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Old 28th October 2011, 10:22 AM   #1
soren5 is offline soren5  Denmark
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Question Wide version of Classic GR dMar-Ken7.3

Hello,

I've got a pair of Alpair 7.3 drivers, which I was planning to put in the Classic GR dMar-Ken7.3 cabinets. I see that the 7.3 update only appears in the slim and not the wide version. I assume that I could change the internal bracing and place the driver on the ‘side’ and in this way make it a wide version like it’s shown in the previous model. As far as I can see the only difference between the old and the new cabinet is the port length – is that correct?

By the way, if I make a wide version of the Classic GR dMar-Ken7.3, could I then make the vent on the front or the back instead of the side, like it’s done on the Classic GR dMar-Ken10.2? Or perhaps I could replace the square vent with a circular tube?

Thanks and regards,
Søren
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Old 28th October 2011, 05:29 PM   #2
chrisb is offline chrisb  Canada
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Quote:
Originally Posted by soren5 View Post
Hello,

I've got a pair of Alpair 7.3 drivers, which I was planning to put in the Classic GR dMar-Ken7.3 cabinets. I see that the 7.3 update only appears in the slim and not the wide version. I assume that I could change the internal bracing and place the driver on the ‘side’ and in this way make it a wide version like it’s shown in the previous model. As far as I can see the only difference between the old and the new cabinet is the port length – is that correct?

By the way, if I make a wide version of the Classic GR dMar-Ken7.3, could I then make the vent on the front or the back instead of the side, like it’s done on the Classic GR dMar-Ken10.2? Or perhaps I could replace the square vent with a circular tube?

Thanks and regards,
Søren

well, in Dave's nomenclature, "GR" has so far implied "Golden Ratio" in terms of aspect ratio of dimensions ( i.e. 1.618 / 1 ) - along with mirror imaged off-center driver mounting, so within those constraints external dimensions could be adjusted - turning the boxes on their sides should be no problem

as for ports - provided the CSA and length are retained (or recalculated if necessary) their location could also probably be played with, but the near aperiodic performance of high aspect ratio slot ports and carefully damping enclosure walls are significant contributors to the smooth and extended LF roll-off of the design, so I'd be inclined to keep that

several years ago we did a simple test with a smaller box design - two pairs of enclosures otherwise identical except for the ports - one pair round and the other slots - even though the slots can be slightly more work (but nowhere near as fiddly as magnet nesting holey braces), we've used them almost exclusively since.


Dave could confirm that only the port dimensions (possibly only length) needed revision with the most recent revision to the Alpair7, and whether it applies to both magnet layers.
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Old 29th October 2011, 01:39 PM   #3
soren5 is offline soren5  Denmark
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Thanks for your comments Chris. The thing is that I'd like to have a clean look for the cabinet, i.e. no visible openings, so ideally I would have the port on the back of the cabinet.

Since Dave's updated version of the cabinet has a shorter port, I'm tempted to build a slot coming out on the rear side of the cabinet. I've made a sketchup drawing of my idea and attached it here (shown without back panel for better view).

The port length of the Classic GR dMar-Ken7.3 is 154mm. If I do the port on the rear I can get a length of 142mm, but considering that the last 90 degree angle would become part of the port, I guess I can add 15mm to that, making the total length 157mm, just 3mm longer than the original design.

Does this make any sense, or should I just stick to the orginal version and have the port on the side?

Thanks,
Søren
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Old 29th October 2011, 06:48 PM   #4
chrisb is offline chrisb  Canada
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Quote:
Originally Posted by soren5 View Post
Thanks for your comments Chris. The thing is that I'd like to have a clean look for the cabinet, i.e. no visible openings, so ideally I would have the port on the back of the cabinet.

Since Dave's updated version of the cabinet has a shorter port, I'm tempted to build a slot coming out on the rear side of the cabinet. I've made a sketchup drawing of my idea and attached it here (shown without back panel for better view).

The port length of the Classic GR dMar-Ken7.3 is 154mm. If I do the port on the rear I can get a length of 142mm, but considering that the last 90 degree angle would become part of the port, I guess I can add 15mm to that, making the total length 157mm, just 3mm longer than the original design.

Does this make any sense, or should I just stick to the orginal version and have the port on the side?

