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markaudio 1st March 2014 12:57 AM

CHS70 - Frame development - Feedback please
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Hi Guys,

Please take a look at the attached pic. It illustrates a frame currently under development for Koizumi in Japan. The pic shows chassis designation: CHS70-3.

Koizumi's brief is asking me to design a light chassis (frame) with a thin wall front mounting. Many Japanese Diyers like to surface mount their drivers instead of cutting recesses, so this frame has a current front mounting rim thickness of 3.75mm (+/-0.02mm). The brief also calls for a 12% mass reduction over the existing CHR70 frame while maintaining the same rigidity specification. Changes to the mix of the polymer frame material includes a new fibre based hardener to help maintain the rigidity requirement.

This CHS70 prototype has an O/D currently set a 121mm. It also includes direct insert semi-locking pin connectors. The pin length is extended to minimise frame melt when soldering. A detachable connector for the lead wires is also under development. This would facilitate connector extraction from the frame for remote cable soldering. Shorter pins maybe deployed as most Japanese Diyers use press fit spade connectors. Note the baffle side of the front rim is solid and flat, unlike the current CHR/P70 which employs box section reinforcement.

The chassis front rim the motor mount is a new arrangement. Its a pentagonal arrangement, 5 legs evenly spaced. The front mounting arrangement also changes to 5 X M3 surface re-enforced screw holes. The baffle hole cut-out diameter in relation to the location of the mounting screws is currently set at +5mm, which should cleave plenty of wood to avoid splitting when fitting the driver.

The actual driver (power-train) is in development for Koizumi and 3 other Japan companies so the new units will be destined for those locations. However, the rights to this technology remains with Markimage Limited (Markaudio brand owner), so depending on your feedback, it could be made available for use by end-users in locations outside Japan.

My questions are:

1 - Would you all like a thin wall front mounting frame of CHR/P70 size?
2 - Will it attract criticism for being "thin"?
3 - Any other thoughts?


Squeak 1st March 2014 03:45 AM

I love the thin front frame!
I think one of the things holding many people back from using your drivers is the trepidation for routing the hole. It has to be perfect to look good and you don't have to be that much off for having trouble with the screws not catching the wood properly.

People wanting to do the routing job will have no trouble doing it anyway, thin or thick frame.

Also the hollow frame, even with the gentlest of hands turning the screws, flexes. If I hold a credit card edge on, on the frame over the part where the screw hole is, I can see more light shining through after tightening the screws.

And yes, I'd very much like to see this in the rest of the world.

About other thoughts.
I know you have said no to this before. But I really think you should do grilles.
People will do them themselves anyway or buy some generic ones (that normally looks real homely).
Why not make easy profit and do it properly and nicely?
A thin magnetic frame with a thin fabric grille should have minimal impact on sound and dispersion.

lorienblack 1st March 2014 05:21 AM

+1 for a purpose made grill. I don't like them particularly, but speaker cones are irresistible to children.

I may be in a minority, and you may laugh, but a grill that could deal with projectiles would help me sleep better.

pk2carlos 1st March 2014 08:27 AM

I also like thin wall mounting frame. It leaves enough wood behind for the screws so you don't necessarily need double or thicker front side of the box.

markaudio 1st March 2014 09:12 AM

Hi Squeak, Lorien, PK, guys,
Thanks for your posts, hope more will follow. Early replies suggest its positive for this frame.

I'm sort of a bit nervous about how the majority might receive a thin poly frame. Its no drama in Japan as they've taken well to the frames we make. The culture towards polycarbonate materials in Japan and Asia generally is its "modern" and "up to date" etc. For Western culture, there's still a "love thing" happening for heavy metal. Or am I being too pessimistic?

Re the covers/grilles, I don't recollect saying "no", as such, but suggesting its a question of commercial viability. I'm not certain there would be enough sales to pay for tooling-up, mould(s), pressing and/or forming, then making-up and packaging grilles. I did make acrylic covers many years back, quite stylish with magnets attaching to the screw heads, worked well. But the never took off. I had to dump quite a lot of stock when I moved my HK warehouse some 5 years ago.

I'll have another think on the grilles....................:idea:

PS..Lorien.......fab work on the twin Alp7 monitor. Well done!


chrisb 1st March 2014 09:24 AM

Just a personal fetish I guess, but I prefer "grilles" to be part of the aesthetic of the enclosure rather than the driver - and to my thinking the former method can allow for less acoustic interference than the latter. I keep on harking back to the frameless "socks" that Linn used on Kaber and Khelidh of the 90's (always was a sucker for elastic "stay-ups")

anyways, thanks Mark as always for sharing and soliciting feedback -

markaudio 1st March 2014 09:37 AM

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Originally Posted by chrisb (Post 3838363)
Just a personal fetish I guess, but I prefer "grilles" to be part of the aesthetic of the enclosure rather than the driver - and to my thinking the former method can allow for less acoustic interference than the latter. I keep on harking back to the frameless "socks" that Linn used on Kaber and Khelidh of the 90's (always was a sucker for elastic "stay-ups")

anyways, thanks Mark as always for sharing and soliciting feedback -

Hi Chris,
Yes, making up a simple frame and stretching some rather sexy black "see-through" (ummmmph...) over it might have a certain appeal;).

I also must admit , I'm a sucker for the grilles on my beloved 2 mint pairs of Victor SX500's - see pic.

As always, cheers for yours and Dave's encouragement. Its appreciated.


JoeyGS 1st March 2014 10:51 AM

If a grill is to be designed would it be ok to just use a good magnet and attach it to the driver screws? The grill would have the magnet and the magnet will stick to the driver screw heads....... Just a thought.....

Scottmoose 1st March 2014 01:07 PM

I've no issue with the thinner frame; from a usability perspective it would be no bad thing, especially for those with limited woodworking tools and / or skill. It will no doubt attract criticism on & off for being 'cheap plastic', but then, the current models sporadically receive similar comments too -universal popularity isn't going to happen so I'd probably just accept this & carry on. Some comparative test data between the polymer & a popular steel or aluminium grade employed for fames might give you something to point to in support of what it is & why it's there. It wouldn't alter the views of those who have made up their mind in advance, but it's something. Chalk up another one re the grills, assuming it's not going to drain resources from other projects. Useful they would be, but DIYers can make grills when necessary. They can't make drivers. Well, not very often anyway.

McDark 1st March 2014 01:18 PM

Mark, your drivers are not for everyone anyway. Front mounting metal frames look outdated and for me they always been just ugly. Properly made pc frame could look and feel much better and modern not only in Asia that's for sure. Thanks for valuing our thoughts, you are the best!

+1 for magnetic grilles BTW. For me personally good looking grilles was always most challenging part of speaker project but children make them necessary.

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