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-   -   CHR-70 GENERATION 3 - COMING SOON (http://www.diyaudio.com/forums/markaudio/184372-chr-70-generation-3-coming-soon.html)

markaudio 4th March 2011 02:24 AM

CHR-70 GENERATION 3 - COMING SOON
 
3 Attachment(s)
Hi Guys,

The CHR-70 is Markaudio's most successful driver in terms of volume sales both for DIY and OEM applications. To date, there are some 34,000 CHR variants on the planet serving various applications. The driver was conceived on the back of a cigaret pack in a restaurant. An "entry level" practical full-ranger, to be an antidote to the looming financial crisis, my expectations for this driver were modest at the time. Well guys, it worked better than any of us anticipated.

The new Gen 3 driver will depart from previous models in several key areas so I'll start by covering detail changes to the frame.

Following up on your feedback, I've introduced allot of changes to the frame's design and construction. So here goes:

1 - The frame dimensions remain the same, so the new driver is backwards compatible for those that want to swap. The only slight change will be the mounting thickness. This may increase by around 0.5-mm. There's a 0.3-mm X 0.3-mm bump ridge built into the frame's edge to aid better sealing into cabs.

2 - The torsional stress load resistance is increased by 220%. Effectively this frame much stiffer than the previous model. This is achieved by increasing the thickness outer side wall and introducing a second re-inforcement ring on the leg radii.

3 - Magnet assembly (motor) to frame location. The traditional method for fixing the magnet assembly (motor) is either rivet or by screws. The better makers will also apply a beed of glue to act as an air seal between the magnet assembly (motor) and frame. Its a poor air-sealing solution, nor is it a 100% reliable method, but its cheap to do so cost-down is the main reason why this method remains in service. The assembly workers have to be good at controlling the glue machine. Any errors and glue goes all over the frame and motor chamber. The worst is the point where the worker has to align the frame to the motor mounting. This has to done quickly before the glue sets. Finding the screw location holes without disturbing the ring of glue is as art and takes ages to get the workers trained up. Even so errors happen, especially on moving assembly line! I've always loathed this part of the driver build. Its one of the reasons you'll see me physically standing over the assembly line constantly checking. It drives me nuts and is a drain on my time that ought to be used more productively on development.

So, the CHR-70 Gen 3 is the first driver to receive a Polychloroprene (CR - Neoprene) seal rated at + 10 Bar @ 2 to 170 Celsius. Pneumatics are part of my old engineering stamping ground so I've been very picky on this aspect of the frame re-design. The O ring will protrude out from its frame location by 0.5-mm (+/-0.05mm), having elastomeric properties that will 100% ensure a crush resistive frame/magnet assm. (motor) fit. Now the whole magnet (motor) assembly can be made separately and one-action fitted onto the frame (thank the gods :D:D:D).

4 - The front face of the new frame is up-graded to the same finish as on the Gen 2 Alpairs. Logos have been added top and bottom. Overall, there's a more "pro" look to this new CHR-70

That's it for now, more to follow.

Cheers

Mark.

Lerg 4th March 2011 03:14 AM

I still have gen 2 drivers sitting in the box waiting to be dropped into an enclosure.

You mention that these new drivers can swapped into places where the old driver fit. Does that mean that the depth will be the same or will it mean modifications are needed for a cabinet brace? Not at all a big concern for me, I am just curious as to how backwards compatible you plan on these being.

I look forward to more details, and I also look forward to actually hearing some of your drivers in action instead staring at cardboard boxes.

markaudio 4th March 2011 03:20 AM

Quote:

Originally Posted by Lerg (Post 2490627)
I still have gen 2 drivers sitting in the box waiting to be dropped into an enclosure.
You mention that these new drivers can swapped into places where the old driver fit. Does that mean that the depth will be the same or will it mean modifications are needed for a cabinet brace? Not at all a big concern for me, I am just curious as to how backwards compatible you plan on these being.

I look forward to more details, and I also look forward to actually hearing some of your drivers in action instead staring at cardboard boxes.

