spikes that often occur.

Please don't be mis-lead by the straight line, it does not mean the signal has DC contents. Even though the signal is clipped it is still a periodic signal and not DC, not even for a short period. Hope this helps. wink.gif
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post #10 of 39 Old 05-29-2013, 12:47 PM
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Originally Posted by JHAz View Post



If the amp is conncted to the whole speaker, not just the tweeter, then until things start distorting, you can assume that at 75 watts output, the MOST the tweeter sees is around 1/4 or about 14 watts.

Your making the assumption people listen to music flat in regards to EQ. Guess what happens when the Treble knob is turned up to +6? or +10?

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post #11 of 39 Old 05-29-2013, 01:03 PM
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Quote:
Originally Posted by jim19611961 View Post

Your making the assumption people listen to music flat in regards to EQ. Guess what happens when the Treble knob is turned up to +6? or +10?

You are making the assumption of a badly desinged power amp by not taking into consideration the carefully degined gain structure even at the highest treble and bass boost, while assuming an amp can easily be driven into it's non-linear stage above it's highest rated (or measured) output by people not being careful enough. Not a typical case to be worried about, IMHO. smile.gif
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post #12 of 39 Old 05-29-2013, 01:50 PM
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You are making the assumption of a badly desinged power amp by not taking into consideration the carefully degined gain structure even at the highest treble and bass boost, while assuming an amp can easily be driven into it's non-linear stage above it's highest rated (or measured) output by people not being careful enough. Not a typical case to be worried about, IMHO. smile.gif

It would have to be a well designed amp indeed to know in advance what person will buy it and have the Treble knob turned up at close to top volume, or not rolleyes.gif

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post #13 of 39 Old 05-29-2013, 01:50 PM
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This always gets many to post, and I purposely didn't intend to mislead calling the output DC.


This is one of the "myths" that I somewhat align myself with. ... Somewhat. redface.gif

I powered a pair of Klipsch RB15, a small 9lb two way, rated at 75watts, with a Behringer EP4000 (450@8/635@4) for the long term. Yep, I'd hit the clip indicators on occasion. The tweeters in the bookshelves are tiny, about the size of a half dollar, and not much thicker wink.gif I've had them apart, examining everything, and the HF components are modest, for sure.


Good posts above.

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post #14 of 39 Old 05-29-2013, 01:57 PM
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Quote:
Originally Posted by jim19611961 View Post

It would have to be a well designed amp indeed to know in advance what person will buy it and have the Treble knob turned up at close to top volume, or not rolleyes.gif

All amps work with standard input levels, be it RCA analog or its digital equivalent (coax/optical or even HDMI), thus with the Master Volume turned up all the way (no attenuation) a well designed power amp will not go into clipping even with the highest treble boost. When you turn down the MV you simply attenuate the incoming signal. All this in Layman's. smile.gif
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post #15 of 39 Old 05-29-2013, 02:22 PM
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Might be worth noting that the first harmonic of an ideal square wave is 9.54 dB below the level of the fundamental, meaning the third harmonic is about 1/10 the power of the fundamental. That would be for a heavily-clipped amp. I suspect power problems were an issue in the 70's when a lot of receivers only had 25 W or so, and a lot of cheap stereos only a few watts, but is much less an issue these days.

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post #16 of 39 Old 05-29-2013, 02:42 PM
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Hi Heinrich,

I'm just going to paraphrase the above posts.
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Originally Posted by Heinrich S View Post

. . . People have told me in the past that you can damage a speaker with too little power. That the tweeter is likely the first to go when using an underpowered amp. . .
This might be a matter of semantics, but:

A speaker is never damaged by too little power. A speaker can be damaged by too much power, caused by overdriving an underpowered amplifier. The tweeter is often the casualty, because the resulting distortion contains enough high-frequency content to slip through the crossover and into the tweeter.

That is the scenario, but I don't think it happens very often, for some of the reasons mentioned. Also, someone would have to put up with the extreme amount distortion required.
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post #17 of 39 Old 05-29-2013, 02:46 PM
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Originally Posted by mogorf View Post

All amps work with standard input levels, be it RCA analog or its digital equivalent (coax/optical or even HDMI), thus with the Master Volume turned up all the way (no attenuation) a well designed power amp will not go into clipping even with the highest treble boost. When you turn down the MV you simply attenuate the incoming signal. All this in Layman's. smile.gif

A loudness contour works that way, yes. But treble and bass tone controls, as well as outboard EQ work regardless of the volume setting.

