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First Build: Pensil P11
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Old 1st July 2020, 01:05 AM   #1
Serevro is offline Serevro  Mexico
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Default First Build: Pensil P11

Hello Everyone,

Recently I stumbled on an ad for the Wrensilva's audio consoles, and the idea of making a similar piece stuck in my head. I'm quite competent making cabinets and have machinery and some materials available. On the other side, I'm an utter neophyte regarding audio; so I started lurking here.

Since I know next to nothing about electronics I opted to go with a full range design. I got a good deal on a pair of Pluvia 11s and so, I have the drivers in my hands. I later opted to make a pair of speakers instead of the audio console, since don't really have room for it.

I usually listen from Spotify via Bluetooth, have a number of classical music CD's which I listen from time to time too. I bought an Onkyo TX8220 to power the speakers, probably arriving later this week. Not a conossieur, as you may notice.

Initially I was thinking into making a folded horn design, but found a review of the Pensil 11 on HiFi Pig that changed my mind. Also it looks easier to build.

Now regarding the build, I'm going to list some hard constraints, some good things, and some questions in no particular order. Would appreciate your input.
  • First of all, I'm using the Pensil A11/P11 plan as base for this build: https://frugal-phile.com/boxlib/pens...silA11-P11.pdf
  • Something not good: I don't have a source for good plywood. On the other hand I have plenty of MDF. I made a preliminar design using 15 mm MDF keeping the internal dimensions untouched. Could use other thicknesses, but I'm used to work with 15 mm and have more finishing options with it.
  • Another not so good thing: I have no clamps. I will "press" the panels using Minifix fittings while the glue cures. I've done that before with furniture, let's see how it works on speakers.
  • Something positive: I have plenty of dampening materials: delcron, felt, PU foam, eggshell foam, etc. Also, have access to some well tooled CNC routers.
  • A question: If not using internal bracing, how do you keep the fiber stuffing from going to the bottom?
  • Regarding the terminal cup: Is there a prefered place to put it or it doesn't matter as much?
Thanks a lot.

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Old 1st July 2020, 07:45 AM   #2
Scottmoose is offline Scottmoose  United Kingdom
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A couple of points:

-You are asking for trouble if you use unbraced, single-thickness 15mm MDF in an LF enclosure of this size.

-Do not use egg-crate foam. I stress this point for every single pensil: I did not design them to use it, and it doesn't (can't) provide the correct damping characteristics. It has uses, but not for these speakers. The default is dacron (hollow-fibre stuffing).

-The stuffing is uniformly distributed throughout the box, keeping it a few inches away from the rear of the driver. Generally it's self-supporting at the densities in question, but you can put a dowel or two across just above the vent. However, if you're going to use MDF, above all insufficiently thick MDF, bracing of some kind is essentially mandatory, with the longitudinal bracing of the type shown in the [Super]Pensil 12P pdf being the most effective.
www.wodendesign.com (commercial site)
www.frugal-horn.com www.frugal-phile.com (community sites)

Last edited by Scottmoose; 1st July 2020 at 07:48 AM.
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Old 1st July 2020, 06:24 PM   #3
chrisb is offline chrisb  Canada
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Location: victoria BC
Having built a few pairs of Pensils and many of Scottís other designs, Iíll strongly second his remarks. In my past active building career, I had access to more than sufficient free off-cuts or wholesale priced MDF, but after a test build of identical enclosure and driver design in the two materials (3/4Ē MDF and 18mm Baltic birch) in the early 2000ís, I used MDF only for templates and base plinths.
Aside from the vent opening, itís critical that all joints are air tight - something thatís certainly not the case for furniture or kitchen cabinets. If you have access to CNC machining, Iíd suggest at least 18mm MDF, and the use of dadoes/rabbeted joints - glue lock joints if you can manage them, but note that MDF can be both become fragile when so machined, and thanks its heat tempered surface hold a sharp enough edge to cause physical injury.

Cue the Greek chorus of debate on the merits of different material types and construction/joinery techniques.

As to to the location of terminals, Iíd personally opine that it hardly matters diddly squat - just make sure that the back panel is both removable for installation / adjustment of damping fill, and well sealed with something like closed cell foam weather stripping tape.
Weíre just a bunch of monkeys on a big blue spinning ball - Don Caron
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Old 3rd July 2020, 05:47 PM   #4
planet10 is offline planet10  Canada
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Location: Victoria, BC, NA, Sol III
First Build: Pensil P11
If MDF is all you have, 15mm is too thing for this box. You could get away with well braced 15mm quality plywood, but you will need to use at least 18mm MDF and it will likely need more bracing than the 15mm ply.

Click the image to open in full size.

From this drawing: the braces that are pararllel to the bffle should not extend to the point that they are behind the driver (you could probably make then in a bit taller.and i would not put any holes underneath were the braces cross. Make sure the braces are off-centre. With 18mm MDF you may need more bracing. Probably another side-to-side set. Account for the volume of th braces when doing the box size calculation.

Stay safe. Stay home. Respect the 2m bubble.
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Old 5th July 2020, 03:53 PM   #5
Serevro is offline Serevro  Mexico
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Thank you for your valuable feedback.

I made the pertinent changes: I'll go with 18 mm MDF for the sides, top and bottom, and 27 mm (15 + 12) in the front. Will use dadoes in most unions.

Next thing I will do is take into account the volume substracted by the braces and back mount.

I'm probably using 2 faces finished MDF for most parts, does the absence of porosity affects substantially the outcome?

Thank you again,

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