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Old 1st June 2011, 04:23 PM   #1
JorgeO is offline JorgeO  Portugal
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Default My first build - Pensil P70

Hi guys,

First sorry for my English.
I'm going to try my first DIY, a pair of loudspeakers, I've orderer the MarkAudio CHP-70 drivers and will build the Pensil P70 project with a tight budget.
Here are some of my doubt about some options, please point out my mistakes
Decided to do the bracing and increased the width by about 10% to compensate the lost volume is it ok to increase only the width or should the increase be divided by all dimensions?
I'm thinking about coating the vertical brace in the part it will compress against the back of the driver with a strip of 3 mm cork does it make any sense? or is the objective to transmit the vibrations to the bracing ? (also cork the parts where the removable back will contact other wood???).
In the vent should I round the inner upper edge as in the Pensil 12 project?
About the wood I've purchased particleboard covered in one side with paper cardboard (two IKEA Galant corner desk top...) it as good WAF, it's heavy (about 20kg per speaker) but is it an acceptable alternative?
For the damping material should I use only dacron or can I be "imaginative", what characteristics should the material have?

Thanks for you help

Jorge
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Old 1st June 2011, 05:03 PM   #2
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Jorge,

Your English is fine.

Quote:
Decided to do the bracing and increased the width by about 10% to compensate the lost volume is it ok to increase only the width or should the increase be divided by all dimensions?
It is not all that necessary to compensate for the volume of the holey brace. If you do, increase the width by 2/3s the thickness of the brace. Increasing width will also affect the terminus at the bottom. You need to maintain the same cross-section area.

Quote:
I'm thinking about coating the vertical brace in the part it will compress against the back of the driver with a strip of 3 mm cork does it make any sense? or is the objective to transmit the vibrations to the bracing ? (also cork the parts where the removable back will contact other wood???).
The main finction of the brace is to transmit/disrtibute driver energy to the back (top & bottom) of the box. A tight fit, but not so tight as to stress the basket, is best here. If you don't get it tight best to shim with something not very squishy. Paper, shim of wood.

Quote:
In the vent should I round the inner upper edge as in the Pensil 12 project?
It doesn't hurt.

Quote:
About the wood I've purchased particleboard covered in one side with paper cardboard (two IKEA Galant corner desk top...) it as good WAF, it's heavy (about 20kg per speaker) but is it an acceptable alternative?
Better than MDF. Pensil is fairly uncritical.

Quote:
For the damping material should I use only dacron or can I be "imaginative", what characteristics should the material have?
You can be creative with certain limits.

dave
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Old 2nd June 2011, 04:48 PM   #3
JorgeO is offline JorgeO  Portugal
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Thanks Dave,

I'll try to post as I go along with the construction.
About the damping, should I concentrate the material in the top of the speaker, glue the material to cover all the inside of the box (carpeting?) or just fill the box evenly?
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Old 2nd June 2011, 09:12 PM   #4
chrisb is offline chrisb  Canada
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Quote:
Originally Posted by JorgeO View Post
Thanks Dave,

I'll try to post as I go along with the construction.
About the damping, should I concentrate the material in the top of the speaker, glue the material to cover all the inside of the box (carpeting?) or just fill the box evenly?

With our Pensils for Alp7, we didn't line the walls, but filled the box with fibrous material. This is were interlocking or crossing braces in at least the lower section of tall / skinny enclosures helps - keeps the fill from slipping out of place.

Click the image to open in full size.
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Old 2nd June 2011, 09:27 PM   #5
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As the Pencils are primarily a TL variation, they were designed to be stuffed rather than lined.
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Old 2nd June 2011, 09:50 PM   #6
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We filled our Pensil 7 build evenly (as suggested by Scott in a recent post) at the specified density and then removed about a 1/3. Room for experimentation is necessary as polyfluff, even if 2 versions look the same, can be quite variable in how well it performs.

dave

Edit: jeez, 2 posts appear after hitting submit, making some of my post moot
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Old 7th June 2011, 12:11 PM   #7
JorgeO is offline JorgeO  Portugal
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The work in under way, used white rapid glue for wood, should have gone for the normal one (no stress need on first try).
Didn't have big enough clamps so decided to use 2 car straps.
Final result it's not exactly 90, it's 1cm tilted on top.
I'll try to do better in the second one.
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Old 9th June 2011, 06:07 AM   #8
fxs is offline fxs  Chile
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i hang up this thread for adding some questions about pencil 7 . It could be useful questions to jorge too..

1.- I realized the vent is about 1-2 mm shorter than 35 mm indicated on the plans. I'm using natural wood (pine) so it's difficult to get an exact cut. It's this too detrimental to the sound? Should i correct it? The cabinet is already built, so i think would prefer not to fix it, if it doesn't make too much difference.

2.- I painted the cabinet, so now the driver t's a few mm protruding over the rest of the front panel (due to the thickness of the paint layer). Again, this could affect too much the sound?

3.- Finally, what is the effect of the stuffing material? how should change to sound from no material, to over stuffed?

Last edited by fxs; 9th June 2011 at 06:09 AM.
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Old 21st June 2011, 03:55 PM   #9
JorgeO is offline JorgeO  Portugal
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Hi,

The drivers arrived yesterday... finally.
Restarting the work. Today I purchased the filling, is it really 1.24 kg? It seems a lot of material to be stuffed inside the boxes.
For the wiring I'm thinking in using CAT6 (shielding seems a good idea around a magnet).
Also, probably, I will drop the framing.
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Old 28th June 2011, 02:51 PM   #10
JorgeO is offline JorgeO  Portugal
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Default First listening impressions

Hello,
Finished the build and started listening to music.
Maybe, first, I should explain my idea for building this system.
1 - Get rid of the 50hz/60hz (in the wich list for 30+years) - powered by a 12V 7Ah battery.
2 - Source should be losseless audio files and mp3.
3 - Should use the minimal amount of components (keep it as simple as possible).
I'm using a TA2024 MK2 amp from Helder Hifi (very positive impression ordered the TA2020 MK3) and a Sansa Clip+ player (FLAC files) and using as comparison my old Siare Fugue400 the first impressions are:
Positive - detail, sound stage, precision (better than the Siare will have to compare with my reference in these aspects the Cabasse Sampan Lourd that I have in the other house)
Could be better - A litle more bass and not very robust sound with large orchestral works (still looking for the best positioning), improved with a different stuffing and with the feet.
Overall I'm quite impressed how a under 200 system can sound like, clearly exceeded my expectations.
Any opinions on how to improve my speakers/system are very welcome (should experiment more with the stuffing? should I consider building a second pair of speakers (other wood other drivers...)?).
Thank you MarkAudio for this positive experience.
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