Hi,
I had a cracked basket around the screw hole in one of my Markaudio Alpair 7.3 although I didn't over-tighten the frame (driver was screwed in by hand and the mounting surface was flat). Please see the picture attached.
There was some helpful discussion in the Markaudio forum how to handle these obviously very fragile drivers and how to fix cracks but that thread was deleted by Markaudio.
As there seemd to be others with the same problem I thought it would be helpful to re-post some information about this issue and how to repair the damage.
Mounting the driver:
"Make sure you drilled pilot holes and pre-thread them prior to installation. Nip up the installation screws to feel a slight tightness. Eyeball the flatness of the frame front. If you're starting to visually distort the frame, you're applying too much torque. I don't recommend using a power driver. Do it be hand, you'll feel the increase in resistance when close to tightening." - mark audio
"1. Drill pilot holes the full diameter of the screw shank.
2. Run a screw through each hole before mounting the driver
3. With the driver in place, torque each screw just up to the point where the seal starts to compress and the driver frame starts of visibly move. You will feel the resistance in the screw driver at this point.
The worse thing you can do is run the screws in with a power driver without the benefit of pilot holes." - Bob Brines
Repairing cracket drivers:
"With the driver removed, turn it face down (DON'T touch the cone as you do this). Gently peal back the seal and apply a small amount of suitable plastic epoxy glue on the crack. Ideally, apply the glue to the inside of the frame where it can't be seen.
1- Test the glue on a non-critical are of the frame first. Check that it doesn't melt the composite.
2 - Apply a small volume of glue only.
Allow to harden and re-install." - markaudio
"I advise using an epoxy as its the industry standard adhesive formula for the strongest bond. Please check the glue makers instructions for material compatibility. Here's an example:
Epoxy Repair: Plastic - UniBond" - markaudio
I had a cracked basket around the screw hole in one of my Markaudio Alpair 7.3 although I didn't over-tighten the frame (driver was screwed in by hand and the mounting surface was flat). Please see the picture attached.
There was some helpful discussion in the Markaudio forum how to handle these obviously very fragile drivers and how to fix cracks but that thread was deleted by Markaudio.
As there seemd to be others with the same problem I thought it would be helpful to re-post some information about this issue and how to repair the damage.
Mounting the driver:
"Make sure you drilled pilot holes and pre-thread them prior to installation. Nip up the installation screws to feel a slight tightness. Eyeball the flatness of the frame front. If you're starting to visually distort the frame, you're applying too much torque. I don't recommend using a power driver. Do it be hand, you'll feel the increase in resistance when close to tightening." - mark audio
"1. Drill pilot holes the full diameter of the screw shank.
2. Run a screw through each hole before mounting the driver
3. With the driver in place, torque each screw just up to the point where the seal starts to compress and the driver frame starts of visibly move. You will feel the resistance in the screw driver at this point.
The worse thing you can do is run the screws in with a power driver without the benefit of pilot holes." - Bob Brines
Repairing cracket drivers:
"With the driver removed, turn it face down (DON'T touch the cone as you do this). Gently peal back the seal and apply a small amount of suitable plastic epoxy glue on the crack. Ideally, apply the glue to the inside of the frame where it can't be seen.
1- Test the glue on a non-critical are of the frame first. Check that it doesn't melt the composite.
2 - Apply a small volume of glue only.
Allow to harden and re-install." - markaudio
"I advise using an epoxy as its the industry standard adhesive formula for the strongest bond. Please check the glue makers instructions for material compatibility. Here's an example:
Epoxy Repair: Plastic - UniBond" - markaudio
Attachments
All very useful no doubt, but 'obviously very fragile' is a trifle exaggerated. I've had many pairs through here & never had a problem with frames over-stressing. There don't appear to be large numbers of people reporting failures either, so I think it's safe to conclude
a/ There are not in fact very many failures, and
b/ You either did not install it correctly, or possibly were unfortunate & got a frame where a weakness existed. Such things can occur in all mechanical appliances.
