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
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
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.
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.
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!
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!
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.
. 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.
Ron E said:
Well, yes, for a normal box I would agree. However, I think he is building an OB. An OB has a knee under which the response starts sloping by 6 dB/octave, and it is also under this knee that the directivity is a dipole. Above that frequency, the two sides have little interference with one another and the whole idea with a dipole is sort of not there.
So if a pure dipole directivity pattern is desired, the baffle should be small to push the knee frequency as high as possible. This is of course a compromise with the bass level since pushing the knee upwards makes the bass weaker.
My recommendation on baffle shape is not about size, but to make the distance between the driver and the edge as different as possible. That is, the driver will "see" a distance to the edge in each direction around the 360 degrees in the baffle plane, and this distance should vary. A circular baffle with the driver in the middle is the worst shape.
Shaping the diffraction with passive crossover or DSP EQ is solving it in the amplitude domain. Getting it as good as possible in the first place is better, because it will be always there in the time domain anyway. Simulators are invaluable for initial better geometrical decisions, before any wood is cut.
felt
Good point by Salas
A source of useful information may be in dlr's website linked above. Look for "Diffraction Effects and Amelioration with Felt". This, along with the adjacent links on his site may increase one's understanding of what is happening.
I would suggest (haven't tried) that felt triangles along the baffle edge may decrease ripple.
Good point by Salas
A source of useful information may be in dlr's website linked above. Look for "Diffraction Effects and Amelioration with Felt". This, along with the adjacent links on his site may increase one's understanding of what is happening.
I would suggest (haven't tried) that felt triangles along the baffle edge may decrease ripple.
Tenson said:
It would help very much if you could show us your measurement (and the type of driver you measured with its position on the baffle). What makes me curious: For a 37 cm wide rectangular baffle the first dipole peak would be somewhere around 800 Hz and the first dipole null roughly around 1500 Hz (double of the peak). Is your "noticeable ripple" clearly distinguishable from that peak and dip?
Another factor in diffraction is the material type you are mounting the driver onto. Part of what you are seeing is the baffle is becoming excited and providing secondary "ringing" which shows up in the frequency response since the sound wave travels at different velocity in the baffle board versus air.
Tenson said:
I believe you need to look a little bit into dipole theory.
At least it doesn´t hurt.
Two starters: Linkwitz and Kreskovsky
You don´t need the math. Just try to understand the response diagrams.
Yes. Even a dipole made from two point sources, which don´t show diffraction by definition, will show those dips and peaks.
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