Can using an active sub cause HF drivers to blow???

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jdurango

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I've had several issues with a pair of high-end 200w/8ohm studio monitors blowing tweeters. They are being powered by an Adcom GFA-555 (200w@8ohm) power amp which is NOT indicating clipping at any point. It occured to me that while these speakers may be rated for 200W @ full range, the sub is removing everything below roughly 80hz (xover point), which would allow the amp to be pushed harder without clipping, thus delivering more juice to the HF drivers....especially since deep bass uses up a larger chunk of wattage.

To make this point clear, even though the speakers are rated @ 200W, you obviously couldn't send them 200W of white noise with a HFP @ 2k.....this would send the entire 200W to a driver probably rated around 50W.

Then again, a lot of music has very little content below about 60-70hz anyway, so using a sub with a HPF in the range would be analogous to listening to music which never had that LF information to begin with.

What do you think? Does using a sub effectively lower the wattage handling of downstream HF drivers? Could this be contributing to the blown drivers? Thanks fellas!
 
Maybe a little more detail of how your set up is wired will help more for others to understand what is going on?

It's hard to tell exactly how the Adcom is getting it's signal . From an output of the sub?  Trying to understand how the sub could output a high passed signal . What model active sub is it?
 
jdurango said:
I've had several issues with a pair of high-end 200w/8ohm studio monitors blowing tweeters. They are being powered by an Adcom GFA-555 (200w@8ohm) power amp which is NOT indicating clipping at any point. It occured to me that while these speakers may be rated for 200W @ full range, the sub is removing everything below roughly 80hz (xover point), which would allow the amp to be pushed harder without clipping, thus delivering more juice to the HF drivers....especially since deep bass uses up a larger chunk of wattage.
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can I assume 2-way or 3-way passive crossover inside the monitors?

Tweeters can not handle 200W that is rough whole speaker rating.
To make this point clear, even though the speakers are rated @ 200W, you obviously couldn't send them 200W of white noise with a HFP @ 2k.....this would send the entire 200W to a driver probably rated around 50W.
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or less, likely less
Then again, a lot of music has very little content below about 60-70hz anyway, so using a sub with a HPF in the range would be analogous to listening to music which never had that LF information to begin with.
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more in modern music than vinyl that had difficulty with extreme bass (especially stereo).
What do you think? Does using a sub effectively lower the wattage handling of downstream HF drivers? Could this be contributing to the blown drivers? Thanks fellas!
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No the sub should be a benefit, can I also assume that the sub is providing the active crossover, to HPF the audio?  One sub with stereo HPF, or two subs?

Tweeters can be stressed by amplifier clipping which should be reduced by adding a powered sub.

Another obvious thing to check for is some active circuit oscillating (unlikely but could explain damage to tweeters).

JR
 
So yes, the sub is a JBL 6312. Main outs of DAW > sub ins > sub outs > amp > speakers.

My point was, the sub is stripping off freq below 80hz, so that LF information is no longer factored into the 200W getting to the monitors, leaving more headroom for the amp at higher frequencies. To draw an extreme of this point, imagine the crossover on the sub was at 2k (ridiculous I know, just illustrating a point). The amp could then push 200W to ONLY the tweeters without clipping at all. This obviously wouldn't be what the manufacturer intended when it rated the monitors at 200W.....especially considering lower frequencies use up far more wattage than higher ones.

Is there a similar thing happening potentially happening with an 80hz xover? For example, is there a standard "weight" or testing method manufacturers use? Say, full range white noise? If two octaves are removed from the low side of this noise, this would leave more headroom for the amp in the higher freqs.

I don't believe oscillations were a factor. I'm sure we would've heard them unless sneaking through at some extremely high freq. I will check the output of the sub today with a scope to be sure.
 
jdurango said:
So yes, the sub is a JBL 6312. Main outs of DAW > sub ins > sub outs > amp > speakers.

My point was, the sub is stripping off freq below 80hz, so that LF information is no longer factored into the 200W getting to the monitors, leaving more headroom for the amp at higher frequencies. To draw an extreme of this point, imagine the crossover on the sub was at 2k (ridiculous I know, just illustrating a point). The amp could then push 200W to ONLY the tweeters without clipping at all. This obviously wouldn't be what the manufacturer intended when it rated the monitors at 200W.....especially considering lower frequencies use up far more wattage than higher ones.

Is there a similar thing happening potentially happening with an 80hz xover? For example, is there a standard "weight" or testing method manufacturers use? Say, full range white noise? If two octaves are removed from the low side of this noise, this would leave more headroom for the amp in the higher freqs.

I don't believe oscillations were a factor. I'm sure we would've heard them unless sneaking through at some extremely high freq. I will check the output of the sub today with a scope to be sure.
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Thanks but I understand the concept very well (trust me).

Removing LF content will generally allow the amplifier to play louder without saturation (clipping), but clipping is not the only way to damage tweeters. If you can now turn up amp another +3dB before clipping that is 2x the power. So you can burn out the drivers the old fashioned way (too much power). 

HF oscillation is not typically audible, and a well designed amplifier should band pass even that out (not my first suspect for the failure). 

To repeat adding a sub and removing LF content from the full range speaker will not stress it at all. OTOH turning it up louder can. 

JR
 
Okay, that's all in line with what I was thinking. I'm dealing with US support for this manufacturer now and just trying to rule out anything that might be causing this problem on my end. It's a very high-end, very expensive, very highly regarded monitor brand, so I'm surprised their speakers would be this much of a cost liability for a professional studio.