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post #18 of 39 Old 05-29-2013, 02:57 PM
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As an aside and FWIW--
As you move from a sinusoid to a square wave at the same amplitude, the heating value or RMS level increases by about 40 percent.

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post #19 of 39 Old 05-29-2013, 05:01 PM
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While clipping is certainly a factor where lower than rated power can damage a speaker, nobody mentioned HF oscillation. This can result in some amps when they are pushed too hard. And some amps are just unstable period, especially the ultra expensive units that are designed with voodoo rather than electrical engineering. If an amp is oscillating at full power at 50khz, your tweeters will fail in short order. What usually happens is bursts of oscillation modulated with the music that in time kills the tweeters. And remember any oscillation in a power amp is likely to be at full power because it's past the volume control. The most you will hear is some hiss from the harmonics of the ultrasonic signal.

Unconventional speaker cables can cause this as well. Speaker cables make from CAT5 cable are notorious for causing amplifier instability. Power amps of any kind don't like capacitive loads.

Another silly hack you sometimes see is removing the DAC analog reconstruction filters from CD players. OK, get enough of that 48khz clock through and most modern amps can easily go out to 100khz, there go your tweeters.

I once took out a set of tweeters from an old reel to reel tape deck that had excessive bias leakage in record mode.

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post #20 of 39 Old 05-29-2013, 07:28 PM
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Quote:
Originally Posted by jim19611961 View Post

Say you have a tweeter rated at 100 watts (with the proper crossover),...

Uhm, I am at a loss which tweeter is rated at 100 watts in a residential speaker, regadless of its cost or the overall speaker power claims.

If you record a clipped signal on purpose at low power or try a square wave for that matter at below the tweeter's rating which is more realistic in the 10 watt range or even less and see if will blow. It is the power that will kill it, period.
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post #21 of 39 Old 05-29-2013, 08:05 PM
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Originally Posted by CharlesJ View Post

Uhm, I am at a loss which tweeter is rated at 100 watts in a residential speaker, regadless of its cost or the overall speaker power claims.

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(These are the tweeters in my actual speakers)

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post #22 of 39 Old 05-30-2013, 05:52 AM - Thread Starter
 
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Quote:
Originally Posted by MarkHotchkiss 
Hi Heinrich, I'm just going to paraphrase the above posts.A speaker is never damaged by too little power. A speaker can be damaged by too much power, caused by overdriving an underpowered amplifier. The tweeter is often the casualty, because the resulting distortion contains enough high-frequency content to slip through the crossover and into the tweeter.

Thank you! That explanation makes complete sense. Probably is semantics in a way, but your explanation just clicked for me. Thanks again and thanks to all who have tried to help me better understand this. So basically if you have a speaker with a power handling of 500 watts then you could use a 20 watt amp and you won't blow anything provided you are within the clean rated power of the amp.

As soon as you clip you exceed the clean power output and then you can potentially damage the tweeter and/or woofer. I assume clipping of the AC waveform generates more high frequency harmonics which explains why tweeters are so vulnerable when amplifier clipping takes place. Woofers need more punishment before damage can occur.

Am I on the right track? Thanks.
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post #23 of 39 Old 05-30-2013, 07:53 AM
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Quote:
Originally Posted by Heinrich S View Post

Thank you! That explanation makes complete sense. Probably is semantics in a way, but your explanation just clicked for me. Thanks again and thanks to all who have tried to help me better understand this. So basically if you have a speaker with a power handling of 500 watts then you could use a 20 watt amp and you won't blow anything provided you are within the clean rated power of the amp.

As soon as you clip you exceed the clean power output and then you can potentially damage the tweeter and/or woofer. I assume clipping of the AC waveform generates more high frequency harmonics which explains why tweeters are so vulnerable when amplifier clipping takes place. Woofers need more punishment before damage can occur.

Am I on the right track? Thanks.

harmonics are, by definition and in practice, integer multiples of a sound. So harmonics are always higher in frequency than the input. Of course with multiple simultaneous sounds, all of which have their own natrual harmonics (how you can tell a violin from a trombone - - the harmonics of the sound) you've got higher harmonics generating their own higher harmonics.

