Baffle edge - ideal curvature?

[Tenson]

Hi,

Is there some ideal curvature pattern to use for reducing baffle diffraction? I guess there would be, in the same way there are ideal shapes to match the impedance of a horn throat to the mouth.

Perhaps simply splitting the shape of a horn down the middle gives you the answer?

[LineArray]

Hi Tenson,

i don't know, if you think about open baffles or
the front baffles of "usual" enclosures.

In case of an open baffle, there is no "optimum" IMO,
because there are many characteristics which are influenced
by baffle shape and size:

- directivity vs. frequency
- lower cutoff frequency
- shape of the "baffle step" in frequency response

Influence of the single targets on "optimum" shape is
somewhat conflictive.

In case of a closed box conflicts are less evil,
but still there.

Conflicts are what makes up the need for creativity
in design. This is why i like those conflicts.

In case of the closed box, there are two extreme baffle
designs, which are interesting to me:

- the "get out of the way" baffle, which is narrow and tries
not to change the drivers dispersion at all.
Typically such a speaker is placed free in the living
room.

- a flat speaker wich large baffle area, which simulates a wall
mounted driver when placed near the rear wall of the room.

But any intermediate design may have its place, if designed well
and tuned to the components it is made of.

Curvature of the edges and the type of surface material cannot
be isolated from the overall baffle shape.

But i think baffle size and driver placement defines the
overall behaviour while edge shape plus surface material
adds some refinement. Especially at higher frequencies,
where baffle size and edge structure are not small against wavelength anymore.

Cheers
Oliver

[Tenson]

Hi,

I am thinking of an open baffle. At the moment I made a test baffle and it is 37cm wide. I get noticeable ripple just above and below 1KHz.

Because of the low-ish frequency, putting a bit of foam on the baffle etc.. doesn't work. So I need to change the curvature of the baffle to give a smoother impedance match at the edges.

I was thinking of trying an exponential flair.

[LineArray]

I suppose you are already using this ?

http://www.tolvan.com/edge/



Oliver

[Tenson]

Hi, yes. As far as I can see it has no facility to simulate a 3D baffle, though?

[LineArray]

No 3D right.

Your ripple is from simulation or from measurement ?

May You send me Your edge files ?

Maybe i'd like to play around with your design.



Oliver

[Tenson]

Hi,

It is from measurement. I can see the diffraction in the impulse response, and if I gate just that part, I see the reflected wave is over the frequency I have the problem. Foam at each side helps a small amount.

I rarely find simulation accurate enough, so I 'just do it'.

I'm sure if I build a curved edge baffle it will help, whatever shape of curve I use. I will probably do what I think looks nicest, lol!

[LineArray]

Maybe modifying the boundary of the baffle
by introducing slots or holes near the boundary and
along the propagation path of the wave is an alternative
to bending.

Anyway both ways are beyond the possibilities of "The Edge".

[Ron E]

The "best" edge is no edge (infinite baffle). If you are wondering about the best baffle edge radius, the larger the better - not a very difficult optimization there . In terms of your 1kHz issue, edge radius won't do much unless it is comparable to the wavelength. Making sure the distance from the driver to the edges is more random will do the most good there. Audio is not magic, it is a balance of compromises.

[Tenson]

Originally posted by Ron E
Audio is not magic

Good, I'm crap at magic.