We had JUST replaced the previous drivers and put only a few hours of listening at moderate-to-higher volumes with absolutely no clipping at any point that anyone noticed either from the DAW or into the amp itself, either audibly or via clip indicators on the 555. It's been maintained by Jim Williams, I can't imagine the amp is the problem. Unless there's some identical anomaly with BOTH crossovers, I can't think what else (other than underpowered HF driver given the rated wattage) would be causing this problem.
 
jdurango said:
Okay, that's all in line with what I was thinking. I'm dealing with US support for this manufacturer now and just trying to rule out anything that might be causing this problem on my end. It's a very high-end, very expensive, very highly regarded monitor brand, so I'm surprised their speakers would be this much of a cost liability for a professional studio.

We had JUST replaced the previous drivers and put only a few hours of listening at moderate-to-higher volumes with absolutely no clipping at any point that anyone noticed either from the DAW or into the amp itself, either audibly or via clip indicators on the 555. It's been maintained by Jim Williams, I can't imagine the amp is the problem. Unless there's some identical anomaly with BOTH crossovers, I can't think what else (other than underpowered HF driver given the rated wattage) would be causing this problem.
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You need to do some objective assessment, using measurements. REW is your friend there. What SPL are you asking in the tweeter's operating range?
Your analysis is correct. The fact that the monitors are relieved of the heavy lifting makes them sound less stressed, which encourages increasing the volume. Whenever a studio engineer or tech mentions moderate volumes I start to doubt.  ;D
What are these monitors? Most tweeters have very low continuous power rating.
 
Jim Willams likes to remove RF protection. I’d check to make sure there isn’t out of band crap blowing the tweeters.
 
Gold said:
Jim Willams likes to remove RF protection. I’d check to make sure there isn’t out of band crap blowing the tweeters.
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Jim Williams likes to do a lot of stuff I don't approve, like replacing standard opamps  with 2000 V/usec video opamps, a lot of stuff which in my opinion does not improve the sound and just opens the door for trouble.
 
user 37518 said:
Jim Williams likes to do a lot of stuff I don't approve, like replacing standard opamps  with 2000 V/usec video opamps, a lot of stuff which in my opinion does not improve the sound and just opens the door for trouble.
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My money is on the  amp being at fault. This  wouldn’t be the first time his mods have been ripped out and cursed.

To his credit I haven’t heard him recommend a video opamp for Audio in a long time.
 
Let's not be in such a rush to pin the tail on Jim Williams, in absentia no less.

There could be any number of fault vectors, including the obvious (too much volume).

Feel free to pile on after we get some real data.

JR

PS: I thought the crazy high slew rate audio amps fell out of fashion last century after their champions figured out how those amps made those high slew rates. They saturated the input LTP and run WFO without NF until the output stage catches up, perhaps great for sample and holds, but not very desirable for continuous linear audio response. When marketing to phools who don't understand specs,  more always sounds better (like multiple thousands of volts per uSec slew rate).  ::)
 
JohnRoberts said:
Let's not be in such a rush to pin the tail on Jim Williams, in absentia no less.
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Easy enough to eliminate the amp. Match listening level with a different amp and see what happens.

My guess is massive RF at the output. Also easy to check. He makes no secret of his recommendations of removing RF protection for that glorious sound.
 
Well, I don't really have a spare set of tweeters laying around to try it again with a different amp, nor do I have another $200 to spend on ANOTHER set of tweeters if the second amp also blows the drivers. The monitors are Amphions. They use SEAS aluminum drivers to my knowledge.

What's the best way to diagnose RF noise from the amp? Place an 8ohm load on the output, play the same music as before at roughly the same levels, and look for content above say 40k that reaches a certain RMS voltage? What level should be considered unsafe? Thanks fellas!
 
BTW, the JW modded GFA555 gets amazing reviews everywhere they are present. I know Jim has is an eccentric as has some controversial ideas. I totally get it. But the proof is in the pudding. I was going to go with Hypex Ncore modules (and may still try them) for these speakers, but ended up with the JW 555 based on glowing reviews. And IME, the amp really does sound amazing, at least as good, if not better than my previous Bryston 4B.....and generates a hell of a lot less heat and back pain as well ;)
 
jdurango said:
What's the best way to diagnose RF noise
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I’d start by putting a scope at the speaker output with the speakers  attached and see if there is any crud there. If there is  RF it should be  low in level compared to the test signal. I don’t have a figure but I’d want it really low in level.
 
user 37518 said:
Last time I checked his 4000V/uSec preamp is still being produced http://audioupgrades.com/ he always brags about his bionic ear capable of hearing stuff the rest of us can't
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I don't care if he claims psychic powers....as long as his end product is good, he's alright in my book! From what I've seen, if you like very clean/clinical stuff, his work is among the best.
 
jdurango said:
Well, I don't really have a spare set of tweeters laying around to try it again with a different amp, nor do I have another $200 to spend on ANOTHER set of tweeters if the second amp also blows the driver
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If it is the amp I’d want to know before using it on another set of speakers.
 
jdurango said:
BTW, the JW modded GFA555 gets amazing reviews everywhere they are present. I know Jim has is an eccentric as has some controversial ideas. I totally get it. But the proof is in the pudding. I was going to go with Hypex Ncore modules (and may still try them) for these speakers, but ended up with the JW 555 based on glowing reviews. And IME, the amp really does sound amazing, at least as good, if not better than my previous Bryston 4B.....and generates a hell of a lot less heat and back pain as well ;)
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JW has a pretty good reputation with his customers and that is what matters.

I am using 6 channels of Hypex UCD modules for my living room home theater system and I like them (so far), but I am easy.

JR 
 
jdurango said:
I don't care if he claims psychic powers....as long as his end product is good, he's alright in my book! From what I've seen, if you like very clean/clinical stuff, his work is among the best.
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I respectfully disagree, I believe most of his "upgrades" are a "scam". But thats just me....
 

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