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Old 22nd July 2013, 07:16 AM   #1
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Default Pensil with 7.3

Need some help with a pensil build, while the speakers are slowly being warmed up.

Due to restricted materials availability locally, the intended cabinets are posing problems by either quality of ply available, or restricted thicknesses (I am off the normal map if you will). I even considered building the main cabinet in 20mm granite which is available, until I worked out the hernia inducing weight of a single speaker.

I even considered using 40mm beech worktop for the sides as it was more consistent than the ply here.

With the throat thickness for the pensil baffle defined as 18 - 20mm, is there a way in which a thicker material can be used (and round the throat edges), or would that have a detrimental effect otherwise ?
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Old 22nd July 2013, 08:28 AM   #2
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Providing it's within a couple of mm, differences will be minimal.
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Old 22nd July 2013, 09:10 AM   #3
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Thanks Scott,
I realised the limits 18-20mm from reading earlier postings, but I was wondering if more like 30 or 40mm could be viable with a taper on the inner bottom part of the baffle to hit the 20mm mark or chamfer/fillet the throat to hit the 20mm on the flat.
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Old 22nd July 2013, 12:02 PM   #4
xrk971 is offline xrk971  United States
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A speaker made of granite would truly be spectacular looking. Perhaps a thinner granite like 1/4 in thick for the front baffle only and thicker plywood or what have you on the back and sides. Getting a driver cutout and holes drilled will have to be done by a granite cutting professional shop.
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Old 22nd July 2013, 01:08 PM   #5
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The A7.3 needs about a 10mm rebate to sit flush, plus 8 to 10mm for the screws. I did talk with a mason about making one in black granite, and it was viable in 16mm for the cabinet, but when it got to the baffle, I believe the translation was "go forth and self reproduce".
Granite cabinet yes, baffle no, and even at that at 40+kg, is impractical. It certainly would look spectacular, particular as it descended the four storeys to the basement...

Ply or beech blockboard are the current favourites....
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Old 22nd July 2013, 01:09 PM   #6
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Quote:
Originally Posted by boblamont View Post
Thanks Scott,
I realised the limits 18-20mm from reading earlier postings, but I was wondering if more like 30 or 40mm could be viable with a taper on the inner bottom part of the baffle to hit the 20mm mark or chamfer/fillet the throat to hit the 20mm on the flat.
If you're able to taper a significant part of the baffle, then yes. If you're talking about a simple chamfer of the back edge of the vent, then unfortunately not. The extra length will lower Fb somewhat away from the stock alignment. However, the difference won't be all that much, so I wouldn't worry about it too much.
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Old 22nd July 2013, 01:31 PM   #7
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Cheers Scott,
Just what I needed to know, will see what the stock situation is tomorrow...
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Old 22nd July 2013, 03:28 PM   #8
chrisb is offline chrisb  Canada
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Having heard speakers made from both solid stone (diamond cored basalt) and "Corian" or equivalent acrylic solid surface counter-top material, I'd say stick with the plywood.

And as boblamont mentioned, good luck finding a shop able to rebate holes for flush mounting the drivers in solid granite, as well the requisite rear side chamfer. Through holes and some degree of profiled edges are easy enough, but if the technology exists to achieve a clean rebated round hole, the machine time would likely cost more than enough high quality plywood to complete the project.

If you need to use the thicker wood material for the front baffle, a few cross-cut passes with a dado blade could effectively reduce the thickness in the vicinity of the vent. You'd also need a deeper chamfer at the driver opening.
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Old 23rd July 2013, 04:50 AM   #9
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The stoneworker guy said he could do it Chris, but warned against it.
He pointed to the weakness of the thin granite left at the back of the speaker rebate through which the mounting screws would have to mounted, the screws applying pressure radially on a thin flange. Granite does not give or form a thread tap like plywood, it fractures. He was not happy about the amount of meat left on the periphery of the baffle at the driver either.

If I have to go thicker for the baffle, it will be a long taper as both suggested.
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Old 23rd July 2013, 05:19 AM   #10
AndrewR is offline AndrewR  United Kingdom
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Just use 18mm Baltic Birch ply. It is probably the best material out there for loudspeakers. It should be readily available, if not then buy from ebay.

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