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-   -   Pensil 7 (Alpair 7) (http://www.diyaudio.com/forums/markaudio/165297-pensil-7-alpair-7-a.html)

markaudio 17th April 2010 11:46 PM

Pensil 7 (Alpair 7)
 
3 Attachment(s)
Hi Guys,
Here's the most recent pics of the Pencil 7 in my home apartment. I've briefly covered experiences with this design in other threads but nothing in depth. But first, my thanks to Scott and Dave for their time and effort in making of this Pencil series.

Here's our plans site. We are gradually building an archive for builders to access. Please feel free to send us any plans (email:support@markaudio.com), we'll credit your work and load them into the archive.

http://www.markaudio.com/plans

Here's the PDF url for builders wishing to download the Pencil series plans:

http://www.markaudio.com/sites/all/f...sil-series.pdf

Starting from the build point of view, on a scale of 1 to 5 stars for ease of build (5 being the most challenging), I rate this cabinet as a 2 star. Essentially, it's just an open box inside with a removable back panel held in place by a series of well placed screws. It would be a 1 star build if the back were fixed but I recommend keeping the rear panel removable for reasons that will be explained later.

To brace, or not to brace?
This question is something of a spin-over from other threads. For this build, it wasn't necessary. The Oakwood is sufficiently stiff. This together with the relative narrow cabinet design did away with the need for bracing. For anyone using thinner material such as ply of MDF with a panel thickness less than 15-mm, it may be useful to fit some cross bracing in-between the driver and the bottom vent.

Coming back to the basic construction, this box is very simple. I'll take some internal pics later but for now, all this build requires is some careful cutting of panels, gluing and clamping to effectively complete the build. You may be able to see from the middle pic that the side panels run the full depth of the cabinet. To make the joint between these and the front panel look nice, a little 2-mm X 2-mm recess was cut for decorative effect. This is very simple to do and does make a big improvement in the look of the cabinet. I'd suggest this trim feature is best done on thickness of 18-mm of greater.

Some thoughts on material selection:
1 - Hard woods - Very nice indeed. Should you be lucky enough to have access to Walnut, Cherry, Oak, High Density Pine, Teak etc. etc. then look for thickness of 12-mm or greater. If 12-mm is selected, you'll almost certainly need some bracing. I'll try to remember to give some more advice on this later in this thread (remind me if I forget). Please check the source of the hardwood. Ask this question of the supplier. Does the hardwood come from a sustainable forest? PLEASE don't buy the wood unless there's some documentary proof that the wood is from a sustained managed forest. I live is Asia. Sadly I regularly witness the destruction of some of the most beautiful and diverse environments on this planet. All DIYer's owe their children a decent future. Please think on this point if and when you make a hardwood purchase.
2 - Ply and laminates- I suggest looking for the better quality laminates, Marine ply's, Birch ply's and High Compression ply's should offer higher density and greater rigidity. I'd recommend a minimum thickness of 15-mm.
3 - MDF. This is the most common build material in use within the speaker cabinet industry. There's some controversy on the effectiveness of this material but in this case, I'm going to give it a recommendation. It wouldn't be my first choice, but if hard woods and ply's aren't readily available, build in MDF, you'll still get a good result. Stick to a thickness greater than 18-mm and consider adding some bracing.

Sorry, I must go soon so I'll add more to this thread later.

Cheers

Mark.

gazzagazza 19th April 2010 09:27 PM

2 Attachment(s)
A couple of pictures of my Pencil 7 build. First one is the usual "clamped waiting for the glue to set" one... the other is one of the cabinets as they are now. I'm still finishing the internal damping material, should have them running in next week.

I've changed the design slightly as you can see. The vent has been moved from the lower front to lower rear. I think it gives a cleaner look to the box.

My regular loudspeakers and the reference I use are Quad ESL 57s as seen behind the Pencil 7 box.

markaudio 20th April 2010 12:43 AM

Hi Gazz,
The build looks excellent! Well done. I'm not sure what happens when the vent is re-positioned. Scott would be the best person to comment (he may have already done this).

All the same, the build looks professional. It's would be interesting to see more pics once the project is complete. Hope you can find the time publish more advice on the build and express your listening impressions.

What are your amplification and source components?

Cheers

Mark.

gazzagazza 20th April 2010 01:17 AM

Hi Mark,

I asked for confirmation here about the port shift before I started. Dave / Planet10 said it would be fine. I assumed that at the wavelengths we're talking about the difference in path length between driver and vent is negligible.

At present my system is in a state of flux. I design amps, and am between products at present. For now I have a Squeezebox based front end into a custom DAC (flac files from music server), into a passive preamp (Goldpoint control, silver wired) then into an evaluation power amp - work in progress... I also have a Linn vinyl front end.

markaudio 20th April 2010 03:32 AM

Hi Gazz,
Glad Dave helped out. I think your efforts will perform well. I guess you made the back panel removable? This feature is worth having if possible as I've found it useful to adjust the amount of damping to suit room influences.

Will be interesting to have your feedback once the system is completed. At present, I'm using one of Tony Wong's 300 B amp (8 watts per channel) with much pleasure, fed by an Accuphase DP-65 CD player. Recently, I tried Derek Shek's (Miniwatt) new Class D, 25-watt prototype on Alpair 7'. I was really surprised by how good the system sounds. Be interesting to read what you come up with by the way of system matching.

Cheers

Mark.

gazzagazza 20th April 2010 07:25 AM

Hi Mark, yes, rear panel is removable. I too am leaning towards low power amplification these days... I'll add info on the build as I progress. Regards...

gazzagazza 20th April 2010 07:33 AM

2 Attachment(s)
In case anyone else wants to construct cabinets the way I have I am attaching two pdf files showing the cabinet dimensions and panel cutting guide.

Scottmoose 20th April 2010 08:14 AM

Rear vents are not especially recommended (I designed them for front-firing -it's to do with room-coupling) but the option is there if you want to experiment.

togura 20th April 2010 06:15 PM

The removable back panel looks good.
I want to know what kind of screws was used to secure the back panel to the cleats. I guess wood screws would get loose after several removes of the panel. Should I use tee nuts and machine screws? Any suggestions how to use tee nuts would be great.
Thanks
Tatsuya

gazzagazza 20th April 2010 09:58 PM

Hi Scott, Thanks for the comment. If the enclosures are clear of the rear wall, and considering the nature of low frequency waves, is there any difference between front and rear? By my calculation at 100Hz the difference is no more than 0.06 of a wavelength. The radiation at the frequencies of interest is omni-directional no? If you could clarify your design's operation in this area it would be helpful.

Quote:

Originally Posted by Scottmoose (Post 2159963)
Rear vents are not especially recommended (I designed them for front-firing -it's to do with room-coupling) but the option is there if you want to experiment.



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