HELP - FOURTH tweeter Blown??? Trouble-shooting?

[jmdesignz2]

Hi

Appreciate anyones help on this?

I am a bit frustrated at this point. I have a pair of Aerial 10T v2 speakers and am now on my 4th tweeter. I am the second owner and have had these for well over 5 years.

 

They arrived with one dead tweeter - replaced within days.

Then recently- I had an issue where a connection was dislodged which caused spurious noise/transients - that damaged both tweeters.

Since then, all precautions have been taken and no such incidents of overloading / transients have occurred.

However, the left channel tweeter just quit working.

 

My questions are:

1) how is this happening?

2) could it be something wrong with the crossovers inside the speakers?

3) could there be something wrong with my amps?

4) how can I prevent this?

 

These are 86db sensitivity speakers, which dip into 3ohm range. The amps are McCormack DNA 1 DLX Monoblocks run off a 20amp dedicated circuit. As mono-blocks, these would put out 380watts per amp at 8ohms.

I am guessing these put out at least 450 watts into 4 ohms and close to 600 watts into 3 ohms?

 

I could not find any measurements for the monoblocks but found stereo measurements from stereophile 1995 DNA DLX Stereo measurements:

 

"With clipping defined as 1% THD, the DNA-1 comfortably exceeded its specifications, putting out 178W into 8 ohms (22.5dBW), 315W into 4 ohms (22dBW), and 530W into 2 ohms (21.2dBW). These figures are with both channels driven at 1kHz—except the 2 ohm measurement, which was made with one channel driven so as not to blow the 8A rail fuse. The THD percentage vs output power plots are shown in fig.2. The amplifier's clipping behavior is unusual in that it soft-clips before the distortion shoots up. The sharp "knee" in the distortion traces typical of solid-state amplifiers is absent.

Read more at http://www.stereophile.com/content/mccormack-power-drive-dna-1-power-amplifier-1995-measurements#CpAcWcHMfZA0TZE4.99"

"...FFT on the Deluxe's output when it reproduced a combination of 19kHz+20kHz at 150W into 4 ohms (fig.4). The intermodulation components at 1kHz, 2kHz, 18kHz, and 21kHz are moderately high in level, although the rest of the spectrum is fairly clean."

Read more at McCormack Power Drive DNA-1 power amplifier 1995 Measurements | Stereophile.com

[semente]

My suggestion is that you start by contacting the manufacturer first. It's quite possible that they may have the answer.

 

R

[jmdesignz2]

My suggestion is that you start by contacting the manufacturer first. It's quite possible that they may have the answer.

 

R

 

I did contact Aerial, they said the tweeters have high handling power and I'm probably playing a demanding passage too loudly.

 

My reply was - at what decibel level should I set as Maximum to avoid this issue?

 

I'm thinking if that tweeter only lasted less than 2 months something else is the issue?

I don't play music at ear splitting levels...

[blownsi]

Try swapping your monoblocks and see if the tweeter blowing follows. I suspect there is something amiss in one of your amps causing excess distortion whether you can hear it or not.

[wgscott]

When I blew out my B&W tweeter, which was entirely my fault (playing with test tones) -- and I told them as much, they still warrantied it. I realize if you got it used, you probably don't have a warranty, but it was refreshing to have them stand behind their product.

[semente]

I did contact Aerial, they said the tweeters have high handling power and I'm probably playing a demanding passage too loudly.

 

My reply was - at what decibel level should I set as Maximum to avoid this issue?

 

I'm thinking if that tweeter only lasted less than 2 months something else is the issue?

I don't play music at ear splitting levels...

 

I'd contact McCormack and perhaps consider having the amps serviced.

 

R

[jmdesignz2]

Try swapping your monoblocks and see if the tweeter blowing follows. I suspect there is something amiss in one of your amps causing excess distortion whether you can hear it or not.

 

Ouch - that would be an expensive test LOL

I just got off the phone with Steve McCormack. Great guy and surprised to get a personal call about the amps and how / what could be causing the tweeters to blow. He agrees that the amps are perfectly capable of driving the speakers cleanly and without clipping that would destroy the tweeters. The level of sound required to clip long and hard enough would be immediately noticeable and incredibly loud. Thus, I have never used them at that level in the past two months since installing the new pair of tweeters.