Hi Lerg,
The recess depth on the new frame should work out at 0.5-mm more than the Gen 2 drivers. For 99% of builds, this small change won't affect the final fit. I am working on a EVA seal that will bond to the back of the frame. I'll announce this feature soon.
Thanks
Mark.

AEIOU 4th March 2011 04:03 AM

Nice
 
How soon will it be available? And is it going to cost (significantly) more than the generation 2?

markaudio 4th March 2011 06:17 AM

Quote:

Originally Posted by AEIOU (Post 2490669)
How soon will it be available? And is it going to cost (significantly) more than the generation 2?

Hi AEIOU,
Around end of next month. Price will be close to the Gen 2 model, a few bucks difference only.

Cheers
Mark.

Rullknufs 4th March 2011 06:21 AM

Seems like a badass driver to me, hehe ;)

ttan98 4th March 2011 12:17 PM

Mark,

What is the new SPL remains unchanged at 84.5dB? I am look for higher spl(e.g. 88dB) full range drive that is cheaper than Alpair 10.2.

markaudio 4th March 2011 12:30 PM

Spider location for the new CHR-70
 
1 Attachment(s)
Hi Guys,
Next installment: Power Handling - The spider to coil location.

Take a look at the attached pic and you'll see 4 drawings for the spider to coil location type. At the moment, Taniguchi san (Ex Fostex) and I are working the issue of power handling in relation to the connection type for the back of the power-train. I'll go through them as the offer different choices of power-train performance.

No. 1 - Is the design I tend to favour but as can be observed, the "green" glue surface that bridges from the internal edge of the spider onto the side of the coil body is minimal. Great for reducing mass but runs a larger risk of joint failure under load.

No.2 - Is the first step towards increasing the connective surface area between spider and coil. You can see the slight "crook" in the last part of the inner spider. This gives us a clear indication level to set-up the glue machine.
This design will add some mass (yet to be calculated).

No.3 - Further increases the connective surface area but also the mass.

No.4 is a design favoured be Taniguchi san. It does give us a larger connective surface area without the need for increased glue volumes, thus mass can be better controlled on this part of the power-train. However, there are some challenges with this method. The first is making sure there is sufficient space for the glue to be applied in-between the sides of the spider and coil. This can be done but may induce an increased assembly fail rate. The second, possibly more critical is the stress point near the inner edge of the spider. We'll have to carefully evaluate the spider material for such a high stress point loading. Taniguchi san's remarks on the drawing indicate a preference for Conex. I'd rather go for some of the more advance cross-cotton weave materials as they offer less mass while their compliance may have greater potential than Conex. The limitation for cotton is the moulding. It may not be possible to achieve the profile as indicated on No. 4 of the drawing.

So chaps, in many ways, this is over to you. We can use Conex to make the spider but the T/S will likely change. For example, we might see SPL drop of up to 2dB, but the rating could be potentially raised by an additional 3 watts.

Ummmmmmph. Any opinions?

Thanks

Mark.

markaudio 4th March 2011 12:41 PM

Quote:

Originally Posted by ttan98 (Post 2490998)
Mark,
What is the new SPL remains unchanged at 84.5dB? I am look for higher spl(e.g. 88dB) full range drive that is cheaper than Alpair 10.2.

Hi TTan,
Good question. Worth you reading my latest post as its very timely.

If you want more SPL, them something else has to go. That will be power-handling. To get a CHR up to 88dB means making a short coil so bass and F range will also be more compromised. By how much, can't say at this stage.

Cheers

Mark.

markaudio 4th March 2011 02:06 PM

Front end change
 
1 Attachment(s)
Hi Guys,
The next change you'll notice when the CHR-70 Gen 3 is launched is the change of dust cap.

This Gen 3 driver will inherit a cap mounted direct to the coil rather than be glued to the cone like the previous generation. Attached is the line drawing for the new cap. This modification completes the CHR/P and Alpair model line-up as all these models now have the Multi-form cone technology and caps that directly fit to the coil.

Depending on the coil selection, we anticipate a slight reduction in moving mass, an increased high-range response and greater dispersion. The maximum cone surface area will be exposed for full profile emittance.

The look of the driver will likely be significantly different with the advent of this new compact cap.

Cheers

Mark.


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