Alpair 12 - Damped Air Coupler box design - diyAudio
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Old 23rd November 2009, 03:30 AM   #1
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Default Alpair 12 - Damped Air Coupler box design

Hi Guys,
I've finally found a little down time to follow up in the Pensil 12 cabinet design initiated by Scott L (many thanks). I've attached 3 updated jpeg plan drawings to show the simple version of this Cabinet design.

There's already some information floating about the forum on the Damped Air principle so this thread is more to do with helping DIYer's have a go at making this design.

This is experimental so there may be modifications along the way. I'll update the drawings as needed. I'll document my findings by adding posts as I progress through the build.

So, please take a look at these 3 attachments and feel free to copy.

Thanks

Mark.
Attached Images
File Type: jpg pensil12drw_front1.jpg (59.2 KB, 3327 views)
File Type: jpg pensil12drw_rear1.jpg (27.2 KB, 3111 views)
File Type: jpg pensil12drw_side1.jpg (22.5 KB, 3077 views)
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Old 23rd November 2009, 03:39 AM   #2
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The design is very simple so I'm not going to dwell on the actual making of the box. I'm not blessed with much spare time so Michael, my wood-working friend made the box.

Take a look at these 3 pics as they should help you visually with the build. Michael works in a cabinet factory with CNC facilities, hence the 45 degree picture frame style joints. My suggestion would be to stick to basic 90 degree butt joints for easy construction.

Since this is somewhat experimental, and given the wide variety of room settings, the rear panel has been made removable so the damping can be adjusted to suit.
Attached Images
File Type: jpg pensil12_front1.jpg (59.0 KB, 3080 views)
File Type: jpg pensil12_rear1.jpg (53.5 KB, 2918 views)
File Type: jpg pensil12_rear3.jpg (73.5 KB, 982 views)
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Old 23rd November 2009, 05:21 AM   #3
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Making a good job of fitting the driver is important. The Alpair 12's cone is thin so take extra care care when handling the driver at this part of the build.

For DIYer's with experience, you may want to skip this post.

See - pictures 1 to 7

1 - Note the logo on the frame. Place this part of the frame in the "12 noon" position in the cabinet.

2 - Once you've got the driver positioned, flip it and place into the cabinet. I've recessed this driver but for those who want to surface mount, you could follow this procedure having pre-marked the driver's frame position on the cabinet. Using a set square or anything that gives a right-angle, line up the mounting holes.

3 - Secure the driver with tape, then check the alignment again with the set-square. Next is hole centring. Pic 3 is the safer method for new DIYers with limited skills. This method is will help you keep the drill bit away from the cone. Using a 4-mm drill bit, gently tap its end with a small hammer to make a centring mark in the cabinet. Repeat for all six holes taking care not to move the driver.

4 - For those who are feeling brave, use the 4-mm bit in a cordless variable speed drill, quickly blipping at low revs for a couple of turns to make the centring marks.

5 - With the hole positions established, remove the Alpair 12, using a 2.8-mm bit, drill out the pilot holes to take the Hex head screws provided with the A12. Note - if you intent using other screws, check with their maker for the correct size pilot hole requirements.

6 - Using a wood glue or all purpose adhesive, apply to the cabinet surface

7- Fit the seal provide with the Alpair 12, position correctly, press down and allow to dry.
Attached Images
File Type: jpg Alp12_driverfit1.jpg (80.0 KB, 1243 views)
File Type: jpg Alp12_driverfit2.jpg (97.3 KB, 1079 views)
File Type: jpg Alp12_driverfit3.jpg (86.4 KB, 1055 views)

Last edited by markaudio; 23rd November 2009 at 05:24 AM.
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Old 23rd November 2009, 08:01 AM   #4
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Onto driver connections.

Take a look at pic 8. Note the temporary push fit connector. I've used these connectors to make life a little easier while experimenting with the damping. I'm reasonably certain the back of the cabinet will be un-screwed several times so having an easy disconnection method is handy. Once the tuning is completed, unpick the push-fits and replace with a permanent solder joint.

Pic 9 shows the use of my connector set that I designed some time back. It easily copes with 20-mm MDF and will cope with a 25-mm (1") thickness.

A quick note on cables. There's lots of choice and tonnes of debate on cable types. Should the choice be copper core audio cable, go for a high quality OFC grade and 1.5-mm to 2.5-mm core thickness is more than sufficient.

Make he cable length around 450-mm. This will make life easier while removing the back panel during the tuning stage. Once the tuning is completed, trim the cable to suit a permanent set-up.
Attached Images
File Type: jpg Alp12_driverfit4.jpg (119.7 KB, 1148 views)

Last edited by markaudio; 23rd November 2009 at 08:06 AM.
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Old 23rd November 2009, 10:57 AM   #5
_henry_ is offline _henry_  Australia
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Hi Mark,

Its good that u have made a reference for us. I will look forward to give it a try later on.

How about Alpair 10 Bass?

Cheers
Henry
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Old 23rd November 2009, 02:48 PM   #6
jleaman is offline jleaman  Belgium
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what about some internal bracing ?
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Old 23rd November 2009, 11:36 PM   #7
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The cabinets made for me by Michael are very rigid so at this stage I won't be adding bracing. There will be a fair amount of damping to be added which should help to keep cab resonance low.
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Old 24th November 2009, 05:23 AM   #8
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Will there be any standmount designs for this driver?
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Old 24th November 2009, 08:39 AM   #9
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I'm working on a standmount.

dave
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Old 24th November 2009, 10:12 AM   #10
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Default ??

Quote:
There's already some information floating about the forum on the Damped Air principle
Hi, are this somewhat similar in concept to the M J King's "mass loaded TLs"
Thanks
JJT
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