Since the frames are a polymer type, some mechanical sympathy / common sense is required when mounting to the baffle -opposite screws / bolts and gradual tightening (not over-torqueing) is needed. This is not difficult, since it really should apply to all drivers (or anything akin -light-switch fittings, socket covers &c.) in any case.
a/ There are not in fact very many failures, and
b/ You either did not install it correctly, or possibly were unfortunate & got a frame where a weakness existed. Such things can occur in all mechanical appliances.
Since the frames are a polymer type, some mechanical sympathy / common sense is required when mounting to the baffle -opposite screws / bolts and gradual tightening (not over-torqueing) is needed. This is not difficult, since it really should apply to all drivers (or anything akin -light-switch fittings, socket covers &c.) in any case.
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That's good to know but on the other hand most people probably never check once the speaker is mounted.
All I can say is that I did not over-tighten and the mounting surface was flat. I have a couple of other drivers made out of plastic and they are all ok. The other Alpair is also ok. It's just this one driver and one screw hole.
I agree. Guess the risk of cracking comes with the use of plastic as a basket material. A metal basket is probably more forgiving. The surround smooths out any small bending. Of course it depends on the type of metal used. Some might crack easily too.
Come on, I know a small crack around a screw-hole must be annoying, but that is not called for. What evidence have you to say that there is a widespread frame cracking problems with these drivers (or any others using a polymer frame for that matter -the very popular Vifa models are an obvious example)? Even a couple of dozen examples wouldn't be statistically significant when you think of the thousands of units out there with polymer frames from various manufacturers. If there was a widespread problem, we'd know about it. And so would the manufacturers. And they'd do something about it at a rate of knots for obvious reasons.
To an extent that can be true, but it varies significantly depending on the polymer type employed, the design of the frame itself and a host of other factors. Very hard polymers can be brittle, softer types less so. Since there appears to be no evidence to suggest there are widespread problems with the MA, Vifa etc. units, they appear to have struck a good balance on this front to date.
Re metal, it can be more forgiving on this score, but it's not devoid of potential problems either. Again, it depends on metal type, frame design, production method &c. Some cast types can let go for instance. I've not had a failure myself, but I've seen a handful of examples equivalent to the shot above, or with a crack over the frame itself. These things happen, and on the whole, the industry doesn't seem to do a bad job in this regard (leaving aside opinions / preferences on the merits of various frame materials aside). Speaking in general terms, any kind of over-tightening when mounting a drive unit is best avoided since it can warp the frame, which may then force the moving components out of alignment. You find this may particularly affect cheaper stamped types, but it's not exclusive to them alone. And so on. Clark Blumenstein for e.g. makes quite a deal on his site over the care with which the drivers on his commercial models are mounted / tightened (mostly Fostex based). Fair play. The pioneers of audio were big on decoupling drivers from baffles (granted not primarily to avoid failures but for acoustics -still, it does avoid some stresses) . Feastrex (goodness knows what's happening there since apparently their designer / manufacturer has left the company) liked rear-mounting via a long bolt & no direct affixing to the baffle via the front of the frame (same). And so on. It's an interesting area.
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spekr, Scott,
Might I suggest that a slightly misaligned screw hole can be another potential reason behind frame stress? The screw doesn't go in straight enough and can put extra pressure on the frame while being screwed in. For such a case you probably would not need to over-tighten too much.
Hope you have been able to repair the crack and have things up and running!
Might I suggest that a slightly misaligned screw hole can be another potential reason behind frame stress? The screw doesn't go in straight enough and can put extra pressure on the frame while being screwed in. For such a case you probably would not need to over-tighten too much.
Hope you have been able to repair the crack and have things up and running!
That's a possibility; it's very easily done (especially for the likes of me
) & not particularly obvious when trying to identify the source of problems. I wouldn't 100% rule out a minor flaw in the frame itself -these things can happen on occasion, though they tend to be very rare in reasonable production scales. That's why all those TVs, toasters, cars, drive units etc. are so reliable. Anyway, hopefully the small crack in the OPs driver is now fixed -the first post suggests it is, which is good.
