CHR-70 back mount - diyAudio
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Old 24th October 2011, 09:42 AM   #1
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Default CHR-70 back mount

I have a couple of CHR-70 (bought a couple of years ago). I wan't to mount them from the back so inly the cone is visible.

Are their any issues I should consider?

1: A hole og 75 mm will only expose the cone, will there be any audible diffraktion noise from the cabinet (the hole will be routed to have minimum front plate thickness where it will meet the cone).

2: Should I make the hole bigger and expose the rubber surround as well?
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Old 24th October 2011, 05:38 PM   #2
chrisb is offline chrisb  Canada
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Quote:
Originally Posted by Kjeldsen View Post
I have a couple of CHR-70 (bought a couple of years ago). I want to mount them from the back so only the cone is visible.
sorry, but I have to ask, WHY? - Mark has gone to great effort with the CHP/CHR /EL70, Alpair 6 and 7 (without extra ring) to design a low profile mounting bezel with minimum diffraction signature. They work best when rebated for flush mounting.


Quote:
Are their any issues I should consider?

1: A hole og 75 mm will only expose the cone, will there be any audible diffraktion noise from the cabinet (the hole will be routed to have minimum front plate thickness where it will meet the cone).
yup, diffraction would be a big big issue

Quote:

2: Should I make the hole bigger and expose the rubber surround as well?
Yes, at the very least you want the hole to expose to the edge of surround/frame juncture, and chamfer or radius the front of opening as well. Of course, you'll then have to worry about having sufficient core of material in front panel to use the stock screw mounting holes - you might need to use something like a sink mounting clip.
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Old 24th October 2011, 06:11 PM   #3
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Why? - it looks way better. I'm doing it right now with some tang bands, but the surround is not inverse here so I guess they behave quite different. Here I have no problem with diffraction. I hoped someone have tried this, but apparently not.

It's quite simple to make a test baffle, so I will do that, and report back.
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Old 24th October 2011, 06:37 PM   #4
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For rear mounting you want to champher the front cutout, and this is a good place to use a piece of aluminum, or at least rebate the inside so that the thickness is thin where the driver front sits. If one rebated the inside so that the back of the bezel was flush with the inside of the baffle a number of large fender washers could be used to hold the driver in place.

Hole should be the size of the outside edge of the active part of the surround, and you will likely need an appropriately thick piece of closed cell foam to fill the small gap between where the surround is glued and the back of the baffle.

dave
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Old 24th October 2011, 08:24 PM   #5
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thanks. good ideas here.

With my tangbands I have routed the cut out, and again a wider hole, that just fits the outer measures of the gasket. Now I have full control so that the unit don't slide. From the back I push it on the magnet, so it sits tightly in the cabinet - no screws needed.

The inside will be rebated as I mentioned (I just didn't know the right word)
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Old 24th October 2011, 11:39 PM   #6
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Hi Kjeldsen,
Chris B is correct in that your back mount design does run the risk of producing a "tunnel" effect. Depending on the thickness of the front baffle, some restriction of dispersion may result. Usually such effects will be audible, a slightly muffled sound is the most noticeable difference.

Take a look at the illustration. Most Full-Range driver's emittance is limited by the use of top mounted front suspension and deeper cone profiles. These traditional design characteristics are easier to manufacture, reducing the cost of production. The Markaudio designs consist of lower profile cones and use a under-hung front suspension to avoid the restriction posed by top-mount types. Markaudio designs produce a wide dispersion characteristic.

Should you wish to continue with rear mounting the drivers, its best to follow Chris's and Dave's mounting advice.

Thanks
Mark.
Attached Images
File Type: jpg dispersion-illustration.jpg (80.2 KB, 225 views)

Last edited by markaudio; 24th October 2011 at 11:44 PM.
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Old 25th October 2011, 07:20 AM   #7
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Thanks - I have modified the image.
The top is my Tangband W4-1320B and the black is the front baffle.

The Markaudio: Should I keep the baffle "under" the green lines as shown? Left is as planet10 shuggests. The right is with the rubber surround covered. I know that the surround is an active part of the speaker, but is the radiating sound from the surround desirable?

dispersion-illustration[1].jpg
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Old 25th October 2011, 08:25 AM   #8
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Quote:
Originally Posted by Kjeldsen View Post
Thanks - I have modified the image.
The top is my Tangband W4-1320B and the black is the front baffle.

The Markaudio: Should I keep the baffle "under" the green lines as shown? Left is as planet10 shuggests. The right is with the rubber surround covered. I know that the surround is an active part of the speaker, but is the radiating sound from the surround desirable?

Attachment 246333
Hi K,
For the CHR-70, its best not to impede its wide dispersion performance. Try to keep the front baffle as thin as possible where close to the driver's front suspension. Shaping the front baffle around the front of the driver is desirable (below the green line if possible). Please don't cover the front suspension.
Thanks
Mark.

Last edited by markaudio; 25th October 2011 at 08:36 AM.
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Old 25th October 2011, 08:59 AM   #9
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Ok thanks. How wide is the dispersion? I havn't seen any other measures than on axis.
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Old 25th October 2011, 09:25 AM   #10
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Quote:
Originally Posted by Kjeldsen View Post
Ok thanks. How wide is the dispersion? I havn't seen any other measures than on axis.
Its wide

Go to : Markaudio | Temporary Page

Download the PDF

Thanks
Mark.
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