Pensil Pics, lets show 'em!

[Douglas Ingram]

Studio Reference Monitors for Alpair 12.

[doorman]

Great job!
What have you got on 'em for finish?
Best, Don

[markaudio]

Originally Posted by Douglas Ingram

Studio Reference Monitors for Alpair 12.

Hi Douglas,
Great looking design! Anymore pics?
Cheers
Mark.

[Douglas Ingram]

Thanks Don. Finish is Epiphanes Spar varnish, because that is what I use a lot of. My day job is a builder of traditional wooden canoes.

Thanks Mark! Coming from you that means a lot. My end goal is to build a recreation of the 1960's Clairtone Project G, which has 18" diameter globes. Dave from Planet 10 turned me on to your drivers and I am working with him to develop a version of his Mar-Ken 12 cab that will fit inside the globe. So, in order to get started, and in order to have a reference, I built these. I was going to build some Super Pensil 12s, but then the comparison would not be as relevant, and I risked getting spoiled on the Super Pensils and I would not like my globes!

Construction was not too critical on these, considering their purpose. So, basic 3/4 cabinet grade Birch plywood with Solid Birch at the corners, rounded over with a 1/2" radius router bit.

The only other reference that I have are a pair of Saburo's that my son built last summer. We have yet to do a side by side comparison, next week after he finishes all his end of term university projects! Right now we have different source material, different amps, different rooms...

What I would like to know, the backs are removable for adjusting the damping, so what do I listen for and what do I do to get optimum results? Right now I have the recycled denim insulation damping lining the interior of the upper chamber.

[markaudio]

Originally Posted by Douglas Ingram

Construction was not too critical on these, considering their purpose. So, basic 3/4 cabinet grade Birch plywood with Solid Birch at the corners, rounded over with a 1/2" radius router bit.

What I would like to know, the backs are removable for adjusting the damping, so what do I listen for and what do I do to get optimum results? Right now I have the recycled denim insulation damping lining the interior of the upper chamber.

Hi Douglas,
Excellent pics and very nice construction. I'm not sure how efficient the Denim will be at damping. It looks quite compacted so there might be the risk of some reflected sound wave energy back toward the rear of the cone. Perhaps you can "fluff" the material more? I think you've got around 10 to 15-mm thickness on the side panels? I usually use 20-mm. Open cell acoustic foam is normally the most efficient, can be sourced from the internet.

I'd suggest at least 25-mm insulation on the back panel. Given the Alp12's cone size, its important to keep any sound waves coming back on to the rear of the cone.

Out of interest, how easy would it be for you to remove the bracing in these cabinets? Dave and Chris (Canada) are keen on bracing which I can appreciate and understand. Bracing should make a more controlled cabinet but my own personal preference on cabs this size is to let the box have some sympathetic resonance. Theoretically, the box frequency will be lower without bracing, possibly desirable on a cabinet this size.

Box resonance is much a matter of personal taste, generally splitting into 2 schools of practice; Those who like tighter sounds add bracing, others who desire something softer and lower work with less or no bracing. Its best to experiment to see what works for you.

Cheers

Mark.

[Scottmoose]

The recycled denim appears to possess good damping properties from the reports I've heard, so it should be fine. Personally, I dislike foam; just doesn't seem to work for me, but YMMV as always.

[planet10]

Originally Posted by markaudio

I'm not sure how efficient the Denim will be at damping. It looks quite compacted so there might be the risk of some reflected sound wave energy back toward the rear of the cone. Perhaps you can "fluff" the material more? I think you've got around 10 to 15-mm thickness on the side panels? I usually use 20-mm. Open cell acoustic foam is normally the most efficient, can be sourced from the internet.

The recyled denim cotton felt (UltraTouch) is really good. Best wall damping material for vented enclosures i've used yet, and to my preference better than foam by some margin.

The less dense 3 1/2" stuff is very good volume fill material.

I'll try to remember to tuck samples into the package building up for you (actually the felt stuff can be seen inside your uFonken). Scott, your sample should be on the water or ready to be loaded onto the boat.

dave

[Douglas Ingram]

The denim insulation is actually 2" thick teased apart to about half of that. More or less, but mostly less as its hard to be precise with this stuff. The inner surface is quite open and fluffy.

My own issue with damping material is that I don't really know how to work it for optimizing performance. I don't really know what to listen for, especially without any reference to compare improving or lessening performance as I play around with damping.

Plus, it won't really do much until my upstream components are improved! Dramatically! These speakers are quite unforgiving. that way.

The center bracing would be difficult to remove, though possible if warranted. These cabinets are part of a developmental process, as mentioned, so tweaking them for ultimate performance is not needed-aside from my personal erudition.

[zman01]

Douglas,

Beautiful set of speakers - congratulations!

You have a very nice flush mount fit for the Alp 12 in your cabinet. How deep did you make the rebate/recess for the drivers?

I am a bit confused here - I measured 11 mm with the driver frame + foam gasket... would be good to know what actually works (too shallow or deep, I wont have the nice flush mount).

Thanks,
Zia

[Douglas Ingram]

Zia,

I used the technical drawing that is on the Mark Audio website for the dimensions and did the routing for mounting prior to receiving the drivers. The foam gasket added a bit more thickness than I was expecting, but with a bit of compression all seems to be OK. Personally, I would prefer a too shallow rebate than one too deep. Having the driver sit a little proud of the front surface is more attractive than sitting in too deep.

Good luck with your Super Pencils! I almost built those instead of.