Advice on a Mark Audio Chr-70 project

[Leon Dupuis]

Hello everybody. I'm from Italy and i'm going to start my first DIY project. I bought a pair of Mark audio Chr-70 and i'm searching for a nice project to build.
Those are some projects that i've found:





I'd like to know what project, in your opinion, is better, or if you could give me an advice on another project.

Regards,M.

[markaudio]

Hello Leon,
This is your first project so the Pensil 70 box should be easier to build. Also the rear panel can be make removable so the box is easier to tune for your room. Just add or take out damping material to get the best sound.
THe Pensil needs no filter, just wire the driver direct to amp.

Cheers
Mark.

[chrisb]

Originally Posted by markaudio

Hello Leon,
This is your first project so the Pensil 70 box should be easier to build. Also the rear panel can be make removable so the box is easier to tune for your room. Just add or take out damping material to get the best sound.
THe Pensil needs no filter, just wire the driver direct to amp.

Cheers
Mark.

I'd definitely recommend the Pensil for a first build, and as Mark says use wood cleats (and perhaps foam weatherstrip tape) to make the rear panel removable - accessing inside the box to adjust fill materials is particularly tight on the enclosures for 70mm drivers.

Also it's very worth while installing criss-cross bracing such as

[markaudio]

Hi Chris,
The criss-cross bracing looks very nice. Might be a bit much for Lean as he's a new guy. Can you and Dave suggest more simple cross bracing to help him and other new Diyers get started?

Hi Leon,
If the bracing looks a too much for you, recommend using a good quality ply wood, or a solid hard wood if you can get it. I'm running Pencils in solid wood for Alpair 7's with no bracing. The boxes are very solid and work well.

Cheers

Mark.

[Leon Dupuis]

Originally Posted by chrisb

I'd definitely recommend the Pensil for a first build, and as Mark says use wood cleats (and perhaps foam weatherstrip tape) to make the rear panel removable - accessing inside the box to adjust fill materials is particularly tight on the enclosures for 70mm drivers.

Also it's very worth while installing criss-cross bracing such as

Originally Posted by markaudio

Hi Chris,
The criss-cross bracing looks very nice. Might be a bit much for Lean as he's a new guy. Can you and Dave suggest more simple cross bracing to help him and other new Diyers get started?

Hi Leon,
If the bracing looks a too much for you, recommend using a good quality ply wood, or a solid hard wood if you can get it. I'm running Pencils in solid wood for Alpair 7's with no bracing. The boxes are very solid and work well.

Cheers

Mark.

Hi Chris and hi Mark. Thank you very much for your kindness. Today i bought the wood to make the Pencils, 18mm birch plywood, i hope it was a good choice. I'd like to know if the criss-cross bracing has only reinforcement function or if it has any influence on the sound. In case i can build it in a second time thanks to the rear panel removable. Sorry for the many questions but i'm a totally newbie.

Regards,M.

[markaudio]

Hi Leon,
18-mm ply is a good choice.

I think Chris, Dave and other use this material.
The criss-cross bracing will make the box more stiff. Should make the bass sound from the box a little tighter. This can help to give the bass sound more detail as the box is moving less. Some guys like this cleaner sound. Others like no bracing as they want a little more warm sound.

Since the rear panel can be removed, you could build the box with no bracing, experiment with its sound and add bracing later to suit your listening tastes.

Take some pics as you make the panels, put them on this thread. The guys can help you through the making process.

Cheers

Mark.

[Squeak]

A (ML)TQWT is only a smidgen more complicated to build than the Pensil (esp. considering the recommended cleats). I'd say, the difference is not even worth mentioning.

That there is no need for a filter in the Pensil, I gather is because of the larger front which gives the necessary bafflestep correction. The same could be achieved with the TQWT by squeezing and widening the box a bit, or simply putting the driver on the "side" of the box.

While I'm sure the Pensil is a fine design, it does seem to take up more space than a TQWT and I'm sure there are differences in the sound.
I'll let it be up to people who have designed and build the Pensil to detail those differences.



Edit: With regards to bracing, simple sawn out pieces of broom handle or other similar cheap thin-ish sticks of wood that you wedge between the panels should work as well as the time-consuming holy-braces, if not better because you can but them at different places on the panel so as to avoid harmonic resonance (BTW the tapering panel in a TQWT works as a brace between the sides too)

[jimbro]

Which generation chr-70 do you have? The pensil cabinets are slightly different.

[chrisb]

Squeak: I've tried both methods and prefer the speed and leaner bass response that Mark describes resulting from the more elaborate bracing schemes, but for a simpler build you're definitely right about the broomstick approach (just don't use MDF for the braces ) . solid maple, birch or other very stiff hardwoods are best used here

[Squeak]

I'm sure you are right. So that leaves the question about the Pensil vs. TQWT.
What are the advantages and drawbacks of each method?
Or what is the general difference in sound signature?

There doesn't seem to a good optimized TQWT design for the CHX-70 drivers though. All of them seem to be generalizations like the Needles and the FH Mk. III if we can count that one.