FWIW, "clipping" is an elusive term. EVERY amplifier is rated for power at some degree of distortion, whether it is 1 percent or one tenth of a percent. Few would say an amp running at 1 percent distortion is "clipping" even though its output contains ten times the distortion used for its power rating. Likely few sould say an amp is clipping (or at least clipping in an injurious way) just because its THD rises above 1%. ANd it's entirely unlikely that an amp at 2% distortion is risking drivers unless you were on the very edge of their capability already and run them loud (probably with highly compressed material so they don't get a second to cool off) for quite a while. It might be possible to "hear" 1% distortion with the right test tones, but I've seen reviewers "relax" their testing standards to 3% when assessing the output power of tube amps.

Both the woofer and the tweeter will be damaged by receiving, over a significant period of time, more power than they are designed to handle. They get hot and can fail. Woofers typically have higehr power handling capacity, so more power is needed to damage them, but IDK that it is different on a percentage basis (and doubtless varies from driver to driver, from driver-in-a-box to same-dirver -in-a-different-box, and according to the frequency content of the material being fed to the driver. FWIW you can also kill a driver by hitting it with a short burst that is far enough above its power handling to cause over-excursion, where the voice coil moves so far it pulls things out of whack. Immediate speaker death.
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post #24 of 39 Old 05-30-2013, 12:58 PM
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Quote:
Originally Posted by jim19611961 View Post

Guess what happens when the Treble knob is turned up to +6? or +10?

Exactly.
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the first harmonic of an ideal square wave is 9.54 dB below the level of the fundamental, meaning the third harmonic is about 1/10 the power of the fundamental. That would be for a heavily-clipped amp.

That too.
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nobody mentioned HF oscillation. This can result in some amps when they are pushed too hard. And some amps are just unstable period, especially the ultra expensive units that are designed with voodoo rather than electrical engineering.

And especially that. biggrin.gif

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post #25 of 39 Old 05-30-2013, 01:38 PM
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Tweeters have two failure modes in my experience.

1. Power dissipation excess.

2. Ultrasonic resonance of the voice coil lead in wires where they are within the gap field but are not supported by epoxy.

The first is easily seen.

The second requires close inspection.

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post #26 of 39 Old 05-31-2013, 01:20 PM
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I realize it's OT, however fwiw; Catching up on this thread, I realize ... I've been around for this hobby for several decades, and I've never blown a tweeter in home audio, or car audio. Seriously, I can't recall a single time.

Like many here, I've owned a plethora of loudspeakers. I've never blown a tweeter, outside of some possible failures in big PAs that a system tech may have changed for me.

Again, I suspect like many here, it's no coincidence that I can't stand a system played into noticeable compression, let alone noticeable nonlinearity/distortion.

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post #27 of 39 Old 05-31-2013, 01:31 PM
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I blew a tweeter with a 12w per channel (sansui 331) amp on speakers rated at more than 40W.

A friend of mine used to blow up the tweeter fuses on his B.I.C speakers twice a year.

My RTR 300d's had the tweeters in both blown up twice each.

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post #28 of 39 Old 05-31-2013, 01:53 PM
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Quote:
Originally Posted by jim19611961 View Post

I blew a tweeter with a 12w per channel (sansui 331) amp on speakers rated at more than 40W.

A friend of mine used to blow up the tweeter fuses on his B.I.C speakers twice a year.

My RTR 300d's had the tweeters in both blown up twice each.

Ever investigated these cases or just carried on blowing tweeters without knowing what the reason is? eek.gif
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post #29 of 39 Old 05-31-2013, 03:52 PM
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Quote:
Originally Posted by mogorf View Post

Ever investigated these cases or just carried on blowing tweeters without knowing what the reason is? eek.gif

1) Turning up the volume too loud (pushing the amp into distortion)
2) Inferior quality components (speaker crossover/tweeter driver)
3) Too little power (and not efficient enough speakers for the sound level I liked)
4) Over use of tone controls and EQ's

Its been almost 30 years since all these cases happened. Addressed all 4 points in one way or another.

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post #30 of 39 Old 05-31-2013, 04:15 PM
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Quote:
Originally Posted by jim19611961 View Post

1) Turning up the volume too loud (pushing the amp into distortion)
2) Inferior quality components (speaker crossover/tweeter driver)
3) Too little power (and not efficient enough speakers for the sound level I liked)
4) Over use of tone controls and EQ's

Its been almost 30 years since all these cases happened. Addressed all 4 points in one way or another.

30 years ago people were killed in traffic accidents because of no airbag!!

Can we move on to the present, please?! smile.gif
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