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Hi Guys,
Please take a closer look at Spkr's pic of the frame damage. Note both the frame front face and its rear edge are uniform. There is no material-shape deformation on this component. Manufacturing defects on these components are visually obvious. The plastic composite deforms (goes out of shape) and out-of-tolerance units get rejected during quality control. Fail rates are extremely low averaging 3 frames per thousand. The proof is in the public domain. There are few references to failures over the years against the hundreds of thousands of these frames in use.
What can be observed from Spkrs pic is an irregular crack, typical of a stress load fracture. This can only be caused by excessive force being applied. Possibly the pilot hole could have been misaligned, although an end user can normally feel the additional tightness when screwing down. In any event, to force a relatively elastic composite material to break in this manner is usually down to the installation method.
It is fair to say that more complex moulded frames require installation care. Pressed steel frames can be delicate, as their bending resistance is nominal. Once taken out of alignment, they rarely spring back into shape. Die-cast has more compressive strength but its brittle fracture tolerance is low, once cracked its gone. Essentially, most smaller frames will usually be weaker than larger substantial units.
The best advice when installing any small driver (under 6.5") is to take time to correctly align pre-thredded holes and go easy when screwing down. Don't use power drivers. Use a hand tool to feel the increase in tension as the screw is close to the nip-up stage. Nip up means "nip-up". Don't be tempted to switch into Brutus mode. I freely admit to cracking a few myself (die cast and mine) over the years, in haste mostly between testing.
I had hoped to successfully resolve this situation with Spkr, but it relies on accepting a degree of responsibility for one's actions; Rather than posting full-force with a default finger-pointing, blame game agenda. Even so, the initial thread in the Markaudio section remained sufficiently open to give Spk time to receive help in the way of a simple frame fix, despite his efforts to damage the driver's following.
Thanks
Mark
Please take a closer look at Spkr's pic of the frame damage. Note both the frame front face and its rear edge are uniform. There is no material-shape deformation on this component. Manufacturing defects on these components are visually obvious. The plastic composite deforms (goes out of shape) and out-of-tolerance units get rejected during quality control. Fail rates are extremely low averaging 3 frames per thousand. The proof is in the public domain. There are few references to failures over the years against the hundreds of thousands of these frames in use.
What can be observed from Spkrs pic is an irregular crack, typical of a stress load fracture. This can only be caused by excessive force being applied. Possibly the pilot hole could have been misaligned, although an end user can normally feel the additional tightness when screwing down. In any event, to force a relatively elastic composite material to break in this manner is usually down to the installation method.
It is fair to say that more complex moulded frames require installation care. Pressed steel frames can be delicate, as their bending resistance is nominal. Once taken out of alignment, they rarely spring back into shape. Die-cast has more compressive strength but its brittle fracture tolerance is low, once cracked its gone. Essentially, most smaller frames will usually be weaker than larger substantial units.
The best advice when installing any small driver (under 6.5") is to take time to correctly align pre-thredded holes and go easy when screwing down. Don't use power drivers. Use a hand tool to feel the increase in tension as the screw is close to the nip-up stage. Nip up means "nip-up". Don't be tempted to switch into Brutus mode. I freely admit to cracking a few myself (die cast and mine) over the years, in haste mostly between testing.
I had hoped to successfully resolve this situation with Spkr, but it relies on accepting a degree of responsibility for one's actions; Rather than posting full-force with a default finger-pointing, blame game agenda. Even so, the initial thread in the Markaudio section remained sufficiently open to give Spk time to receive help in the way of a simple frame fix, despite his efforts to damage the driver's following.
Thanks
Mark
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Mark, "posting full-force", "finger-pointing" and "blame game agenda"? That's a rather distorted depiction of what I ever did and said. I just stated the facts, didn't blame anyone, didn't point fingers. You follow me here, edited my posts and even deleted a whole thread. Let it go. Everybody is entitled to have an opinion. Even me.
Like these 7.3 and recommend others try out very valueable for the money, but.....observe.
Because they have special practice when mounting and some have failed in this mounting, themselves as author to the mistake and thereby to take own responsibility for failure, now seems procedure that don't question if failure in the frame could be reason, yourself are wrong seems to be practice (the devices personal handled didn't have a note in package about special practice for mounting, personal needed to active use the web for this info, though don't know if info is missing inside package at other places).
