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Tony Wilkes View Drop Down
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Joined: 02 August 2004
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Points: 4840 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Tony Wilkes Quote  Post ReplyReply Direct Link To This Post Posted: 07 July 2009 at 8:47pm
Originally posted by Contour Contour wrote:

I have to agree with Elliot. A thick baffle is very effective, even if the total baffle is only slighty larger then the driver. In that case using 36mm instead of 18mm will also not cost you many internal litres. Because of the cut-out for the driver, almost no wood remains.
 
Best regards,
 
Walt


Sorry you are wrong.

Its a good job you lot do not design Aeroplanes the buggers would never get off the ground Smile

Tony
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Contour View Drop Down
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Points: 625 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Contour Quote  Post ReplyReply Direct Link To This Post Posted: 07 July 2009 at 8:52pm
Hello Tony,
 
I design light weight container cranes (www.kalmarind.com) so I know how important weight is and how to minimize it.
 
For a heavey duty 18" like a Void V18 or PD1850 a thick baffle is really benificial.
 
The Punisher is a very well braced design (for a horn) but with testing with extreme bass heavey music on each bass note the cabinet was moving about 5cm to the back. I agree with you a very effective way to stop this is to add mass so that friction of cabinet with ground is large enough to prevent cabinet from moving.
 
Best regards,
 
MSc. W. de Jong IWE


Edited by Contour - 07 July 2009 at 8:56pm
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Tony Wilkes View Drop Down
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Points: 4840 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Tony Wilkes Quote  Post ReplyReply Direct Link To This Post Posted: 07 July 2009 at 8:58pm
Originally posted by Contour Contour wrote:

Hello Tony,
 
I design light weight container cranes (www.kalmarind.com) so I know how important weight is and how to minimize it.
 
For a heavey duty 18" like a Void V18 or PD1850 a thick baffle is really benificial.
 
 
Best regards,
 
MSc. W. de Jong IWE


In that case you should know better.

Tony

p.s. Just noticed the port is braced doh.
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Contour View Drop Down
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I have tested it myself so I am convinced it works.
 
If you have a 18" driver lets say hole diameter is around 414mm
 
Lets say total baffle width is 520mm (about 3cm from chassis to sideplate of cabinet)
 
Because the driver is round still a unsupported length of about 128mm remains. Since all the force from the driver goes trough the baffle, only 18mm thickness is not much.
 
Best regards,
 
Walt
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Contour View Drop Down
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I now see on the pictures that battens are used all around the baffle board. So already this gives some reinforcement and decreases the unsupported length.
 
Best regards,
 
Walt
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SteveAATW View Drop Down
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Points: 1173 		Post Options Post Options   Thanks (0) Thanks(0)   Quote SteveAATW Quote  Post ReplyReply Direct Link To This Post Posted: 07 July 2009 at 9:10pm
I'm not a mech or god forbid civ eng, but from what I do know of structural stuff the wedge bracing and the structure as a whole gives a higher strength for smaller area of wood than cross bracing across and down the cab. Ultimately its MDF and I don't trust something I can snap over my knee, hence the wedge bracing being ply, and port bracing 2x1 pine - it gave a much better material to screw into and put some force into to pull the whole box together while it glued. It's probably OTT, but then so is the driver LOL
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Tony Wilkes View Drop Down
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Points: 4840 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Tony Wilkes Quote  Post ReplyReply Direct Link To This Post Posted: 07 July 2009 at 9:15pm
Originally posted by Contour Contour wrote:

 
Because the driver is round still a unsupported length of about 128mm remains. Since all the force from the driver goes trough the baffle, only 18mm thickness is not much.
 
Best regards,
 
Walt


If you accept that the wood on the edges is too short at 30mm  to distort (vibrate)  for the 128mm to distort the only way for that to happen would be for the driver frame to flex, which is what I wrote earlier.

This may well happen to an insignificant degree but not in any amount that would affect performance.

Regards

Tony
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Elliot Thompson View Drop Down
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Points: 5176 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 08 July 2009 at 11:59am
Another thing that I never mentioned is the resonance of the wood. If one would perform the knuckle test using a 36 mm versus an 18 mm piece of wood, you will hear the tone is higher with the thicker wood. From my findings, this creates less wood resonance when amplifying frequencies ranging from 50 – 25 Hertz.

If anyone is interested, I will record the difference in tone having a 36 mm board versus 18 mm conducting the knuckle test.

Best Regards,


Elliot Thompson
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SteveAATW View Drop Down
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Points: 1173 		Post Options Post Options   Thanks (0) Thanks(0)   Quote SteveAATW Quote  Post ReplyReply Direct Link To This Post Posted: 10 July 2009 at 1:45am
Been playing with this a bit more tonight, the thing is brutal - 2 x Res1 at full pelt can just about keep up with it. Though even with a 48dB Butterworth slope at 35Hz, you can't push it much past 800-900W input before the edge of the cone starts to make some worrying noises, it might just be the noise it's meant to make when moving that much air, but the movement of the cone looks worrying in comparison to previous experience (though that has been limited to things like the 18XB, which are much tamer beasts), its not a VC hitting pole piece or nasty distortion noise, but its slightly unerving whatevers causing it. Time to build some twins LOL
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Tony Wilkes View Drop Down
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Points: 4840 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Tony Wilkes Quote  Post ReplyReply Direct Link To This Post Posted: 10 July 2009 at 7:23am
Steve,

Just a thought take the high pass up to about 50hz and try again.

Do you know the actual tuning frequency of your box (not the theoretical).

Tony
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SteveAATW View Drop Down
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Points: 1173 		Post Options Post Options   Thanks (0) Thanks(0)   Quote SteveAATW Quote  Post ReplyReply Direct Link To This Post Posted: 10 July 2009 at 11:31am
Erm, no, no idea how to find it either Embarrassed

Theoretical 39Hz. It did cross my mind that it might be a lot lower than that and the drivers losing it
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Tony Wilkes View Drop Down
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Points: 4840 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Tony Wilkes Quote  Post ReplyReply Direct Link To This Post Posted: 10 July 2009 at 11:40am
Originally posted by SteveAATW SteveAATW wrote:

Erm, no, no idea how to find it either Embarrassed

Theoretical 39Hz. It did cross my mind that it might be a lot lower than that and the drivers losing it


I would be more worried if it was higher and therefore unloading the driver below the port frequency but still above your high-pass.

This is one reason why I do not like the big shelf ports as there is no loading at all below port tuning.

This is why I asked you to try it with the high-pass set at a higher frequency.

Tony


Edited by Tony Wilkes - 10 July 2009 at 11:41am
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