# Air-tight Box via Milling or CNC?



## matt scarlett (20 Dec 2017)

Is milling/CNC so accurate that one could create an air-tight box (using six pieces of said metal) without any form of adhesive mastic?


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## bugbear (20 Dec 2017)

matt scarlett":mb0vig3l said:


> Is milling/CNC so accurate that one could create an air-tight box (using six pieces of said metal) without any form of adhesive mastic?


No. How are you planning to join the 6 pieces together?

BugBear


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## matt scarlett (20 Dec 2017)

Just a theory at the moment. I design speakers for a hobby. Not that I build sealed speakers, but I wondered how Magico built theirs. https://www.google.co.uk/search?q=insid ... 00&bih=766

I know a few companies do make speakers in metal, but i'm thinking the weight (transport) would be problematic. Maybe for a personal project i could outsource my project to a machinist, but for hobby/production i was thinking along the lines of some form of Plastic.


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## worn thumbs (20 Dec 2017)

Wouldn't it depend to some extent on the air pressure differential,if any,between the inside and outside of the box?At low pressure and with parameters for a high quality surface finish,I would have thought that a box could be machined that would be for all practical purposes airtight.I was reading a report a few weeks ago about the Sentronics fuel flow sensor which is widely used in motorsport and it depends on high quality machining as sealants might corrupt the accuracy and efficiency of the unit.Since liquids are more viscous than air it would be a bit bold to claim that the outcome of using good machining and careful assembly would be identical but the inference is there.


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## matt scarlett (20 Dec 2017)

I guess for the purpose of Magico speakers, bit of mastic isn't going to be an issue. It was interesting. For me I design transmission line enclosures, and so a sealed speaker wouldn't be needed, however, even with the folds/waveguides in the t-line enclosure, I'd want them to be pretty close to flush. 

https://transmissionlinedesigns.wordpress.com/


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## bugbear (20 Dec 2017)

matt scarlett":2sj4tjq3 said:


> I guess for the purpose of Magico speakers, bit of mastic isn't going to be an issue. It was interesting. For me I design transmission line enclosures, and so a sealed speaker wouldn't be needed, however, even with the folds/waveguides in the t-line enclosure, I'd want them to be pretty close to flush.


Ah - I think we're back to the concept of the "decent square" thread. There's airtight (a platonic ideal) and airtight enough for a loudspeaker to work. What rate a air leakage would have an acoustic effect?

I suspect (in fact) that any good loudspeaker design would include a slow leak, otherwise you've changes in atmospheric pressure might well destroy (or at least displace) a cone.

BugBear


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## matt scarlett (20 Dec 2017)

One main concern with sealed speakers is air leak where the driver is mounted. Some claim a difference when one tightens the screw on a pair of Factory speakers (B&W, Kef, Dynaudio), giving it a change on frequency response. The assumption is that speakers that come out of the factory need a touch of tuning. Not 100% certain on that hypothesis 

With metal enclosure, the possible added dilemma is the cabinet itself. Doesn't seem to be any type of mastic in these Stenheim speakers.


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## matt scarlett (20 Dec 2017)

I see some mastic around the tweeter housing, but i'm guessing that some sort of gasket might also be used (blue acrylic)


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