Ascend Sierra Tower + Emotiva XPA-11 = Burnt Voicecoil

J

jeeper

Enthusiast
You drive it hard into large power resistors, and watch the output on the Scope and see if DC gets superimposed on the output. I bet that is the problem. I have been there. DC offset is the only time I have burnt out woofer voice coils. I have to admit to burning out the odd tweeter, may be a couple, from over enthusiastic levels.

This problem only started with the introduction of direct coupled output stages. One of the first was the Crown DC 300 A. I also had a very early Quad 405, send a speaker up in smoke. Peter Walker apologized and sent me the clamp circuit for the output. He also gave me new boards, as the output transistors were promptly discontinued, and so that led to the prompt new iteration of the power amp boards.

I would have enormous suspicion of that Emotiva amp. Ascend will probably not be so kind to you if you fry more VCs!

Ascend call that mid range driver, a mid woofer. So I suspect that the speaker is really a 2.5 way, with the cross to mid being acoustic. That is actually I good plan. But that would mean that there would be no cap in series with the midrange. That is actually quite a good design. You might check with Ascend to see if that is correct and if there is a cap in series with that mid or not. If there is no cap, DC offset is likely. If there is a cap, it was not DC offset. Since they call it a mid woofer, I suspect there is no cap in series with the VC.
Will send a note to Dave and get his confirmation, and to Emotiva as well.

In terms of Ascend being "kind" ... well, they were nice and all, but I had to pay for the two woofers... so I'm sure they'll keep selling me additional woofers if the problem persists (not implying they should've covered it under warranty if culprit was amp).
 
slipperybidness

slipperybidness

Audioholic Warlord
Yeah, it's a powerful amp for sure.

You guys know me, I like it loud sometimes and have the same speakers. I've never heard distortion or misbehaving even with 103 dB peaks at 14 - 15 feet. For both mids to go like that I think would require some serious juice. Maybe there is something to @TLS Guy's DC offset theory...

@jeeper, were you by chance using them outdoors for a party or something?
DC offset is basically a completely cilpped signal that is just constantly feeding power to the voice coils. DC offset would be lower than a clipped signal, but what I'm saying is that when you see clipping on an o-scope, it looks the same as a DC signal.

And, TLS has a point, caps in series won't pass a DC signal.

1 thing is certain-- I would NOT be hooking my speakers up to that amp again until I had 100% certainty that the amp is not at fault! And right now, from the limited info, the finger seems to point to the amp. For the $ at stake here, that amp needs to be investigated asap. The fact that it happened to both speakers would make it unlikely that it was a speaker/driver problem.
 
slipperybidness

slipperybidness

Audioholic Warlord
That's a pretty interesting hypothesis. Especially about the transistor failing after getting to a certain temperature point. Any thoughts on how I might be able to get it tested?
Have you contacted Emo yet?
 
Pogre

Pogre

Audioholic Slumlord
I'm tempted to make a thread at the Ascend forums, but I think I've seen you post over there @jeeper and I don't wanna step on your toes if you'd rather not.
 
highfigh

highfigh

Audioholic Slumlord
Hi all - long time follower, but first time posting here... I have my HT setup with a Marantz AV7705, Emotiva XPA-11, and a bunch of speakers from Ascend Acoustics (front/surrounds) and RSL for Atmos.

The front L/R are the Ascend Sierra Towers, and Center is a Sierra Horizon. These are connected to the mono-blocks of the amp.

I was recently playing some music in stereo mode, not that loud (-8, -6 db tops), and turns out that I busted my midrange woofers. There was the distinct smell of burned rubber, and it the midrange from both towers were done. One completely gave out (no sound at all), while the other was distorted.

Contacted Ascend, and they were super nice and helped me get replacement woofers. They thought the amp was not powerful enough and probably clipped. I don't see how that might be the case...

Tested the amp with some other speakers, and there's no hum or pops when on, playing music, or when switching on/off.

Any thoughts on these corridors of knowledge what the issue might be? I just don't want this happening again...


Thanks in advance!
Jeeper
The first thing I would check is the level settings for each source in the Marantz, to make sure none are above -0dB. Next, I would make sure that the output level from the Marantz at -6dB or wherever you listen isn't exceeding the sensitivity of the power amp.