If trying to analize devices by measuring, then if you don't get plots as published for the device or by a user certified special for this task, your results or gear are wrong.
Put these in one of the suggested boxes for audio reproduction and sometimes even suggested used in studios for prodution, now if you don't like the sound as others, do questioning sound or neutrality, do questioning why it sometimes reveal more musical details than reference gear or good headphones, yourself and results are wrong.
Try share your experience where these are strong, do make compromise, or they weak. Don't, only share about their strong side, your experience other sides are wrong, tried regulated or sometimes deleted as never happened.
Again yes i like these 7.3 and really recommend others try out either diy or ready made speakers, guess you figure out i don't agree above is good.
Experience A10.2...
Do i have cracks, yes three, the two of them located close to mounting hole, the third in middle of nowhere.
Do i mount them as suggested practice, yes.
Do i question my mounting, yes seen afterwards maybe my pilot centering could be little misaligned for both drivers, but preasure at screw very light.
Did both drivers crack, no only the one.
Did they crack when mouting, no it happened after about a year, would say suddenly it was there, first the two cracks little later third one.
Do i think it's production failure in frame, chance could be because the other driver mounted and treated exactly same way.
Did i RMA, no, thought too long time ago from buying to fight responsibility.
Did the package hold mounting practice info, no, my luck active finding the info this domain before mounting, else i had tightening as in metal and all 6 holes probably had been broken at day one.
Do i intend buy the brand again, sure.
Because they have special practice when mounting and some have failed in this mounting, themselves as author to the mistake and thereby to take own responsibility for failure, now seems procedure that don't question if failure in the frame could be reason, yourself are wrong seems to be practice (the devices personal handled didn't have a note in package about special practice for mounting, personal needed to active use the web for this info, though don't know if info is missing inside package at other places).
If trying to analize devices by measuring, then if you don't get plots as published for the device or by a user certified special for this task, your results or gear are wrong.
Put these in one of the suggested boxes for audio reproduction and sometimes even suggested used in studios for prodution, now if you don't like the sound as others, do questioning sound or neutrality, do questioning why it sometimes reveal more musical details than reference gear or good headphones, yourself and results are wrong.
Try share your experience where these are strong, do make compromise, or they weak. Don't, only share about their strong side, your experience other sides are wrong, tried regulated or sometimes deleted as never happened.
Again yes i like these 7.3 and really recommend others try out either diy or ready made speakers, guess you figure out i don't agree above is good.
Experience A10.2...
Do i have cracks, yes three, the two of them located close to mounting hole, the third in middle of nowhere.
Do i mount them as suggested practice, yes.
Do i question my mounting, yes seen afterwards maybe my pilot centering could be little misaligned for both drivers, but preasure at screw very light.
Did both drivers crack, no only the one.
Did they crack when mouting, no it happened after about a year, would say suddenly it was there, first the two cracks little later third one.
Do i think it's production failure in frame, chance could be because the other driver mounted and treated exactly same way.
Did i RMA, no, thought too long time ago from buying to fight responsibility.
Did the package hold mounting practice info, no, my luck active finding the info this domain before mounting, else i had tightening as in metal and all 6 holes probably had been broken at day one.
Do i intend buy the brand again, sure.
As I've likely said before, I've built literally scores of speaker systems with almost every model of driver by Mark in the past 7 or so years - including the OEM EL70, EL66 and ERT6, and while Dave & I have managed to dent more than a couple of the metal cones (as have other folks), I've yet to crack a frame - either from over tightening, or physical abuse.
We could ride the blame-o-rama merry go round for weeks, but how about we get past that, and try to solve spkr's most immediate problem?
From a private conversation, I've been corrected on my earlier assumption that he was using them with the "optional" extra bezel ring. If it's not too late or difficult to modify the existing cabinet, or machining set up if not yet built, I'd imagine that repairing the crack with epoxy or even a CA adhesive, and attaching the outer ring per Mark's posted instruction should be more than adequate?
These are excellent drivers and deserve what I think is relatively little effort to effect their repair.
We could ride the blame-o-rama merry go round for weeks, but how about we get past that, and try to solve spkr's most immediate problem?
