Ameliorating the diffraction problem completely, home audio

[thadman]

Also, I'm not sure if I made this explicitly clear, but I am working with a dipole alignment, NOT a monopole alignment. Wouldn't the diffractions effects be severely down in level at the edges since it propagates in a figure eight radiation pattern?

 

[CeramicMan]

Also, I'm not sure if I made this explicitly clear, but I am working with a dipole alignment, NOT a monopole alignment. Wouldn't the diffractions effects be severely down in level at the edges since it propagates in a figure eight radiation pattern?

Ahaa... ok. Well the figure-8 pattern is caused by destructive interference of diffracted sound waves. So it's only as good as the matching between the front and rear drivers.

I suspect that baffle diffraction would only really become an issue for the midrange and tweeter, where the waves might form new point sources or line sources, so they don't cancel out properly.

 

[thadman]

Ahaa... ok. Well the figure-8 pattern is caused by destructive interference of diffracted sound waves. So it's only as good as the matching between the front and rear drivers.

Yes, I'm aware of what causes the figure 8 radiation pattern. The waves are destroyed as they begin to radiate into 4 pi space.

How would I calculate the distance the rear wave has traveled to combine in phase with the front wave (I believe it occurs one octave below fundamental wavelength of baffle)

I suspect that baffle diffraction would only really become an issue for the midrange and tweeter, where the waves might form new point sources or line sources, so they don't cancel out properly.

If I made them symmetrical on the baffle, why would they become new point or line sources? Can you please go further in depth

 

[CeramicMan]

If I made them symmetrical on the baffle, why would they become new point or line sources? Can you please go further in depth

Like Svante suggested earlier, a curved surface can be thought of a series of small discontinuities that cause partial reflections, which all add up to create a smeared reflection. However, that also implies that some of the sound never reaches the 90 degree mark on the curved baffle where it would start getting cancelled out.

So in the context of a dipole design, it might be good to make the baffle edges as sharp as possible... I had monopole designs in mind in my earlier posts, sorry.

 

[CeramicMan]

Something like this maybe?...

 

[Svante]

How do we calculate the time delay of a curved baffle? Do the single diffractions sum to the total diffraction as the effective width of the baffle or something else?

The thing is that a well designed baffle does not have one delay. It is only if you put the driver at the centre of acircular baffle that there will be one delay, and that would correspond to the added pathway for the sound that has gone to the edge and bounced from there towards the listener.

For other geometries the same thing happens, but the time delay is different for different parts of the baffle, which results in a time-smeared edge pulse. This is good.

If you have not yet played around with The Edge in my signature, please do. it can help you understand the baffle step better.

And yes, you are right in that the dealyed and smeared edge reflection does not sound like an echo. This is due to the short delay. Rather it affects the frequency response, but that effect is OTOH quite audible and should be compensated for.

 

[thadman]

The thing is that a well designed baffle does not have one delay. It is only if you put the driver at the centre of acircular baffle that there will be one delay, and that would correspond to the added pathway for the sound that has gone to the edge and bounced from there towards the listener.

For other geometries the same thing happens, but the time delay is different for different parts of the baffle, which results in a time-smeared edge pulse. This is good.

If you have not yet played around with The Edge in my signature, please do. it can help you understand the baffle step better.

And yes, you are right in that the dealyed and smeared edge reflection does not sound like an echo. This is due to the short delay. Rather it affects the frequency response, but that effect is OTOH quite audible and should be compensated for.

I have edge, and have used it considerably but didn't realize it could be applied to 3D shapes. How would I model a curved baffle or teardrop baffle (ie like the one ceramicman recommended) in edge? I realize edge can model open baffle, but does that necessarily imply dipole?

Could you comment on the dipole alignment? Being figure 8 (down several dB at the edges), they illuminate the edges considerably less...and should follow this pattern throughout the dipoles bandwidth. Is that why Linkwitz always has a symmetric driver layout? Couldn't this easily be fixed with equalization as diffraction should affect on-axis as well as off-axis equally.