Read the specs for the power amp- it's possible that you exceeded the long term power handling capacity of the speakers, although I have seen more woofers die because of that than mids, although nothing says this isn't the failure mode for these speakers. If the Marantz surpassed the input sensitivity of the power amp AND the output power surpassed the speaker's capacity, this was just about unavoidable if the music was playing that loudly for a long time. It would also be a good idea to rest your ears after a listening session at that level.

This kind of situation is the reason I limit the output from AVRs and preamps when I can- if it can't exceed -10dB, it's not likely to damage all but the lowest power-handling capacity speakers.
 
highfigh

highfigh

Audioholic Slumlord
DC offset is basically a completely cilpped signal that is just constantly feeding power to the voice coils. DC offset would be lower than a clipped signal, but what I'm saying is that when you see clipping on an o-scope, it looks the same as a DC signal.

And, TLS has a point, caps in series won't pass a DC signal.

1 thing is certain-- I would NOT be hooking my speakers up to that amp again until I had 100% certainty that the amp is not at fault! And right now, from the limited info, the finger seems to point to the amp. For the $ at stake here, that amp needs to be investigated asap. The fact that it happened to both speakers would make it unlikely that it was a speaker/driver problem.
DC can come through leaky output transistors, it's not from clipped signal unless the amp is being treated like a farm animal. Leaky transistors can show DC offset when no signal is entering the input of the amp and it's usually adjusted internally, or remedied through component replacement.
 
J

jeeper

Enthusiast
I'm tempted to make a thread at the Ascend forums, but I think I've seen you post over there @jeeper and I don't wanna step on your toes if you'd rather not.
I'll post there as well... As far as I'm concerned this is not a mud-slinging exercise, but rather an effort to figure out what went wrong, how to fix and prevent.
 
P

PENG

Audioholic Slumlord
I'll post there as well... As far as I'm concerned this is not a mud-slinging exercise, but rather an effort to figure out what went wrong, how to fix and prevent.
While waiting, can you measure the dc offset voltage with the amp turned on, set the volume of the AV7705 to minimum and see what you are getting? Assuming you have a multi-meter.

Have you tested the amp with another speaker to see if it appears to work normally?
 
Pogre

Pogre

Audioholic Slumlord
I'll post there as well... As far as I'm concerned this is not a mud-slinging exercise, but rather an effort to figure out what went wrong, how to fix and prevent.
I don't get the impression you're slinging mud. I think you've been clear and respectful about it, and it's a legit concern. I see this is a troubleshooting exercise so you can isolate and prevent it from happening again. I don't think anyone will begrudge you for that. I want to know too. I have the same speakers, lol.
 
P

PENG

Audioholic Slumlord
You drive it hard into large power resistors, and watch the output on the Scope and see if DC gets superimposed on the output. I bet that is the problem. I have been there. DC offset is the only time I have burnt out woofer voice coils. I have to admit to burning out the odd tweeter, may be a couple, from over enthusiastic levels.

This problem only started with the introduction of direct coupled output stages. One of the first was the Crown DC 300 A. I also had a very early Quad 405, send a speaker up in smoke. Peter Walker apologized and sent me the clamp circuit for the output. He also gave me new boards, as the output transistors were promptly discontinued, and so that led to the prompt new iteration of the power amp boards.

I would have enormous suspicion of that Emotiva amp. Ascend will probably not be so kind to you if you fry more VCs!

Ascend call that mid range driver, a mid woofer. So I suspect that the speaker is really a 2.5 way, with the cross to mid being acoustic. That is actually I good plan. But that would mean that there would be no cap in series with the midrange. That is actually quite a good design. You might check with Ascend to see if that is correct and if there is a cap in series with that mid or not. If there is no cap, DC offset is likely. If there is a cap, it was not DC offset. Since they call it a mid woofer, I suspect there is no cap in series with the VC.
Not too many hobbyist have scopes but many do own a multimeter. He could just measure the amp output with a multimeter, with the volume of the preamp at minimum, disconnect the speakers and measure the dc voltage. If that's high then we know there is a problem. If not, then yes it is possible at high output under load the dc offset voltage may increase to damaging level but that would seem unlikely if the amp is functioning normally otherwise.
 