 

Michael Kelly of Aerial is also great to deal with. I want to make clear that each of these Four tweeters were purchased and not free.

However, having support of a product made in the late 90's is fantastic.

 

My conversation with Steve of SMCAudio has lead me to believe that there could be some source of ultrasonic noise down chain. I am going to implement a hi freq slope filter in my LIO8 to see if that increases the lifespan of these tweeters.

 

Steve McCormack is also a fantastic stand up guy

[sphinxsix]

Usually in such cases the distortion causes the problem not SPL (volume).

[jmdesignz2]

Usually in such cases the distortion causes the problem not SPL (volume).

 

Correct- but according to Steve, the only time clipping and distortion would occur is at incredibly high SPL / power levels since the amps are so powerful.

[jmdesignz2]

I'd contact McCormack and perhaps consider having the amps serviced.

 

R

 

Steve called me and he never once brought that up so I would assume that would mean the amps are fine. Ultrasonic oscillation from down chain is currently the prime suspect.

[sphinxsix]

Correct- but according to Steve, the only time clipping and distortion would occur is at incredibly high SPL / power levels since the amps are so powerful.

Ok, so if you also don't hear loud clicking sounds while turning on/off the amps or while your for example refrigerator starts working I'd blame the Aerial tweeters. Did you try to google search if some other owners had similiar problems?

 

As for the ultrasonic oscillation - it should be possible to measure it, I believe.

[jmdesignz2]

Ok, so if you also don't hear loud clicking sounds while turning on/off the amps or while your for example refrigerator starts working I'd blame the Aerial tweeters. Did you try to google search if some other owners had similiar problems?

 

As for the ultrasonic oscillation - it should be possible to measure it, I believe.

 

Google says only I am having this issue

Amps are on dedicated circuit and the rest of the system is on a different dedicated circuit. The other electrical appliances are on different circuits so no clicks can come from the fridge.

I always turn on the amps after I turn on the LIO8. If I did the reverse I get thumps/turn on pop.

[davide256]

Any chance you could add a fuse to protect the tweeter? Many years ago when I got my first Magnepans I bypassed the tweeter fuse, came back one day and the tweeter sections were blown. As near as I could tell I'd left the amp on and some kind of electrical event while I was out blew them (power surge, static discharge?)

[gmgraves]

Hi

Appreciate anyones help on this?

I am a bit frustrated at this point. I have a pair of Aerial 10T v2 speakers and am now on my 4th tweeter. I am the second owner and have had these for well over 5 years.

 

They arrived with one dead tweeter - replaced within days.

Then recently- I had an issue where a connection was dislodged which caused spurious noise/transients - that damaged both tweeters.

Since then, all precautions have been taken and no such incidents of overloading / transients have occurred.

However, the left channel tweeter just quit working.

 

My questions are:

1) how is this happening?

2) could it be something wrong with the crossovers inside the speakers?

3) could there be something wrong with my amps?

4) how can I prevent this?

 

These are 86db sensitivity speakers, which dip into 3ohm range. The amps are McCormack DNA 1 DLX Monoblocks run off a 20amp dedicated circuit. As mono-blocks, these would put out 380watts per amp at 8ohms.

I am guessing these put out at least 450 watts into 4 ohms and close to 600 watts into 3 ohms?

 

I could not find any measurements for the monoblocks but found stereo measurements from stereophile 1995 DNA DLX Stereo measurements:

 

"With clipping defined as 1% THD, the DNA-1 comfortably exceeded its specifications, putting out 178W into 8 ohms (22.5dBW), 315W into 4 ohms (22dBW), and 530W into 2 ohms (21.2dBW). These figures are with both channels driven at 1kHz—except the 2 ohm measurement, which was made with one channel driven so as not to blow the 8A rail fuse. The THD percentage vs output power plots are shown in fig.2. The amplifier's clipping behavior is unusual in that it soft-clips before the distortion shoots up. The sharp "knee" in the distortion traces typical of solid-state amplifiers is absent.

