Ascend Sierra Tower + Emotiva XPA-11 = Burnt Voicecoil

[PENG]

AH has an interesting article on how a speaker can be destroyed. We all know that it can be done, but it is still good to read this one. Incidentally, the one used for the tests happened to be a 6.5" mid woofer, by Axiom.

Loudspeakers & Power Ratings Part III: The Test Results | Audioholics

Or just read the conclusions.

Conclusions
There are two ways to kill a loudspeaker; thermal or mechanical.

In this experiment we destroyed one of these small drivers in each way. The most dangerous and destructive signal used was one composed of a single low frequency tone burst on for 11 cycles and off for 99. Despite this signal containing only 55 watts of RMS power, the speaker failed as a result of the peak voltage, correlating to a power (into nominal impedance) of 1100 watts peak. Peaks of very short duration can serve to destroy a loudspeaker even though they are of such a short duration, they are not able to heat up the speaker significantly. Frequency content and Peak to RMS ratio (crest factor) are critical in determining the potential for loudspeaker destruction of a test signal. The loudspeakers impedance magnitude gives us clues as to the potential harm from a signal based on the variation of impedance with frequency.

High frequencies are NOT DANGEROUS to the typical woofer, and the notion that clipped signals of a given RMS value are more dangerous to a woofer than unclipped signals is not necessarily correct. Clipped signals do put a higher percentage of amplifier power into the tweeter or high frequency device, and are therefore more dangerous to multi driver systems or high frequency units. Low frequency drivers (woofers) have very high impedances at high frequencies and are therefore not able to easily draw power from the amplifier at the highest frequencies. Without specifying the frequency content and crest factor of the test signal used, the POWER HANDLING NUMBER IS MEANINGLESS!

 

[PENG]

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.

Really, the website didn't say that or I missed. It has a mid woofer and then two woofers so I thought it would be a 3-way. Well, like I said anything is possible.

 

[Beave]

FWIW, my understanding of the Ascend tower design is what Pogre and TLS Guy have been saying: there is no electrical highpass filter on the midwoofer. So whether you call it a 2.5 way or a 3 way comes down to semantics.

 

[Verdinut]

FWIW, my understanding of the Ascend tower design is what Pogre and TLS Guy have been saying: there is no electrical highpass filter on the midwoofer. So whether you call it a 2.5 way or a 3 way comes down to semantics.

It's not a question of semantics, it's a question of using less crossover components in one design as opposed to another. That has an important effect on overall frequency response as well, and the mid-bass driver has to be a good match with the woofer(s) for the projected design.

 

[Beave]

I don't understand your point. Do you consider it a three way or a 2.5 way?

 

[TLS Guy]

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 is 2.5 way. The mid/woofer will not have a high pass filter only the low pass between mid and tweeter.

 

[Beave]

No it is 2.5 way. The mid/woofer will not have a high pass filter only the low pass between mid and tweeter.

But the midwoofer is in a sealed compartment that yields an acoustics highpass rolloff above the bass, ie, the midwoofer rolls off naturally in the lows at a frequency well above where the two woofers roll off., ie, it doesn't run as low as the two woofers do.

So it's sort of a three-way, and sort of a 2.5 way, thus my statements above.

 

[PENG]

No it is 2.5 way. The mid/woofer will not have a high pass filter only the low pass between mid and tweeter.

Thank you, Pogre told me that too, now I know. As Beave said, even without the high pass filter, it could still be considered 3 way but I get your point that it could be prone to d.c damage. Regardless, I still think chance is greater that it was damaged by being over driven based on the information provided so far.

 

[highfigh]

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.

You probably know this but most meters don't react fast enough to measure power output at anything above 60Hz because they don't need to in general use but if it has a frequency counter, it might be accurate enough. Still, a scope is best.

 

[highfigh]

But the midwoofer is in a sealed compartment that yields an acoustics highpass rolloff above the bass, ie, the midwoofer rolls off naturally in the lows at a frequency well above where the two woofers roll off., ie, it doesn't run as low as the two woofers do.

So it's sort of a three-way, and sort of a 2.5 way, thus my statements above.

It does roll off acoustically, but the energy from lower frequencies still reaches the voice coil- the small enclosure just makes these frequencies almost inaudible. Also, the signal is still trying to make the cone move as if it were in free air or a larger enclosure, so the small space will restrict the cone's movement even though the voice coil is trying to pull it in and that could easily cause the former to separate from the cone.

 

[highfigh]

When I looked at the web page for the amplifier, I decided to ask if their amps have protection from DC at the output terminals- here's the response-

"All Emotiva amplifiers have DC protection where they will shut down if DC is detected on the speaker outputs. The amplifiers also have short and thermal protection. Let us know if you need anything else.".