P

PENG

Audioholic Slumlord
I don't know if this would be a factor, but they do have the midrange in its own sealed compartment and tuned to roll off naturally to the bass drivers.
Yes, in that case, I would think there is likely a cap in series in the crossover circuit for mid range. I highly doubt dc offset is the root cause in this case if his amp is performing normally otherwise. Given the volume setting so high, I think it is quite possible that the mid woofer just got cooked due to being driven at high level for a prolong period of time.

@jeeper , I think when @ryanosaur asked about the trim level, you said "no boost" but I am not sure if your "boost" means the trim level setting Ryan was referring to, can you confirm that? "Trim level" generally refers to the level settings in the speaker menu, not boost via GEQ, or REQ or the boost set in the source level via the input menu. Also, when that happened, was Audyssey on, if yes, was DEQ on?

All these need to be factored in when trying to correlate volume setting (such as your -6) with the actual amp output level. Anything is possible, but I do think there is a greater chance that the speaker was over driven than it was damaged by dc. By the way one question to ask Emotiva is whether their amps have d.c. offset protection. Even AVRs have such protection.
 
TLS Guy

TLS Guy

Seriously, I have no life.
Yes, in that case, I would think there is likely a cap in series in the crossover circuit for mid range. I highly doubt dc offset is the root cause in this case if his amp is performing normally otherwise. Given the volume setting so high, I think it is quite possible that the mid woofer just got cooked due to being driven at high level for a prolong period of time.

@jeeper , I think when @ryanosaur asked about the trim level, you said "no boost" but I am not sure if your "boost" means the trim level setting Ryan was referring to, can you confirm that? "Trim level" generally refers to the level settings in the speaker menu, not boost via GEQ, or REQ or the boost set in the source level via the input menu. Also, when that happened, was Audyssey on, if yes, was DEQ on?

All these need to be factored in when trying to correlate volume setting (such as your -6) with the actual amp output level. Anything is possible, but I do think there is a greater chance that the speaker was over driven than it was damaged by dc. By the way one question to ask Emotiva is whether their amps have d.c. offset protection. Even AVRs have such protection.
In a set up like that, you would not put a cap in series with the mid/woofer. That arrangement allows for accurate and precise BSC correction and is phase linear.

My two mains have that arrangement, where the crossover to the long lines is acoustic and not electronic. I did take the precaution though, of using two high powered bass/mids. They also have metal cones which helps greatly with heat dissipation from the VCs.

So in that arrangement the Midwoofer does get more power. If there was to be DC offset, that driver would burn first, as it would take twice the heating load of the woofers.

So it could be overdrive, or DC offset. However the only time I have actually seen a driver smoke is with DC offset. One of my occurrences had flame as well as smoke!
 
P

PENG

Audioholic Slumlord
In a set up like that, you would not put a cap in series with the mid/woofer. That arrangement allows for accurate and precise BSC correction and is phase linear.

My two mains have that arrangement, where the crossover to the long lines is acoustic and not electronic. I did take the precaution though, of using two high powered bass/mids. They also have metal cones which helps greatly with heat dissipation from the VCs.

So in that arrangement the Midwoofer does get more power. If there was to be DC offset, that driver would burn first, as it would take twice the heating load of the woofers.

So it could be overdrive, or DC offset. However the only time I have actually seen a driver smoke is with DC offset. One of my occurrences had flame as well as smoke!
I don't think you can say for sure though as it depends on the design. For example, my BMR is a 3 way Dennis Murphy design, and it has a series cap. Isn't the Ascend Tower 3-way too?
 
Pogre

Pogre

Audioholic Slumlord
I'm still looking for the post, but I know Dave said that the crossover for the mid is acoustic, in part for a shallower roll off to take advantage of the mid's fr. It is listed as a "2.5 way speaker" too so I still think DC offset is on the table. I did find what he had to say about power handling in the intro thread.

"Loudspeaker power handling = massive!
(we have yet to reach the speaker's limits but I would estimate it to be about 350 clean watts)". They can handle a good bit of unclipped power. I know I've had mine cranked a few times with no trouble, tho admittedly only for a song or 2 before turning it back down.
 
Pogre

Pogre

Audioholic Slumlord
I don't think you can say for sure though as it depends on the design. For example, my BMR is a 3 way Dennis Murphy design, and it has a series cap. Isn't the Ascend Tower 3-way too?
No, it's a 2.5 way. I'm almost positive TLS is right about that part. I'm still looking for the post where Dave explained it.
 
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