Read more at http://www.stereophile.com/content/mccormack-power-drive-dna-1-power-amplifier-1995-measurements#CpAcWcHMfZA0TZE4.99"

"...FFT on the Deluxe's output when it reproduced a combination of 19kHz+20kHz at 150W into 4 ohms (fig.4). The intermodulation components at 1kHz, 2kHz, 18kHz, and 21kHz are moderately high in level, although the rest of the spectrum is fairly clean."

Read more at McCormack Power Drive DNA-1 power amplifier 1995 Measurements | Stereophile.com

 

OK, let's do a little troubleshooting. Aside from the loose connection which damaged both tweeters (understandable, and a hard lesson that many, if not most of us have had to learn: always turn the system OFF before fiddling with interconnects) do both channel's tweeters "go bad" or just one channel's? If it's only, say, either the left or the right but not both, then your problem is likely that channel's power amp. If it's both channel's, then the problem is likely upstream; your preamp, or one of your source components. My guess would be something is oscillating at ultra-high frequencies those sending huge amounts of power at frequencies you can't hear into your speakers. overloading the tweeters, which are not designed to handle that much power continuously. If you know someone with an oscilloscope, see if you can borrow it, start at the speaker leads, with everything on but no signal. While looking at both channels, try all sources: phono (if you have it), digital players, DACs, tuners, everything. If you see a strong VHF signal on one or both channels. Turn the system off and disconnect the preamp from the power amps, then turn the power amps back on. If it appears in just one channel, disconnect only that channel input from the preamp and turn the amp back on. If the oscillation continues, then you know that you have a bad power amp. If it stops, then you know that the problem is further back up your component chain. Just keep following the oscillation up the chain by disconnecting the next connection below the suspect component (or switch your preamp away from it) in turn until the 'scope shows the oscillation has stopped. that's your culprit.

 

If there is no oscillation, OTOH, then the culprit has to be the speakers themselves. Perhaps (though unlikely) one or both high-pass capacitors in the crossover have shorted allowing full power across the tweeter. Perhaps the previous owner bypassed the crossover altogether for some reason. This is very possible. Are your speakers bi-ampable? If so, a previous owner could have actually removed the crossover because he was bi-amping and had a low level crossover BEFORE the two amps he was using to bi-amp each speaker system therefore rendering the crossover in the speakers themselves redundant.

 

I have a friend who had a pair of Magnepan MMG speakers powered by a fairly substantial Pioneer receiver He never listened to music loudly, and his receiver was powerful enough not to be clipping (which will damage speakers. In fact more speakers are damaged by amps with too little power (clipping amplifier) than are ever damaged by too much). Anyway, this fellow's Maggies kept blowing tweeter fuses in both channels. He blamed the speakers and did't know anything about electronics and didn't realize how unlikely that was. I took my oscilloscope to his house and performed the troubleshooting procedure that I outlined for you, above. I found that something in the Pioneer Receiver was causing an oscillation at almost 100 KHz. His speaker's fuses were blowing to protect his tweeters whenever he turned the volume up beyond a certain point, so the culprit was before the power amp stages of the Pioneer. I never found out which because he took it to his dealer and they had it repaired. He didn't ask them what was wrong with it.

 

I hope this helps you to pin-down your problem! Good luck.

[jmdesignz2]

> Tektronix-468-Oscilloscope-with-Digital-Storage

>

> I found one for less than $200 shipped

>

> Should I grab it?

 

What setting should be used and how? Any good video links?

