ClassicGR Mar-Ken10.2 - anyone built? Have mods, what do you think about them?

[mikkokam]

I am building a very special project that involves Mar-Ken10.2 Classic golden ratio boxes. Would be interesting to hear any experiences from people who have built these enclosures -

1) The first question:
how is the bass end (seem a bit small enclosures at 13.5 liters minus the bracket, (and a part of the vents) and the driver?) - and if/how have you tuned the vents.

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The special twist in my project is that it is a standalone wireless device with a Chinese tube amp mounted on springs *inside a single box* with two Mar-Ken10.2 GR enclosures next to it and an iPad/iPhone docking station on top (plus a BT streaming unit just in case) - all in one box. Source will be Spotify high bit rate (320 kbit/s using the Ogg Vorbis q9 codec). For Bluetooth, a modified OSX setting from a Macbook Pro at a higher quality (the defaults suck).
The box will be 19 mm MDF plus a laser-cut aluminium top plate with knobs and the dock.

2) The second question
I would like to actually use the enclosures longitudinally: looking at the plan, placing the driver on top; rotating the enclosure so that it is 446 mm in (external) depth, 276 mm tall and 185 mm wide. Vents as they are in the plan - opening sideways from the box.

Would this cause problems? Do I need to change the vents?

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Shall post pictures and plans as I proceed. This is a one-off DIY for myself only, no commercial intentions...

Thanks for any help in advance!

Mikko

[planet10]

Originally Posted by mikkokam

I am building a very special project that involves Mar-Ken10.2 Classic golden ratio boxes.

We've not built the CGR-MK10, but have done a sufficient number of others to get a feel for how they compare to the full-on miniOnken builds.

Bass is usually a bit fatter and a bit more extended (due to not as high a aspect ratio of the vents), but not quite as controlled. Imaging and the ability to dissappear are not as high (due to smaller champher)

The driver can be mounted on any face that it will fit on and if needed the vent slot moved to a convenient spot (have a look at the CGR dMar-Ken7 for explicit examples). You might also find that the recently posted SSP version of the CGR might be a more appropriate starting point, as the top of the CGR puts the driver closer to the sides than i would recommend.

The net box volume is 13 litre, and the venting is based on that in the dMar-Ken10.2.

dave

[mikkokam]

Thanks Dave,

I shall look at CGR dMar-Ken7 vent ideas - it might be possible to move the vents to the back of the box, if the box is not placed too close to the back wall, I guess.
The bass end: good to know, fatter & extended is a good thing for this project: Imaging and the ability to disappear will not be a priority anyhow, given that I am building a single box with both speakers installed less than a meter apart... (near field listening - the box will be 2-3 meters from the sofa).

Thanks,
Mikko

[mikkokam]

Dave, a couple more questions, if you have time to help me out.
Running some form factors with SolidWorks now. Gave up the single box idea and shall split the device into 2 boxes to get a better imaging.

What tuning frequency are the 10.2 CGR vents designed with?
Is the net 13 liters with the brace & the driver subtracted from the volume? (What is the volume of the 10.2 driver roughly?)

Thanks,
Mikko

[planet10]

Originally Posted by mikkokam

What tuning frequency are the 10.2 CGR vents designed with?

Not a detail that i know off the top and given the way these are simmed not something i'm going to give out.

Is the net 13 liters with the brace & the driver subtracted from the volume? (What is the volume of the 10.2 driver roughly?)

13 litres net. I don't have the estimate of driver volume handy.

dave

[mikkokam]

OK,
I measured the driver and it's about 0.25 liters.

Ran some rough sims with WinISD and seems for 13 liters those vents are in the neighborhood of 44-45 Hz. With that simulation, it becomes -3 dB at 50 Hz, with a slight boost at 70 - 120 Hz. Real life is of course different.

Was thinking of making a quick MDF proto and scaling the CGR box slightly to 17.6 liters net with a bit shorter vents for a tuning frequency of 42-44 Hz. A quick simulation at WinISD gives -3 dB at 43 Hz with only little boost around 70-100 Hz.


If the proto sounds bad, I can always go back to the CGR or SSP version for 10.2. MDF is cheap... :-)

[planet10]

Originally Posted by mikkokam

Ran some rough sims with WinISD and seems for 13 liters those vents are in the neighborhood of 44-45 Hz. With that simulation, it becomes -3 dB at 50 Hz, with a slight boost at 70 - 120 Hz. Real life is of course different.

Real life is different because of the very high ratio vents. Actual response is between the sealed and the vented sim.

dave

[mikkokam]

OK,
have now built the system mostly - feet and the amp box missing. The amp box will get an aluminum top plate with engravings, the feet will be aluminum, too.

I chose to go with a 3-box setup; the tube amp and some other electronics (Bluetooth, iPhone dock and some other integrated gadgets) in a separate box. This box will be have spring feet (plus an air pillow inside for the tube amp) and may sit on the other speaker.

This is a CAD rendering of the plan I made before starting:


For speakers, I chose to make an original version other than the CGR or SSP to suit this project.

Differences:
_The dimensions are different.
_MDF is 19 mm.
_The driver is on the narrow face.
_There is only a single vent. The dimensions are adapted. The exit and input ends are rounded from all 4 sides.
_The bracing is different and there is some additional bracing.
_Lining: Sonofil



These boxes could be run vertically, too - narrow form factor has more WAF than a wide :-) This is after primer and 1st paint coat:


The finish is an off-white spray-paint (fully matte, warm white) to keep the looks very minimalistic. Had never used a spray-gun, so this was a learning experience, too:


Now breaking in the drivers with a tube amp and some easy music:


Low volume, first impressions are promising.
At first, there was a clear hiss on lower frequencies, and I got worried - but traced it down to one missing screw on a driver (!) - the pre-bored hole was leaking through.

Seems like an excellent driver even in these first time DIY builder's boxes. I am going to adjust the Sonofil after break-in by ear and my measuring microphone. Need to do something about the room at the same time, too - there are clear nulls at some frequencies. Oddly the situation is the worst at the very place of listening to music.

This was my first speaker DIY. Made many mistakes along the way - but it is easier to learn by doing... :-)

[jimbro]

That's a hell of a CAD rendering - looks just like a picture :-) Great job. Keep us posted on your impressions.

[mikkokam]

Thanks, will do.
The model is rendered using a real picture as a background to get an idea of the size and looks. Tried black and white versions but there's already too much black in this room - even the sofa.