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 Post subject: Tweeter enclosure....
PostPosted: Sat Nov 29, 2008 9:50 am 
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Sheep

Joined: Mon Mar 12, 2007 7:45 pm
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While on holidays in Berlin, I came across a set of tweeters (Visaton), and duly bought them.

For those with tweeters external to the main mid enclosure...what did you make the chassis for them out of ?

Graphite seems good - but exceptionally heavy and expensive, wood resonates :S.

L


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PostPosted: Tue Aug 11, 2009 5:48 pm 
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Psychobiker wrote:
For those with tweeters external to the main mid enclosure...what did you make the chassis for them out of ?


Hi

Tweeter is to handle hi audio frequencies of short wavelengths.
Shorter the sound wavelengths coming out of the tweeter diaphram means easily to get reflected by any surrounding enclosures.

Take a look at brandname loudspeakers, e.g. B&W of England. You can see their top models all get their tweeters mounted on top the the cabinet with minimum enclosure to prevent undue HF sound reflections.

I added to my KEF 2-way bookselfers (already upgraded by replacing its ringing-like-hell dome tweeter with a SEAS soft-fabric dome tweeter) a Motorola piezo cone tweeter to extend its HF to beyond 20Hz. I mounted the metal cased piezo tweeter on top of the KEF cabinet in line with the SEAS dome tweeter. NO no enclosure.

The idea is to minimize RF soundwave reflections.

c-J

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PostPosted: Tue Aug 11, 2009 10:01 pm 
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Benjamin
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I think you mean "HF". No sound waves at RF.

Jocko


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PostPosted: Wed Aug 12, 2009 7:56 am 
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Sheep

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In the electromagnetic spectrum, HF = 1.8-30MHz.

You mean high AF (audio frequency). Yes, that's true - as small an enclosure as physically possible!

Liam, EI6GXB


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PostPosted: Wed Aug 12, 2009 9:57 am 
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Goat

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how close to the no enclosure, does 2Pi loading come?

How much damping of the faceplate and rounding of the extremities of the flat plate needs to be done the approach the no enclosure loading.

Why, because most tweeters come with a small 2Pi loading plate as part of their physical make-up.

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PostPosted: Mon Aug 17, 2009 1:38 pm 
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Psychobiker wrote:
does 2Pi loading come?


HI. Psychobiker.

What is "2Pi loading" of a tweeter?

c-J

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PostPosted: Mon Aug 17, 2009 3:07 pm 
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Goat

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Hi,
4Pi loading is radiating into spherical space.
2Pi loading is radiating into a hemispherical space.
Most tweeters are mounted into a flat plate and this plate is then attached to the flat face of the speaker baffle/box.
This is 2Pi loading.
I don't know of any examples but if two boundary planes meet and the tweeter is on/in the junction of the two planes then that is Pi loading.

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PostPosted: Tue Aug 18, 2009 2:55 pm 
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andrewt wrote:
4Pi loading is radiating into spherical space.
2Pi loading is radiating into a hemispherical space.


Hi Psychobiker.

I think mine is a 3/4 sphere loading.

So I think my approach using the 'super' tweeter (mine is a Motorola piezo paper cone tweeter with factory built sealed steel backcase. I mounted it with a small thin aluminum faceplate on top of my KEF 2-way bookselver cabinet, in line of the loudspeaker dome mid-tweeter vertical axis.

So the super tweeter have 3/4 spheral free air load. To minimize minor HF reflection caused by the sharp edges of the faceplate, I glued on a thin layer of open-cell plastic foam to cover the faceplate surround as well as the surround of the entire loudspeaker cabinet front face. Yes, it makes the loudspeaker look very homebrew like. I don't mind as it works sonically better considering I already redesigned & rebuilt the crappy stock X-over network into bi-wiring & moved it outboard behind the power amps.

c-J

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