 

OK, let's do a little troubleshooting. Aside from the loose connection which damaged both tweeters (understandable, and a hard lesson that many, if not most of us have had to learn: always turn the system OFF before fiddling with interconnects) do both channel's tweeters "go bad" or just one channel's? If it's only, say, either the left or the right but not both, then your problem is likely that channel's power amp. If it's both channel's, then the problem is likely upstream; your preamp, or one of your source components. My guess would be something is oscillating at ultra-high frequencies those sending huge amounts of power at frequencies you can't hear into your speakers. overloading the tweeters, which are not designed to handle that much power continuously. If you know someone with an oscilloscope, see if you can borrow it, start at the speaker leads, with everything on but no signal. While looking at both channels, try all sources: phono (if you have it), digital players, DACs, tuners, everything. If you see a strong VHF signal on one or both channels. Turn the system off and disconnect the preamp from the power amps, then turn the power amps back on. If it appears in just one channel, disconnect only that channel input from the preamp and turn the amp back on. If the oscillation continues, then you know that you have a bad power amp. If it stops, then you know that the problem is further back up your component chain. Just keep following the oscillation up the chain by disconnecting the next connection below the suspect component (or switch your preamp away from it) in turn until the 'scope shows the oscillation has stopped. that's your culprit.

 

If there is no oscillation, OTOH, then the culprit has to be the speakers themselves. Perhaps (though unlikely) one or both high-pass capacitors in the crossover have shorted allowing full power across the tweeter. Perhaps the previous owner bypassed the crossover altogether for some reason. This is very possible. Are your speakers bi-ampable? If so, a previous owner could have actually removed the crossover because he was bi-amping and had a low level crossover BEFORE the two amps he was using to bi-amp each speaker system therefore rendering the crossover in the speakers themselves redundant.

 

I have a friend who had a pair of Magnepan MMG speakers powered by a fairly substantial Pioneer receiver He never listened to music loudly, and his receiver was powerful enough not to be clipping (which will damage speakers. In fact more speakers are damaged by amps with too little power (clipping amplifier) than are ever damaged by too much). Anyway, this fellow's Maggies kept blowing tweeter fuses in both channels. He blamed the speakers and did't know anything about electronics and didn't realize how unlikely that was. I took my oscilloscope to his house and performed the troubleshooting procedure that I outlined for you, above. I found that something in the Pioneer Receiver was causing an oscillation at almost 100 KHz. His speaker's fuses were blowing to protect his tweeters whenever he turned the volume up beyond a certain point, so the culprit was before the power amp stages of the Pioneer. I never found out which because he took it to his dealer and they had it repaired. He didn't ask them what was wrong with it.

 

I hope this helps you to pin-down your problem! Good luck.

[jmdesignz2]

delete double post

[Bob Stern]

A short-circuited capacitor within the crossover network (in series with the tweeter) could explain a blown tweeter in one loudspeaker, but it seems unlikely that the same defect would appear in both loudspeakers.

 

Some power amps intermittently produce ultrasonic oscillations when driving certain reactive loads. Nelson Pass and Matthew Polk independently discovered a simple solution that purportedly solves the problem in most cases: Connect a series-connected resistor and capacitor across the loudspeaker terminals. The recommended capacitor value is 0.1 uF per Pass or 0.047 uF per Polk. Both recommend a resistor of 5 or 6 ohms. See Polk's US patent 4177431 or Pass's article "Speaker Cables: Science or Snake Oil" in Speaker Builder, Feb 1980.

 

Neither recommended a particular type of capacitor, but I think a ceramic disc would have the lowest inductance at RF. For the same reason, the resistor should not be wirewound.

[jmdesignz2]

A short-circuited capacitor within the crossover network (in series with the tweeter) could explain a blown tweeter in one loudspeaker, but it seems unlikely that the same defect would appear in both loudspeakers.

 

Some power amps intermittently produce ultrasonic oscillations when driving certain reactive loads. Nelson Pass and Matthew Polk independently discovered a simple solution that purportedly solves the problem in most cases: Connect a series-connected resistor and capacitor across the loudspeaker terminals. The recommended capacitor value is 0.1 uF per Pass or 0.047 uF per Polk. Both recommend a resistor of 5 or 6 ohms. See Polk's US patent 4177431 or Pass's article "Speaker Cables: Science or Snake Oil" in Speaker Builder, Feb 1980.

 

Neither recommended a particular type of capacitor, but I think a ceramic disc would have the lowest inductance at RF. For the same reason, the resistor should not be wirewound.

 

Bob- thanks. Have you done this and what is the effect on high frequency signals that are not oscillations in the cable but signals from downchain of the amps?

