Baffle step compinsation for a sphere?

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I'm not sure you would have any real "baffle-step" at all. It may be that below whatever frequency your 3 inch driver starts to beam (wave length the diameter of the cone?) would be the corner of something like baffle step. It's a good question, it'll be interesting to see the variety of answers.

Best Regards,
TerryO
 
If you are referring to baffle step compensation, all baffles have a baffle loss frequency, in which the baffle no longer loads the driver as a half-space. A sphere unloads faster as you go down in frequency, since it dissappears in all directions equally.

However, whether or not you need to compensate for this depends on what your lower crossover frequency is for the particular driver. If the crossover frequency is above the baffle loss frequency, then you shouldn't need to compensate for it.

Driver directivity also comes into play. If the driver is not radiating at 90 degrees off axis, then the baffle is not acoustically loading the driver. However, at the lower crossover frequency, the driver is usually radiating fairly widely.

It also depends if more than one driver is operating in the same frequency range, and they are "acoustically close" together. Each driver can provide a load to the other driver similar to a baffle.

You need to do the math. One cannot do that with the limited info you've given.
 
Sorry for being too vague. The driver is a full range with a 150hz LR4 highpass (hivi b3n to be exact). Of course a subwoofer is incorporated for <150hz output.

As a whole, I have a weak grasp of filters and the math involved with them. Much beyond a simple cap and coil crossover is a confusing web of components to me :xeye: . However, i'm always trying to learn more. :smash: I figured a sphere would be the easiest to create BSC for.
 
If you want to run these down to 150Hz then the baffle step definitely comes into play. I don't know if the frequency calculation above was for a flat baffle of 5 in size or not. If it was, I'd say a spherical baffle would cause loss above that frequency.
Think about it, the five inch width of a sphere is behind the driver.

Google baffle step and you should find the info you need. It may be easy to shelve down the high frequencies rather than boost the lower ones. Whatever you do, don't believe you have to equalize the step on axis. Baffle loss is a loss of acoustic load, which lowers the power output. I won't get into the math, but if you equalize on axis, the power output will be too high, because equalizing doen't change the load lost by the baffle. Baffle loss will cause a 6 db loss on axis. If you boost the bass up 3 db on axis, you may find this to have a flatter power response, and sound more correct.

To mitigate baffle loss, you may want to consider something other than a sphere. If you place the driver in the side of a vertical cylinder, and put a hemisphere on the top, you can get better baffle support to a lower frequency than a sphere, while pretty much keeping it pretty rigid, with the diffraction almost as low as a sphere, while making it easier to build and mount.
 
woody said:
The best article I have seen on baffel step was http://www.trueaudio.com/st_diff1.htm The
math was simple realy simple.

Yes, in this particular case that page is good. The page referrs to a classical paper by Olson that actually measured the baffle step of a sphere.

What is bad about the page is that it generalises the findings from the sphere to a formula (yes it is simple, but not very accurate) based on the baffle width only.

As can be seen in the Olson images on the page a sphere has a rather smooth baffle step, which is easy to compensate for.

Resonances inside a spherical cabinet are problematic, however. But that was not the question here.
 
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