 

[TLS Guy]

I don't understand your point. Do you consider it a three way or a 2.5 way?

The speaker is a 2.5 way. That is electrically. However when you combine the electrical and acoustic response then it is 3 way. You must remember that any speaker crossover is the sum of the electrical AND acoustic responses.

I'm a huge believer in relying on acoustic responses of the drivers to carry a lot of the heavy lifting of the crossover. You get a much better phase and transient response that way. That means you have to really do your homework. From a design point of view it is actually harder, but the crossover is generally simpler. It is in that area that speaker design becomes a true art.

 

[Pogre]

Dave did pop in with some input.

"A DC offset in your amplifier is what I was alluding to when I asked you if you heard any low level hums or "pops" when you turn your amp on or off. Typically, with a DC offset, you can hear a low level hum in the background or pops on amp power on/off etc, or see the woofers move in/out during amp power on/off. However, this is very much dependent on the amp design.

Something definitely happened, it is rare enough for a voice coil to burn, but for both of them at the same time to go, it is a sure sign *something* happened.

Another possibility is low AC line voltage, and I have seen this more often these days - especially here in California. If your line voltage drops, this will cause your amp to clip and the distortion this produces can be quite damaging, especially if there is a DC component to it, which can happen depending on the amp design. Luckily, the RAAL 70-20 has good protection from the damaging effects of transverse waves caused by clipping and DC can't hit the tweeter.

Do you have access to a voltmeter?

Edit: I should probably also mention that I have come across this same issue before with the same amplifier (DC Offset)"

When I asked about clipping killing the tweet first he added:

"For any other tweeter, yes - heavy clipping would take the tweeter out first. However, the RAAL 70-20 has a unique damping feature (unique only to the 70-20) which enables the ribbon to better handle the problems associated with a clipped signal. BThis is one of the reasons why I love this tweeter and am willing to pay a fortune to use them..."

End of the day he aligns with the advice here and suggests testing it, but said he's encountered the DC offset issue with that same amp in the past. I love that Ascend has a forum and Dave does watch it and replies. He's replied to every single thread I've posted over there. Even the dumb ones... lol.

 

[Replicant 7]

AH has an interesting article on how a speaker can be destroyed. We all know that it can be done, but it is still good to read this one. Incidentally, the one used for the tests happened to be a 6.5" mid woofer, by Axiom.

Loudspeakers & Power Ratings Part III: The Test Results | Audioholics

View attachment 51945

Or just read the conclusions.

Conclusions
There are two ways to kill a loudspeaker; thermal or mechanical.

In this experiment we destroyed one of these small drivers in each way. The most dangerous and destructive signal used was one composed of a single low frequency tone burst on for 11 cycles and off for 99. Despite this signal containing only 55 watts of RMS power, the speaker failed as a result of the peak voltage, correlating to a power (into nominal impedance) of 1100 watts peak. Peaks of very short duration can serve to destroy a loudspeaker even though they are of such a short duration, they are not able to heat up the speaker significantly. Frequency content and Peak to RMS ratio (crest factor) are critical in determining the potential for loudspeaker destruction of a test signal. The loudspeakers impedance magnitude gives us clues as to the potential harm from a signal based on the variation of impedance with frequency.

High frequencies are NOT DANGEROUS to the typical woofer, and the notion that clipped signals of a given RMS value are more dangerous to a woofer than unclipped signals is not necessarily correct. Clipped signals do put a higher percentage of amplifier power into the tweeter or high frequency device, and are therefore more dangerous to multi driver systems or high frequency units. Low frequency drivers (woofers) have very high impedances at high frequencies and are therefore not able to easily draw power from the amplifier at the highest frequencies. Without specifying the frequency content and crest factor of the test signal used, the POWER HANDLING NUMBER IS MEANINGLESS!

Interesting read, so @PENG, 55 watts can kill a driver? Did I read that right in Gene's test results? So all those power handling spec's that All manufacturers post of their speakers are not accurate and meaningless?

 

[jeeper]

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.

I didn't check with a multimeter, but I did connect an old/cheap speaker to the amp... and there wasn't any humming or pops when turning on/off. This is why I was wondering if the happened at a certain temperature, reached under higher load...

 

[highfigh]

Interesting read, so @PENG, 55 watts can kill a driver? Did I read that right in Gene's test results? So all those power handling spec's that All manufacturers post of their speakers are not accurate and meaningless?

55? 20W can kill a tweeter. It's all about heat and lack of ability to dissipate it.

The criteria for power handling specs in consumer speakers aren't the same as what commercial/industrial speaker manufacturers use.