 

I was thinking possibly using ferrite chokes on the speaker cables would filter out the ultrasonics?

[gmgraves]

> Tektronix-468-Oscilloscope-with-Digital-Storage

>

> I found one for less than $200 shipped

>

> Should I grab it?

 

What setting should be used and how? Any good video links?

 

Almost any Tektronix 'scope is a fine piece of gear, in fact, they're the Rolls-Royce of oscilloscopes. This one is overkill for audio, though with a non-storage bandwidth of 100 MHz and it's two channel and solid state (older Tektronix scopes are tubed. Stay away from those). I've seen these puppies at less than $150 in good working condition. Be advised that this model is really heavy and very large. Consider another model or try to find a 'scope cart for this model. It shouldn't be that difficult to find.

 

I don't understand the question: "What setting should be used and how?"

 

But here is a video showing how to use a 468.

 

 

Make sure that any Tektronix scope that you buy comes with at least two 10X Tektronix probes. Without the probes, the scopes are are a lot more difficult to use.

[gmgraves]

Bob- thanks. Have you done this and what is the effect on high frequency signals that are not oscillations in the cable but signals from downchain of the amps?

 

I was thinking possibly using ferrite chokes on the speaker cables would filter out the ultrasonics?

 

No, that won't work. IF (and you need to determine that first) you have an oscillation, ferrite cores won't solve it. It's a malfunction and THAT needs to be addressed. The ferrite cores would be merely a bandaid, and an ineffectual one at that.

[semente]

Wouldn't it be best to ship the crossovers to the manufacturer?

 

R

[Bob Stern]

No, that won't work. IF (and you need to determine that first) you have an oscillation, ferrite cores won't solve it. It's a malfunction and THAT needs to be addressed. The ferrite cores would be merely a bandaid, and an ineffectual one at that.

Oscillation in response to certain reactive loads is not necessarily a malfunction of either the amplifier or the crossover network. It is the normal behavior of some amplifier designs as explained in the patents by:

 

Matthew Polk:

https://www.google.com/patents/US4177431

 

Bruce Brisson (MIT cables):

https://www.google.com/patents/US4954787

 

There is no harm in installing Polk's damping network (called a Zobel network when used in other applications) without bothering to test for the presence of ultrasonic oscillations. Any harmful oscillations may be hard to detect even with an expensive oscilloscope because they may rise to measurable levels only in response to certain signals fed to the amplifier.

 

I doubt that ferrite chokes would work, or else Polk and Pass would have suggested them as alternatives. A ferrite choke would have the opposite effect of their solution: it would increase the load impedance at high frequencies, whereas the Polk/Pass solution decreases the load impedance at high frequencies to that of the resistor.

[jmdesignz2]

I biwire my speakers. Should I install these zobel networks on each pair of speaker inputs?

[jmdesignz2]

Wouldn't it be best to ship the crossovers to the manufacturer?

 

R

 

I talked to Michael Kelly of Aerial and he said that if something was wrong with the crossovers, it would be audibly obvious.

[jmdesignz2]

Bob-

What do you think of this for the caps? 5% tolerance Wima .047?

http://www.mouser.com/ds/2/440/WIMA_MKS_2-11660.pdf

 

 

Oscillation in response to certain reactive loads is not necessarily a malfunction of either the amplifier or the crossover network. It is the normal behavior of some amplifier designs as explained in the patents by:

 

Matthew Polk:

https://www.google.com/patents/US4177431

 

Bruce Brisson (MIT cables):

https://www.google.com/patents/US4954787

 

There is no harm in installing Polk's damping network (called a Zobel network when used in other applications) without bothering to test for the presence of ultrasonic oscillations. Any harmful oscillations may be hard to detect even with an expensive oscilloscope because they may rise to measurable levels only in response to certain signals fed to the amplifier.

 

I doubt that ferrite chokes would work, or else Polk and Pass would have suggested them as alternatives. A ferrite choke would have the opposite effect of their solution: it would increase the load impedance at high frequencies, whereas the Polk/Pass solution decreases the load impedance at high frequencies to that of the resistor.