From a private conversation, I've been corrected on my earlier assumption that he was using them with the "optional" extra bezel ring. If it's not too late or difficult to modify the existing cabinet, or machining set up if not yet built, I'd imagine that repairing the crack with epoxy or even a CA adhesive, and attaching the outer ring per Mark's posted instruction should be more than adequate?
These are excellent drivers and deserve what I think is relatively little effort to effect their repair.
Thanks nice to know about TC9FD. Little funny you mention this driver because delivery service should have been here today delivering 2x those Vifa and a Dayton UMM6 microphone, last is intend to dig deeper in REW exercising
.You right probably hundreds or thousands have been mounted successfully.
Solve spekr's cracked frame yes, but after being deleted see underneath and by a uploaded photo seen by people out of physical range of the driver where treated and judged as an RMA case, where he just requested how to repair unless that first post yesterday was moderated (think title was), my understanding if he want to breathe and have an opinion, guess he has all information to repair, probably just need get tools for repair and to decide when.
Yes these drivers excellent.
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The way this went out of control IMO was directly after the initial post in the commercial section- he was jumped on by a few regulars who should know better and that just fanned the flames
Now its time to cool down, and wish Mark well with his upcoming treatment - hopefully everything has been explained and I personally have not had any problems with my 10P's
Now its time to cool down, and wish Mark well with his upcoming treatment - hopefully everything has been explained and I personally have not had any problems with my 10P's
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Quite right. What they did fits Mark's description of "posting full-force", "finger-pointing", "blame game agenda" to a T. Lesson learned, stay away from the Markaudio forum. They obviously have their own agenda over there. Having an open discussion is not part of it.
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Is the basket reinforced with glass fiber? The description of the TG9FD-10-08 says "glass fiber cone and rubber surround, and plastic basket". Telling from the picture the plastic around the mounting holes seems to be thicker when compared to the Alpair though (see attached picture)?
http://www.tymphany.com/files/TG9FD10-08 Spec Sheet Rev 2 2012-9-6 .pdf
Thanks nice to know about TC9FD. Little funny you mention this driver because delivery service should have been here today delivering 2x those Vifa and a Dayton UMM6 microphone, last is intend to dig deeper in REW exercising
Hope you post measurements of this driver as it seems to have a much smoother response on and off axis than the Alpair 7.3. Maybe in a new thread in the full range forum?
Attachments
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Not as far as I know. It's a fairly basic frame in a solid polymer -at least, the ones I've had here have been. Given the retail point, they can't realistically do more with it on that score.
X has posted many measurements of the TC9 (a unit I refer to above), many times, so plenty for you to look at already. A fine unit, but a very different driver to the A7 -significantly smaller, doesn't use any of the same materials and has completely different specs. & design goals etc., so comparing them will show that they are completely different, but nothing more profound than that.
X has posted many measurements of the TC9 (a unit I refer to above), many times, so plenty for you to look at already. A fine unit, but a very different driver to the A7 -significantly smaller, doesn't use any of the same materials and has completely different specs. & design goals etc., so comparing them will show that they are completely different, but nothing more profound than that.
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Maybe it's structurally better to have a solid basket and not the fragile looking fishbone-like structure of the Alpairs? I don't know, just a question.
Maybe having more mounting holes would also help? This one has 6 of them - http://uk.rs-online.com/web/p/speaker-drivers/7614280/
Well, the design goal for any full range driver should be smooth on and off axis response, low distortion levels, high SPL and wide low/high frequency extension. Now pick the trade-off you're willing to make. Unfortunately not much data is available to make an informed decision. Manufacturers don't provide that data, some even actively suppress such data because their marketing is based on customer beliefs and not on facts.
Don't understand your comment about "resonant sensitivity in the cone". A more dampened cone appears more desirable to me as it reproduces the signal more accurate. The "fine detail" you're talking about is distortion because it's not part of the original signal. It might sound better but that is a subjective criteria that should be better left to the discretion of the person creating a recording. If your goal is to make a recording sound good by chosing/designing a speaker that sounds good with that recording then you ultimately end up with as many speakers as recordings.
We're off topic now. Please take it to another thread if you want to discuss this further.
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