Thanks,
Søren
I'd ask Dave - he may already have a (few dozen) unreleased sketches along similar lines
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Old 29th October 2011, 07:09 PM   #5
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I ony found out earlier that i actually had never posted the CGR MK7.3 doc, so i scrambled to get one up. Just now i added the missing wide version.

\The high aspect ratio of the slot vent is a critical part of the design, replace it with a circular vent and the bass will get fat and less controlled.

It is possible to move the vent to the front or back, but to obtain the required length requires making it L-shaped. You have to fit a 154mm long vent into a box that is 120mm deep (135mm if you count the baffle thickness). If you want the vent to dissapear you can rotate the vent shelf as shown in the earlier CGR MK7 doc and fire it out the bottom or top, or you can run the vent shelf parallel to the back and vent out the back, bottom, or top. In that case you will need to increase the gross volume to compensate for the extra pieces that create the width of the vent slot.

dave
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Old 29th October 2011, 08:39 PM   #6
soren5 is offline soren5  Denmark
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But how come the newly added wide version of the CGR MK7.3 has different dimensions than the slim version? They are also different from the earlier CGR MK7, which measured 142mm x 231mm internally, both the wide and the slim version.

If I understand you correctly Dave, then I could make an L-shaped vent, but if the 142mm internal depth is in fact correct, then wouldn't my above suggested drawing work? It's 142mm long, but with the added 15mm after the 90 degree turn I get 157mm, which is only 3mm longer than the correct length of the port.

By the way, and this is just a thought... If the high aspect ratio of the slot vent is critical, could I then have the aspect ratio even higher and make the slot wider but not as high, and in this way keep the cross-sectional area? Would that work?

Thanks for the help.

Søren
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Old 30th October 2011, 02:47 AM   #7
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Quote:
Originally Posted by soren5 View Post
But how come the newly added wide version of the CGR MK7.3 has different dimensions than the slim version?

Looks like i screwed up somewhere... i was in a hurry putting that together.
They are also different from the earlier CGR MK7, which measured 142mm x 231mm internally, both the wide and the slim version.

Quote:
If I understand you correctly Dave, then I could make an L-shaped vent, but if the 142mm internal depth is in fact correct, then wouldn't my above suggested drawing work? It's 142mm long, but with the added 15mm after the 90 degree turn I get 157mm, which is only 3mm longer than the correct length of the port.
142mm internal depth looks like the correct one By my calcs you end up with 158, so if you subtracted add a flair by increaseing the width of the gap by 2mm you'd be OK. You'd need to increase the height enuff to cover the volume added by the extra vent -- the tidy way to do it, is to stretch it all the way across and than add a vent spacer of appropriate width to bring the open bits the same.

Quote:
By the way, and this is just a thought... If the high aspect ratio of the slot vent is critical, could I then have the aspect ratio even higher and make the slot wider but not as high, and in this way keep the cross-sectional area? Would that work?
You could... you'll still need to adjust cabinet volume

dave
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Old 30th October 2011, 03:07 AM   #8
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Just did some checking... i really screwed up, neither the slim or wide are optimum, the wide would be right if the vent shelf length was increased to 158mm (173mm total length).

It wouldn't be a dMar-Ken7.3 but a cMar-Ken7.3 so it is a work in progress that escaped.

The slim enclosure also needs a longer vent, and a bit less volume.

dave
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Old 30th October 2011, 07:32 AM   #9
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I spent the evening revising the entire set. Soren, you should be pleased with page 4 (the vent can be flipped to exit at the rear.

QC appreciated.

dave
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Old 30th October 2011, 11:59 AM   #10
soren5 is offline soren5  Denmark
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Hi Dave,

Thanks for taking the time to look at this. The Soren Edition was exactly what I was looking for!

I'm still confused about the port length though. In the PDF you just linked to there are three different lengths shown.

The wide and slim version with the 'original' slot vent has a length of 160mm (page 1+3). The slim version with 18mm panels has a port length of 173mm (page 2). And finally the new version on page 4 has a port length of 142mm. Aren't these port lengths supposed to be the same?

I suppose that the new version shown on page 4 actually has a longer port due to the L-shape. However, shouldn't the port length then be 147mm? In this way the L-shaped part of the slot would have a with of 10mm, keeping the SCA 2160 sq mm.

/Søren
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