How much stock should I put in these simulations

[Bas Horneman]

I used Diffraction & Boundary Simulator 1.20.

First off I calculated the golden ratio position in my open baffle and did a sim.
Then I used the NoBox plan. i.e. 90cm from floor and center of the baffle.
The result of the simulations is attached.

Driver is Visaton B200.

I noticed that there was a dip around 1kHz with the "nobox" placement and a bump before. The Golden Ratio graph looks less ragged.

 

[Bas Horneman]

Bump.


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[Scottmoose]

Short answer: it depends. Technically an offset is usually preferable (although golden ratio is a bit of a myth in some ways). However, you have to factor room response into these things, which usually screw things up below ~300Hz, and the polar response of the drive unit. The B200 has a rapidly narrowing power response as frequency increases, & while this has it's obvious drawbacks, it does tend to render it a little less vulnerable to some (some) baffle effects.

 

[Bas Horneman]

Thanks Scottmoose. I'm aware of the offset usually being preferable. I have an old Phillps document where they suggest that. The golden ratio was just a starting point. But seems at least from a simulation aspect to have one of the flattest responses.

Anyway thanks for your reply.

 

[wintermute]

Hi Bas, did you try the driver centered at the same height as the golden ratio one? I've found with BDS that the vertical position on the baffle can make a big difference.

I read once somewhere (I think it was duntechs site but I checked there and didn't see it) that the particular designer had moved away from asymetric baffle placement due to negative effects (I think from memory on imaging). I ended up going with centre placement after reading that.... I wish I had the reference...

Tony.

 

[Bas Horneman]

Hi Tony,

The sim with golden ratio height. But centered.

Regards,
Bas

 

[xrk971]

Bas,
Where do you get this software?
Thanks,
X

 

[Bas Horneman]

Hi X,

Loudspeaker Design Software

Scroll all the way down.

Regards,
Bas

 

[GM]

Using your baffle as a monopole measured at the old 4 ft standard distance and setting the room boundaries to '0' to mimic a corner, calculating x = 15.41", y = 27.4" looks close enough for me; ditto as a dipole 4" from rear wall and measured 45 deg off axis horizontally.

With the rest of the boundaries missing though, not to mention another speaker, furniture, etc., it's accuracy will rapidly degrade except over a narrow BW.

Still, a useful tool, especially for near-field apps.

GM

 

[Bas Horneman]

Still, a useful tool, especially for near-field apps.

Thanks.

 

[wintermute]

Hi Tony,

The sim with golden ratio height. But centered.

Regards,
Bas

Thanks Bas, certainly smoother than the first one, but not as smooth as the GR one. I've only modelled boxed enclosures, but did find a correlation between the sim and the actual measurements, though in my case the actual was worse (but followed the general trend) than the sim 🙂

Tony.

 

[Bas Horneman]

Hi Tony. What to do what to do. 🙂 Perhaps I should buy a cheap board and cut a few holes and try a couple of positions.

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[xrk971]

Foam core board works well for this sort of stuff. Also try isocyanurate home insualtion sheating boards.

 

[wintermute]

I think that is the best approach Bas. and xrk971's suggestion is a great way to achieve it. You are looking for the diffraction effects here so if you do some off axis measurements you should be able to work out what are diffraction effects and what are resonances (thinking that a thin baffle might have more of a resonance problem than a nice solid one).

The thing that can affect things is the drivers natural response, and how that combines with the diffraction effects, in my case it combined to make things worse, but you can potentially try to use (the effects) to your advantage 🙂 20/20 hindsight (or the wisdom of prototypin)!!

Tony.