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-   -   Mark Audio CHR-70 gen1 self destruction. (http://www.diyaudio.com/forums/full-range/199845-mark-audio-chr-70-gen1-self-destruction.html)

speakrsrfun 4th November 2011 05:07 PM

Mark Audio CHR-70 gen1 self destruction.
 
OK let first start of by stating that the Mark Audio drivers are generally a great buy and work very well for what they are intended, and up to this point I have been very satisfied. Now with that being said I'd like to express my displeasure in one of my drivers self destructing after 1 week of playing out of the box, and the second one from the same box being wired out of phase from the other (from the factory not me). Hmmmmm, I've bought several pairs of the CHR-70 as I've built many cabinets for friends and family based on how good this little guy is, now my biggest concern is with the structural longevity of the metal cones. See the one driver that self destructed in fact still works(ie no VC short), and seems to do everything good accept female voice/brass, with this it vibrates and honks like mad. Soooo long story short I pulled it out of my Onken style cabinet and low and behold little stress fractures all around the surround directed toward the center of the cone. Currently the cracks are only 1/8-1/4" long but they are through and through and let air escape and vibrate like crazy on female voice and brass inst. I'm primarily a Jazz listener with some varying degrees of other music played through my systems but never real loud or abusive.

Anyone else have this issue?

Hey Mark Fenlon any ideas brother?

Anywho just a small rant to vent my displeasure, keep rocking.

chrisb 4th November 2011 05:56 PM

I'd wager that far more of the metal coned drivers have been damaged in handling / installing in cabinets (or could be that's just us ?), but Mark and others have noted issues with both stressing of frames by over-torquing of mounting screws, and at least a couple of incidences of damage from over-driving have been reported.

Some photos might possibly help Mark to guess at the cause?

speakrsrfun 4th November 2011 07:02 PM

Yeah I'll post some up later tonight, thanks Chris this does shed some light on possibilities for damage.

speakrsrfun 6th November 2011 04:34 AM

Sorry for the delay on the pics, I've had company and a bit of a hard time getting the cracks to show up right in the pic. o please bear with me as I get the pics all sorted out.

rlrohlfs 7th November 2011 06:04 PM

I had similar issues with the Alpair 10.1. They performed for the first two weeks and then developed stress lines, surround delamination and stopped functioning. I was suprised by the short lifespan given that I've had multiple sets of the Jordan Jx92s' in use since 2008 without problem. Considering the difference in price between the Alpair and the Jordan's as well as the lack of availablity of the Jordan's I'd like to use the Alpair 10's again. I've been watching this forum for user feedback on the Alpair gen 2's before making any further investment.

I also have a set of the Alpair 12's that have been in use for most of this year. They show no sign of the above issues. Perhaps only the first generation of Alpairs had problems.???

-
Rick

dainrobert 7th November 2011 08:58 PM

Get them photos up. I would like to see this before ordering. Sounds like a fatigue failure, but the photos will tell. Get close up shots please!

markaudio 7th November 2011 09:45 PM

Hi Guys,
The Gen. 1 drivers used a softer grade alloy. These cones were part hand-made so were more variable in thickness and profile consistency. All Gen. 2, Gen. 3 and Alpair 12 Gen. 1 drivers now use the Multiform cones. These are much stronger. Somewhere on the forum are several posts from members who commented on CHR-70's that have taken allot of punishments and still kept going.

Take a look at this thread as the issue has been covered here:

http://www.diyaudio.com/forums/marka...t-woofers.html

A word of caution. No full-range driver can take allot of power. With the benefit of easy make movies, I've had several examples on recent times sent from guys who say they don't over-load the drivers, only to find they do.

Other thing to note is more members are asking me to increase SPL. That means I have to reduce mass, that means power-handling will remain limited. Anyone that's operating a high SPL or small full ranger driver will (or should) know this.

Alpair 10 Gen 2. Its a driver that I've built right up to the limit. Its cone is less than 1000 micron thick. With its trick coil, its strictly a low load driver. Take a look at the Makraudio forum for advice on how to use this driver and other Markaudio driver, there's plenty of comment on various threads.

New Alpair 12 (Gen 2). Many members are asking me to get this driver over the 90dB threshold. I can do this, but again, its comes at a price. You know what this will be.

Its up to you guys. I can start building drivers with more power handling capacity, that's much easier work for me (or any maker) to do. But you'll sacrifice musicality, bandwidth and SPL. Which is it to be?

Cheers
Mark.

weltersys 7th November 2011 11:17 PM

1 Attachment(s)
Mark,

Excursion up to and including Xmax is by definition supposed to be within the linear range of operation for a loudspeaker, regardless of whether it is designated full range, mid range, woofer or whatever marketeers choose to call it.

Operation of a loudspeaker in the linear range of operation should not cause damage.

In post #44 of the “alpairs-arent-woofers” thread you link, you say:

“So I'd still urge guys to adopt a practical observational approach when using Full-rangers. For example, on a Gen 2. Alpair 10, ideally the cone shouldn't move more than about 3 to 4-mm (1 way) on a big roll of drum, or other similar dramatic moment in the music. For regular LF beat music, better to work on around 2-mm a guide.”

I agree observation of excursion is a good way of preventing cone damage.

That said, the Gen 2 Alpair 10 specs list an Xmax of 8.5 (one way) which means the cone should be able to do 17 mm peak to peak movement without causing mechanical damage.

You don’t list the Xmech (AKA Xlim) figure on the specification sheet.

If you are recommending the cone should not move more than 4-mm (1 way) safely on transients, which is only 8 mm peak to peak, you should revise the PDF showing Xmech as 4 mm and perhaps not bother listing an Xmax of more than double that which you seem to think may cause cone damage.

Art Welter

ra7 7th November 2011 11:18 PM

I had an issue with the Alpair 12 as well. Had them breaking in for a few weeks and they developed stress fractures on the cone. FWIW, no other driver I've owned has done this (Jordans included). I promptly returned them and got my money back.

Who wants to to worry about blowing the drivers while turning it up? To each his own.

Edit: Agree with Art above. The big attraction of the MA line and the Jordans is the large X-max, which in the case of the Jordans is not out of line with the specs.

dainrobert 7th November 2011 11:45 PM

What would be a safe threshold power level to feed the speaker? What would be the upper limit of output SPL for extended periods? I intend to run these off a small tube amp to play soft music and vocals, but I do expect to get at least six years of service form such an investment!


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