Here's an Ascend page for the Sierra Tower-

Sierra Tower Specifications

From the link-
"1 Half-space 2 Continuous Pink Noise rating is IEC-shaped pink noise with a 6 dB crest factor for 100 hours continuously.
- Continuous Program power is a conservative expression of the system’s ability to handle normal speech and music program material, and is defined as 3 dB above the Continuous Pink Noise Rating.
- 3 Calculated based on power rating and measured sensitivity, exclusive of power compression Note: Reference Axis=0 degrees/on axis, Reference Plane=on axis, Horizontal Plane=on axis. "

https://jblpro.com/en-US/site_elements/control-25av-ls-spec-sheet

The speaker in the link is also rated for use in 'Life Safety' applications, which means that in use for paging during an emergency, it needs to work, period, to the point of total destruction. Not that it's inherently a better speaker, but the testing for this kind of speaker is more stringent because home audio speakers aren't usually expected to receive the max power shown in the spec sheet. IF the amp was at full power + and/or the Marantz was overdriving the input of the power amp, I would say that the expectations for the system are less than realistic and possibly, the setup menu needs to be checked to make sure this can't happen again.

 

[TLS Guy]

I didn't check with a multimeter, but I did connect an old/cheap speaker to the amp... and there wasn't any humming or pops when turning on/off. This is why I was wondering if the happened at a certain temperature, reached under higher load...

If this has been seen before with this amp, be very careful. A properly designed amp should never cause this issue, not one case. That would make me drop that amp like a hot potato. That is also a potential home fire risk.

 

[highfigh]

That is also a potential home fire risk.

That's probably a bit extreme- in the 50 years since I started working with audio equipment, I haven't seen an amplifier cause a fire that wasn't short-lived. I have seen caps pop, tubes burst, resistors flash and wires burn, but they weren't speaker wires and they were always contained within the chassis. Amplifier kits, OTOH, are a wild card and if they were built by a hobbyist who didn't know the risks, it could start a fire. Even Sansui at their worst (the R-series receivers and whatever integrated amps they were troweling out at the time) launched output transistors so often one of our service techs used to say "Sansui put those outputs in, to protect the fuses".

 

[Replicant 7]

55? 20W can kill a tweeter. It's all about heat and lack of ability to dissipate it.

The criteria for power handling specs in consumer speakers aren't the same as what commercial/industrial speaker manufacturers use.

Here's an Ascend page for the Sierra Tower-

Sierra Tower Specifications

From the link-
"1 Half-space 2 Continuous Pink Noise rating is IEC-shaped pink noise with a 6 dB crest factor for 100 hours continuously.
- Continuous Program power is a conservative expression of the system’s ability to handle normal speech and music program material, and is defined as 3 dB above the Continuous Pink Noise Rating.
- 3 Calculated based on power rating and measured sensitivity, exclusive of power compression Note: Reference Axis=0 degrees/on axis, Reference Plane=on axis, Horizontal Plane=on axis. "

https://jblpro.com/en-US/site_elements/control-25av-ls-spec-sheet

The speaker in the link is also rated for use in 'Life Safety' applications, which means that in use for paging during an emergency, it needs to work, period, to the point of total destruction. Not that it's inherently a better speaker, but the testing for this kind of speaker is more stringent because home audio speakers aren't usually expected to receive the max power shown in the spec sheet. IF the amp was at full power + and/or the Marantz was overdriving the input of the power amp, I would say that the expectations for the system are less than realistic and possibly, the setup menu needs to be checked to make sure this can't happen again.

No huh! 20 watts can fried Tweeter?. I think you missed my point on what Gene's finding of his test results.

 

[Replicant 7]

That's probably a bit extreme- in the 50 years since I started working with audio equipment, I haven't seen an amplifier cause a fire that wasn't short-lived. I have seen caps pop, tubes burst, resistors flash and wires burn, but they weren't speaker wires and they were always contained within the chassis. Amplifier kits, OTOH, are a wild card and if they were built by a hobbyist who didn't know the risks, it could start a fire. Even Sansui at their worst (the R-series receivers and whatever integrated amps they were troweling out at the time) launched output transistors so often one of our service techs used to say "Sansui put those outputs in, to protect the fuses".

I don't believe Doc's statement is extreme at all, the possibility of a fire with a amp design like that could happen. "Potential" is there for it to happen. Back when EMO had that XPA-2 amp umm around 2011 there was one dude who had one, if I remember he stated it caught on fire, blew up or something like that. But it was found out that he was using it in bridge mode if I'm not mistaken and with the speakers he was driving had dropped to around a 2 Ohm load.