New CHR-70

[markaudio]

Hi Guys

Here’s the new CHR-70. I’ve spent some time working on this driver, mainly tweaking the response in the 10K to 15K range since the old model had a a peak around 12K, (small in terms of bandwidth). The new CHR-70 benefits from the use of my new Multiform cone and cap production method. I’ve mentioned this on other threads so will summarise (as per the pic).

New Multiform Cone and Cap.
The traditional method of making metal cones is to spin the metal sheet while at the same time, push the material on to a former. This work is done by hand. I did make a machine that ran the metal on to the former. This removed some of the variation but I still wasn’t satisfied. So, with help from Japan, I re-tooled, brought in some new machinery and now use all CNC controlled production for these cones and caps. All the cutting, forming and shape adjustment is now the hand of the computers. There a seven processes to go from a raw sheet to the finished cone.
For those who have the old model, if you fancy buying the new CHR, you’ll see the difference by comparing the old to the new cones and caps. You'll notice the better tight fit of cap to cone and the improved smoothness of the cone's contours.

Revised Spider
I’ve reshaped the spider to improve on LF oscillation. The driver’s Fo is lowered a couple of Hz. The main benefit of the improved spider is in the production tolerance. The old spider was made to a stiffness rating of 1.3/50g @ +/-1.5, better than most commercial drivers. Now we are making to 1.4/50g @ +/-1.2. The result is all mass production drivers will be close matched. Having tested 32 units pulled off the end of line at random, all came within +/-3Hz Fo of each other.

Mounting Holes.
I’ve increased the size of the mounting holes (now 4.1-mm) to suit M4 wood screws. All these new drivers come with black powder coated M4 Hex wood screws. Once you’ve made the driver cut out in your cabinet, offer up the driver, use a 4-mm drill bit in each hole, ONLY to mark the centre. Having marked the drill point, remove the driver and drill with a 2.8-mm wood bit, job done! I’ve also increased the thickness of the seal, it’s now 2-mm, so works better.

Available in 2 new colours, Brushed Metal and Champagne (I didn’t invent these posh names but they do sound nice).

Have Fun!!!!

Mark.

[Geek]

Hi Mark,

Thanks for your great work with these. They are truly a spectacular driver

Originally Posted by markaudio

I’ve increased the size of the mounting holes (now 4.1-mm) to suit M4 wood screws.

THANK YOU!!!!!!!!!!!!!!

I won't have to drill out any more holes to fit the #6 screws used on this side of the pond

Cheers!

[markaudio]

Hi Gregg,
Yep the screws make easy work, a standard M4 Allen key (I think some call them Hex keys?) does the job. I always recommend winding the screws in by hand so as not to over-tighten the frame. Then a gentle further tighten after a couple of weeks.

Mark

[markaudio]

OK,
Here's the graphs, installation pic and parameters below.
Re the installation, It's OK to make a 103-mm internal hole, if you can cut accurately.

Cheers,

Mark.

Fo= 68 Hz
Sd= 50.02 Cm²
Vas= 4.2 Ltr
Cms= 1.167m M/N
Mmd= 4.476 g
Mms= 4.681 g
BL= 3.092 T·M
Qms= 1.997
Qes= 0.754
Qts= 0.547
Levc= 0.024 mH
No= 0.169 %
SPLo= 84.5 dB
xmax= 4.5-mm
Pwr= 20 Watts

[Scottmoose]

Nice one Mark.

For reference guys, I can't speak for anyone else's boxes, but the Lotus cabinet does not require any changes, although this is essentially, a new driver. Beautiful work on the cone in particular.

[gapmedia]

Hi Mark,

Do you have a price for the drivers yet?

Good steel M4 T-Nuts/Blind Nuts soooo much easier to find than M3 - Yaaaah! (In Australia anyway) If there is enough wood between mounting hole and cutout for support I guess!?

Looking forward to trying these in your Pensil70 design, I assume they will work in it okay?

regards,

Simon

[markaudio]

Hi Simon,
Good to hear from you.
I'll email tomorrow with details. No problem with the screw size in the cut out.
Sure, they will be fine in Pensil70.
Cheers,
Mark.

[gapmedia]

Hi Mark,

I'm really happy with the Pensils, I have been waiting to try the new drivers before taking the next step. Good reaction from those (friends) who have seen and listened to them so far. Convoluted foam really cleaned up the bass on the second (dark stain) pair built, and also seemed to remove the slight metalic sheen noticed on some (only some) voices. Maybe the drivers 'aging nicely' or the foam reducing back waves that were causing 'ringing' in the cones?

regards,
Simon

[markaudio]

Hi Simon,
Yes the foam most likely is doing a good job. Any wave returning to the rear of the cone is not good. It's important to minimise any potential cancellation effects from inside the cabinet. Looks like you've done a good job.

Maybe you'd like to start a thread in the Full Range form? I'm certain there's allot of guys who'd like to know more about your experiences with CHR's and Pensil70

Cheers,

Mark.

[markaudio]

Hi Simon,
Or feel free to start a Pensil70 thread in this Markaudio section.
Cheers,
Mark.